WO2024082264A1 - 二次电池及其制备方法和用电装置 - Google Patents

二次电池及其制备方法和用电装置 Download PDF

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Publication number
WO2024082264A1
WO2024082264A1 PCT/CN2022/126669 CN2022126669W WO2024082264A1 WO 2024082264 A1 WO2024082264 A1 WO 2024082264A1 CN 2022126669 W CN2022126669 W CN 2022126669W WO 2024082264 A1 WO2024082264 A1 WO 2024082264A1
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Prior art keywords
carbon black
conductive carbon
positive electrode
optionally
secondary battery
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PCT/CN2022/126669
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English (en)
French (fr)
Inventor
庄恒旭
吴燕英
王星会
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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Priority to KR1020247040664A priority Critical patent/KR20250007644A/ko
Priority to PCT/CN2022/126669 priority patent/WO2024082264A1/zh
Priority to JP2024569551A priority patent/JP7842903B2/ja
Priority to EP22962448.1A priority patent/EP4539185A4/en
Priority to CN202280088214.1A priority patent/CN118556320A/zh
Publication of WO2024082264A1 publication Critical patent/WO2024082264A1/zh
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/30—Batteries in portable systems, e.g. mobile phone, laptop
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the technical field of secondary batteries, and in particular to a secondary battery and a preparation method and an electrical device thereof.
  • Secondary batteries usually include positive and negative electrode sheets, electrolytes, and separators disposed between the positive and negative electrode sheets.
  • a conductive agent is usually added to the electrode sheets to make them meet a certain conductivity.
  • the addition of the conductive agent reduces the proportion of active materials in the electrode sheets, resulting in a decrease in energy density.
  • the present application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery that aims to achieve lower internal resistance while improving the energy density and cycle performance of the battery.
  • the first aspect of the present application provides a secondary battery, comprising a positive electrode plate, wherein the positive electrode plate comprises a positive electrode collector and a positive electrode film layer arranged on at least one surface of the positive electrode collector, wherein the positive electrode film layer comprises a conductive agent, wherein the conductive agent comprises a first conductive carbon black and a second conductive carbon black, wherein the specific surface area of the second conductive carbon black is greater than the specific surface area of the first conductive carbon black.
  • the internal resistance and cycle performance of the battery can be improved without increasing the amount of conductive agent.
  • the specific surface area of the first conductive carbon black is denoted as S1
  • the specific surface area of the second conductive carbon black is denoted as S2, then S2/S1 ⁇ 4, optionally, 5 ⁇ S2/S1 ⁇ 17.
  • the specific surface area ratio of the first conductive carbon black to the second conductive carbon black within the above range, the internal resistance and cycle performance of the battery can be improved better.
  • the specific surface area of the first conductive carbon black is ⁇ 140 m 2 /g, and may be 50 m 2 /g-130 m 2 /g; and/or,
  • the specific surface area of the second conductive carbon black is 200 m 2 /g to 1200 m 2 /g, and can be 300 m 2 /g to 1000 m 2 /g.
  • the conductive agent satisfies at least one of the following (1)-(4):
  • the mass proportion of the conductive agent in the positive electrode film layer is ⁇ 5%, which can be 0.8%-3.0%;
  • the mass proportion of the first conductive carbon black in the positive electrode film layer is ⁇ 4.2%, and can be optionally 0.4%-3%;
  • the mass proportion of the second conductive carbon black in the positive electrode film layer is ⁇ 2.5%, and can be optionally 0.1%-2%;
  • the mass ratio of the first conductive carbon black to the second conductive carbon black is (0.4-8):1, and can be optionally (0.5-7):1.
  • the oil absorption value of the first conductive carbon black is ⁇ 260, and/or the oil absorption value of the second conductive carbon black is ⁇ 300.
  • the water content of the first conductive carbon black is ⁇ 5000 ppm, and/or the water content of the second conductive carbon black is ⁇ 10000 ppm.
  • the conductive agent further comprises carbon nanotubes
  • the diameter of the carbon nanotube is 4-10 nm
  • the carbon nanotubes have a tube length of 0.3-50 ⁇ m;
  • the aspect ratio of the carbon nanotube is 50-12500;
  • the carbon nanotubes include multi-walled carbon nanotubes
  • the mass proportion of the carbon nanotubes in the positive electrode film layer is ⁇ 1.2%
  • the mass ratio of the second conductive carbon black to the carbon nanotubes is (0.1-10):1.
  • the first conductive carbon black and the second conductive carbon black are each independently selected from at least one of furnace black, acetylene black, Super p and Ketjen black.
  • the second aspect of the present application also provides a method for preparing the secondary battery described in the first aspect of the present application, comprising preparing a positive electrode sheet by the following steps:
  • the first dispersant comprises a vinylidene fluoride polymer
  • the first dispersant includes a first dispersant compound obtained by copolymerizing vinylidene fluoride homopolymer or vinylidene fluoride with vinylidene fluoride containing active groups, wherein the active groups include at least one of carboxyl, epoxy, hydroxyl or sulfonic acid groups, optionally carboxyl or epoxy.
  • the second dispersant is selected from ethylene and maleic anhydride copolymer or styrene and maleic anhydride copolymer.
  • the ratio of the sum of the mass of the first conductive carbon black and the second conductive carbon black to the mass of the first dispersant is (0.4-2.0):1, and can be optionally (0.75-1.8):1.
  • the ratio of the sum of the mass of the first conductive carbon black and the second conductive carbon black to the mass of the second dispersant is (8-30):1, and can be optionally (9-25):1.
  • step S3 a second dispersant and carbon nanotubes (CNTs) are added to slurry 1, and slurry 2 is obtained after mixing evenly.
  • CNTs carbon nanotubes
  • the content a of the first conductive carbon black, the content b of the second conductive carbon black and the content c of the carbon nanotubes satisfy: 0.2 ⁇ ((a+b) ⁇ c)/(a ⁇ b) ⁇ 10, optionally 0.4 ⁇ ((a+b) ⁇ c)/(a ⁇ b) ⁇ 6, wherein a, b and c are respectively based on the total weight of the conductive paste on a dry weight basis.
  • the third aspect of the present application provides an electrical device, comprising at least one selected from the secondary battery of the first aspect of the present application and the secondary battery prepared by the method of the second aspect of the present application.
  • the electric device of the present application includes the secondary battery provided by the present application, it has at least the same advantages as the secondary battery.
  • FIG. 1 is a schematic diagram of a battery cell according to an embodiment of the present application.
  • FIG. 2 is an exploded view of the battery cell according to the embodiment of the present application shown in FIG. 1 .
  • FIG. 3 is a schematic diagram of a battery module according to an embodiment of the present application.
  • FIG. 4 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.
  • FIG. 6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.
  • Scope disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range.
  • the scope limited in this way can be to include end value or not include end value, and can be combined arbitrarily, that is, any lower limit can form a scope with any upper limit combination.
  • any lower limit can form a scope with any upper limit combination.
  • the scope of 60-120 and 80-110 is listed for a particular parameter, it is understood that the scope of 60-110 and 80-120 is also expected.
  • the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 are listed the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.
  • a-b represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers.
  • the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations.
  • a parameter is expressed as an integer ⁇ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • the method may further include step (c), which means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.
  • 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).
  • more conductive paste needs to be used which reduces the proportion of active materials in the positive electrode film layer, which is not conducive to improving the energy density.
  • those skilled in the art usually add graphene with higher conductivity to the conductive paste.
  • graphene is expensive and does not have a cost advantage.
  • the inventors found that by using two types of first conductive carbon black and second conductive carbon black with different specific surface areas to prepare positive electrode active slurry, the internal resistance of the secondary battery can be effectively improved, the amount of conductive agent can be reduced, and the proportion of active materials can be increased, thereby improving the energy density.
  • carbon black is cheap, has cost advantages, and has better dispersibility.
  • the internal resistance of the secondary battery can be further improved, which is conducive to improving the energy density of the corresponding secondary battery and improving the cycle performance.
  • the first aspect of the present application provides a secondary battery, comprising a positive electrode plate, the positive electrode plate comprising a positive electrode collector and a positive electrode film layer arranged on at least one surface of the positive electrode collector, the positive electrode film layer comprising a conductive agent, the conductive agent comprising a first conductive carbon black and a second conductive carbon black, the specific surface area of the second conductive carbon black being greater than the specific surface area of the first conductive carbon black.
