WO2024119332A1 - 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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WO2024119332A1
WO2024119332A1 PCT/CN2022/136685 CN2022136685W WO2024119332A1 WO 2024119332 A1 WO2024119332 A1 WO 2024119332A1 CN 2022136685 W CN2022136685 W CN 2022136685W WO 2024119332 A1 WO2024119332 A1 WO 2024119332A1
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Prior art keywords
optionally
coating
filler
particles
porous substrate
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PCT/CN2022/136685
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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 to CN202411272926.6A priority Critical patent/CN119324293A/zh
Priority to CN202411273496.XA priority patent/CN119324295A/zh
Priority to CN202411273358.1A priority patent/CN119330381B/zh
Priority to JP2025508458A priority patent/JP2025526848A/ja
Priority to EP22967495.7A priority patent/EP4525180A4/en
Priority to PCT/CN2022/136685 priority patent/WO2024119332A1/zh
Priority to CN202411272975.XA priority patent/CN119324294A/zh
Priority to CN202280018074.0A priority patent/CN116897462B/zh
Priority to KR1020257004831A priority patent/KR20250036237A/ko
Application filed by Contemporary Amperex Technology Co Ltd filed Critical Contemporary Amperex Technology Co Ltd
Publication of WO2024119332A1 publication Critical patent/WO2024119332A1/zh
Priority to US18/977,759 priority patent/US20250112333A1/en
Anticipated expiration legal-status Critical
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    • Y02E60/10—Energy storage using batteries

Definitions

  • secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.
  • energy storage power systems such as hydropower, thermal power, wind power and solar power stations
  • power tools electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.
  • thermal safety issues have received more and more attention.
  • the current methods for improving 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 have both high energy density, high thermal safety performance, and good cycle performance and kinetic performance is the key challenge in the design of secondary batteries.
  • any embodiment of the present application 0.0002 ⁇ m 2 ⁇ S 1 ⁇ 0.0080 ⁇ m 2 , optionally, 0.0004 ⁇ m 2 ⁇ S 1 ⁇ 0.0050 ⁇ m 2 .
  • the heat resistance of the separator can be improved on the one hand, and the active ion transmission will not be hindered on the other hand, thereby enabling the secondary battery to better balance high energy density, high thermal safety performance, and good cycle performance and kinetic performance.
  • any embodiment of the present application optionally, 0.50g/m 2 ⁇ 1 ⁇ 1.50g/m 2 , more optionally, 0.75g/m 2 ⁇ 1 ⁇ 1.40g/m 2 .
  • the surface density ⁇ 1 of the coating is within the above range, it is beneficial for the secondary battery to have both high energy density and high thermal safety performance, and can also make the coating have a suitable average pore area, and can further improve the heat resistance and ion conductivity of the separator.
  • the porosity P 2 of the porous substrate is within the above range, it is beneficial to improve the ion conductivity of the separator and the capacity performance characteristics of the secondary battery.
  • the BET specific surface area of the first filler is ⁇ 15m 2 /g, and can be optionally 18m 2 /g to 65m 2 /g.
  • the coating can have a suitable average pore area, and the heat resistance and ion conductivity of the isolation membrane can be further improved; in addition, the affinity between the first filler and the three-dimensional skeleton structure can be improved, so that the coating has a more stable spatial network structure, and the isolation membrane has better heat resistance and higher ion conductivity.
  • the content of the second filler is ⁇ 20wt%, and can be optionally 2wt% to 15wt%, based on the total weight of the coating.
  • the coating can have a suitable average pore area, and the heat resistance and ion conductivity of the isolation membrane can be further improved; in addition, 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, which is beneficial to ion transmission, and at the same time, the heat resistance of the isolation membrane can be improved.
  • the ion conductivity of the separator is ⁇ 0.6 ms/cm 2 , and may be ⁇ 0.9 ms/cm 2 .
  • the separator of the present application has high ion conductivity, thereby improving the cycle performance and/or kinetic performance of the secondary battery.
  • the transverse tensile strength of the separator is ⁇ 2000 kg/cm 2 , and can be optionally 2500 kg/cm 2 to 4500 kg/cm 2 .
  • the separator of the present application has high tensile strength in both the transverse and longitudinal directions, so that when the secondary battery expands, the probability of the separator being damaged is low, thereby improving the safety performance of the secondary battery.
  • the method further comprises the following steps: applying a slurry containing a granular binder on at least a portion of the surface of the coating layer, and forming an adhesive layer after drying.
  • range disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range.
  • the range defined in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and 80-110 is listed for a specific parameter, it is understood that the range of 60-110 and 80-120 is also expected.
  • the “include” and “comprising” mentioned in this application represent open-ended or closed-ended expressions.
  • the “include” and “comprising” may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.
  • the term "or” is inclusive.
  • the phrase “A or B” means “A, B, or both A and B”. More specifically, any of the following conditions satisfies the condition "A or B”: 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).
  • the isolation membranes currently used in commercial secondary batteries are usually polyolefin porous membranes, such as polyethylene porous membranes, polypropylene porous membranes or polypropylene/polyethylene/polypropylene three-layer composite membranes, with a melting point between 130°C and 160°C. Therefore, when its thickness is reduced, the heat resistance of the isolation membrane becomes worse, and a significant thermal shrinkage effect will occur when heated, causing the positive and negative electrodes inside the battery to directly contact, resulting in an internal short circuit, thereby increasing the safety risk of secondary batteries.
  • the current measures mainly include coating a heat-resistant inorganic ceramic layer on the polyolefin porous membrane, which can increase the mechanical strength of the separator, reduce the shrinkage of the separator when heated, and reduce the risk of short circuit between the positive and negative electrodes inside the battery.
  • the inorganic ceramic layer has limited effect on improving the heat resistance of the separator, and in order to ensure that the separator has high heat resistance, it is necessary to increase the coating thickness of the inorganic ceramic layer, but this will extend the active ion transmission distance, affect the cycle performance and kinetic performance of the secondary battery, and also fail to balance the energy density of the secondary battery.
  • the average pore area S1 of the coating is smaller than the average pore area S2 of the porous substrate, thereby making the coating have high heat resistance; since the coating of the present application has high heat resistance, the thickness of the coating can be reduced (for example, the thickness of the coating can be less than or equal to 2 ⁇ m), shortening the active ion transmission distance, and thus the secondary battery can also take into account high energy density and good cycle performance and kinetic performance; in addition, since the coating of the present application has high heat resistance, a thinner porous substrate can be selected, thereby further improving the energy density of the secondary battery.
  • the average pore area S2 of the porous substrate satisfies 0.0005 ⁇ m2 ⁇ S2 ⁇ 0.0100 ⁇ m2 , and optionally, 0.0008 ⁇ m2 ⁇ S2 ⁇ 0.0080 ⁇ m2 .
  • the average pore area S2 of the porous substrate is within the above range, it is beneficial to improve the ion conductivity of the separator and the capacity performance characteristics of the secondary battery.
  • the image processing detection system can be used to obtain the pore area data of the coating of the isolation membrane and the porous substrate, and then the Mintab software can be used to obtain the pore area distribution diagram and the average pore area of the coating of the isolation membrane and the porous substrate.
  • the ratio of the total pore area of the coating of the isolation membrane to the number of pores in the coating is the average pore area S 1 of the coating of the isolation membrane
  • the ratio of the total pore area of the porous substrate of the isolation membrane to the number of pores in the porous substrate is the average pore area S 2 of the porous substrate of the isolation membrane.
  • the average pore size d1 of the isolation membrane satisfies 15nm ⁇ d1 ⁇ 50nm , and optionally, 20nm ⁇ d2 ⁇ 40nm .
  • the heat resistance of the isolation membrane can be improved, and on the other hand, the active ion transmission will not be hindered, thereby enabling the secondary battery to better balance high energy density, high thermal safety performance, and good cycle performance and kinetic performance.
  • the average pore size d2 of the porous substrate satisfies 25nm ⁇ d2 ⁇ 60nm , optionally, 30nm ⁇ d2 ⁇ 50nm .
  • the average pore size d2 of the porous substrate is within the above range, it is beneficial to improve the ion conductivity of the separator and the capacity performance characteristics of the secondary battery.
  • the porosity P1 of the separator satisfies 20% ⁇ P1 ⁇ 60 %, optionally, 25% ⁇ P1 ⁇ 45 %.
  • the porosity P1 of the separator is within the above range, it is beneficial for the secondary battery to have both high thermal safety performance and good cycle performance and kinetic performance.
  • the porosity P2 of the porous substrate satisfies 15% ⁇ P2 ⁇ 45 %, and optionally, 20% ⁇ P2 ⁇ 40 %.
  • the porosity P2 of the porous substrate is within the above range, it is beneficial to improve the ion conductivity of the separator and the capacity performance characteristics of the secondary battery.
  • the porosity P 1 of the isolation membrane and the porosity P 2 of the porous substrate can be tested with reference to GB/T 24586-2009.
  • the test instrument can be the AccuPyc II 1340 fully automatic true density tester of Micromeritics Company of the United States.
  • the thickness of the porous substrate is ⁇ 8 ⁇ m, and can be 3 ⁇ m to 6 ⁇ m.
  • the coating of the present application can significantly improve the heat resistance of the separator, thereby allowing a thinner porous substrate to be used, thereby helping to improve the energy density of the secondary battery.
  • the filler includes a first filler, and the average particle size of the first filler is ⁇ 150 nm, and can be optionally 15 nm to 150 nm, or 15 nm to 120 nm.
  • the first filler has the advantages of a small average particle size, a large specific surface area, and good affinity with the three-dimensional skeleton structure, so that it can be better overlapped with the three-dimensional skeleton structure, so that the coating has a more stable spatial network structure, thereby increasing the ion conductivity of the isolation membrane, and improving the heat resistance of the isolation membrane and the infiltration and retention characteristics of the electrolyte, and thus the secondary battery using the isolation membrane of the present application can take into account high thermal safety performance, long service life, and good cycle performance and kinetic performance.
  • the average particle size of the first filler is within the above range, it can also make the coating have a suitable average pore area, and can further improve the heat resistance and ion conductivity of the isolation membrane.
  • the average particle size of the first filler in the primary particle morphology is 15 nm to 80 nm, optionally 20 nm to 80 nm, 30 nm to 75 nm.
  • the average particle size of the first filler in the secondary particle morphology is 50nm to 150nm, optionally 50nm to 135nm, 50nm to 120nm, 55nm to 150nm, 55nm to 135nm, 55nm to 120nm.
  • 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 their surface usually has hydroxyl groups, which makes it easy to build a stable spatial network structure with materials (such as nanocellulose, etc.) constituting a three-dimensional skeleton structure.
  • Organic particles have good thermal stability and are not easy to decompose.
  • the organic particles can also melt and be sucked into the micropores of the porous substrate due to capillary action to play a role of closed holes and circuit breakers, which is beneficial to improve the safety performance of the secondary battery.
  • the inorganic particles include at least one of boehmite ( ⁇ -AlOOH), aluminum oxide (Al 2 O 3 ), barium sulfate (BaSO 4 ), magnesium oxide (MgO), magnesium hydroxide (Mg(OH) 2 ), silicon oxide SiO x (0 ⁇ x ⁇ 2), tin dioxide (SnO 2 ), titanium oxide (TiO 2 ), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO 2 ), yttrium oxide (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 ).
  • boehmite ⁇ -AlOOH
  • Al 2 O 3 aluminum oxide
  • BaSO 4 barium sulfate
  • MgO magnesium oxide
  • the inorganic particles include at least one of boehmite ( ⁇ -AlOOH), aluminum oxide ( Al2O3 ), barium sulfate ( BaSO4 ), magnesium oxide (MgO), silicon oxide SiOx (0 ⁇ x ⁇ 2), titanium oxide ( TiO2 ), zinc oxide (ZnO), cerium oxide ( CeO2 ) and barium titanate ( BaTiO3 ).
