WO2022133926A1 - 锂离子二次电池及其制备方法、电池模块、电池包和装置 - Google Patents

锂离子二次电池及其制备方法、电池模块、电池包和装置 Download PDF

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WO2022133926A1
WO2022133926A1 PCT/CN2020/139106 CN2020139106W WO2022133926A1 WO 2022133926 A1 WO2022133926 A1 WO 2022133926A1 CN 2020139106 W CN2020139106 W CN 2020139106W WO 2022133926 A1 WO2022133926 A1 WO 2022133926A1
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lithium
positive electrode
electrolyte
battery
active material
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PCT/CN2020/139106
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English (en)
French (fr)
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谢浩添
陈培培
孙信
王帮润
黄建涛
陈兴布
陈晓
柳娜
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/CN2020/139106 priority Critical patent/WO2022133926A1/zh
Priority to CN202080102737.8A priority patent/CN115803932A/zh
Priority to EP20966498.6A priority patent/EP4131487A1/en
Publication of WO2022133926A1 publication Critical patent/WO2022133926A1/zh
Priority to US18/186,952 priority patent/US20230282824A1/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
    • H01M10/0568—Liquid materials characterised by the solutes
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
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    • 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
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    • 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
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • H—ELECTRICITY
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    • 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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
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    • 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
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H—ELECTRICITY
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    • 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
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    • 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
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
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    • 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
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • 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
    • 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
    • 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
    • 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
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the technical field of batteries, and in particular, to a lithium ion secondary battery and a preparation method thereof, a battery module, a battery pack and a device.
  • a lithium ion secondary battery is a rechargeable battery that can continue to be used by activating an active material by charging it after discharge.
  • lithium-ion secondary batteries rely on the reciprocal deintercalation of lithium ions between positive and negative electrodes to achieve charging and discharging. Due to its outstanding features such as high energy density, long cycle life, no pollution, and no memory effect, lithium-ion secondary batteries are widely used in various electronic products, and rapidly spread to large-scale devices such as electric vehicles and energy storage systems.
  • lithium-ion secondary batteries In large-scale devices, a plurality of lithium-ion secondary batteries are usually assembled into battery modules or battery packs to meet the demand for high capacity. At this time, thermal runaway of any one or several lithium-ion secondary batteries will bring about a major safety hazard. In order to promote the further development of electric vehicles and energy storage systems, it is necessary to improve the safety performance of lithium-ion secondary batteries with higher energy density.
  • a first aspect of the present application provides a lithium ion secondary battery, including a positive electrode piece, a negative electrode piece, and an electrolyte, wherein the positive electrode piece includes a positive electrode active material and a positive electrode lithium supplement material, and the positive electrode lithium supplement material includes a lithium-rich metal oxide
  • the lithium-rich metal oxide contains one or more elements of Ni, Co, Fe, Mn, and Cu
  • the electrolyte contains an electrolyte lithium salt and a solvent
  • the total mass of the fluorine element in the anion of the electrolyte lithium salt is relative to The proportion of the total mass of the electrolyte is ⁇ 14%.
  • 1.5% ⁇ 9.5% is ⁇ 1.
  • the lithium-rich metal oxide contains one or more of Ni, Co, Fe, Mn, and Cu, which can increase the amount of lithium intercalation, so that more active lithium can be released during the charging process of the battery, which can be more effective Therefore, the irreversible loss of lithium is compensated, so that the battery has a high high-temperature cycle life or high-temperature storage life.
  • batteries using active materials with higher coulombic efficiency such as lithium iron phosphate as the positive electrode can also have improved initial discharge capacity.
  • the amount of metal deposition on the surface of the negative electrode is significantly reduced, which not only further reduces the side reactions of the electrolyte and reduces the gas production, but also reduces the risk of the deposited metal piercing the separator during the heating process of the battery and causing a short circuit in the battery. Effectively improve the high temperature safety performance of the battery.
  • the ratio of the total mass of the fluorine element in the anion of the electrolyte lithium salt to the total mass of the electrolyte is 2% ⁇ 9.3%.
  • ⁇ is 2.5% to 9.2%.
  • the proportion of the total mass of the fluorine element in the anion of the electrolyte lithium salt relative to the total mass of the electrolyte is within the above range, which can further reduce the dissolution of metal ions, and is conducive to the electrolyte to obtain higher ionic conductivity, so that the battery can be While obtaining high high temperature safety performance, it also has high high temperature cycle performance and high temperature storage performance.
  • the lithium-rich metal oxide may be selected from Li x M 1 O 0.5(2+x) , Li 2 M 2 O 3 , Li 2 M 3 O 4 , Li 3 M 4 O 4 , One or more of Li 5 M 5 O 4 and Li 5 M 6 O 6 , wherein x ⁇ 1, M 1 is selected from Ni, Co, Fe, Mn, Zn, Mg, Ca, Cu, Sn One or more, M 2 is selected from one or more of Ni, Co, Fe, Mn, Sn, Cr, M 3 is selected from Ni, Co, Fe, Mn, Sn, Cr, V, Nb One or more, M 4 is selected from one or more of Ni, Co, Fe, Mn, Sn, Cr, V, Mo, Nb, M 5 is selected from Ni, Co, Fe, Mn, Sn, Cr , one or more of Mo, M 6 is selected from one or more of Ni, Co, Mn, the valence of each element in M 1 , M 2 , M 3 , M
  • the lithium-rich metal oxide may include Li 2 MnO 2 , Li 5 FeO 4 , Li 6 CoO 4 , Li 2 NiO 2 , Li 2 Cu x1 Ni 1-x1-y1 M y1 O 2
  • Li 3 VO 4 and Li 3 NbO 4 wherein 0 ⁇ x1 ⁇ 1, 0 ⁇ y1 ⁇ 0.1, M is selected from Zn, Sn , one or more of Mg, Fe and Mn.
  • the above-mentioned lithium-rich metal oxide has a relatively high delithiation capacity and a suitable first delithiation voltage, so that it can have a better effect of replenishing lithium, thereby helping to improve the energy density of the battery.
  • appropriate lithium-rich metal oxides can also help improve the high-temperature cycle life or high-temperature storage performance of the battery.
  • the lithium-rich metal oxide may contain free lithium, the free lithium includes one or more of LiOH, LiHCO 3 and Li 2 CO 3 , and the free lithium is in the lithium-rich metal oxide The mass proportion of ⁇ 5wt%. Optionally, ⁇ 3wt%. Further optionally, 0.3wt% ⁇ 0.7wt%. Free lithium in Li-rich metal oxides can consume HF, thereby further reducing metal ion dissolution. When the content of free lithium is within an appropriate range, it can not only reduce the electrochemically inert materials in the pole piece, so that the battery has a higher energy density, but also reduce the decomposition and gas production of free lithium, so that the battery can obtain higher high-temperature cycle performance and High temperature storage performance.
  • At least a portion of the outer surface of the lithium-rich metal oxide may have a coating layer.
  • the coating layer includes one or more of metal fluorides, oxides, metal phosphates, carbon materials, and conductive polymers.
  • the metal fluoride may be selected from AlF3 .
  • the oxide can be selected from one or more of V 2 O 5 , Al 2 O 3 , ZrO 2 , TiO 2 , ZnO, SiO 2 and B 2 O 3 .
  • the metal phosphate can be selected from one or more of AlPO 4 , FePO 4 , Co 3 (PO 4 ) 2 and Ni 3 (PO 4 ) 2 .
  • the coating layer can isolate the contact between the lithium-rich metal oxide and the external environment, thereby effectively alleviating the self-capacity loss of the lithium-rich metal oxide due to water absorption or side reactions in the battery, and reducing the dissolution of metal ions. Therefore, the use of Li-rich metal oxides modified by the coating layer can further improve the high-temperature safety performance of the battery, and can improve the high-temperature cycle performance and high-temperature storage performance.
