WO2022246798A1 - 锂离子二次电池、电池模块、电池包、以及用电装置 - Google Patents

锂离子二次电池、电池模块、电池包、以及用电装置 Download PDF

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WO2022246798A1
WO2022246798A1 PCT/CN2021/096742 CN2021096742W WO2022246798A1 WO 2022246798 A1 WO2022246798 A1 WO 2022246798A1 CN 2021096742 W CN2021096742 W CN 2021096742W WO 2022246798 A1 WO2022246798 A1 WO 2022246798A1
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lithium
positive electrode
ion secondary
secondary battery
electrolyte
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PCT/CN2021/096742
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English (en)
French (fr)
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彭畅
陈培培
邹海林
梁成都
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宁德时代新能源科技股份有限公司
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Priority to PCT/CN2021/096742 priority Critical patent/WO2022246798A1/zh
Priority to JP2022548006A priority patent/JP7371268B2/ja
Priority to EP21912316.3A priority patent/EP4120418B1/en
Priority to CN202180006343.7A priority patent/CN115699388A/zh
Priority to US17/820,944 priority patent/US11909000B2/en
Publication of WO2022246798A1 publication Critical patent/WO2022246798A1/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
    • 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
    • H01M10/0568—Liquid materials characterised by the solutes
    • 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
    • H01M4/36—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
    • 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
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/10—Primary casings, jackets or wrappings of a single cell or a single battery
    • H01M50/102—Primary casings, jackets or wrappings of a single cell or a single battery characterised by their shape or physical structure
    • H01M50/103—Primary casings, jackets or wrappings of a single cell or a single battery characterised by their shape or physical structure prismatic or rectangular
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/20—Mountings; Secondary casings or frames; Racks, modules or packs; Suspension devices; Shock absorbers; Transport or carrying devices; Holders
    • H01M50/204—Racks, modules or packs for multiple batteries or multiple cells
    • H01M50/207—Racks, modules or packs for multiple batteries or multiple cells characterised by their shape
    • H01M50/209—Racks, modules or packs for multiple batteries or multiple cells characterised by their shape adapted for prismatic or rectangular 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
    • 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
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • 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
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • 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
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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 field of lithium-ion secondary batteries, in particular to a lithium-ion secondary battery with high energy density, a battery module, a battery pack, and an electrical device.
  • Lithium-ion battery has become the most popular energy storage system due to its low cost, long life, and good safety. It has been widely used in pure electric vehicles, hybrid electric vehicles, smart grids and other fields. However, the current lithium-ion secondary batteries are difficult to meet people's higher demand for battery life. To get rid of people's "mileage anxiety" about electric vehicles, it is urgent to develop lithium-ion secondary batteries with higher energy density.
  • the energy density can be effectively increased by increasing the discharge gram capacity of the active material per unit volume in the lithium-ion secondary battery. For example, by reducing the carbon content as a conductive agent on the pole piece or the carbon coating amount on the surface of the positive electrode material particles, the weight of the active material per unit volume can be increased, thereby increasing the discharge gram capacity of the active material per unit volume. In addition, by increasing the coating weight of the active material and reducing the proportion of the inactive substrate, the discharge gram capacity of the active material per unit volume can be further increased.
  • the above strategy achieves high energy density, it will lead to a significant increase in the internal resistance of the battery. When charging at a high rate, the battery will release heat severely and therefore be under high temperature conditions.
  • lithium salts in the electrolyte such as LiPF 6 will accelerate the decomposition to produce HF, PF 5 and other gases.
  • These highly reactive components will accelerate the destruction of the SEI film, resulting in the exposure of active materials to the electrolyte, resulting in the loss of active materials.
  • the repair process of the SEI film will continue to consume active lithium and electrolyte, resulting in further deterioration of the cycle performance and storage life of the battery cell.
  • This application is made in view of the above-mentioned problems, and its purpose is to provide a lithium-ion secondary battery to solve the problems of high-energy-density batteries that generate a lot of heat during charging, resulting in decomposition of the electrolyte, and poor cycle and storage life of the batteries. question.
  • the first aspect of the present application provides a lithium ion secondary battery, which has a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the positive electrode sheet includes a positive electrode current collector and is arranged on the positive electrode current collector.
  • the electrolyte contains a lithium salt (M y+ ) x/y R 1 (SO 2 N - ) x SO 2 R 2 , wherein the My + is a metal ion, and R 1 and R 2 are each independently a fluorine atom, An alkyl group with 1-20 carbon atoms, a fluoroalkyl group with 1-20 carbon atoms or a fluoroalkoxy group with 1-20 carbon atoms, and the x is 1, 2 or 3, so Said y is 1, 2 or 3; the mass percentage of the lithium salt in the electrolyte is set as k2%;
  • the lithium ion secondary battery satisfies 0.34 ⁇ k2/k1 ⁇ 8.
  • the lithium ion secondary battery satisfies at least one of the following conditions 1) to 3):
  • the energy density and/or charge and discharge performance and/or cycle life of the battery can be further improved.
  • the My + is selected from Li + , Na + , K + , Rb + , Cs + , Mg 2+ , Ca 2+ , Ba 2+ , Al 3+ , Fe 2+ , Fe 3 + , Ni 2+ , and at least one of Ni 3+ , optionally, My + is at least one selected from Li + , Na + , K + , Rb + and Cs + .
  • the R 1 and R 2 are each independently a fluorine atom, an alkyl group with 1-10 carbon atoms, a fluoroalkyl group with 1-10 carbon atoms, or a fluoroalkyl group with 1-10 carbon atoms. 10 is a fluoroalkoxy group.
  • the R 1 and R 2 are each independently CH 3 , CF 3 or F.
  • the electrolyte of the lithium-ion secondary battery also contains a low-impedance additive, optionally, the low-impedance additive is fluorosulfonate NSO 3 F, difluorooxalate borate NDFOB, di At least one of fluorophosphate NPO 2 F 2 , difluorodioxalate NDFOP, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, where N is the metal of the salt Ions, for example, can be Li + , Na + , K + , Rb + , Cs + ; optionally, the low impedance additive is lithium fluorosulfonate, lithium difluorooxalate borate, tris(trimethylsilyl) At least one of phosphoric acid ester and lithium difluorophosphate.
  • these low-impedance additives can reduce the impedance of the protective film (SEI film) on the surface of the positive and negative electrodes
  • the mass percentage of the low-impedance additive in the electrolyte is 0.1%-10%, optionally 0.2%-5%.
  • the cycle performance of the battery can be further improved by selecting the mass percentage of the low impedance additive.
  • the electrolyte of the lithium-ion secondary battery also contains a lithium salt that inhibits aluminum foil corrosion.
  • the lithium salt that inhibits aluminum foil corrosion is selected from LiPF 6 , LiAsF 6 , and LiBF 4 at least one of the By adding a lithium salt that inhibits the corrosion of aluminum foil, it can inhibit the corrosion of aluminum foil and reduce the internal temperature rise of the battery cell.
  • the mass percentage of the lithium salt for inhibiting aluminum foil corrosion in the electrolyte is 0.1%-10%, optionally 0.2%-5%, optionally 1%-3%.
  • the total lithium salt content in the electrolyte of the lithium ion secondary battery is in the range of 5wt%-50wt%, optionally in the range of 5wt%-37wt%, optionally in the range of 5wt%- Within the range of 23wt%, based on the total weight of the electrolyte.