  • the internal resistance and cycle performance of the battery can be improved without increasing the amount of conductive agent.
  • the specific surface area of the first conductive carbon black is denoted as S1
  • the specific surface area of the second conductive carbon black is denoted as S2, then S2/S1 ⁇ 4, optionally, 5 ⁇ S2/S1 ⁇ 17.
  • the specific surface area ratio of the first conductive carbon black to the second conductive carbon black within the above range, the internal resistance and cycle performance of the battery can be improved better.
  • the specific surface area of the first conductive carbon black is ⁇ 140 m 2 /g, and may be 50 m 2 /g-130 m 2 /g, and may be 55 m 2 /g-80 m 2 /g; and/or,
  • the specific surface area of the second conductive carbon black is 200 m 2 /g-1200 m 2 /g, optionally 300 m 2 /g-1000 m 2 /g, further optionally 400 m 2 /g-900 m 2 /g, further optionally 500 m 2 /g-800 m 2 /g.
  • the conductive agent satisfies at least one of the following (1)-(4):
  • the mass proportion of the conductive agent in the positive electrode film layer is ⁇ 5%, which may be 0.8%-3.0%, or 0.9%-2.5%;
  • the mass proportion of the first conductive carbon black in the positive electrode film layer is ⁇ 4.2%, which may be 0.4%-3%, or 0.5%-2.5%;
  • the mass proportion of the second conductive carbon black in the positive electrode film layer is ⁇ 2.5%, which may be 0.1%-2%, or 0.4%-1%;
  • the mass ratio of the first conductive carbon black to the second conductive carbon black is (0.4-8):1, and can be optionally (0.5-7):1.
  • the oil absorption value of the first conductive carbon black is ⁇ 260, and/or the oil absorption value of the second conductive carbon black is ⁇ 300.
  • oil absorption value is well known in the art and can be measured using instruments and methods known in the art.
  • oil absorption value test standard ASTM D2414 can be referred to and measured using an oil absorption value tester (such as HiTEC Keithley SourceMeter).
  • the water content of the first conductive carbon black is ⁇ 5000 ppm, and/or the water content of the second conductive carbon black is ⁇ 10000 ppm.
  • the water content can be measured using instruments and methods known in the art. For example, it can be measured by referring to the GB/T 11133-2015 Karl Fischer method and using a coulometric water titrator (such as 774 Test method).
  • the conductive agent further comprises carbon nanotubes
  • the diameter of the carbon nanotube is 4-10 nm, and further optionally 5-8 nm;
  • the carbon nanotube has a tube length of 0.3-50 ⁇ m, and further optionally 0.8-40 ⁇ m;
  • the aspect ratio of the carbon nanotube is 50-12500, and further optionally 100-8000;
  • the carbon nanotubes include multi-walled carbon nanotubes
  • the mass proportion of the carbon nanotubes in the positive electrode film layer is ⁇ 1.2%, optionally ⁇ 0.6%;
  • the mass ratio of the second conductive carbon black to the carbon nanotubes is (0.1-10):1, optionally (0.2-6):1, and further optionally (0.3-4):1.
  • the diameter of the carbon nanotubes is measured by GBT 26826-2011, and the length of the carbon nanotubes is measured by the scanning electron microscopy statistical method.
  • the first conductive carbon black and the second conductive carbon black are each independently selected from at least one of furnace black, acetylene black, Super p and Ketjen black;
  • the first conductive carbon black and the second conductive carbon black may be the same type of carbon black, or different types of carbon black, and may be the same type of carbon black.
  • the positive electrode film layer further includes a dispersant, and the dispersant includes a first dispersant and a second dispersant.
  • the first dispersant includes a vinylidene fluoride polymer
  • the first dispersant includes a first dispersant compound obtained by copolymerizing vinylidene fluoride homopolymer or vinylidene fluoride with vinylidene fluoride containing active groups, wherein the active groups include at least one of carboxyl, epoxy, hydroxyl or sulfonic acid groups, and may be carboxyl or epoxy.
  • the number average molecular weight of the first dispersant is from 100,000 to 5,000,000, and optionally from 500,000 to 3,000,000.
  • the second dispersant is selected from ethylene and maleic anhydride copolymers, styrene and maleic anhydride copolymers, and optionally has a number average molecular weight of 10,000 to 200,000, and optionally 50,000 to 150,000.
  • the number average molecular weight is determined by gel permeation chromatography (GPC) in accordance with GB/T 21863-2008 "Gel Permeation Chromatography (GPC) Using Tetrahydrofuran as Eluent” (equivalent to the German standard DIN 55672-1:2007 “Gel Permeation Chromatography (GPC) Part 1: Using Tetrahydrofuran (THF) as Elution Solvent”).
  • 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.
  • the positive electrode current collector has two surfaces opposite to each other in its own 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 current collector may be a metal foil or a composite current collector.
  • aluminum foil may be used as the metal foil.
  • the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base.
  • the composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the positive electrode material is a compound that can reversibly insert and deinsert Li + .
  • the positive electrode active material may be a positive electrode active material for a battery known in the art.
  • the positive electrode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds.
  • the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.
  • lithium transition metal oxides may include, but are not limited to , lithium cobalt oxide (such as LiCoO2 ), lithium nickel oxide (such as LiNiO2 ), lithium manganese oxide (such as LiMnO2 , LiMn2O4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi1 / 3Co1 / 3Mn1 / 3O2 (also referred to as NCM333 ), LiNi0.5Co0.2Mn0.3O2 (also referred to as NCM523 ) , LiNi0.5Co0.25Mn0.25O2 (also referred to as NCM211 ) , LiNi0.6Co0.2Mn0.2O2 (also referred to as NCM622 ), LiNi0.8Co0.1Mn0.1O2 (also referred to as NCM811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05
  • lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO 4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.
  • lithium iron phosphate such as LiFePO 4 (also referred to as LFP)
  • LiMnPO 4 lithium manganese phosphate
  • LiMnPO 4 lithium manganese phosphate
  • LiMnPO 4 lithium manganese phosphate and carbon
  • the positive electrode active material is optionally a lithium-containing composite oxide with a layered structure or a spinel structure, such as a lithium manganese nickel composite oxide represented by LiCoO2 , LiMn2O4 , LiNiO2 , LiNi1 /2Mn1 /2O2 , etc. , a lithium manganese nickel cobalt composite oxide represented by LiNi1 / 3Mn1 /3Co1 / 3O2 , LiNi0.6Mn0.2Co0.2O2 , etc.
  • a lithium manganese nickel composite oxide represented by LiCoO2 , LiMn2O4 , LiNiO2 , LiNi1 /2Mn1 /2O2 , etc.
  • a lithium manganese nickel cobalt composite oxide represented by LiNi1 / 3Mn1 /3Co1 / 3O2 , LiNi0.6Mn0.2Co0.2O2 , etc.
  • lithium-containing composite oxide such as LiNi1 -xyzCoxAlyMgzO2 (wherein, 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 0.1 , 0 ⁇ z ⁇ 0.1, 0 ⁇ 1 - xyz ⁇ 1 ).
  • lithium-containing composite oxides in which part of the constituent elements in the above-mentioned lithium-containing composite oxides are replaced by additive elements such as Ge, Ti, Zr, Mg, Al, Mo, Sn, etc. are also included in the scope of the present application.
  • positive electrode active materials In addition to the above-mentioned positive electrode active materials, other conventional materials that can be used as positive electrode active materials for batteries can also be used. These positive electrode active materials can be used alone or in combination of two or more. For example, by using a lithium-containing composite oxide with a layered structure and a lithium-containing composite oxide with a spinel structure at the same time, it is possible to seek to achieve both high capacity and improved safety.
  • the positive electrode active material includes lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, lithium cobalt oxide, lithium nickel cobalt oxide, lithium nickel manganese oxide, lithium iron phosphate and lithium titanate, and their derivatives or combinations thereof in which each element position is substituted or doped with a transition metal or a non-transition metal.
  • the mass proportion of the positive electrode active material in the positive electrode film layer is 90% to 97.1%, and optionally 95% to 7.1%.
  • the positive electrode film layer may also optionally include a binder, such as polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene oxide, and other binders commonly used in the battery field.
