WO2024036820A1 - 隔离膜、其制备方法及其相关的二次电池和用电装置 - Google Patents

隔离膜、其制备方法及其相关的二次电池和用电装置 Download PDF

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Publication number
WO2024036820A1
WO2024036820A1 PCT/CN2022/136684 CN2022136684W WO2024036820A1 WO 2024036820 A1 WO2024036820 A1 WO 2024036820A1 CN 2022136684 W CN2022136684 W CN 2022136684W WO 2024036820 A1 WO2024036820 A1 WO 2024036820A1
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WIPO (PCT)
Prior art keywords
filler
optionally
particles
isolation film
coating
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PCT/CN2022/136684
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English (en)
French (fr)
Inventor
徐�明
杨建瑞
魏满想
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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Priority claimed from PCT/CN2022/112580 external-priority patent/WO2023245836A1/zh
Priority to JP2025502898A priority Critical patent/JP2025525594A/ja
Priority to KR1020257003115A priority patent/KR20250028476A/ko
Priority to CN202510479064.2A priority patent/CN120300404A/zh
Priority to CN202510479096.2A priority patent/CN120300405A/zh
Priority to CN202510479109.6A priority patent/CN120300406A/zh
Application filed by Contemporary Amperex Technology Co Ltd filed Critical Contemporary Amperex Technology Co Ltd
Priority to EP22955589.1A priority patent/EP4546541A4/en
Priority to CN202280018076.XA priority patent/CN117044026B/zh
Publication of WO2024036820A1 publication Critical patent/WO2024036820A1/zh
Priority to US19/029,606 priority patent/US20250167398A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/44—Fibrous material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/446—Composite material consisting of a mixture of organic and inorganic materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure

Definitions

  • the present application belongs to the field of battery technology, and specifically relates to an isolation film, its preparation method and related secondary batteries and electrical devices.
  • secondary batteries have been widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.
  • energy storage power systems such as hydraulic, thermal, wind and solar power stations
  • their safety issues, especially thermal safety issues have received more and more attention.
  • the current methods used to improve the thermal safety performance of secondary batteries are often not conducive to balancing the energy density and service life of secondary batteries. Therefore, how to make secondary batteries take into account high energy density, high thermal safety performance, long cycle life and good kinetic performance is a key challenge in secondary battery design.
  • the purpose of this application is to provide a separation film, its preparation method and related secondary batteries and electrical devices, which can enable the secondary battery to take into account high energy density, high thermal safety performance, long cycle life and good dynamic performance. .
  • a first aspect of the present application provides an isolation membrane, including a porous substrate and a coating disposed on at least one surface of the porous substrate, wherein the coating includes a three-dimensional skeleton structure and a first filler, and the third At least part of a filler is filled in the three-dimensional skeleton structure, and the average particle size of the first filler is less than or equal to 200 nm.
  • the isolation membrane can be made to have both low weight and high performance.
  • Heat resistance and high ion conductivity enable secondary batteries to combine high energy density, high thermal safety performance, long cycle life and good kinetic properties.
  • the average particle size of the first filler is 15 nm to 180 nm, optionally 30 nm to 150 nm.
  • the first filler can have a higher specific surface area, so that the particle size of the first filler can better match the three-dimensional skeleton structure, so that the first filler and the three-dimensional skeleton structure can be better matched.
  • the skeleton structure can better overlap to form an integrated effect, increase the affinity between the first filler and the three-dimensional skeleton structure, increase the heat resistance and ion conductivity of the isolation membrane, and at the same time increase the isolation membrane's resistance to the electrolyte. Wetting and retention properties.
  • the first filler includes at least one of primary particles and secondary particles.
  • the first filler includes a combination of primary particles and secondary particles.
  • the content of the first filler in primary particulate form is less than the content of the first filler in secondary particulate form based on the total weight of the first filler.
  • the content of the first filler in primary particle form is less than or equal to 30 wt% based on the total weight of the first filler.
  • the average particle size of the first filler in primary particle shape is 15 nm to 80 nm, optionally 30 nm to 65 nm.
  • the average particle size of the first filler with secondary particle morphology is 50 nm to 200 nm, optionally 55 nm to 150 nm.
  • the BET specific surface area of the first filler is ⁇ 25m 2 /g, optionally 30m 2 /g to 65m 2 /g.
  • the specific surface area of the first filler is within the above range, it has better affinity with the three-dimensional skeleton structure, can increase the heat resistance and ion conductivity of the isolation membrane, and can also increase the resistance of the isolation membrane to the electrolyte. Wetting and retention properties.
  • the content of the first filler is ⁇ 50wt%, optionally 60wt% to 90wt%, based on the total weight of the coating.
  • the content of the first filler is within the above range, it can ensure that the coating slurry has a suitable viscosity, which is more conducive to coating; in addition, it is also conducive to forming an integrated effect with the three-dimensional skeleton structure, thereby making the coating It has a more stable spatial network structure, which can further improve the heat resistance and ion conductivity of the isolation film.
  • the content of the three-dimensional skeleton structure is 5wt% to 40wt%, optionally 8wt% to 25wt%, based on the total weight of the coating.
  • the content of the three-dimensional skeleton structure is within the above range, it can ensure that the coating slurry has a suitable viscosity, which is more conducive to coating; in addition, it is also conducive to the overlapping of the three-dimensional skeleton structure and the first filler to form an integrated effect. It can make the coating have a more stable spatial network structure, which can further improve the heat resistance, ion conductivity, electrolyte infiltration and retention characteristics and voltage breakdown resistance of the isolation film.
  • the first filler includes at least one of inorganic particles and organic particles.
  • the inorganic particles include boehmite, aluminum oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicon oxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, oxide At least one of nickel, hafnium dioxide, cerium oxide, zirconium titanate, barium titanate and magnesium fluoride, more optionally, the inorganic particles include boehmite, alumina, barium sulfate, magnesium oxide, silicon At least one of an oxygen compound, titanium oxide, zinc oxide, cerium oxide and barium titanate.
  • the organic particles include polystyrene particles, polyacrylic wax particles, melamine formaldehyde resin particles, phenolic resin particles, polyester particles, polyimide particles, polyamideimide particles, polyaramid particles, polyamide particles, etc. At least one of phenyl sulfide particles, polysulfone particles, polyethersulfone particles, polyether ether ketone particles and polyaryl ether ketone particles.
  • the first filler includes inorganic particles, and the crystal form of the inorganic particles includes at least one of theta crystal form, gamma crystal form, and n crystal form; optionally, the The crystal form of the inorganic particles includes at least one of a ⁇ crystal form and a ⁇ crystal form.
  • the content of the inorganic particles of the ⁇ crystalline form is ⁇ 50wt%, more optionally 55wt% to 84wt%, based on the total amount of the inorganic particles in the first filler. Weight scale.
  • the content of the inorganic particles of the ⁇ crystalline form is ⁇ 10wt%, more optionally 15wt% to 44wt%, based on the total amount of the inorganic particles in the first filler. Weight scale.
  • the content of the inorganic particles of the n crystal form is ⁇ 5wt%, more optionally ⁇ 2.5wt%, based on the total weight of the inorganic particles in the first filler count.
  • the three-dimensional skeleton structure is formed of fibers, and the morphology of the fibers optionally includes at least one of rod-like, tube-like, rod-like and fiber-like.
  • Selecting first fillers of different crystal forms helps to improve at least one of the heat resistance, ion conductivity, bonding strength, and electrolyte wetting and retention properties of the isolation film.
  • the average diameter of the material constituting the three-dimensional skeleton structure is ⁇ 40 nm, optionally ranging from 10 nm to 35 nm.
  • the ion conductivity and voltage breakdown resistance characteristics of the isolation membrane can be further improved, and it can also help to form an integration effect by overlapping with the first filler. This can also further improve the heat resistance of the isolation film.
  • the average length of the material constituting the three-dimensional skeleton structure is 100 nm to 600 nm, optionally 200 nm to 500 nm.
  • the heat resistance and ion conductivity of the isolation film can be further improved.
  • the aspect ratio of the material constituting the three-dimensional skeleton structure is 5 to 60, optionally 10 to 30.
  • the aspect ratio of the material constituting the three-dimensional skeleton structure is within the above range, the ion conductivity of the isolation membrane and the wetting and retention characteristics of the electrolyte can be further improved.
  • the material constituting the three-dimensional skeleton structure includes at least one of organic materials and inorganic materials.
  • the organic material includes at least one of nanocellulose, polytetrafluoroethylene nanofibers and polyamide nanofibers.
  • the nanocellulose includes cellulose nanofibers, cellulose nanowhiskers. and at least one of bacterial nanocellulose.
  • the inorganic material includes at least one of halloysite nanotubes, nanorod-shaped alumina, nanorod-shaped boehmite, nanorod-shaped silica and glass fiber.
  • the material constituting the three-dimensional skeleton structure includes nanocellulose, and the nanocellulose includes at least one of unmodified nanocellulose and modified nanocellulose.
  • the modified nanocellulose includes a modifying group including an amine group, a carboxyl group, an aldehyde group, a sulfonic acid group, a boric acid group and a phosphate group. At least one of, more optionally, at least one of a sulfonic acid group, a boric acid group and a phosphoric acid group.
  • nanocellulose When nanocellulose has the above-mentioned specific modified groups, on the one hand, it can effectively improve the heat resistance of the isolation film and improve the thermal safety performance of the secondary battery; on the other hand, it can also improve the bonding between the coating and the porous substrate. Bond strength.
  • the nanocellulose When the nanocellulose has the above-mentioned specific modified groups, it is also conducive to the overlapping of the nanocellulose and the first filler to form an integrated effect, which can make the coating have a more stable spatial network structure, thereby improving the isolation film.
  • the wetting and retention properties of the electrolyte improve the ion conductivity and voltage breakdown resistance of the isolation membrane.
  • the presence of modified groups can also reduce the proportion of hydroxyl groups, thereby ensuring that the coating slurry has a suitable viscosity, which is more conducive to coating, thus improving the production efficiency of the isolation film and the uniformity of the coating.
  • the modified nanocellulose includes a hydroxyl group and a modifying group
  • the molar ratio of the modifying group to the hydroxyl group is 1:4 to 4:1 , more optionally 2:3 to 7:3.
  • the molar ratio of the modified group to the hydroxyl group is within the above range, the heat resistance, ion conductivity, and electrolyte wetting and retention characteristics of the isolation membrane can be further improved.
  • the material constituting the three-dimensional skeleton structure includes a sulfonic acid group, and the content of sulfur element in the material constituting the three-dimensional skeleton structure is ⁇ 0.1wt%, optionally 0.2wt% to 0.5 wt%, based on the total weight of the materials constituting the three-dimensional skeleton structure.
  • the coating further includes a second filler, at least a part of the second filler is embedded in the coating, and the average particle size of the first filler is recorded as d 1 , so The average particle diameter of the second filler is recorded as d 2 , then d 2 /d 1 >1.
  • the second filler has a larger average particle size, which can better play its supporting role in the coating, reduce the shrinkage of the first filler, and reduce the amount of binder, thereby improving the heat resistance of the isolation film;
  • the larger particle size of the filler also helps the coating to have more pore structure and less water content when the dosage is small, which can further improve the ion conductivity of the isolation membrane and the infiltration and penetration of the electrolyte. Maintain the characteristics while also improving the cycle performance and/or kinetic performance of the secondary battery.
  • the first filler includes at least one of primary particles and secondary particles, the average particle size of the first filler in the form of primary particles is recorded as d 11 , and the secondary particles
  • the average particle diameter of the first filler with particle morphology is recorded as d 12 , 3.0 ⁇ d 2 /d 11 ⁇ 10.0, optionally, 3.5 ⁇ d 2 /d 11 ⁇ 8.0; and/or, 1.2 ⁇ d 2 /d 12 ⁇ 6.0, optionally, 2.0 ⁇ d 2 /d 12 ⁇ 5.5.
  • the secondary battery can better balance high energy density, high thermal safety performance, long cycle life and good dynamic performance.
  • the second filler has a primary particle morphology.
  • the average particle size of the second filler is 120 nm to 350 nm, optionally 150 nm to 300 nm.
  • the BET specific surface area of the second filler is ⁇ 20m 2 /g, optionally 6m 2 /g to 15m 2 /g.
  • the second filler includes at least one of inorganic particles and organic particles.
  • the second filler includes inorganic particles with primary particle morphology, and the crystal form of the inorganic particles with primary particle morphology includes at least one of ⁇ crystal form and ⁇ crystal form, Options include alpha crystalline form.
  • the ⁇ -crystalline second filler has the advantages of high hardness, good heat resistance, low dielectric constant, high safety and high true density, which can further improve the heat resistance of the coating.
  • the second filler includes inorganic particles with primary particle morphology
  • the crystal form of the inorganic particles with primary particle morphology includes ⁇ crystal form
  • the content of ⁇ crystal form is ⁇ 70wt %, optionally 85 wt% to 100 wt%, based on the total weight of the inorganic particles of the primary particle morphology in the second filler.
  • the content of the second filler is ⁇ 30wt%, optionally 5wt% to 25wt%, based on the total weight of the coating.
  • the supporting role of the second filler can be better exerted, the moisture content of the coating can be reduced, and the coating can maintain a stable pore structure during long-term charge and discharge processes.
  • the coating further includes a non-granular binder.
  • the non-granular binder includes an aqueous solution binder.
  • the content of the non-granular binder in the coating is ⁇ 2 wt%, based on the total weight of the coating.
  • the three-dimensional skeleton structure and the first filler in the coating of the present application can form a stable spatial network structure, thereby enabling the isolation film to maintain high adhesion while reducing the amount of binder.
  • the thickness of the porous substrate is ⁇ 6 ⁇ m, optionally 3 ⁇ m to 5 ⁇ m.
  • the coating of the present application can significantly improve the heat resistance of the isolation film, thereby enabling the use of thinner porous substrates, thereby helping to increase the energy density of secondary batteries.
  • the thickness of the coating is ⁇ 2 ⁇ m, optionally 0.5 ⁇ m to 1.5 ⁇ m. This helps to increase the energy density of secondary batteries.
  • the isolation film further includes an adhesive layer, the adhesive layer is disposed on at least a portion of the surface of the coating, and the adhesive layer includes a granular adhesive.
  • the adhesive layer can not only prevent the coating from peeling off and improve the safety performance of the secondary battery, but also improve the interface between the isolation film and the electrode and improve the cycle performance of the secondary battery.
  • the granular binder includes acrylate monomer homopolymer or copolymer, acrylic monomer homopolymer or copolymer, fluorine-containing olefin monomer homopolymer or At least one of the copolymers.
  • the longitudinal thermal shrinkage rate of the isolation film at 150° C. for 1 hour is ⁇ 6%, optionally 0.5% to 4%.
  • the transverse thermal shrinkage rate of the isolation film at 150° C. for 1 hour is ⁇ 6%, optionally 0.5% to 4%.
  • the isolation film of the present application has low thermal shrinkage in both transverse and longitudinal directions at a high temperature of 150°C, thereby improving the safety performance of secondary batteries.
  • the longitudinal tensile strength of the isolation film is ⁇ 2000kg/cm 2 , optionally 2500kg/cm 2 to 4500kg/cm 2 .
  • the transverse tensile strength of the isolation film is ⁇ 2000kg/cm 2 , optionally 2500kg/cm 2 to 4500kg/cm 2 .
  • the isolation film of the present application has high tensile strength in both the transverse and longitudinal directions. Therefore, when the secondary battery expands, the isolation film is less likely to be damaged, thereby improving the safety performance of the secondary battery.
  • the wetted length of the isolation film is ⁇ 30mm, optionally from 30mm to 80mm.
  • the wetting speed of the isolation film is ⁇ 3 mm/s, and may be selected from 3 mm/s to 10 mm/s.
  • the isolation membrane of the present application has good wetting and retention characteristics for the electrolyte, thereby improving the ion conductivity of the isolation membrane and the capacity performance characteristics of the secondary battery.
  • the air permeability of the isolation film is ⁇ 300s/100mL, and can be selected from 100s/100mL to 230s/100mL.
  • the isolation film of the present application has good air permeability, thereby improving the ion conductivity and secondary battery capacity performance characteristics.
  • the isolation film has a voltage breakdown strength of ⁇ 1KV.
  • the isolation film of the present application has high voltage breakdown strength, thereby improving the safety performance of the secondary battery.
  • the second aspect of this application provides a method for preparing the isolation membrane of the first aspect of this application, including the following steps: providing a porous substrate; mixing the material used to form the three-dimensional skeleton structure and the first filler in a solvent in a predetermined ratio, Formulate a coating slurry; apply the coating slurry on at least one surface of the porous substrate, and obtain an isolation film after drying, wherein the isolation film includes a porous substrate and a porous substrate.
  • a coating on at least one surface of a substrate comprising a three-dimensional skeleton structure and a first filler, at least a part of the first filler being filled in the three-dimensional skeleton structure, and the average of the first filler
  • the particle size is less than or equal to 200nm.
  • the coating slurry further includes a second filler, the average particle diameter of the first filler is denoted d 1 , and the average particle diameter of the second filler is denoted d 2 , then d 2 /d 1 >1.
  • a third aspect of the present application provides a secondary battery, including the separator film of the first aspect of the present application or a separator film prepared by the method of the second aspect of the present application.
  • a fourth aspect of the present application provides an electrical device, including the secondary battery of the third aspect of the present application.
  • the isolation film of the present application can enable the secondary battery to take into account high energy density, high thermal safety performance, and good cycle performance and dynamic performance.
  • the electrical device of the present application includes the secondary battery provided by the present application, and therefore has at least the same characteristics as the two The same advantages as secondary batteries.
  • FIG. 1 is a schematic diagram of an embodiment of the secondary battery of the present application.
  • FIG. 2 is an exploded schematic view of the embodiment of the secondary battery of FIG. 1 .
  • FIG. 3 is a schematic diagram of an embodiment of the battery module of the present application.
  • FIG. 4 is a schematic diagram of an embodiment of the battery pack of the present application.
  • FIG. 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4 .
  • FIG. 6 is a schematic diagram of an embodiment of a power consumption device including the secondary battery of the present application as a power source.
  • Ranges disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5.
  • the numerical range “a-b” represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers.
  • the numerical range “0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations.
  • a certain parameter is an integer ⁇ 2
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • step (c) means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c). , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.
  • condition "A or B” is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).
  • a secondary battery includes an electrode assembly and an electrolyte.
  • the electrode assembly includes a positive electrode piece, a negative electrode piece, and an isolation film.
  • the isolation film is placed between the positive electrode piece and the negative electrode piece to prevent short circuit between the positive electrode and the negative electrode. function, and at the same time, active ions can pass freely to form a loop.
  • the isolation film used in commercial secondary batteries is usually a polyolefin porous film, such as a polyethylene porous film, a polypropylene porous film or a polypropylene/polyethylene/polypropylene three-layer composite film, with a melting point between 130°C and 160°C.
  • the heat resistance of the isolation film becomes worse, and an obvious thermal shrinkage effect will occur when heated, causing direct contact between the positive and negative electrodes inside the battery, resulting in an internal short circuit, thereby increasing the number of secondary batteries. security risks.
  • the current measures are mainly to coat a heat-resistant inorganic ceramic layer on the polyolefin porous membrane, which can increase the mechanical strength of the isolation membrane, reduce the shrinkage of the isolation membrane when heated, and reduce the battery life. Risk of internal short circuit between positive and negative terminals.
  • the particle size of commercially available inorganic ceramic particles is larger, which will increase the overall thickness of the isolation film, resulting in the inability to balance the energy density of secondary batteries, especially in the field of power batteries, which is not conducive to improving the cruising range; in addition, commercially available inorganic ceramic particles Ceramic particles also have limited effect on improving the heat resistance of the isolation film.
  • Nanosized inorganic ceramic particles can reduce the coating thickness and alleviate the adverse impact on the energy density of secondary batteries.
  • nanosized inorganic ceramic particles can easily block the polyolefin porous membrane, resulting in poor capacity and dynamic performance of the secondary battery.
  • the isolation membrane can be made to have both low weight and high performance.
  • Heat resistance and high ion conductivity enable secondary batteries to combine high energy density, high thermal safety performance, long cycle life and good kinetic performance.
  • the first aspect of the embodiment of the present application provides an isolation membrane, including a porous substrate and a coating disposed on at least one surface of the porous substrate, wherein the coating includes a three-dimensional skeleton structure and a third A filler, at least part of the first filler is filled in the three-dimensional skeleton structure, and the average particle size of the first filler is less than or equal to 200 nm.
  • “three-dimensional skeleton structure” refers to a structure with a three-dimensional spatial shape and certain pores, which can be formed by overlapping materials constituting the three-dimensional skeleton structure.
  • the average particle size of the first filler is less than or equal to 200 nm, which has the advantages of large specific surface area and good affinity with the three-dimensional skeleton structure, and is conducive to forming a stable spatial network structure with the three-dimensional skeleton structure, thereby increasing the isolation film.
  • the ionic conductivity can also improve the heat resistance of the isolation film.
  • At least part of the first filler is filled in the three-dimensional skeleton structure, thereby helping the first filler and the three-dimensional skeleton structure to form a nesting effect, thereby increasing the heat resistance of the isolation film and reducing the degree of shrinkage of the isolation film when heated. , reduce the risk of short circuit of the positive and negative electrodes, make the secondary battery have high thermal safety performance, and maintain high bonding strength between the coating and the porous substrate to prevent the first filler from falling off during the long-term charging and discharging process of the secondary battery.
  • the coating of the present application has high heat resistance, which can reduce the thickness of the coating (for example, the thickness of the coating can be less than or equal to 2 ⁇ m), shorten the transmission distance of active ions, and then the secondary battery can also take into account high energy density and good performance. Cycle performance and kinetic performance; in addition, the coating of the present application has high heat resistance, which allows the use of thinner porous substrates, thereby further improving the energy density of secondary batteries.
