WO2023093880A1 - 一种锂离子电池 - Google Patents

一种锂离子电池 Download PDF

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WO2023093880A1
WO2023093880A1 PCT/CN2022/134648 CN2022134648W WO2023093880A1 WO 2023093880 A1 WO2023093880 A1 WO 2023093880A1 CN 2022134648 W CN2022134648 W CN 2022134648W WO 2023093880 A1 WO2023093880 A1 WO 2023093880A1
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negative electrode
ion battery
lithium
lithium ion
battery according
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PCT/CN2022/134648
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English (en)
French (fr)
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郭盼龙
储霖
陈伟平
李素丽
曾长安
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珠海冠宇电池股份有限公司
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Publication of WO2023093880A1 publication Critical patent/WO2023093880A1/zh
Priority to US18/394,166 priority Critical patent/US20240178453A1/en

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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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • 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
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • 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
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • 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
    • 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
    • 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
    • H01M2004/027—Negative electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H01M2300/0037—Mixture of solvents
    • H01M2300/0042—Four or more solvents
    • 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 disclosure belongs to the technical field of lithium-ion batteries, and in particular relates to a lithium-ion battery.
  • lithium-ion batteries have always been a hot topic in scientific research and industrial research; increasing the energy density of lithium-ion batteries can significantly improve the performance of end products, such as smart electronic products will obtain higher battery life. Improving the gram capacity of materials is the main means to increase the energy density of lithium-ion batteries.
  • the theoretical specific capacity of silicon (Si)-based negative electrode materials is as high as 4200mAh/g, and its lithium intercalation and desorption platform is more suitable. It is an ideal high-capacity negative electrode material for lithium-ion batteries.
  • the volume expansion of Si can reach more than 300%, and the internal stress generated by the drastic volume change can easily lead to the powdering and peeling of the negative electrode, which affects the performance of the battery.
  • the present disclosure provides a lithium-ion battery, which improves the transmission rate of lithium ions between the negative electrode (especially the silicon negative electrode) and the electrolyte through the interaction between the electrolyte and the binder, and improves the negative electrode (especially the silicon negative electrode) and the electrolyte.
  • the SEI film on the surface of the silicon negative electrode is improved, thereby reducing the impedance of the lithium-ion battery, improving the interface situation of the lithium-ion battery, and improving the low-temperature charging performance and high-rate discharge performance of the lithium-ion battery.
  • the binding agent of the present disclosure and the electrolyte solution The matching enables the obtained lithium-ion battery to have high energy density while having excellent low-temperature charging performance and high-rate discharge performance.
  • a lithium-ion battery the lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, a diaphragm and a non-aqueous electrolyte; wherein the negative electrode sheet includes a negative electrode collector and a negative electrode coated on one or both sides of the negative electrode collector Active material layer, the negative electrode active material layer includes negative electrode active material, negative electrode conductive agent and negative electrode binding agent; Described non-aqueous electrolytic solution includes ethylene sulfate (DTD), fluoroethylene carbonate (FEC) and carboxylic acid Ester organic solvents;
  • DTD ethylene sulfate
  • FEC fluoroethylene carbonate
  • carboxylic acid Ester organic solvents ethylene sulfate
  • the lithium-ion battery satisfies the following relationship:
  • A is the mass percent of ethylene sulfate in the nonaqueous electrolytic solution
  • B is the mass percent of fluoroethylene carbonate in the nonaqueous electrolytic solution
  • Y is the mass percent of carboxylic acid ester organic solvent in the nonaqueous electrolytic solution.
  • Mass percent is the mass percent of the negative electrode binder in the negative electrode active material layer.
  • A, B, X and Y represent mass percentage, and the unit is wt%.
  • A+B is 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 or a range consisting of two or two of the above-mentioned values.
  • X/(A+B+Y) is 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2 or the range consisting of two or two points above.
  • 0.05 ⁇ X/Y ⁇ 0.2 Preferably, 0.05 ⁇ X/Y ⁇ 0.2.
  • X/Y is 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25 or the range of two or two points above.
  • the mass percentage A of the ethylene sulfate in the non-aqueous electrolyte is 0.1-2.5wt%, such as 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt% , 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2wt%, 2.2wt% or 2.5wt%.
  • the mass percentage B of the fluoroethylene carbonate in the non-aqueous electrolyte is 7.5-20.9wt%, such as 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 19.5 wt%, 20 wt%, 20.5 wt%, or 20.9 wt%.
  • the mass percentage Y of the carboxylate organic solvent in the non-aqueous electrolyte is 0.5-40wt%, such as 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2wt%, 2.2wt%, 2.5wt%, 2.8wt%, 3wt%, 3.2wt%, 3.5wt%, 3.8wt%, 4wt%, 4.5wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt% %, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 25wt%, 30wt%, 35wt% or 40wt%.
  • the lithium-ion battery when the content of ethylene sulfate (DTD) and fluoroethylene carbonate (FEC) in the non-aqueous electrolyte satisfies 10 ⁇ A+B ⁇ 21, the lithium-ion battery can form a relatively stable and conductive Specifically, the FEC in the non-aqueous electrolyte can form a stable SEI film on the surface of the negative electrode, thereby ensuring the stable charge and discharge performance of the lithium-ion battery.
  • DTD ethylene sulfate
  • FEC fluoroethylene carbonate
  • the viscosity of the carboxylate organic solvent is small, which can improve the low-temperature charging performance and high-rate discharge performance of the lithium-ion battery.
  • the content X of the negative electrode binder is combined with the carboxylate organic solvent
  • the content of Y satisfies 0.02 ⁇ X/Y ⁇ 0.25
  • the binding effect of the negative electrode binder is better, and the swelling rate of the negative electrode binder is also low, which can greatly reduce the negative electrode (especially silicon negative electrode) Expansion rate during charge and discharge.
  • the obtained lithium ion battery will have large impedance, many side reactions, and the negative electrode binder If the swelling is not within the appropriate range, a better stretching effect cannot be obtained, and a better adhesion force cannot be achieved.
  • the negative electrode binder helps to stabilize the SEI film on the surface of the negative electrode and reduces the impedance of the negative electrode surface, thereby shortening the lithium
  • the ion diffusion path improves the low-temperature charge and high-rate discharge performance of the lithium-ion battery, that is, the lithium-ion battery of the present disclosure achieves excellent low-temperature charge performance and high-rate discharge performance while having high energy density.
  • the carboxylate organic solvent is at least one selected from ethyl propionate, propyl propionate and propyl acetate.