  • a binder such as polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene oxide, and other binders commonly used in the battery field.
  • the dry weight of the binder accounts for 0.1% to 3.5% of the total weight of the positive electrode film layer on a dry weight basis, and may be 0.5% to 2.5%.
  • the second aspect of the present application also provides a method for preparing the secondary battery described in the first aspect of the present application, comprising preparing a positive electrode sheet by the following steps:
  • the first dispersant includes a vinylidene fluoride polymer
  • the first dispersant includes a first dispersant compound obtained by copolymerizing vinylidene fluoride homopolymer or vinylidene fluoride with vinylidene fluoride containing active groups, wherein the active groups include at least one of carboxyl, epoxy, hydroxyl or sulfonic acid groups, and may be carboxyl or epoxy.
  • the second dispersant is selected from ethylene and maleic anhydride copolymers or styrene and maleic anhydride copolymers.
  • the ratio of the sum of the mass of the first conductive carbon black and the second conductive carbon black to the mass of the first dispersant is (0.4-2.0):1, and can be optionally (0.75-1.8):1.
  • the ratio of the sum of the mass of the first conductive carbon black and the second conductive carbon black to the mass of the second dispersant is (8-30):1, and can be optionally (9-25):1.
  • the respective mixing can be performed by the following operations: the stirring line speed is 5 m/s to 25 m/s, optionally 8 m/s to 20 m/s, and the stirring time is 10 minutes to 60 minutes, optionally 13 minutes to 40 minutes.
  • the solvent is selected from at least one of N-methylpyrrolidone (NMP), N,N-dimethylacetamide, and dimethyl sulfoxide.
  • step S3 a second dispersant and carbon nanotubes (CNTs) are added to slurry 1 and mixed evenly to obtain slurry 2.
  • CNTs carbon nanotubes
  • the content a of the first conductive carbon black, the content b of the second conductive carbon black, and the content c of the carbon nanotubes satisfy: 0.2 ⁇ ((a+b) ⁇ c)/(a ⁇ b) ⁇ 10, optionally 0.4 ⁇ ((a+b) ⁇ c)/(a ⁇ b) ⁇ 6, wherein a, b and c are respectively based on the total weight of the conductive paste on a dry weight basis.
  • the secondary battery of the present application is described below with reference to the accompanying drawings as appropriate.
  • the secondary battery may be in the form of a battery cell, a battery module, or a battery pack.
  • a battery cell is provided.
  • a battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator.
  • active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet.
  • the electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet.
  • the separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.
  • the second aspect of the present application provides a secondary battery, which includes the separator described in the first aspect of the present application.
  • the secondary battery also includes a positive electrode sheet, a negative electrode sheet and an electrolyte.
  • the present application can also be used in lithium metal batteries to replace the traditional separator.
  • the negative electrode can be lithium metal or lithium alloy, or there is no negative electrode.
  • the corresponding positive electrode material is as described above. If it is a lithium metal battery without a negative electrode, the positive electrode material needs to provide a lithium source.
  • the preparation of the secondary battery can be carried out by methods commonly used in the art.
  • the positive electrode sheet, the negative electrode sheet and the isolation membrane can be made into an electrode assembly through a winding process or a lamination process, and then the electrolyte is injected into the electrode assembly and sealed to produce a secondary battery.
  • the secondary battery described in the present application includes a button battery.
  • the materials of the positive electrode sheet and the negative electrode sheet may be the same or different.
  • the button battery can be prepared by a method commonly used by those skilled in the art.
  • the positive electrode sheet, the separator and the negative electrode sheet can be assembled into an electrode assembly, and then the electrolyte is injected into the electrode assembly and sealed to prepare a button battery.
  • 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.
  • the negative electrode current collector has two surfaces opposite to each other in its own 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 current collector may be a metal foil or a composite current collector.
  • the metal foil copper foil may be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate.
  • the composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative electrode material is a compound capable of inserting and deinserting lithium metal or lithium.
  • the negative electrode active material may be a negative electrode active material for a battery known in the art.
  • various materials such as alloys or oxides of aluminum, silicon, tin, etc., and carbon materials may be used as negative electrode active materials.
  • oxides may include titanium dioxide, etc.
  • carbon materials may include graphite, pyrolytic carbon, coke, glassy carbon, sintered bodies of organic polymer compounds, mesophase carbon microbeads, etc.
  • the tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys.
  • the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.
  • the dry weight of the negative electrode active material accounts for 75% to 99%, optionally 80% to 97%, of the total weight of the negative electrode film layer on a dry weight basis.
  • the negative electrode film layer may also optionally include a binder, such as polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene oxide, and other binders commonly used in the battery field.
  • a binder such as polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene oxide, and other binders commonly used in the battery field.
  • the dry weight of the binder accounts for 0.1-3.5% of the total weight of the negative electrode film layer on a dry weight basis, and optionally 0.5-2.5%.
  • the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • a conductive agent which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the dry weight of the conductive agent accounts for 0.05-5%, optionally 0.5-3%, of the total weight of the negative electrode film layer on a dry weight basis.
  • the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).
  • a thickener eg, sodium carboxymethyl cellulose (CMC-Na)
  • the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.
  • a solvent such as deionized water
  • the electrolyte plays the role of conducting ions between the positive electrode and the negative electrode.
  • the present application has no specific restrictions on the type of electrolyte, which can be selected according to needs.
  • the electrolyte can be liquid, gel or all-solid.
  • the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.
  • a non-aqueous solvent (organic solvent) is used as the non-aqueous electrolyte.
  • the non-aqueous solvent includes carbonates, ethers, and the like.
  • carbonates include cyclic carbonates and chain carbonates.
  • Cyclic carbonates can include ethylene carbonate, propylene carbonate, butylene carbonate, gamma-butyrolactone, thioesters (ethylene glycol sulfide) and the like.
  • Chain carbonates can include low-viscosity polar chain carbonates and aliphatic branched-chain carbonate compounds represented by dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and the like.
  • a mixed solvent of cyclic carbonates (particularly ethylene carbonate) and chain carbonates is particularly preferred.
  • ethers examples include tetraethylene glycol dimethyl ether (TEGDME), ethylene glycol dimethyl ether (DME), and 1,3-dioxolane (DOL).
  • TEGDME tetraethylene glycol dimethyl ether
  • DME ethylene glycol dimethyl ether
  • DOL 1,3-dioxolane
  • non-aqueous solvents such as chain alkyl esters such as methyl propionate, chain triesters such as trimethyl phosphate, nitrile solvents such as 3-methoxypropionitrile, and branched compounds with ether bonds represented by dendrimers can also be used.
  • fluorinated solvents can also be used.
  • fluorinated solvent examples include H( CF2 ) 2OCH3 , C4F9OCH3 , H( CF2 ) 2OCH2CH3 , H ( CF2 ) 2OCH2CF3 , H ( CF2 ) 2CH2O ( CF2 ) 2H , and CF3CHFCF2OCH3 , CF3CHFCF2OCH2CH3 , and CF3CHFCF2OCH3 .
  • (perfluoroalkyl) alkyl ethers of a straight-chain structure such as 2-trifluoromethyl hexafluoropropyl methyl ether, 2-trifluoromethyl hexafluoropropyl ethyl ether, 2-trifluoromethyl hexafluoropropyl propyl ether, 3-trifluoromethyl octafluorobutyl methyl ether, 3-trifluoromethyl octafluorobutyl ethyl ether, 3-trifluoromethyl octafluorobutyl propyl ether, 4-trifluoromethyl decafluoropentyl methyl ether, 4-trifluoromethyl decafluoropentyl ethyl ether, 4-trifluoromethyl decafluoropentyl propyl ether, 5-trifluoromethyl dodecafluorohexyl methyl ether, 5-trifluoromethyl
  • lithium salts such as lithium perchlorates, organoboron lithium salts, lithium salts of fluorine-containing compounds, and lithium imide salts are preferred.
  • electrolyte salts examples include LiClO 4 , LiPF 6 , LiBF 4 , LiAsF 6 , LiSbF 6 , LiCF 3 SO 3 , LiCF 3 CO 2 , LiC 2 F 4 (SO 3 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiC(CF 3 SO 2 ) 3 , LiC n F 2n+1 SO 3 (n ⁇ 2), and LiN(R f OSO 2 ) 2 (wherein R f is a fluoroalkyl group).