  • At least a portion of the first filler is filled in the three-dimensional skeleton structure, and other portions of the first filler can be located on the surface of the three-dimensional skeleton structure and/or the three-dimensional skeleton structure
  • a small part of the first filler may also be embedded in the porous substrate, for example, when the electrode assembly is wound During the process, due to the external pressure, a small part of the first filler at the interface position is embedded in the matrix and/or pores of the porous substrate.
  • the three-dimensional skeleton structure may be formed from fibrous objects, and the morphology of the fibrous objects may optionally include at least one of a rod shape, a tube shape (eg, a hollow tube shape), a rod shape, and a fiber shape.
  • Appropriately shaped materials are conducive to the formation of a more stable spatial network structure between the three-dimensional skeleton structure and the first filler, which can further improve the heat resistance, ion conductivity, and electrolyte infiltration and retention characteristics of the isolation membrane.
  • fibrous material refers to a material with an aspect ratio of 5 or more.
  • the materials constituting the three-dimensional skeleton structure include at least one of organic materials and inorganic materials.
  • the organic material includes at least one of nanocellulose, polytetrafluoroethylene nanofibers and polyamide nanofibers.
  • the inorganic material includes at least one of halloysite nanotubes, nanorod-shaped alumina, nanorod-shaped boehmite, nanorod-shaped silica and glass fiber.
  • the material constituting the three-dimensional skeleton structure may include nanocellulose.
  • the nanocellulose includes cellulose nanofibrils (Cellulose nanofibrils, CNF, also known as nanofibrillar cellulose or microfibrillated cellulose), cellulose nanowhiskers (Cellulose nanocrystals, CNC, also known as At least one of cellulose nanocrystals, nanocrystalline cellulose) and bacterial nanocellulose (Bacterial nanocellulose, BNC, also known as bacterial cellulose or microbial cellulose).
  • CNF Cellulose nanofibrils
  • CNC also known as At least one of cellulose nanocrystals, nanocrystalline cellulose
  • bacterial nanocellulose Bacterial nanocellulose, BNC, also known as bacterial cellulose or microbial cellulose
  • Nanocellulose refers to the general name of cellulose with any dimension in the nanoscale (for example, within 100 nm), which has the characteristics of both cellulose and nanoparticles.
  • Nanocellulose can be a polymer nanomaterial extracted from wood, cotton, etc. in nature through one or more means of chemistry, physics, biology, etc. It has wide sources, low cost, biodegradability, and high modulus. , high specific surface area, etc., so it is an excellent substitute for traditional petrochemical resources and can effectively alleviate problems such as environmental pollution and petrochemical resource shortages. Nanocellulose also has good high temperature resistance and has small volume change after heating, which can improve the heat resistance of the isolation film.
  • nanocellulose has a smaller density, so It can also reduce the weight of the secondary battery and increase the weight energy density of the secondary battery.
  • the three-dimensional skeleton structure formed by nanocellulose can also have tiny nanopores to prevent current leakage, thereby enabling the isolation film to have both good electrolyte wetting and retention properties and good voltage breakdown resistance properties.
  • the nanocellulose may include at least one of unmodified nanocellulose (also known as hydroxyl nanocellulose) and modified nanocellulose, optionally modified nanocellulose.
  • Modified nanocellulose refers to nanocellulose that includes both hydroxyl groups and modified groups.
  • the modified nanocellulose includes a modifying group, and the modifying group includes at least one of an amine group, a carboxyl group, an aldehyde group, a sulfonic acid group, a boric acid group and a phosphate group, Optionally includes at least one of a sulfonic acid group, a boronic acid group and a phosphoric acid group.
  • nanocellulose has the above-mentioned specific modified groups
  • it can effectively improve the heat resistance of the isolation film and improve the thermal safety performance of the secondary battery; on the other hand, it can also improve the coating Bond strength between the layer and the porous substrate.
  • the nanocellulose has the above-mentioned specific modified groups, it is also conducive to the overlapping of the nanocellulose and the first filler to form an integrated effect, which can make the coating have a more stable spatial network structure, thereby improving the isolation film.
  • the wetting and retention properties of the electrolyte improve the ion conductivity and voltage breakdown resistance of the isolation membrane.
  • the presence of modified groups can also reduce the proportion of hydroxyl groups, thereby ensuring that the coating slurry has a suitable viscosity, which is more conducive to coating, thus improving the production efficiency of the isolation film and the uniformity of the coating.
  • the molar ratio of the modifying group to the hydroxyl group may be 1:4 to 4:1, optionally 2:3 to 7:3.
  • the molar ratio of the modified group to the hydroxyl group is within the above range, the heat resistance, ion conductivity, and electrolyte wetting and retention characteristics of the isolation membrane can be further improved.
  • the further improvement effect of the modified group on the heat resistance and ion conductivity of the isolation membrane may not be obvious; when the modified group When the molar ratio of the group to the hydroxyl group is too large, the electrolyte infiltration and retention characteristics of the isolation membrane may become poor, which may affect the cycle performance and safety performance of the secondary battery. It may also cause the heat resistance of the isolation membrane to decrease. Furthermore, the effect of improving the thermal safety performance of the secondary battery may be affected.
  • the types of modified groups in nanocellulose can be determined using infrared spectroscopy.
  • the infrared spectrum of the material can be tested to determine the characteristic peaks it contains, thereby determining the type of modifying group.
  • the materials can be analyzed by infrared spectroscopy using instruments and methods known in the art, such as using an infrared spectrometer (such as the IS10 Fourier transform infrared spectrometer of the American Nicoreet Company), according to GB/T 6040-2019 Infrared General principles of spectral analysis methods were tested.
  • an infrared spectrometer such as the IS10 Fourier transform infrared spectrometer of the American Nicoreet Company
  • the material constituting the three-dimensional skeleton structure includes a sulfonic acid group, and the content of sulfur element in the material constituting the three-dimensional skeleton structure is ⁇ 0.1wt%, optionally 0.2wt% to 0.5wt% , based on the total weight of the materials constituting the three-dimensional skeleton structure.
  • the material constituting the three-dimensional skeleton structure includes nanocellulose.
  • the content of sulfur element in the materials constituting the three-dimensional skeleton structure can be tested according to the following method: after drying the materials constituting the three-dimensional skeleton structure, grind them in a mortar (such as an agate mortar) for 30 minutes, and then use Test with a ray diffractometer (such as Miniflex600-C) to obtain the sulfur content.
  • a mortar such as an agate mortar
  • a ray diffractometer such as Miniflex600-C
  • the average diameter of the material constituting the three-dimensional skeleton structure may be ⁇ 40 nm, optionally 10 nm to 35 nm.
  • the ion conductivity and voltage breakdown resistance characteristics of the isolation membrane can be further improved, and it can also help to form an integration effect by overlapping with the first filler. This can also further improve the heat resistance of the isolation film. And it can effectively avoid the following situation: when the average diameter of the materials constituting the three-dimensional skeleton structure is too large, the mutual entanglement effect of the three-dimensional skeleton structure formed by it is insufficient and the pores are large, which may lead to the heat resistance and voltage resistance of the isolation film.
  • the breakdown characteristics are not excellent enough, and it is not conducive to the integration effect with the first filler. Moreover, during the drying process of the coating, the three-dimensional skeleton structure is easy to collapse due to the lack of support from the first filler, and is easily combined with the porous matrix. Direct contact with the material will cause pore blocking problems, which may affect the ion conductivity of the isolation membrane.
  • the average length of the material constituting the three-dimensional skeleton structure may be 100 nm to 600 nm, optionally 200 nm to 500 nm.
  • the heat resistance and ion conductivity of the isolation film can be further improved.
  • the coating slurry will have high viscosity and poor flow, which may affect the coating of the coating slurry and thus affect the quality of the coating. For example, it may affect the heat resistance of the isolation film. and ionic conductivity.
  • the aspect ratio of the material constituting the three-dimensional skeleton structure may be 5 to 60, optionally 10 to 30.
  • the aspect ratio of the material constituting the three-dimensional skeleton structure is within the above range, the ion conductivity of the isolation membrane and the wetting and retention characteristics of the electrolyte can be further improved.
  • the aspect ratio of the material constituting the three-dimensional skeleton structure is too small, the overlap effect with the first filler is poor, the heat resistance of the coating becomes worse, and during the drying process of the coating , the three-dimensional skeleton structure is easy to collapse due to the lack of support from the first filler, which can easily cause plugging problems, hinder ion transmission and water discharge, which may affect the thermal safety performance, cycle performance and dynamic performance of the secondary battery; when formed When the aspect ratio of the three-dimensional skeleton structure material is too large, the pores of the three-dimensional skeleton structure formed by it are smaller, which may lead to a smaller ion conductivity of the isolation membrane.
  • the average length and average diameter of the materials constituting the three-dimensional skeleton structure can be determined by the following method: cut out a 3.6mm ⁇ 3.6mm sample from any area of the isolation film, and measure the sample using a scanning electron microscope (such as ZEISS Sigma 300)
  • a scanning electron microscope such as ZEISS Sigma 300
  • For the microstructure of the intermediate coating select the high vacuum mode, the operating voltage is 3kV, and the magnification is 30,000 times to obtain the SEM image; based on the obtained SEM image, select multiple (for example, more than 5) test areas for length measurement.
  • the size of each test area is 0.5 ⁇ m ⁇ 0.5 ⁇ m, and then the average length of each test area is taken as the average length of the material constituting the three-dimensional skeleton structure; according to the obtained SEM image, use Nano Measurer particle size distribution statistics Software, select multiple (for example, more than 5) test areas for diameter statistics.
  • the size of each test area is 0.5 ⁇ m ⁇ 0.5 ⁇ m. Then, take the average value of the diameters obtained in each test area as the material constituting the three-dimensional skeleton structure. The average diameter.
  • the content of the three-dimensional skeleton structure may be 5 wt% to 40 wt%, optionally 8 wt% to 25 wt%, 10 wt% to 25 wt%, based on the total weight of the coating.
  • the materials constituting the three-dimensional skeleton structure have a larger specific surface area. Therefore, under the same mass, the coating formed has a larger specific surface area and more pores, which results in poor heat resistance of the isolation film. At the same time, the materials constituting the three-dimensional skeleton structure have a larger specific surface area and more pores.
  • the hydrogen bonding effect of materials (such as nanocellulose) is extremely strong.
  • the content of the three-dimensional skeleton structure When the content is high, it will lead to a high viscosity of the coating slurry, which is not conducive to achieving thin coatings and is not conducive to commercial production.
  • the content of the three-dimensional skeleton structure When the content of the three-dimensional skeleton structure is within the above range, it can ensure that the coating slurry has a suitable viscosity, which is more conducive to coating; in addition, it is also conducive to the overlapping of the three-dimensional skeleton structure and the first filler to form an integrated effect. It can make the coating have a more stable spatial network structure, which can further improve the heat resistance, ion conductivity, electrolyte infiltration and retention characteristics and voltage breakdown resistance of the isolation film.
  • the average particle size of the first filler is 15nm to 180nm, optionally 20nm to 170nm, 25nm to 160nm, 30nm to 150nm, 40nm to 140nm, 50nm to 135nm.
  • the first filler can have a higher specific surface area, so that the particle size of the first filler can better match the three-dimensional skeleton structure, so that the first filler and the three-dimensional skeleton structure can be better matched.
  • the skeleton structure can better overlap to form an integrated effect, increase the affinity between the first filler and the three-dimensional skeleton structure, increase the heat resistance and ion conductivity of the isolation membrane, and at the same time increase the isolation membrane's resistance to the electrolyte. Wetting and retention properties.
  • the first filler includes at least one of primary particles and secondary particles.
  • the first filler includes a combination of primary particles and secondary particles.
  • the first filler in the shape of primary particles can help reduce the moisture content of the coating and improve the ionic conductivity of the coating, thereby better improving the cycle performance of the secondary battery; the first filler in the shape of secondary particles can better Overlapping with the three-dimensional skeleton structure creates an integrated effect, which enables the coating to have a more stable spatial network structure, thereby further improving the heat resistance of the isolation film.
  • the first filler includes a combination of primary particles and secondary particles, and based on the total weight of the first filler, the content of the first filler in the form of primary particles is less than that of the secondary particles.
  • the content of the first filler in the particle morphology is less than that of the secondary particles.
  • the first filler includes a combination of primary particles and secondary particles, and the content of the first filler in the form of primary particles is less than or equal to 30 wt% based on the total weight of the first filler, Optional 8wt% to 30wt%, 8wt% to 28wt%, 10wt% to 30wt%, 10wt% to 28wt%, 12wt% to 30wt%, 12wt% to 28wt%, 15wt% to 30wt%, 15wt% to 28wt% , 17.5wt% to 30wt%, 17.5wt% to 28wt%.
  • the average particle size of the first filler in the primary particle shape is 15 nm to 95 nm, optionally 15 nm to 80 nm, 20 nm to 80 nm, 30 nm to 75 nm, 35 nm to 75 nm, 35 nm to 70 nm, 30 nm to 70nm, 30nm to 65nm.
  • the average particle diameter of the first filler with secondary particle morphology is 50nm to 200nm, optionally 50nm to 180nm, 50nm to 150nm, 50nm to 135nm, 50nm to 120nm, 55nm to 180nm, 55nm. to 150nm, 55nm to 135nm, 55nm to 120nm, 65nm to 180nm, 65nm to 150nm, 65nm to 135nm, 65nm to 120nm.
  • the BET specific surface area of the first filler is ⁇ 25m 2 /g, optionally 30m 2 /g to 80m 2 /g, 30m 2 /g to 65m 2 /g.
  • the specific surface area of the first filler is within the above range, it has better affinity with the three-dimensional skeleton structure and can overlap with the three-dimensional skeleton structure to form an integrated effect, thereby increasing the heat resistance and ion conduction of the isolation membrane. efficiency, and at the same time, it can also increase the wetting and retention characteristics of the isolation membrane to the electrolyte.
  • the first filler includes at least one of inorganic particles and organic particles, optionally including inorganic particles, or a combination of inorganic particles and organic particles.
  • Inorganic particles have the characteristics of high hardness, high thermal stability and not easy to decompose, and usually have hydroxyl groups on their surfaces, which can easily form a stable spatial network structure with materials that form a three-dimensional skeleton structure (such as nanocellulose, etc.).
  • Organic particles have good thermal stability and are not easily decomposed.
  • the organic particles can also melt and be decomposed due to capillary action. It is absorbed into the micropores of the porous substrate to close the cells and break the circuit, which is beneficial to improving the safety performance of the secondary battery.
  • the inorganic particles include boehmite ( ⁇ -AlOOH), aluminum oxide (Al 2 O 3 ), barium sulfate (BaSO 4 ), magnesium oxide (MgO), magnesium hydroxide (Mg(OH) 2 ) , silicon oxide compound SiO (Y 2 O 3 ), nickel oxide (NiO), hafnium dioxide (HfO 2 ), cerium oxide (CeO 2 ), zirconium titanate (ZrTiO 3 ), barium titanate (BaTiO 3 ) and magnesium fluoride (MgF 2 ) at least one of the following.
  • the inorganic particles include boehmite ( ⁇ -AlOOH), aluminum oxide (Al 2 O 3 ), barium sulfate (BaSO 4 ), magnesium oxide (MgO), silicon oxide compound SiO x (0 ⁇ x ⁇ 2), at least one of titanium oxide (TiO 2 ), zinc oxide (ZnO), cerium oxide (CeO 2 ) and barium titanate (BaTiO 3 ).
  • the organic particles include polystyrene particles, polyacrylic wax particles, melamine formaldehyde resin particles, phenolic resin particles, polyester particles, polyimide particles, polyamideimide particles, polyaramid particles, polyamide particles, etc. At least one of phenyl sulfide particles, polysulfone particles, polyethersulfone particles, polyether ether ketone particles and polyaryl ether ketone particles.
  • the first filler includes inorganic particles
  • the crystal form of the inorganic particles includes at least one of theta crystal form, gamma crystal form, and n crystal form.
  • the crystal form of the inorganic particles includes at least one of a ⁇ crystal form and a ⁇ crystal form.
  • the inorganic particles of the ⁇ crystal form have diffraction peaks at 36.68° ⁇ 0.2° and 31.21° ⁇ 0.2° in 2 ⁇ in an X-ray diffraction spectrum measured using an X-ray diffractometer.
  • the content of the ⁇ crystalline inorganic particles in the first filler may be ⁇ 50 wt%, optionally 55 to 84 wt% based on the total weight of the inorganic particles in the first filler. count.
  • Inorganic particles of the ⁇ crystal form have diffraction peaks at 2 ⁇ of 66.95° ⁇ 0.2° and 45.91° ⁇ 0.2° in an X-ray diffraction spectrum measured using an X-ray diffractometer.
  • the content of the ⁇ crystalline inorganic particles in the first filler may be ⁇ 10 wt%, optionally 15 to 44 wt%, based on the total amount of the inorganic particles in the first filler. Weight scale.
  • the inorganic particles of the eta crystal form have diffraction peaks at 31.89° ⁇ 0.2° and 19.37° ⁇ 0.2° in 2 ⁇ in an X-ray diffraction spectrum measured using an X-ray diffractometer.
  • the content of the n-crystalline inorganic particles in the first filler may be ⁇ 5wt%, optionally ⁇ 2.5wt%, and more optionally ⁇ 1.5wt%, based on the first filler. based on the total weight of the inorganic particles.
  • Inorganic particles of the ⁇ crystal form have moderate specific surface area and hardness, which can better improve the heat resistance and ion conductivity of the isolation film at the same time; inorganic particles of the ⁇ crystal form and eta crystal form have the advantage of large specific surface areas. .
  • Selecting first fillers of different crystal forms helps to improve at least one of the heat resistance, ion conductivity, bonding strength, and electrolyte wetting and retention properties of the isolation film.
  • the first filler may include inorganic particles, and the crystal forms of the inorganic particles include theta crystal form, gamma crystal form, and n crystal form, and the inorganic form of the theta crystal form in the first filler
  • the content of the particles can be 55wt% to 84wt%
  • the content of the inorganic particles of the ⁇ crystalline form can be 15wt% to 44wt%
  • the content of the inorganic particles of the eta crystalline form can be ⁇ 2.5wt%, all based on the first filler. based on the total weight of the inorganic particles.
  • the X-ray diffraction spectrum of inorganic particles can be tested as follows: after drying the inorganic particles, grind them in a mortar (such as agate mortar) for 30 minutes, and then use an X-ray diffractometer (such as Miniflex600-C) for testing. An X-ray diffraction spectrum was obtained.
  • a mortar such as agate mortar
  • an X-ray diffractometer such as Miniflex600-C
  • the first filler may include inorganic particles, and the inorganic particles may be prepared as follows: the precursor solution of the inorganic particles is oxidized by high-pressure sputtering, and then heated at 600°C to 900°C. Heating at 150 to 3 hours to form inorganic particles with primary particle morphology, and then drying and shaping at 150°C to 250°C (for example, 30 minutes to 60 minutes) to obtain inorganic particles with secondary particle morphology Particles (obtained through primary particle assembly).
  • the content of the first filler is ⁇ 50wt%, optionally 50wt% to 90wt%, 55wt% to 90wt%, 60wt% to 90wt%, 50wt% to 85wt%, 55wt% to 85wt% , 60wt% to 85wt%, 50wt% to 82.5wt%, 55wt% to 82.5wt%, 60wt% to 82.5wt%, based on the total weight of the coating.
  • the content of the first filler is within the above range, it can ensure that the coating slurry has a suitable viscosity, which is more conducive to coating; in addition, it is also conducive to forming an integrated effect with the three-dimensional skeleton structure, thereby making the coating It has a more stable spatial network structure, which can further improve the heat resistance and ion conductivity of the isolation film.
  • the coating further includes a second filler, at least a portion of the second filler being embedded in the coating.
  • the coating includes a first filler and a second filler, the average particle diameter of the first filler is denoted as d 1 , and the average particle diameter of the second filler is denoted as d 2 , then d 2 /d 1 >1.
  • the second filler has a larger average particle size, which can better play its supporting role in the coating, reduce the shrinkage of the first filler, and reduce the amount of binder, thereby improving the heat resistance of the isolation film;
  • the larger particle size of the filler also helps the coating to have more pore structure and less water content when the dosage is small, which can further improve the ion conductivity of the isolation membrane and the infiltration and penetration of the electrolyte. Maintain the characteristics while also improving the cycle performance and/or kinetic performance of the secondary battery.
  • the first filler includes at least one of primary particles and secondary particles.
  • the average particle diameter of the first filler in the form of primary particles is recorded as d 11
  • the average particle diameter of the first filler in the form of secondary particles is d 11
  • the particle size is recorded as d 12 .
  • 3.0 ⁇ d2 / d11 ⁇ 10.0 optionally, 3.5 ⁇ d2 / d11 ⁇ 8.0 , 3.5 ⁇ d2 / d11 ⁇ 6.0 .
  • the first filler and the second filler helps to reduce the moisture content of the coating, so that the coating maintains a stable pore structure during long-term charge and discharge processes, and at the same time, it can also improve the heat resistance of the isolation film, thereby enabling The secondary battery can better balance high energy density, high thermal safety performance, long cycle life and good dynamic performance.
  • 1.2 ⁇ d2 / d12 ⁇ 6.0 optionally, 2.0 ⁇ d2 / d12 ⁇ 5.5 , 2.0 ⁇ d2 / d12 ⁇ 5.0 , 2.0 ⁇ d2 / d12 ⁇ 4.5 .
  • the first filler and the second filler helps to reduce the moisture content of the coating, so that the coating maintains a stable pore structure during long-term charge and discharge processes, and at the same time, it can also improve the heat resistance of the isolation film, thereby enabling The secondary battery can better balance high energy density, high thermal safety performance, long cycle life and good dynamic performance.