  • the organic particles include at least one of polystyrene particles, polyacrylic wax particles, melamine formaldehyde resin particles, phenolic resin particles, polyester particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles and polyaryletherketone particles.
  • the first filler includes inorganic particles
  • the crystal form of the inorganic particles includes at least one of the ⁇ crystal form, the ⁇ crystal form, and the ⁇ crystal form.
  • the crystal form of the inorganic particles includes at least one of the ⁇ crystal form and the ⁇ crystal form.
  • the inorganic particles of the ⁇ crystal form have diffraction peaks at 2 ⁇ of 36.68° ⁇ 0.2° and 31.21° ⁇ 0.2° in an X-ray diffraction spectrum measured by using an X-ray diffractometer.
  • the content of the inorganic particles of the ⁇ crystal form in the first filler may be ⁇ 50wt%, optionally 60wt% to 82wt%, based on the total weight of the inorganic particles in the first filler.
  • the ⁇ -crystalline inorganic particles have diffraction peaks at 2 ⁇ of 66.95° ⁇ 0.2° and 45.91° ⁇ 0.2° in an X-ray diffraction spectrum measured by using an X-ray diffractometer.
  • the content of the ⁇ -crystalline inorganic particles in the first filler may be ⁇ 10wt%, optionally 17wt% to 38wt%, based on the total weight of the inorganic particles in the first filler.
  • the ⁇ -crystal inorganic particles have diffraction peaks at 2 ⁇ of 31.89° ⁇ 0.2° and 19.37° ⁇ 0.2° in an X-ray diffraction spectrum measured by using an X-ray diffractometer.
  • the content of the ⁇ -crystal inorganic particles in the first filler may be ⁇ 5wt%, optionally ⁇ 1.5wt%, and more optionally ⁇ 1wt%, based on the total weight of the inorganic particles in the first filler.
  • the inorganic particles of the ⁇ crystal form have a moderate specific surface area and hardness, thereby being able to better improve both the heat resistance and ion conductivity of the isolation membrane; the inorganic particles of the ⁇ crystal form and the ⁇ crystal form have the advantage of a large specific surface area.
  • Selecting first fillers of different crystal types helps to improve at least one of the heat resistance, ion conductivity, and electrolyte wetting and retention properties of the separator.
  • the first filler may include inorganic particles, and the crystal forms of the inorganic particles include ⁇ crystal form, ⁇ crystal form and ⁇ crystal form, and the content of the ⁇ crystal form inorganic particles in the first filler may be 60wt% to 82wt%, the content of the ⁇ crystal form inorganic particles may be 17wt% to 38wt%, and the content of the ⁇ crystal form inorganic particles may be ⁇ 1.5wt%, all based on the total weight of the inorganic particles in the first filler.
  • the X-ray diffraction spectrum of inorganic particles can be obtained by testing as follows: After drying the inorganic particles, grind them in a mortar (such as an agate mortar) for 30 minutes, and then use an X-ray diffractometer (such as Miniflex600-C) to test and obtain the X-ray diffraction spectrum.
  • the test can use a Cu target, a Ni filter, a tube voltage of 40KV, a tube current of 15mA, and a continuous scanning range of 5°-80°.
  • the first filler may include inorganic particles
  • the inorganic particles can be prepared as follows: a precursor solution of the inorganic particles is subjected to an oxidation reaction by high-pressure sputtering, and then heated at 600°C to 900°C (for example, 1 hour to 3 hours) to form inorganic particles with a primary particle morphology, and then dried and shaped at 150°C to 250°C (for example, 30 minutes to 60 minutes) to obtain inorganic particles with a secondary particle morphology after self-assembly of the primary particles.
  • the content of the first filler is ⁇ 55wt%, and can be 60wt% to 90wt%, based on the total weight of the coating.
  • the coating can have a suitable average pore area, and can further improve the heat resistance and ion conductivity of the isolation membrane; in addition, it is also beneficial for the coating to have a more stable spatial network structure, thereby further improving the heat resistance and ion conductivity of the isolation membrane.
  • the filler includes a first filler and a second filler, and an average particle size of the second filler is greater than an average particle size of the first filler.
  • the second filler has a larger 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 membrane; the second filler has a larger particle size, which helps to make the coating have more pore structure and less water content when the amount used is small, thereby further improving the ion conductivity of the isolation membrane and the wetting and retention characteristics of the electrolyte.
  • the average particle size of the second filler is less than or equal to 400nm, and can be optionally 100nm to 300nm.
  • the coating can have a suitable average pore area, and the heat resistance and ion conductivity of the isolation membrane can be further improved; in addition, 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, which is beneficial to ion transmission and can also improve the heat resistance of the isolation membrane.
  • the BET specific surface area of the second filler is ⁇ 15m 2 /g, and can be 7m 2 /g to 12m 2 /g.
  • the coating can have a suitable average pore area, and the heat resistance and ion conductivity of the isolation membrane can be further improved; in addition, 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, which is beneficial to ion transmission and can also improve the heat resistance of the isolation membrane.
  • 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 5 or more, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of electrochemical reactions.
  • the inorganic particles having a dielectric constant of 5 or more include at least one of 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, lithium magnesium silicate, sodium magnesium silicate, bentonite , hectorite, zirconium titanate, barium titanate, Pb(Zr,Ti) O3 (abbreviated as PZT), Pb1 - mLamZr1 - nTinO3 (abbreviated as PLZT, 0 ⁇ m ⁇ 1, 0 ⁇ n ⁇ 1), Pb
  • the modification method of each inorganic particle can be chemical modification and/or physical modification.
  • the chemical modification method includes coupling agent modification (for example, using silane coupling agent, titanate coupling agent, etc.), surfactant modification, polymer grafting modification, etc.
  • the physical modification method can be mechanical force dispersion, ultrasonic dispersion, high energy treatment, etc.
  • the modification treatment can reduce the agglomeration of inorganic particles, thereby enabling the coating to have a more stable and uniform spatial network structure; in addition, by selecting a coupling agent, surfactant or polymer with a specific functional group to modify the inorganic particles, it is also helpful to improve the coating's wetting and retention characteristics for the electrolyte and improve the coating's adhesion to the porous substrate.
  • the inorganic particles having ion conductivity but not storing ions include Li3PO4 , lithium titanium phosphate Lix1Tiy1 ( PO4 ) 3 , lithium aluminum titanium phosphate Lix2Aly2Tiz1 ( PO4 ) 3 , (LiAlTiP) x3Oy3 type glass , lithium lanthanum titanate Lix4Lay4TiO3 , lithium germanium thiophosphate Lix5Gey5Pz2Sw , lithium nitride Lix6Ny6 , SiS2 type glass Lix7Siy7Sz3 and P2S5 type glass Lix8Py8S At least one of z4 , 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,
  • the inorganic particles capable of undergoing electrochemical reaction 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 at least one of polyethylene particles, polypropylene particles, cellulose, cellulose modifiers (e.g., carboxymethyl cellulose), melamine resin particles, phenolic resin particles, polyester particles (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), silicone resin particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, polyaryletherketone particles, and copolymers of butyl acrylate and ethyl methacrylate (e.g., cross-linked polymers of butyl acrylate and ethyl methacrylate).
  • polyethylene particles polypropylene particles
  • cellulose modifiers e.g., carboxymethyl cellulose
  • melamine resin particles e.g., carboxymethyl cellulose
  • phenolic resin particles e
  • the second filler has a primary particle morphology.
  • the second filler includes inorganic particles in the form of primary particles, and the crystal form of the inorganic particles in the form of primary particles includes at least one of ⁇ crystal form and ⁇ crystal form, and optionally includes ⁇ crystal form.
  • the ⁇ crystal form of the second filler has the advantages of high hardness, good heat resistance, low dielectric constant, high safety and high true density, thereby further improving 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 inorganic particles with an ⁇ -crystal form is ⁇ 80wt%, optionally 85wt% to 100wt%, 90wt% to 100wt%, 95wt% to 100wt%, based on the total weight of the inorganic particles with a primary particle morphology in the second filler.
  • the ⁇ -crystal inorganic particles have diffraction peaks at 2 ⁇ of 57.48° ⁇ 0.2° and 43.34° ⁇ 0.2° in an X-ray diffraction spectrum measured by using an X-ray diffractometer.
  • the content of the second filler is ⁇ 20wt%, and can be 2wt% to 15wt%, based on the total weight of the coating.
  • the coating can have a suitable average pore area, and the heat resistance and ion conductivity of the isolation membrane can be further improved; in addition, 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, which is beneficial to ion transmission, and can also improve the heat resistance of the isolation membrane.
  • the three-dimensional skeleton structure may be formed by a fibrous object, and the morphology of the fibrous object may optionally include at least one of a rod, a tube (e.g., a hollow tube), a rod, and a fiber.
  • the material of the appropriate shape is conducive to the three-dimensional skeleton structure and the filler forming a stable spatial network structure, thereby further improving the heat resistance and ion conductivity of the isolation membrane.
  • "fibrous object” refers to a material with an aspect ratio of 5 or more.
  • the average diameter of the material constituting the three-dimensional skeleton structure is ⁇ 40nm, and can be optionally 10nm to 35nm.
  • the average diameter of the material constituting the three-dimensional skeleton structure is within the above range, it is helpful for the material constituting the three-dimensional skeleton structure to overlap with the filler to form an integrated effect. And it can effectively avoid the following situation: when the average diameter of the material constituting the three-dimensional skeleton structure is too large, the mutual entanglement effect of the three-dimensional skeleton structure formed by it is insufficient, which may cause the heat resistance and voltage breakdown resistance characteristics of the isolation membrane to be not excellent enough.
  • the average length of the material constituting the three-dimensional skeleton structure is 100nm to 800nm, and can be optionally 200nm to 600nm.
  • the heat resistance and ion conductivity of the isolation membrane can be further improved.
  • the aspect ratio of the material constituting the three-dimensional skeleton structure is 5 to 60, and can be optionally 10 to 30.
  • the heat resistance and ion conductivity of the isolation membrane can be further improved.
  • the following situations can be effectively avoided: when the aspect ratio of the material constituting the three-dimensional skeleton structure is too small, its overlap effect with the filler is poor, the heat resistance of the coating deteriorates, and during the coating drying process, the three-dimensional skeleton structure is prone to collapse due to the lack of support from the filler, and then it is easy to cause pore blocking problems, hindering ion transmission and water discharge, which may affect the thermal safety performance, cycle performance and dynamic performance of the secondary battery; when the aspect ratio of the material constituting the three-dimensional skeleton structure is too large, this may cause the ion conductivity of the isolation membrane to become smaller, and then the cycle performance and/or dynamic performance of the secondary battery to deteriorate.
  • the average length and average diameter of the material constituting the three-dimensional skeleton structure can be determined by the following method: a 3.6 mm ⁇ 3.6 mm sample is cut out from any area of the isolation membrane, and the microscopic morphology of the coating in the sample is measured using a scanning electron microscope (e.g., ZEISS Sigma 300), and a high vacuum mode is selected with an operating voltage of 3 kV and a magnification of 30,000 times to obtain a SEM image; based on the obtained SEM image, multiple (e.g., more than 5) test areas are selected for length statistics, each test area having a size of 0.5 ⁇ m ⁇ 0.5 ⁇ m, and then the average value of the lengths obtained from each test area is taken as the average length of the material constituting the three-dimensional skeleton structure; based on the obtained SEM image, multiple (e.g., more than 5) test areas are selected for diameter statistics using Nano Measurer particle size distribution statistical software, each test area having a size of 0.5 ⁇ m
  • the material constituting the three-dimensional skeleton structure includes at least one of an organic material and an inorganic material.
  • the material constituting the three-dimensional skeleton structure as long as it has electrical insulation, electrochemical stability and stability to the electrolyte, there is no particular restriction on the material, and it can be either an organic material or an inorganic material.