  • the electrolyte lithium salt may include lithium difluorooxalate borate (LiDFOB), lithium bis-oxalate borate (LiBOB), lithium difluorophosphate (LiDFP), lithium difluorodioxalate phosphate (LiDFOP) , Lithium Tetrafluorooxalate Phosphate (LiTFOP), Lithium Bisfluorosulfonimide (LiFSI), Lithium Bistrifluoromethanesulfonimide (LiTFSI), Lithium Tetrafluoroborate (LiBF 4 ), Lithium Trifluoromethanesulfonate ( LiCF 3 SO 3 ), lithium bis(trifluoromethylsulfonyl)methyl (LiCH(CF 3 SO 2 ) 2 ), lithium tris(trifluoromethylsulfonyl) methyl (LiC(CF 3 SO 2 ) 3 ) ), and optionally includes lithium
  • a suitable electrolyte lithium salt is beneficial to make the fluorine content of the electrolyte within the required range, and at the same time, it can also make the electrolyte have high thermal stability and electrochemical stability, thereby further improving the high temperature safety performance of the battery. And can improve high temperature cycle life and high temperature storage performance.
  • the electrolyte lithium salt may include one or more of lithium bisoxalate borate (LiBOB), lithium difluorobisoxalate phosphate (LiDFOP), and lithium bisfluorosulfonimide (LiFSI).
  • LiBOB lithium bisoxalate borate
  • LiDFOP lithium difluorobisoxalate phosphate
  • LiFSI lithium bisfluorosulfonimide
  • the concentration of the electrolyte lithium salt in the electrolyte is 0.7 mol/L to 4 mol/L, optionally 0.7 mol/L to 3 mol/L.
  • Appropriate content of lithium salt in the electrolyte can enable the electrolyte to obtain higher ionic conductivity, thereby improving the energy density and cycle performance of the battery.
  • the concentration of LiPF 6 in the electrolyte is ⁇ 0.4 mol/L. Since LiPF 6 is easily ionized in the electrolyte to form fluorine-containing particles such as F - , PF 5 , and PF 6 - , these fluorine-containing particles are easy to cause the dissolution of metal ions in the electrolyte.
  • the content of LiPF 6 in the electrolyte is small, which is beneficial to reduce the above problems.
  • the concentration of LiPF 6 in the electrolyte within the above range, the ⁇ value of the electrolyte can be further controlled, thereby further reducing the self-discharge rate.
  • the positive active material may be selected from Li z CoO 2 , Li z NiO 2 , Li z MnO 2 , Li z Mn 2 O 4 , Li z Ni a Co b Mn c M' d O 2 , Li z Ni 1-u Co u O 2 , Li z Co 1-u Mn u O 2 , Li z Ni 1-u Mn u O 2 , Li z Ni ⁇ Co ⁇ Mn ⁇ O 4 , Li z Mn 2- One or more of ⁇ Ni ⁇ O 4 , Li z Mn 2- ⁇ Co ⁇ O 4 , Li z FePO 4 , Li z CoPO 4 , Li z MnPO 4 , and their modified materials, wherein M' One or more selected from Al, Mo, Nd, Zn, z independently satisfies 0.5 ⁇ z ⁇ 1.3, 0 ⁇ a ⁇ 1, 0 ⁇ b ⁇ 1, 0 ⁇ c ⁇ 1, 0 ⁇ d ⁇ 1 , a
  • the use of Li z FePO 4 and its modified materials is beneficial for the battery to obtain higher high temperature safety performance.
  • the positive electrode active material is contained in the positive electrode active material layer of the positive electrode sheet.
  • the areal density of the positive electrode active material layer is ⁇ 18 mg/cm 2 , further optionally, 18 mg/cm 2 to 21 mg/cm 2 . Designing a larger layer density of the positive active material can improve the energy density of the battery.
  • the positive electrode active material may include one or more of Li z Ni a Co b Mn c M' d O 2 and modified materials thereof, wherein 0.5 ⁇ z ⁇ 1.3, 0.5 ⁇ a ⁇ 1, 0 ⁇ b ⁇ 0.2, 0 ⁇ c ⁇ 0.3, 0 ⁇ d ⁇ 1, M' is selected from one or more of Al, Mo, Nd, and Zn.
  • the use of the positive electrode active material enables the battery to obtain higher energy density.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material; wherein, the positive electrode lithium supplement material is uniformly distributed on the positive electrode active material In the layer, and/or, the positive electrode lithium supplementing material is arranged between the positive electrode current collector and the positive electrode active material layer in the form of a supplementary lithium film layer, and/or, the positive electrode lithium supplementing material is arranged in the positive electrode active material layer in the form of a supplementary lithium film layer.
  • the material layer faces away from the surface of the positive current collector. In the form of a lithium-replenishing film layer, the safety performance of the battery can be further improved.
  • the mass ratio of the positive electrode active material to the positive electrode lithium supplement material is 99.9:0.1-85:15, optionally 98.5:1.5-93:7, Further optionally, it is 98:2 to 95:5.
  • the ratio of the positive electrode active material to the positive electrode lithium supplement material is within an appropriate range, which can provide sufficient lithium, thereby helping to improve the high temperature cycle performance and high temperature storage performance of the battery, and can also improve the battery overcharge. performance.
  • the positive electrode sheet can also have a higher proportion of active materials, which helps to make the battery have a higher energy density.
  • a second aspect of the present application provides a method for preparing a lithium ion secondary battery, including the following steps: providing a positive electrode piece, the positive electrode piece comprising a positive electrode active material and a positive electrode lithium supplement material, and the positive electrode lithium supplement material includes a lithium-rich metal oxide
  • the lithium-rich metal oxide contains one or more elements of Ni, Co, Fe, Mn, and Cu
  • an electrolyte solution is provided, the electrolyte solution includes an electrolyte lithium salt and a solvent, and the anion of the electrolyte lithium salt contains fluorine
  • the ratio of the total mass of the elements to the total mass of the electrolyte is ⁇ 14%, optionally, 1.5% ⁇ 9.5%; the positive electrode piece, the negative electrode piece and the electrolyte are assembled to obtain secondary lithium ions Battery.
  • a third aspect of the present application provides a battery module including the lithium ion secondary battery according to the present application.
  • a fourth aspect of the present application provides a battery pack including the battery module according to the present application.
  • a fifth aspect of the present application provides an apparatus including at least one of a lithium ion secondary battery, a battery module, or a battery pack according to the present application.
  • the battery module, battery pack and device provided by the present application include the lithium ion secondary battery according to the present application, and thus can have corresponding beneficial effects.
  • FIG. 1 is a schematic diagram of an embodiment of the secondary battery of the present application.
  • FIG. 2 is an exploded schematic view of an embodiment of the secondary battery of the present application.
  • FIG. 3 is a schematic diagram of an embodiment of the battery module of the present application.
  • FIG. 4 is a schematic diagram of an embodiment of the battery pack of the present application.
  • FIG. 5 is an exploded view of FIG. 4 .
  • FIG. 6 is a schematic diagram of an embodiment of a device in which the secondary battery of the present application is used as a power source.
  • any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with any other lower limit to form an unspecified range, and likewise any upper limit can be combined with any other upper limit to form an unspecified range.
  • every point or single value between the endpoints of a range is included within the range, even if not expressly recited.
  • each point or single value may serve as its own lower or upper limit in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.
  • a lithium ion secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte.
  • active ions lithium ions
  • the separator is arranged between the positive pole piece and the negative pole piece, and mainly plays the role of preventing the short circuit of the positive and negative poles, and at the same time allows lithium ions to pass through.
  • the electrolyte is mainly used to conduct ions between the positive electrode and the negative electrode.
  • lithium ions are extracted from the positive active material, conducted through the electrolyte, and embedded in the negative active material.
  • some lithium ions participate in the reaction of forming a solid electrolyte interface (SEI) film on the surface of the negative active material, resulting in the loss of active lithium.
  • SEI solid electrolyte interface
  • the repair and growth of the SEI film and the side reactions of the electrolyte on the surface of the lithium-intercalated negative electrode may occur in the subsequent cycle charge-discharge process and storage process of the battery, which will irreversibly consume lithium ions.
  • Depletion of active lithium can result in lower cycling and/or storage performance of the battery.
  • the lithium consumption reaction will also increase the gas production inside the battery, resulting in poor safety performance.
  • the above effects are more serious at high temperature (for example, above 45°C, such as 45°C to 80°C or 45°C to 60°C, etc.).
  • the loss of active lithium in the first charge to form the SEI film will also result in a lower first discharge capacity, which is not conducive to the improvement of battery energy density.
  • the means of pre-replenishing lithium mainly include negative electrode lithium supplement and positive electrode lithium supplement.
  • the negative electrode lithium supplementation usually uses metal lithium powder or lithium ribbon to pre-lithiate the negative electrode active material.