  • the second filler has an average particle size d 2 of 120 nm to 350 nm, optionally 150 nm to 300 nm.
  • the supporting role of the second filler can be better exerted, the moisture content of the coating can be reduced, the coating can maintain a stable pore structure during long-term charge and discharge processes, and the heat resistance of the isolation film can also be improved.
  • the BET specific surface area of the second filler is ⁇ 20m 2 /g, optionally 6m 2 /g to 15m 2 /g.
  • the second filler includes at least one of inorganic particles and organic particles.
  • the inorganic particles may include at least one of inorganic particles having a dielectric constant of more than 5, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of electrochemical reactions.
  • the inorganic particles with a dielectric constant of more than 5 include boehmite, aluminum oxide, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, Cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, Magnesium aluminum silicate, magnesium lithium silicate, sodium magnesium silicate, bentonite, hectorite, zirconium titanate, barium titanate, Pb(Zr,Ti)O 3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti n O 3 (abbreviated as PLZT, 0 ⁇ m ⁇ 1, 0 ⁇ n ⁇ 1), Pb(Mg 3 Nb
  • each inorganic particle may be modified by chemical modification and/or physical modification.
  • the chemical modification methods include coupling agent modification (for example, using silane coupling agent, titanate coupling agent, etc.), surfactant modification, polymer graft modification, etc.
  • the physical modification method can be mechanical dispersion, ultrasonic dispersion, high-energy treatment, etc.
  • the agglomeration of inorganic particles can be reduced through modification treatment, thereby making the coating have a more stable and uniform spatial network structure; in addition, the inorganic particles can be modified by selecting coupling agents, surfactants or polymers with specific functional groups. The particles also help to improve the wetting and retention properties of the coating to the electrolyte, and improve the adhesion of the coating to the porous substrate.
  • the inorganic particles that have ion conductivity but do not store ions include Li 3 PO 4 , lithium titanium phosphate Li x1 Ti y1 (PO 4 ) 3 , lithium aluminum titanium phosphate Li x2 A ly2 Ti z1 (PO 4 ) 3.
  • the inorganic particles capable of electrochemical reactions include at least one of lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials and lithium-titanium compounds.
  • the organic particles include, but are not limited to, polyethylene particles, polypropylene particles, cellulose, cellulose modifiers (such as carboxymethylcellulose), melamine resin particles, phenolic resin particles, polyester particles (such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), silicone resin particles, polyimide particles, polyamide-imide particles, polyarylene Amide particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyether ether ketone particles, polyaryl ether ketone particles, copolymers of butyl acrylate and ethyl methacrylate (such as butyl acrylate and methyl acrylate At least one of the cross-linked polymers of ethyl acrylate).
  • the second filler has a primary particle morphology.
  • the second filler includes inorganic particles with primary particle morphology
  • the crystal form of the inorganic particles with primary particle morphology includes at least one of ⁇ crystal form and ⁇ crystal form, optionally including ⁇ crystal form.
  • the ⁇ -crystalline second filler has the advantages of high hardness, good heat resistance, low dielectric constant, high safety and high true density, which can further improve the heat resistance of the coating.
  • the second filler includes inorganic particles with a primary particle morphology
  • the crystal form of the inorganic particles with a primary particle morphology includes an ⁇ crystal form
  • the content of the ⁇ crystal form is ⁇ 70 wt%, which can be It is selected as 75wt% to 100wt%, 85wt% to 100wt%, 95wt% to 100wt%, based on the total weight of the inorganic particles of the primary particle morphology in the second filler.
  • the inorganic particles of the ⁇ crystal form have diffraction peaks at 2 ⁇ of 57.48° ⁇ 0.2° and 43.34° ⁇ 0.2° in an X-ray diffraction spectrum measured using an X-ray diffractometer.
  • the content of the second filler is ⁇ 30wt%, optionally 5wt% to 25wt%, 6wt% to 22wt%, 6wt% to 20wt%, 8wt% to 18wt%, based on the coating of total weight.
  • the supporting role of the second filler can be better exerted, the moisture content of the coating can be reduced, and the coating can maintain a stable pore structure during long-term charge and discharge processes.
  • the coating may also include a non-granular binder.
  • a non-granular binder There is no particular limitation on the type of non-granular binder in this application, and any well-known material with good adhesiveness can be selected.
  • the non-granular binder includes an aqueous solution binder, which has the advantages of good thermodynamic stability and environmental protection, thereby facilitating the preparation and coating of the coating slurry.
  • the aqueous solution-type binder may include aqueous solution-type acrylic resin (for example, acrylic acid, methacrylic acid, sodium acrylate monomer homopolymer or copolymer with other comonomers), polyvinyl alcohol (PVA) , at least one of isobutylene-maleic anhydride copolymer and polyacrylamide.
  • aqueous solution-type acrylic resin for example, acrylic acid, methacrylic acid, sodium acrylate monomer homopolymer or copolymer with other comonomers
  • PVA polyvinyl alcohol
  • isobutylene-maleic anhydride copolymer at least one of isobutylene-maleic anhydride copolymer and polyacrylamide.
  • the content of the non-granular binder in the coating is ⁇ 2 wt%, based on the total weight of the coating.
  • the three-dimensional skeleton structure and the first filler in the coating of the present application can form a stable spatial network structure, thereby enabling the isolation film to maintain high adhesion while reducing the amount of binder.
  • the thickness of the coating may be ⁇ 2 ⁇ m, optionally 0.5 ⁇ m to 1.5 ⁇ m. This helps to increase the energy density of secondary batteries.
  • the thickness of the coating refers to the thickness of the coating on one side of the porous substrate.
  • the thickness of the porous substrate may be ⁇ 6 ⁇ m, optionally 3 ⁇ m to 5 ⁇ m.
  • the coating of the present application can significantly improve the heat resistance of the isolation film, thereby enabling the use of thinner porous substrates, thereby helping to increase the energy density of secondary batteries.
  • the porous substrate can include a porous polyolefin-based resin film (such as polyolefin-based resin film). At least one of ethylene, polypropylene, polyvinylidene fluoride), at least one of porous glass fiber and porous non-woven fabric.
  • the porous substrate may be a single-layer film or a multi-layer composite film. When the porous substrate is a multi-layer composite film, the materials of each layer may be the same or different.
  • the isolation film may further include an adhesive layer disposed on at least a portion of the surface of the coating, the adhesive layer including a granular adhesive.
  • the adhesive layer can not only prevent the coating from peeling off and improve the safety performance of the secondary battery, but also improve the interface between the isolation film and the electrode and improve the cycle performance of the secondary battery.
  • the granular binder includes at least one of acrylic monomer homopolymers or copolymers, acrylic monomer homopolymers or copolymers, and fluorine-containing olefin monomer homopolymers or copolymers.
  • the comonomers include, but are not limited to, at least one of the following: acrylate monomers, acrylic acid monomers, olefin monomers, halogen-containing olefin monomers, fluoroether monomers, etc.
  • the particulate binder includes a vinylidene fluoride-based polymer, such as a homopolymer of vinylidene fluoride monomer (VDF) and/or a copolymer of vinylidene fluoride monomer and comonomer.
  • VDF vinylidene fluoride monomer
  • the comonomer may be at least one of olefin monomers, fluorine-containing olefin monomers, chlorine-containing olefin monomers, acrylate monomers, acrylic acid monomers, and fluoroether monomers.
  • the comonomer may include at least one of the following: trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoroethylene Propylene (HFP), perfluoro (alkyl vinyl) ether (such as perfluoro (methyl vinyl) ether PMVE, perfluoro (ethyl vinyl) ether PEVE, perfluoro (propyl vinyl) ether PPVE), Perfluoro(1,3-dioxole) and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD).
  • VF3 trifluoroethylene
  • CTFE chlorotrifluoroethylene
  • TFE tetrafluoroethylene
  • HFP hexafluoroethylene Propylene
  • perfluoro (alkyl vinyl) ether such as perfluoro (methyl vinyl) ether PMVE, perfluoro (
  • the longitudinal thermal shrinkage rate of the isolation film at 150° C. for 1 hour is ⁇ 6%, optionally 0.5% to 4%.
  • the transverse thermal shrinkage rate of the isolation film at 150° C. for 1 hour is ⁇ 6%, optionally 0.5% to 4%.
  • the isolation film of the present application has low thermal shrinkage in both transverse and longitudinal directions at a high temperature of 150°C, thereby improving the safety performance of secondary batteries.
  • the longitudinal tensile strength of the isolation film is ⁇ 2000kg/cm 2 , optionally 2500kg/cm 2 to 4500kg/cm 2 .
  • the transverse tensile strength of the isolation film is ⁇ 2000kg/cm 2 , optionally 2500kg/cm 2 to 4500kg/cm 2 .
  • the isolation film of the present application has high tensile strength in both the transverse and longitudinal directions. Therefore, when the secondary battery expands, the isolation film is less likely to be damaged, thereby improving the safety performance of the secondary battery.
  • the wetted length of the isolation film is ⁇ 30mm, optionally 30mm to 80mm.
  • the wetting speed of the isolation film is ⁇ 3 mm/s, optionally 3 mm/s to 10 mm/s.
  • the isolation membrane of the present application has good wetting and retention characteristics for the electrolyte, thereby improving the ion conductivity of the isolation membrane and the capacity performance characteristics of the secondary battery.
  • the air permeability of the isolation film is ⁇ 300s/100mL, optionally between 100s/100mL and 230s/100mL.
  • the isolation film of the present application has good air permeability, thereby improving the ion conductivity and secondary battery capacity performance characteristics.
  • the isolation film has a voltage breakdown strength of ⁇ 1 KV.
  • the isolation film of the present application has high voltage breakdown strength, thereby improving the safety performance of the secondary battery.
  • the average particle size of a material is a meaning known in the art, and can be measured using instruments and methods known in the art.
  • a picture can be obtained by measuring the material or isolation film through a scanning electron microscope, a transmission electron microscope, or a particle size distribution instrument, and randomly selecting multiple (for example, more than 10) test particles (for example, having a first filler, a second filler) from the picture. etc.), and the average value of the shortest diagonal length of the particles is calculated as the average particle size.
  • the specific surface area of a material has a well-known meaning in the art, and can be measured using instruments and methods known in the art.
  • the nitrogen adsorption specific surface area analysis test can be performed by the Tri-Star 3020 specific surface area pore size analysis tester of the American Micromeritics Company.
  • thermal shrinkage rate, tensile strength and air permeability of the isolation film all have meanings known in the art, and can be measured using methods known in the art. For example, you can refer to the standard GB/T 36363-2018 for testing.
  • the wetting length and wetting speed of the isolation film have well-known meanings in the art, and can be measured using methods known in the art.
  • An exemplary test method is as follows: Cut the isolation film into a sample with a width of 5mm and a length of 100mm, fix both ends of the sample and place it horizontally; drop 0.5mg of electrolyte in the center of the sample for the specified time (1min in this application) Finally, take pictures and measure the length of electrolyte diffusion, thereby obtaining the wetting length and wetting speed of the isolation film.
  • multiple (for example, 5 to 10) samples can be taken for testing, and the test results are obtained by calculating the average value.
  • the electrolyte can be prepared as follows: mix ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) at a mass ratio of 30:50:20 to obtain an organic solvent. 6 was dissolved in the above organic solvent to prepare an electrolyte solution with a concentration of 1 mol/L.
  • the voltage breakdown strength of the isolation film has a meaning known in the art, and can be measured using methods known in the art.
  • An exemplary test method is as follows: Cut the isolation film into a rectangular sample of 450mm ⁇ 650mm, and use a withstand voltage tester to measure it.
  • the test instrument can be the CS2671AX withstand voltage tester.
  • the coating parameters (such as thickness, etc.) of the above-mentioned isolation membrane are the coating parameters of one side of the porous substrate.
  • the coating is disposed on both sides of the porous substrate, if the coating parameters on either side meet the requirements of this application, it is deemed to fall within the protection scope of this application.
  • the second aspect of the embodiment of the present application provides a method for preparing the isolation film of the first aspect of the embodiment of the present application, including the following steps: providing a porous base material; adding a material used to form a three-dimensional skeleton structure and a first filler in a predetermined ratio.
  • the isolation film includes a porous substrate and a device A coating on at least one surface of the porous substrate, the coating comprising a three-dimensional skeleton structure and a first filler, at least a part of the first filler being filled in the three-dimensional skeleton structure, and the third
  • the average particle size of a filler is less than or equal to 200 nm.
  • the coating slurry further includes a second filler, the average particle diameter of the first filler is denoted d 1 , and the average particle diameter of the second filler is denoted d 2 , then d 2 / d 1 > 1.
  • the solvent used in formulating the coating slurry may be water, such as deionized water.
  • the coating slurry may also include other components, such as dispersants, wetting agents, binders, etc.
  • the material used to form the three-dimensional skeleton structure includes at least one of organic materials and inorganic materials.
  • the organic material includes at least one of nanocellulose, polytetrafluoroethylene nanofibers and polyamide nanofibers.
  • the inorganic material includes at least one of halloysite nanotubes, nanorod-shaped alumina, nanorod-shaped boehmite, nanorod-shaped silica and glass fiber.
  • the material constituting the three-dimensional skeleton structure includes nanocellulose.
  • the nanocellulose can be obtained as follows: providing a cellulose powder with a whiteness of ⁇ 80%; mixing and reacting the obtained cellulose powder with a modified solution, washing and removing impurities, and then Adjust the pH to neutral, grind and cut to obtain nanocellulose.
  • the above-mentioned cellulose powder with a whiteness of ⁇ 80% can be purchased commercially, or chemical methods (such as acidolysis, alkali treatment, Tempo catalytic oxidation), biological methods (such as enzyme treatment), or mechanical methods can be used. (such as ultra-fine grinding, ultrasonic crushing, high-pressure homogenization), etc.
  • the fiber raw materials used to prepare the above-mentioned cellulose powder with a whiteness of ⁇ 80% may include plant fibers, such as cotton fiber (such as cotton fiber, kapok fiber), hemp fiber (such as sisal fiber, ramie fiber, jute fiber, flax fiber, Hemp fiber, abaca fiber, etc.), at least one of brown fiber, wood fiber, bamboo fiber, and grass fiber.
  • the above-mentioned cellulose powder with a whiteness of ⁇ 80% can also be prepared in the following manner: after the fiber raw material is opened and deslaged, it is treated with an alkali solution (such as a NaOH aqueous solution, the concentration of which can be 4wt% to 20wt %, optionally 5wt% to 15wt%) cooking, and then sequentially undergo water washing to remove impurities (for example, the number of water washings is 3 to 6 times), bleaching (for example, sodium hypochlorite and/or hydrogen peroxide can be used), pickling to remove impurities, and water washing to remove impurities. impurities, water displacing, and airflow drying to obtain cellulose powder.
  • an alkali solution such as a NaOH aqueous solution, the concentration of which can be 4wt% to 20wt %, optionally 5wt% to 15wt
  • water washing for example, the number of water washings is 3 to 6 times
  • bleaching for example, sodium hypoch
  • the modification solution may be an acid solution (such as sulfuric acid aqueous solution, boric acid aqueous solution, phosphoric acid aqueous solution, acetic acid aqueous solution) or an alkali solution (such as urea organic solvent solution).
  • the modified solution is an acid solution.
  • the concentration of the acid solution may be 5 to 80 wt%.
  • a sulfuric acid aqueous solution is selected as the modification solution
  • the concentration of the acid solution can be 40 wt% to 80 wt%, whereby cellulose powder with sulfonic acid groups can be obtained.
  • a boric acid aqueous solution is selected as the modification solution
  • the concentration of the acid solution can be 5 wt% to 10 wt%, whereby cellulose powder with boric acid groups can be obtained.
  • a phosphoric acid aqueous solution is selected as the modification solution
  • the concentration of the acid solution can be 45 wt% to 75 wt%, whereby cellulose powder with phosphate groups can be obtained.
  • an acetic acid aqueous solution is selected as the modification solution
  • the concentration of the acid solution can be 40 wt% to 80 wt%, whereby cellulose powder with carboxylic acid groups can be obtained.
  • the urea organic solvent solution is a urea xylene solution, whereby cellulose powder with amine groups can be obtained.
  • the mass ratio of the cellulose powder to the modified solution may be 1:2.5 to 1:50, optionally 1:5 to 1:30.
  • the mass ratio of the cellulose powder to the acid solution can be 1:5 to 1:30.
  • the mass ratio of the cellulose powder to the acid solution can be 1:20 to 1:50.
  • the modified solution is a phosphoric acid aqueous solution, the mass ratio of the cellulose powder to the acid solution can be 1:5 to 1:30.
  • an acetic acid aqueous solution is selected as the modification solution, the mass ratio of the cellulose powder to the acid solution can be 1:5 to 1:30.
  • a urea organic solvent solution is selected as the modification solution, the mass ratio of the cellulose powder to the urea organic solvent solution may be 1:4 to 1:40.
  • the reaction when the modified solution is an acid solution, the reaction can be performed at a temperature no higher than 80°C, optionally at a temperature of 30°C to 60°C, and the cellulose
  • the reaction time between the powder and the modified solution can be 0.5h to 4h, optionally 1h to 3h.
  • the reaction when the modified solution is an alkaline solution, the reaction can be carried out at a temperature of 100°C to 145°C, and the reaction time between the cellulose powder and the modified solution can be 1 hour to 145°C. 5h.
  • a grinder can be used for grinding, and a high-pressure homogenizer can be used for cutting.
  • Nanocellulose with different average diameters and/or different average lengths can be obtained by adjusting the grinding parameters of the grinder (such as the number of grinding times, grinding time, etc.) and the cutting parameters of the high-pressure homogenizer.
  • a coating machine may be used when applying the coating slurry.
  • This application has no special restrictions on the model of the coating machine.
  • a commercially available coating machine can be used.
  • the coater includes a gravure roller; the gravure roller is used to transfer the slurry onto the porous substrate.
  • the coating slurry can be coated by transfer coating, spin spray coating, dip coating, etc.
  • the method further includes the following steps: applying a slurry containing a granular binder on at least a portion of the surface of the coating, and drying to form an adhesive layer.
  • the preparation method of the isolation film of the present application obtains the coating through one-time coating, which greatly simplifies the production process of the isolation film.
  • isolation film of the present application Some raw materials and their content and other parameters used in the preparation method of the isolation film of the present application can be referred to the isolation film of the first aspect of the embodiment of the application, and will not be described again here.
  • each raw material used in the preparation method of the isolation film of the present application can be obtained commercially.
  • a third aspect of the embodiment of the present application provides a secondary battery.
  • Secondary batteries also known as rechargeable batteries or storage batteries, refer to batteries that can be recharged to activate active materials and continue to be used after the battery is discharged.
  • a secondary battery includes an electrode assembly and an electrolyte.
  • the electrode assembly includes a positive electrode piece, a negative electrode piece, and a separator.
  • the isolation film is disposed between the positive electrode piece and the negative electrode piece, It mainly plays the role of preventing short circuit between the positive and negative electrodes, and at the same time allows active ions to pass through.
  • the secondary battery may be a lithium-ion battery, a sodium-ion battery, etc.
  • the secondary battery may be a lithium-ion secondary battery.
  • the secondary battery of the third aspect of the embodiment of the present application includes the separator of the first aspect of the embodiment of the present application or a separator prepared by the method of the second aspect of the embodiment of the present application.
  • the separator film is spaced between the positive electrode plate and the between the negative electrode pieces.
  • at least the side of the isolation film close to the negative electrode piece has the coating of the present application. Therefore, the secondary battery of the present application can take into account high energy density, high thermal safety performance, long cycle life and good dynamic performance.
  • the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and including a positive active material.
  • the positive electrode current collector has two surfaces opposite in its thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive active material may include, but is not limited to, at least one of lithium-containing transition metal oxides, lithium-containing phosphates and their respective modified compounds.
  • the lithium transition metal oxide may include, but are not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt At least one of manganese oxide, lithium nickel cobalt aluminum oxide and their respective modified compounds.
  • lithium-containing phosphate may include, but are not limited to, lithium iron phosphate, composites of lithium iron phosphate and carbon, lithium manganese phosphate, composites of lithium manganese phosphate and carbon, lithium iron manganese phosphate, lithium iron manganese phosphate and carbon. at least one of the composite materials and their respective modifying compounds.
  • the cathode active material for the lithium-ion battery may include a lithium transition metal oxide with the general formula Li a Ni b Co c M d O e Af and its at least one of the modified compounds. 0.8 ⁇ a ⁇ 1.2, 0.5 ⁇ b ⁇ 1, 0 ⁇ c ⁇ 1, 0 ⁇ d ⁇ 1, 1 ⁇ e ⁇ 2, 0 ⁇ f ⁇ 1, M is selected from Mn, Al, Zr, Zn, Cu, Cr , at least one of Mg, Fe, V, Ti and B, and A is selected from at least one of N, F, S and Cl.
  • a lithium transition metal oxide with the general formula Li a Ni b Co c M d O e Af and its at least one of the modified compounds. 0.8 ⁇ a ⁇ 1.2, 0.5 ⁇ b ⁇ 1, 0 ⁇ c ⁇ 1, 0 ⁇ d ⁇ 1, 1 ⁇ e ⁇ 2, 0 ⁇ f ⁇ 1, M is selected from Mn, Al, Zr, Zn, Cu, Cr , at least one of Mg, Fe, V, Ti and B, and A is
  • cathode active materials for lithium ion batteries may include LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM333), LiNi 0.5 Co 0.2 At least one of Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O 2 , LiFePO 4 , and LiMnPO 4 kind.
  • the positive active material may include but is not limited to sodium-containing transition metal oxides, polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.) , at least one of Prussian blue materials.