  • fluorine-containing organic lithium salts are particularly preferred. Fluorine-containing organic lithium salts are easily soluble in non-aqueous electrolytes because they have large anionic properties and are easily separated into ions.
  • the concentration of the electrolyte lithium salt in the non-aqueous electrolyte is, for example, 0.3 mol/L (mole/liter) or more, preferably 0.7 mol/L or more; it may be 1.7 mol/L or less, more preferably 1.2 mol/L or less.
  • concentration of the electrolyte lithium salt is too low, the ion conductivity is too low, and when it is too high, there is a concern that the electrolyte salt will not be completely dissolved and will precipitate.
  • the electrolyte may further include additives, which are not particularly limited in this application.
  • the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.
  • the battery cell further includes a separator.
  • the present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation.
  • the materials of each layer can be the same or different, without particular limitation.
  • the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.
  • the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the battery cell may also be a soft package, such as a bag-type soft package.
  • the material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.
  • FIG1 is a battery cell 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 can be covered on the opening to close the receiving cavity.
  • the positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process 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 battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • battery cells may be assembled into a battery module.
  • the number of battery cells contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.
  • FIG3 is a battery module 3 as an example.
  • a plurality of battery cells 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 battery cells 5 may be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.
  • the battery cells can be assembled into a battery pack.
  • the battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.
  • FIG4 and FIG5 are battery packs 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, and the upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery modules 4.
  • the plurality of battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides an electric device, the electric device includes the secondary battery provided in the present application.
  • the secondary battery 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 may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.
  • a secondary battery can be selected according to its usage requirements.
  • Fig. 6 is an example of an electric device.
  • 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 device may be a mobile phone, a tablet computer, a notebook computer, etc.
  • the device is usually required to be light and thin, and a battery cell may be used as a power source.
  • the first conductive carbon black (Super P), the second conductive carbon black (Ketjen black) and the first dispersant (PVDF 5130) were dry-mixed at a mass ratio of 3:1:3, and dispersed in a stirring tank at a linear speed of 10 m/s for 15 min; wherein the specific surface area SSA (i.e., S1) of the first conductive carbon black is 60 m 2 /g, the specific surface area SSA (i.e., S2) of the second conductive carbon black is 600 m 2 /g, and S2/S1 is 10;
  • the obtained product was added into NMP solvent and dispersed at a linear speed of 15 m/s for 30 min to obtain slurry 1 with a solid content of 10.5%;
  • the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) was added to the above mixture and mixed continuously to obtain a positive electrode active slurry.
  • the added mass ratio of the positive electrode active material was 96.3%, based on the weight of the dried positive electrode film layer.
  • the positive electrode active slurry is coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through drying, cold pressing, slitting, cutting and other processes.
  • the surface density of the positive electrode sheet is 300 mg/mm 2 and the compaction density is 3.3 g/cm 3 .
  • the negative electrode active material artificial graphite, conductive agent carbon black (Super P), binder styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) were mixed evenly in a proper amount of solvent deionized water at a mass ratio of 96:1:1.5:1.5 to obtain a negative electrode slurry; the negative electrode slurry was coated on the negative electrode current collector copper foil, and the negative electrode sheet was obtained through drying, cold pressing, striping and cutting processes.
  • the surface density of the negative electrode sheet is 185mg/ mm2