  • the lithium supplementation scheme of the positive electrode can be to add a lithium-rich compound as a supplementary lithium material to the positive electrode, avoiding the use of metallic lithium.
  • Li-rich compounds release lithium during battery charging, which can compensate for the irreversible loss of active lithium during the formation of the SEI film during the first charging of the battery and the subsequent cycling and storage processes, thereby improving the discharge capacity retention rate of the battery after cycling and/or storage.
  • the inventors found that the battery using the positive electrode supplementary lithium still has the problem of low high temperature safety performance.
  • the inventor further conducted a lot of research and found that by adding a suitable positive electrode lithium supplement material to the positive electrode plate, and making the electrolyte in the electrolyte
  • the anion of the lithium salt in the electrolyte contains fluorine element.
  • the proportion of the total mass of ⁇ to the total mass of the electrolyte is ⁇ 14%, which can achieve the above purpose of the invention.
  • the ratio ⁇ of the total mass of the fluorine element in the anion of the electrolyte lithium salt to the total mass of the electrolyte can be measured by ion chromatography.
  • the positive electrode plate includes a positive electrode active material and a positive electrode lithium supplement material, and the positive electrode lithium supplement material includes a lithium-rich metal oxide, and the lithium-rich metal oxide contains Ni, Co, Fe, Mn, and Cu. one or more elements; and the electrolyte contains an electrolyte lithium salt and a solvent, and the ratio of the total mass of the fluorine element in the anion of the electrolyte lithium salt to the total mass of the electrolyte is ⁇ 14%.
  • the lithium-rich metal oxide contains one or more of Ni, Co, Fe, Mn, and Cu, which can increase the amount of lithium intercalation.
  • the lithium-rich metal oxide has a high delithiation capacity, which can release more active lithium during the battery charging process, thereby more effectively making up for the irreversible loss of lithium, so that the battery can have a high temperature under high temperature conditions. Higher cycle life or storage life.
  • batteries with higher positive first-time efficiency such as lithium iron phosphate/graphite batteries, can also have improved first-time discharge capacity.
  • the lithium-rich metal oxide will undergo a drastic change in the lattice during the delithiation process, and at this time, the electrolyte solution satisfies the ratio of the total mass of the fluorine element in the anion of the electrolyte lithium salt to the total mass of the electrolyte solution in an appropriate range It can effectively alleviate the problem of metal ion dissolution.
  • the dissolved amount of metal ions is significantly reduced, which can reduce the amount of metal deposition on the surface of the negative electrode, which not only further reduces the side reaction of the electrolyte, reduces the gas production, but also reduces the deposition of metal piercing the separator during the heating process of the battery. risk of short circuit, thereby further improving the high temperature safety performance of the battery.
  • the shuttle effect of metal ions or the self-discharge of the battery caused by deposition on the surface of the negative electrode can be significantly reduced, thereby improving the capacity of the battery and further improving the battery’s performance. discharge capacity.
  • the reduction reaction of metal ions on the surface of the negative electrode is reduced, so the damage to the SEI film is reduced, which can reduce the consumption of electrolyte and active lithium caused by the continuous repair of the SEI film, so that the battery can be cycled or stored at high temperatures. It has a high discharge capacity retention rate during the process. Therefore, the high-temperature cycle performance or high-temperature storage performance of the battery is further improved.
  • the proportion ⁇ of the total mass of the fluorine element in the anion of the electrolyte lithium salt relative to the total mass of the electrolyte is ⁇ 13.8%, ⁇ 13.5%, ⁇ 13%, ⁇ 12.5%, ⁇ 12%, ⁇ 11.5%, ⁇ 11%, ⁇ 10.5%, ⁇ 10%, ⁇ 9.5%, ⁇ 9.3%, ⁇ 9%, ⁇ 8.5%, ⁇ 8%, ⁇ 7.5%, ⁇ 7%, ⁇ 6.5 %, ⁇ 6%, ⁇ 5.5%, ⁇ 5%, ⁇ 4.5%, ⁇ 4%, ⁇ 3.5%, ⁇ 3%, or ⁇ 2.5%.
  • the ⁇ value of the electrolyte is in an appropriate range, which can further reduce the dissolution of metal ions, and is more conducive to improving the high temperature safety performance of the battery.
  • the high-temperature storage performance or high-temperature cycle performance of the battery can be further improved.
  • the ⁇ of the electrolyte is ⁇ 0%, ⁇ 0.5%, ⁇ 0.8%, ⁇ 1%, ⁇ 1.1%, ⁇ 1.2%, ⁇ 1.3%, ⁇ 1.4%, ⁇ 1.5%, ⁇ 1.6% , ⁇ 1.8%, ⁇ 2%, ⁇ 2.3%, or ⁇ 2.5%.
  • the electrolyte contains an appropriate amount of fluorine, which is beneficial for the electrolyte to obtain higher ionic conductivity, thereby improving the initial discharge capacity, high-temperature cycle performance and high-temperature storage performance of the battery.
  • the battery can also have higher power performance.
  • the ⁇ of the electrolyte is 0 ⁇ 10%, 0 ⁇ 9.3%, 1% ⁇ 9.5%, 1.5% ⁇ 9.5%, 2% ⁇ 9.3%, 2.5% ⁇ 9.2%, 0.5% ⁇ 8.5% , 1% to 8%, 1% to 7.5%, 1.2% to 7%, 1.3% to 6.5%, 1.5% to 5%, or 2% to 5%, etc.
  • the positive electrode sheet generally includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.
  • the positive electrode current collector has two surfaces opposite in its own thickness direction, and the positive electrode active material layer is provided on either or both of the two surfaces of the positive electrode current collector.
  • the positive electrode current collector can be a metal foil or a composite current collector (a metal material can be arranged on the polymer material layer to form a composite current collector).
  • the positive electrode current collector may use aluminum foil.
  • the positive electrode active material layer contains a positive electrode active material.
  • a positive electrode active material a material known in the art for a positive electrode of a lithium ion secondary battery and capable of reversibly intercalating and deintercalating lithium ions can be used.
  • the modification in the modified material may be one or more of doping modification and cladding modification.
  • the positive active material may include one or more of Li z FePO 4 and its modified materials, wherein 0.5 ⁇ z ⁇ 1.3.
  • z 1.
  • Li z FePO 4 and its modified materials have high thermal stability, which is beneficial for the battery to obtain higher high temperature safety performance.
  • the battery can also have a long high-temperature cycle life and high high-temperature storage performance.
  • the modified material of Li z FePO 4 may be one in which Fe is replaced by Fe such as Sc, V, Cr, Mn, Ti, Al, Co, Ni, Cu, Zn, etc. and the atomic radius of Fe is different from that of Fe. Partial substitution of adjacent metal elements.
  • modifying materials of Li z FePO 4 include Li z Fe 1-k Me k PO 4 , wherein Me is selected from one of Sc, V, Cr, Mn, Ti, Al, Co, Ni, Cu, Zn or several, 0 ⁇ k ⁇ 0.5. Optionally, 0.01 ⁇ k ⁇ 0.2.
  • Me is selected from one or more of Mn, Ti, Al, Ni, Cu, and Zn.
  • the inventors have further found that when the positive electrode active material includes one or more of Li z FePO 4 and its modified materials, the performance of the battery can be further improved if the positive electrode sheet simultaneously satisfies one or more of the following conditions.
  • the areal density of the cathode active material layer is > 18 mg/cm 2 .
  • the areal density of the positive electrode active material layer is 18mg/cm 2 -26mg/cm 2 , further optionally, 18mg/cm 2 -25mg/cm 2 , 18mg/cm 2 -23mg/cm 2 , 18mg/cm 2 to 21 mg/cm 2 , 19 mg/cm 2 to 22 mg/cm 2 , or 20 mg/cm 2 to 25 mg/cm 2 .
  • a larger layer density of the positive electrode active material can be designed, whereby the energy density of the battery can be further improved.
  • the compaction density of the positive electrode active material layer may be 2.0 g/cm 3 to 2.6 g/cm 3 , for example, 2.2 g/cm 3 to 2.4 g/cm 3 .
  • the compaction density of the positive electrode active material layer is in an appropriate range, which can ensure the good electron transport performance of the positive electrode sheet, and at the same time have a porosity suitable for electrolyte infiltration, which is beneficial to the battery to obtain high cycle performance.