  • the positive electrode active material in the lithium ion secondary battery is selected from one or more of lithium transition metal oxides, olivine-structured lithium-containing phosphates and their respective modified compounds, and can be
  • a second aspect of the present application provides a battery module including the lithium ion secondary battery of the first aspect of the present application.
  • a third aspect of the present application provides a battery pack, which includes the battery module of the second aspect of the present application.
  • the fourth aspect of the present application provides an electric device, which is selected from the lithium ion secondary battery of the first aspect of the present application, the battery module of the second aspect of the present application or the battery pack of the third aspect of the present application more than one of .
  • FIG. 1 is a schematic diagram of a lithium ion secondary battery according to an embodiment of the present application.
  • FIG. 2 is an exploded view of the lithium ion secondary battery according to one 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 according to one embodiment of the present application shown in FIG. 4 .
  • FIG. 6 is a schematic diagram of a device in which a lithium-ion secondary battery is used as a power source according to an embodiment of the present application.
  • any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with any other lower limit to form an unexpressed range, just as any upper limit can be combined with any other upper limit to form an unexpressed range.
  • each individually disclosed point or individual value may serve as a lower or upper limit by itself in combination with any other point or individual value or with other lower or upper limits to form an unexpressly recited range.
  • a lithium-ion secondary battery typically includes a positive pole piece, a negative pole piece, a separator, and an electrolyte.
  • active ions are intercalated and extracted back and forth between the positive electrode and the negative electrode.
  • the separator is arranged between the positive pole piece and the negative pole piece to play the role of isolation.
  • the electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece.
  • the lithium ion secondary battery of the first aspect of the present application has a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, and the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector,
  • the positive electrode material layer comprises a positive electrode active material and carbon, wherein,
  • the electrolyte contains lithium salt (M y+ ) x/y R 1 (SO 2 N ⁇ ) x SO 2 R 2 , and its structural formula can be written as:
  • R 1 and R 2 are each independently a fluorine atom, an alkyl group with 1-20 carbon atoms, a fluoroalkyl group with 1-20 carbon atoms, or a fluoroalkyl group with 1 carbon atom -20 fluoroalkoxy, and the x is 1, 2 or 3, and the y is 1, 2 or 3; the mass percentage of the lithium salt in the electrolyte is set to k2%;
  • the lithium ion secondary battery satisfies 0.34 ⁇ k2/k1 ⁇ 8.
  • the carbon contained in the positive electrode material layer includes carbon coated on the surface of the positive electrode active material and carbon optionally contained as a conductive agent in the positive electrode slurry used to prepare the positive electrode material layer.
  • the internal temperature rise of the battery mainly comes from the temperature rise of the positive pole piece, and the temperature rise of the positive pole piece is mainly related to the thickness and conductivity of the positive pole piece.
  • the heat generated inside the cell is basically positively correlated with the temperature rise coefficient k1.
  • k1 is too small, the loading capacity of the positive electrode material is too low, and the carbon content of the positive electrode material layer is too high, and the proportion of inactive substrates is large, which will affect the energy density of the battery; while k1 is too large, the heat generated by the battery cell will be too high, In addition, if the loading of the positive electrode material is too high and the carbon content of the positive electrode material layer is too low, the solid phase transmission rate of lithium ions will be low and the charge and discharge performance of the battery will be deteriorated.
  • the heat resistance coefficient of the electrolyte can be significantly improved, and the decomposition of the electrolyte at high temperature can be reduced. So that the battery has a longer cycle life.
  • the inventors have also found that the relationship between the mass percentage k2 of the thermally stable salt (M y+ ) x/y R 1 (SO 2 N) x SO 2 R 2 in the electrolyte and the temperature rise coefficient k1 of the positive electrode sheet has a great influence on the battery cycle The life expectancy is greatly affected.
  • k2 and k1 satisfy the above relational formula, while ensuring high energy density of the battery, sufficient thermal stability of the electrolyte can be ensured, the decomposition of the electrolyte can be suppressed, and a long cycle life of the battery can be ensured.
  • the lithium ion secondary battery satisfies: 3.3 ⁇ k1 ⁇ 14.5.
  • the energy density and/or charge and discharge performance of the battery can be further improved.
  • the lithium ion secondary battery satisfies: 0.48 ⁇ k2/k1 ⁇ 7.
  • the cycle life of the battery can be further improved.
  • the lithium ion secondary battery satisfies: 1% ⁇ Mc% ⁇ 7%.
  • the lithium ion secondary battery satisfies: 1% ⁇ Mc% ⁇ 5%. If the carbon content is too high, it may lead to the following situation: the proportion of positive electrode active material per unit volume is low, thereby reducing the energy density of the battery, and it will cause the surface area of the positive electrode material to be too large, so that it is easy to absorb water and agglomerate, making it difficult to process the pole piece; if carbon If the content is too low, the following conditions may be caused: the conductivity of the pole piece becomes poor, and lithium precipitation may occur during charging, which affects the cycle life of the battery and poses a safety risk.
  • the lithium ion secondary battery satisfies: 18 ⁇ Cw ⁇ 32. If the loading Cw of the positive electrode material is too low, it may lead to a large proportion of inactive substrates (such as current collectors), thereby reducing the energy density, and if the Cw is too large, it may make coating more difficult and greatly increase the lithium ion density.
  • the transmission path of ions in the direction perpendicular to the pole piece makes it difficult for lithium ions to quickly extract and insert into the active material, which affects the power performance of the cell.
  • the My + is selected from Li + , Na + , K + , Rb + , Cs + , Mg 2+ , Ca 2+ , Ba 2+ , Al 3+ , Fe 2+ , Fe 3 + , Ni 2+ , and at least one of Ni 3+ , optionally, My + is at least one selected from Li + , Na + , K + , Rb + and Cs + .
  • the migration number of the above-mentioned cations is larger, which makes the power performance of the battery better.
  • the R 1 and R 2 are each independently a fluorine atom, an alkyl group with 1-10 carbon atoms, a fluoroalkyl group with 1-10 carbon atoms, or a 1-10 carbon atom group. 10 is a fluoroalkoxy group.
  • the R 1 and R 2 are each independently CH 3 , CF 3 or F.
  • the electrolyte solution also contains a low-impedance additive, optionally, the low-impedance additive is NSO 3 F (fluorosulfonate), NDFOB (difluorooxalate borate), NPO 2 F At least one of 2 (difluorophosphate), NDFOP (difluorodioxalate), tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, where N is a salt Metal ions, for example, may be Li + , Na + , K + , Rb + , Cs + .
  • the low impedance additive is LiSO 3 F (lithium fluorosulfonate), LiDFOB (lithium difluorooxalate borate), tris(trimethylsilyl) phosphate and LiPO 2 F 2 (lithium difluorophosphate) at least one of the
  • the mass percentage of the low-impedance additive in the electrolyte is 0.1%-10%, optionally 0.2%-5%.
  • the impedance of the protective film (SEI film) on the surface of the positive and negative pole pieces also has a great influence on the internal temperature rise of the battery. The increase in the resistance value of the SEI film will further lead to the failure of the battery during charging. temperature rise.
  • the low-impedance additive can preferentially reduce the electrolyte solvent on the surface of the negative electrode during the formation process, forming an extremely low-impedance and dense protective film on the surface of the negative electrode, thereby inhibiting the solvent in the electrolyte and other high-impedance components. Reductive decomposition of additives on the surface of the negative electrode, thereby reducing the impedance of the SEI film.