  • the compaction density is 1.6g/ cm3 .
  • 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.
  • a 13 ⁇ m thick polyethylene (PE) porous polymer film was used as the isolation membrane.
  • 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 with a group margin of 89%.
  • the preparation method of the secondary battery is similar to that of Example 1, wherein only the conductive agent in the positive electrode slurry is changed and carbon nanotubes (CNT) are optionally added, as shown in Table 1 for details.
  • CNT carbon nanotubes
  • the preparation method of the secondary battery is similar to that of Example 1, except that only the first conductive carbon black is used when preparing the positive electrode slurry.
  • the preparation method of the secondary battery is similar to that of Example 1, except that only the second conductive carbon black is used when preparing the positive electrode slurry.
  • the specific surface area test was carried out according to GB/T 19587-2017, using the Tri-Star 3020 specific surface area pore size analyzer from Micromeritics, USA, to perform nitrogen adsorption specific surface area analysis test, and the specific surface area of the material was calculated using the BET (Brunauer Emmett Teller) method. The test results are shown in Table 1.
  • the battery is charged to 4.25V at a constant current of 0.5C, and then charged to a current of 0.05C at a constant voltage.
  • the battery is then discharged at a constant current of 0.5C for 30 minutes to adjust the battery to 50% SOC (State of Charge).
  • SOC State of Charge
  • the battery voltage at this time is recorded as U1.
  • the battery is then discharged at a constant current of 4C for 30 seconds, with a sampling point of 0.1 seconds, and the voltage at the end of discharge is recorded as U2.
  • the secondary batteries prepared in the embodiments and comparative examples were charged at a constant current of 1C to a charge cut-off voltage of 4.25V, then charged at a constant voltage to a current of ⁇ 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to a discharge cut-off voltage of 2.8V, left to stand for 5 minutes.
  • This is a charge and discharge cycle.
  • the battery was subjected to a cyclic charge and discharge test according to this method until the battery capacity decayed to 80%. The number of cycles at this time was recorded, which was the cycle life of the battery at 25°C.

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Abstract

提供了一种二次电池，包括正极极片，正极极片包括正极集流体和设置在正极集流体至少一个表面上的正极膜层，正极膜层包括导电剂，其中导电剂包括第一导电炭黑和第二导电炭黑，第二导电炭黑的比表面积大于第一导电炭黑的比表面积。此外，还提供了二次电池的制备方法和用电装置。二次电池实现了较低的内阻，同时改善了电池的能量密度和循环性能。

Description

二次电池及其制备方法和用电装置 技术领域
本申请涉及二次电池技术领域，尤其涉及一种二次电池及其制备方法和用电装置。
背景技术
近年来，二次电池在风力、火力、水力、太阳能电站等储能系统以及电动工具、电动自行车等多个领域得到了非常广泛的应用。
二次电池通常包括正、负极极片、电解液和设置在正负极极片之间的隔离膜。在制备极片时，为使极片满足一定的电导率，通常会向极片中添加导电剂。然而，导电剂的加入降低了活性材料在极片中的占比，从而导致能量密度下降。
因此，如何开发出一种二次电池，其在实现较低内阻的同时，还能实现较高的能量密度和电学性能仍是研发人员亟需解决的一项课题。
发明内容
本申请是鉴于上述课题而进行的，其目的在于，提供一种二次电池，旨在实现较低的内阻，同时改善电池的能量密度和循环性能。
为达到上述目的，本申请的第一方面提供了一种二次电池，包括正极极片，所述正极极片包括正极集流体和设置在所述正极集流体至少一个表面上的正极膜层，所述正极膜层包括导电剂，所述导电剂包括第一导电炭黑和第二导电炭黑，所述第二导电炭黑的比表面积大于所述第一导电炭黑的比表面积。
通过使用两种比表面积不同的导电炭黑，可以在不增加导电剂用量的情况下改善电池的内阻和循环性能。
在任意实施方式中，所述第一导电炭黑的比表面积记为S1，所述第二导电炭黑的比表面积记为S2，则S2/S1≥4，可选地，5≤S2/S1≤ 17。
通过将第一导电炭黑与第二导电炭黑的比表面积之比设定在上述范围内，可以更好地实现电池的内阻和循环性能的改善。
在任意实施方式中，所述第一导电炭黑的比表面积≤140m 2/g，可选为50m 2/g-130m 2/g；和/或，
所述第二导电炭黑的比表面积为200m 2/g至1200m 2/g，可选为300m 2/g至1000m 2/g。
在任意实施方式中，所述导电剂满足下述(1)-(4)中的至少一种：
(1)所述导电剂在所述正极膜层中的质量占比≤5％，可选为0.8％-3.0％；
(2)所述第一导电炭黑在所述正极膜层中的质量占比≤4.2％，可选为0.4％-3％；
(3)所述第二导电炭黑在所述正极膜层中的质量占比≤2.5％，可选为0.1％-2％；
(4)所述第一导电炭黑与所述第二导电炭黑的质量之比为(0.4-8):1，可选为(0.5-7):1。
在任意实施方式中，所述第一导电炭黑的吸油值≤260，和/或，所述第二导电炭黑的吸油值≤300。
在任意实施方式中，所述第一导电炭黑的水含量≤5000ppm，和/或，所述第二导电炭黑的水含量≤10000ppm。
在任意实施方式中，所述导电剂还包括碳纳米管；
可选地，所述碳纳米管的管径为4-10nm；
可选地，所述碳纳米管的管长为0.3-50μm；
可选地，所述碳纳米管的长径比为50-12500；
可选地，所述碳纳米管包括多壁碳纳米管；
可选地，所述碳纳米管在所述正极膜层中的质量占比≤1.2％；
可选地，所述第二导电碳黑与所述碳纳米管的质量之比为(0.1-10):1。
在任意实施方式中，所述第一导电炭黑和所述第二导电炭黑各自独立地选自炉法炭黑、乙炔黑、Super p和科琴黑中的至少一种。
本申请的第二方面还提供一种制备本申请第一方面所述的二次电池的方法，包括采用以下步骤制备正极极片：
S1，将第一导电碳、第二导电碳和第一分散剂在搅拌罐中进行干混，得到混合物粉料，其中所述第二导电炭黑的比表面积大于所述第一导电炭黑的比表面积；
S2，在所述混合物粉料中加入溶剂，混合均匀后得到浆料1，
S3，将第二分散剂加入到浆料1中，混合均匀后得到浆料2；
S4，将正极活性材料加入到所述浆料2中并混合均匀，得到正极材料浆料；
S5，将所述正极材料浆料涂覆在正极集流体的至少一个表面上，干燥后形成正极膜层。
在任意实施方式中，所述第一分散剂包括偏氟乙烯基聚合物；
可选地，所述第一分散剂包括偏氟乙烯均聚物或偏氟乙烯与含活性基团的偏氟乙烯共聚得到的第一分散剂化合物，其中所述活性基团包括羧基、环氧基、羟基或磺酸基中的至少一种，可选地为羧基或环氧基。
在任意实施方式中，所述第二分散剂选自乙烯与马来酸酐共聚物或苯乙烯与马来酸酐共聚物。
在任意实施方式中，所述第一导电炭黑与所述第二导电炭黑的质量之和与所述第一分散剂的质量之比为(0.4-2.0):1，可选为(0.75-1.8):1。
在任意实施方式中，所述第一导电炭黑与所述第二导电炭黑的质量之和与所述第二分散剂的质量之比为(8-30):1，可选为(9-25):1。
在任意实施方式中，在S3步骤中，将第二分散剂和碳纳米管(CNT)加入到浆料1中，混合均匀后得到浆料2。
在任意实施方式中，所述第一导电炭黑的含量a、所述第二导电炭黑的含量b与所述碳纳米管的含量c满足：0.2≤((a+b)×c)/(a×b)≤10，可选地0.4≤((a+b)×c)/(a×b)≤6，其中所述a、b和c分别基于所述导电浆料以干重计的总重量计。
本申请的第三方面提供一种用电装置，包括选自本申请的第一方面的二次电池和由本申请第二方面的方法制备的二次电池中的至少一种。