  • cathode active materials for sodium ion batteries may include NaFeO 2 , NaCoO 2 , NaCrO 2 , NaMnO 2 , NaNiO 2 , NaNi 1/2 Ti 1/2 O 2 , NaNi 1/2 Mn 1/2 O 2 , Na 2/3 Fe 1/3 Mn 2/3 O 2 , NaNi 1/3 Co 1/3 Mn 1/3 O 2 , NaFePO 4 , NaMnPO 4 , NaCoPO 4 , Prussian blue materials, the general formula is X p M' q (PO 4 ) r O x Y 3-x at least one of the materials.
  • M' is a transition metal cation, optionally at least one of V, Ti, Mn, Fe, Co, Ni, Cu and Zn
  • Y is a halogen anion, optionally at least one of F, Cl and Br.
  • the modified compounds of each of the above-mentioned positive electrode active materials may be doping modifications and/or surface coating modifications of the positive electrode active materials.
  • the positive electrode film layer optionally further includes a positive electrode conductive agent.
  • a positive electrode conductive agent includes superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, and graphene. and at least one of carbon nanofibers.
  • the mass percentage of the cathode conductive agent is ⁇ 5 wt%.
  • the positive electrode film layer optionally further includes a positive electrode binder.
  • the positive electrode binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene At least one of ethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.
  • the mass percentage of the cathode binder is ⁇ 5 wt% based on the total weight of the cathode film layer.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • a metal foil aluminum foil can be used.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.
  • the polymer material base layer may include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and At least one of polyethylene (PE).
  • the positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying, and cold pressing.
  • the positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder and any other components in a solvent and stirring evenly.
  • the solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material.
  • the negative electrode current collector has two surfaces opposite in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative active material may be a negative active material known in the art for secondary batteries.
  • the negative active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.
  • the silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitride composite and silicon alloy material.
  • the tin-based material may include at least one of elemental tin, tin oxide and tin alloy materials.
  • the negative electrode film layer optionally further includes a negative electrode conductive agent.
  • a negative electrode conductive agent may include superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite at least one of ene and carbon nanofibers.
  • the mass percentage of the negative electrode conductive agent is ⁇ 5 wt%.
  • the negative electrode film layer optionally further includes a negative electrode binder.
  • the negative electrode binder may include styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (for example, At least one of polyacrylic acid (PAA), polymethacrylic acid (PMAA), polyacrylic acid sodium (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA) and carboxymethyl chitosan (CMCS). kind.
  • the mass percentage of the negative electrode binder is ⁇ 5 wt% based on the total weight of the negative electrode film layer.
  • the negative electrode film layer optionally includes other additives.
  • other auxiliaries may include thickeners, such as sodium carboxymethylcellulose (CMC), PTC thermistor materials, and the like.
  • CMC sodium carboxymethylcellulose
  • PTC thermistor materials such as sodium carboxymethylcellulose (CMC)
  • the mass percentage content of the other additives is ⁇ 2wt%.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the metal foil copper foil can be used.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.
  • the polymer material base layer may include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and At least one of polyethylene (PE).
  • the negative electrode film layer is usually formed by coating the negative electrode slurry on the negative electrode current collector, drying, and cold pressing.
  • the negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional auxiliaries in a solvent and stirring evenly.
  • the solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.
  • the negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer.
  • the negative electrode sheet described in the present application further includes a conductive undercoat layer (for example, made of Conductive agent and adhesive).
  • the negative electrode sheet described in this application further includes a protective layer covering the surface of the negative electrode film layer.
  • the electrolyte solution includes electrolyte salts and solvents.
  • the types of the electrolyte salt and the solvent are not specifically limited and can be selected according to actual needs.
  • the electrolyte salt may include but is not limited to lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), hexafluoroborate Lithium fluoroarsenate (LiAsF 6 ), lithium bisfluorosulfonimide (LiFSI), lithium bistrifluoromethanesulfonimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoromethanesulfonate borate (LiDFOB) ), at least one of lithium difluoroborate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorodioxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTF
  • the electrolyte salt may include but is not limited to sodium hexafluorophosphate (NaPF 6 ), sodium tetrafluoroborate (NaBF 4 ), sodium perchlorate (NaClO 4 ), sodium hexafluoromethanesulfonate (NaAsF 6 ), sodium bisfluorosulfonimide (NaFSI), sodium bistrifluoromethanesulfonimide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), difluoroxalic acid boric acid At least one of sodium (NaDFOB), sodium dioxaloborate (NaBOB), sodium difluorophosphate (NaPO 2 F 2 ), sodium difluorodioxalophosphate (NaDFOP) and sodium tetrafluorooxalophosphate (NaTFOP).
  • NaPF 6 sodium hexafluorophosphate
  • NaBF 4 sodium tetra
  • the solvent may include, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), Dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), At least one of ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sul
  • additives are optionally included in the electrolyte.
  • the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery performance. Additives for low temperature power performance, etc.
  • the positive electrode piece, the isolation film and the negative electrode piece can be made into an electrode assembly through a winding process and/or a lamination process.
  • the secondary battery may include an outer packaging.
  • the outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the soft bag may be made of plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).
  • This application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. As shown in FIG. 1 , a square-structured secondary battery 5 is shown as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 is used to cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process and/or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and can be adjusted according to needs.
  • the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte may be assembled to form a secondary battery.
  • the positive electrode sheet, isolation film, and negative electrode sheet can be formed into an electrode assembly through a winding process and/or a lamination process.
  • the electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After vacuum packaging, static Through processes such as placement, formation, and shaping, secondary batteries are obtained.
  • the secondary batteries according to the present application can be assembled into a battery module.
  • the number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG. 3 is a schematic diagram of the battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 arranged in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 is used to cover the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • a fourth aspect of the embodiments of the present application provides an electrical device, which includes at least one of a secondary battery, a battery module or a battery pack of the present application.
  • the secondary battery, battery module or battery pack may be used as a power source for the electrical device or as an energy storage unit for the electrical device.
  • the electrical device may be, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric Golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • the power-consuming device can select a secondary battery, a battery module or a battery pack according to its usage requirements.
  • FIG. 6 is a schematic diagram of an electrical device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.
  • battery packs or battery modules can be used.
  • the power-consuming device may be a mobile phone, a tablet computer, a laptop computer, etc.
  • the electrical device is usually required to be light and thin, and secondary batteries can be used as power sources.
  • Nanocellulose C2 to C4 were prepared according to a similar method to nanocellulose C1, and the differences are detailed in Table 1. During the preparation process, nanocellulose with different average diameters and/or different average lengths can be obtained by adjusting the parameters of the grinder processing and the cutting parameters of the high-pressure homogenizer equipment.
  • Unmodified nanocellulose is used, with an average length of 350nm and an average diameter of 18nm.
  • the product model is CNWS-50. It is purchased from Zhongke Leiming (Beijing) Technology Co., Ltd. and can be further processed using a grinder and/or a high-pressure homogenizer. to obtain nanocellulose with different average diameters and/or different average lengths.
  • the molar ratio of modified groups and hydroxyl groups in nanocellulose C1 to C5 can be measured by the following method: According to the phthalic anhydride method in GB/T 12008.3-2009, the raw material cellulose and nanocellulose C1 to The hydroxyl value of C5 (the number of milligrams of potassium hydroxide equivalent to the hydroxyl content per gram of sample), the numerical unit obtained is mg KOH/g, which is converted into mmol/g as the hydroxyl content. Subtracting the hydroxyl content of nanocellulose C1 to C5 from the hydroxyl content of the raw cellulose, the content of the modified group (that is, the content of the modified hydroxyl group) can be obtained. From this, the relationship between the modified group and the hydroxyl group can be calculated. The molar ratio of.
  • PE porous substrate provided: thickness 5.2 ⁇ m.
  • coating slurry Mix the nanocellulose C1 prepared above, the first filler, the second filler, and the binder aqueous solution type polyacrylic acid in an appropriate amount of solvent deionized water according to the mass ratio of 16.0:62.5:20.0:1.5. A coating slurry is obtained.