  • the organic material comprises at least one of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers.
  • the inorganic material comprises at least one of halloysite nanotubes, nanorod-shaped aluminum oxide, nanorod-shaped boehmite, nanorod-shaped silicon oxide, and glass fiber.
  • the material constituting the three-dimensional skeleton structure includes nanocellulose.
  • the nanocellulose includes at least one of cellulose nanofibers (Cellulose nanofibrils, CNF, also known as nanofibrillated cellulose or microfibrillated cellulose), cellulose nano whiskers (Cellulose nanocrystals, CNC, also known as cellulose nanocrystals, nanocrystalline cellulose) and bacterial nanocellulose (Bacterial nanocellulose, BNC, also known as bacterial cellulose or microbial cellulose).
  • the nanocellulose includes cellulose nano whiskers, which have the advantage of high crystallinity, thereby better improving the heat resistance of the isolation membrane.
  • Nanocellulose refers to the general term for cellulose with any dimension at the nanometer level (e.g., within 100nm), which has both the characteristics of cellulose and the characteristics of nanoparticles.
  • Nanocellulose can be a polymer nanomaterial extracted from wood, cotton, etc. in nature by one or more means of chemistry, physics, biology, etc. It has the advantages of wide sources, low cost, biodegradability, high modulus, and high specific surface area. Therefore, it is an excellent substitute for traditional petrochemical resources and can effectively alleviate environmental pollution and petrochemical resource shortages.
  • Nanocellulose also has good high temperature resistance and a small volume change after heating, thereby improving the heat resistance of the isolation membrane; at the same time, compared with traditional inorganic ceramic particles, the density of nanocellulose is small, thereby reducing the weight of the secondary battery and improving 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 membrane to take into account good electrolyte infiltration and retention characteristics and good voltage breakdown resistance.
  • the nanocellulose includes hydroxyl groups and anionic modifying groups.
  • the anion modifying group optionally includes at least one of an amine group, a carboxyl group, a sulfonic acid group, a boric acid group and a phosphate group, and more optionally includes at least one of a sulfonic acid group, a boric acid group and a phosphate group.
  • nanocellulose has the above-mentioned specific anionic modified groups
  • it can effectively improve the heat resistance of the separator and the thermal safety performance of the secondary battery; on the other hand, it can also improve the bonding strength between the coating and the porous substrate.
  • nanocellulose has the above-mentioned specific anionic modified groups
  • the presence of anionic 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, thereby also improving the production efficiency of the separator and the uniformity of the coating.
  • the molar ratio of the anion-modified group to the hydroxyl group is 1:4 to 4:1, and can be optionally 2:3 to 7:3.
  • the molar ratio of the anion-modified group to the hydroxyl group is within a suitable range, the heat resistance, ion conductivity, and electrolyte wetting and retention characteristics of the isolation membrane can be further improved.
  • the following situations can be effectively avoided: when the molar ratio of the anion-modified group to the hydroxyl group is too small, the further improvement effect of the anion-modified group on the heat resistance and ion conductivity of the isolation membrane may not be obvious; when the molar ratio of the anion-modified group to the hydroxyl group is too large, the isolation membrane may have poor wetting and retention characteristics for the electrolyte, which may affect the cycle performance and/or kinetic performance of the secondary battery, and may also cause the heat resistance of the isolation membrane to decrease, which may also affect the improvement effect of the thermal safety performance of the secondary battery.
  • the type of anionic modified groups in nanocellulose can be determined by infrared spectroscopy.
  • the infrared spectrum of the material can be tested to determine the characteristic peaks contained therein, thereby determining the type of anionic modified groups.
  • the material can be analyzed by infrared spectroscopy using instruments and methods known in the art, such as an infrared spectrometer (such as the IS10 Fourier transform infrared spectrometer of Nicolet Corporation, USA), and tested in accordance with GB/T 6040-2019 General Rules for Infrared Spectroscopic Analysis.
  • the material constituting the three-dimensional skeleton structure includes sulfonic acid groups, 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 material constituting the three-dimensional skeleton structure.
  • the sulfur content in the material constituting the three-dimensional skeleton structure can be tested as follows: the material constituting the three-dimensional skeleton structure is dried, ground in a mortar (such as an agate mortar) for 30 minutes, and then tested using an X-ray diffractometer (such as Miniflex600-C) to obtain the sulfur content. During the test, a Cu target material, a Ni filter, a tube voltage of 40KV, a tube current of 15mA, and a continuous scanning range of 5°-80° can be used.
  • the content of the three-dimensional skeleton structure is ⁇ 40wt%, optionally 5wt% to 25wt%, based on the total weight of the coating.
  • the coating can have a suitable average pore area, and can further improve the heat resistance and ion conductivity of the isolation membrane.
  • the coating also includes a non-granular binder.
  • a 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 binder may include at least one of an aqueous solution type acrylic resin (e.g., a homopolymer of acrylic acid, methacrylic acid, sodium acrylate monomers or a copolymer with other comonomers), polyvinyl alcohol (PVA), isobutylene-maleic anhydride copolymer, and polyacrylamide.
  • an aqueous solution type acrylic resin e.g., a homopolymer of acrylic acid, methacrylic acid, sodium acrylate monomers or a copolymer with other comonomers
  • PVA polyvinyl alcohol
  • isobutylene-maleic anhydride copolymer e.g., 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 fillers in the coating can form a stable spatial network structure, thereby enabling the isolation film to maintain high adhesion while reducing the amount of binder used.
  • the isolation film further comprises an adhesive layer, the adhesive layer is disposed on at least a portion of the surface of the coating, and the adhesive layer comprises a granular binder.
  • the adhesive layer can not only prevent the coating from falling 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 an acrylate monomer homopolymer or copolymer, an acrylic acid monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer.
  • the comonomer includes but is not limited to at least one of the following: an acrylate monomer, an acrylic acid monomer, an olefin monomer, a halogen-containing olefin monomer, a fluoroether monomer, etc.
  • the granular 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 a comonomer.
  • the comonomer may be at least one of an olefin monomer, a fluorine-containing olefin monomer, a chlorine-containing olefin monomer, an acrylate monomer, an acrylic monomer, and a fluoroether monomer.
  • the comonomer may include at least one of trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro (alkyl vinyl) ether (e.g., 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 hexafluoropropylene
  • perfluoro (alkyl vinyl) ether e.g., perfluoro (methyl vinyl) ether PMVE, perfluor
  • the longitudinal heat shrinkage rate of the isolation film at 150° C. for 1 hour is ⁇ 6%, and can be optionally 0.5% to 4%.
  • the transverse heat shrinkage rate of the isolation film at 150° C. for 1 hour is ⁇ 6%, and can be optionally 0.5% to 4%.
  • the separator of the present application has low thermal shrinkage in both the transverse and longitudinal directions at a high temperature of 150° C., thereby improving the safety performance of the secondary battery.
  • the ion conductivity of the isolation membrane is ⁇ 0.6 ms/cm 2 , and may be ⁇ 0.9 ms/cm 2 .
  • the separator of the present application has high ion conductivity, thereby being able to improve the cycle performance and/or kinetic performance of the secondary battery.
  • the resistance value of the isolation film is ⁇ 1.3 ⁇ , and can be ⁇ 1.0 ⁇ .
  • the separator of the present application has a low resistance value, thereby being able to improve the cycle performance and/or kinetic performance of the secondary battery.
  • the longitudinal tensile strength of the isolation film is ⁇ 2000 kg/cm 2 , and can be optionally 2500 kg/cm 2 to 4500 kg/cm 2 .
  • the transverse tensile strength of the isolation film is ⁇ 2000 kg/cm 2 , and can be optionally 2500 kg/cm 2 to 4500 kg/cm 2 .
  • the separator of the present application has high tensile strength in both the transverse and longitudinal directions, so that when the secondary battery expands, the probability of the separator being damaged is low, thereby improving the safety performance of the secondary battery.
  • the wetted length of the isolation film is ⁇ 30 mm, and can be optionally 30 mm to 80 mm.
  • the wetting speed of the isolation film is ⁇ 3 mm/s, and can be optionally 3 mm/s to 10 mm/s.
  • the separator of the present application has good wettability and retention properties for the electrolyte, thereby improving the ion conductivity of the separator and the capacity performance characteristics of the secondary battery.
  • the air permeability of the isolation membrane is ⁇ 300s/100mL, and can be optionally 100s/100mL to 230s/100mL.
  • the separator of the present application has good air permeability, thereby being able to improve ion conductivity and secondary battery capacity performance characteristics.
  • the average particle size of a material has a well-known meaning in the art and can be measured using instruments and methods known in the art.
  • a scanning electron microscope, a transmission electron microscope, or a particle size distribution instrument can be used to measure a material or a separator to obtain an image, and a plurality of (e.g., more than 10) test particles (e.g., having a first filler, a second filler) can be randomly selected from the image, and the average value of the shortest diagonal length of the particles can be 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. For example, it can be tested by nitrogen adsorption specific surface area analysis test method with reference to GB/T 19587-2017, and calculated by BET (Brunauer Emmett Teller) method. Alternatively, the nitrogen adsorption specific surface area analysis test can be performed by a Tri-Star 3020 specific surface area pore size analysis tester from Micromeritics, USA.
  • the heat shrinkage, tensile strength and air permeability of the isolation film have the meanings known in the art and can be measured by methods known in the art. For example, they can be tested with reference to the standard GB/T 36363-2018.
  • the wetting length and wetting speed of the isolation membrane have the meanings known in the art and can be measured by methods known in the art.
  • An exemplary test method is as follows: cut the isolation membrane into samples with a width of 5 mm and a length of 100 mm, fix the two ends of the sample and place it horizontally; take 0.5 mg of electrolyte and drop it in the center of the sample. After reaching the specified time (1 min in this application), take a picture and measure the length of the electrolyte diffusion, thereby obtaining the wetting length and wetting speed of the isolation membrane.
  • 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: ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a mass ratio of 30:50:20 to obtain an organic solvent, and fully dried LiPF 6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol/L.
  • the ion conductivity and resistance value of the isolation membrane can be obtained by AC impedance spectroscopy test. Specifically, the isolation membrane is cut into discs of a certain area, dried, placed between two stainless steel electrodes, and sealed to form a button battery after absorbing a sufficient amount of electrolyte, and then the AC impedance spectroscopy test is carried out.
  • the coating parameters (such as surface density, thickness, etc.) of the above-mentioned isolation membrane are the coating parameters of one side of the porous substrate.
  • the coating parameters on either side satisfy the requirements of this application and are considered to fall within the protection scope of this application.
  • a second aspect of the embodiment of the present application provides a method for preparing an isolation membrane according to the first aspect of the embodiment of the present application, comprising the following steps: providing a porous substrate; mixing the material constituting the three-dimensional skeleton structure and the filler in a solvent in a predetermined proportion, and then stirring them evenly at a certain shear rate to prepare a coating slurry; coating the coating slurry on at least one surface of the porous substrate, and obtaining an isolation membrane after drying, wherein the isolation membrane comprises a porous substrate and a coating arranged on at least one surface of the porous substrate, the coating comprising a three-dimensional skeleton structure and a filler, at least a portion of the filler is filled in the three-dimensional skeleton structure, and along the thickness direction of the isolation membrane, the average pore area of the coating is recorded as S1 , and the average pore area of the porous substrate is recorded as S2 , then 0 ⁇ S1 / S2 ⁇ 1.
  • the solvent used in preparing the coating slurry may be water, such as deionized water.
  • the coating slurry may further include other components, for example, a dispersant, a wetting agent, a binder, etc.
  • the shear rate is ⁇ 30 m/s, and can be 15 m/s to 30 m/s.
  • the dried coating can have a suitable average pore area, and the heat resistance and ion conductivity of the isolation membrane can be further improved.
  • the solid content of the coating slurry is 8% to 30%, and optionally 10% to 20%.