  • the non-aqueous electrolytic solution further includes functional additives, and the functional additives are selected from one or more of the following compounds: 1,3-propane sultone, 1,3-propylene sulfonic acid Lactone, vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, lithium difluorophosphate, lithium bistrifluoromethanesulfonimide, lithium bisfluorosulfonimide.
  • the functional additives are selected from one or more of the following compounds: 1,3-propane sultone, 1,3-propylene sulfonic acid Lactone, vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, lithium difluorophosphate, lithium bistrifluoromethanesulfonimide, lithium bisfluorosulfonimide.
  • the non-aqueous electrolyte solution further includes carbonates, such as cyclic carbonates and/or linear carbonates.
  • the cyclic carbonate is selected from at least one of ethylene carbonate and propylene carbonate
  • the linear carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate kind.
  • the non-aqueous electrolytic solution further includes an electrolyte lithium salt.
  • the electrolyte lithium salt is selected from at least one of lithium hexafluorophosphate and lithium perchlorate.
  • the concentration of the electrolyte lithium salt in the non-aqueous electrolytic solution is 0.5 ⁇ 2.0 mol/L.
  • the negative electrode active material includes a silicon-based negative electrode material.
  • the silicon-based negative electrode material is selected from at least one of elemental silicon and silicon oxide.
  • the negative electrode active material further includes a carbon-based negative electrode material.
  • the carbon-based negative electrode material includes at least one of artificial graphite, natural graphite, mesocarbon microspheres, hard carbon, and soft carbon.
  • the mass ratio of the silicon-based negative electrode material to the carbon-based negative electrode material is 10:0 to 1:9, such as 1:9, 2:8, 3:7, 4: 6, 5:5, 6:4, 7:3, 8:2, 9:1 or 10:0.
  • the negative electrode binder is selected from polyanionic binders.
  • the polyanionic binder includes a polymer, and the molecular chain of the polymer contains at least one or more combinations of the following groups:
  • the molar percentage of the above-mentioned groups contained in the polyanionic binder is 5-100 mol%, such as 5 mol%, 10 mol%, 20 mol%, 30 mol%, 40 mol%, 50 mol%. , 60 mol%, 70 mol%, 80 mol%, 90 mol% or 100 mol%.
  • the polyanionic binder containing the above-mentioned groups when the molar percentage of the above-mentioned groups is greater than or equal to 5%, the low-temperature charge performance and high-rate discharge performance of the battery can be improved.
  • this type of group is characterized by strong electron-withdrawing groups or delocalized electron groups around the anion, which makes the bond between the anion and the cation weaker, and the lithium ion is less bound by electrostatic interaction and is easy to migrate.
  • the ion conductivity is higher, which can participate in the transmission of lithium ions, and can shorten the diffusion path of lithium ions, thereby improving the low-temperature charging performance and high-rate discharge performance of the battery.
  • the mole percentage of the above-mentioned groups contained in the polyanionic binder is preferably 10-60 mol%.
  • the polymer further includes a repeating unit structure formed by a flexible monomer, and the flexible monomer includes at least one of acrylate, acrylonitrile, vinyl alcohol and acrylic acid.
  • the mole percentage of the repeating unit structure formed by the flexible monomer contained in the polyanionic binder is 0 to 95 mol%, such as 0 mol%, 5 mol%, 10 mol%, 20 mol%, 30 mol%, 40 mol% %, 50 mol%, 60 mol%, 70 mol%, 80 mol%, 90 mol% or 95 mol%.
  • the mole percentage of the above-mentioned groups contained in the polyanionic binder is 10%-80%.
  • the flexibility of the polyanionic binder can be further improved, so that the polyanionic binder has both high ionic conductivity and high elastic modulus and elongation at break.
  • the polymer has the structure shown in formula I,
  • the ion conductivity of the polyanionic binder is 10 -3 -10 -8 S/cm.
  • the elastic modulus of the polyanionic binder is 0.2MPa ⁇ 1000MPa.
  • the elongation at break of the polyanionic binder is 5%-200%.
  • the polyanionic binder has a high modulus of elasticity, and at the same time it can pass through intermolecular forces such as hydrogen bonds and static electricity, so that the thickness expansion of the silicon negative electrode when lithium ions are intercalated and extracted is like Spring-type enlargement and shrinkage, that is, the polyanion binder of the present disclosure can participate in lithium ion transmission, can shorten the diffusion path of lithium ions, thereby improving the low-temperature charging performance and high-rate discharge performance of lithium-ion batteries.
  • the mass percentage X of the negative electrode binder in the negative electrode active material layer is 0.5 to 15 wt%, such as 0.5 wt%, 0.6 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%.
  • the negative electrode conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.
  • the mass percentage of the negative electrode conductive agent in the negative electrode active material layer is 0.5-15wt%, such as 0.5wt%, 0.6wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt% , 1.8wt%, 2wt%, 2.2wt%, 2.5wt%, 2.8wt%, 3wt%, 3.2wt%, 3.5wt%, 3.8wt%, 4wt%, 4.5wt%, 5wt%, 6wt%, 7wt% , 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on one or both sides of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, a positive electrode conductive agent and a positive electrode adhesive. Binder.
  • the positive electrode conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and carbon fiber.
  • the positive electrode binder is selected from at least one of sodium carboxymethylcellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.
  • the positive electrode active material is selected from lithium cobalt oxide or lithium cobalt oxide that has been doped with one or more elements of Al, Mg, Ti, and Zr.
  • the chemical formula of lithium cobaltate coated with one or more elements in Ti and Zr is Li x Co 1-y1-y2-y3-y4 A y1 B y2 C y3 D y4 O 2 ; 0.95 ⁇ x ⁇ 1.05 , 0.01 ⁇ y1 ⁇ 0.1, 0 ⁇ y2 ⁇ 0.1, 0 ⁇ y3 ⁇ 0.1, 0 ⁇ y4 ⁇ 0.1, A, B, C, D are selected from one or more elements among Al, Mg, Ti, Zr.
  • the mass percentage of the positive electrode conductive agent in the positive electrode active material layer is 0.5-15 wt%.
  • the mass percentage of the positive electrode binder in the positive electrode active material layer is 0.5-15 wt%.
  • the mass percentage of the positive electrode active material in the positive electrode active material layer is 70-99 wt%.
  • the main function of the separator is to separate the positive and negative plates of the battery, prevent short circuit caused by contact between the two poles, and allow ions in the electrolyte to pass through.