  • the first filler is aluminum oxide primary particles (average particle size is 50nm, content is 12.5wt%, based on the total weight of the coating) and aluminum oxide secondary particles (average particle size is 100nm, content is 50wt%, based on the total weight of the coating) based on the total weight of the mixture), and the contents of the ⁇ crystal form, ⁇ crystal form, ⁇ crystal form and eta crystal form in the first filler are 1.5wt%, 70.7wt%, 27.3wt% and 0.5wt% respectively, based on the 1.Based on the total weight of filler.
  • the second filler is alumina primary particles (average particle size: 240 nm), and the crystal form of the second filler is mainly ⁇ crystal form, with a mass ratio of more than 99.5%, based on the total weight of the second filler.
  • Coating Coat the prepared coating slurry on both surfaces of the PE porous substrate with a coating machine, and go through the drying and slitting processes to obtain an isolation film.
  • the coating thickness on one side of the PE porous substrate is 1.0 ⁇ m.
  • Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:70 to obtain an organic solvent.
  • Fully dried LiPF 6 was dissolved in the above organic solvent to prepare an electrolyte solution with a concentration of 1 mol/L.
  • the positive electrode sheet, isolation film, and negative electrode sheet are stacked and wound in sequence to obtain an electrode assembly; the electrode assembly is placed in the outer packaging, dried and then injected with electrolyte. After vacuum packaging, standing, formation, shaping and other processes, Get a secondary battery.
  • the secondary battery was prepared using a method similar to Example 1, except that the particle size of the first filler was different in the preparation of the separator film.
  • the specific parameters are shown in Table 2.
  • the secondary battery was prepared using a method similar to Example 1, except that the type and/or addition amount of nanocellulose and the first filler in the preparation of the separator were different.
  • the specific parameters are shown in Table 2.
  • the secondary battery was prepared using a method similar to Example 1. The difference is that in the preparation of the separator, the first filler is alumina secondary particles with an average particle size of 100 nm, and the first filler has ⁇ crystalline and ⁇ crystalline forms.
  • the contents of the crystalline form, the ⁇ crystalline form and the eta crystalline form are 1.5wt%, 70.7wt%, 27.3wt% and 0.5wt% respectively, based on the total weight of the first filler.
  • the secondary battery was prepared using a method similar to Example 1, except that in the preparation of the separator, primary alumina particles were used as the first filler.
  • the average particle size of the primary particles of alumina is 50nm, and the contents of ⁇ crystal form, ⁇ crystal form, ⁇ crystal form and eta crystal form are 1.5wt%, 70.7wt%, 27.3wt% and 0.5wt% respectively, based on alumina Total weight of primary particles.
  • the secondary battery was prepared using a method similar to Example 1, except for the preparation process of the separator film.
  • PE porous substrate provided: thickness 5.2 ⁇ m.
  • Preparation of coating slurry Mix primary alumina particles (average particle size is 700nm, ⁇ crystalline mass accounts for more than 99.5%) and binder according to a mass ratio of 94:6 and then dissolve in deionized water to obtain coating slurry material.
  • Coating Coat the prepared coating slurry on both surfaces of the PE porous substrate with a coating machine, and go through the drying and slitting processes to obtain an isolation film.
  • the coating thickness on one side of the PE porous substrate is 1.8 ⁇ m.
  • Sample preparation Use a punch machine to punch the isolation film prepared above into samples with a width of 50mm and a length of 100mm. Take 5 parallel samples and place them on A4 paper and fix them. Then place the A4 paper containing the samples on a layer with a thickness of 1mm to 5mm corrugated paper.
  • Sample test Put the A4 paper placed on the corrugated paper into the blast oven.
  • the temperature of the blast oven is set to 150°C. After the temperature reaches the set temperature and stabilizes for 30 minutes, start timing until the set time is reached (this application After 1 hour), measure the length and width of the isolation film, and the values are marked a and b respectively.
  • the ion conductivity of the isolation membrane was measured experimentally by AC impedance spectroscopy. Specifically, the isolation film was cut into discs of a certain area, dried, and placed between two stainless steel electrodes. After absorbing a sufficient amount of electrolyte, it was sealed to form a button cell. An electrochemical workstation was used to conduct AC impedance spectroscopy experiments. , obtain the ion conductivity of the isolation membrane.
  • the electrochemical workstation can be Shanghai Chenhua CHI 660C electrochemical workstation.
  • the AC signal frequency range is 0.01Hz to 1MHz, and the sine wave potential amplitude is 5mV. For accuracy, take the average of 5 parallel samples as the test result.
  • the electrolyte used is prepared as follows: mix ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a mass ratio of 30:50:20 to obtain an organic solvent. LiPF 6 was dissolved in the above organic solvent to prepare an electrolyte solution with a concentration of 1 mol/L.
  • the isolation membrane can be made to have low thermal shrinkage. efficiency and high ion conductivity, and can also enable secondary batteries to have both high thermal safety performance and good cycle performance.

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Abstract

本申请提供一种隔离膜、其制备方法及其相关的二次电池和用电装置，所述隔离膜包括多孔基材和设置在所述多孔基材的至少一个表面上的涂层，所述涂层包括三维骨架结构和第一填料，所述第一填料中的至少一部分填充在所述三维骨架结构中，且所述第一填料的平均粒径小于等于200 nm。本申请能使二次电池兼顾高能量密度、高热安全性能、长循环寿命和良好的动力学性能。

Description

隔离膜、其制备方法及其相关的二次电池和用电装置
相关申请的交叉引用
本申请要求享有于2022年08月15日提交的名称为“隔离膜、其制备方法及其相关的二次电池和用电装置”的专利申请PCT/CN2022/112580的优先权，该申请的全部内容通过引用并入本文中。
技术领域
本申请属于电池技术领域，具体涉及一种隔离膜、其制备方法及其相关的二次电池和用电装置。
背景技术
近年来，二次电池被广泛应用于水力、火力、风力和太阳能电站等储能电源系统，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。随着二次电池的应用及推广，其安全问题，特别是热安全问题受到越来越多的关注。然而，目前用于提升二次电池热安全性能的方式往往不利于平衡二次电池的能量密度和使用寿命。因此，如何使二次电池兼顾高能量密度、高热安全性能、长循环寿命和良好的动力学性能是二次电池设计的关键挑战所在。
发明内容
本申请的目的在于提供一种隔离膜、其制备方法及其相关的二次电池和用电装置，其能使二次电池兼顾高能量密度、高热安全性能、长循环寿命和良好的动力学性能。
本申请第一方面提供一种隔离膜，包括多孔基材和设置在所述多孔基材的至少一个表面上的涂层，其中，所述涂层包括三维骨架结构和第一填料，所述第一填料中的至少一部分填充在所述三维骨架结构中，且所述第一填料的平均粒径小于等于200nm。
本申请的发明人在研究过程中惊奇发现，通过在隔离膜多孔基材表面上设置包括三维骨架结构和平均粒径小于等于200nm的第一填料的涂层，能够使隔离膜兼顾低重量、高耐热性和高离子导通率，进而还能够使二次电池兼顾高能量密度、高热安全性能、长循环寿命和良好的动力学性能。
在本申请的任意实施方式中，所述第一填料的平均粒径为15nm至180nm，可选为30nm至150nm。第一填料的平均粒径在上述范围内时，能使第一填料具有较高的比表面积，使第一填料颗粒尺寸与三维骨架结构进行更好地匹配，由此可以使第一填料与三维骨架结构更好地搭接形成一体化效果，增加第一填料与三维骨架结构之间的亲和性，增加隔离膜的耐热性和离子导通率，同时还能增加隔离膜对电解液的浸润和保持特性。
在本申请的任意实施方式中，所述第一填料包括一次颗粒和二次颗粒中的至少一种。
在本申请的任意实施方式中，所述第一填料包括一次颗粒和二次颗粒的组合。
在本申请的任意实施方式中，基于所述第一填料的总重量计，所述一次颗粒形貌的第一填料的含量小于所述二次颗粒形貌的第一填料的含量。
在本申请的任意实施方式中，基于所述第一填料的总重量计，所述一次颗粒形貌的第一填料的含量小于等于30wt％。
在本申请的任意实施方式中，所述一次颗粒形貌的第一填料的平均粒径为15nm至80nm，可选为30nm至65nm。
在本申请的任意实施方式中，所述二次颗粒形貌的第一填料的平均粒径为50nm至200nm，可选为55nm至150nm。
在本申请的任意实施方式中，所述第一填料的BET比表面积为≥25m 2/g，可选为30m 2/g至65m 2/g。第一填料的比表面积在上述范围内时，其与三维骨架结构之间的亲和性更好，能增加隔离膜的耐热性和离子导通率，同时还能增加隔离膜对电解液的浸润和保持特性。
在本申请的任意实施方式中，所述第一填料的含量为≥50wt％，可选为60wt％至90wt％，基于所述涂层的总重量计。第一填料的含量在上述范围内时，能够保证涂层浆料具有合适的粘度，更有利于涂布；此外，还有利于与三维骨架结构搭接形成一体化效果，由此能使涂层具有更稳定的空间网络结构，从而能够进一步提升隔离膜的耐热性和离子导通率。
在本申请的任意实施方式中，所述三维骨架结构的含量为5wt％至40wt％，可选为8wt％至25wt％，基于所述涂层的总重量计。当三维骨架结构的含量在上述范围内时，能够保证涂层浆料具有合适的粘度，更有利于涂布；此外，还有利于三维骨架结构与第一填料搭接形成一体化效果，由此能使涂层具有更稳定的空间网络结构，从而能够进一步提升隔离膜的耐热性、离子导通率、对电解液的浸润和保持特性以及耐电压击穿能力。
在本申请的任意实施方式中，所述第一填料包括无机颗粒和有机颗粒中的至少一种。可选地，所述无机颗粒包括勃姆石、氧化铝、硫酸钡、氧化镁、氢氧化镁、硅氧化合物、二氧化锡、氧化钛、氧化钙、氧化锌、氧化锆、氧化钇、氧化镍、二氧化铪、氧化铈、钛酸锆、钛酸钡和氟化镁中的至少一种，更可选地，所述无机颗粒包括勃姆石、氧化铝、硫酸钡、氧化镁、硅氧化合物、氧化钛、氧化锌、氧化铈和钛酸钡中的至少一种。可选地，所述有机颗粒包括聚苯乙烯颗粒、聚丙烯酸蜡颗粒、三聚氰胺甲醛树脂颗粒、酚醛树脂颗粒、聚酯颗粒、聚酰亚胺颗粒、聚酰胺亚胺颗粒、聚芳酰胺颗粒、聚苯硫醚颗粒、聚砜颗粒、聚醚砜颗粒、聚醚醚酮颗粒和聚芳醚酮颗粒中的至少一种。
在本申请的任意实施方式中，所述第一填料包括无机颗粒，且所述无机颗粒的晶型包括θ晶型、γ晶型和η晶型中的至少一种；可选地，所述无机颗粒的晶型包括θ晶型和γ晶型中的至少一种。
在本申请的任意实施方式中，可选地，θ晶型的无机颗粒的含量为≥50wt％，更可选为55wt％至84wt％，基于所述第一填料中的所述无机颗粒的总重量计。
在本申请的任意实施方式中，可选地，γ晶型的无机颗粒的含量为≥10wt％，更可选为15wt％至44wt％，基于所述第一填料中的所述无机颗粒的总重量计。
在本申请的任意实施方式中，可选地，η晶型的无机颗粒的含量为≤5wt％，更可选为≤2.5wt％，基于所述第一填料中的所述无机颗粒的总重量计。
在本申请的任意实施方式中，所述三维骨架结构由纤维状物形成，所述纤维状物的形貌可选地包括棒状、管状、杆状和纤维状中的至少一种。
通过选择不同晶型的第一填料有助于提升隔离膜的耐热性、离子导通率、粘结强度和对电解液的浸润和保持特性中的至少一者。
在本申请的任意实施方式中，构成所述三维骨架结构的材料的平均直径为≤40nm，可选为10nm至35nm。当构成三维骨架结构的材料的平均直径在上述范围内时，能够进一步提升隔离膜的离子导通率和耐电压击穿特性，同时还有助于与第一填料搭接形成一体化效果，由此还能够进一步提升隔离膜的耐热性。
在本申请的任意实施方式中，构成所述三维骨架结构的材料的平均长度为100nm至600nm，可选为200nm至500nm。当构成三维骨架结构的材料的平均长度在上述范围内时，能够进一步提升隔离膜的耐热性和离子导通率。
在本申请的任意实施方式中，构成所述三维骨架结构的材料的长径比为5至60，可选为10至30。当构成三维骨架结构的材料的长径比在上述范围内时，能够进一步提升隔离膜的离子导通率以及对电解液的浸润和保持特性。
在本申请的任意实施方式中，构成所述三维骨架结构的材料包括有机材料和无机材料中的至少一种。可选地，所述有机材料包括纳米纤维素、聚四氟乙烯纳米纤维和聚酰胺纳米纤维中的至少一种，可选地，所述纳米纤维素包括纤维素纳米纤维、纤维素纳米晶须和细菌纳米纤维素中的至少一种。可选地，所述无机材料包括埃洛石纳米管、纳米棒状氧化铝、纳米棒状勃姆石、纳米棒状氧化硅和玻璃纤维中的至少一种。
在本申请的任意实施方式中，构成所述三维骨架结构的材料包括纳米纤维素，所述纳米纤维素包括未改性纳米纤维素和改性纳米纤维素中的至少一种。
在本申请的任意实施方式中，可选地，所述改性纳米纤维素包括改性基团，所述改性基团包括胺基、羧基、醛基、磺酸基、硼酸基和磷酸基中的至少一种，更可选地包括磺酸基、硼酸基和磷酸基中的至少一种。
当纳米纤维素具有上述特定的改性基团时，一方面能够有效提升隔离膜的耐热性，提升二次电池的热安全性能；另一方面还能提升涂层与多孔基材之间的粘结强度。当纳米纤维素具有上述特定的改性基团时，还有利于纳米纤维素与第一填料搭接形成一体化效果，由此能使涂层具有更稳定的空间网络结构，从而能够提升隔离膜对电解液的浸润和保持特性，提升隔离膜的离子导通率和耐电压击穿特性。此外，改性基团的存在还能降低羟基的比例，由此能够保证涂层浆料具有合适的粘度，更有利于涂布，从而还能提升隔离膜的生产效率和涂层的均匀性。
在本申请的任意实施方式中，可选地，所述改性纳米纤维素包括羟基和改性基团，且所述改性基团与所述羟基的摩尔比为1:4至4:1，更可选为2:3至7:3。当改性基团与羟基的摩尔比在上述范围内时，能够进一步提升隔离膜的耐热性、离子导通率以及对电解液的浸润和保持特性。在本申请的任意实施方式中，构成所述三维骨架结构的材料包括磺酸基，且构成所述三维骨架结构的材料中的硫元素的含量为≥0.1wt％，可选为0.2wt％至0.5wt％，基于所述构成所述三维骨架结构的材料的总重量计。
在本申请的任意实施方式中，所述涂层还包括第二填料，所述第二填料中的至少一部分嵌入所述涂层中，所述第一填料的平均粒径记为d 1，所述第二填料的平均粒径记为d 2，则d 2/d 1＞1。第二填料的平均粒径较大，由此能够更好地发挥其在涂层中的支撑作用，减少第一填料的收缩，降低粘结剂用量，从而提升隔离膜的耐热性；第二填料的粒径较大，还有助于在用量较少时使涂层具有更多的孔道结构和更少的水含量，进而能够进一步提升隔离膜的离子导通率以及对电解液的浸润和保持特性，同时还能够提升二次电池的循环性能和/或动力学性能。
在本申请的任意实施方式中，所述第一填料包括一次颗粒和二次颗粒中的至少一种，所述一次颗粒形貌的第一填料的平均粒径记为d 11，所述二次颗粒形貌的第一填料的平均粒径记为d 12，3.0≤d 2/d 11≤10.0，可选地，3.5≤d 2/d 11≤8.0；和/或，1.2≤d 2/d 12≤6.0，可选地，2.0≤d 2/d 12≤5.5。
通过第一填料和第二填料的配合作用，有助于减少涂层水分含量，使涂层在长期充放电过程中保持稳定的孔道结构，同时还能提升隔离膜的耐热性，由此能够使二次电池更好地兼顾高能量密度、高热安全性能、长循环寿命和良好的动力学性能。
在本申请的任意实施方式中，所述第二填料具有一次颗粒形貌。
在本申请的任意实施方式中，所述第二填料的平均粒径为120nm至350nm，可选为150nm至300nm。由此能够更好地发挥第二填料的支撑作用，减少涂层水分含量，使涂层在长期充放电过程中保持稳定的孔道结构，同时还能提升隔离膜的耐热性。
在本申请的任意实施方式中，所述第二填料的BET比表面积为≤20m 2/g，可选为6m 2/g至15m 2/g。由此能够更好地发挥第二填料的支撑作用，减少涂层水分含量，使涂层在长期充放电过程中保持稳定的孔道结构，同时还能提升隔离膜的耐热性。
在本申请的任意实施方式中，所述第二填料包括无机颗粒和有机颗粒中的至少一种。
在本申请的任意实施方式中，所述第二填料包括一次颗粒形貌的无机颗粒，且所述一次颗粒形貌的无机颗粒的晶型包括α晶型和γ晶型中的至少一种，可选包括α晶型。α晶型的第二填料具有硬度高、耐热性好、介电常数低、安全性高和真密度大的优势，由此能够进一步改善涂层的耐热性。
在本申请的任意实施方式中，所述第二填料包括一次颗粒形貌的无机颗粒，且所述一次颗粒形貌的无机颗粒的晶型包括α晶型，且α晶型的含量为≥70wt％，可选为85wt％至100wt％，基于所述第二填料中的所述一次颗粒形貌的无机颗粒的总重量计。
在本申请的任意实施方式中，所述第二填料的含量为≤30wt％，可选为5wt％至25wt％，基于所述涂层的总重量计。第二填料的含量在上述范围内时，能够更好地发挥第二填料的支撑作用，减少涂层水分含量，使涂层在长期充放电过程中保持稳定的孔道结构。
在本申请的任意实施方式中，所述涂层还包括非颗粒状的粘结剂。可选地，所述非颗粒状的粘结剂包括水溶液型粘结剂。
在本申请的任意实施方式中，所述涂层中的所述非颗粒状的粘结剂的含量为≤2wt％，基于所述涂层的总重量计。本申请的涂层中的三维骨架结构与第一填料等能够形成稳定的空间网络结构，由此能够在减少粘结剂用量的前提下使隔离膜还能保持高粘结性。
在本申请的任意实施方式中，所述多孔基材的厚度为≤6μm，可选为3μm至5μm。本申请的涂层能使隔离膜的耐热性得到显著提升，由此可以选用更薄的多孔基材，从而有助于提升二次电池的能量密度。