  • the coating surface density of the coating slurry on one side is 0.50 g/m 2 to 1.50 g/m 2 , and can be 0.75 g/m 2 to 1.40 g/m 2 .
  • the dried coating can have a suitable average pore area, and the heat resistance and ion conductivity of the separator can be further improved.
  • the coating thickness of the coating slurry on one side is ⁇ 2 ⁇ m, and can be 0.5 ⁇ m to 1.3 ⁇ m.
  • the dried coating can have a suitable average pore area, and can further improve the heat resistance and ion conductivity of the isolation membrane.
  • the material for constituting the three-dimensional skeleton structure may include at least one of an organic material and an inorganic material.
  • 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, which may be cellulose nano whiskers (Cellulose nanocrystals, CNC, also known as cellulose nanocrystals, nanocrystalline cellulose).
  • the nanocellulose can be obtained according to the following method: providing cellulose powder with a whiteness ⁇ 80%; mixing and reacting the obtained cellulose powder with a modified solution, washing and removing impurities to obtain cellulose nano whiskers; adjusting the pH of the obtained cellulose nano whiskers to neutral, and grinding and cutting to obtain nanocellulose.
  • the cellulose powder with a whiteness of ⁇ 80% can be purchased from the market, or obtained by chemical methods (such as acid hydrolysis, alkali treatment, Tempo catalytic oxidation), biological methods (such as enzyme treatment), mechanical methods (such as ultrafine grinding, ultrasonic crushing, high-pressure homogenization), etc.
  • the fiber raw material used to prepare the cellulose powder with a whiteness of ⁇ 80% can include plant fibers, such as cotton fibers (such as cotton fibers, kapok fibers), hemp fibers (such as sisal fibers, ramie fibers, jute fibers, flax fibers, hemp fibers, abaca fibers, etc.), palm fibers, wood fibers, bamboo fibers, and grass fibers.
  • the cellulose powder with a whiteness of ⁇ 80% can also be prepared by the following method: after the fiber raw material is loosened and deslagging, it is cooked with an alkali solution (for example, an aqueous solution of NaOH, whose concentration can be 4wt% to 20wt%, optionally 5wt% to 15wt%), and then sequentially washed with water to remove impurities (for example, the number of washings is 3 to 6 times), bleached (for example, sodium hypochlorite and/or hydrogen peroxide can be used), acid washed to remove impurities, washed with water to remove impurities, water driven, and air drying to obtain cellulose powder.
  • an alkali solution for example, an aqueous solution of NaOH, whose concentration can be 4wt% to 20wt%, optionally 5wt% to 15wt
  • an alkali solution for example, an aqueous solution of NaOH, whose concentration can be 4wt% to 20wt%, optionally
  • the modified solution may be an acid solution (eg, aqueous sulfuric acid solution, aqueous boric acid solution, aqueous phosphoric acid solution, aqueous acetic acid solution) or an alkaline solution (eg, urea organic solvent solution).
  • the modified solution is an acid solution.
  • the concentration of the acid solution may be 5wt% to 80wt%.
  • the concentration of the acid solution may be 40wt% to 80wt%, thereby obtaining a cellulose powder having a sulfonic acid group.
  • the concentration of the acid solution may be 5wt% to 10wt%, thereby obtaining a cellulose powder having a boric acid group.
  • the concentration of the acid solution may be 45wt% to 75wt%, thereby obtaining a cellulose powder having a phosphoric acid group.
  • the concentration of the acid solution may be 40wt% to 80wt%, thereby obtaining a cellulose powder having a carboxylic acid group.
  • the urea organic solvent solution is a urea xylene solution, thereby obtaining cellulose powder having amine groups.
  • the mass ratio of the cellulose powder to the modified solution may be 1:2.5 to 1:50, and may be 1:5 to 1:30.
  • the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30.
  • the mass ratio of the cellulose powder to the acid solution may be 1:20 to 1:50.
  • the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30.
  • the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30.
  • the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30.
  • the mass ratio of the cellulose powder to the acid solution may be 1:4 to 1:40.
  • the reaction when the modified solution is an acid solution, the reaction can be carried out at a temperature not higher than 80°C, optionally at 30°C to 60°C, and the reaction time of the cellulose 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 may be performed at 100° C. to 145° C., and the reaction time of the cellulose powder and the modified solution may be 1 h to 5 h.
  • grinding can be performed using a grinder, and cutting can be performed using a high-pressure homogenizer.
  • Nanocellulose with different average diameters and/or different average lengths can be obtained by adjusting the grinding parameters (e.g., grinding times, grinding time, etc.) of the grinder and the cutting parameters of the high-pressure homogenizer.
  • the coating slurry may be applied using a coater.
  • the present application has no particular restrictions on the type of coater, for example, a commercially available coater may be used.
  • the coater includes a gravure roller; the gravure roller is used to transfer the slurry to the porous substrate.
  • the coating slurry may be applied by transfer coating, spin spray coating, dip coating, etc.
  • the method further comprises the following steps: applying a slurry containing a granular binder on at least a portion of the surface of the coating layer, and forming an adhesive layer after drying.
  • the preparation method of the isolation film of the present application obtains the coating layer by one-time coating, which greatly simplifies the production process of the isolation film.
  • Some parameters such as raw materials and their contents used in the preparation method of the isolation membrane of the present application can refer to the isolation membrane of the first aspect of the implementation method of the present application, and will not be repeated here.
  • a third aspect of the embodiments 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 being discharged.
  • secondary batteries include electrode assemblies and electrolytes.
  • the electrode assemblies include positive electrode sheets, negative electrode sheets, and separators.
  • the separators are arranged between the positive electrode sheets and the negative electrode sheets, and mainly play the role of preventing the positive and negative electrodes from short-circuiting, while allowing active ions to pass through.
  • the present application has no particular limitation on the type of secondary battery.
  • 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 comprises the separator of the first aspect of the embodiment of the present application or the separator prepared by the method of the second aspect of the embodiment of the present application, and the separator is spaced between the positive electrode sheet and the negative electrode sheet.
  • the separator is spaced between the positive electrode sheet and the negative electrode sheet.
  • at least one side of the separator close to the negative electrode sheet has the coating of the present application.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material.
  • the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode active material may include but is not limited to at least one of a lithium-containing transition metal oxide, a lithium-containing phosphate and their respective modified compounds.
  • the lithium transition metal oxide may include but are not limited to at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and their respective modified compounds.
  • lithium-containing phosphate may include but are not limited to at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon and their respective modified compounds.
  • the positive electrode active material for the lithium ion battery may include at least one of a lithium transition metal oxide and a modified compound thereof of the general formula Li a Ni b Co c M d O e A f . 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 at least one of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from at least one of N, F, S and Cl.
  • a positive electrode active material for a lithium ion battery may include at least one of LiCoO2 , LiNiO2 , LiMnO2 , LiMn2O4 , LiNi1/ 3Co1 / 3Mn1 / 3O2 (NCM333 ) , LiNi0.5Co0.2Mn0.3O2 ( NCM523 ) , LiNi0.6Co0.2Mn0.2O2 ( NCM622 ) , LiNi0.8Co0.1Mn0.1O2 (NCM811), LiNi0.85Co0.15Al0.05O2 , LiFePO4 , and LiMnPO4 .
  • the positive electrode active material may include but is not limited to at least one of sodium-containing transition metal oxides, polyanion materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.
  • the positive electrode active material for a sodium ion battery may include at least one of NaFeO2 , NaCoO2 , NaCrO2 , NaMnO2 , NaNiO2 , NaNi1/2Ti1/ 2O2 , NaNi1/2Mn1/ 2O2 , Na2 / 3Fe1 / 3Mn2 / 3O2 , NaNi1 / 3Co1 / 3Mn1 / 3O2 , NaFePO4 , NaMnPO4 , NaCoPO4 , Prussian blue-based materials, and materials of the general formula XpM'q ( PO4 ) rOxY3 -x .
  • X is selected from at least one of H + , Li + , Na + , K + and NH4 + , M' is a transition metal cation, optionally at least one of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halogen anion, optionally at least one of F, Cl and Br.
  • the modified compound of each positive electrode active material mentioned above may be a compound obtained by doping and/or surface coating the positive electrode active material.
  • the positive electrode film layer may further include a positive electrode conductive agent.
  • a positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the mass percentage of the positive electrode conductive agent is ⁇ 5wt%.
  • the positive electrode film layer may also optionally include a positive electrode binder.
  • the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylic resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • vinylidene fluoride-tetrafluoroethylene-propylene terpolymer vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer
  • tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • a metal foil aluminum foil may 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 at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and 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 them uniformly.
  • the solvent can 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 to each other 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 electrode active material may be a negative electrode active material for a secondary battery known in the art.
  • the negative electrode 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-nitrogen composite, and silicon alloy material.
  • the tin-based material may include at least one of elemental tin, tin oxide, and tin alloy material.
  • the negative electrode film layer may further include a negative electrode conductive agent.
  • a negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the mass percentage of the negative electrode conductive agent is ⁇ 5wt%.
  • the negative electrode film layer may further include a negative electrode binder.
  • the present application does not particularly limit the type of the negative electrode binder.
  • the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA) and carboxymethyl chitosan (CMCS).
  • SBR styrene-butadiene rubber
  • SR-1B water-soluble unsaturated resin
  • aqueous acrylic resin e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS
  • PAM polyacrylamide
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • CMCS carboxymethyl chitosan
  • the negative electrode film layer may further include other additives.
  • other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.
  • CMC sodium carboxymethyl cellulose
  • PTC thermistor materials etc.
  • the mass percentage of the other additives is ⁇ 2wt%.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • a metal foil a copper foil may 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 at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and 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 auxiliary agents in a solvent and stirring them uniformly.
  • the solvent can 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 plate described in the present application also includes a conductive primer layer (for example, composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector.
  • the negative electrode plate described in the present application also includes a protective layer covering the surface of the negative electrode film layer.
  • the electrolyte solution includes an electrolyte salt and a solvent.
  • 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 at least one of lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium
  • the electrolyte salt may include but is not limited to at least one of sodium hexafluorophosphate (NaPF 6 ), sodium tetrafluoroborate (NaBF 4 ), sodium perchlorate (NaClO 4 ), sodium hexafluoroarsenate (NaAsF 6 ), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalatoborate (NaDFOB), sodium dioxalatoborate (NaBOB), sodium difluorophosphate (NaPO 2 F 2 ), sodium difluorobis(oxalatophosphate) (NaDFOP) and sodium tetrafluorooxalatophosphate (NaPF 6 ), sodium tetrafluoroxalatophosphate
  • the solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl 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), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl s
  • the electrolyte may further include additives, for example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, additives that improve battery low temperature power performance, etc.
  • the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, additives that improve battery low temperature power performance, etc.
  • the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly by a winding process and/or a lamination process.
  • the secondary battery may include an outer package, which may be used to package the electrode assembly and the electrolyte.
  • the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package.
  • the material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).
  • FIG1 is a secondary battery 5 of a square structure as an example.
  • the outer package may include a shell 51 and a cover plate 53.
  • the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity.
  • the shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity.
  • the positive electrode sheet, the negative electrode sheet and the isolation film may form an electrode assembly 52 through a winding process and/or a lamination process.
  • the electrode assembly 52 is encapsulated in the receiving cavity.
  • the electrolyte is infiltrated in the electrode assembly 52.
  • the number of electrode assemblies 52 contained in the secondary battery 5 may be one or more, which can be adjusted according to demand.
  • the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery.
  • the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process and/or a lamination process, and the electrode assembly is placed in an outer package, and the electrolyte is injected after drying, and a secondary battery is obtained through vacuum packaging, standing, forming, shaping and other processes.
  • the secondary batteries according to the present application can be assembled into a battery module.
  • the battery module can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG3 is a schematic diagram of a 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. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.