  • the charging cut-off voltage of the lithium-ion battery is 4.48V or above.
  • binder in this disclosure refers to the binder in lithium ion batteries, which is an inactive component in lithium ion battery electrode sheets, and is one of the important materials that must be used to prepare lithium ion battery electrode sheets.
  • the main function of "binder” is to connect the electrode active material, conductive agent and electrode collector, so that there is an overall connection between them, thereby reducing the impedance of the electrode, and at the same time making the electrode sheet have good mechanical properties and machinability performance to meet the needs of actual production.
  • the present disclosure provides a lithium ion battery, which improves the transmission rate of lithium ions between the negative electrode (especially the silicon negative electrode) and the electrolyte through the interaction between the electrolyte and the binder, and improves the negative electrode (especially the silicon negative electrode)
  • the SEI film on the surface is improved, thereby reducing the impedance of the lithium-ion battery, improving the interface of the lithium-ion battery, and improving the low-temperature charging performance and high-rate discharge performance of the lithium-ion battery.
  • the matching of the binder and the electrolyte in the present disclosure makes it possible to obtain
  • the lithium-ion battery has high energy density and excellent low-temperature charging performance and high-rate discharge performance.
  • the present disclosure introduces DTD, FEC and carboxylate organic solvents into the non-aqueous electrolyte, and further adjusts the content X of the negative electrode binder in the negative electrode sheet, and the content A of DTD and the content B of FEC in the non-aqueous electrolyte and the relationship between the content Y of the carboxylate organic solvent, so that it satisfies: 10 ⁇ A+B ⁇ 21, 0.02 ⁇ X/(A+B+Y) ⁇ 0.2, 0.02 ⁇ X/Y ⁇ 0.25, which can be used
  • a stable and low-impedance SEI interface is formed on the surface of the negative electrode, which can also improve the conductivity of the non-aqueous electrolyte at low temperature and the migration rate of lithium ions, and further improve the low-temperature charging performance and high-rate discharge performance of the battery; in addition, it can also make lithium The cycle expansion rate of the ion battery is reduced.
  • Figure 1 NMR spectrum of negative electrode binder A.
  • negative electrode binder A The structure of negative electrode binder A is as follows, and the specific steps of its preparation process are as follows:
  • the monomer containing lithium ions and the flexible monomer are dissolved in the DMF solvent according to the molar ratio of 7:3, and the initiator azobisisobutylene that is 1% in the molar ratio of the total monomer is added Nitrile, reacted at 80°C for 10h under vacuum. Add the reacted solution into the acetone solvent to precipitate the reaction product, filter and dry it for later use, and obtain the negative electrode binder A.
  • the structure of the negative electrode binder A was confirmed by nuclear magnetic spectrum, as shown in FIG. 1 .
  • the positive electrode active material lithium cobalt oxide (LCO), the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed according to the weight ratio of 97:1.5:1.5, N-methylpyrrolidone (NMP) is added, and the mixture is mixed in a vacuum mixer Stir under the action until the mixed system becomes a positive electrode slurry with uniform fluidity; evenly coat the positive electrode slurry on the aluminum foil of the current collector; bake the above-mentioned coated aluminum foil in an oven with 5 different temperature gradients, and then It was dried in an oven at 120° C. for 8 hours, and then rolled and cut to obtain the desired positive electrode sheet.
  • NMP N-methylpyrrolidone
  • Negative electrode active material mass ratio is graphite and silicon oxide of 90:10
  • thickener carboxymethylcellulose sodium (CMC-Na)
  • binder negative electrode binder A prepared above
  • the conductive agent acetylene black
  • acetylene black is mixed according to the weight ratio of 98-X:1:X:1, and deionized water is added, and the negative electrode slurry is obtained under the action of a vacuum mixer; the negative electrode slurry is evenly coated on the high-strength carbon-coated copper foil , to obtain a pole piece; the obtained pole piece was dried at room temperature and then transferred to an oven at 80° C. for 10 hours, and then rolled and cut to obtain a negative pole piece.
  • a polyethylene isolation film with a coating layer of 8 ⁇ m thickness is selected.
  • the positive electrode sheet, separator, and negative electrode sheet prepared above in order to ensure that the separator film is between the positive and negative electrode sheets to play the role of isolation, and then obtain the bare cell without liquid injection by winding; the bare cell
  • the core is placed in the outer packaging foil, and the corresponding electrolyte prepared above is injected into the dried bare cell, and the corresponding lithium-ion battery is obtained through vacuum packaging, standing, formation, shaping, and sorting.
  • Comparative examples 1 to 7 in Table 1 are a group of comparative battery packs, the content of DTD is 0.5%, the content of FEC is 10%, and the content of carboxylate organic solvent is 30%. Only the content of negative electrode binder A is changed. Effect of negative electrode binder A on battery performance.
  • the negative electrode sheet can be bonded well, and the negative electrode binder has a certain effect on the construction of a stable SEI interface in the optimal state. At this time, the performance of the battery exhibited is better.
  • the dosage range of the negative electrode binder is exceeded, due to the increase of the battery impedance, the side reactions on the surface of the negative electrode sheet will also increase accordingly, the performance of the battery will deteriorate, and the thickness expansion rate will also increase to a certain extent, thus affecting the lithium ion battery.
  • the diffusion path affects the low-temperature charge performance and high-rate discharge performance of the battery.
  • Comparative example 8 to comparative example 19 in Table 1 are a group of comparative battery packs, the content of negative electrode binder A is 3%, the content of carboxylate organic solvent is 30%, the FEC content and DTD content are changed, and the FEC content and DTD are investigated effect on battery performance.
  • the SEI interface structure is incomplete, the side reactions at the interface increase, a large amount of electrolyte is consumed, the solvent is easily reduced on the surface of the pole piece, and the battery may have problems such as lithium precipitation and flatulence. Therefore, when the battery is cycled, the capacity retention rate is low, and the thickness expansion rate is large; and at low temperatures, the incomplete SEI film is easy to cause lithium deposition in the battery and deteriorate battery performance.
  • the SEI film on the surface of the negative electrode sheet is too thick, resulting in an increase in battery impedance and hindering the rate of lithium ion transmission, which may lead to lithium precipitation in the later stages of the battery cycle, thereby Affect the low-temperature charging performance and high-rate discharge performance of the battery.
  • Comparative Example 20 to Example 24 in Table 1 are a group of comparative battery packs.