由于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
图1是本申请一实施方式的电池单体的示意图。
图2是图1所示的本申请一实施方式的电池单体的分解图。
图3是本申请一实施方式的电池模块的示意图。
图4是本申请一实施方式的电池包的示意图。
图5是图4所示的本申请一实施方式的电池包的分解图。
图6是本申请一实施方式的二次电池用作电源的用电装置的示意图。
附图标记说明：
1电池包；2上箱体；3下箱体；4电池模块；5电池单体；51壳体；52电极组件；53顶盖组件
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二次电池及其制备方法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。
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。
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)。
发明人在研究过程中发现，现有技术中使用的导电浆料的导电性能较差，为满足极片对导电性能的要求，需使用较多的导电浆料，这减少了活性材料在正极膜层中的占比，从而不利于提高能量密度。为此，本领域技术人员通常会向导电浆料中加入电导率更高的石墨烯。然而，石 墨烯价格昂贵，不具有成本优势。
发明人在进行大量研究后以外发现，通过使用两种比表面积不同的第一导电炭黑和第二导电炭黑来制备正极活性浆料，可有效地改善二次电池的内阻，降低导电剂的用量，提高了活性材料的占比，从而提高能量密度。同时，相对于石墨烯，炭黑价格低廉，具备成本优势，并且分散性也更好。此外，通过进一步优化体系中各物质的配比，可进一步改善二次电池的内阻，从而有利于提高相应二次电池的能量密度，改善循环性能。
为此，本申请的第一方面提供了一种二次电池，包括正极极片，所述正极极片包括正极集流体和设置在所述正极集流体至少一个表面上的正极膜层，所述正极膜层包括导电剂，所述导电剂包括第一导电炭黑和第二导电炭黑，所述第二导电炭黑的比表面积大于所述第一导电炭黑的比表面积。
通过使用两种比表面积不同的导电炭黑，可以在不增加导电剂用量的情况下改善电池的内阻和循环性能。
在一些实施方式中，所述第一导电炭黑的比表面积记为S1，所述第二导电炭黑的比表面积记为S2，则S2/S1≥4，可选地，5≤S2/S1≤17。
通过将第一导电炭黑与第二导电炭黑的比表面积之比设定在上述范围内，可以更好地实现电池的内阻和循环性能的改善。
在一些实施方式中，所述第一导电炭黑的比表面积≤140m 2/g，可选为50m 2/g-130m 2/g，进一步可选为55m 2/g-80m 2/g；和/或，
所述第二导电炭黑的比表面积200m 2/g-1200m 2/g，可选为300m 2/g-1000m 2/g，还可选为400m 2/g-900m 2/g，进一步可选为500m 2/g-800m 2/g。
在一些实施方式中，所述导电剂满足下述(1)-(4)中的至少一种：
(1)所述导电剂在所述正极膜层中的质量占比≤5％，可选为0.8％-3.0％，还可选为0.9％-2.5％；
(2)所述第一导电炭黑在所述正极膜层中的质量占比≤4.2％，可选为0.4％-3％，还可选为0.5％-2.5％；
(3)所述第二导电炭黑在所述正极膜层中的质量占比≤2.5％，可选为0.1％-2％，还可选为0.4％-1％；
(4)所述第一导电炭黑与所述第二导电炭黑的质量之比为(0.4-8):1，可选为(0.5-7):1。
在一些实施方式中，所述第一导电炭黑的吸油值≤260，和/或，所述第二导电炭黑的吸油值≤300。
吸油值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ASTM D2414吸油值测试标准，采用吸油值测试仪(例如HiTEC Keithley SourceMeter)测定。
在一些实施方式中，所述第一导电炭黑的水含量≤5000ppm，和/或，所述第二导电炭黑的水含量≤10000ppm。
水含量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 11133-2015卡尔费休法，采用库仑水分滴定仪(例如774 Test method)测定。
在一些实施方式中，所述导电剂还包括碳纳米管；
可选地，所述碳纳米管的管径为4-10nm，进一步可选为5-8nm；
可选地，所述碳纳米管的管长为0.3-50μm，进一步可选为0.8-40μm；
可选地，所述碳纳米管的长径比为50-12500，进一步可选为100-8000；
可选地，所述碳纳米管包括多壁碳纳米管；
可选地，所述碳纳米管在所述正极膜层中的质量占比≤1.2％，可选地≤0.6％；
可选地，所述第二导电碳黑与所述碳纳米管的质量之比为(0.1-10):1，可选为(0.2-6):1，还可选为(0.3-4):1。
在本申请中，碳纳米管的管径通过GBT 26826-2011测定，碳纳米管的管长通过扫描电镜统计法测定。
在一些实施方式中，所述第一导电炭黑和所述第二导电炭黑各自独立地选自炉法炭黑、乙炔黑、Super p和科琴黑中的至少一种；
可选地，所述第一导电炭黑和所述第二导电炭黑可为同一种炭黑，也可为不同种炭黑，可选为同一种炭黑。
在一些实施方式中，所述正极膜层还包括分散剂，所述分散剂包括第一分散剂和第二分散剂。
在一些实施方式中，所述第一分散剂包括偏氟乙烯基聚合物；
可选地，所述第一分散剂包括偏氟乙烯均聚物或偏氟乙烯与含活性基团的偏氟乙烯共聚得到的第一分散剂化合物，其中所述活性基团包括羧基、环氧基、羟基或磺酸基中的至少一种，可选为羧基或环氧基。
在一些实施方式中，所述第一分散剂的数均分子量为100,000至5,000,000，可选为500,000至3,000,000。
在一些实施方式中，所述第二分散剂选自乙烯与马来酸酐共聚物、苯乙烯与马来酸酐共聚物，可选地，其数均分子量为10,000至200,000，可选为50,000至150,000。
在本申请中，数均分子量采用凝胶渗透色谱(GPC)法，按照GB/T 21863-2008《凝胶渗透色谱法(GPC)用四氢呋喃做淋洗液》测定(等同采用德国标准DIN 55672-1：2007《凝胶渗透色谱法(GPC)第1部分：用四氢呋喃(THF)作洗脱溶剂》)。
在本申请中，正极极片包括正极集流体以及设置在正极集流体至少一个表面上的正极膜层。作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极膜层设置在正极集流体相对的两个表面的其中任意一者或两者上。
在一些实施方式中，所述正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将金属材料(铝、铝合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(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)、聚乙烯(PE)等的 基材)上而形成。
在本申请中，正极材料是能可逆地嵌入与脱嵌Li +的化合物。
在一些实施方式中，正极活性材料可采用本领域公知的用于电池的正极活性材料。作为示例，正极活性材料可包括以下材料中的至少一种：橄榄石结构的含锂磷酸盐、锂过渡金属氧化物及其各自的改性化合物。但本申请并不限定于这些材料，还可以使用其他可被用作电池正极活性材料的传统材料。这些正极活性材料可以仅单独使用一种，也可以将两种以上组合使用。其中，锂过渡金属氧化物的示例可包括但不限于锂钴氧化物(如LiCoO 2)、锂镍氧化物(如LiNiO 2)、锂锰氧化物(如LiMnO 2、LiMn 2O 4)、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(如LiNi 1/3Co 1/3Mn 1/3O 2(也可以简称为NCM 333)、LiNi 0.5Co 0.2Mn 0.3O 2(也可以简称为NCM 523)、LiNi 0.5Co 0.25Mn 0.25O 2(也可以简称为NCM 211)、LiNi 0.6Co 0.2Mn 0.2O 2(也可以简称为NCM 622)、LiNi 0.8Co 0.1Mn 0.1O 2(也可以简称为NCM 811)、锂镍钴铝氧化物(如LiNi 0.85Co 0.15Al 0.05O 2)及其改性化合物等中的至少一种。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸铁锂(如LiFePO 4(也可以简称为LFP))、磷酸铁锂与碳的复合材料、磷酸锰锂(如LiMnPO 4)、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中的至少一种。
在一些实施方式中，可选地，正极活性材料是层状结构或尖晶石状结构的含锂复合氧化物，例如以LiCoO 2、LiMn 2O 4、LiNiO 2、LiNi 1/2Mn 1/2O 2等为代表的锂锰镍复合氧化物，以LiNi l/3Mn 1/3Co 1/3O 2、LiNi 0.6Mn 0.2Co 0.2O 2等为代表的锂锰镍钴复合氧化物，或LiNi 1-x-y-zCo xAl yMg zO 2(式中，0≤x≤1、0≤y≤0.1、0≤z≤0.1、0≤1-x-y-z≤1)等含锂复合氧化物。此外，上述含锂复合氧化物中的构成元素的一部分，被Ge、Ti、Zr、Mg、Al、Mo、Sn等添加元素所取代的含锂复合氧化物等也包含在本申请的范围内。
除上述正极活性材料以外，还可以使用其他可被用作电池正极活性材料的传统材料。这些正极活性材料可以仅单独使用一种，也可以将两 种以上组合使用。例如，通过同时使用层状结构的含锂复合氧化物与尖晶石结构的含锂复合氧化物，可以谋求兼顾大容量化及安全性的提高。
在一些实施方式中，所述正极活性材料包括镍钴锰酸锂、镍钴铝酸锂、锰酸锂、钴酸锂、镍钴酸锂、镍锰酸锂、磷酸铁锂和钛酸锂及其各元素位置被过渡金属或非过渡金属取代或掺杂的衍生物或其组合。
在一些实施方式中，所述正极活性材料在所述正极膜层中的质量占比为90％至97.1％，可选95％至7.1％。
在一些实施方式中，正极膜层还可选地包括粘结剂，例如聚偏二氟乙烯、聚四氟乙烯、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、聚环氧乙烷等电池领域中通常使用的粘结剂。
在一些实施方式中，所述粘结剂的干重占正极膜层总重量以干重计的0.1％至3.5％，可选为0.5％至2.5％。
本申请的第二方面还提供一种制备本申请第一方面所述的二次电池的方法，包括采用以下步骤制备正极极片：
S1，将第一导电碳、第二导电碳和第一分散剂在搅拌罐中进行干混，得到混合物粉料，其中所述第二导电炭黑的比表面积大于所述第一导电炭黑的比表面积；
S2，在所述混合物粉料中加入溶剂，混合均匀后得到浆料1，
S3，将第二分散剂加入到浆料1中，混合均匀后得到浆料2；
S4，将正极活性材料加入到所述浆料2中并混合均匀，得到正极材料浆料；
S5，将所述正极材料浆料涂覆在正极集流体的至少一个表面上，干燥后形成正极膜层。