  • the content of the low-impedance additive is within the above range, the viscosity of the electrolyte will not increase, and the conductivity of the electrolyte can be maintained.
  • the electrolyte also contains a lithium salt that inhibits aluminum foil corrosion.
  • the lithium salt that inhibits aluminum foil corrosion is at least one selected from LiPF 6 , LiAsF 6 , and LiBF 4 .
  • the mass percentage of the lithium salt for inhibiting aluminum foil corrosion in the electrolyte is 0.1%-10%, optionally 0.2%-5%, optionally 1%-3%.
  • the lithium salt for inhibiting the corrosion of the aluminum foil can inhibit the corrosion of the aluminum foil, thereby inhibiting the increase of the impedance of the aluminum current collector, reducing the internal temperature rise of the battery cell, and improving the safety performance of the battery cell.
  • the aluminum foil corrosion inhibiting lithium salt content is in the above range, the aluminum foil corrosion can be inhibited, and the high temperature resistance performance of the electrolytic solution will not be adversely affected.
  • the total lithium salt content in the electrolyte is in the range of 5wt%-50wt%, optionally in the range of 5wt%-37wt%, optionally in the range of 5wt%-23wt%, based on The total weight of the electrolyte.
  • the positive electrode active material is selected from one or more of lithium transition metal oxides, olivine-structured lithium-containing phosphates and their respective modified compounds.
  • olivine-structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese phosphate, a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, lithium manganese iron phosphate One or more of the composite materials with carbon and their modified compounds. These materials are all commercially available. Carbon may be coated on the surface of the positive electrode active material.
  • the carbon content Mc of the positive electrode material layer can be measured using equipment and methods known in the art. For example, it can be measured by infrared absorption method after scraping off the positive electrode material layer on the positive electrode current collector, for example, refer to GB/T20123-2006 Determination of total carbon and sulfur content of steel-infrared absorption method after combustion in high frequency induction furnace.
  • the electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece.
  • the electrolytic solution includes electrolyte salts and solvents.
  • the electrolyte salt can be a common electrolyte salt in lithium ion secondary batteries, such as lithium salt, including lithium salt that can be the above-mentioned lithium salt as a high thermal stability salt, lithium salt as a low impedance additive, or lithium salt that inhibits aluminum foil corrosion. Salt.
  • the electrolyte salt may be selected from LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiAsF 6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonimide), LiTFSI (bistrifluoromethane Lithium sulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiPO 2 F 2 (lithium difluorophosphate), LiDFOP (lithium difluorodifluorooxalate phosphate), LiSO 3 F (lithium fluorosulfonate), NDFOP (difluorodioxalate), Li 2 F(SO 2 N) 2 SO 2 F, KFSI, CsFSI, Ba(FSI) 2 and LiFSO 2 NSO 2 CH 2 CH 2 CF 3 more than one of them
  • the solvent is not particularly limited, and can be selected according to actual needs.
  • the solvent is a non-aqueous solvent.
  • the solvent may include one or more of chain carbonates, cyclic carbonates, and carboxylates.
  • the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), Dipropyl Carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Butylene Carbonate (BC), Fluoroethylene Carbonate (FEC), Methyl Formate (MF), Methyl Acetate Ester (MA), Ethyl Acetate (EA), Propyl Acetate (PA), Methyl Propionate (MP), Ethyl Propionate (EP), Propyl Propionate (PP), Methyl Butyrate (MB) , e
  • the electrolyte may optionally include other additives.
  • additives can include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performances of batteries, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and battery low-temperature performance. additives, etc.
  • the additive is selected from cyclic carbonate compounds containing unsaturated bonds, halogen-substituted cyclic carbonate compounds, sulfate ester compounds, sulfite compounds, sultone compounds, disulfonic acid compounds, nitrile compounds , aromatic compounds, isocyanate compounds, phosphazene compounds, cyclic acid anhydride compounds, phosphite compounds, phosphate compounds, borate compounds, and carboxylate compounds.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector, and the positive electrode material layer includes positive electrode active material and carbon.
  • the positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode material layer is disposed on any one or both of the two opposing surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • aluminum foil can 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 can be formed by metal materials (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) Formed on substrates such as polyethylene formate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.
  • the positive electrode material layer optionally includes a conductive agent.
  • a conductive agent there is no specific limitation on the type of conductive agent, which can be selected by those skilled in the art according to actual needs.
  • the conductive agent used for the positive electrode material may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the positive electrode material layer also optionally includes a binder.
  • the binder can be styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer One or more of (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).
  • SBR styrene-butadiene rubber
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • PAA polyacrylic acid
  • CMC carboxymethyl cellulose
  • PVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • the positive electrode sheet can be prepared according to methods known in the art.
  • a positive electrode active material coated with carbon, a conductive agent, and a binder can be dispersed in a solvent (such as N-methylpyrrolidone (NMP)) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode On the current collector, after drying, cold pressing and other processes, the positive electrode sheet is obtained.
  • NMP N-methylpyrrolidone
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode active material.
  • the negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode material layer is disposed on any one or both of the two opposing surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • copper foil can be used as the metal foil.
  • the composite current collector may include a base layer of polymer material and a metal layer formed on at least one surface of the base material of polymer material.
  • Composite current collectors can be formed by metal materials (such as copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) Formed on substrates such as polyethylene formate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.
  • the negative electrode material layer usually includes negative electrode active material and optional binder, optional conductive agent and other optional additives, usually formed by coating and drying negative electrode slurry into.
  • the negative electrode slurry coating is usually formed by dispersing the negative electrode active material and optional conductive agent and binder in a solvent and stirring them evenly.
  • the solvent can be N-methylpyrrolidone (NMP) or deionized water.
  • the negative electrode active material is not limited, and active materials known in the art that can be used for the negative electrode of lithium ion secondary batteries can be used, and those skilled in the art can select according to actual needs.
  • the negative electrode active material can be selected from one or more of graphite, soft carbon, hard carbon, mesocarbon microspheres, carbon fibers, carbon nanotubes, simple silicon, silicon oxide compounds, silicon-carbon composites, and lithium titanate. kind.
  • the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the binder may be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), One or more of polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • SBR styrene-butadiene rubber
  • PAA polyacrylic acid
  • PAAS sodium polyacrylate
  • PAM polyacrylamide
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • PMAA polymethacrylic acid
  • CMCS carboxymethyl chitosan
  • thickeners such as sodium carboxymethylcellulose (CMC-Na)
  • CMC-Na sodium carboxymethylcellulose
  • a separator is also included in a lithium ion secondary battery using an electrolytic solution.
  • the separator is arranged between the positive pole piece and the negative pole piece to play the role of isolation.
  • the present application has no special limitation on the type of isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.
  • the material of the isolation film can be selected from more than one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the separator can be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multilayer composite film, the materials of each layer may be the same or different, and there is no particular limitation.
  • the positive pole piece, the negative pole piece and the separator can be made into an electrode assembly through a winding process or a lamination process.
  • a lithium ion secondary battery may include an outer package.
  • the outer package can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer package of the lithium-ion secondary battery may be a hard case, such as a hard plastic case, aluminum case, steel case, and the like.
  • the outer packaging of the lithium-ion secondary battery may also be a soft bag, such as a pouch-type soft bag.