  • the content of negative electrode binder A is 3%
  • the content of DTD is 0.5%
  • the content of FEC is 10%.
  • Only the content of carboxylate organic solvents is changed. The effect of the content of carboxylate organic solvent on the battery performance was investigated.
  • the negative electrode binder will also interact with the carboxylate organic solvent.
  • carboxylate organic solvent is less, the swelling rate of the negative electrode binder in the electrolyte is small, and the toughness is small.
  • the thickness expansion rate in the charging and discharging process is relatively large, and the effect of the negative electrode binder cannot be well applied.
  • the content of carboxylate organic solvents is within the appropriate range of use, the swelling of the negative electrode binder in the electrolyte reaches an appropriate level.
  • the toughness of the negative electrode binder is the largest, and the thickness expansion rate of the silicon negative electrode in the process of charging and discharging At this time, the negative electrode binder can act as a spring, and the electrode sheets in the battery are well bonded.
  • the appropriate FEC and DTD content enables the battery to form a low-impedance and stable SEI interface, so the performance of the battery is better.
  • the thickness expansion rate is also within the normal range.
  • the content of the carboxylate organic solvent is too large, the swelling of the negative electrode binder is too large, which will affect the effect of the negative electrode binder instead.

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Abstract

本公开提供一种锂离子电池，其拥有高能量密度的同时兼具优异循环寿命及较低循环膨胀率，通过在非水电解液中引入硫酸亚乙酯、氟代碳酸乙烯酯和羧酸酯类有机溶剂，并进一步调整负极片中负极粘结剂含量X，与非水电解液中DTD含量A、FEC含量B和羧酸酯类有机溶剂含量Y之间的关系，使其满足：10≤A+B≤21，0.02≤X/(A+B+Y)≤0.2，0.02≤X/Y≤0.25，可以使负极表面能形成稳定且低阻抗SEI界面，从而改善电池的低温充电性能及大倍率放电性能；同时，能够提升电解液在低温下的电导率及锂离子的迁移速率，进一步提升电池的低温充电性能及大倍率放电性能；此外，还能够使锂离子电池的循环膨胀率减小。

Description

一种锂离子电池 技术领域
本公开属于锂离子电池技术领域，具体涉及到一种锂离子电池。
背景技术
近年来，高能量密度锂离子电池一直是科研与产业领域研究的热门主题；提升锂离子电池的能量密度可以使终端产品在性能上有显著提升，如智能电子产品会获得更高的续航能力。提高材料的克容量是提升锂离子电池的能量密度主要手段。硅(Si)基负极材料的理论比容量高达4200mAh/g，同时其嵌脱锂平台较适宜，是一种理想的锂离子电池用高容量负极材料。
然而，在充放电过程中，Si的体积膨胀可达到300％以上，剧烈的体积变化所产生的内应力容易导致负极粉化、剥落，影响电池的性能。
发明内容
研究发现，现有的粘结剂与电解液匹配性差，在电解液中粘结强度急剧下降，导致负极材料(特别是硅基负极材料)之间的粘结性变差。为此，本公开提供一种锂离子电池，其是通过电解液与粘结剂的相互作用，提升锂离子在负极(特别是硅负极)和电解液间的传输速率，并对负极(特别是硅负极)表面的SEI膜进行改善，从而降低锂离子电池的阻抗，改善锂离子电池的界面情况，提升锂离子电池的低温充电性能及大倍率放电性能，本公开的粘结剂与电解液的匹配使得获得的锂离子电池拥有高能量密度的同时兼具优异的低温充电性能及大倍率放电性能。
本公开目的是通过如下技术方案实现的：
一种锂离子电池，所述锂离子电池包括正极片、负极片、隔膜和非水电解 液；其中，所述负极片包括负极集流体和涂覆在负极集流体一侧或两侧表面的负极活性物质层，所述负极活性物质层包括负极活性物质、负极导电剂和负极粘结剂；所述非水电解液包括硫酸亚乙酯(DTD)、氟代碳酸乙烯酯(FEC)和羧酸酯类有机溶剂；
所述锂离子电池满足如下关系式：