  • the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.
  • FIG. 4 and FIG. 5 are schematic diagrams of a battery pack 1 as an example.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3, wherein the upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4.
  • the plurality of battery modules 4 may be arranged in the battery box in any manner.
  • the fourth aspect of the embodiment of the present application provides an electric device, which includes at least one of the secondary battery, battery module or battery pack of the present application.
  • the secondary battery, battery module or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device.
  • the electric device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.
  • the electrical device may select a secondary battery, a battery module or a battery pack according to its usage requirements.
  • Fig. 6 is a schematic diagram of an electric device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • a battery pack or a battery module may be used.
  • the electric device may be a mobile phone, a tablet computer, a notebook computer, etc.
  • the electric device is usually required to be light and thin, and a secondary battery may be used as a power source.
  • the cotton linters were opened and deslagging by a cotton opener, and then boiled at 150°C for 2 hours using a 5wt% NaOH aqueous solution.
  • the cotton linters were then washed with water to remove impurities (washed 3 times), bleached with sodium hypochlorite, washed with dilute hydrochloric acid to remove impurities, washed with water to remove impurities (washed once), driven out of water, and dried with air flow to obtain cotton cellulose powder with a whiteness of ⁇ 85%.
  • the pH of the cellulose nanowhiskers with sulfonic acid groups was first adjusted to neutral with a 10wt% NaOH aqueous solution, then ground with a grinder, and then cut at the nanoscale using a high-pressure homogenizer to obtain nanocellulose with sulfonic acid modified groups with an average length of 500nm and an average diameter of 22nm, and the molar ratio of sulfonic acid groups to hydroxyl groups was 5:3.
  • the molar ratio of anionic modified groups to hydroxyl groups in nanocellulose can be measured by the following method: According to the phthalic anhydride method in GB/T12008.3-2009, the hydroxyl values of raw cellulose and nanocellulose (the number of milligrams of potassium hydroxide equivalent to the hydroxyl content in each gram of sample) are tested respectively, and the numerical unit obtained is mg KOH/g, which is converted into mmol/g as the hydroxyl content.
  • the content of anionic modified groups i.e. the content of modified hydroxyl groups
  • Unmodified nanocellulose with an average length of 500 nm and an average diameter of 22 nm product model CNWS-50, purchased from Zhongke Leiming (Beijing) Technology Co., Ltd., 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.
  • PE porous substrate thickness 4.8 ⁇ m, porosity 32%.
  • Preparation of coating slurry The prepared nanocellulose C1, the first filler aluminum oxide (secondary particle morphology, average particle size of 75nm), and the binder aqueous solution type polyacrylic acid are mixed in an appropriate amount of solvent deionized water at a mass ratio of 16:83:1, and then stirred at a shear rate of 23m/s to obtain a coating slurry with a solid content of 15wt%.
  • the contents of ⁇ crystal, ⁇ crystal, ⁇ crystal and ⁇ crystal in the first filler are 1.1wt%, 68.7wt%, 29.6wt% and 0.6wt%, respectively, based on the total weight of the first filler.
  • Coating The prepared coating slurry is coated on both surfaces of the PE porous substrate by a coating machine, and a separator is obtained through drying and slitting processes.
  • the coating thickness on one side of the PE porous substrate is 0.8 ⁇ m and the surface density is 1.25 g/m 2 .
  • the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), the conductive agent carbon black (Super P), and the binder polyvinylidene fluoride (PVDF) are uniformly mixed in a proper amount of solvent N-methylpyrrolidone (NMP) at a mass ratio of 96.2:2.7:1.1 to obtain a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through processes such as drying, cold pressing, slitting, and cutting.
  • the negative electrode active material artificial graphite, the conductive agent carbon black (Super P), the binder styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) are uniformly mixed in a proper amount of solvent deionized water at a mass ratio of 96.4:0.7:1.8:1.1 to obtain a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector copper foil, and the negative electrode sheet is obtained through the processes of drying, cold pressing, slitting and cutting.
  • Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:70 to obtain an organic solvent, and fully dried LiPF 6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol/L.
  • the positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound in order to obtain an electrode assembly; the electrode assembly is placed in an outer package, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, shaping and other processes, a secondary battery is obtained.
  • the secondary battery was prepared in a similar manner to Example 1, with the differences shown in Table 1.
  • the second filler in Examples 12-15 was in primary particle morphology, and the crystal form of the second filler was mainly ⁇ crystal form, accounting for more than 99% by mass based on the total weight of the second filler.
  • the secondary battery was prepared by a method similar to that of Example 1, except for the preparation process of the isolation membrane.
  • PE porous substrate thickness 4.8 ⁇ m, porosity 32%.
  • Preparation of coating slurry Alumina (average particle size of 600 nm, primary particle morphology, ⁇ crystal mass accounting for more than 99%) and a binder are mixed in a mass ratio of 94:6 and dissolved in deionized water, and then stirred at a shear speed of 23 m/s to obtain a coating slurry with a solid content of 38 wt%.
  • Alumina average particle size of 600 nm, primary particle morphology, ⁇ crystal mass accounting for more than 99%
  • a binder are mixed in a mass ratio of 94:6 and dissolved in deionized water, and then stirred at a shear speed of 23 m/s to obtain a coating slurry with a solid content of 38 wt%.
  • Coating The prepared coating slurry was coated on both surfaces of the PE porous substrate by a coating machine, and a separator was obtained through drying and slitting processes.
  • the coating thickness on one side of the PE porous substrate was 1.7 ⁇ m and the surface density was 1.80 g/m 2 .
  • the ionic conductivity of the isolation membrane is obtained by AC impedance spectroscopy experiment. Specifically, the isolation membrane is cut into discs of a certain area, dried, and placed between two stainless steel electrodes. After absorbing a sufficient amount of electrolyte, it is sealed to form a button battery. An electrochemical workstation is used to perform an AC impedance spectroscopy experiment to obtain the ionic conductivity of the isolation membrane.
  • the electrochemical workstation can be a Shanghai Chenhua CHI 660C electrochemical workstation, with an AC signal frequency range of 0.01Hz to 1MHz and a sine wave potential amplitude of 5mV. For accuracy, the average value of 5 parallel samples is taken as the test result.
  • the electrolyte used was prepared as follows: ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed in a mass ratio of 30:50:20 to obtain an organic solvent, and fully dried LiPF 6 was dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol/L.
  • a test isolation membrane sample of a certain size for example, 15 mm ⁇ 15 mm
  • wrap the isolation membrane sample with copper foil and cut it under freezing conditions (for example, -80°C) using an ion beam polisher (for example, Hitachi Arblade 5000); spray gold on the isolation membrane sample, and then refer to JY/T010-1996 to obtain a SEM image of the isolation membrane cross section using a scanning electron microscope (for example, Sigma 300 scanning electron microscope from ZEISS, Germany) (the magnification can be 1000 to 30000 times); use an image processing detection system (for example, Yihong isolation membrane detection system 2022-0408) to obtain the average pore area S1 of the isolation membrane coating and the average pore area S2 of the porous substrate of the isolation membrane using a multi-segment binarization method.
  • an image processing detection system for example, Yihong isolation membrane detection system 2022-0408
  • the ratio of the total pore area of the coating of the isolation membrane to the number of pores in the coating is the average pore area S 1 of the coating of the isolation membrane, and the ratio of the total pore area of the porous substrate of the isolation membrane to the number of pores in the porous substrate is the average pore area S 2 of the porous substrate of the isolation membrane.
  • the average value of 5 parallel samples is taken as the test result.
  • Sample preparation The isolation film prepared above was punched into samples with a width of 50 mm and a length of 100 mm using a punching machine. Five parallel samples were placed on A4 paper and fixed. The A4 paper containing the samples was then placed on corrugated paper with a thickness of 1 mm to 5 mm.
  • Sample test Place the A4 paper on the corrugated paper into a blast oven, set the temperature of the blast oven to 150°C, and start timing after the temperature reaches the set temperature and stabilizes for 30 minutes. After the set time (1 hour in this application) is reached, measure the length and width of the isolation film, and the values are marked as a and b respectively.
  • Examples 1-16 provide a coating comprising nanocellulose (forming a three-dimensional skeleton structure) and a filler on both surfaces of the porous substrate of the isolation membrane, and reasonably control the average pore area S 1 of the coating and the average pore area S 2 of the porous substrate to satisfy 0 ⁇ S 1 /S 2 ⁇ 1.