  • the positive active material may include one or more of Li z Ni a Co b Mn c M' d O 2 and modified materials thereof, wherein 0.5 ⁇ z ⁇ 1.3, 0.5 ⁇ a ⁇ 1, 0 ⁇ b ⁇ 0.2, 0 ⁇ c ⁇ 0.3, 0 ⁇ d ⁇ 1, and M' is selected from one or more of Al, Mo, Nd, and Zn.
  • 0.8 ⁇ z ⁇ 1.2 0.5 ⁇ a ⁇ 0.9, 0.6 ⁇ a ⁇ 0.85, or 0.65 ⁇ a ⁇ 0.8.
  • the positive electrode active material may be selected from LiNi 0.5 Co 0.2 Mn 0.3 O 2 , LiNi 0.6 Co 0.2 Mn 0.2 O 2 , LiNi 0.8 Co 0.1 Mn 0.1 O 2 , modified materials of the above materials, and the like.
  • the use of the above-mentioned positive electrode active material enables the battery to obtain a higher energy density.
  • the lithium rich metal oxide may be selected from Li x M 1 O 0.5(2+x) , Li 2 M 2 O 3 , Li 2 M 3 O 4 , Li 3 M 4 O 4 , Li 5 M One or more of 5 O 4 , Li 5 M 6 O 6 , wherein x ⁇ 1, M 1 is selected from one or more of Ni, Co, Fe, Mn, Zn, Mg, Ca, Cu, Sn Several, M 2 is selected from one or more of Ni, Co, Fe, Mn, Sn, Cr, M 3 is selected from one or more of Ni, Co, Fe, Mn, Sn, Cr, V, Nb Several, M 4 is selected from one or more of Ni, Co, Fe, Mn, Sn, Cr, V, Mo, Nb, M 5 is selected from Ni, Co, Fe, Mn, Sn, Cr, Mo One or more of M 6 is selected from one or more of Ni, Co and Mn, and the valence states of each element in M 1 , M 2 , M 3
  • the lithium-rich metal oxide may include one of Li 2 MnO 2 , Li 5 FeO 4 , Li 6 CoO 4 , Li 2 NiO 2 , Li 2 Cu x1 Ni 1-x1-y1 M y1 O 2 one or more, and optionally one or more of Li 3 VO 4 and Li 3 NbO 4 .
  • the lithium - rich metal oxide may include one of Li2MnO2 , Li5FeO4 , Li6CoO4 , Li2NiO2 , Li2Cux1Ni1 - x1 - y1My1O2 , or several.
  • the lithium-rich metal oxide may include one or more of Li 5 FeO 4 , Li 6 CoO 4 , Li 2 Cu x1 Ni 1-x1-y1 M y1 O 2 .
  • Li 2 Cu x1 Ni 1-x1-y1 M y1 O 2 0 ⁇ x1 ⁇ 1, 0 ⁇ y1 ⁇ 0.1
  • M is selected from one or more of Zn, Sn, Mg, Fe and Mn.
  • the above-mentioned lithium-rich metal oxides have a high delithiation capacity, and also have a suitable first delithiation voltage, which can match the charging potential of the positive electrode active material, and better exert the effect of lithium supplementation, so it can further improve the battery. Energy Density. Moreover, appropriate lithium-rich metal oxides can also help to improve high-temperature cycle life or high-temperature storage performance.
  • the lithium-rich metal oxide may include or be Li 2 Cu x1 Ni 1-x1-y1 M y1 O 2 .
  • the atomic number ratio of Ni/Cu is 0.1-4.
  • the atomic number ratio of Ni/Cu is 1:4 ⁇ 4:1, 1:2 ⁇ 4:1, 2:3 ⁇ 4:1, 3:7 ⁇ 7:3, 4:6 ⁇ 7:3 , or 4:6 to 6:4.
  • the lithium-rich metal oxide has a first delithiation capacity > 250 mAh/g.
  • the first delithiation capacity of the lithium-rich metal oxide is ⁇ 300 mAh/g, ⁇ 350 mAh/g, ⁇ 400 mAh/g, or ⁇ 450 mAh/g.
  • Lithium-rich metal oxides have a higher first-time delithiation capacity, and can release more active lithium when used in batteries, thereby helping to improve the energy density of batteries. Further, the battery can also achieve longer cycle life or storage life.
  • the lithium-rich metal oxide has a first delithiation plateau voltage of 2.0V to 4.5V (vs. Li/Li + ).
  • the first delithiation plateau voltage of the lithium-rich metal oxide is 2.5V ⁇ 4.2V, 3V ⁇ 4.2V, 2.8V ⁇ 4V, 3.0V ⁇ 3.75V, 3.2V ⁇ 3.6V, or 3.4V ⁇ 4.1V etc. (relative to Li/Li + ).
  • the lithium-rich metal oxide has a lower delithiation platform voltage, which can match the delithiation potential of the positive electrode active material, so that the capacity of the lithium-replenishing material and the active material can be better exerted, and the lithium-replenishing effect can be improved.
  • the lithium-rich metal oxide may contain free lithium, and the free lithium includes one or more of LiOH, LiHCO 3 and Li 2 CO 3 . Free lithium in Li-rich metal oxides can consume HF, thereby further reducing metal ion dissolution.
  • the mass proportion of free lithium in the lithium-rich metal oxide ⁇ 5wt%.
  • the content of free lithium in the lithium-rich metal oxide is in an appropriate range, which can reduce the decomposition of free lithium and produce gas, so that the pole piece maintains a good reaction interface, so that the battery can obtain higher high temperature cycle performance and high temperature storage performance.
  • free lithium is an electrochemically inert material, and reducing the free lithium content in the positive electrode is beneficial to the battery to obtain a higher energy density.
  • the outer surface of the lithium-rich metal oxide has a coating.
  • the coating layer may include one or more of metal fluorides, oxides, metal phosphates, carbon materials, and conductive polymers.
  • the oxide is selected from oxides or lithium composite oxides of elements other than C in the periodic table of elements from Groups IB to VIIB, Group VIII, Group IIIA, and Group IV.
  • the coating layer may include one or more of metal fluorides, oxides, and metal phosphates.
  • Lithium-rich metal oxides are generally basic, especially when the basicity is relatively high (eg, pH is about 12), and it is easier to absorb moisture from the environment.
  • the introduction of moisture into the battery by lithium-rich metal oxides will cause a series of side reactions and other problems, which will affect the capacity of the battery and further improve the cycle life.
  • the coating layer can play a role of isolation and reduce the contact between the lithium-rich metal oxide and the external environment, thereby reducing the amount of water absorption, so it can effectively alleviate the capacity loss caused by water absorption, and enable the battery to obtain a higher energy density and cycle capacity retention rate .
  • the coating layer can also isolate the direct contact between the lithium-rich metal oxide and the electrolyte, thereby further reducing the dissolution of metal ions, thereby further improving the high temperature safety performance, high temperature cycle performance and high temperature storage performance of the battery.
  • the metal fluoride can be selected from AlF3 .
  • the oxide may be selected from V 2 O 5 , Al 2 O 3 , ZrO 2 , TiO 2 , ZnO, SiO 2 , Co 3 O 4 , B 2 O 3 , Li 2 MnO 3 , LiAlO 2 , One or more of Li 2 TiO 3 and Li 2 ZrO 3 .
  • the oxide can be selected from one or more of V 2 O 5 , Al 2 O 3 , ZrO 2 , TiO 2 , ZnO, SiO 2 and B 2 O 3 .
  • Appropriate oxides can improve the stability of the coating layer and help to better isolate the contact of lithium-rich metal oxides with the external environment or electrolyte, thereby further reducing water absorption and metal ion dissolution.
  • the phosphate can be selected from one or more of Li 3 PO 4 , AlPO 4 , FePO 4 , Co 3 (PO 4 ) 2 , and Ni 3 (PO 4 ) 2 .
  • the phosphate can be selected from one or more of AlPO 4 , FePO 4 , Co 3 (PO 4 ) 2 , and Ni 3 (PO 4 ) 2 .
  • Appropriate phosphate can improve the stability of the coating layer and help to better isolate the contact of lithium-rich metal oxides with the external environment or electrolyte, thereby further reducing water absorption and metal ion dissolution.
  • the carbon material may be selected from one or more of graphene, carbon nanotubes, and carbon fibers.