10≤A+B≤21，
0.02≤X/(A+B+Y)≤0.2，
0.02≤X/Y≤0.25；
其中，A为硫酸亚乙酯在非水电解液中的质量百分比，B为氟代碳酸乙烯酯在非水电解液中的质量百分比，Y为羧酸酯类有机溶剂在非水电解液中的质量百分比，X为负极粘结剂在负极活性物质层中的质量百分比。
A、B、X及Y表示质量百分比，单位为wt％。当用于公式计算中时只取数字部分(不含单位)，例如，当A为5wt％，B为5wt％时，A+B＝10而不是0.1。
优选地，12≤A+B≤18。示例性地，A+B为10、11、12、13、14、15、16、17、18、19、20、21或上述两两点值组成的范围。
优选地，0.05≤X/(A+B+Y)≤0.18。示例性地，X/(A+B+Y)为0.02、0.03、0.04、0.05、0.06、0.07、0.08、0.09、0.10、0.11、0.12、0.13、0.14、0.15、0.16、0.17、0.18、0.19、0.2或上述两两点值组成的范围。
优选地，0.05≤X/Y≤0.2。示例性地，X/Y为0.02、0.03、0.04、0.05、0.06、0.07、0.08、0.09、0.10、0.11、0.12、0.13、0.14、0.15、0.16、0.17、0.18、0.19、0.20、0.21、0.22、0.23、0.24、0.25或上述两两点值组成的范围。
在一实施例中，所述硫酸亚乙酯在非水电解液中的质量百分比A为0.1～2.5wt％，例如为0.1wt％、0.2wt％、0.3wt％、0.4wt％、0.5wt％、0.6wt％、0.7wt％、0.8wt％、0.9wt％、1wt％、1.2wt％、1.5wt％、1.8wt％、2wt％、2.2wt％或2.5wt％。
在一实施例中，所述氟代碳酸乙烯酯在非水电解液中的质量百分比B为7.5～20.9wt％，例如为7wt％、8wt％、9wt％、10wt％、11wt％、12wt％、13wt％、 14wt％、15wt％、16wt％、17wt％、18wt％、19wt％、19.5wt％、20wt％、20.5wt％或20.9wt％。
在一实施例中，所述羧酸酯类有机溶剂在非水电解液中的质量百分比Y为0.5～40wt％，例如为1wt％、1.2wt％、1.5wt％、1.8wt％、2wt％、2.2wt％、2.5wt％、2.8wt％、3wt％、3.2wt％、3.5wt％、3.8wt％、4wt％、4.5wt％、5wt％、6wt％、7wt％、8wt％、9wt％、10wt％、11wt％、12wt％、13wt％、14wt％、15wt％、16wt％、17wt％、18wt％、19wt％、20wt％、25wt％、30wt％、35wt％或40wt％。
在一实施例中，当非水电解液中的硫酸亚乙酯(DTD)、氟代碳酸乙烯酯(FEC)的含量满足10≤A+B≤21时，锂离子电池能够形成较稳定且导电性好的SEI膜，具体地，非水电解液中的FEC能在负极表面形成稳定的SEI膜，从而能够保证锂离子电池稳定的充放电性能，DTD能够在负极表面生成离子导电性好的有机磺酸盐，从而降低了界面阻抗；当硫酸亚乙酯(DTD)、氟代碳酸乙烯酯(FEC)的加入量不在上述范围(10≤A+B≤21)内时，当DTD含量和FEC含量之和小于最优值(如A+B<10)时，SEI膜构造不完整，界面的副反应增多，消耗大量的电解液，溶剂容易在极片表面被还原，电池可能出现析锂、胀气等问题，导致电池循环时容量保持率低，循环厚度膨胀大，且在低温下容易因为SEI膜不完整导致电池析锂，恶化电池性能；当DTD含量和FEC含量之和大于最优值(A+B>21)时，极片表面的SEI膜成膜太厚，导致电池阻抗的增大，锂离子传输的速率受阻，可能导致电池循环出现后期出现析锂现象，从而影响电池的循环和大倍率放电性能。
在一实施例中，羧酸酯类有机溶剂的粘度较小，能够改善锂离子电池的低温充电性能及大倍率放电性能，特别地，当负极粘结剂的含量X与羧酸酯类有机溶剂的含量Y满足0.02≤X/Y≤0.25时，负极粘结剂的粘结效果是较优的，且负极粘结剂的溶胀率也较低，从而能够大大的降低负极(特别是硅负极)在充放电过程中的膨胀率。当负极粘结剂的含量X与羧酸酯类有机溶剂的含量Y不在上述 范围(0.02≤X/Y≤0.25)内时，获得的锂离子电池的阻抗大、副反应多、负极粘结剂的溶胀不在合适的范围内，无法得到较好的伸缩效应，达不到较好的粘结力。
在一实施例中，当四者的关系满足0.02≤X/(A+B+Y)≤0.2，负极粘结剂有助于稳定负极表面的SEI膜，降低负极表面的阻抗，从而达到缩短锂离子的扩散路径，改善锂离子电池的低温充电及大倍率放电性能，即本公开的锂离子电池在具备高能量密度的同时实现优异的低温充电性能及大倍率放电性能。
在一实施例中，所述羧酸酯类有机溶剂选自丙酸乙酯、丙酸丙酯和乙酸丙酯中的至少一种。
在一实施例中，所述非水电解液还包括功能添加剂，所述功能添加剂选自如下化合物中的一种或多种：1,3-丙磺酸内酯、1,3-丙烯磺酸内酯、碳酸亚乙烯酯、氟代碳酸乙烯酯、硫酸乙烯酯、二氟磷酸锂、双三氟甲烷磺酰亚胺锂、双氟磺酰亚胺锂。
在一实施例中，所述非水电解液还包括碳酸酯，所述碳酸酯例如是环状碳酸酯和/或线性碳酸酯。
其中，所述的环状碳酸酯选自碳酸乙烯酯和碳酸丙烯酯中的至少一种，所述的线性碳酸酯选自碳酸二甲酯、碳酸二乙酯和碳酸甲乙酯中的至少一种。
在一实施例中，所述非水电解液还包括电解质锂盐。
根据本公开，所述电解质锂盐选自六氟磷酸锂和高氯酸锂中的至少一种。
在一实施例中，所述非水电解液中电解质锂盐的浓度为0.5～2.0mol/L。
在一实施例中，所述负极活性物质包括硅基负极材料。
在一实施例中，所述硅基负极材料选自选自单质硅、氧化亚硅中的至少一种。
在一实施例中，所述负极活性物质还进一步包括碳基负极材料。
在一实施例中，所述碳基负极材料包括人造石墨、天然石墨、中间相碳微球、硬碳、软碳中的至少一种。
在一实施例中，所述负极活性物质中，硅基负极材料和碳基负极材料的质量比为10:0～1:9，例如为1:9、2:8、3:7、4:6、5:5、6:4、7:3、8:2、9:1或10:0。
在一实施例中，所述负极粘结剂选自聚阴离子型粘结剂。
在一实施例中，所述聚阴离子粘结剂包括聚合物，所述聚合物的分子链上至少含有以下基团中的一种或几种组合：