  • This enables the isolation membrane to have both low thermal shrinkage and high ion conductivity, and also enables the secondary battery 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填料，所述填料中的至少一部分填充在所述三维骨架结构中，沿所述隔离膜的厚度方向，所述涂层的平均孔面积记为S 1，所述多孔基材的平均孔面积记为S 2，则0<S 1/S 2<1。本申请能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。

Description

隔离膜、其制备方法及其相关的二次电池和用电装置 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、高热安全性能以及良好的循环性能和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、高热安全性能以及良好的循环性能和动力学性能。
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填料，所述填料中的至少一部分填充在所述三维骨架结构中，沿所述隔离膜的厚度方向，所述涂层的平均孔面积记为S 1，所述多孔基材的平均孔面积记为S 2，则0<S 1/S 2<1。
本申请的发明人在研究过程中惊奇发现，通过使涂层包括三维骨架结构和填料，使填料中的至少一部分填充在所述三维骨架结构中，且使涂层的平均孔面积S 1与多孔基材的平均孔面积S 2满足0<S 1/S 2<1，能够使隔离膜兼顾高耐热性和高离子导通率，并且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。
在本申请的任意实施方式中，0.06≤S 1/S 2<1，可选地，0.30≤S 1/S 2≤0.97。
在本申请的任意实施方式中，0.0002μm 2≤S 1≤0.0080μm 2，可选地，0.0004μm 2≤S 1≤0.0050μm 2。涂层的平均孔面积S 1在上述范围内时，一方面能够提升隔离膜的耐热性，另一方面还不会妨碍活性离子传输，由此能够使二次电池更好地兼顾高能量密度、高热安全性能以及良好的循环性能和动力学性能。
在本申请的任意实施方式中，0.0005μm 2≤S 2≤0.0100μm 2，可选地，0.0008μm 2≤S 2≤0.0080μm 2。多孔基材的平均孔面积S 2在上述范围内时，有利于提升隔离膜的离子导通率以及二次电池容量发挥特性。
在本申请的任意实施方式中，所述隔离膜的平均孔径记为d 1，所述多孔基材的平均孔径记为d 2，则d 1/d 2<1；可选地，0.3≤d 1/d 2≤0.8。隔离膜的平均孔径d 1与多孔基材的平 均孔径d 2的比值d 1/d 2在上述范围内时，能够在保证隔离膜具有高耐热性的前提下，还具有较高的离子导通率。
在本申请的任意实施方式中，15nm≤d 1≤50nm，可选地，20nm≤d 2≤40nm。隔离膜的平均孔径d 1在上述范围内时，一方面能够提升隔离膜的耐热性，另一方面还不会妨碍活性离子传输，由此能够使二次电池更好地兼顾高能量密度、高热安全性能以及良好的循环性能和动力学性能。
在本申请的任意实施方式中，25nm≤d 2≤60nm，可选地，30nm≤d 2≤50nm。多孔基材的平均孔径d 2在上述范围内时，有利于提升隔离膜的离子导通率以及二次电池容量发挥特性。
在本申请的任意实施方式中，所述涂层的面密度记为ρ 1，所述多孔基材的面密度记为ρ 2，则0.15≤ρ 1/ρ 2≤0.80；可选地，0.20≤ρ 1/ρ 2≤0.50。ρ 1/ρ 2在上述范围内时，有利于涂层具有高耐热性，还有利于二次电池兼顾高能量密度以及高热安全性能。
在本申请的任意实施方式中，可选地，0.50g/m 2≤ρ 1≤1.50g/m 2，更可选地，0.75g/m 2≤ρ 1≤1.40g/m 2。涂层的面密度ρ 1在上述范围内时，有利于二次电池兼顾高能量密度以及高热安全性能，还能够使涂层具有合适的平均孔面积，还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，可选地，1.50g/m 2≤ρ 2≤4.50g/m 2，更可选地，2.00g/m 2≤ρ 2≤4.00g/m 2。多孔基材的面密度ρ 2在上述范围内时，能够使多孔基材具有合适的平均孔面积，还有利于提升隔离膜的离子导通率以及二次电池容量发挥特性。
在本申请的任意实施方式中，所述隔离膜的孔隙率记为P 1，所述多孔基材的孔隙率记为P 2，则0.4≤P 2/P 1<1；可选地，0.55≤P 2/P 1≤0.85。P 2/P 1在上述范围内时，有利于二次电池兼顾高热安全性能以及良好的循环性能和动力学性能。
在本申请的任意实施方式中，20％≤P 1≤60％，可选地，25％≤P 1≤45％。隔离膜的孔隙率P 1在上述范围内时，有利于二次电池兼顾高热安全性能以及良好的循环性能和动力学性能。
在本申请的任意实施方式中，15％≤P 2≤45％，可选地，20％≤P 2≤40％。多孔基材的孔隙率P 2在上述范围内时，有利于提升隔离膜的离子导通率以及二次电池容量发挥特性。
在本申请的任意实施方式中，所述填料包括第一填料，所述第一填料的平均粒径为≤150nm，可选为15nm至120nm。第一填料具有平均粒径较小、比表面积大、与三维骨架结构亲和性好的优势，由此能够与三维骨架结构更好地搭接在一起，使涂层具有更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和对电解液的浸润和保持特性。此外，当第一填料的平均粒径在上述范围内时，还能够使涂层具有合适的平均孔面积，并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75nm。
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150nm，可选为55nm至120nm。
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，θ晶型的无机颗粒的含量为≥50wt％，可选为60wt％至82wt％，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，γ晶型的无机颗粒的含量为≥10wt％，可选为17wt％至38wt％，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，η晶型的无机颗粒的含量为≤5wt％，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。
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、离子导通率以及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，所述第一填料的BET比表面积为≥15m 2/g，可选为18m 2/g至65m 2/g。当第一填料的BET比表面积在上述范围内时，能够使涂层具有合适的平均孔面积，还能够进一步提升隔离膜的耐热性和离子导通率；此外，还能提升第一填料与三维骨架结构之间的亲和性，从而使涂层具有更稳定的空间网络结构，进而隔离膜具有更好的耐热性以及更高的离子导通率。
在本申请的任意实施方式中，所述第一填料的含量为≥55wt％，可选为60wt％至90wt％，基于所述涂层的总重量计。当第一填料的含量在上述范围内时，能够使涂层具有合适的平均孔面积，还能够进一步提升隔离膜的耐热性和离子导通率；此外，还有利于涂层具有更稳定的空间网络结构，从而还能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，所述填料还包括第二填料，所述第二填料的平均粒径大于所述第一填料的平均粒径。第二填料的粒径较大，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，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。
在本申请的任意实施方式中，所述第二填料的平均粒径小于等于400nm，可选为100nm至300nm。
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BET比表面积为≤15m 2/g，可选为7m 2/g至12m 2/g。当第二填料的BET比表面积在上述范围内时，能够使涂层具有合适的平均孔面积，还能够进一步提升隔离膜的耐热性和离子导通率；此外，还能够更好地发挥 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，进而有利于离子传输，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，所述第二填料的含量为≤20wt％，可选为2wt％至15wt％，基于所述涂层的总重量计。当第二填料的含量在上述范围内时，能够使涂层具有合适的平均孔面积，还能够进一步提升隔离膜的耐热性和离子导通率；此外，还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，进而有利于离子传输，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晶型的无机颗粒的含量为≥80wt％，可选为90wt％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，所述三维骨架结构的含量为≤40wt％，可选为5wt％至25wt％，基于所述涂层的总重量计。三维骨架结构的含量在上述范围内时，能够使涂层具有合适的平均孔面积，还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。
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，有助于构成三维骨架结构的材料与填料搭接形成一体化效果。
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800nm，可选为200nm至600nm。当构成三维骨架结构的材料的平均长度在合适的范围内时，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合适的范围内时，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。
在本申请的任意实施方式中，所述纳米纤维素包括羟基和阴离子改性基团。
在本申请的任意实施方式中，所述阴离子改性基团包括胺基、羧基、磺酸基、硼酸基和磷酸基中的至少一种，可选包括磺酸基、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阴离子改性基团时，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阴离子改性基团时，还有利于纳米纤维素与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，并且还有利于匹配高电压正极活性材料，并进一步提升二次电池的能量密度。此外，阴离子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，所述阴离子改性基团与所述羟基的摩尔比为1:4至4:1，可选为2:3至7:3。当阴离子改性基团与羟基的摩尔比在合适的范围内时，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，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。涂层中的三维骨架结构与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≤8μm，可选为3μm至6μm。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1.3μm。本申请的涂层具有高耐热性，由此可以降低涂层的厚度，并进一步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，所述隔离膜的离子导通率为≥0.6ms/cm 2，可选为≥0.9ms/cm 2。本申请的隔离膜具有高离子导通率，由此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，所述隔离膜的电阻值为≤1.3Ω，可选为≤1.0Ω。本申请的隔离膜具有低电阻值，由此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。
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；将构成所述三维骨架结构的材料和填料按照预定比例在溶剂中混合，然后在一定剪切速度下搅拌均匀，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填料，所述填料中的至少一部分填充在所述三维骨架结构中，沿所述隔离膜的厚度方向，所述涂层的平均孔面积记为S 1，所述多孔基材的平均孔面积记为S 2，则0<S 1/S 2<1。
在本申请的任意实施方式中，所述剪切速度为≤30m/s，可选为15m/s至30m/s。剪切速度在上述范围内时，能够使干燥后的涂层具有合适的平均孔面积，还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，所述涂层浆料的固含量为8％至30％，可选为10％至20％。
在本申请的任意实施方式中，所述涂层浆料的单面的涂布面密度为0.50g/m 2至1.50g/m 2，可选为0.75g/m 2至1.40g/m 2。涂层浆料的涂布面密度在上述范围内时，能够使干燥后的涂层具有合适的平均孔面积，还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，所述涂层浆料的单面的涂布厚度为≤2μm，可选为0.5μm至1.3μm。涂层浆料的涂布厚度在上述范围内时，能够使干燥后的涂层具有合适的平均孔面积，还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，发明人在进一步研究中发现，无机陶瓷层对隔离膜耐热性的改善效果有限，而为了保证隔离膜具有高耐热性，则需要增加无机陶瓷层的涂布厚度，但是由此会延长活性离子传输距离，影响二次电池的循环性能和动力学性能，同时也无法平衡二次电池的能量密度。
因此，现有技术的隔离膜往往很难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。
本申请的发明人在研究过程中惊奇发现，通过在隔离膜多孔基材的表面上设置包括三维骨架结构和填料的涂层，并使涂层的平均孔面积小于多孔基材的平均孔面积，能够使隔离膜兼顾高耐热性和高离子导通率，还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。
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。
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填料，所述填料中的至少一部分填充在所述三维骨架结构中，沿所述隔离膜的厚度方向，所述涂层的平均孔面积记为S 1，所述多孔基材的平均孔面积记为S 2，则0<S 1/S 2<1。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。
发明人在研究隔离膜耐热性的过程中发现，目前多孔基材表面的涂层(例如无机陶瓷层等)的耐热性不佳，而为了保证涂层具有高耐热性，通常需要增加涂层的厚度，但是由此损失了二次电池的能量密度、循环性能以及动力学性能。
发明人在进一步研究中发现，通过使涂层包括三维骨架结构和填料，使填料中的至少一部分填充在所述三维骨架结构中，且使涂层的平均孔面积S 1与多孔基材的平均孔面积S 2满足0<S 1/S 2<1，能够使隔离膜兼顾高耐热性和高离子导通率，并且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。
涂层包括三维骨架结构和填料，且填料中的至少一部分填充在三维骨架结构中，由此有助于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，避免填料在二次电池长期充放电过程中脱落。此外，当填料中的至少一部分填充在三维骨架结构中时，填料与三维骨架结构之间的接触位点较多，由此可以降低涂层中粘结剂的使用量，从而有效降低了粘结剂堵孔的风险，并能进一步改善二次电池的循环性能和动力学性能。在一些实施例中，所述填料中的至少一部分填充在所述三维骨架结构中，所述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填料嵌入多孔基材的基体和/或孔中。
涂层的平均孔面积S 1小于多孔基材的平均孔面积S 2，由此可以使涂层具有高耐热性；由于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，由于本申请的涂层具有高耐热性，由此还可以选用更薄的多孔基材，进而能够进一步提升二次电池的能量密度。
发明人在进一步研究中还发现，涂层的平均孔面积S 1与多孔基材的平均孔面积S 2的比值S 1/S 2也不宜太小。当S 1/S 2太小时，涂层的平均孔面积往往较小，由此可能妨碍活性离子的传输，影响二次电池的循环性能和/或动力学性能。在一些实施例中，0.06≤S 1/S 2<1，可选地，0.10≤S 1/S 2≤0.99，0.20≤S 1/S 2≤0.98，0.30≤S 1/S 2≤0.97，0.30≤S 1/S 2≤0.80，0.30≤S 1/S 2≤0.70，0.35≤S 1/S 2≤0.94，0.35≤S 1/S 2≤0.85，0.40≤S 1/S 2≤0.92，0.40≤S 1/S 2≤0.80，0.40≤S 1/S 2≤0.70，0.45≤S 1/S 2≤0.90。