  • the material of the soft bag may be plastic, and examples of plastic include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).
  • FIG. 1 shows a lithium-ion secondary battery 5 having a square structure as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plates enclose to form an accommodating cavity.
  • the housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 can cover the opening to close the accommodating cavity.
  • the positive pole piece, the negative pole piece and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the accommodating chamber. Electrolyte is infiltrated in the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the lithium-ion secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • the lithium-ion secondary battery can be assembled into a battery module, and the number of lithium-ion secondary batteries contained in the battery module can be one or more, and the specific number can be determined by those skilled in the art according to the application and capacity of the battery module. choose.
  • FIG. 3 is a battery module 4 as an example.
  • a plurality of lithium-ion secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of lithium-ion secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may also include a housing with a containing space in which a plurality of lithium-ion secondary batteries 5 are housed.
  • the above battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be selected by those skilled in the art according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3 , the upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides a device, which includes more than one of the lithium-ion secondary battery, battery module, or battery pack provided in the present application.
  • the lithium-ion secondary battery, battery module, or battery pack can be used as a power source of the device, and can also be used as an energy storage unit of the device.
  • the device can be, but not limited to, a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • a lithium ion secondary battery, a battery module, or a battery pack can be selected according to its use requirements.
  • Figure 6 is an example device.
  • the device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • battery packs or battery modules can be employed.
  • a device may be a cell phone, tablet, laptop, or the like.
  • the device is usually required to be light and thin, and a lithium-ion secondary battery can be used as a power source.
  • Lithium iron phosphate (LFP), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are dissolved in solvent N-methylpyrrolidone ( NMP), fully stirred and mixed uniformly to obtain positive electrode slurry, wherein the carbon-coated lithium iron phosphate used has the carbon content shown in Table 1. Then, according to the Cw value to be achieved, the positive electrode slurry is evenly coated on the aluminum positive electrode current collector, and then dried, cold pressed, and cut to obtain the positive electrode sheet.
  • Negative electrode active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC-Na) are dissolved in the solvent according to the weight ratio of 95:2:2:1 deionized water, mixed uniformly to prepare negative electrode slurry. Then determine the negative electrode loading capacity according to the Cw value of the corresponding positive electrode. According to the negative electrode loading capacity shown in Table 1, evenly coat the negative electrode slurry on the copper foil of the negative electrode current collector. After drying, cold press and cut to obtain the negative electrode sheet .
  • the organic solvent EC/EMC was mixed uniformly according to the volume ratio of 3/7, and 3wt% of vinylene carbonate and the Show the high thermal stability salt of weight percent and optional additive, stir, obtain corresponding electrolytic solution, the weight percent of described vinylene carbonate and the weight percent shown in table 2 are all based on the gross weight meter of gained electrolytic solution .