在一些实施方式中，所述第一分散剂包括偏氟乙烯基聚合物；
可选地，所述第一分散剂包括偏氟乙烯均聚物或偏氟乙烯与含活性基团的偏氟乙烯共聚得到的第一分散剂化合物，其中所述活性基团包括羧基、环氧基、羟基或磺酸基中的至少一种，可选为羧基或环氧基。
在一些实施方式中，所述第二分散剂选自乙烯与马来酸酐共聚物或 苯乙烯与马来酸酐共聚物。
在一些实施方式中，所述第一导电炭黑与所述第二导电炭黑的质量之和与所述第一分散剂的质量之比为(0.4-2.0):1，可选为(0.75-1.8):1。
在一些实施方式中，所述第一导电炭黑与所述第二导电炭黑的质量之和与所述第二分散剂的质量之比为(8-30):1，可选为(9-25):1。
在一些实施方式中，在步骤S1至S4中，各自的混合可采用以下操作进行：搅拌线速度为5m/s至25m/s，可选为8m/s至20m/s，搅拌小时为10分钟至60分钟，可选为13分钟至40分钟。
在一些实施方式中，所述溶剂选自N-甲基吡咯烷酮(NMP)、N,N-二甲基乙酰胺、二甲基亚砜中的至少一种。
在一些实施方式中，在S3步骤中，将第二分散剂和碳纳米管(CNT)加入到浆料1中，混合均匀后得到浆料2。
在一些实施方式中，所述第一导电炭黑的含量a、所述第二导电炭黑的含量b与所述碳纳米管的含量c满足：0.2≤((a+b)×c)/(a×b)≤10，可选地0.4≤((a+b)×c)/(a×b)≤6，其中所述a、b和c分别基于所述导电浆料以干重计的总重量计。
以下适当参照附图对本申请的二次电池进行说明。二次电池可以包括电池单体的形式，可以包括电池模块的形式，可以包括电池包的形式。
本申请的一个实施方式中，提供一种电池单体。
通常情况下，电池单体包括正极极片、负极极片、电解质和隔离膜。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。电解质在正极极片和负极极片之间起到传导离子的作用。隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使离子通过。
[二次电池]
本申请的第二方面提供一种二次电池，其包括本申请第一方面所述的隔离膜。通常，除隔离膜以外，二次电池还包括正极极片、负极极片和电解液。
特别地，本申请也可用于锂金属电池，代替传统隔离膜使用。其负极可以为锂金属或锂合金，或者无负极。相应的正极材料如上所述。若为无负极锂金属电池，则正极材料需提供锂源。
二次电池的制备可通过本领域通常使用的方法进行，例如，可将正极极片、负极极片和隔离膜通过卷绕工艺或叠片工艺制成电极组件，然后向电极组件中注入电解液并密封而制得二次电池。
需要说明的是，本申请所述二次电池包括扣式电池。当所述二次电池为扣式电池时，正极极片和负极极片的材料可以相同或不同。此外，可通过本领域技术人员通常使用的方法来制备扣式电池。作为示例，可将正极极片、隔离膜和负极极片组装成电极组件，然后向电极组件中注入电解液并密封而制得扣式电池。
下面分别对二次电池的上述部件进行说明。
[负极极片]
负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极膜层。作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极膜层设置在负极集流体相对的两个表面中的任意一者或两者上。
在一些实施方式中，所述负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(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)、聚乙烯(PE)等的基材)上而形成。
在本申请中，负极材料是能够嵌入-脱嵌锂金属、锂的化合物。
在一些实施方式中，负极活性材料可采用本领域公知的用于电池的负极活性材料。作为示例，可使用铝、硅、锡等的合金或氧化物、碳材料等各种材料作为负极活性材料。可选地，氧化物可以举出二氧化钛等， 碳材料可以举出石墨、热解碳类、焦炭类、玻璃状碳类、有机高分子化合物的烧成体、中间相碳微珠等。所述锡基材料可选自单质锡、锡氧化合物以及锡合金中的至少一种。但本申请并不限定于这些材料，还可以使用其他可被用作电池负极活性材料的传统材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
在一些实施方式中，可选地，所述负极活性材料的干重占所述负极膜层以干重计的总重量的75％至99％，可选80％至97％。
在一些实施方式中，负极膜层还可选地包括粘结剂，例如聚偏二氟乙烯、聚四氟乙烯、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、聚环氧乙烷等电池领域中通常使用的粘结剂。
在一些实施方式中，可选地，所述粘结剂的干重占负极膜层以干重计的总重量的0.1-3.5％，可选为0.5-2.5％。
在一些实施方式中，负极膜层还可选地包括导电剂。导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，可选地，所述导电剂的干重占负极膜层以干重计的总重量的0.05-5％，可选为0.5-3％。
在一些实施方式中，负极膜层还可选地包括其他助剂，例如增稠剂(如羧甲基纤维素钠(CMC-Na))等。
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组分，例如负极活性材料、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成负极浆料；将负极浆料涂覆在负极集流体上，经烘干、冷压等工序后，即可得到负极极片。
[电解质]
电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以是液态的、凝胶态的或全固态的。
在一些实施方式中，所述电解质采用电解液。所述电解液包括电解 质盐和溶剂。
在一些实施方式中，使用非水溶剂(有机溶剂)作为非水电解液。非水溶剂包括碳酸酯类、醚类等。
在一些实施方式中，碳酸酯类包括环状碳酸酯和链状碳酸酯。环状碳酸酯可以举出碳酸亚乙酯、碳酸亚丙酯、碳酸亚丁酯、γ-丁内酯、硫类酯(乙二醇硫化物)等。链状碳酸酯可以举出碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯等为代表的低粘度的极性链状碳酸酯、脂肪族支链型碳酸酯类化合物。环状碳酸酯(特别是碳酸乙烯酯)与链状碳酸酯的混合溶剂是特别优选的。
醚类可以举出二甲醚四甘醇(TEGDME)、乙二醇二甲醚(DME)、1,3-二氧戊烷(DOL)等。
另外，除上述非水溶剂外，还可以采用丙酸甲酯等链状烷基酯类、磷酸三甲酯等链状磷酸三酯；3-甲氧基丙腈等腈类溶剂；以树枝状化合物为代表的具有醚键的支链型化合物等非水溶剂(有机溶剂)。
另外，也可采用氟类溶剂。
作为氟类溶剂，例如，可以举出H(CF 2) 2OCH 3、C 4F 9OCH 3、H(CF 2) 2OCH 2CH 3、H(CF 2) 2OCH 2CF 3、H(CF 2) 2CH 2O(CF 2) 2H等、或CF 3CHFCF 2OCH 3、CF 3CHFCF 2OCH 2CH 3等直链结构的(全氟烷基)烷基醚，例如2-三氟甲基六氟丙基甲醚、2-三氟甲基六氟丙基乙醚、2-三氟甲基六氟丙基丙醚、3-三氟甲基八氟丁基甲醚、3-三氟甲基八氟丁基乙醚、3-三氟甲基八氟丁基丙醚、4-三氟甲基十氟戊基甲醚、4-三氟甲基十氟戊基乙醚、4-三氟甲基十氟戊基丙醚、5-三氟甲基十二氟己基甲醚、5-三氟甲基十二氟己基乙醚、5-三氟甲基十二氟己基丙醚、6-三氟甲基十四氟庚基甲醚、6-三氟甲基十四氟庚基乙醚、6-三氟甲基十四氟庚基丙醚、7-三氟甲基十六氟辛基甲醚、7-三氟甲基十六氟辛基乙醚、7-三氟甲基十六氟辛基丙醚等。
另外，上述异(全氟烷基)烷基醚与上述直链结构的(全氟烷基)烷基醚也可并用。
作为非水电解液中使用的电解质盐，优选锂的高氯酸盐、有机硼锂 盐、含氟化合物的锂盐、锂酰亚胺盐等锂盐。
作为这样的电解质盐的例子，例如，可以举出LiClO 4、LiPF 6、LiBF 4、LiAsF 6、LiSbF 6、LiCF 3SO 3、LiCF 3CO 2、LiC 2F 4(SO 3) 2、LiN(C 2F 5SO 2) 2、LiC(CF 3SO 2) 3、LiC nF 2n+1SO 3(n≥2)、LiN(R fOSO 2) 2(式中，R f为氟烷基)等。在这些锂盐中，含氟有机锂盐是特别优选的。含氟有机锂盐，由于阴离子性大且易分离成离子，在非水电解液中易溶解。
电解质锂盐在非水电解液中的浓度，例如为0.3mol/L(摩尔/升)以上，更可选0.7mol/L以上；可选1.7mol/L以下，更可选1.2mol/L以下。当电解质锂盐的浓度过低时，离子传导度过小，过高时，担心未能溶解完全的电解质盐析出。
在一些实施方式中，所述电解液还可选地包括添加剂，本申请不作特别限定。例如添加剂可以包括负极成膜添加剂、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、改善电池高温或低温性能的添加剂等。
[隔离膜]
在一些实施方式中，电池单体中还包括隔离膜。本申请对隔离膜的种类没有特别的限制，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多孔结构隔离膜。
在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，电池单体可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，电池单体的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。电池单体的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。
本申请对电池单体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。例如，图1是作为一个示例的方形结构的电池单体5。
在一些实施方式中，参照图2，外包装可包括壳体51和盖板53。其中，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能够盖设于所述开口，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封装于所述容纳腔内。电解液浸润于电极组件52中。电池单体5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
在一些实施方式中，电池单体可以组装成电池模块，电池模块所含电池单体的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块的应用和容量进行选择。
图3是作为一个示例的电池模块3。参照图3，在电池模块4中，多个电池单体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电池单体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，多个电池单体5容纳于该容纳空间。