在一些实施例中，涂层的平均孔面积S 1满足0.0002μm 2≤S 1≤0.0080μm 2，可选地，0.0004μm 2≤S 1≤0.0050μm 2，0.0008μm 2≤S 1≤0.0048μm 2。涂层的平均孔面积S 1在上述范 围内时，一方面能够提升隔离膜的耐热性，另一方面还不会妨碍活性离子传输，由此能够使二次电池更好地兼顾高能量密度、高热安全性能以及良好的循环性能和动力学性能。
在一些实施例中，多孔基材的平均孔面积S 2满足0.0005μm 2≤S 2≤0.0100μm 2，可选地，0.0008μm 2≤S 2≤0.0080μm 2。多孔基材的平均孔面积S 2在上述范围内时，有利于提升隔离膜的离子导通率以及二次电池容量发挥特性。
在本申请中，隔离膜的涂层的平均孔面积S 1以及隔离膜的多孔基材的平均孔面积S 2，可以通过隔离膜的截面图像进行测试得到。
隔离膜的涂层的平均孔面积S 1是指隔离膜的截面图像中的涂层的总孔面积与涂层中的孔数量的比值。
隔离膜的多孔基材的平均孔面积S 2是指隔离膜的截面图像中的多孔基材的总孔面积与多孔基材中的孔数量的比值。
在本申请中，隔离膜的截面图像为沿隔离膜的厚度方向的图像。可以从隔离膜中任选一区域裁切出一定尺寸(例如15mm×15mm)的待测隔离膜样品，通过离子束抛光仪(例如日立Arblade 5000)在冷冻条件下(例如-80℃)切割获得隔离膜横截面；参考JY/T010-1996，使用扫描电子显微镜(例如德国ZEISS公司的Sigma 300型扫描电子显微镜)扫描获得隔离膜截面的SEM图(放大倍数可为1000倍至30000倍)；使用图像处理检测系统(例如易鸿隔离膜检测系统2022-0408)利用多段二值化方法获取隔离膜的涂层的平均孔面积S 1以及隔离膜的多孔基材的平均孔面积S 2。
在使用离子束抛光仪进行切割时，可以将测试样品用铜箔或铝箔包裹后进行切割处理。在获得隔离膜截面的SEM图时，可以对测试样品进行喷金处理。
使用图像处理检测系统，可以分别获得隔离膜的涂层和多孔基材的孔面积数据，然后可以通过Mintab软件，分别获得隔离膜的涂层和多孔基材的孔面积分布图以及平均孔面积。隔离膜的涂层的总孔面积与涂层中的孔数量的比值即为隔离膜的涂层的平均孔面积S 1，隔离膜的多孔基材的总孔面积与多孔基材中的孔数量的比值即为隔离膜的多孔基材的平均孔面积S 2。
在一些实施例中，所述隔离膜的平均孔径记为d 1，所述多孔基材的平均孔径记为d 2，则d 1/d 2<1，可选地，0.2≤d 1/d 2≤0.9，0.3≤d 1/d 2≤0.8，0.4≤d 1/d 2≤0.7。隔离膜的平均孔径d 1与多孔基材的平均孔径d 2的比值d 1/d 2在上述范围内时，能够在保证隔离膜具有高耐热性的前提下，还具有较高的离子导通率。
在一些实施例中，隔离膜的平均孔径d 1满足15nm≤d 1≤50nm，可选地，20nm≤d 2≤40nm。隔离膜的平均孔径d 1在上述范围内时，一方面能够提升隔离膜的耐热性，另一方面还不会妨碍活性离子传输，由此能够使二次电池更好地兼顾高能量密度、高热安全性能以及良好的循环性能和动力学性能。
在一些实施例中，多孔基材的平均孔径d 2满足25nm≤d 2≤60nm，可选地，30nm≤d 2≤50nm。多孔基材的平均孔径d 2在上述范围内时，有利于提升隔离膜的离子导通率以及二次电池容量发挥特性。
隔离膜的平均孔径d 1、多孔基材的平均孔径d 2可以采用毛细管孔隙率测试仪(泡点法)进行测试。示例性测试方法如下：取直径为25mm圆形样品，并在上面滴3-5滴浸润液，待样品完全浸润后放入模具中，然后使用惰性气体对待测样品中的孔道浸润液挤压， 挤压气压和流量与孔径成反比，通过软件采样及压力和孔径折算分析，获得待测样品的平均孔径。测试仪器可为PMI公司的CFP 1500型孔径分析仪，测试压力可为100psi至350psi。
在一些实施例中，所述涂层的面密度记为ρ 1，所述多孔基材的面密度记为ρ 2，则0.15≤ρ 1/ρ 2≤0.80，可选地，0.20≤ρ 1/ρ 2≤0.50。ρ 1/ρ 2在上述范围内时，有利于涂层具有高耐热性，还有利于二次电池兼顾高能量密度以及高热安全性能。
在一些实施例中，涂层的面密度ρ 1满足0.50g/m 2≤ρ 1≤1.50g/m 2，可选地，0.60g/m 2≤ρ 1≤1.40g/m 2，0.75g/m 2≤ρ 1≤1.40g/m 2，0.75g/m 2≤ρ 1≤1.30g/m 2。涂层的面密度ρ 1在上述范围内时，有利于二次电池兼顾高能量密度以及高热安全性能。涂层的面密度ρ 1在上述范围内时，还能够使涂层具有合适的平均孔面积，还能够进一步提升隔离膜的耐热性和离子导通率。在本申请中，涂层的面密度是指位于多孔基材单侧的涂层的面密度。
在一些实施例中，多孔基材的面密度ρ 2满足1.50g/m 2≤ρ 2≤4.50g/m 2，可选地，2.00g/m 2≤ρ 2≤4.00g/m 2。多孔基材的面密度ρ 2在上述范围内时，能够使多孔基材具有合适的平均孔面积，还有利于提升隔离膜的离子导通率以及二次电池容量发挥特性。
在一些实施例中，所述隔离膜的孔隙率记为P 1，所述多孔基材的孔隙率记为P 2，则0.4≤P 2/P 1<1；可选地，0.55≤P 2/P 1≤0.85。P 2/P 1在上述范围内时，有利于二次电池兼顾高热安全性能以及良好的循环性能和动力学性能。
在一些实施例中，隔离膜的孔隙率P 1满足20％≤P 1≤60％，可选地，25％≤P 1≤45％。隔离膜的孔隙率P 1在上述范围内时，有利于二次电池兼顾高热安全性能以及良好的循环性能和动力学性能。
在一些实施例中，多孔基材的孔隙率P 2满足15％≤P 2≤45％，可选地，20％≤P 2≤40％。多孔基材的孔隙率P 2在上述范围内时，有利于提升隔离膜的离子导通率以及二次电池容量发挥特性。
隔离膜的孔隙率P 1、多孔基材的孔隙率P 2可以参考GB/T 24586-2009进行测试。测试方法如下：将隔离膜或多孔基材冲切成直径为14mm的小圆片样品，测试厚度，并按照圆柱体积计算公式，计算隔离膜或多孔基材的表观体积V 1；参考GB/T 24586-2009，使用惰性气体如氦气或氮气作为介质，采用气体置换法，利用真密度测试仪测得隔离膜或多孔基材的真实体积V 2。则隔离膜或多孔基材的孔隙率＝(V 1-V 2)/V 1×100％。测试仪器可以为美国Micromeritics公司的AccuPyc II 1340型全自动真密度测试仪。
在一些实施例中，所述多孔基材的厚度为≤8μm，可选为3μm至6μm。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。
在一些实施例中，所述涂层的厚度为≤2μm，可选为0.5μm至1.3μm。本申请的涂层具有高耐热性，由此可以降低涂层的厚度，并进一步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。
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，所述填料包括第一填料，所述第一填料的平均粒径为≤150nm，可选为15nm至150nm，15nm至120nm。
第一填料具有平均粒径较小、比表面积大、与三维骨架结构亲和性好的优势，由此能够与三维骨架结构更好地搭接在一起，使涂层具有更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和对电解液的浸润和保持特性，进而采用本申请的隔离膜的二次电池能可兼顾高热安全性能、长使用寿命以及良好的循环性能和动力学性能。此外，当第一填料的平均粒径在上述范围内时，还能够使涂层具有合适的平均孔面积，并能够进一步提升隔离膜的耐热性和离子导通率。
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。
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80nm，可选为20nm至80nm，30nm至75nm。
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150nm，可选为50nm至135nm，50nm至120nm，55nm至150nm，55nm至135nm，55nm至120nm。
在一些实施例中，所述第一填料的BET比表面积为≥15m 2/g，可选为18m 2/g至65m 2/g。当第一填料的BET比表面积在上述范围内时，能够使涂层具有合适的平均孔面积，还能够进一步提升隔离膜的耐热性和离子导通率；此外，还能提升第一填料与三维骨架结构之间的亲和性，从而使涂层具有更稳定的空间网络结构，进而隔离膜具有更好的耐热性以及更高的离子导通率。
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60wt％至82wt％，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17wt％至38wt％，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≤1.5wt％，更可选为≤1wt％，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、离子导通率以及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60wt％至82wt％，γ晶型的无机颗粒的含量可为17wt％至38wt％，η晶型的无机颗粒的含量可为≤1.5wt％，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)获得一次颗粒自组装后的二次颗粒形貌的无机颗粒。
在一些实施例中，所述第一填料的含量为≥55wt％，可选为60wt％至90wt％，基于所述涂层的总重量计。当第一填料的含量在上述范围内时，能够使涂层具有合适的平均孔面积，还能够进一步提升隔离膜的耐热性和离子导通率；此外，还有利于涂层具有更稳定的空间网络结构，从而还能进一步提升隔离膜的耐热性和离子导通率。
在一些实施例中，所述填料包括第一填料和第二填料，且所述第二填料的平均粒径大于所述第一填料的平均粒径。
第二填料的粒径较大，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，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。
在一些实施例中，所述第二填料的平均粒径小于等于400nm，可选为100nm至300nm。当第二填料的平均粒径在上述范围内时，能够使涂层具有合适的平均孔面积，还能够进一步提升隔离膜的耐热性和离子导通率；此外，还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，进而有利于离子传输，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≤15m 2/g，可选为7m 2/g至12m 2/g。当第二填料的BET比表面积在上述范围内时，能够使涂层具有合适的平均孔面积，还能够进一步提升隔离膜的耐热性和离子导通率；此外，还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，进而有利于离子传输，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晶型的无机颗粒含量为≥80wt％，可选为85wt％至100wt％，90wt％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≤20wt％，可选为2wt％至15wt％，基于所述涂层的总重量计。当第二填料的含量在上述范围内时，能够使涂层具有合适的平均孔面积，还能够进一步提升隔离膜的耐热性和离子导通率；此外，还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，进而有利于离子传输，同时还能提升隔离膜的耐热性。
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填料形成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以及离子导通率。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，有助于构成三维骨架结构的材料与填料搭接形成一体化效果。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，由此可能导致隔离膜的耐热性、耐电压击穿特性等不够优异。
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为100nm至800nm，可选为200nm至600nm。当构成三维骨架结构的材料的平均长度在合适的范围内时，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合适的范围内时，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长径比过小时，其与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，由此可能导致隔离膜的离子导通率变小，进而二次电池的循环性能和/或动力学性能变差。
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，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。作为构成所述三维骨架结构的材料，只要满足具有电绝缘性、电化学稳定和对电解液稳定即可，对材质并无特别限制，其既可以为有机材料，也可以为无机材料。
在一些实施例中，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。在一些实施例中，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。可选地，所述纳米纤维素包括纤维素纳米晶须，其具有结晶度高的优势，由此能够更好地改善隔离膜的耐热性。
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，所述纳米纤维素包括羟基和阴离子改性基团。
在一些实施例中，可选地，所述阴离子改性基团包括胺基、羧基、磺酸基、硼酸基和磷酸基中的至少一种，更可选包括磺酸基、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阴离子改性基团时，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阴离子改性基团时，还有利于纳米纤维素与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，并且还有利于匹配高电压正极活性材料，并进一步提升二次电池的能量密度。此外，阴离子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，所述阴离子改性基团与所述羟基的摩尔比为1:4至4:1，可选为2:3至7:3。当阴离子改性基团与羟基的摩尔比在合适的范围内时，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：当阴离子改性基团与羟基的摩尔比过小时，阴离子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；当阴离子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/或动力学性能，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。
纳米纤维素中阴离子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，从而确定阴离子改性基团的种类。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。
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，所述三维骨架结构的含量为≤40wt％，可选为5wt％至25wt％，基于所述涂层的总重量计。三维骨架结构的含量在上述范围内时，能够使涂层具有合适的平均孔面积，还能够进一步提升隔离膜的耐热性和离子导通率。
在一些实施例中，所述涂层还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。
在一些实施例中，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。涂层中的三维骨架结构与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。
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，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％。
在一些实施例中，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。
在一些实施例中，所述隔离膜的离子导通率为≥0.6ms/cm 2，可选为≥0.9ms/cm 2。
本申请的隔离膜具有高离子导通率，由此能够提升二次电池的循环性能和/或动力学性能。
在一些实施例中，所述隔离膜的电阻值为≤1.3Ω，可选为≤1.0Ω。
本申请的隔离膜具有低电阻值，由此能够提升二次电池的循环性能和/或动力学性能。