  • the positive electrode sheet obtained in the above (1) and the negative electrode sheet obtained in the above (2) use the polypropylene film as the separator, and stack the positive electrode sheet, separator, and negative electrode sheet in order, so that The separator is placed between the positive and negative pole pieces to play the role of isolation, and then wound to obtain the electrode assembly.
  • the electrode assembly is placed in the battery casing, after being dried, the electrolyte solution is injected, and then the lithium ion secondary battery is obtained through chemical formation and standing.
  • Test instrument high-frequency infrared carbon-sulfur analyzer, model HCS-140, purchased from Shanghai Dekai Instrument Co., Ltd.
  • the lithium-ion battery was charged at a constant current of 0.5C to 3.65V, then charged at a constant voltage of 3.65V until the current was less than 0.05C, and then discharged at 0.33C to 2.5V to obtain the discharge energy Q.
  • Use a vernier caliper to measure the length, width, and height of the cell, and calculate the volume V, and the volume energy density Q/V
  • Table 2 shows Mc, Cw, k1, k2, volumetric energy density, and cycle performance at 45° C. of lithium-ion batteries of various examples and comparative examples.
  • Examples 1-25 use both an electrolyte containing a high-stability lithium salt and a positive electrode sheet with a large load on the positive electrode material layer and a low carbon content, which enables the battery to take into account both high energy density and long cycle life.
  • Example 1 Comparing Example 1 with Example 2, it can be seen that the k2/k1 value of Example 1 is in the range of 0.48-7, thus obtaining better cycle performance than Example 2. Comparing Example 1 with Example 4, it can be seen that the k1 value of Example 1 is in the range of 3.3-14.5, thus obtaining better cycle performance than Example 4.

Abstract

本申请涉及一种锂离子二次电池，其电解液中含有高热稳定性盐(M y+) x/yR 1(SO 2N -) xSO 2R 2，其中所述M y+为金属离子，R 1、R 2各自独立地为氟原子、碳原子数为1-20的烷基、碳原子数为1-20的氟代烷基或碳原子数为1-20的氟代烷氧基，并且所述x为1、2或3，所述y为1、2或3；将该盐在所述电解液中的质量百分比设为k2％；所述正极极片的温升系数k1满足2.5≤k1≤32，其中k1＝Cw/Mc，Cw为正极集流体负载有正极材料层的任一侧表面上单位面积的正极材料负载量(mg/cm 2)，Mc为正极材料层的含碳量(％)；并且，所述锂离子二次电池满足0.34≤k2/k1≤8。本申请的锂离子二次电池兼具高能量密度与长寿命。本申请还涉及包含所述锂离子二次电池的电池模块、电池包和用电装置。

Description

锂离子二次电池、电池模块、电池包、以及用电装置 技术领域
本申请涉及锂离子二次电池领域，尤其涉及一种具有高能量密度的锂离子二次电池、电池模块、电池包、以及用电装置。
背景技术
锂离子电池因其成本低、寿命长，安全性好等特点成为最受欢迎的能量存储***，现已被广泛应用于纯电动汽车，混合电动汽车，智能电网等领域。但目前的锂离子二次电池难以满足人们对续航能力的更高需求，要破除人们对电动汽车“里程焦虑”的问题，就迫切需要开发具有更高能量密度的锂离子二次电池。
通过提高锂离子二次电池中单位体积下的活性材料的放电克容量，可以有效增加能量密度。例如，通过减少极片上作为导电剂的碳含量或正极材料颗粒表面碳包覆量，可以增加单位体积下活性材料的重量，从而增加单位体积下活性材料的放电克容量。此外，通过增加活性材料的涂布重量，减少非活性基材的使用占比，可以进一步提升单位体积下活性材料的放电克容量。但如上策略在实现高能量密度的同时，会导致电芯内阻显著增大，在高倍率充电时，电芯放热严重并因此处于高温条件下。此时，电解液中的锂盐如LiPF 6会加速分解产生HF、PF 5等气体，这些高反应活性成分会加速破坏SEI膜，导致活性物质暴露在电解液中，导致活性材料的损失。而SEI膜的修复过程会持续消耗活性锂和电解液，导致电芯循环性能和存储寿命进一步恶化。
因此，存在提高锂离子二次电池的能量密度同时确保电芯循环和存储寿命的需求。
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锂离子二次电池，以解决高能量密度的电芯在充电时大量发热而导致电解液分解，电芯循环和存储寿命较差的问题。
为了达到上述目的，本申请第一方面提供一种锂离子二次电池，其具有正极极片、负极极片、隔离膜及电解液，所述正极极片包括正极集流体和设置于正极集流体至少一个表面上的正极材料层，所述正极材料层包含正极活性物质和碳，其中，
所述电解液中含有锂盐(M y+) x/yR 1(SO 2N -) xSO 2R 2，其中所述M y+为金属离子，R 1、R 2各自独立地为氟原子、碳原子数为1-20的烷基、碳原子数为1-20的氟代烷基或碳原子数为1-20的氟代烷氧基，并且所述x为1、2或3，所述y为1、2或3；将该锂盐在所述电解液中的质量百分比设为k2％；
所述正极极片的温升系数k1满足2.5≤k1≤32，其中k1＝Cw/Mc，Cw为正极集流体负载有正极材料层的任一侧表面上单位面积的正极材料负载量(mg/cm 2)，Mc为所述正极材料层的含碳量(％)；
并且，所述锂离子二次电池满足0.34≤k2/k1≤8。
通过使用含有高热稳定性盐(M y+) x/yR 1(SO 2N -) xSO 2R 2的电解液，并使高热稳定性盐(M y+) x/y(R 1SO 2N) xSO 2R 2的含量与正极极片的正极材料负载量和碳含量满足特定的关系，能够在提高电芯的体积能量密度的同时，减轻高温对电解液的影响，从而获得更好的电芯性能，解决高能量密度与长寿命难以兼顾的问题。
在任意实施方式中，所述锂离子二次电池满足下述条件1)至3)中的至少一项：
1)3.3≤k1≤14.5；
2)0.48≤k2/k1≤7；
3)1≤Mc≤7。
通过满足上述条件1)至3)中的至少一项，可以进一步改进电池的能量密度和/或充放电性能和/或循环寿命。
在任意实施方式中，所述M y+为选自Li +、Na +、K +、Rb +、Cs +、Mg 2+、Ca 2+、Ba 2+、Al 3+、Fe 2+、Fe 3+、Ni 2+、以及Ni 3+中的至少一种，可选地，M y+为选自Li +、Na +、K +、Rb +以及Cs +中的至少一种。通过选择上述阳离子，可以进一步改善电芯功率性能。
在任意实施方式中，所述R 1、R 2各自独立地为氟原子、碳原子数为1-10的烷基、碳原子数为1-10的氟代烷基或碳原子数为1-10的氟代烷氧基，可选地，所述R 1、R 2各自独立地为CH 3、CF 3或F。通过选择R 1、R 2的结构，有助于改善电池的循环性能。
在任意实施方式中，所述锂离子二次电池的电解液中还含有低阻抗添加剂，可选地，所述低阻抗添加剂为氟磺酸盐NSO 3F、二氟草酸硼酸盐NDFOB、二氟磷酸盐NPO 2F 2、二氟二草酸盐NDFOP、三(三甲基硅烷基)磷酸酯、三(三甲基硅烷基)亚磷酸酯中的至少一种，其中N为盐的金属离子，例如可选为Li +、Na +、K +、Rb +、Cs +；可选地，所述低阻抗添加剂为氟磺酸锂、二氟草酸硼酸锂、三(三甲基硅烷基)磷酸酯和二氟磷酸锂中的至少一种。这些低阻抗添加剂能够降低正负极极片表面上保护膜(SEI膜)的阻抗，减轻温升导致的电池性能恶化。