在一些实施方式中，上述电池单体可以组装成电池包。在一些实施方式中，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为一个或多个，具体数量本领域技术人员可根据电池包的应用和容量进行选择。
图4和图5是作为一个示例的电池包1。参照图4和图5，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能够盖设于下箱体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。
另外，本申请还提供一种用电装置，所述用电装置包括本申请提供 的二次电池。所述二次电池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。所述用电装置可以包括移动设备(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，但不限于此。
作为所述用电装置，可以根据其使用需求来选择二次电池。
图6是作为一个示例的用电装置。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二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用电池单体作为电源。
实施例
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。除非特别说明，实施例部分中使用的物质质量均以不包含结晶水的质量计。
实施例1
二次电池的制备
1、正极极片的制备
将第一导电炭黑(Super P)、第二导电炭黑(科琴黑)和第一分散剂(PVDF 5130)以质量比3:1:3进行干混，在搅拌罐中以10m/s的线速度分散15min；其中，第一导电炭黑的比表面积SSA(即S1)＝60m 2/g，第二导电炭黑的比表面积SSA(即S2)＝600m 2/g，S2/S1＝10；
将所得产物加入到NMP溶剂中，以15m/s的线速度分散30min，得到浆料1，固含量为10.5％；
将第二分散剂(乙烯与马来酸酐共聚物，Mn＝100000)加入到浆料1中，然后以15m/s的线速度分散15min，得到浆料2，第一导电炭黑+第二导电炭黑与第二分散剂以质量比10:1进行混合；
将正极活性材料LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)加入上述混合物中继续混合得到正极活性浆料，正极活性材料的加入质量比为96.3％，以干燥后的正极膜层的重量计。
将正极活性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。正极极片的面密度为300mg/mm 2，压实密度为3.3g/cm 3。
2、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96:1:1.5:1.5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。负极极片的面密度为185mg/mm 2，压实密度为1.6g/cm 3。
3、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。
4、隔离膜
以厚度13μm聚乙烯(PE)多孔聚合薄膜作为隔离膜。
5、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，群裕度89％。
实施例2-16
二次电池的制备方法与实施例1类似，其中仅改变正极浆料中的导电剂并任选地加入碳纳米管(CNT)，具体见表1。
对比例1
二次电池的制备方法与实施例1类似，但其中在制备正极浆料时，仅使用第一导电碳黑。
对比例2
二次电池的制备方法与实施例1类似，但其中在制备正极浆料时，仅使用第二导电碳黑。
相关参数测试方法
1.比表面积测试
比表面积的测试参照GB/T 19587-2017，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氮气吸附比表面积分析测试方法测试，并用BET(Brunauer Emmett Teller)法计算得出材料的比表面积。测试结果参见表1。
2. 25℃下的DCR测试
在25℃下，将电池以0.5C恒流充电到4.25V，再恒压充电至电流为0.05C。然后将电池以0.5C恒流放电30分钟，以调整电池至50％SOC(荷电状态，State of Charge)，此时电池的电压记为U1。然后将电池以4C恒流放电30秒，采用0.1秒采点，放电末期电压记为U2。用电池50％SOC时的放电DCR表示电池的初始DCR，电池的初始DCR＝(U1-U2)/4C。
3. 25℃下的循环性能测试
在25℃下，将各实施例和对比例制备得到的二次电池以1C倍率恒流充电至充电截止电压4.25V，之后恒压充电至电流≤0.05C，静置 5min，再以0.33C倍率恒流放电至放电截止电压2.8V，静置5min，此为一个充放电循环。按照此方法对电池进行循环充放电测试，直至电池容量衰减至80％。记录此时的循环圈数，此即为电池在25℃下的循环寿命。
表1实施例1-16及对比例1-2的实验条件和结果
Figure PCTCN2022126669-appb-000001
表2由实施例1-16和对比例1-2制备的二次电池的电学性能
实施例 DCR/mΩ 25℃下的循环寿命/圈
1 1.77 2292
2 1.87 2175
3 2.00 1929
4 1.79 2244
5 2.37 1221
6 1.79 2247
8 1.94 2046
9 1.81 2211
10 1.84 2193
11 1.88 2172
12 2.15 1617
13 1.84 2232
14 1.77 2292
15 1.77 2259
16 1.78 2307
对比例1 2.26 1455
对比例2 2.52 1053
由表1和表2可以看出，通过使用本申请的两种导电炭黑，在不增加导电剂用量的情况下，可以实现优良的导电性能，改善的电池循环性能。
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它方式也包含在本申请的范围内。

Claims (16)

  1. 一种二次电池，包括正极极片，所述正极极片包括正极集流体和设置在所述正极集流体至少一个表面上的正极膜层，所述正极膜层包括导电剂，其中所述导电剂包括第一导电炭黑和第二导电炭黑，所述第二导电炭黑的比表面积大于所述第一导电炭黑的比表面积。
  2. 根据权利要求1所述的二次电池，其中所述第一导电炭黑的比表面积记为S1，所述第二导电炭黑的比表面积记为S2，则S2/S1≥4，可选地，5≤S2/S1≤17。
  3. 根据权利要求1或2所述的二次电池，其中，
    所述第一导电炭黑的比表面积≤140m 2/g，可选为50m 2/g-130m 2/g；和/或，
    所述第二导电炭黑的比表面积200m 2/g-1200m 2/g，可选为300m 2/g-1000m 2/g。
  4. 根据权利要求1至3中任一项所述的二次电池，其中，所述导电剂满足下述(1)-(4)中的至少一种：
    (1)所述导电剂在所述正极膜层中的质量占比≤5％，可选为0.8％-3.0％；
    (2)所述第一导电炭黑在所述正极膜层中的质量占比≤4.2％，可选为0.4％-3％；
    (3)所述第二导电炭黑在所述正极膜层中的质量占比≤2.5％，可选为0.1％-2％；
    (4)所述第一导电炭黑与所述第二导电炭黑的质量之比为(0.4-8):1，可选为(0.5-7):1。
  5. 根据权利要求1至4所述的二次电池，其中，所述第一导电炭黑的吸油值≤260；和/或，所述第二导电炭黑的吸油值≤300。
  6. 根据权利要求1至5中任一项所述的二次电池，其中，所述第一导电炭黑的水含量≤5000ppm；和/或，所述第二导电炭黑的水含量≤10000ppm。
  7. 根据权利要求1至6中任一项所述的二次电池，其中，所述 导电剂还包括碳纳米管；
    可选地，所述碳纳米管的管径为4-10nm；
    可选地，所述碳纳米管的管长为0.3-50μm；
    可选地，所述碳纳米管的长径比为50-12500；
    可选地，所述碳纳米管包括多壁碳纳米管；
    可选地，所述碳纳米管在所述正极膜层中的质量占比≤1.2％；
    可选地，所述第二导电碳黑与所述碳纳米管的质量之比为(0.1-10):1。
  8. 根据权利要求1至7中任一项所述的二次电池，其中，所述第一导电炭黑和所述第二导电炭黑各自独立地选自炉法炭黑、乙炔黑、科琴黑中的至少一种。
  9. 一种二次电池的制备方法，包括采用以下步骤制备正极极片：
    S1，将第一导电碳、第二导电碳和第一分散剂在搅拌罐中进行干混，得到混合物粉料，其中所述第二导电炭黑的比表面积大于所述第一导电炭黑的比表面积；
    S2，在所述混合物粉料中加入溶剂，混合均匀后得到浆料1，
    S3，将第二分散剂加入到浆料1中，混合均匀后得到浆料2；
    S4，将正极活性材料加入到所述浆料2中并混合均匀，得到正极材料浆料；
    S5，将所述正极材料浆料涂覆在正极集流体的至少一个表面上，干燥后形成正极膜层。
  10. 根据权利要求9所述的制备方法，其中，所述第一分散剂包括偏氟乙烯基聚合物；
    可选地，所述第一分散剂包括偏氟乙烯均聚物或偏氟乙烯与含活性基团的偏氟乙烯共聚得到的第一分散剂化合物，其中所述活性基团包括羧基、环氧基、羟基或磺酸基中的至少一种，可选为羧基或环氧基。
  11. 根据权利要求9或10中任一项所述的制备方法，其中，所述第二分散剂选自乙烯与马来酸酐共聚物或苯乙烯与马来酸酐共聚 物。
  12. 根据权利要求9至11中任一项所述的制备方法，其中，所述第一导电炭黑与所述第二导电炭黑的质量之和与所述第一分散剂的质量之比为(0.4-2.0):1，可选为(0.75-1.8):1。
  13. 根据权利要求9至12中任一项所述的制备方法，其中，所述第一导电炭黑与所述第二导电炭黑的质量之和与所述第二分散剂的质量之比为(8-30):1，可选为(9-25):1。
  14. 根据权利要求9至13中任一项所述的制备方法，其中，在S3步骤中，将第二分散剂和碳纳米管加入到浆料1中，混合均匀后得到浆料2。
  15. 根据权利要求14所述的制备方法，其中，所述第一导电炭黑的含量a、所述第二导电炭黑的含量b与所述碳纳米管的含量c满足：0.2≤((a+b)×c)/(a×b)≤10，可选地0.4≤((a+b)×c)/(a×b)≤6，其中所述a、b和c分别基于所述导电浆料以干重计的总重量计。
  16. 一种用电装置，包括权利要求1至8中任一项所述的二次电池或者包括根据权利要求9至15中任一项所述方法制备的二次电池。
PCT/CN2022/126669 2022-10-21 2022-10-21 二次电池及其制备方法和用电装置 Ceased WO2024082264A1 (zh)

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