  • the conductive polymer may be selected from one or more of polythiophenes, polypyrroles, polyanilines, polypyridines, and modified polymers of the above materials.
  • the modified polymer may be a polyethylene glycol modified polymer.
  • polythiophenes may be selected from polythiophene, poly-3,4-ethylenedioxythiophene, and the like.
  • the cladding layer comprises one or more of metal fluorides, oxides, phosphates and conductive polymers.
  • the cladding layer includes Al 2 O 3 and polyethylene glycol-modified poly-3,4-ethylenedioxythiophene.
  • the cladding layer includes Li 3 PO 4 and polypyrrole.
  • the cladding layer may be a single layer or a multi-layer composite cladding layer.
  • the positive electrode lithium supplement material can be supported on the positive electrode current collector in any form that can release lithium into the electrolyte.
  • the cathode lithium supplement material may be uniformly distributed in the cathode active material layer. That is, the positive electrode active material layer contains the positive electrode active material and the positive electrode lithium supplementing material.
  • the positive electrode lithium supplement material is uniformly distributed in the positive electrode active material layer, and the content W of the positive electrode lithium supplement material is 0.1%-10% based on the total weight of the positive electrode active material layer.
  • W ⁇ 0.5%, ⁇ 1%, ⁇ 1.5%, ⁇ 2%, ⁇ 3%, or ⁇ 4%.
  • the content of the positive electrode lithium supplement material in the positive electrode plate is within an appropriate range, which can provide sufficient lithium to make up for the active lithium consumed by the SEI film or side reactions, thereby improving the capacity retention rate of the battery during high-temperature cycling or high-temperature storage.
  • the inventor also found that when the positive electrode plate contains an appropriate amount of positive electrode lithium supplement material, the overcharge window of the battery can be further improved, so that the battery can obtain higher overcharge performance.
  • the content of the positive electrode lithium-supplementing material in the positive electrode plate is within the above-mentioned range, which can also ensure that the positive electrode has a high proportion of active materials, which is helpful for the battery to obtain a high energy density.
  • W is 1%-10%, 1%-8%, 1%-6%, 2%-6%, 3%-6%, 1%-5%, 1.5%-3%, 2% to 5%, 2% to 4%, 4% to 10%, 6% to 10%, or 8% to 10%.
  • the positive electrode lithium supplement material is disposed on the positive electrode current collector in the form of a lithium supplement film layer.
  • the lithium supplementing film layer is a thin film layer containing a positive electrode lithium supplementing material.
  • the lithium supplementing film layer and the positive electrode active material layer may be stacked on the surface of the positive electrode current collector.
  • the lithium supplementing film layer is disposed between the positive electrode current collector and the positive electrode active material layer.
  • the lithium supplementary film layer between the positive electrode current collector and the positive electrode active material layer can reduce the risk of contact between the burrs of the positive electrode current collector and the negative electrode, and also help to improve the short-circuit resistance. Improve the safety performance of the battery.
  • the lithium supplementing film layer is disposed on the surface of the positive electrode active material layer facing away from the positive electrode current collector.
  • the inventors found that when the separator is melted or punctured to cause a short circuit in the battery, since the surface of the positive electrode active material layer away from the positive electrode current collector is provided with a lithium-replenishing film layer, the short-circuit resistance can be improved, and the short-circuit reaction can be reduced. It can further improve the high temperature safety performance of the battery.
  • the lithium supplementary film layer is located on the outer surface of the positive electrode active material layer, which also helps to improve the overcharge performance of the battery.
  • the lithium supplementing film layer and the positive electrode active material layer may or may not be in contact with each other.
  • the mass ratio of the positive electrode active material to the positive electrode lithium supplementing material is 99.9:0.1-85:15, optionally 99.5:0.5-90:10, 99.5:0.5 ⁇ 92:8, 99:1 ⁇ 89:11, 99:1 ⁇ 93:7, 98.5:1.5 ⁇ 93:7, 98.5:1.5 ⁇ 94:6, 98:2 ⁇ 94:6, 98:2 ⁇ 95 :5, or 98:2 to 96:4.
  • the content of the positive electrode lithium supplement material in the positive electrode sheet is within an appropriate range, which can provide sufficient lithium, thereby helping to improve the high-temperature cycle performance and high-temperature storage performance of the battery, and also improve the battery's overcharge performance.
  • the positive electrode sheet can also have a higher proportion of active materials, which helps the battery to have a higher energy density.
  • the positive electrode active material layer and/or the lithium supplementing film layer may also optionally contain a binder.
  • the binder may include one or more of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).
  • the positive electrode active material layer and/or the lithium supplementing film layer may optionally contain a conductive agent.
  • the conductive agent may include one or more of superconducting carbon, carbon black (eg, acetylene black, ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the positive electrode active material layer and the optional lithium supplementing film layer can be disposed on one surface or both surfaces of the positive electrode current collector. If the parameters of the film layer or material on either side of the positive electrode current collector satisfy the present application, it is considered to fall within the protection scope of the present application.
  • the compaction density, areal density and other ranges of the positive electrode active material layer described in this application all refer to the parameters of the positive electrode active material layer in the positive electrode sheet that can be used for assembling batteries after being compacted by cold pressing.
  • the chemical composition and Ni/Cu atomic number ratio of the lithium-rich metal oxide can be tested by methods known in the art.
  • inductively coupled plasma emission spectroscopy An exemplary test method for the Ni/Cu atomic number ratio of the lithium-rich metal oxide is as follows: at 25°C, take 0.5 g of the lithium-rich metal oxide and digest it in 100 mL of a 0.1 mol/L HCl solution for 30 min. The digestion can be carried out under stirring (eg, magnetic stirring, mechanical stirring or microwave stirring, etc.). Put the digested solution into an inductively coupled plasma emission spectrometer (for example, Thermo Fisher scientific ICAP7400 in the United States), and choose to test the content of Cu and Ni elements.
  • an inductively coupled plasma emission spectrometer for example, Thermo Fisher scientific ICAP7400 in the United States
  • the test conditions are: the cleaning pump is 40-60 rpm (revolution per minute), the radio frequency power is 950-1150 W, the atomizer pressure is 24-32 Psi (pound force/square inch), and the flow rate of the auxiliary device is set to 0.5L/min. According to the content of Cu and Ni elements, the ratio of Ni/Cu atomic number is calculated.
  • the chemical composition of the lithium-rich metal oxide can be determined with reference to the above-mentioned method.
  • the mass proportion of free lithium in the lithium-rich metal oxide can be determined by a method known in the art, such as a titration method.
  • Test reference standard GB/T 9725-2007 General rules for potentiometric titration of chemical reagents.
  • An exemplary test method is as follows: using a 905 Titrando potentiometric titrator with a composite pH electrode; taking 30 g of lithium-rich metal oxide in an iodine volumetric flask, adding 100 mL of deionized water, and dispersing at 25 °C for 30 min at a speed of 360 r/min, After standing for 10min, vacuum filtration with a 0.45 ⁇ m microporous membrane to obtain a dispersion; then titrate the dispersion with 0.05mol/L HCl solution; according to the titration, calculate the free lithium content and the concentration of free lithium in the lithium-rich metal The mass fraction of oxides.
  • the compaction density of the positive electrode active material layer is the meaning known in the art, and can be tested by methods known in the art.
  • the compaction density of the positive electrode active material layer area density of the positive electrode active material layer/thickness of the positive electrode active material layer.
  • the thickness of the positive electrode active material layer can be measured by a method known in the art, such as a micrometer (eg, Mitutoyo 293-100, with an accuracy of 0.1 ⁇ m).
  • the electrolyte solution includes an electrolyte lithium salt and a solvent, and the ratio of the total mass of the fluorine element in the anion of the electrolyte lithium salt to the total mass of the electrolyte solution is ⁇ 14%.
  • ⁇ is ⁇ 13.8%, ⁇ 13.5%, ⁇ 13%, ⁇ 12.5%, ⁇ 12%, ⁇ 11.5%, ⁇ 11%, ⁇ 10.5%, ⁇ 10%, ⁇ 9.5%, ⁇ 9.3 %, ⁇ 9%, ⁇ 8.5%, ⁇ 8%, ⁇ 7.5%, ⁇ 7%, ⁇ 6.5%, ⁇ 6%, ⁇ 5.5%, ⁇ 5%, ⁇ 4.5%, ⁇ 4%, ⁇ 3.5%, ⁇ 3%, or ⁇ 2.5%.