在本申请的任意实施方式中，所述涂层的厚度为≤2μm，可选为0.5μm至1.5μm。由此有助于提升二次电池的能量密度。
在本申请的任意实施方式中，所述隔离膜还包括粘接层，所述粘接层设置在所述涂层的至少一部分表面上，所述粘接层包括颗粒状的粘结剂。粘接层不仅能够防止涂层脱落，提升二次电池的安全性能，而且能够改善隔离膜与电极的界面，提升二次电池的循环性能。
在本申请的任意实施方式中，所述颗粒状的粘结剂包括丙烯酸酯类单体均聚物或共聚物、丙烯酸类单体均聚物或共聚物、含氟烯烃单体均聚物或共聚物中的至少一种。
在本申请的任意实施方式中，所述隔离膜在150℃、1h下的纵向热收缩率为≤6％，可选为0.5％至4％。
在本申请的任意实施方式中，所述隔离膜在150℃、1h下的横向热收缩率为≤6％，可选为0.5％至4％。
本申请的隔离膜在150℃的高温下，横向和纵向两个方向均具有低热收缩率，由此能够提升二次电池的安全性能。
在本申请的任意实施方式中，所述隔离膜的纵向拉伸强度为≥2000kg/cm 2，可选为2500kg/cm 2至4500kg/cm 2。
在本申请的任意实施方式中，所述隔离膜的横向拉伸强度为≥2000kg/cm 2，可选为2500kg/cm 2至4500kg/cm 2。
本申请的隔离膜在横向和纵向两个方向均具有高拉伸强度，由此在二次电池膨胀时，隔离膜出现破损的概率较小，从而能够提升二次电池的安全性能。
在本申请的任意实施方式中，所述隔离膜的润湿长度为≥30mm，可选为30mm至80mm。
在本申请的任意实施方式中，所述隔离膜的润湿速度为≥3mm/s，可选为3mm/s至10mm/s。
本申请的隔离膜对电解液具有良好的浸润和保持特性，由此能够提升隔离膜的离子导通率和二次电池容量发挥特性。
在本申请的任意实施方式中，所述隔离膜的透气度为≤300s/100mL，可选为100s/100mL至230s/100mL。本申请的隔离膜具有良好的透气度，由此能够提升离子导通率和二次电池容量发挥特性。
在本申请的任意实施方式中，所述隔离膜的耐电压击穿强度为≥1KV。本申请的隔离膜具有较高的耐电压击穿强度度，由此能够提升二次电池的安全性能。
本申请第二方面提供一种制备本申请第一方面的隔离膜的方法，包括以下步骤：提供多孔基材；将用于构成三维骨架结构的材料和第一填料按照预定比例在溶剂中混合，配制成涂层浆料；将所述涂层浆料涂布于所述多孔基材的至少一个表面上，干燥后获得隔离膜，其中，所述隔离膜包括多孔基材和设置在所述多孔基材的至少一个表面上的涂 层，所述涂层包括三维骨架结构和第一填料，所述第一填料中的至少一部分填充在所述三维骨架结构中，且所述第一填料的平均粒径小于等于200nm。
在本申请的任意实施方式中，所述涂层浆料还包括第二填料，所述第一填料的平均粒径记为d 1，所述第二填料的平均粒径记为d 2，则d 2/d 1＞1。
本申请第三方面提供一种二次电池，包括本申请第一方面的隔离膜或通过本申请第二方面的方法制备的隔离膜。
本申请第四方面提供一种用电装置，包括本申请第三方面的二次电池。
本申请的隔离膜能够使二次电池兼顾高能量密度、高热安全性能以及良好的循环性能和动力学性能，本申请的用电装置包括本申请提供的二次电池，因而至少具有与所述二次电池相同的优势。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍。显而易见地，下面所描述的附图仅仅是本申请的一些实施方式，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请的二次电池的一实施方式的示意图。
图2是图1的二次电池的实施方式的分解示意图。
图3是本申请的电池模块的一实施方式的示意图。
图4是本申请的电池包的一实施方式的示意图。
图5是图4所示的电池包的实施方式的分解示意图。
图6是包含本申请的二次电池作为电源的用电装置的一实施方式的示意图。
在附图中，附图未必按照实际的比例绘制。附图标记说明如下：1电池包，2上箱体，3下箱体，4电池模块，5二次电池，51壳体，52电极组件，53盖板。
具体实施方式
以下，适当地参照附图详细说明具体公开了本申请的隔离膜、其制备方法及其相关的二次电池和用电装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合 的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案，并且这样的技术方案应被认为包含在本申请的公开内容中。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案，并且这样的技术方案应被认为包含在本申请的公开内容中。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
如果没有特别的说明，在本申请中，术语“第一”、“第二”等是用于区别不同对象，而不是用于描述特定顺序或主次关系。
除非另有说明，本申请中使用的术语具有本领域技术人员通常所理解的公知含义。
除非另有说明，本申请中提到的各参数的数值可以用本领域常用的各种测试方法进行测定，例如，可以按照本申请的实施例中给出的测试方法进行测定。
通常情况下，二次电池包括电极组件和电解液，电极组件包括正极极片、负极极片和隔离膜，隔离膜设置在正极极片和负极极片之间，主要起到防止正极和负极短路的作用，同时可以使活性离子自由通过形成回路。
随着二次电池的应用及推广，人们对二次电池能量密度、使用寿命和动力学性能的要求越来越高。隔离膜减薄是提升二次电池能量密度的一个有效措施。目前商业化二次电池采用的隔离膜通常为聚烯烃多孔膜，例如聚乙烯多孔膜、聚丙烯多孔膜或聚丙烯/聚乙烯/聚丙烯三层复合膜，其熔点在130℃至160℃之间，由此，当其厚度减薄后，隔离膜的耐热性变差，受热时会发生明显的热收缩效应从而使得电池内部正极和负极直接接触导致内短路产生，进而增加了二次电池的安全风险。
为了解决上述问题，目前采用的措施主要是在聚烯烃多孔膜上涂布一层耐热性的无机陶瓷层，其能增加隔离膜的机械强度、减少隔离膜在受热时的收缩程度，降低电池内部正极和负极短路风险。但是，市售无机陶瓷颗粒的粒径较大，由此会增加隔离膜整体厚度，导致无法平衡二次电池的能量密度，特别是在动力电池领域，不利于续航里程提升；此外，市售无机陶瓷颗粒对隔离膜耐热性的改善效果也有限。无机陶瓷颗粒纳米化 可以降低涂层厚度，缓解对二次电池能量密度的不利影响，但是纳米化无机陶瓷颗粒容易堵塞聚烯烃多孔膜，导致二次电池的容量发挥和动力学性能变差。同时，由于纳米化无机陶瓷颗粒的比表面积较高，且颗粒之间的接触形式为点接触，由此需要使用大量粘结剂以保证颗粒之间的粘结性，但是粘结剂用量较大时易出现堵孔问题，从而对二次电池的动力学性能不利。
因此，现有技术的隔离膜往往很难兼顾二次电池的高能量密度、高热安全性能、长循环寿命和良好的动力学性能。
本申请的发明人在研究过程中惊奇发现，通过在隔离膜多孔基材表面上设置包括三维骨架结构和平均粒径小于等于200nm的第一填料的涂层，能够使隔离膜兼顾低重量、高耐热性和高离子导通率，进而还能够使二次电池兼顾高能量密度、高热安全性能、长循环寿命和良好的动力学性能。
隔离膜
具体地，本申请实施方式第一方面提供了一种隔离膜，包括多孔基材和设置在所述多孔基材的至少一个表面上的涂层，其中，所述涂层包括三维骨架结构和第一填料，所述第一填料中的至少一部分填充在所述三维骨架结构中，且所述第一填料的平均粒径小于等于200nm。在本申请中，“三维骨架结构”是指具有三维空间形状且具有一定孔隙的结构体，其可由构成所述三维骨架结构的材料相互搭接而成。
第一填料的平均粒径小于等于200nm，由此可具有比表面积大、与三维骨架结构亲和性好的优势，并且有利于与三维骨架结构形成稳定的空间网络结构，从而既能增加隔离膜的离子导通率，又能提升隔离膜的耐热性。
第一填料中的至少一部分填充在三维骨架结构中，由此有助于第一填料与三维骨架结构形成嵌套效果，从而既能增加隔离膜的耐热性，降低隔离膜受热时的收缩程度，降低正极和负极短路风险，使二次电池具有高热安全性能，又能使涂层与多孔基材之间保持高粘结强度，避免第一填料在二次电池长期充放电过程中脱落。同时，第一填料中的至少一部分填充在三维骨架结构中，由此第一填料与三维骨架结构之间的接触位点还较多，从而可以降低涂层中粘结剂的使用量，进而可以有效降低粘结剂堵孔的风险，并能进一步改善二次电池的循环性能和动力学性能。
本申请的涂层具有高耐热性，由此可以降低涂层的厚度(例如涂层的厚度可小于等于2μm)，缩短活性离子传输距离，进而二次电池还能够兼顾高能量密度以及良好的循环性能和动力学性能；此外，本申请的涂层具有高耐热性，由此可以选用更薄的多孔基材，从而进一步提升二次电池的能量密度。
在一些实施例中，所述第一填料中的至少一部分填充在所述三维骨架结构中，所述第一填料中的其他部分可位于所述三维骨架结构的表面和/或所述三维骨架结构与所述多孔基材之间的界面，并且在所述三维骨架结构与所述多孔基材之间的界面位置，还可能出现少部分第一填料嵌入多孔基材中，例如在电极组件卷绕过程中，由于受到外界压力作用而使界面位置的少部分第一填料嵌入多孔基材的基体和/或孔中。
[三维骨架结构]
在一些实施例中，所述三维骨架结构可由纤维状物形成，所述纤维状物的形貌可选地包括棒状、管状(例如中空管状)、杆状和纤维状中的至少一种。合适形状的材料有 利于三维骨架结构与第一填料形成更稳定的空间网络结构，由此能够进一步提升隔离膜的耐热性、离子导通率以及对电解液的浸润和保持特性。在本申请中，“纤维状物”是指长径比为5以上的材料。
在一些实施例中，构成所述三维骨架结构的材料包括有机材料和无机材料中的至少一种。
可选地，所述有机材料包括纳米纤维素、聚四氟乙烯纳米纤维和聚酰胺纳米纤维中的至少一种。可选地，所述无机材料包括埃洛石纳米管、纳米棒状氧化铝、纳米棒状勃姆石、纳米棒状氧化硅和玻璃纤维中的至少一种。
在一些实施例中，构成所述三维骨架结构的材料可包括纳米纤维素。可选地，所述纳米纤维素包括纤维素纳米纤维(Cellulose nanofibrils，CNF，又称为纳米纤丝纤维素或微纤化纤维素)、纤维素纳米晶须(Cellulose nanocrystals，CNC，又称为纤维素纳米晶、纳米晶体纤维素)和细菌纳米纤维素(Bacterial nanocellulose，BNC，又称为细菌纤维素或微生物纤维素)中的至少一种。
纳米纤维素是指任一维尺寸在纳米级(例如100nm以内)的纤维素的总称，其既具有纤维素的特性，又具有纳米颗粒的特性。纳米纤维素可以是通过化学、物理、生物等中的一种或多种手段从自然界中的木材、棉花等提取出的高分子纳米材料，具有来源广泛、成本低、生物可降解、模量高、比表面积高等优势，因此其是传统石化资源的优良替代品，可以有效地缓解环境污染和石化资源紧张等问题。纳米纤维素还具有良好的耐高温特性，且受热后体积变化较小，由此能够提升隔离膜的耐热性；同时，与传统无机陶瓷颗粒相比，纳米纤维素的密度较小，由此还能够降低二次电池的重量，提升二次电池的重量能量密度。此外，由纳米纤维素形成的三维骨架结构还可以具有微小的纳米孔，防止电流泄露，由此还能够使隔离膜兼顾良好的对电解液的浸润和保持特性以及良好的耐电压击穿特性。
在一些实施例中，所述纳米纤维素可包括未改性纳米纤维素(又称羟基纳米纤维素)和改性纳米纤维素中的至少一种，可选地为改性纳米纤维素。
改性纳米纤维素是指同时包括羟基和改性基团的纳米纤维素。在一些实施例中，所述改性纳米纤维素包括改性基团，且所述改性基团包括胺基、羧基、醛基、磺酸基、硼酸基和磷酸基中的至少一种，可选地包括磺酸基、硼酸基和磷酸基中的至少一种。
发明人在进一步研究中发现，当纳米纤维素具有上述特定的改性基团时，一方面能够有效提升隔离膜的耐热性，提升二次电池的热安全性能；另一方面还能提升涂层与多孔基材之间的粘结强度。当纳米纤维素具有上述特定的改性基团时，还有利于纳米纤维素与第一填料搭接形成一体化效果，由此能使涂层具有更稳定的空间网络结构，从而能够提升隔离膜对电解液的浸润和保持特性，提升隔离膜的离子导通率和耐电压击穿特性。此外，改性基团的存在还能降低羟基的比例，由此能够保证涂层浆料具有合适的粘度，更有利于涂布，从而还能提升隔离膜的生产效率和涂层的均匀性。
在一些实施例中，所述改性基团与所述羟基的摩尔比可为1:4至4:1，可选为2:3至7:3。当改性基团与羟基的摩尔比在上述范围内时，能够进一步提升隔离膜的耐热性、离子导通率以及对电解液的浸润和保持特性。并且能够有效避免以下情况：当改性基团与羟基的摩尔比过小时，改性基团所起到的对隔离膜耐热性和离子导通率的进一步改善效 果可能不明显；当改性基团与羟基的摩尔比过大时，隔离膜对电解液的浸润和保持特性可能变差，进而可能影响二次电池的循环性能和安全性能，同时还可能导致隔离膜的耐热性下降，进而还可能影响对二次电池的热安全性能的改善效果。
纳米纤维素中改性基团的种类可以采用红外光谱法进行测定。例如，可以测试材料的红外光谱，确定其包含的特征峰，从而确定改性基团的种类。具体地，可以用本领域公知的仪器及方法对材料进行红外光谱法分析，例如采用红外光谱仪(如美国尼高力公司的IS10型傅里叶变换红外光谱仪)，依据GB/T 6040-2019红外光谱分析方法通则进行测试。
在一些实施例中，构成所述三维骨架结构的材料包括磺酸基，且构成所述三维骨架结构的材料中的硫元素的含量为≥0.1wt％，可选为0.2wt％至0.5wt％，基于所述构成所述三维骨架结构的材料的总重量计。可选地，构成所述三维骨架结构的材料包括纳米纤维素。
构成所述三维骨架结构的材料中的硫元素的含量可以按照如下方法测试得到：将构成所述三维骨架结构的材料烘干后，在研钵(如玛瑙研钵)中研磨30min，之后使用X射线衍射仪(如Miniflex600-C)进行测试，得到硫元素的含量。测试时可采用Cu靶材，Ni滤波片，管压40KV，管流15mA，连续扫描范围5°-80°。
在一些实施例中，构成所述三维骨架结构的材料的平均直径可为≤40nm，可选为10nm至35nm。当构成三维骨架结构的材料的平均直径在上述范围内时，能够进一步提升隔离膜的离子导通率和耐电压击穿特性，同时还有助于与第一填料搭接形成一体化效果，由此还能够进一步提升隔离膜的耐热性。并且能够有效避免以下情况：当构成三维骨架结构的材料的平均直径过大时，其形成的三维骨架结构的相互缠绕效果不足且孔隙较大，由此可能导致隔离膜的耐热性和耐电压击穿特性不够优异，同时还不利于与第一填料搭接形成一体化效果，并且在涂层烘干过程中，三维骨架结构由于缺少第一填料的支撑作用还容易坍塌，进而容易与多孔基材直接接触产生堵孔问题，由此可能会影响隔离膜的离子导通率。
在一些实施例中，构成所述三维骨架结构的材料的平均长度可为100nm至600nm，可选为200nm至500nm。当构成三维骨架结构的材料的平均长度在上述范围内时，能够进一步提升隔离膜的耐热性和离子导通率。并且能够有效避免以下情况：当构成三维骨架结构的材料的平均长度过短时，其与第一填料的搭接效果较差，涂层的耐热性变差，并且在涂层烘干过程中，三维骨架结构由于缺少第一填料的支撑作用还容易坍塌，进而容易产生堵孔问题，阻碍离子传输和水分排出，从而可能影响二次电池的热安全性能、循环性能和动力学性能；当构成三维骨架结构的材料的平均长度过长时，涂层浆料粘度大、流动差，由此可能会影响涂层浆料的涂布进而影响涂层的质量，例如可能影响隔离膜的耐热性和离子导通率。
在一些实施例中，构成所述三维骨架结构的材料的长径比可为5至60，可选为10至30。当构成三维骨架结构的材料的长径比在上述范围内时，能够进一步提升隔离膜的离子导通率以及对电解液的浸润和保持特性。并且能够有效避免以下情况：当构成三维骨架结构的材料的长径比过小时，其与第一填料的搭接效果较差，涂层的耐热性变差，并且在涂层烘干过程中，三维骨架结构由于缺少第一填料的支撑作用还容易坍塌，进而容 易产生堵孔问题，阻碍离子传输和水分排出，从而可能影响二次电池的热安全性能、循环性能和动力学性能；当构成三维骨架结构的材料的长径比过大时，其形成的三维骨架结构的孔隙较小，由此可能导致隔离膜的离子导通率变小。
构成三维骨架结构的材料的平均长度和平均直径可以通过以下方法进行测定：从隔离膜中任选一区域裁切出3.6mm×3.6mm的样品，利用扫描电子显微镜(例如ZEISS Sigma 300)测绘样品中涂层的微观形貌结构，选择高真空模式，工作电压为3kV，放大倍数为3万倍，获得SEM图；根据获得的SEM图，选取多个(例如5个以上)测试区域进行长度的统计，每个测试区域的尺寸为0.5μm×0.5μm，之后取各个测试区域得到的长度的平均值作为构成三维骨架结构的材料的平均长度；根据获得的SEM图，利用Nano Measurer粒径分布统计软件，选取多个(例如5个以上)测试区域进行直径的统计，每个测试区域的尺寸为0.5μm×0.5μm，之后取各个测试区域得到的直径的平均值作为构成三维骨架结构的材料的平均直径。
在一些实施例中，所述三维骨架结构的含量可为5wt％至40wt％，可选为8wt％至25wt％，10wt％至25wt％，基于所述涂层的总重量计。构成三维骨架结构的材料的比表面积较大，因此在相同质量下，形成的涂层的比表面积大、孔隙较多，由此导致隔离膜的耐热性较差；同时，构成三维骨架结构的材料(例如纳米纤维素)的氢键作用极强，含量较高时，会导致涂层浆料的粘度较大，不利于实现薄涂布，也不利于商业生产。当三维骨架结构的含量在上述范围内时，能够保证涂层浆料具有合适的粘度，更有利于涂布；此外，还有利于三维骨架结构与第一填料搭接形成一体化效果，由此能使涂层具有更稳定的空间网络结构，从而能够进一步提升隔离膜的耐热性、离子导通率、对电解液的浸润和保持特性以及耐电压击穿能力。
[第一填料]
在一些实施例中，所述第一填料的平均粒径为15nm至180nm，可选为20nm至170nm，25nm至160nm，30nm至150nm，40nm至140nm，50nm至135nm。第一填料的平均粒径在上述范围内时，能使第一填料具有较高的比表面积，使第一填料颗粒尺寸与三维骨架结构进行更好地匹配，由此可以使第一填料与三维骨架结构更好地搭接形成一体化效果，增加第一填料与三维骨架结构之间的亲和性，增加隔离膜的耐热性和离子导通率，同时还能增加隔离膜对电解液的浸润和保持特性。
在一些实施例中，所述第一填料包括一次颗粒和二次颗粒中的至少一种，可选地，所述第一填料包括一次颗粒和二次颗粒的组合。一次颗粒形貌的第一填料有利于减少涂层水分含量，提升涂层的离子导通率，从而更好地提升二次电池的循环性能；二次颗粒形貌的第一填料能够更好地与三维骨架结构搭接形成一体化效果，由此能使涂层具有更稳定的空间网络结构，从而能够进一步提升隔离膜的耐热性。
在一些实施例中，所述第一填料包括一次颗粒和二次颗粒的组合，且基于所述第一填料的总重量计，所述一次颗粒形貌的第一填料的含量小于所述二次颗粒形貌的第一填料的含量。
在一些实施例中，所述第一填料包括一次颗粒和二次颗粒的组合，且基于所述第一填料的总重量计，所述一次颗粒形貌的第一填料的含量小于等于30wt％，可选为8wt％至 30wt％，8wt％至28wt％，10wt％至30wt％，10wt％至28wt％，12wt％至30wt％，12wt％至28wt％，15wt％至30wt％，15wt％至28wt％，17.5wt％至30wt％，17.5wt％至28wt％。
在一些实施例中，所述一次颗粒形貌的第一填料的平均粒径为15nm至95nm，可选为15nm至80nm，20nm至80nm，30nm至75nm，35nm至75nm，35nm至70nm，30nm至70nm，30nm至65nm。
在一些实施例中，所述二次颗粒形貌的第一填料的平均粒径为50nm至200nm，可选为50nm至180nm，50nm至150nm，50nm至135nm，50nm至120nm，55nm至180nm，55nm至150nm，55nm至135nm，55nm至120nm，65nm至180nm，65nm至150nm，65nm至135nm，65nm至120nm。
在一些实施例中，所述第一填料的BET比表面积为≥25m 2/g，可选为30m 2/g至80m 2/g，30m 2/g至65m 2/g。第一填料的比表面积在上述范围内时，其与三维骨架结构之间的亲和性更好，能够与三维骨架结构搭接形成一体化效果，从而增加隔离膜的耐热性和离子导通率，同时还能增加隔离膜对电解液的浸润和保持特性。
在一些实施例中，所述第一填料包括无机颗粒和有机颗粒中的至少一种，可选地包括无机颗粒，或者无机颗粒和有机颗粒的组合。无机颗粒具有硬度高、热稳定性高且不易分解的特性，且其表面通常具有羟基，由此容易与构成三维骨架结构的材料(例如纳米纤维素等)搭建形成稳定的空间网络结构。有机颗粒具有热稳定性好且不易分解的特性，同时，当二次电池因为过充滥用、热滥用等使其内部温度达到有机颗粒的熔点时，有机颗粒还可以融化，并因毛细作用而被吸入多孔基材的微孔中起到闭孔和断路的作用，从而有利于提升二次电池的安全性能。
可选地，所述无机颗粒包括勃姆石(γ-AlOOH)、氧化铝(Al 2O 3)、硫酸钡(BaSO 4)、氧化镁(MgO)、氢氧化镁(Mg(OH) 2)、硅氧化合物SiO x(0＜x≤2)、二氧化锡(SnO 2)、氧化钛(TiO 2)、氧化钙(CaO)、氧化锌(ZnO)、氧化锆(ZrO 2)、氧化钇(Y 2O 3)、氧化镍(NiO)、二氧化铪(HfO 2)、氧化铈(CeO 2)、钛酸锆(ZrTiO 3)、钛酸钡(BaTiO 3)和氟化镁(MgF 2)中的至少一种。更可选地，所述无机颗粒包括勃姆石(γ-AlOOH)、氧化铝(Al 2O 3)、硫酸钡(BaSO 4)、氧化镁(MgO)、硅氧化合物SiO x(0＜x≤2)、氧化钛(TiO 2)、氧化锌(ZnO)、氧化铈(CeO 2)和钛酸钡(BaTiO 3)中的至少一种。
可选地，所述有机颗粒包括聚苯乙烯颗粒、聚丙烯酸蜡颗粒、三聚氰胺甲醛树脂颗粒、酚醛树脂颗粒、聚酯颗粒、聚酰亚胺颗粒、聚酰胺亚胺颗粒、聚芳酰胺颗粒、聚苯硫醚颗粒、聚砜颗粒、聚醚砜颗粒、聚醚醚酮颗粒和聚芳醚酮颗粒中的至少一种。
在一些实施例中，所述第一填料包括无机颗粒，且所述无机颗粒的晶型包括θ晶型、γ晶型和η晶型中的至少一种。可选地，所述无机颗粒的晶型包括θ晶型和γ晶型中的至少一种。
θ晶型的无机颗粒在通过使用X射线衍射仪测定的X射线衍射谱图中，在2θ为36.68°±0.2°和31.21°±0.2°处具有衍射峰。在一些实施例中，所述第一填料中的θ晶型的无机颗粒的含量可为≥50wt％，可选为55wt％至84wt％基于所述第一填料中的所述无机颗粒的总重量计。
γ晶型的无机颗粒在通过使用X射线衍射仪测定的X射线衍射谱图中，在2θ为66.95°±0.2°和45.91°±0.2°处具有衍射峰。在一些实施例中，所述第一填料中的γ晶型的无机颗粒的含量可为≥10wt％，可选为15wt％至44wt％，基于所述第一填料中的所述无机颗粒的总重量计。
η晶型的无机颗粒在通过使用X射线衍射仪测定的X射线衍射谱图中，在2θ为31.89°±0.2°和19.37°±0.2°处具有衍射峰。在一些实施例中，所述第一填料中的η晶型的无机颗粒的含量可为≤5wt％，可选为≤2.5wt％，更可选为≤1.5wt％，基于所述第一填料中的所述无机颗粒的总重量计。
θ晶型的无机颗粒具有适中的比表面积和硬度，由此能够更好地同时改善隔离膜的耐热性和离子导通率；γ晶型和η晶型的无机颗粒具有比表面积大的优势。
通过选择不同晶型的第一填料有助于提升隔离膜的耐热性、离子导通率、粘结强度和对电解液的浸润和保持特性中的至少一者。
在一些实施例中，所述第一填料可包括无机颗粒，且所述无机颗粒的晶型包括θ晶型、γ晶型和η晶型，并且所述第一填料中的θ晶型的无机颗粒的含量可为55wt％至84wt％，γ晶型的无机颗粒的含量可为15wt％至44wt％，η晶型的无机颗粒的含量可为≤2.5wt％，均基于所述第一填料中的所述无机颗粒的总重量计。
无机颗粒的X射线衍射谱图可以按照如下方法测试得到：将无机颗粒烘干后，在研钵(如玛瑙研钵)中研磨30min，之后使用X射线衍射仪(如Miniflex600-C)进行测试，得到X射线衍射谱图。测试时可采用Cu靶材，Ni滤波片，管压40KV，管流15mA，连续扫描范围5°-80°。
在一些实施例中，所述第一填料可包括无机颗粒，所述无机颗粒可以按照如下方法制备：将无机颗粒的前驱体溶液通过高压溅射的方式进行氧化反应，之后在600℃至900℃下进行加热(例如1小时至3小时)形成一次颗粒形貌的无机颗粒，然后还可以再在150℃至250℃下进行干燥定型(例如30分钟至60分钟)获得二次颗粒形貌的无机颗粒(通过一次颗粒组装获得)。
在一些实施例中，所述第一填料的含量为≥50wt％，可选为50wt％至90wt％，55wt％至90wt％，60wt％至90wt％，50wt％至85wt％，55wt％至85wt％，60wt％至85wt％，50wt％至82.5wt％，55wt％至82.5wt％，60wt％至82.5wt％，基于所述涂层的总重量计。第一填料的含量在上述范围内时，能够保证涂层浆料具有合适的粘度，更有利于涂布；此外，还有利于与三维骨架结构搭接形成一体化效果，由此能使涂层具有更稳定的空间网络结构，从而能够进一步提升隔离膜的耐热性和离子导通率。
[第二填料]
在一些实施例中，所述涂层还包括第二填料，所述第二填料中的至少一部分嵌入所述涂层中。此外，还可能存在部分第二填料凸出于所述涂层的表面。
在一些实施例中，所述涂层包括第一填料和第二填料，所述第一填料的平均粒径记为d 1，所述第二填料的平均粒径记为d 2，则d 2/d 1＞1。第二填料的平均粒径较大，由此能够更好地发挥其在涂层中的支撑作用，减少第一填料的收缩，降低粘结剂用量，从而提升隔离膜的耐热性；第二填料的粒径较大，还有助于在用量较少时使涂层具有更多的孔 道结构和更少的水含量，进而能够进一步提升隔离膜的离子导通率以及对电解液的浸润和保持特性，同时还能够提升二次电池的循环性能和/或动力学性能。