Figure PCTCN2022134648-appb-000001
在一实施例中，所述聚阴离子型粘结剂中含有的上述基团的摩尔百分含量为5～100mol％，例如为5mol％、10mol％、20mol％、30mol％、40mol％、50mol％、60mol％、70mol％、80mol％、90mol％或100mol％。在含有上述基团的聚阴离子型粘结剂中，当含有的上述基团的摩尔百分含量大于等于5％，可以改善电池的低温充电性能及大倍率放电性能。具体地，该类基团的特点是阴离子周围含有较强的吸电子基团或离域电子基团，使阴阳离子间的键能较弱，锂离子受静电作用束缚较小，容易迁移，锂离子电导率更高，可以参与到锂离子传输中，能够缩短锂离子的扩散路径，从而改善电池的低温充电性能及大倍率放电性能。
在一实施例中，所述聚阴离子型粘结剂中含有的上述基团的摩尔百分含量优选地，为10～60mol％。
在一实施例中，所述聚合物中还包括柔性单体形成的重复单元结构，所述柔性单体包括丙烯酸酯、丙烯腈、乙烯醇和丙烯酸中的至少一种。
其中，所述聚阴离子型粘结剂中含有的柔性单体形成的重复单元结构的摩尔百分含量为0～95mol％，例如为0mol％、5mol％、10mol％、20mol％、30mol％、40mol％、50mol％、60mol％、70mol％、80mol％、90mol％或95mol％。
在一实施例中，所述聚阴离子型粘结剂中含有的上述基团的摩尔百分含量 为10％-80％。
通过在聚阴离子粘结剂中引入柔性单体进行共聚，可以进一步改善聚阴离子粘结剂的柔韧性，使该类聚阴离子粘结剂既具备高的离子电导率又具备高的弹性模量和断裂伸长率。
在一实例中，所述聚合物具有式I所示结构，
Figure PCTCN2022134648-appb-000002
其中m＝10-200，优选为20-120；n＝0-190，优选为20-16；p＝1-50，优选为1-10。
在一实施例中，所述聚阴离子粘结剂的离子电导率为10 -3～10 -8S/cm。
在一实施例中，所述聚阴离子粘结剂的弹性模量为0.2MPa～1000MPa。
在一实施例中，所述聚阴离子粘结剂的断裂伸长率为5％～200％。
在一实施例中，所述聚阴离子型粘结剂具有高的弹性模量，同时其可以通过氢键和静电等分子间作用力，使得硅负极在锂离子嵌入和脱出时的厚度膨胀是像弹簧式的增大和缩小，即本公开的聚阴离子粘结剂可以参与到锂离子传输中，能够缩短锂离子的扩散路径，从而改善锂离子电池的低温充电性能及大倍率放电性能。
在一实施例中，所述负极粘结剂在负极活性物质层中的质量百分比X为0.5～15wt％，例如为0.5wt％、0.6wt％、0.8wt％、1wt％、1.2wt％、1.5wt％、1.8wt％、2wt％、2.2wt％、2.5wt％、2.8wt％、3wt％、3.2wt％、3.5wt％、3.8wt％、4wt％、4.5wt％、5wt％、6wt％、7wt％、8wt％、9wt％、10wt％、11wt％、12wt％、13wt％、14wt％或15wt％。
在一实施例中，所述负极导电剂选自导电炭黑、乙炔黑、科琴黑、导电石 墨、导电碳纤维、碳纳米管、金属粉、碳纤维中的至少一种。
在一实施例中，所述负极导电剂在负极活性物质层中的质量百分比为0.5～15wt％，例如为0.5wt％、0.6wt％、0.8wt％、1wt％、1.2wt％、1.5wt％、1.8wt％、2wt％、2.2wt％、2.5wt％、2.8wt％、3wt％、3.2wt％、3.5wt％、3.8wt％、4wt％、4.5wt％、5wt％、6wt％、7wt％、8wt％、9wt％、10wt％、11wt％、12wt％、13wt％、14wt％或15wt％。
在一实施例中，所述正极片包括正极集流体和涂覆在正极集流体一侧或两侧表面的正极活性物质层，所述正极活性物质层包括正极活性物质、正极导电剂和正极粘结剂。
在一实施例中，所述正极导电剂选自导电炭黑、乙炔黑、科琴黑、导电石墨、导电碳纤维、碳纳米管、金属粉、碳纤维中的至少一种。
在一实施例中，所述正极粘结剂选自羧甲基纤维素钠、丁苯胶乳、聚四氟乙烯、聚氧化乙烯中的至少一种。
在一实施例中，所述正极活性物质选自钴酸锂或经过Al、Mg、Ti、Zr中的一种或多种元素掺杂包覆处理的钴酸锂，所述经过Al、Mg、Ti、Zr中一种或多种元素掺杂包覆处理的钴酸锂的化学式为Li xCo 1-y1-y2-y3-y4A y1B y2C y3D y4O 2；0.95≤x≤1.05，0.01≤y1≤0.1，0≤y2≤0.1，0≤y3≤0.1，0≤y4≤0.1，A、B、C、D选自Al、Mg、Ti、Zr中的一种或多种元素。
在一实施例中，所述正极导电剂在正极活性物质层中的质量百分比为0.5～15wt％。
在一实施例中，所述正极粘结剂在正极活性物质层中的质量百分比为0.5～15wt％。
在一实施例中，所述正极活性物质在正极活性物质层中的质量百分比为70～99wt％。
在一实施例中，所述隔膜的主要作用是将电池正负极片分隔开来，防止两极接触造成短路，并且能使电解质中的离子通过。
在一实施例中，所述锂离子电池的充电截止电压为4.48V及以上。
术语与解释：
本公开中术语“粘结剂”是指锂离子电池中的粘结剂，是锂离子电池电极片中的非活性成分，是制备锂离子电池电极片必须使用的重要材料之一。“粘结剂”的主要作用是连接电极活性物质、导电剂和电极集流体，使它们之间具有整体的连接性，从而减小电极的阻抗，同时使电极片具有良好的机械性能和可加工性能，满足实际生产的需要。
本公开的有益效果：
本公开提供一种锂离子电池，其是通过电解液与粘结剂的相互作用，提升锂离子在负极(特别是硅负极)和电解液间的传输速率，并对负极(特别是硅负极)表面的SEI膜进行改善，从而降低锂离子电池的阻抗，改善锂离子电池的界面情况，提升锂离子电池的低温充电性能及大倍率放电性能，本公开的粘结剂与电解液的匹配使得获得的锂离子电池其拥有高能量密度的同时兼具优异的低温充电性能及大倍率放电性能。
具体的，本公开通过在非水电解液中引入DTD、FEC和羧酸酯类有机溶剂，并进一步调整负极片中负极粘结剂含量X，与非水电解液中DTD含量A、FEC含量B和羧酸酯类有机溶剂含量Y之间的关系，使其满足：10≤A+B≤21，0.02≤X/(A+B+Y)≤0.2，0.02≤X/Y≤0.25，可以使负极表面形成稳定且低阻抗的SEI界面，还能够提升非水电解液在低温下的电导率及锂离子的迁移速率，进一步提升电池的低温充电性能及大倍率放电性能；此外，还能够使锂离子电池的循环膨胀率减小。