  • ⁇ is ⁇ 0%, ⁇ 0.5%, ⁇ 0.8%, ⁇ 1%, ⁇ 1.1%, ⁇ 1.2%, ⁇ 1.3%, ⁇ 1.4%, ⁇ 1.5%, ⁇ 1.6%, ⁇ 1.8 %, ⁇ 2%, ⁇ 2.3%, or ⁇ 2.5%.
  • ⁇ is 0 ⁇ 10%, 0 ⁇ 9.3%, 1% ⁇ 9.5%, 1.5% ⁇ 9.5%, 2% ⁇ 9.3%, 2.5% ⁇ 9.2%, 0.5% ⁇ 8.5%, 1% ⁇ 8 %, 1% to 7.5%, 1.2% to 7%, 1.3% to 6.5%, 1.5% to 5%, or 2% to 5%, etc.
  • the ratio ⁇ of the total mass of the fluorine element in the anion of the electrolyte lithium salt to the total mass of the electrolyte can be determined by ion chromatography.
  • Exemplary test methods are as follows: use an ion chromatograph (eg ICS-900); chromatography column is an anion separation column (eg Shodex IC SI-90 4E, 4.6 x 250mm); suppressor use an anion suppressor (eg ACRS 500, 4mm) ;
  • the detector uses a conductivity detector; the eluent uses an aqueous solution containing 1.8 mmol/L Na 2 CO 3 +1.8 mmol/L NaHCO 3 +20% acetonitrile (volume/volume), and the flow rate is 1.0 mL/min.
  • the test can be carried out with reference to JY/T 020-1996 "General Principles of Ion Chromatography Analysis Methods".
  • the measured anion species of all electrolyte lithium salts and their respective contents in the electrolyte and then multiply the content of each anion by the mass percentage of fluorine in the anion to the anion, and sum up to calculate the amount of the anion in the electrolyte.
  • the sample of the electrolyte can be taken directly (before being injected into the battery) for testing, or it can be sampled and tested from the secondary battery with cyclic charge and discharge cycles within 200 cycles.
  • the electrolyte lithium salt may be selected from one or more of a combination of LiPF 6 and an organic lithium salt, LiBF 4 , a combination of LiBF 4 and an organic lithium salt, and an organic lithium salt.
  • the electrolyte lithium salt can be selected from one or more of LiBF 4 , a combination of LiBF 4 and an organic lithium salt, and an organic lithium salt.
  • the electrolyte lithium salt may be selected from organic lithium salts.
  • the organic anion of the organolithium salt may be fluorine-containing or fluorine-free.
  • the organic lithium salt may be selected from lithium difluorooxalate borate (LiDFOB), lithium bisoxalate borate (LiBOB), lithium difluorophosphate (LiDFP), lithium difluorobisoxalate phosphate (LiDFOP), tetrafluorooxalate Lithium Phosphate (LiTFOP), Lithium Bisfluorosulfonimide (LiFSI), Lithium Bistrifluoromethanesulfonimide (LiTFSI), Lithium Trifluoromethanesulfonate (LiCF 3 SO 3 ), Bis(trifluoromethanesulfonate) One or more of acyl)methyl lithium (LiCH(CF 3 SO 2 ) 2 ) and tris(trifluoromethylsulfonyl) methyl lithium (LiC(CF 3 SO)
  • the organic lithium salt may include one or more of LiDFOB, LiBOB, LiTFOP, LiTFSI, LiDFOP, and LiFSI. Further optionally, the organic lithium salt may include one or more of LiDFOB, LiBOB, LiTFOP, LiDFOP, and LiFSI. Further alternatively, the organic lithium salt may include one or more of LiBOB, LiDFOP, and LiFSI.
  • a suitable electrolyte lithium salt is beneficial to make the fluorine content of the electrolyte within the required range, and at the same time, the electrolyte can have a higher ionic conductivity, which can improve the capacity of the battery and the capacity during the cycle. retention rate, thereby further improving the first discharge capacity and cycle life.
  • a suitable electrolyte lithium salt can also have high thermal stability and electrochemical stability, which can further improve the high-temperature cycle life and high-temperature storage performance of the battery, and can improve the high-temperature safety performance of the battery. Among them, the thermal diffusion performance or hot box performance of the battery is significantly improved.
  • the concentration of the electrolyte lithium salt in the electrolyte is 0.7 mol/L ⁇ 4 mol/L.
  • the concentration of the electrolyte lithium salt in the electrolyte is 0.7mol/L ⁇ 3mol/L, 0.9mol/L ⁇ 2mol/L, 1mol/L ⁇ 1.5mol/L, 1mol/L ⁇ 4mol/L, or 2mol/L ⁇ 4mol/L.
  • Appropriate content of lithium salt in the electrolyte can enable the electrolyte to obtain higher ionic conductivity, further enhance the capacity of the positive electrode lithium supplement material, and improve the energy density of the battery.
  • LiPF 6 is included in the electrolyte, and the concentration of LiPF 6 in the electrolyte is ⁇ 0.4 mol/L.
  • the concentration of LiPF 6 in the electrolyte is ⁇ 0.3 mol/L, ⁇ 0.2 mol/L, or ⁇ 0.1 mol/L.
  • the concentration of LiPF 6 in the electrolyte is 0 ⁇ 0.4 mol/L, 0.05 mol/L ⁇ 0.3 mol/L, or 0.1 mol/L ⁇ 0.2 mol/L, etc.
  • LiPF 6 is easily ionized in the electrolyte to form fluorine-containing particles such as F - , PF 5 , PF 6 - , etc.
  • these fluorine-containing particles are easy to cause metal ions to dissolve in the electrolyte.
  • the content of LiPF 6 in the electrolyte is small, which is beneficial to reduce the above problems.
  • the ⁇ value of the electrolyte can be further controlled, thereby further reducing the self-discharge rate.
  • the solvent of the electrolyte may include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) ), one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and methyl butyrate.
  • EC ethylene carbonate
  • PC propylene carbonate
  • DEC diethyl carbonate
  • DMC dimethyl carbonate
  • EMC ethyl methyl carbonate
  • the solvent includes one or more of EC and PC, and includes one or more of DEC, DMC, and EMC.
  • solvents include EC, EMC, and optionally PC.
  • the volume ratio of EC is 20%-40%
  • the volume ratio of PC is 0%-20%
  • the volume ratio of EMC is 60%-80%.
  • the volume ratio of EC, PC and EMC is 1:1:3, or 3:0:7, etc.
  • the solvent of the electrolyte further optionally includes one or more of ⁇ -butyrolactone (GBL) and dimethyl methylphosphonate (DMMP). This is conducive to reducing the density of the electrolyte, reducing the weight of the battery, thereby improving the energy density.
  • GBL ⁇ -butyrolactone
  • DMMP dimethyl methylphosphonate
  • optional additives are also included in the solvent.
  • the additives may be selected from additives known in the art for secondary battery electrolytes.
  • the additive may include one or more of the first additive, the second additive and the third additive.
  • Examples of the first additive may include one of heptamethyldisilazane (HEMDS), ethanolamine (MEA), 1,3-propanesultone (1,3-PS), succinonitrile (SN) or several.
  • HEMDS heptamethyldisilazane
  • MEA ethanolamine
  • 1,3-propanesultone (1,3-PS) 1,3-propanesultone
  • succinonitrile (SN) succinonitrile
  • Examples of the second additive may include one or more of tris(trimethylsilane) phosphate (TMSP) and tris(trimethylsilane) borate (TMSB).
  • TMSP tris(trimethylsilane) phosphate
  • TMSB tris(trimethylsilane) borate
  • the second additive can oxidize the positive electrode to form a protective film, which can reduce the dissolution of metal ions and protect the positive electrode active material, thereby further improving the high temperature safety performance of the battery, and also improving the high temperature cycle life or high temperature storage performance.
  • Examples of the third additive may include one or more of lithium polytartrate borate (PLTB), lithium polybis(trimethylolpropane)borate (PLDB), and lithium polypentaerythritol borate (PLPB).
  • PLTB lithium polytartrate borate
  • PLDB lithium polybis(trimethylolpropane)borate
  • PLPB lithium polypentaerythritol borate
  • the third additive has high thermal stability, which helps to improve the high temperature safety performance of the battery.