在任意实施方式中，所述低阻抗添加剂在所述电解液中的质量百分比为0.1％～10％，可选为0.2％～5％。通过选择低阻抗添加剂的质量百分比， 可以进一步改善电池循环性能。
在任意实施方式中，所述锂离子二次电池的电解液中还含有抑制铝箔腐蚀的锂盐，可选地，所述抑制铝箔腐蚀的锂盐为选自LiPF 6、LiAsF 6、以及LiBF 4中的至少一种。通过添加抑制铝箔腐蚀的锂盐，可以抑制铝箔腐蚀，减少电芯内部温升。
在任意实施方式中，所述抑制铝箔腐蚀的锂盐在所述电解液中的质量百分比为0.1％～10％，可选为0.2％～5％，可选为1％～3％。通过选择抑制铝箔腐蚀的锂盐的含量，能够进一步改善电池的循环性能。
在任意实施方式中，所述锂离子二次电池的电解液中的总锂盐含量在5wt％-50wt％范围内，可选地在5wt％-37wt％范围内，可选地在5wt％-23wt％范围内，基于电解液总重量计。通过选择电解液中的总锂盐含量，能够改善锂离子二次电池的循环寿命和功率性能。
在任意实施方式中，所述锂离子二次电池中的正极活性物质选自锂过渡金属氧化物、橄榄石结构的含锂磷酸盐及其各自的改性化合物中的一种或几种，可选地，所述锂过渡金属氧化物选自锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、满足a+b+c＝1且a＜0.8的锂镍钴锰氧化物LiNi aCo bMn cO 2、锂镍钴铝氧化物及其改性化合物中的一种或几种。
本申请的第二方面提供一种电池模块，其包括本申请第一方面的锂离子二次电池。
本申请的第三方面提供一种电池包，其包括本申请第二方面的电池模块。
本申请的第四方面提供一种用电装置，其包括选自本申请的第一方面的锂离子二次电池、本申请的第二方面的电池模块或本申请的第三方面的电池包中的一种以上。
附图说明
为了更清楚地说明本申请的技术方案，下面将对本申请实施例中所需要使用的附图作简单的介绍。显而易见地，下面所描述的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请一实施方式的锂离子二次电池的示意图。
图2是图1所示的本申请一实施方式的锂离子二次电池的分解图。
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锂离子二次电池用作电源的装置的示意图。
附图标记说明
1电池包
2上箱体
3下箱体
4电池模块
5锂离子二次电池
51壳体
52电极组件
53盖板
具体实施方式
为了简明，本申请具体地公开了一些数值范围。然而，任意下限可以 与任意上限组合形成未明确记载的范围；以及任意下限可以与其它下限组合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，每个单独公开的点或单个数值自身可以作为下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
锂离子二次电池
通常情况下，锂离子二次电池包括正极极片、负极极片、隔离膜及电解质。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。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。电解质在正极极片和负极极片之间起到传导离子的作用。
本申请第一方面的锂离子二次电池具有正极极片、负极极片、隔离膜及电解液，所述正极极片包括正极集流体和设置于正极集流体至少一个表面上的正极材料层，所述正极材料层包含正极活性物质和碳，其中，
所述电解液中含有锂盐(M y+) x/yR 1(SO 2N -) xSO 2R 2，其结构式可写作：
Figure PCTCN2021096742-appb-000001
其中所述M y+为金属离子，R 1、R 2各自独立地为氟原子、碳原子数为1-20的烷基、碳原子数为1-20的氟代烷基或碳原子数为1-20的氟代烷氧基，并且所述x为1、2或3，所述y为1、2或3；将该锂盐在所述电解液中的质量百分比设为k2％；
所述正极极片的温升系数k1满足2.5≤k1≤32，其中k1＝Cw/Mc，Cw为正极集流体负载有正极材料层的任一侧表面上单位面积的正极材料负载量(mg/cm 2)，Mc为正极材料层的含碳量(％)；
并且，所述锂离子二次电池满足0.34≤k2/k1≤8。
其中，正极材料层中包含的碳包括正极活性物质表面上包覆的碳和制备正极材料层所用的正极浆料中任选地包含的作为导电剂的碳。
在充电过程中，电芯内部温升主要来源于正极极片的温升，而正极极片的温升主要与正极极片厚度和导电性相关。正极极片的厚度与正极集流体负载有正极材料层的任一侧表面上单位面积的正极材料负载量Cw有关，导电性与正极材料层的含碳量Mc有关。因此，定义正极极片温升系数k1＝Cw/Mc。当充电电流一定时，电芯内部的产热量基本与温升系数k1成正相关。如果k1太小，则正极材料负载量太低，并且正极材料层含碳量太高，非活性基材的比例大，影响降低电池能量密度；而k1太大，则电芯产热量过高，并且正极材料负载量太高且正极材料层含碳量太低，会导致锂离子固相传输速率低，恶化电池充放电性能。
另外，通过在电解液中加入高热稳定性的(M y+) x/yR 1(SO 2N) xSO 2R 2，可以显著提高电解液的耐热系数，减少电解液在高温下分解，从而使得电池具有较长的循环寿命。但发明人在研究中发现，高热稳定性盐浓度太高时，会导致电解液粘度增加，电导率恶化，进而导致电芯内阻增加，而盐浓度太低时，电解液热稳定性不足，可能在高温下分解，从而缩短电芯寿命。此外，发明人还发现，电解液中热稳定性盐(M y+) x/yR 1(SO 2N) xSO 2R 2的质量百分比k2与正极极片温升系数k1的关系对电池循环寿命影响较大。当k2与k1满足上述关系式时，能在保证电池具有高的能量密度的同时，也能保证有足够的电解液热稳定性，抑制电解液的分解，保证电池具有较长的循环寿命。
在一些实施方式中，所述的锂离子二次电池满足：3.3≤k1≤14.5。通过对k1数值的进一步选择，可以进一步改进电池的能量密度和/或充放电性能。
在一些实施方式中，所述的锂离子二次电池满足：0.48≤k2/k1≤7。 通过对k2/k1数值的进一步选择，可以进一步改进电池的循环寿命。
在一些实施方式中，所述的锂离子二次电池满足：1％≤Mc％≤7％，可选地，所述的锂离子二次电池满足：1％＜Mc％≤5％。如果碳含量太高，可能会导致以下情况：单位体积下正极活性物质比例低，从而降低电池能量密度，并且会导致正极材料表面积过大，从而易吸水、团聚，导致极片难以加工；如果碳含量太低，可能会导致以下情况：极片导电性变差，充电过程中可能发生析锂，影响电池循环寿命，且带来安全风险。
在一些实施方式中，所述的锂离子二次电池满足：18≤Cw≤32。如果正极材料负载量Cw太低，可能会导致非活性基材(如集流体)的占比大，从而降低能量密度，而Cw太大，可能使得涂布难度变高，且大幅度增加了锂离子在垂直于极片方向上的传输路径，导致锂离子难以快速脱出和嵌入活性材料，影响电芯功率性能。
在一些实施方式中，所述M y+为选自Li +、Na +、K +、Rb +、Cs +、Mg 2+、Ca 2+、Ba 2+、Al 3+、Fe 2+、Fe 3+、Ni 2+、以及Ni 3+中的至少一种，可选地，M y+为选自Li +、Na +、K +、Rb +以及Cs +中的至少一种。上述阳离子的迁移数更大，使得电芯功率性能更优。
在一些实施方式中，所述R 1、R 2各自独立地为氟原子、碳原子数为1-10的烷基、碳原子数为1-10的氟代烷基或碳原子数为1-10的氟代烷氧基，可选地，所述R 1、R 2各自独立地为CH 3、CF 3或F。通过选择R 1、R 2的结构，能够提高锂离子迁移数并使锂离子更容易解离，同时电解液粘度较小，使得电解液电导率较高，从而可有助于改善电池的循环性能。
在一些实施方式中，所述电解液中还含有低阻抗添加剂，可选地，所述低阻抗添加剂为NSO 3F(氟磺酸盐)、NDFOB(二氟草酸硼酸盐)、NPO 2F 2(二氟磷酸盐)、NDFOP(二氟二草酸盐)、三(三甲基硅烷基)磷酸酯、三(三甲基硅烷基)亚磷酸酯中的至少一种，其中N为盐的金属离子， 例如可选为Li +、Na +、K +、Rb +、Cs +。可选地，所述低阻抗添加剂为LiSO 3F(氟磺酸锂)、LiDFOB(二氟草酸硼酸锂)、三(三甲基硅烷基)磷酸酯和LiPO 2F 2(二氟磷酸锂)中的至少一种。可选地，所述低阻抗添加剂在所述电解液中的质量百分比为0.1％～10％，可选为0.2％～5％。除了正极极片温升外，正负极极片表面上保护膜(SEI膜)的阻抗对电芯内部温升影响也较大，SEI膜阻抗值增大，会进一步导致充电过程中电芯的温升。不希望限于理论，低阻抗添加剂在化成过程中，能优先于电解液溶剂在负极表面还原，在负极表面形成一层极低阻抗且致密的保护膜，进而抑制电解液中的溶剂和其他高阻抗添加剂在负极表面的还原分解，从而减少SEI膜的阻抗。另外，低阻抗添加剂含量在上述范围内，则电解液粘度不会增加，能够保持电解液的电导率。
在一些实施方式中，所述电解液中还含有抑制铝箔腐蚀的锂盐，可选地，所述抑制铝箔腐蚀的锂盐为选自LiPF 6、LiAsF 6、以及LiBF 4中的至少一种。可选地，所述抑制铝箔腐蚀的锂盐在所述电解液中的质量百分比为0.1％～10％，可选为0.2％～5％，可选为1％～3％。所述抑制铝箔腐蚀的锂盐可以抑制铝箔腐蚀，从而抑制铝集流体的阻抗增大，减少电芯内部温升，提升电芯安全性能。当抑制铝箔腐蚀锂盐含量在上述范围时，能够抑制铝箔腐蚀，并且不会对电解液的耐高温性能带来不良影响。
在一些实施方式中，所述电解液中的总锂盐含量在5wt％-50wt％范围内，可选地在5wt％-37wt％范围内，可选地在5wt％-23wt％范围内，基于电解液总重量计。通过选择电解液中的总锂盐含量，能够改善锂离子二次电池的循环寿命和功率性能。