附图说明
图1：负极粘结剂A的核磁谱图。
具体实施方式
下文将结合具体实施例对本公开做更进一步的详细说明。应当理解，下列实施例仅为示例性地说明和解释本公开，而不应被解释为对本公开保护范围的限制。凡基于本公开上述内容所实现的技术均涵盖在本公开旨在保护的范围内。
下述实施例中所使用的实验方法如无特殊说明，均为常规方法；下述实施例中所用的试剂、材料等，如无特殊说明，均可从商业途径得到。
在本公开的描述中，需要说明的是，术语“第一”、“第二”等仅用于描述目的，而并非指示或暗示相对重要性。
实施例和对比例
(1)负极粘结剂A的制备：
负极粘结剂A的结构如下所示，其制备过程具体步骤如下：
Figure PCTCN2022134648-appb-000003
将含有锂离子的单体和柔性单体(具体结构如上所述)按照摩尔比为7:3溶解于DMF溶剂中，加入占总单体的摩尔比为1％的引发剂偶氮二异丁腈，在真空状态下80℃反应10h。将反应后的溶液加入到丙酮溶剂中，使反应产物析出，过滤干燥备用，得到负极粘结剂A。该负极粘结剂A的结构通过核磁谱图确认，如图1所示。
(2)正极片的制备
将正极活性材料钴酸锂(LCO)、粘结剂聚偏氟乙烯(PVDF)、导电剂乙炔黑按照重量比97:1.5:1.5进行混合，加入N-甲基吡咯烷酮(NMP)，在真空搅 拌机作用下搅拌，直至混合体系成均一流动性的正极浆料；将正极浆料均匀涂覆在集流体铝箔上；将上述涂覆好的铝箔在5段不同温度梯度的烘箱烘烤后，再将其在120℃的烘箱干燥8h，然后经过辊压、分切得到所需的正极片。
(3)负极片的制备
将负极活性材料(质量比为90:10的石墨和氧化亚硅)、增稠剂(羧甲基纤维素钠(CMC-Na))、粘结剂(上述制备的负极粘结剂A)、导电剂(乙炔黑)按照重量比98-X:1:X:1进行混合，加入去离子水，在真空搅拌机作用下获得负极浆料；将负极浆料均匀涂覆在高强度涂炭铜箔上，得到极片；将所得极片在室温晾干后转移至80℃烘箱干燥10h，然后经过辊压、分切得到负极片。
(4)电解液的制备
在充满惰性气体(氩气)的手套箱中(H 2O＜0.1ppm，O 2＜0.1ppm)，将碳酸乙烯酯、碳酸丙烯酯、碳酸二乙酯、丙酸丙酯(其中，碳酸乙烯酯、碳酸丙烯酯、碳酸二乙酯的质量比为1:1:1，丙酸丙酯的含量详见表1)混合均匀，然后往其中快速加入1.25mol/L的充分干燥的六氟磷酸锂(LiPF 6)，溶解于非水有机溶剂中，搅拌均匀，继续添加硫酸亚乙酯(DTD)和氟代碳酸乙烯酯(FEC)(其中，硫酸亚乙酯(DTD)和氟代碳酸乙烯酯(FEC)的含量详见表1)，再次搅拌均匀，经过水分和游离酸检测合格后，得到基础电解液。
(5)隔离膜的制备
选用8μm厚的带涂覆层的聚乙烯隔离膜。
(6)锂离子电池的制备
将上述准备的正极片、隔离膜、负极片按顺序叠放好，保证隔离膜处于正、负极片之间起到隔离的作用，然后通过卷绕得到未注液的裸电芯；将裸电芯置于外包装箔中，将上述制备好的相应的电解液注入到干燥后的裸电芯中，经过真空封装、静置、化成、整形、分选等工序，获得相应的锂离子电池。
(7)锂离子电池的低温充电测试
取测完OCV后50％SOC的电池，测试其电压、内阻、厚度T1，然后将该电 池置于0℃恒温环境下静置4小时，以0.5C/0.5C倍率进行充放电测试，截止电压范围为3.0V～4.48V，充放循环50周，记录循环放电容量并除以第一次循环的放电容量，得到循环容量保持率，循环50周结束后将满电电池从0℃恒温箱中取出，立即测试其循环50周后冷态满电的厚度T2，计算电池循环50周时的厚度膨胀率。其中，厚度膨胀率(％)＝(T2-T1)/T1×100％。此外，对0℃0.5C/0.5C循环50周后的电池做解剖处理，观察并记录负极界面的情况。测试结果见表2。
(8)锂离子电池的倍率放电测试
取测完OCV后50％SOC的电池，室温下先静置10min，以0.5C电流放电至3.0V，静置10min，再以0.5C恒流恒压充电至4.48V，静置10min，以不同的倍率(如0.5C、1C、3C、5C、10C)的电流放电至3.0V，分别记录不同放电倍率下的放电容量，以0.5C放电容量作为基准，计算不同倍率下的放电容量保持率(相对于0.5C容量)，具体性能数据见表3。
表1对比例和实施例的锂离子电池的组成
Figure PCTCN2022134648-appb-000004
Figure PCTCN2022134648-appb-000005
表2对比例和实施例的锂离子电池的低温充电性能测试结果
Figure PCTCN2022134648-appb-000006
Figure PCTCN2022134648-appb-000007
表3对比例和实施例的锂离子电池的大倍率性能测试结果
Figure PCTCN2022134648-appb-000008
表1中对比例1至对比例7为一组对比电池组，DTD含量为0.5％，FEC含量为10％，羧酸酯类有机溶剂含量为30％，只改变负极粘结剂A含量，考察负极粘结剂A对电池性能的影响。
当负极粘结剂A的含量在逐步增大时，X/(A+B+Y)及X/Y也呈现增大的趋势，其中对比例1、对比例5、对比例6、对比例7的X/(A+B+Y)及X/Y得到的数值是超出上文所述的0.02≤X/(A+B+Y)≤0.2，0.02≤X/Y≤0.25。从表2的循环容量保持率及厚度膨胀率结果显示，随着负极粘结剂A含量的逐步增加，锂离子电池的0℃循环容量保持率及厚度膨胀率呈现一个先增大后减小的趋势；表3中锂离子电池的大倍率放电的性能也是同样的规律。说明负极粘结剂的用量在合适的范围内时能够使负极片粘结良好，负极粘结剂在最优状态下对于构建稳定的SEI界面有一定的作用。此时，表现出来的电池的性能较优。一旦超出负极粘结剂的用量范围，由于电池阻抗的增大，负极片表面的副反应也相应增加，电池的性能会出现劣化，厚度膨胀率也会有一定的增大，从而影响了锂离子扩散路径，从而影响电池的低温充电性能及大倍率放电性能。
表1中对比例8至对比例19为一组对比电池组，负极粘结剂A含量为3％，羧酸酯类有机溶剂含量为30％，改变FEC含量和DTD含量，考察FEC含量和DTD含量对电池性能的影响。