所述第一填料包括一次颗粒和二次颗粒中的至少一种，所述一次颗粒形貌的第一填料的平均粒径记为d 11，所述二次颗粒形貌的第一填料的平均粒径记为d 12。
在一些实施例中，3.0≤d 2/d 11≤10.0，可选地，3.5≤d 2/d 11≤8.0，3.5≤d 2/d 11≤6.0。通过第一填料和第二填料的配合作用，有助于减少涂层水分含量，使涂层在长期充放电过程中保持稳定的孔道结构，同时还能提升隔离膜的耐热性，由此能够使二次电池更好地兼顾高能量密度、高热安全性能、长循环寿命和良好的动力学性能。
在一些实施例中，1.2≤d 2/d 12≤6.0，可选地，2.0≤d 2/d 12≤5.5，2.0≤d 2/d 12≤5.0，2.0≤d 2/d 12≤4.5。通过第一填料和第二填料的配合作用，有助于减少涂层水分含量，使涂层在长期充放电过程中保持稳定的孔道结构，同时还能提升隔离膜的耐热性，由此能够使二次电池更好地兼顾高能量密度、高热安全性能、长循环寿命和良好的动力学性能。
在一些实施例中，所述第二填料的平均粒径d 2为120nm至350nm，可选为150nm至300nm。由此能够更好地发挥第二填料的支撑作用，减少涂层水分含量，使涂层在长期充放电过程中保持稳定的孔道结构，同时还能提升隔离膜的耐热性。
在一些实施例中，所述第二填料的BET比表面积为≤20m 2/g，可选为6m 2/g至15m 2/g。由此能够更好地发挥第二填料的支撑作用，减少涂层水分含量，使涂层在长期充放电过程中保持稳定的孔道结构，同时还能提升隔离膜的耐热性。
在一些实施例中，所述第二填料包括无机颗粒和有机颗粒中的至少一种。
在一些实施例中，所述无机颗粒可包括具有5以上介电常数的无机颗粒、具有离子传导性但不储存离子的无机颗粒和能够发生电化学反应的无机颗粒中的至少一种。
可选地，所述具有5以上介电常数的无机颗粒包括勃姆石、氧化铝、氧化锌、氧化硅、氧化钛、氧化锆、氧化钡、氧化钙、氧化镁、氧化镍、氧化锡、氧化铈、氧化钇、氧化铪、氢氧化铝、氢氧化镁、碳化硅、碳化硼、氮化铝、氮化硅、氮化硼、氟化镁、氟化钙、氟化钡、硫酸钡、硅酸镁铝、硅酸镁锂、硅酸镁钠、膨润土、水辉石、钛酸锆、钛酸钡、Pb(Zr,Ti)O 3(简写为PZT)、Pb 1-mLa mZr 1-nTi nO 3(简写为PLZT，0＜m＜1，0＜n＜1)、Pb(Mg 3Nb 2/3)O 3-PbTiO 3(简写为PMN-PT)、及其各自的改性无机颗粒中的至少一种。可选地，各无机颗粒的改性方式可为化学改性和/或物理改性。所述化学改性方式包括偶联剂改性(例如采用硅烷偶联剂、钛酸酯偶联剂等)、表面活性剂改性、聚合物接枝改性等。所述物理改性方式可为机械力分散、超声分散、高能处理等。通过改性处理能够减少无机颗粒的团聚，由此能使涂层具有更稳定和更均一的空间网络结构；此外，通过选择具有特定官能团的偶联剂、表面活性剂或聚合物以改性无机颗粒，还有助于提升涂层对电解液的浸润和保持特性、提升涂层对多孔基材的粘结性。
可选地，所述具有离子传导性但不储存离子的无机颗粒包括Li 3PO 4、磷酸钛锂Li x1Ti y1(PO 4) 3、磷酸钛铝锂Li x2Al y2Ti z1(PO 4) 3、(LiAlTiP) x3O y3型玻璃、钛酸镧锂Li x4La y4TiO 3、硫代磷酸锗锂Li x5Ge y5P z2S w、氮化锂Li x6N y6、SiS 2型玻璃Li x7Si y7S z3和P 2S 5型玻璃Li x8P y8S z4中的至少一种，0＜x1＜2，0＜y1＜3，0＜x2＜2，0＜y2＜1，0＜z1＜3，0＜x3＜4，0＜y3＜13，0＜x4＜2，0＜y4＜3，0＜x5＜4，0＜y5＜1，0＜z2＜1，0＜w＜ 5，0＜x6＜4，0＜y6＜2，0＜x7＜3，0＜y7＜2，0＜z3＜4，0＜x8＜3，0＜y8＜3，0＜z4＜7。由此能够进一步提升隔离膜的离子导通率。
可选地，所述能够发生电化学反应的无机颗粒包括含锂过渡金属氧化物、含锂磷酸盐、碳基材料、硅基材料、锡基材料和锂钛化合物中的至少一种。
在一些实施例中，所述有机颗粒包括但不限于聚乙烯颗粒、聚丙烯颗粒、纤维素、纤维素改性剂(例如羧基甲基纤维素)、三聚氰胺树脂颗粒、酚醛树脂颗粒、聚酯颗粒(例如聚对苯二甲酸乙二酯、聚萘二甲酸乙二酯、聚对苯二甲酸丁二酯)、有机硅树酯颗粒、聚酰亚胺颗粒、聚酰胺酰亚胺颗粒、聚芳酰胺颗粒、聚苯硫醚颗粒、聚砜颗粒、聚醚砜颗粒、聚醚醚酮颗粒、聚芳醚酮颗粒、丙烯酸丁酯与甲基丙烯酸乙酯的共聚物(例如丙烯酸丁酯与甲基丙烯酸乙酯的交联聚合物)中的至少一种。
在一些实施例中，所述第二填料具有一次颗粒形貌。
在一些实施例中，所述第二填料包括一次颗粒形貌的无机颗粒，且所述一次颗粒形貌的无机颗粒的晶型包括α晶型和γ晶型中的至少一种，可选包括α晶型。α晶型的第二填料具有硬度高、耐热性好、介电常数低、安全性高和真密度大的优势，由此能够进一步改善涂层的耐热性。
在一些实施例中，所述第二填料包括一次颗粒形貌的无机颗粒，且所述一次颗粒形貌的无机颗粒的晶型包括α晶型，且α晶型的含量为≥70wt％，可选为75wt％至100wt％，85wt％至100wt％，95wt％至100wt％，基于所述第二填料中的所述一次颗粒形貌的无机颗粒的总重量计。
α晶型的无机颗粒在通过使用X射线衍射仪测定的X射线衍射谱图中，在2θ为57.48°±0.2°和43.34°±0.2°处具有衍射峰。
在一些实施例中，所述第二填料的含量为≤30wt％，可选为5wt％至25wt％，6wt％至22wt％，6wt％至20wt％，8wt％至18wt％，基于所述涂层的总重量计。第二填料的含量在上述范围内时，能够更好地发挥第二填料的支撑作用，减少涂层水分含量，使涂层在长期充放电过程中保持稳定的孔道结构。
在一些实施例中，所述涂层还可包括非颗粒状的粘结剂。本申请对非颗粒状的粘结剂的种类没有特别的限制，可以选用任意公知的具有良好粘结性的材料。可选地，所述非颗粒状的粘结剂包括水溶液型粘结剂，其具有热力学稳定性好且环保的优势，由此有利于涂层浆料的制备和涂布。作为示例，所述水溶液型粘结剂可包括水溶液型丙烯酸类树脂(例如，丙烯酸、甲基丙烯酸、丙烯酸钠单体均聚物或与其他共聚单体的共聚物)、聚乙烯醇(PVA)、异丁烯-马来酸酐共聚物和聚丙烯酰胺中的至少一种。
可选地，所述涂层中的所述非颗粒状的粘结剂的含量为≤2wt％，基于所述涂层的总重量计。本申请的涂层中的三维骨架结构与第一填料等能够形成稳定的空间网络结构，由此能够在减少粘结剂用量的前提下使隔离膜还能保持高粘结性。
在一些实施例中，所述涂层的厚度可为≤2μm，可选为0.5μm至1.5μm。由此有助于提升二次电池的能量密度。在本申请中，涂层的厚度是指位于多孔基材单侧的涂层的厚度。
在一些实施例中，所述多孔基材的厚度可为≤6μm，可选为3μm至5μm。本申请的涂层能使隔离膜的耐热性得到显著提升，由此可以选用更薄的多孔基材，从而有助于提升二次电池的能量密度。
本申请对多孔基材的材质没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的基材，例如，所述多孔基材可包括多孔聚烯烃基树脂膜(例如聚乙烯、聚丙烯、聚偏氟乙烯中的至少一种)、多孔玻璃纤维和多孔无纺布中的至少一种。所述多孔基材可以是单层薄膜，也可以是多层复合薄膜。所述多孔基材为多层复合薄膜时，各层的材料可以相同，也可以不同。
在一些实施例中，所述隔离膜还可包括粘接层，所述粘接层设置在所述涂层的至少一部分表面上，所述粘接层包括颗粒状的粘结剂。粘接层不仅能够防止涂层脱落，提升二次电池的安全性能，而且能够改善隔离膜与电极的界面，提升二次电池的循环性能。
可选地，所述颗粒状的粘结剂包括丙烯酸酯类单体均聚物或共聚物、丙烯酸类单体均聚物或共聚物、含氟烯烃单体均聚物或共聚物中的至少一种。所述共聚单体包括但不限于如下中的至少一种：丙烯酸酯类单体、丙烯酸类单体、烯烃单体、含卤素烯烃单体、氟醚类单体等。
可选地，所述颗粒状的粘结剂包括偏二氟乙烯基聚合物，例如偏二氟乙烯单体(VDF)的均聚物和/或偏二氟乙烯单体与共聚单体的共聚物。所述共聚单体可为烯烃单体、含氟烯烃单体、含氯烯烃单体、丙烯酸酯类单体、丙烯酸类单体、氟醚类单体中的至少一种。可选地，所述共聚单体可包括如下中的至少一种：三氟乙烯(VF3)、三氟氯乙烯(CTFE)、1,2-二氟乙烯、四氟乙烯(TFE)、六氟丙烯(HFP)、全氟(烷基乙烯基)醚(例如全氟(甲基乙烯基)醚PMVE、全氟(乙基乙烯基)醚PEVE、全氟(丙基乙烯基)醚PPVE)、全氟(1,3-间二氧杂环戊烯)和全氟(2,2-二甲基-1,3-间二氧杂环戊烯)(PDD)。
在一些实施例中，隔离膜在150℃、1h下的纵向热收缩率为≤6％，可选为0.5％至4％。
在一些实施例中，隔离膜在150℃、1h下的横向热收缩率为≤6％，可选为0.5％至4％。
本申请的隔离膜在150℃的高温下，横向和纵向两个方向均具有低热收缩率，由此能够提升二次电池的安全性能。
在一些实施例中，隔离膜的纵向拉伸强度为≥2000kg/cm 2，可选为2500kg/cm 2至4500kg/cm 2。
在一些实施例中，隔离膜的横向拉伸强度为≥2000kg/cm 2，可选为2500kg/cm 2至4500kg/cm 2。
本申请的隔离膜在横向和纵向两个方向均具有高拉伸强度，由此在二次电池膨胀时，隔离膜出现破损的概率较小，从而能够提升二次电池的安全性能。
在一些实施例中，隔离膜的润湿长度为≥30mm，可选为30mm至80mm。
在一些实施例中，隔离膜的润湿速度为≥3mm/s，可选为3mm/s至10mm/s。
本申请的隔离膜对电解液具有良好的浸润和保持特性，由此能够提升隔离膜的离子导通率和二次电池容量发挥特性。
在一些实施例中，隔离膜的透气度为≤300s/100mL，可选为100s/100mL至230s/100mL。本申请的隔离膜具有良好的透气度，由此能够提升离子导通率和二次电池容量发挥特性。
在一些实施例中，隔离膜的耐电压击穿强度为≥1KV。本申请的隔离膜具有较高的耐电压击穿强度度，由此能够提升二次电池的安全性能。
在本申请中，材料的平均粒径为本领域公知的含义，可采用本领域已知的仪器及方法进行测定。例如可以通过扫描电子显微镜、透射电子显微镜、颗粒尺寸分布仪器对材料或隔离膜进行测定获得图片，从图片上随机选取多个(例如10个以上)测试颗粒(例如具有第一填料、第二填料等)，统计颗粒最短对角线长度的平均值作为平均粒径。
在本申请中，材料的比表面积为本领域公知的含义，可采用本领域已知的仪器及方法进行测定。例如可以参照GB/T 19587-2017，采用氮气吸附比表面积分析测试方法测试，并用BET(BrunauerEmmett Teller)法计算得出。可选地，氮气吸附比表面积分析测试可以通过美国Micromeritics公司的Tri-Star 3020型比表面积孔径分析测试仪进行。
在本申请中，隔离膜的热收缩率、拉伸强度和透气度均具有本领域公知的含义，可以采用本领域已知的方法进行测量。例如，均可参照标准GB/T 36363-2018进行测试。
在本申请中，隔离膜的润湿长度、润湿速度均具有本领域公知的含义，可以采用本领域已知的方法进行测量。示例性测试方法如下：将隔离膜裁切成宽度为5mm、长度为100mm的样品，将样品两端固定后水平放置；取0.5mg电解液滴在样品中央，达到规定时间(本申请为1min)后，拍照并测量电解液扩散的长度，由此得到隔离膜的润湿长度和润湿速度。为了保证测试结果的准确性，可取多个(例如5至10个)样品进行测试，并且测试结果通过计算平均值得到。电解液可以按照如下方法配制：将碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)和碳酸二乙酯(DEC)按照质量比30:50:20进行混合得到有机溶剂，将充分干燥的LiPF 6溶解于上述有机溶剂中配制成浓度为1mol/L的电解液。
在本申请中，隔离膜的耐电压击穿强度具有本领域公知的含义，可以采用本领域已知的方法进行测量。例如可以参照GB/T 13542.2-2009、GB/T 1408-2006，使用耐压测试仪进行测定。示例性测试方法如下：将隔离膜裁切成450mm×650mm的长方形试样，使用耐压测试仪进行测定。测试仪器可以采用CS2671AX型耐压测试仪。
需要说明的是，上述隔离膜的涂层参数(例如厚度等)均为多孔基材单侧的涂层参数。当涂层设置在多孔基材的两侧时，其中任意一侧的涂层参数满足本申请，即认为落入本申请的保护范围内。
制备方法
本申请实施方式第二方面提供一种制备本申请实施方式第一方面的隔离膜的方法，包括以下步骤：提供多孔基材；将用于构成三维骨架结构的材料和第一填料按照预定比例在溶剂中混合，配制成涂层浆料；将所述涂层浆料涂布于所述多孔基材的至少一个表面上，干燥后获得隔离膜，其中，所述隔离膜包括多孔基材和设置在所述多孔基材的至少一个表面上的涂层，所述涂层包括三维骨架结构和第一填料，所述第一填料中的至少一部分填充在所述三维骨架结构中，且所述第一填料的平均粒径小于等于200nm。
在一些实施例中，所述涂层浆料还包括第二填料，所述第一填料的平均粒径记为d 1，所述第二填料的平均粒径记为d 2，则d 2/d 1＞1。
在一些实施例中，配制涂层浆料时使用的溶剂可以为水，例如去离子水。
在一些实施例中，所述涂层浆料还可以包括其他组分，例如，还可以包括分散剂、润湿剂、粘结剂等。
在一些实施例中，所述用于构成三维骨架结构的材料包括有机材料和无机材料中的至少一种。可选地，所述有机材料包括纳米纤维素、聚四氟乙烯纳米纤维和聚酰胺纳米纤维中的至少一种。可选地，所述无机材料包括埃洛石纳米管、纳米棒状氧化铝、纳米棒状勃姆石、纳米棒状氧化硅和玻璃纤维中的至少一种。
在一些实施例中，所述构成所述三维骨架结构的材料包括纳米纤维素。
在一些实施例中，所述纳米纤维素可以按照如下方法获得：提供白度≥80％的纤维素粉末；将所获得的纤维素粉末与改性溶液混合并反应后，经过洗涤除杂，然后将pH调节至中性，并经研磨、切割获得纳米纤维素。
可选地，上述白度≥80％的纤维素粉末可以通过市购获得，或者采用化学法(例如酸解法、碱处理法、Tempo催化氧化法)、生物法(例如酶处理法)、机械法(例如超细研磨、超声破碎、高压均质)等获得。用于制备上述白度≥80％的纤维素粉末的纤维原料可以包括植物纤维，例如棉纤维(例如棉花纤维、木棉纤维)、麻纤维(例如剑麻纤维、苎麻纤维、黄麻纤维、亚麻纤维、大麻纤维、蕉麻纤维等)、棕纤维、木纤维、竹纤维、草纤维中的至少一种。
在一些实施例中，上述白度≥80％的纤维素粉末也可通过以下方式制备获得：将纤维原料经过开松除渣后，用碱液(例如NaOH水溶液，其浓度可为4wt％至20wt％，可选为5wt％至15wt％)蒸煮，然后再顺序经过水洗除杂(例如水洗次数为3次至6次)、漂白(例如可用次氯酸钠和/或双氧水)、酸洗除杂、水洗除杂、驱水、气流干燥，获得纤维素粉末。
在一些实施例中，所述改性溶液可为酸溶液(例如硫酸水溶液、硼酸水溶液、磷酸水溶液、醋酸水溶液)或碱溶液(例如尿素有机溶剂溶液)。可选地，所述改性溶液为酸溶液。
可选地，所述酸溶液的浓度可为5wt％至80wt％。当改性溶液选用硫酸水溶液时，所述酸溶液的浓度可为40wt％至80wt％，由此可以获得具有磺酸基的纤维素粉末。当改性溶液选用硼酸水溶液时，所述酸溶液的浓度可为5wt％至10wt％，由此可以获得具有硼酸基的纤维素粉末。当改性溶液选用磷酸水溶液时，所述酸溶液的浓度可为45wt％至75wt％，由此可以获得具有磷酸基的纤维素粉末。当改性溶液选用醋酸水溶液时，所述酸溶液的浓度可为40wt％至80wt％，由此可以获得具有羧酸基的纤维素粉末。
可选地，所述尿素有机溶剂溶液为尿素二甲苯溶液，由此可以获得具有胺基的纤维素粉末。
在一些实施例中，可选地，所述纤维素粉末与所述改性溶液的质量比可为1:2.5至1:50，可选为1:5至1:30。
当改性溶液选用硫酸水溶液时，所述纤维素粉末与所述酸溶液的质量比可为1:5至1:30。当改性溶液选用硼酸水溶液时，所述纤维素粉末与所述酸溶液的质量比可为1:20至1:50。当改性溶液选用磷酸水溶液时，所述纤维素粉末与所述酸溶液的质量比可为1:5至1:30。当改性溶液选用醋酸水溶液时，所述纤维素粉末与所述酸溶液的质量比可为1:5至 1:30。当改性溶液选用尿素有机溶剂溶液时，所述纤维素粉末与所述尿素有机溶剂溶液的质量比可为1:4至1:40。
在一些实施例中，当所述改性溶液为酸溶液时，所述反应可在不高于80℃的条件下进行，可选为在30℃至60℃的条件下进行，所述纤维素粉末与所述改性溶液的反应时间可为0.5h至4h，可选为1h至3h。
在一些实施例中，当所述改性溶液为碱溶液时，所述反应可在100℃至145℃的条件下进行，所述纤维素粉末与所述改性溶液的反应时间可为1h至5h。
在一些实施例中，研磨可以采用研磨机，切割可以采用高压均质机。通过调节研磨机的研磨参数(例如研磨次数、研磨时间等)以及高压均质机的切割参数能够获得具有不同平均直径和/或不同平均长度的纳米纤维素。
在一些实施例中，所述涂层浆料涂布时可采用涂布机。本申请对涂布机的型号没有特殊限制，例如可以采用市购涂布机。所述涂布机包括凹版辊；所述凹版辊用于将浆料转移到多孔基材上。
在一些实施例中，所述涂层浆料的涂布方式可以采用转移涂布、旋转喷涂、浸涂等。
在一些实施例中，所述方法还包括以下步骤：将包含颗粒状的粘结剂的浆料涂布于所述涂层的至少一部分表面上，干燥后形成粘接层。
本申请的隔离膜的制备方法通过一次涂布制得涂层，大大简化了隔离膜的生产工艺流程。
本申请的隔离膜的制备方法中使用的一些原料及其含量等参数可以参考本申请实施方式第一方面的隔离膜，此处不再赘述。
如果没有特别的说明，在本申请的隔离膜的制备方法中所使用的各原料均可以通过市购获得。
二次电池
本申请实施方式第三方面提供一种二次电池。
二次电池又称为充电电池或蓄电池，是指在电池放电后可通过充电的方式使活性材料激活而继续使用的电池。通常情况下，二次电池包括电极组件和电解液，所述电极组件包括正极极片、负极极片和隔离膜，所述隔离膜设置在所述正极极片和所述负极极片之间，主要起到防止正极和负极短路的作用，同时可以使活性离子通过。
本申请对二次电池种类没有特别的限制，例如，所述二次电池可以为锂离子电池、钠离子电池等，特别地，所述二次电池可以为锂离子二次电池。
本申请实施方式第三方面的二次电池包括本申请实施方式第一方面的隔离膜或通过本申请实施方式第二方面的方法制备的隔离膜，所述隔离膜间隔于所述正极极片和所述负极极片之间。可选地，至少所述隔离膜靠近所述负极极片的一侧具有本申请的涂层。由此，本申请的二次电池能兼顾高能量密度、高热安全性能、长循环寿命和良好的动力学性能。
[正极极片]
在一些实施例中，所述正极极片包括正极集流体以及设置在所述正极集流体至少一个表面且包括正极活性材料的正极膜层。例如，所述正极集流体具有在自身厚度方向相对的两个表面，所述正极膜层设置在所述正极集流体的两个相对表面中的任意一者或两 者上。
当本申请的二次电池为锂离子电池时，所述正极活性材料可包括但不限于含锂过渡金属氧化物、含锂磷酸盐及其各自的改性化合物中的至少一种。所述锂过渡金属氧化物的示例可包括但不限于锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物及其各自的改性化合物中的至少一种。所述含锂磷酸盐的示例可包括但不限于磷酸铁锂、磷酸铁锂与碳的复合材料、磷酸锰锂、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料及其各自的改性化合物中的至少一种。
在一些实施例中，为了进一步提升二次电池的能量密度，用于锂离子电池的正极活性材料可以包括通式为Li aNi bCo cM dO eA f的锂过渡金属氧化物及其改性化合物中的至少一种。0.8≤a≤1.2，0.5≤b＜1，0＜c＜1，0＜d＜1，1≤e≤2，0≤f≤1，M选自Mn、Al、Zr、Zn、Cu、Cr、Mg、Fe、V、Ti和B中的至少一种，A选自N、F、S和Cl中的至少一种。
作为示例，用于锂离子电池的正极活性材料可包括LiCoO 2、LiNiO 2、LiMnO 2、LiMn 2O 4、LiNi 1/3Co 1/3Mn 1/3O 2(NCM333)、LiNi 0.5Co 0.2Mn 0.3O 2(NCM523)、LiNi 0.6Co 0.2Mn 0.2O 2(NCM622)、LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)、LiNi 0.85Co 0.15Al 0.05O 2、LiFePO 4、LiMnPO 4中的至少一种。
当本申请的二次电池为钠离子电池时，所述正极活性材料可包括但不限于含钠过渡金属氧化物、聚阴离子材料(如磷酸盐、氟磷酸盐、焦磷酸盐、硫酸盐等)、普鲁士蓝类材料中的至少一种。
作为示例，用于钠离子电池的正极活性材料可包括NaFeO 2、NaCoO 2、NaCrO 2、NaMnO 2、NaNiO 2、NaNi 1/2Ti 1/2O 2、NaNi 1/2Mn 1/2O 2、Na 2/3Fe 1/3Mn 2/3O 2、NaNi 1/3Co 1/3Mn 1/3O 2、NaFePO 4、NaMnPO 4、NaCoPO 4、普鲁士蓝类材料、通式为X pM’ q(PO 4) rO xY 3-x的材料中的至少一种。在通式X pM’ q(PO 4) rO xY 3-x中，0＜p≤4，0＜q≤2，1≤r≤3，0≤x≤2，X选自H +、Li +、Na +、K +和NH 4 +中的至少一种，M’为过渡金属阳离子，可选地为V、Ti、Mn、Fe、Co、Ni、Cu和Zn中的至少一种，Y为卤素阴离子，可选地为F、Cl和Br中的至少一种。
在本申请中，上述各正极活性材料的改性化合物可以是对所述正极活性材料进行掺杂改性和/或表面包覆改性。
在一些实施例中，所述正极膜层还可选地包括正极导电剂。本申请对所述正极导电剂的种类没有特别的限制，作为示例，所述正极导电剂包括超导碳、导电石墨、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯和碳纳米纤维中的至少一种。在一些实施例中，基于所述正极膜层的总重量，所述正极导电剂的质量百分含量为≤5wt％。
在一些实施例中，所述正极膜层还可选地包括正极粘结剂。本申请对所述正极粘结剂的种类没有特别的限制，作为示例，所述正极粘结剂可包括聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物和含氟丙烯酸酯类树脂中的至少一种。在一些实施例中，基于所述正极膜层的总重量，所述正极粘结剂的质量百分含量为≤5wt％。
在一些实施例中，所述正极集流体可采用金属箔片或复合集流体。作为金属箔片的 示例，可采用铝箔。所述复合集流体可包括高分子材料基层以及形成于所述高分子材料基层至少一个表面上的金属材料层。作为示例，所述金属材料可包括铝、铝合金、镍、镍合金、钛、钛合金、银和银合金中的至少一种。作为示例，所述高分子材料基层可包括聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)和聚乙烯(PE)中的至少一种。
所述正极膜层通常是将正极浆料涂布于正极集流体上，经干燥、冷压而成的。所述正极浆料通常是将正极活性材料、可选的导电剂、可选的粘结剂以及任意的其他组分分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)，但不限于此。
[负极极片]
在一些实施例中，所述负极极片包括负极集流体以及设置在所述负极集流体至少一个表面且包括负极活性材料的负极膜层。例如，所述负极集流体具有在自身厚度方向相对的两个表面，所述负极膜层设置在所述负极集流体的两个相对表面中的任意一者或两者上。
所述负极活性材料可采用本领域公知的用于二次电池的负极活性材料。作为示例，所述负极活性材料可包括但不限于天然石墨、人造石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂中的至少一种。所述硅基材料可包括单质硅、硅氧化物、硅碳复合物、硅氮复合物和硅合金材料中的至少一种。所述锡基材料可包括单质锡、锡氧化物和锡合金材料中的至少一种。
在一些实施例中，所述负极膜层还可选地包括负极导电剂。本申请对所述负极导电剂的种类没有特别的限制，作为示例，所述负极导电剂可包括超导碳、导电石墨、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯和碳纳米纤维中的至少一种。在一些实施例中，基于所述负极膜层的总重量，所述负极导电剂的质量百分含量为≤5wt％。
在一些实施例中，所述负极膜层还可选地包括负极粘结剂。本申请对所述负极粘结剂的种类没有特别的限制，作为示例，所述负极粘结剂可包括丁苯橡胶(SBR)、水溶性不饱和树脂SR-1B、水性丙烯酸类树脂(例如，聚丙烯酸PAA、聚甲基丙烯酸PMAA、聚丙烯酸钠PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)和羧甲基壳聚糖(CMCS)中的至少一种。在一些实施例中，基于所述负极膜层的总重量，所述负极粘结剂的质量百分含量为≤5wt％。
在一些实施例中，所述负极膜层还可选地包括其他助剂。作为示例，其他助剂可包括增稠剂，例如，羧甲基纤维素钠(CMC)、PTC热敏电阻材料等。在一些实施例中，基于所述负极膜层的总重量，所述其他助剂的质量百分含量为≤2wt％。
在一些实施例中，所述负极集流体可采用金属箔片或复合集流体。作为金属箔片的示例，可采用铜箔。所述复合集流体可包括高分子材料基层以及形成于所述高分子材料基层至少一个表面上的金属材料层。作为示例，所述金属材料可包括铜、铜合金、镍、镍合金、钛、钛合金、银和银合金中的至少一种。作为示例，所述高分子材料基层可包括聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)和聚乙烯(PE)中的至少一种。