在一些实施方式中，所述正极活性物质选自锂过渡金属氧化物、橄榄石结构的含锂磷酸盐及其各自的改性化合物中的一种或几种。锂过渡金属氧化物的示例可包括但不限于锂钴氧化物、锂镍氧化物、锂锰氧化物、锂 镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物LiNi aCo bMn cO 2(a+b+c＝1，a＜0.8)、锂镍钴铝氧化物及其改性化合物中的一种或几种。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、磷酸铁锂与碳的复合材料、磷酸锰锂、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料及其改性化合物中的一种或几种。这些材料均可以通过商业途径获得。正极活性物质表面上可包覆有碳。
在本申请中，正极材料层的含碳量Mc可以采用本领域已知的设备和方法进行测量。例如，可通过将正极集流体上的正极材料层刮下后采用红外吸收法测量，例如参照GB/T20123-2006钢铁总碳硫含量的测定-高频感应炉燃烧后红外吸收法。
[电解液]
电解液在正极极片和负极极片之间起到传导离子的作用。电解液包括电解质盐和溶剂。
在本申请中，电解质盐可为锂离子二次电池中的常用电解质盐，例如锂盐，包括可为上述作为高热稳定性盐的锂盐、作为低阻抗添加剂的锂盐或抑制铝箔腐蚀的锂盐。作为实例，电解质盐可选自LiPF 6(六氟磷酸锂)、LiBF 4(四氟硼酸锂)、LiAsF 6(六氟砷酸锂)、LiFSI(双氟磺酰亚胺锂)、LiTFSI(双三氟甲磺酰亚胺锂)、LiTFS(三氟甲磺酸锂)、LiDFOB(二氟草酸硼酸锂)、LiPO 2F 2(二氟磷酸锂)、LiDFOP(二氟二草酸磷酸锂)、LiSO 3F(氟磺酸锂)、NDFOP(二氟二草酸盐)、Li 2F(SO 2N) 2SO 2F、KFSI、CsFSI、Ba(FSI) 2及LiFSO 2NSO 2CH 2CH 2CF 3中的一种以上。
所述溶剂的种类没有特别的限制，可根据实际需求进行选择。在一些实施方式中，所述溶剂为非水性溶剂。可选地，所述溶剂可包括链状碳酸酯、环状碳酸酯、羧酸酯中的一种或几种。在一些实施方式中，溶剂可选 自碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸亚乙酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1，4-丁内酯(GBL)、四氢呋喃、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的一种以上。
在一些实施方式中，所述电解液中还可选地包括其他添加剂。例如添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、以及改善电池低温性能的添加剂等。作为示例，所述添加剂选自含有不饱和键的环状碳酸酯化合物、卤素取代的环状碳酸酯化合物、硫酸酯化合物、亚硫酸酯化合物、磺酸内酯化合物、二磺酸化合物、腈化合物、芳香化合物、异氰酸酯化合物、磷腈化合物、环状酸酐化合物、亚磷酸酯化合物、磷酸酯化合物、硼酸酯化合物、羧酸酯化合物中的至少一种。
[正极极片]
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的正极材料层，所述正极材料层包括正极活性物质和碳。
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，正极材料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。
本申请的锂离子二次电池中，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(例如铝、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。
正极材料层可选地包括导电剂。但对导电剂的种类不做具体限制，本领域技术人员可以根据实际需求进行选择。作为示例，用于正极材料的导电剂可以选自超导碳、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一种以上。
正极材料层还可选地包括粘结剂。作为示例，粘结剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂(water-based acrylic resin)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚丙烯酸(PAA)、羧甲基纤维素(CMC)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB)中的一种或几种。
本申请中可按照本领域已知的方法制备正极极片。作为示例，可以将包覆碳的正极活性物质、导电剂和粘结剂分散于溶剂(例如N-甲基吡咯烷酮(NMP))中，形成均匀的正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，得到正极极片。
[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材料层，所述负极材料层包括负极活性物质。
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，负极材料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。
本申请的锂离子二次电池中，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(例如铜、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。
本申请的锂离子二次电池中，所述负极材料层通常包含负极活性物质以及可选的粘结剂、可选的导电剂和其他可选助剂，通常是由负极浆料涂布干燥而成的。负极浆料涂通常是将负极活性物质以及可选的导电剂和粘结剂等分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水。
所述负极活性物质的具体种类不做限制，可以采用本领域已知的能够用于锂离子二次电池负极的活性物质，本领域技术人员可以根据实际需求进行选择。作为示例，负极活性物质可选自石墨、软碳、硬碳、中间相碳微球、碳纤维、碳纳米管、单质硅、硅氧化合物、硅碳复合物、钛酸锂中的一种或几种。
作为示例，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一种以上。
作为示例，粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的一种以上。
其他可选助剂例如是增稠剂(如羧甲基纤维素钠(CMC-Na))等。
[隔离膜]
采用电解液的锂离子二次电池中还包括隔离膜。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。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一种以上。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，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施方式中，锂离子二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，锂离子二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。锂离子二次电池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(PP)、聚对苯二甲酸丁二醇酯(PBT)以及聚丁二酸丁二醇酯(PBS)等。
本申请对锂离子二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，图1是作为一个示例的方形结构的锂离子二次电池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。锂离子二次电池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，锂离子二次电池可以组装成电池模块，电池模块所含锂离子二次电池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4。参照图3，在电池模块4中，多个锂离子二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个锂离子二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个锂离子二次电池5容纳于该容纳空间。
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本领域技术人员可以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，本申请还提供一种装置，所述装置包括本申请提供的锂离子二次电池、电池模块、或电池包中的一种以上。所述锂离子二次电池、电池模块、或电池包可以用作所述装置的电源，也可以用作所述装置的能量存储单元。所述装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能***等。
作为所述装置，可以根据其使用需求来选择锂离子二次电池、电池模块或电池包。