  • the negative pole piece used in conjunction with the positive pole piece of the present application can be selected from various conventional negative pole pieces commonly used in the art, and the structures and preparation methods thereof are well known in the art.
  • the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.
  • the negative electrode active material layer may include the negative electrode active material and optionally a binder, optionally a conductive agent, and other optional additives.
  • the negative electrode active material is, for example, a carbonaceous material such as graphite (artificial graphite or natural graphite), conductive carbon black, carbon fiber, etc., such as Si, Sn, Ge, Bi, Sn, In and other metal or semi-metal materials or their alloys, containing lithium Nitride or lithium-containing oxide, lithium metal or lithium aluminum alloy, etc.
  • a carbonaceous material such as graphite (artificial graphite or natural graphite), conductive carbon black, carbon fiber, etc., such as Si, Sn, Ge, Bi, Sn, In and other metal or semi-metal materials or their alloys, containing lithium Nitride or lithium-containing oxide, lithium metal or lithium aluminum alloy, etc.
  • the conductive agent may include one or more of superconducting carbon, carbon black (eg, acetylene black, ketjen black, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the binder can include styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyvinyl alcohol (PVA), sodium alginate (SA) and carboxymethyl chitosan (CMCS). one or more.
  • SBR styrene-butadiene rubber
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • CMCS carboxymethyl chitosan
  • Other optional additives such as thickeners (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, and the like.
  • the release film may be selected from glass fibers, non-woven fabrics, polyethylene films, polypropylene films, polyvinylidene fluoride films, and multilayer composite films of two or more of them.
  • the positive electrode sheet, the negative electrode sheet and the separator may be fabricated into an electrode assembly through a winding process or a lamination process.
  • the secondary battery may include an outer package.
  • the outer packaging can be used to encapsulate the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, and the like.
  • the outer package of the secondary battery may also be a soft package, such as a pouch-type soft package.
  • the material of the soft bag may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), and the like.
  • FIG. 1 is a secondary battery 5 of 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 plate are enclosed to form a accommodating cavity.
  • the housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 is used to cover the opening to close the accommodating cavity.
  • the positive pole piece, the negative pole piece and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the accommodating cavity.
  • the electrolyte solution is infiltrated in the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 may be one or several, and may be adjusted according to requirements.
  • the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG. 3 is a battery module 4 as an example.
  • the plurality of secondary batteries 5 may be arranged in sequence along the longitudinal direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed with fasteners.
  • the battery module 4 may further include a housing having an accommodating space in which the plurality of secondary batteries 5 are accommodated.
  • the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery case and a plurality of battery modules 4 disposed in the battery case.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 is used to cover the lower box 3 and form a closed space for accommodating the battery modules 4 .
  • the plurality of battery modules 4 may be arranged in the battery case in any manner.
  • the present application also provides a preparation method of a lithium ion secondary battery, including the following steps: providing a positive electrode piece, the positive electrode piece comprising a positive electrode active material and a positive electrode lithium supplement material, and the positive electrode lithium supplement material comprises a lithium-rich metal oxide,
  • the lithium-rich metal oxide contains one or more elements of Ni, Co, Fe, Mn, and Cu;
  • an electrolyte solution is provided, the electrolyte solution includes an electrolyte lithium salt and a solvent, and the anion of the electrolyte lithium salt contains fluorine elements.
  • the proportion of the total mass to the total mass of the electrolyte is ⁇ 14%, optionally, 1.5% ⁇ 9.5%; the positive pole piece, the negative pole piece and the electrolyte are assembled to obtain a lithium ion secondary battery.
  • the positive electrode sheet can be prepared by the following steps: dispersing the positive electrode active material and the positive electrode lithium-supplementing material and optionally a binder and optionally a conductive agent in a solvent and stirring uniformly to form a positive electrode slurry; The positive electrode slurry is coated on the positive electrode current collector, dried and cold pressed to form a positive electrode active material layer.
  • the solvent may be N-methylpyrrolidone (NMP).
  • the step of preparing the positive electrode sheet may further include: dispersing the positive electrode lithium supplement material and optionally a binder and optionally a conductive agent in a solvent and stirring uniformly to form a lithium supplement slurry;
  • the lithium slurry is coated on the positive electrode current collector, and is dried and cold-pressed to form a lithium-replenishing film layer.
  • the solvent can be NMP.
  • the lithium-replenishing slurry and the positive electrode slurry can be applied simultaneously or separately.
  • the lithium-replenishing coating and the positive electrode coating can be dried simultaneously or separately, and can be cold-pressed simultaneously or separately.
  • the step of preparing the positive electrode sheet includes the step of preparing the lithium supplementing film layer
  • the positive electrode lithium supplementing material can be omitted in the positive electrode slurry.
  • the positive electrode lithium supplement material can be prepared by the following method: mixing lithium oxide and precursors of each metal, and sintering in a non-oxidizing gas atmosphere to obtain a lithium-rich metal oxide.
  • the metal precursor can be selected from metal oxides, metal hydroxides, and the like.
  • the non-oxidizing gas atmosphere is, for example, an inert gas atmosphere, a nitrogen atmosphere, or the like.
  • the sintering temperature may be 600°C to 800°C.
  • the sintering time can be 5h-15h, or 10h-20h, etc.
  • a crushing and classifying step is optionally also included after sintering to obtain a lithium-rich metal oxide with an appropriate particle size distribution.
  • the lithium-rich metal oxide has a volume average particle size D v 50 of 3 ⁇ m to 7 ⁇ m, alternatively 3 ⁇ m to 5 ⁇ m, or 4 ⁇ m to 6 ⁇ m.
  • a washing step is also optionally included after sintering.
  • the impurities on the surface of the particles are washed away by the washing step, which helps to improve one or more of the energy density, cycle performance and storage performance of the battery.
  • anhydrous ethanol can be used for washing.
  • the washing time can be 0.5h to 1h.
  • the granules are dried after washing.
  • the drying temperature may be 80°C to 200°C, for example, 120°C to 160°C.
  • the drying time can be 5h-15h, for example, 8h-12h.
  • the washing step is performed after the crushing and classifying step. This helps to more fully wash away impurities and improve the purity of the lithium-rich metal oxide.
  • S1 Weigh out the oxide powders of Li 2 O, NiO, CuO and optional metal M, and mix them uniformly by ball milling.
  • Li 2 O may be appropriately excessive.
  • the ratio of the molar content of Li to the total molar content of metal elements other than Li is 2:05:1 to 2.12:1.
  • the molar ratio of Li, Ni, and Cu elements is 2.05:0.4:0.6.
  • the mixed powder is sintered in a non-oxidizing gas atmosphere (eg, nitrogen atmosphere).
  • the sintering temperature may be 600°C to 800°C, optionally 650°C to 750°C.
  • the sintering time can be 5h-15h, optionally 8h-10h.
  • the lithium-rich metal oxide can be obtained by naturally cooling to room temperature.
  • the sintered product can also be subjected to a subsequent crushing, classifying step and/or washing step to obtain a lithium-rich metal oxide.
  • the temperature may be increased to the sintering temperature at a temperature ramp rate of 1°C/min to 10°C/min.
  • the heating rate is 1°C/min ⁇ 5°C/min, 3°C/min ⁇ 8°C/min, or 3°C/min ⁇ 5°C/min.
  • the sintered product is crushed and classified to obtain a classified product.
  • the volume-average particle diameter D v 50 of the classified product is optionally 3 ⁇ m ⁇ 7 ⁇ m, further optionally 3 ⁇ m ⁇ 5 ⁇ m, or 4 ⁇ m ⁇ 6 ⁇ m.
  • S4 washing the classified product, and drying to obtain the final product of lithium-rich metal oxide.
  • washing can be done with absolute ethanol.
  • the washing time can be 0.5h ⁇ 1h.
  • the drying temperature may be 80°C to 200°C, for example, 120°C to 160°C.
  • the negative electrode sheet can be prepared as follows: the negative electrode active material and optionally the conductive agent and optionally the binder are dispersed in a solvent (such as NMP or deionized water), and then coated on the negative electrode current collector after stirring evenly. After drying and cold pressing, a negative pole piece is obtained.
  • a solvent such as NMP or deionized water
  • the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process or a lamination process; the electrode assembly is placed in an outer package, injected with an electrolyte, vacuum-sealed, left to stand, Processes such as chemical formation and shaping are carried out to obtain a lithium ion secondary battery.