所述负极膜层通常是将负极浆料涂布于负极集流体上，经干燥、冷压而成的。所述负极浆料通常是将负极活性材料、可选的导电剂、可选地粘结剂、其他可选的助剂分散 于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水，但不限于此。
所述负极极片并不排除除了所述负极膜层之外的其他附加功能层。例如在某些实施例中，本申请所述的负极极片还包括夹在所述负极集流体和所述负极膜层之间、设置在所述负极集流体表面的导电底涂层(例如由导电剂和粘结剂组成)。在另外一些实施例中，本申请所述的负极极片还包括覆盖在所述负极膜层表面的保护层。
[电解液]
在二次电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出，电解液在正极极片和负极极片之间起到传导活性离子的作用。本申请对电解液的种类没有特别的限制，可根据实际需求进行选择。
所述电解液包括电解质盐和溶剂。所述电解质盐和所述溶剂的种类不受具体的限制，可根据实际需求进行选择。
当本申请的二次电池为锂离子电池时，作为示例，所述电解质盐可包括但不限于六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、高氯酸锂(LiClO 4)、六氟砷酸锂(LiAsF 6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二草酸硼酸锂(LiBOB)、二氟磷酸锂(LiPO 2F 2)、二氟二草酸磷酸锂(LiDFOP)和四氟草酸磷酸锂(LiTFOP)中的至少一种。
当本申请的二次电池为钠离子电池时，作为示例，所述电解质盐可包括但不限于六氟磷酸钠(NaPF 6)、四氟硼酸钠(NaBF 4)、高氯酸钠(NaClO 4)、六氟砷酸钠(NaAsF 6)、双氟磺酰亚胺钠(NaFSI)、双三氟甲磺酰亚胺钠(NaTFSI)、三氟甲磺酸钠(NaTFS)、二氟草酸硼酸钠(NaDFOB)、二草酸硼酸钠(NaBOB)、二氟磷酸钠(NaPO 2F 2)、二氟二草酸磷酸钠(NaDFOP)和四氟草酸磷酸钠(NaTFOP)中的至少一种。
作为示例，所述溶剂可包括但不限于碳酸乙烯酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸乙烯酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)和二乙砜(ESE)中的至少一种。
在一些实施例中，所述电解液中还可选地包括添加剂。例如，所述添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、改善电池低温功率性能的添加剂等。
在一些实施例中，所述正极极片、所述隔离膜和所述负极极片可通过卷绕工艺和/或叠片工艺制成电极组件。
在一些实施例中，所述二次电池可包括外包装。该外包装可用于封装上述电极组件及电解液。
在一些实施例中，所述二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。所述二次电池的外包装也可以是软包，例如袋式软包。所述软包的材质可以是塑料，如聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)和聚丁二酸丁二醇酯(PBS)中的至少一种。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。如图1是作为一个示例的方形结构的二次电池5。
在一些实施例中，如图2所示，外包装可包括壳体51和盖板53。壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53用于盖设所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺和/或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，可根据需求来调节。
本申请的二次电池的制备方法是公知的。在一些实施例中，可将正极极片、隔离膜、负极极片和电解液组装形成二次电池。作为示例，可将正极极片、隔离膜、负极极片经卷绕工艺和/或叠片工艺形成电极组件，将电极组件置于外包装中，烘干后注入电解液，经过真空封装、静置、化成、整形等工序，得到二次电池。
在本申请的一些实施例中，根据本申请的二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。
图3是作为一个示例的电池模块4的示意图。如图3所示，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施例中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
图4和图5是作为一个示例的电池包1的示意图。如图4和图5所示，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2用于盖设下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
用电装置
本申请实施方式第四方面提供一种用电装置，所述用电装置包括本申请的二次电池、电池模块或电池包中的至少一种。所述二次电池、电池模块或电池包可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
所述用电装置可以根据其使用需求来选择二次电池、电池模块或电池包。
图6是作为一个示例的用电装置的示意图。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的用电装置可以是手机、平板电脑、笔记本电脑等。该用电装置通常要求轻薄化，可以采用二次电池作为电源。
实施例
下述实施例更具体地描述了本申请公开的内容，这些实施例仅仅用于阐述性说明，因为在本申请公开内容的范围内进行各种修改和变化对本领域技术人员来说是明显的。除非另有声明，以下实施例中所报道的所有份、百分比和比值都是基于质量计，而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
纳米纤维素C1的制备
将棉花短绒通过开棉机开松除渣后，使用5wt％的NaOH水溶液在150℃蒸煮2h，然后再顺序经过水洗除杂(水洗次数为3次)、次氯酸钠漂白、稀盐酸洗涤除杂、水洗除杂(水洗次数为1次)、驱水、气流干燥后，获得白度为≥85％的棉花纤维素粉末。
将所获得的棉花纤维素粉末1kg与60wt％的硫酸水溶液30kg混合，在55℃至60℃下反应1.5h，反应结束后，经过水洗除杂(水洗次数为3次)、过滤、除酸除杂，
再用10wt％的NaOH水溶液将pH调至中性，然后用研磨机研磨，再使用高压均质机设备进行纳米级切割，得到平均长度为350nm、平均直径为18nm的具有磺酸基改性基团的纳米纤维素C1，并且磺酸基与羟基的摩尔比为5:3。
纳米纤维素C2至C4的制备
纳米纤维素C2至C4按照与纳米纤维素C1类似的方法制备，不同之处详见表1。在制备过程中，可以通过调节研磨机处理的参数以及高压均质机设备的切割参数获得具有不同平均直径和/或不同平均长度的纳米纤维素。
纳米纤维素C5的制备
将棉花短绒通过开棉机开松除渣后，使用5wt％的NaOH水溶液在150℃蒸煮2h，然后再顺序经过水洗除杂(水洗次数为3次)、次氯酸钠漂白、稀盐酸洗涤除杂、水洗除杂(水洗次数为1次)、驱水、气流干燥后，获得白度为≥85％的棉花纤维素粉末。在10℃条件下，将获得的棉花纤维素粉末与20wt％的NaOH水溶液混合，搅拌2h、过滤、水洗2次后，获得纤维素粉末。
将所获得的纤维素粉末50g与尿素200g置于带油水分离器的三口反应器中，待尿素溶解后，再加入5g二甲苯，搅拌下升温至137℃，反应4h后终止，然后经过水洗(水洗次数为3次)、过滤、干燥，获得纤维素氨基甲酸酯。
将所获得的纤维素氨基甲酸酯溶解在5wt％的NaOH水溶液中，得到均匀的纤维素氨基甲酸酯溶液，然后用研磨机研磨，再使用高压均质机设备进行纳米级切割，得到平均长度为350nm、平均直径为18nm的具有胺基改性基团的纳米纤维素C5，并且胺基与与羟基的摩尔比为4:3。
纳米纤维素C6的制备
采用未改性纳米纤维素，平均长度为350nm、平均直径为18nm，产品型号为CNWS-50，购自中科雷鸣(北京)科技有限公司，可以使用研磨机和/或高压均质机进一步处理，以获得具有不同平均直径和/或不同平均长度的纳米纤维素。
纳米纤维素C1至C5中改性基团与羟基的摩尔比可以通过以下方法测得：依据GB/T  12008.3-2009中的邻苯二甲酸酐法分别测试得到原料纤维素和纳米纤维素C1至C5的羟值(与每克试样中羟基含量相当的氢氧化钾毫克数)，得到的数值单位为mg KOH/g，将其转化为mmol/g，作为羟基含量。以原料纤维素的羟基含量减去纳米纤维素C1至C5的羟基含量，即可得改性基团的含量(即被改性的羟基的含量)，由此计算得到改性基团与羟基的摩尔比。
表1
Figure PCTCN2022136684-appb-000001
实施例1
隔离膜的制备
提供PE多孔基材：厚度为5.2μm。
配制涂层浆料：将上述制备的纳米纤维素C1、第一填料、第二填料、粘结剂水溶液型聚丙烯酸按照质量比16.0:62.5:20.0:1.5在适量的溶剂去离子水中混合均匀，得到涂层浆料。
第一填料为氧化铝一次颗粒(平均粒径为50nm，含量为12.5wt％，基于涂层的总重量计)和氧化铝二次颗粒(平均粒径为100nm，含量为50wt％，基于涂层的总重量计)的混合物，并且第一填料中α晶型、θ晶型、γ晶型和η晶型的含量分别为1.5wt％、70.7wt％、27.3wt％和0.5wt％，基于第一填料总重量计。第二填料为氧化铝一次颗粒(平均粒径为240nm)，并且第二填料的晶型主要为α晶型，质量占比在99.5％以上，基于第二填料总重量计。
涂布：将所配制的涂层浆料用涂布机涂布于PE多孔基材的两个表面上，通过干燥、分切工序，得到隔离膜。位于PE多孔基材单侧的涂层厚度为1.0μm。
正极极片的制备
将正极活性材料LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)、导电剂炭黑(Super P)、粘结剂聚偏二氟乙烯(PVDF)按照质量比96.2:2.7:1.1在适量的溶剂N-甲基吡咯烷酮(NMP)中混合均匀，得到正极浆料；将正极浆料涂布于正极集流体铝箔上，通过烘干、冷压、分条、裁切等工序，得到正极极片。
负极极片的制备
将负极活性材料人造石墨、导电剂炭黑(Super P)、粘结剂丁苯橡胶(SBR)和羧甲基纤维素钠(CMC)按照质量比96.4:0.7:1.8:1.1在适量的溶剂去离子水中混合均匀，得到负极浆料；将负极浆料涂布于负极集流体铜箔上，通过烘干、冷压、分条、裁切工序，得到负极极片。
电解液的制备
将碳酸乙烯酯(EC)和碳酸甲乙酯(EMC)按照质量比30:70进行混合得到有机溶剂，将充分干燥的LiPF 6溶解于上述有机溶剂中配制成浓度为1mol/L的电解液。
二次电池的制备
将正极极片、隔离膜、负极极片按顺序堆叠并卷绕，得到电极组件；将电极组件置于外包装中，干燥后注入电解液，经过真空封装、静置、化成、整形等工序，得到二次电池。
实施例2-4
二次电池采用与实施例1类似的方法制备，不同之处在于隔离膜的制备中第一填料的颗粒尺寸不同，具体参数详见表2。
实施例5-14
二次电池采用与实施例1类似的方法制备，不同之处在于隔离膜的制备中纳米纤维素和第一填料的种类和/或加入量不同，具体参数详见表2。
实施例15
二次电池采用与实施例1类似的方法制备，不同之处在于隔离膜的制备中，第一填料为氧化铝二次颗粒，平均粒径为100nm，且第一填料中α晶型、θ晶型、γ晶型和η晶型的含量分别为1.5wt％、70.7wt％、27.3wt％和0.5wt％，基于第一填料总重量计。
实施例16
二次电池采用与实施例1类似的方法制备，不同之处在于隔离膜的制备中，第一填料采用氧化铝一次颗粒。氧化铝一次颗粒的平均粒径为50nm，且α晶型、θ晶型、γ晶型和η晶型的含量分别为1.5wt％、70.7wt％、27.3wt％和0.5wt％，基于氧化铝一次颗粒的总重量计。
对比例1
二次电池采用与实施例1类似的方法制备，不同之处在于隔离膜的制备工艺。
提供PE多孔基材：厚度为5.2μm。
配制涂层浆料：将氧化铝一次颗粒(平均粒径为700nm，α晶型质量占比99.5％以上)与粘结剂按照质量比94:6混合后溶于去离子水中，得到涂层浆料。
涂布：将所配制的涂层浆料用涂布机涂布于PE多孔基材的两个表面上，通过干燥、分切工序，得到隔离膜。位于PE多孔基材单侧的涂层厚度为1.8μm。
测试部分
(1)隔离膜的热收缩率测试
样品制备：将上述制备的隔离膜用冲压机冲切成宽度为50mm、长度为100mm的样品，取5个平行样品放置在A4纸上并固定，再将装有样品的A4纸放置在厚度为1mm至5mm的瓦楞纸上。
样品测试：将放置在瓦楞纸上面的A4纸放入鼓风式烘箱，鼓风式烘箱温度设置为150℃，待温度达到设定温度并稳定30分钟后，开始计时，到达设定时间(本申请为1小时)后，测量隔离膜的长度和宽度，数值分别标记为a和b。
热收缩率计算：纵向(MD)热收缩率＝[(100-a)/100]×100％，横向(TD)热收缩率＝[(50-b)/50]×100％，取5个平行样品的平均值作为测试结果。
(2)隔离膜的离子导通率测试
隔离膜的离子导通率通过交流阻抗谱实验测试得到。具体地，将隔离膜裁成一定面积的圆片，烘干后，置于两个不锈钢电极之间，待吸收足够量的电解液后密封形成扣式电池，采用电化学工作站进行交流阻抗谱实验，获得隔离膜的离子导通率。电化学工作 站可采用上海辰华CHI 660C电化学工作站，交流信号频率范围为0.01Hz至1MHz，正弦波电位幅值为5mV。为了准确性，取5个平行样品的平均值作为测试结果。
采用的电解液按照如下方式配制：将碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)和碳酸二乙酯(DEC)按照质量比30:50:20进行混合得到有机溶剂，将充分干燥的LiPF 6溶解于上述有机溶剂中配制成浓度为1mol/L的电解液。
(3)二次电池的热箱测试
在25℃下，将二次电池以1C恒流充电至4.2V，继续恒压充电至电流为≤0.05C，静置5min；然后在DHG-9070A DHG系列高温烘箱中带夹具测试各二次电池，以5℃/min的速率从室温升至80℃±2℃，保持30min；之后再以5℃/min升温速度升温，每升温5℃，保温30min。升温过程中监控二次电池表面温度变化，当温度开始急剧上升时对应的烘箱温度即为二次电池的热箱失效温度。二次电池的热箱失效温度越高，表明二次电池的热安全性能越好。为了准确性，取5个平行样品的平均值作为测试结果。
(4)二次电池的循环性能测试
在25℃下，将二次电池以1C恒流充电至4.2V，继续恒压充电至电流为≤0.05C，此时二次电池为满充状态，记录此时的充电容量，即为第1圈充电容量；将二次电池静置5min后，以1C恒流放电至2.8V，此为一个循环充放电过程，记录此时的放电容量，即为第1圈放电容量。将二次电池按照上述方法进行循环充放电测试，记录每圈循环后的放电容量。二次电池25℃循环1000圈后的容量保持率(％)＝1000圈循环后的放电容量/第1圈放电容量×100％。为了准确性，取5个平行样品的平均值作为测试结果。
由表2可见，通过在隔离膜的多孔基材的两个表面设置包含纳米纤维素(构成三维骨架结构)和平均粒径小于等于200nm的第一填料的涂层，能够使隔离膜兼顾低热收缩率和高离子导通率，还能使二次电池兼顾高热安全性能和良好的循环性能。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其他方式也包含在本申请的范围内。
Figure PCTCN2022136684-appb-000002

Claims (23)

  1. 一种隔离膜，包括多孔基材和设置在所述多孔基材的至少一个表面上的涂层，其中，所述涂层包括三维骨架结构和第一填料，所述第一填料中的至少一部分填充在所述三维骨架结构中，且所述第一填料的平均粒径小于等于200nm。
  2. 根据权利要求1所述的隔离膜，其中，所述第一填料的平均粒径为15nm至180nm，可选为30nm至150nm。
  3. 根据权利要求1或2所述的隔离膜，其中，所述第一填料包括一次颗粒和二次颗粒中的至少一种；
    可选地，所述第一填料包括一次颗粒和二次颗粒的组合；
    可选地，基于所述第一填料的总重量计，所述一次颗粒形貌的第一填料的含量小于所述二次颗粒形貌的第一填料的含量；
    可选地，基于所述第一填料的总重量计，所述一次颗粒形貌的第一填料的含量小于等于30wt％；
    可选地，所述一次颗粒形貌的第一填料的平均粒径为15nm至80nm，更可选为30nm至65nm；
    可选地，所述二次颗粒形貌的第一填料的平均粒径为50nm至200nm，更可选为55nm至150nm。
  4. 根据权利要求1-3任一项所述的隔离膜，其中，所述第一填料的BET比表面积为≥25m 2/g，可选为30m 2/g至65m 2/g。
  5. 根据权利要求1-4任一项所述的隔离膜，其中，
    所述第一填料的含量为≥50wt％，可选为60wt％至90wt％，基于所述涂层的总重量计；和/或，
    所述三维骨架结构的含量为5wt％至40wt％，可选为8wt％至25wt％，基于所述涂层的总重量计。
  6. 根据权利要求1-5任一项所述的隔离膜，其中，所述第一填料包括无机颗粒和有机颗粒中的至少一种；
    可选地，所述无机颗粒包括勃姆石、氧化铝、硫酸钡、氧化镁、氢氧化镁、硅氧化合物、二氧化锡、氧化钛、氧化钙、氧化锌、氧化锆、氧化钇、氧化镍、二氧化铪、氧化铈、钛酸锆、钛酸钡和氟化镁中的至少一种，更可选地，所述无机颗粒包括勃姆石、氧化铝、硫酸钡、氧化镁、硅氧化合物、氧化钛、氧化锌、氧化铈和钛酸钡中的至少一种；
    可选地，所述有机颗粒包括聚苯乙烯颗粒、聚丙烯酸蜡颗粒、三聚氰胺甲醛树脂颗粒、酚醛树脂颗粒、聚酯颗粒、聚酰亚胺颗粒、聚酰胺亚胺颗粒、聚芳酰胺颗粒、聚苯硫醚颗粒、聚砜颗粒、聚醚砜颗粒、聚醚醚酮颗粒和聚芳醚酮颗粒中的至少一种。
  7. 根据权利要求1-6任一项所述的隔离膜，其中，所述第一填料包括无机颗粒，且所述无机颗粒的晶型包括θ晶型、γ晶型和η晶型中的至少一种；
    可选地，所述无机颗粒的晶型包括θ晶型和γ晶型中的至少一种；
    可选地，θ晶型的无机颗粒的含量为≥50wt％，更可选为55wt％至84wt％，基于所述第一填料中的所述无机颗粒的总重量计；
    可选地，γ晶型的无机颗粒的含量为≥10wt％，更可选为15wt％至44wt％，基于所述第一填料中的所述无机颗粒的总重量计；
    可选地，η晶型的无机颗粒的含量为≤5wt％，更可选为≤2.5wt％，基于所述第一填料中的所述无机颗粒的总重量计。
  8. 根据权利要求1-7任一项所述的隔离膜，其中，所述三维骨架结构由纤维状物形成，所述纤维状物的形貌可选地包括棒状、管状、杆状和纤维状中的至少一种。
  9. 根据权利要求1-8任一项所述的隔离膜，其中，
    构成所述三维骨架结构的材料的平均直径为≤40nm，可选为10nm至35nm；和/或，
    构成所述三维骨架结构的材料的平均长度为100nm至600nm，可选为200nm至500nm；和/或，
    构成所述三维骨架结构的材料的长径比为5至60，可选为10至30。
  10. 根据权利要求1-9任一项所述的隔离膜，其中，构成所述三维骨架结构的材料包括有机材料和无机材料中的至少一种；
    可选地，所述有机材料包括纳米纤维素、聚四氟乙烯纳米纤维和聚酰胺纳米纤维中的至少一种，可选地，所述纳米纤维素包括纤维素纳米纤维、纤维素纳米晶须和细菌纳米纤维素中的至少一种；
    可选地，所述无机材料包括埃洛石纳米管、纳米棒状氧化铝、纳米棒状勃姆石、纳米棒状氧化硅和玻璃纤维中的至少一种。
  11. 根据权利要求1-10任一项所述的隔离膜，其中，构成所述三维骨架结构的材料包括纳米纤维素，所述纳米纤维素包括未改性纳米纤维素和改性纳米纤维素中的至少一种；
    可选地，所述改性纳米纤维素包括改性基团，所述改性基团包括胺基、羧基、醛基、磺酸基、硼酸基和磷酸基中的至少一种，更可选地包括磺酸基、硼酸基和磷酸基中的至少一种；
    可选地，所述改性纳米纤维素包括羟基和改性基团，且所述改性基团与所述羟基的摩尔比为1:4至4:1，更可选为2:3至7:3。
  12. 根据权利要求1-11任一项所述的隔离膜，其中，构成所述三维骨架结构的材料包括磺酸基，且构成所述三维骨架结构的材料中的硫元素的含量为≥0.1wt％，可选为0.2wt％至0.5wt％，基于所述构成所述三维骨架结构的材料的总重量计。
  13. 根据权利要求1-12任一项所述的隔离膜，其中，所述涂层还包括第二填料，所述第二填料中的至少一部分嵌入所述涂层中，所述第一填料的平均粒径记为d 1，所述第二填料的平均粒径记为d 2，则d 2/d 1＞1。
  14. 根据权利要求13所述的隔离膜，其中，
    所述第一填料包括一次颗粒和二次颗粒中的至少一种，所述一次颗粒形貌的第一填料的平均粒径记为d 11，所述二次颗粒形貌的第一填料的平均粒径记为d 12，
    3.0≤d 2/d 11≤10.0，可选地，3.5≤d 2/d 11≤8.0；和/或，
    1.2≤d 2/d 12≤6.0，可选地，2.0≤d 2/d 12≤5.5。
  15. 根据权利要求13或14所述的隔离膜，其中，所述第二填料满足如下条件(1)至(7)中的至少一者：
    (1)所述第二填料具有一次颗粒形貌；
    (2)所述第二填料的平均粒径为120nm至350nm，可选为150nm至300nm；
    (3)所述第二填料的BET比表面积为≤20m 2/g，可选为6m 2/g至15m 2/g；
    (4)所述第二填料包括无机颗粒和有机颗粒中的至少一种；
    (5)所述第二填料包括一次颗粒形貌的无机颗粒，且所述一次颗粒形貌的无机颗粒的晶型包括α晶型和γ晶型中的至少一种，可选包括α晶型；
    (6)所述第二填料包括一次颗粒形貌的无机颗粒，且所述一次颗粒形貌的无机颗粒的晶型包括α晶型，且α晶型的含量为≥70wt％，可选为85wt％至100wt％，基于所述第二填料中的所述一次颗粒形貌的无机颗粒的总重量计；
    (7)所述第二填料的含量为≤30wt％，可选为5wt％至25wt％，基于所述涂层的总重量计。
  16. 根据权利要求1-15任一项所述的隔离膜，其中，所述涂层还包括非颗粒状的粘结剂；
    可选地，所述非颗粒状的粘结剂包括水溶液型粘结剂；
    可选地，所述涂层中的所述非颗粒状的粘结剂的含量为≤2wt％，基于所述涂层的总重量计。
  17. 根据权利要求1-16任一项所述的隔离膜，其中，
    所述多孔基材的厚度为≤6μm，可选为3μm至5μm；和/或，
    所述涂层的厚度为≤2μm，可选为0.5μm至1.5μm。
  18. 根据权利要求1-17任一项所述的隔离膜，其中，所述隔离膜还包括粘接层，所述粘接层设置在所述涂层的至少一部分表面上，所述粘接层包括颗粒状的粘结剂；
    可选地，所述颗粒状的粘结剂包括丙烯酸酯类单体均聚物或共聚物、丙烯酸类单体均聚物或共聚物、含氟烯烃单体均聚物或共聚物中的至少一种。
  19. 根据权利要求1-18任一项所述的隔离膜，其中，所述隔离膜满足如下条件(1)至(8)中的至少一者：
    (1)所述隔离膜在150℃、1h下的纵向热收缩率为≤6％，可选为0.5％至4％；
    (2)所述隔离膜在150℃、1h下的横向热收缩率为≤6％，可选为0.5％至4％；
    (3)所述隔离膜的纵向拉伸强度为≥2000kg/cm 2，可选为2500kg/cm 2至4500kg/cm 2；
    (4)所述隔离膜的横向拉伸强度为≥2000kg/cm 2，可选为2500kg/cm 2至4500kg/cm 2；
    (5)所述隔离膜的润湿长度为≥30mm，可选为30mm至80mm；
    (6)所述隔离膜的润湿速度为≥3mm/s，可选为3mm/s至10mm/s；
    (7)所述隔离膜的透气度为≤300s/100mL，可选为100s/100mL至230s/100mL；
    (8)所述隔离膜的耐电压击穿强度为≥1KV。
  20. 一种制备权利要求1-19任一项所述的隔离膜的方法，包括以下步骤：提供多孔基材；将用于构成三维骨架结构的材料和第一填料按照预定比例在溶剂中混合，配制成涂层浆料；将所述涂层浆料涂布于所述多孔基材的至少一个表面上，干燥后获得隔离膜，其中，所述隔离膜包括多孔基材和设置在所述多孔基材的至少一个表面上的涂层，所述 涂层包括三维骨架结构和第一填料，所述第一填料中的至少一部分填充在所述三维骨架结构中，且所述第一填料的平均粒径小于等于200nm。
  21. 根据权利要求20所述的方法，其中，所述涂层浆料还包括第二填料，所述第一填料的平均粒径记为d 1，所述第二填料的平均粒径记为d 2，则d 2/d 1＞1。
  22. 一种二次电池，其包括权利要求1-19任一项所述的隔离膜或通过权利要求20-21任一项所述的方法制备的隔离膜。
  23. 一种用电装置，其包括权利要求22所述的二次电池。
PCT/CN2022/136684 2022-08-15 2022-12-05 隔离膜、其制备方法及其相关的二次电池和用电装置 Ceased WO2024036820A1 (zh)

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