图6是作为一个示例的装置。该装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该装置对锂离子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，可以采用锂离子二次电池作为电源。
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。
1.锂离子二次电池的制备
(1)正极极片的制备
将作为正极活性物质的包覆碳的磷酸铁锂(LFP)、导电剂乙炔黑、粘结剂聚偏二氟乙烯(PVDF)按表1所示的重量比溶于溶剂N-甲基吡咯烷酮(NMP)中，充分搅拌混合均匀后得到正极浆料，其中所用的包覆碳的磷酸铁锂具有表1所示的碳含量。之后根据要达到的Cw值，将正极浆料均匀涂覆于铝正极集流体上，之后经过烘干、冷压、分切，得到正极极片。
(2)负极片的制备
将负极活性物质人造石墨、导电剂乙炔黑、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC-Na)按照重量比为95∶2∶2∶1溶于溶剂去离子水中，均匀混合后制备成负极浆料。然后根据对应的正极的Cw值确定负极负载量，按照表1所示的负极负载量将负极浆料均匀涂覆在负极集流体铜箔上，烘干后经过冷压、分切得到负极极片。
表1(采用相同参数数值的实施例或对比例列于同一行)
Figure PCTCN2021096742-appb-000002
(3)电解液的制备
在氩气气氛手套箱中(H 2O＜0.1ppm，O 2＜0.1ppm)，将有机溶剂EC/EMC按照体积比3/7混合均匀，加入3wt％的碳酸亚乙烯酯和表2中所示重量百分比的高热稳定性盐和任选的添加剂，搅拌均匀，得到相应的电解液，所述碳酸亚乙烯酯的重量百分比和表2中所示的重量百分比均基于所得电解液的总重量计。
(4)锂离子二次电池的制备
使用上述(1)中制得的正极极片和上述(2)中制得的负极极片，以聚丙烯膜作为隔离膜，将正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正、负极极片之间起到隔离的作用，然后卷绕得到电极组件。将电极组件置于电池壳体中，干燥后注入电解液，再经过化成、静置，制得锂离子二次电池。
2.锂离子二次电池的测试
(1)正极极片碳含量测试
测试仪器：高频红外碳硫分析仪，型号HCS-140，商购自上海德凯仪器有限公司。
参照GB/T20123-2006钢铁总碳硫含量的测定-高频感应炉燃烧后红外吸收法(常规方法)。测试过程：将正极集流体上的正极材料层刮下，将其在富氧条件下在上述高频炉中进行加热燃烧，将材料中包含的碳氧化成二氧化碳。将生成的气体经处理后引入相应的吸收池中，对相应的红外辐射进行吸收，并经由探测器转化成对应的数字信号。所得数字信号经由计算机采样，经线性校正，转换成与二氧化碳浓度成正比的数值，进行累加，得到累加值。将所得累加值除以样品重量，乘以校正系数，扣除空白，即可得到样品中的碳百分含量Mc(％)。
(2)锂离子二次电池的45℃循环性能测试
在45℃下，将锂离子二次电池以1C恒流充电至3.65V，然后以3.65V恒压充电至电流小于0.05C，然后将锂离子电池以1C恒流放电至2.5V，此为一个充放电过程。如此反复进行充电和放电，计算锂离子电池容量保持率为80％时的循环圈数。各实施例和对比例的45℃循环圈数如表1所示。
(3)体积能量密度测试
在25℃下，将锂离子电池以0.5C恒流充电至3.65V，然后以3.65V恒压充电至电流小于0.05C，然后再以0.33C放电到2.5V，得到放电能量Q。利用游标卡尺测量电芯的长，宽，高，计算得到体积V，体积能量密度＝Q/V
表2中示出了各实施例和对比例的锂离子电池的Mc、Cw、k1、k2以及体积能量密度和45℃循环性能。
Figure PCTCN2021096742-appb-000003
Figure PCTCN2021096742-appb-000004
由表1可见，对比例1的k1过低，相应地，电池的能量密度较低。对比例2～3中，通过增加正极材料层的负载量和减少碳含量，k1提高，相应地，电池的体积能量密度显著提升，但是过高的k1导致电芯循环寿命明显变差。即使对比例3使用了高热稳定性盐并且k2/k1的数值落入本申请范围内，循环寿命仍然较低。另一方面，对比例4-5的k1值落入本申请范围内，但k2/k1过高或过低，因此循环寿命偏低。
相比而言，实施例1-25同时使用含高稳定性锂盐的电解液以及正极材料层负载量大且含碳量低的正极极片，能使电芯同时兼顾高能量密度和长循环寿命。
实施例1与实施例2相比，可以看出，实施例1的k2/k1值在0.48-7的范围内，从而比实施例2获得了更好的循环性能。实施例1与实施例4相比，可以看出，实施例1的k1值在3.3-14.5的范围内，从而比实施例4获得了更好的循环性能。
从实施例8-24中可以看出，通过在电解液中添加低阻抗添加剂，可以在保证电池具有高能量密度的同时进一步提高电池的循环寿命。
从实施例16-21可以看出，在电解液中加入抑制铝箔腐蚀的锂盐，能抑制铝箔腐蚀，减少铝箔的阻抗值增大，从而进一步提升电池循环寿命。并且，当抑制铝箔腐蚀的锂盐的质量百分比在0.2％-5％范围内时(实施例16、19-20)，能进一步提升电池循环寿命。
虽然已经参考实施例对本申请进行了描述，但在不脱离本申请的范围的情况下，可以对其进行各种改进并且可以用等效物替换其中的部件。尤其是，只要不存在结构冲突，各个实施例中所提到的各项技术特征均可以任意方式组合起来。本申请并不局限于文中公开的特定实施例，而是包括落入权利要求的范围内的所有技术方案。

Claims (13)

  1. 一种锂离子二次电池，其具有正极极片、负极极片、隔离膜及电解液，所述正极极片包括正极集流体和设置于正极集流体至少一个表面上的正极材料层，所述正极材料层包含正极活性物质和碳，其中，
    所述电解液中含有高热稳定性盐(M y+) x/yR 1(SO 2N -) xSO 2R 2，其中所述M y+为金属离子，R 1、R 2各自独立地为氟原子、碳原子数为1-20的烷基、碳原子数为1-20的氟代烷基或碳原子数为1-20的氟代烷氧基，并且所述x为1、2或3，所述y为1、2或3；将该盐在所述电解液中的质量百分比设为k2％；
    所述正极极片的温升系数k1满足2.5≤k1≤32，其中k1＝Cw/Mc，Cw为正极集流体负载有正极材料层的任一侧表面上单位面积的正极材料负载量(mg/cm 2)，Mc为所述正极材料层的含碳量(％)；
    并且，所述锂离子二次电池满足0.34≤k2/k1≤8。
  2. 根据权利要求1所述的锂离子二次电池，其满足下述条件1)至3)中的至少一项：
    1)3.3≤k1≤14.5；
    2)0.48≤k2/k1≤7；
    3)1≤Mc≤7。
  3. 根据权利要求1或2所述的锂离子二次电池，其中，所述M y+为选自Li +、Na +、K +、Rb +、Cs +、Mg 2+、Ca 2+、Ba 2+、Al 3+、Fe 2+、Fe 3+、Ni 2+、以及Ni 3+中的至少一种，可选地，M y+为选自Li +、Na +、K +、Rb +以及Cs +中的至少一种。
  4. 根据权利要求1-3中任一项所述的锂离子二次电池，其中，所述R 1、R 2各自独立地为氟原子、碳原子数为1-10的烷基、碳原子数为1-10 的氟代烷基或碳原子数为1-10的氟代烷氧基，可选地，所述R 1、R 2各自独立地为CH 3、CF 3或F。
  5. 根据权利要求1-4中任一项所述的锂离子二次电池，其中，所述电解液中还含有低阻抗添加剂，可选地，所述低阻抗添加剂为氟磺酸盐NSO 3F、二氟草酸硼酸盐NDFOB、二氟磷酸盐NPO 2F 2、二氟二草酸盐NDFOP、三(三甲基硅烷基)磷酸酯、三(三甲基硅烷基)亚磷酸酯中的至少一种，其中N为盐的金属离子，例如可选为Li +、Na +、K +、Rb +、Cs +；可选地，所述低阻抗添加剂为氟磺酸锂、二氟草酸硼酸锂、三(三甲基硅烷基)磷酸酯和二氟磷酸锂中的至少一种。
  6. 根据权利要求5所述的锂离子二次电池，其中，所述低阻抗添加剂在所述电解液中的质量百分比为0.1％～10％，可选为0.2％～5％。
  7. 根据权利要求1-6中任一项所述的锂离子二次电池，其中，所述电解液中还含有抑制铝箔腐蚀的锂盐，可选地，所述抑制铝箔腐蚀的锂盐为选自LiPF 6、LiAsF 6、以及LiBF 4中的至少一种。
  8. 根据权利要求7所述的锂离子二次电池，其中，所述抑制铝箔腐蚀的锂盐在所述电解液中的质量百分比为0.1％～10％，可选为0.2％～5％，可选为1％～3％。
  9. 根据权利要求1-8中任一项所述的锂离子二次电池，其中，所述电解液中的总锂盐含量在5wt％-50wt％范围内，可选地在5wt％-37wt％范围内，可选地在5wt％-23wt％范围内，基于电解液总重量计。
  10. 根据权利要求1-9中任一项所述的锂离子二次电池，其中，所述正极活性物质选自锂过渡金属氧化物、橄榄石结构的含锂磷酸盐及其各自的改性化合物中的一种或几种，可选地，所述锂过渡金属氧化物选自锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、满足a+b+c＝1且a＜0.8的锂镍钴锰氧化物LiNi aCo bMn cO 2、锂镍 钴铝氧化物及其改性化合物中的一种或几种。
  11. 一种电池模块，其包括权利要求1-10中任一项所述的锂离子二次电池。
  12. 一种电池包，其包括权利要求11所述的电池模块。
  13. 一种用电装置，其包括选自权利要求1-10中任一项所述的锂离子二次电池、权利要求11所述的电池模块或权利要求12所述的电池包中的一种以上。
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