当DTD含量和FEC含量逐步增大时，表2的循环容量保持率及厚度膨胀率结果显示，随着DTD含量和FEC含量的逐步增加，电池的循环容量保持率呈现一个先增大后减小的趋势，厚度膨胀率则出现了先减小后增大的趋势。说明FEC能在硅基负极表面建立起较完整及稳定的SEI界面，DTD能够在负极表面生成离子导电性好的有机磺酸盐，从而降低了界面阻抗，且两者组合的作用满足10≤A+B≤21时，电池能够形成较稳定且导电性好的SEI界面，电池性能也较优。DTD含量和FEC含量之和小于最优值时，SEI界面构造不完整，界面的副反应增多，消耗大量的电解液，溶剂容易在极片表面被还原，电池可能出现析锂、胀气等问题，所以电池循环时容量保持率低，厚度膨胀率大；且在低温下容易因为SEI膜不完整导致电池析锂，恶化电池性能。DTD含量和FEC含量之和大于最优值时，负极片表面的SEI膜成膜太厚，导致电池阻抗的增大，锂离子传输的速率受阻，可能导致电池循环出现后期出现析锂现象，从而影响电池的低温充电性能和大倍率 放电性能。
表1中对比例20至实施例24为一组对比电池组，负极粘结剂A含量为3％，DTD含量为0.5％，FEC含量为10％，只改变羧酸酯类有机溶剂的含量，考察羧酸酯类有机溶剂的含量对电池性能的影响。
当羧酸酯类有机溶剂的含量逐步增大时，X/(A+B+Y)和X/Y呈现了减小的趋势，从表2的低温拆解界面情况、循环容量保持率及厚度膨胀率结果显示，随着羧酸酯类有机溶剂含量的逐步增加，电池的循环容量保持率及厚度膨胀率呈现一个先增大后减小的趋势，且电池的界面也出现了逐渐改善的趋势。表3的大倍率放电容量比也同样出现了先增大后减小的趋势。这是由于羧酸酯类有机溶剂的粘度较小，能够在低温下保持较高的离子迁移率，从而改善电池的低温充电性能及大倍率放电性能。同时负极粘结剂跟羧酸酯类有机溶剂也会产生相互作用，当羧酸酯类有机溶剂较少时，负极粘结剂在电解液中的溶胀率较小，韧性较小，硅负极在充放电过程中的厚度膨胀率较大，负极粘结剂的作用没法很好地得到应用。羧酸酯类有机溶剂含量在合适的使用范围内，负极粘结剂在电解液中的溶胀达到合适的程度，此时负极粘结剂的韧性最大，硅负极在充放电过程中的厚度膨胀率大，此时的负极粘结剂能够起到一个弹簧的作用，电池中极片粘结良好，同时，合适的FEC和DTD含量使电池能够形成低阻抗稳定的SEI界面，所以电池的性能较优，厚度膨胀率也在正常范围内。但羧酸酯类有机溶剂含量过大时，负极粘结剂的溶胀过大，反而会影响负极粘结剂的作用。
以上，对本公开的实施方式进行了说明。但是，本公开不限定于上述实施方式。凡在本公开的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本公开的保护范围之内。

Claims (15)

  1. 一种锂离子电池，所述锂离子电池包括正极片、负极片、隔膜和非水电解液；其中，所述负极片包括负极集流体和涂覆在所述负极集流体一侧或两侧表面的负极活性物质层，所述负极活性物质层包括负极活性物质、负极导电剂和负极粘结剂；所述非水电解液包括硫酸亚乙酯、氟代碳酸乙烯酯和羧酸酯类有机溶剂；
    所述锂离子电池满足如下关系式：
    10≤A+B≤21，
    0.02≤X/(A+B+Y)≤0.2，
    0.02≤X/Y≤0.25；
    其中，A为硫酸亚乙酯在非水电解液中的质量百分比，B为氟代碳酸乙烯酯在非水电解液中的质量百分比，Y为羧酸酯类有机溶剂在非水电解液中的质量百分比，X为负极粘结剂在负极活性物质层中的质量百分比。
  2. 根据权利要求1所述的锂离子电池，其中，12≤A+B≤18。
  3. 根据权利要求1-2任一项所述的锂离子电池，其中，0.05≤X/(A+B+Y)≤0.18。
  4. 根据权利要求1-3任一项所述的锂离子电池，其中，0.05≤X/Y≤0.2。
  5. 根据权利要求1-4任一项所述的锂离子电池，其中，所述硫酸亚乙酯在非水电解液中的质量百分比A为0.1～2.5wt％。
  6. 根据权利要求1-5任一项所述的锂离子电池，其中，所述氟代碳酸乙烯酯在非水电解液中的质量百分比B为7.5～20.9wt％。
  7. 根据权利要求1-6任一项所述的锂离子电池，其中，所述羧酸酯类有机溶剂在非水电解液中的质量百分比Y为0.5～40wt％。
  8. 根据权利要求1-7任一项所述的锂离子电池，其中，所述负极粘结剂在负极活性物质层中的质量百分比X为0.5～15wt％。
  9. 根据权利要求1-8任一项所述的锂离子电池，其中，所述羧酸酯类有机溶剂选自丙酸乙酯、丙酸丙酯和乙酸丙酯中的至少一种。
  10. 根据权利要求1-9任一项所述的锂离子电池，其中，所述负极活性物质包括硅基负极材料，所述硅基负极材料选自单质硅、氧化亚硅中的至少一种；
    优选地，所述负极活性物质还包括碳基负极材料，所述碳基负极材料包括人造石墨、天然石墨、中间相碳微球、硬碳、软碳中的至少一种。
  11. 根据权利要求1-10任一项所述的锂离子电池，其中，所述负极粘结剂包括聚阴离子型粘结剂，所述聚阴离子粘结剂包括聚合物，所述聚合物的分子链上至少含有以下基团中的一种或几种组合：
    Figure PCTCN2022134648-appb-100001
  12. 根据权利要求11所述的锂离子电池，其中，所述聚阴离子型粘结剂中含有所述基团的摩尔百分含量为5～100mol％，优选为10％-60mol％。
  13. 根据权利要求11或12所述的锂离子电池，其中，所述聚合物中还包括柔性单体形成的重复单元结构，所述柔性单体包括丙烯酸酯、丙烯腈、乙烯醇和丙烯酸中的至少一种。
  14. 根据权利要求13所述的锂离子电池，其中，所述聚阴离子型粘结剂中含有的柔性单体形成的重复单元结构的摩尔百分含量为0～95mol％，优选为10％-80mol％。
  15. 根据权利要求11-14中任一项所述的锂离子电池，所述聚合物具有式I所示结构，
    Figure PCTCN2022134648-appb-100002
    其中m＝10-200，优选为20-120；n＝0-190，优选为20-160；p＝1-50，优选为1-10。
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