在一些实施例中，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。
在一些实施例中，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。
在一些实施例中，所述隔离膜的润湿长度为≥30mm，可选为30mm至80mm。
在一些实施例中，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。
在一些实施例中，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。
在本申请中，材料(例如第一填料、第二填料)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)，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(例如第一填料、第二填料)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。
隔离膜的离子导通率和电阻值可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，进行交流阻抗谱实验。
需要说明的是，上述隔离膜的涂层参数(例如面密度、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；将构成所述三维骨架结构的材料和填料按照预定比例在溶剂中混合，然后在一定剪切速度下搅拌均匀，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填料， 所述填料中的至少一部分填充在所述三维骨架结构中，沿所述隔离膜的厚度方向，所述涂层的平均孔面积记为S 1，所述多孔基材的平均孔面积记为S 2，则0<S 1/S 2<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，所述剪切速度为≤30m/s，可选为15m/s至30m/s。剪切速度在上述范围内时，能够使干燥后的涂层具有合适的平均孔面积，还能够进一步提升隔离膜的耐热性和离子导通率。
在一些实施例中，所述涂层浆料的固含量为8％至30％，可选为10％至20％。
在一些实施例中，所述涂层浆料的单面的涂布面密度为0.50g/m 2至1.50g/m 2，可选为0.75g/m 2至1.40g/m 2。涂层浆料的涂布面密度在上述范围内时，能够使干燥后的涂层具有合适的平均孔面积，还能够进一步提升隔离膜的耐热性和离子导通率。
在一些实施例中，所述涂层浆料的单面的涂布厚度为≤2μm，可选为0.5μm至1.3μm。涂层浆料的涂布厚度在上述范围内时，能够使干燥后的涂层具有合适的平均孔面积，还能够进一步提升隔离膜的耐热性和离子导通率。
在一些实施例中，所述用于构成三维骨架结构的材料可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，可选为纤维素纳米晶须(Cellulose nanocrystals，CNC，又称为纤维素纳米晶、纳米晶体纤维素)。
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，获得纤维素纳米晶须；将获得的纤维素纳米晶须的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，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、高热安全性能以及良好的循环性能和动力学性能。
[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
纤维素粉末制备
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。
纤维素的酯化
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，再顺序经过水洗除杂(水洗次数为3次)、过滤、除酸除杂，获得具有磺酸基的纤维素纳米晶须。
纤维素的中和
用10wt％的NaOH水溶液先将具有磺酸基的纤维素纳米晶须的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500nm、平均直径为22nm的具有磺酸基改性基团的纳米纤维素，并且磺酸基与羟基的摩尔比为5:3。
纳米纤维素中阴离子改性基团与羟基的摩尔比可以通过以下方法测得：依据GB/T12008.3-2009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的羟基含量，即可得 阴离子改性基团的含量(即被改性的羟基的含量)，由此计算得到阴离子改性基团与羟基的摩尔比。
纳米纤维素C2的制备
采用未改性纳米纤维素，平均长度为500nm、平均直径为22nm，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。
实施例1
隔离膜的制备
提供PE多孔基材：厚度为4.8μm，孔隙率为32％。
配制涂层浆料：将上述制备的纳米纤维素C1、第一填料氧化铝(二次颗粒形貌，平均粒径为75nm)、粘结剂水溶液型聚丙烯酸按照质量比16:83:1在适量的溶剂去离子水中混合均匀，然后在23m/s的剪切速度下搅拌，得到固含量为15wt％的涂层浆料。第一填料中α晶型、θ晶型、γ晶型和η晶型的含量分别为1.1wt％、68.7wt％、29.6wt％和0.6wt％，基于第一填料总重量计。
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0.8μm、面密度为1.25g/m 2。
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2-16
二次电池采用与实施例1类似的方法制备，不同之处示出在表1中。实施例12-15中的第二填料为一次颗粒形貌，且第二填料的晶型主要为α晶型，质量占比在99％以上，基于第二填料的总重量计。
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4.8μm，孔隙率为32％。
配制涂层浆料：将氧化铝(平均粒径为600nm，一次颗粒形貌，α晶型质量占比99％以上)与粘结剂按照质量比94:6混合后溶于去离子水中，然后在23m/s的剪切速度下搅拌，得到固含量为38wt％的涂层浆料。
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1.7μm、面密度为1.80g/m 2。
测试部分
(1)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。
(2)涂层以及多孔基材的平均孔面积测试
从隔离膜中任选一区域裁切出一定尺寸(例如15mm×15mm)的待测隔离膜样品，将隔离膜样品使用铜箔包裹后，通过离子束抛光仪(例如日立Arblade 5000)在冷冻条件下(例如-80℃)切割获得隔离膜样品的横截面；对隔离膜样品进行喷金处理，然后参考JY/T010-1996，使用扫描电子显微镜(例如德国ZEISS公司的Sigma 300型扫描电子显微镜)扫描获得隔离膜截面的SEM图(放大倍数可为1000倍至30000倍)；使用图像处理检测系统(例如易鸿隔离膜检测系统2022-0408)利用多段二值化方法获取隔离膜的涂层的平均孔面积S 1以及隔离膜的多孔基材的平均孔面积S 2。隔离膜的涂层的总孔面积与涂层中的孔数量的比值即为隔离膜的涂层的平均孔面积S 1，隔离膜的多孔基材的总孔面积与多孔基材中的孔数量的比值即为隔离膜的多孔基材的平均孔面积S 2。为了准确性，取5个平行样品的平均值作为测试结果。
(3)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。
(4)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。
(5)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，实施例1-16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)和填料的涂层，并合理控制涂层的平均孔面积S 1与多孔基材的平均孔面积S 2满足0<S 1/S 2<1，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 PCTCN2022136685-appb-000001
Figure PCTCN2022136685-appb-000002

Claims (27)

  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填料，所述填料中的至少一部分填充在所述三维骨架结构中，沿所述隔离膜的厚度方向，所述涂层的平均孔面积记为S 1，所述多孔基材的平均孔面积记为S 2，则0<S 1/S 2<1。
  2. 根据权利要求1所述的隔离膜，其中，0.06≤S 1/S 2<1，可选地，0.30≤S 1/S 2≤0.97。
  3. 根据权利要求1或2所述的隔离膜，其中，
    0.0002μm 2≤S 1≤0.0080μm 2，可选地，0.0004μm 2≤S 1≤0.0050μm 2；和/或，
    0.0005μm 2≤S 2≤0.0100μm 2，可选地，0.0008μm 2≤S 2≤0.0080μm 2。
  4. 根据权利要求1-3任一项所述的隔离膜，其中，所述隔离膜的平均孔径记为d 1，所述多孔基材的平均孔径记为d 2，则d 1/d 2<1；
    可选地，0.3≤d 1/d 2≤0.8；
    可选地，15nm≤d 1≤50nm，更可选地，20nm≤d 2≤40nm；
    可选地，25nm≤d 2≤60nm，更可选地，30nm≤d 2≤50nm。
  5. 根据权利要求1-4任一项所述的隔离膜，其中，所述涂层的面密度记为ρ 1，所述多孔基材的面密度记为ρ 2，则0.15≤ρ 1/ρ 2≤0.80；
    可选地，0.20≤ρ 1/ρ 2≤0.50；
    可选地，0.50g/m 2≤ρ 1≤1.50g/m 2，更可选地，0.75g/m 2≤ρ 1≤1.40g/m 2；
    可选地，1.50g/m 2≤ρ 2≤4.50g/m 2，更可选地，2.00g/m 2≤ρ 2≤4.00g/m 2。
  6. 根据权利要求1-5任一项所述的隔离膜，其中，所述隔离膜的孔隙率记为P 1，所述多孔基材的孔隙率记为P 2，则0.4≤P 2/P 1<1；
    可选地，0.55≤P 2/P 1≤0.85；
    可选地，20％≤P 1≤60％，更可选地，25％≤P 1≤45％；
    可选地，15％≤P 2≤45％，更可选地，20％≤P 2≤40％。
  7. 根据权利要求1-6任一项所述的隔离膜，其中，所述填料包括第一填料，所述第一填料的平均粒径为≤150nm，可选为15nm至120nm。
  8. 根据权利要求7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75nm；
    可选地，所述二次颗粒形貌的第一填料的平均粒径为50nm至150nm，可选为55nm至120nm。
  9. 根据权利要求7或8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。
  10. 根据权利要求7-9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60wt％至82wt％，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17wt％至38wt％，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≤1.5wt％，基于所述第一填料中的所述无机颗粒的总重量计。
  11. 根据权利要求7-10任一项所述的隔离膜，其中，
    所述第一填料的BET比表面积为≥15m 2/g，可选为18m 2/g至65m 2/g；和/或，
    所述第一填料的含量为≥55wt％，可选为60wt％至90wt％，基于所述涂层的总重量计。
  12. 根据权利要求7-11任一项所述的隔离膜，其中，所述填料还包括第二填料，所述第二填料的平均粒径大于所述第一填料的平均粒径；
    可选地，所述第二填料的平均粒径小于等于400nm，可选为100nm至300nm。
  13. 根据权利要求12所述的隔离膜，其中，所述第二填料满足如下条件(1)至(6)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BET比表面积为≤15m 2/g，可选为7m 2/g至12m 2/g；
    (3)所述第二填料的含量为≤20wt％，可选为2wt％至15wt％，基于所述涂层的总重量计；
    (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晶型的无机颗粒的含量为≥80wt％，可选为90wt％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。
  14. 根据权利要求1-13任一项所述的隔离膜，其中，所述三维骨架结构的含量为≤40wt％，可选为5wt％至25wt％，基于所述涂层的总重量计。
  15. 根据权利要求1-14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。
  16. 根据权利要求1-15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；
    构成所述三维骨架结构的材料的平均长度为100nm至800nm，可选为200nm至600nm；
    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。
  17. 根据权利要求1-16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。
  18. 根据权利要求1-17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；
    可选地，所述纳米纤维素包括羟基和阴离子改性基团；
    可选地，所述阴离子改性基团包括胺基、羧基、磺酸基、硼酸基和磷酸基中的至少一种，更可选包括磺酸基、硼酸基和磷酸基中的至少一种；
    可选地，所述阴离子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。
  19. 根据权利要求1-18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。
  20. 根据权利要求1-19任一项所述的隔离膜，其中，
    所述多孔基材的厚度为≤8μm，可选为3μm至6μm；和/或，
    所述涂层的厚度为≤2μm，可选为0.5μm至1.3μm。
  21. 根据权利要求1-20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。
  22. 根据权利要求1-21任一项所述的隔离膜，其中，所述隔离膜满足如下条件(1)至(9)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)所述隔离膜的离子导通率为≥0.6ms/cm 2，可选为≥0.9ms/cm 2；
    (4)所述隔离膜的电阻值为≤1.3Ω，可选为≤1.0Ω；
    (5)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；
    (6)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；
    (7)所述隔离膜的润湿长度为≥30mm，可选为30mm至80mm；
    (8)所述隔离膜的润湿速度为≥3mm/s，可选为3mm/s至10mm/s；
    (9)所述隔离膜的透气度为≤300s/100mL，可选为100s/100mL至230s/100mL。
  23. 一种制备权利要求1-22任一项所述的隔离膜的方法，包括以下步骤：提供多孔基材；将构成所述三维骨架结构的材料和填料按照预定比例在溶剂中混合，然后在一定剪切速度下搅拌均匀，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填料，所述填料中的至少一部分填充在所述三维骨架结构中，沿所述隔离膜的厚度方向，所述涂层的平均孔面积记为S 1，所述多孔基材的平均孔面积记为S 2，则0<S 1/S 2<1。
  24. 根据权利要求23所述的方法，其中，
    所述剪切速度为≤30m/s，可选为15m/s至30m/s；和/或，
    所述涂层浆料的固含量为8％至30％，可选为10％至20％；和/或，
    所述涂层浆料的单面的涂布面密度为0.50g/m 2至1.50g/m 2，可选为0.75g/m 2至1.40g/m 2；和/或，
    所述涂层浆料的单面的涂布厚度为≤2μm，可选为0.5μm至1.3μm。
  25. 根据权利要求23或24所述的方法，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。
  26. 一种二次电池，其包括权利要求1-22任一项所述的隔离膜或通过权利要求23-25任一项所述的方法制备的隔离膜。
  27. 一种用电装置，其包括权利要求26所述的二次电池。
PCT/CN2022/136685 2022-12-05 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 WO2024119332A1 (zh)

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