  • the optional technical features of the lithium ion secondary battery of the present application are also applicable to the preparation method of the present application.
  • the present application also provides a device comprising at least one of the lithium-ion secondary battery, battery module, or battery pack of the present application.
  • Lithium-ion secondary batteries, battery modules, or battery packs can be used as a power source for the device or as an energy storage unit for the device.
  • Examples of devices may be, but are not limited to, mobile devices (eg, cell phones, laptops, etc.), electric vehicles (eg, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf balls) vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • the device may select a lithium-ion secondary battery, a battery module or a battery pack according to its usage requirements.
  • Figure 6 is an apparatus as an example.
  • the device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like.
  • the device can adopt a battery pack or a battery module according to actual use requirements.
  • the device may be a mobile phone, a tablet computer, a laptop computer, and the like.
  • the device is generally required to be thin and light, and a lithium-ion secondary battery can be used as a power source.
  • the temperature is raised to 680° C. at a heating rate of 3° C./min, and the temperature is maintained for 10 h, and the mixed powder is sintered. Cool down naturally after sintering.
  • Li 2 Cu x1 Ni 1-x1 O 2 cathode lithium supplementing materials with other Ni/Cu ratios can be prepared by referring to the above method.
  • Ni(OH) 2 synthesized by a co-precipitation method
  • the mixed powder was sintered at 250°C for 2h, 450°C for 2h under nitrogen atmosphere, and then heated to 700°C for 10h at a heating rate of 1°C/min to obtain Li 2 NiO 2 .
  • Lithium oxide (purity >97%, Aldrich) and iron oxide (purity >99%, Aldrich) were uniformly mixed at a Li/Fe atomic molar ratio of 5:1, and pretreated at 450 °C for 8 h under argon atmosphere , and then grinded uniformly, then heated to 750°C at a rate of 5°C/min, sintered at this temperature for 18h, and finally cooled to room temperature naturally to obtain Li 5 FeO 4 cathode lithium supplementary material.
  • lithium oxide purity > 97%, Aldrich
  • cobalt oxide purity > 99%, Aldrich
  • the ratio is (98 ⁇ 0.97):(98 ⁇ 0.01):(98 ⁇ 0.02):2, fully stirring and mixing in the solvent NMP to obtain a positive electrode slurry.
  • the positive electrode slurry is coated on two opposite surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode pole piece is obtained.
  • the areal density of the positive electrode active material layer was 19.5 mg/cm 2
  • the compaction density was 2.4 g/cm 3 .
  • the negative active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR) and thickener sodium carboxymethyl cellulose (CMC-Na) are dispersed in a solvent according to a weight ratio of 96.5:0.7:1.8:1 to remove
  • SBR binder styrene-butadiene rubber
  • CMC-Na thickener sodium carboxymethyl cellulose
  • Ethylene carbonate EC and ethyl methyl carbonate EMC are mixed by volume ratio 3:7 to obtain a solvent; then electrolyte lithium salt LiTFSI and LiDFOP are dissolved in the above-mentioned solvent, and mixed to obtain electrolyte.
  • the concentration of LiTFSI in the electrolyte was 0.8M (mol/L), and the concentration of LiDFOP was 0.2M.
  • the positive pole piece, the polyethylene PE/polypropylene PP porous composite separator, and the negative pole piece are stacked in sequence, and then wound to obtain an electrode assembly; the electrode assembly is put into an outer package, injected with an electrolyte, and packaged to obtain lithium ions secondary battery.
  • the preparation of the lithium ion secondary battery is similar to that of Example 1, the difference is that the relevant preparation parameters of the positive electrode and the electrolyte are adjusted, as shown in Table 1.
  • the positive electrode lithium supplement material is provided in the form of a lithium supplement film layer on the surface of the positive electrode active material layer away from the positive electrode current collector.
  • the lithium-replenishing film layer uses PVDF as a binder.
  • the preparation of the lithium ion secondary battery is similar to that in Example 1, the difference is that the relevant preparation parameters of the positive electrode and the electrolyte are adjusted, wherein the positive active material is LiNi 0.5 Co 0.2 Mn 0.3 O 2 (abbreviated as NCM523);
  • the areal density of the active material layer is 18 mg/cm 2 , and the compacted density is 3.4 g/cm 3 ;
  • the areal density of the negative electrode active material layer is 10.7 mg/cm 2 , and the compacted density is 1.7 g/cm 3 ; the other parameters are detailed in table 3.
  • the positive electrode lithium supplementing material is disposed on the surface of the positive electrode active material layer away from the positive electrode current collector in the form of a lithium supplementing film layer.
  • the lithium-replenishing film layer uses PVDF as a binder.
  • the mass ratio of free lithium refers to the mass ratio in the lithium-rich metal oxide.
  • the content of the positive electrode lithium supplement material refers to the mass percentage content in the positive electrode active material layer.
  • the proportion of fluorine ⁇ refers to the proportion of the total mass of the fluorine element in the anion of the electrolyte lithium salt relative to the total mass of the electrolyte in the electrolyte.
  • First charge specific capacity (mAh/g) first cycle charge capacity/mass of positive active material
  • First discharge specific capacity (mAh/g) first cycle discharge capacity/mass of positive active material
  • the battery was charged at a constant current rate of 1C to the end-of-charge voltage, and then charged at a constant voltage to a current of 0.05C; then discharged at a constant current of 1C to the end-of-discharge voltage, and then left for 5 minutes, this is a cycle of charge and discharge process, record the discharge capacity at this time, which is the discharge capacity of the first cycle.
  • the battery was subjected to a cyclic charge-discharge test according to the above method, and the discharge capacity of each cycle was recorded.
  • Battery cycle capacity retention rate X cycle (%) X cycle discharge capacity / first cycle discharge capacity ⁇ 100%
  • an acid solution such as aqua regia
  • the digestion time can be 30min; adding the digested solution to the ICAP 7400 spectrometer, the metal ion deposition amount of the negative pole piece can be quantitatively analyzed.
  • the battery failure standard can refer to the EUCAR battery abuse standard level, when the battery reaches the HL3 level (the battery starts to smoke), it is judged to be invalid), stop charging. . Record the SOC of the battery at this time.
  • the battery failure standard can refer to the EUCAR battery abuse standard level, when the battery reaches the HL3 level (the battery starts to emit smoke) The above is judged to be invalid).
  • the battery failure standard can refer to the EUCAR battery abuse standard level, when the battery reaches the HL3 level (the battery starts to emit smoke) The above is judged to be invalid).
  • the capacity retention rate of the battery after being stored at 60° C. for 30 days (E n ⁇ E 0 )/E 0 ⁇ 100%. Take the average value of the high temperature storage capacity retention rate of 5 batteries.
  • the end-of-charge voltage of LiFePO 4 battery is 3.65V, and the end-of-discharge voltage is 2.5V; the end-of-charge voltage of LiNi 0.5 Co 0.2 Mn 0.3 O 2 battery is 4.35V, and the end-of-discharge voltage is 2.8V.
  • the batteries of Examples 1 to 27 and Comparative Examples 1 to 2 are referred to as LFP batteries for short, and the test results are shown in Table 2.
  • the batteries of Examples 28 to 48 and Comparative Examples 3 to 4 are referred to as NCM batteries for short, and the test results are shown in Table 4.
  • the lithium-rich metal oxide is added to the positive electrode active material layer of the LFP battery as the positive electrode lithium supplement material, and the lithium-rich metal oxide contains Ni, One or more elements of Co, Fe, Mn, Cu, and at the same time make the electrolyte meet ⁇ 14%, which can effectively compensate for the active lithium consumed by SEI film formation and side reactions, and make the battery have less metal The amount of ion dissolution. Therefore, the LFP battery can not only obtain higher initial discharge capacity, high temperature cycle performance and high temperature storage performance, but also the failure temperature of the battery in the high temperature safety test is significantly increased, so it also obtains higher high temperature safety performance. In addition, the maximum temperature reached by the battery after thermal failure is also significantly reduced, further indicating its improved high-temperature safety performance.
  • Comparative Example 1 the positive electrode lithium supplement material was not added, and the fluorine element content of the anion of the electrolyte lithium salt in the electrolyte was relatively high, so that the first discharge capacity, high temperature cycle performance and high temperature storage performance of the battery were all low, and the battery was safe at high temperature.
  • the failure temperature in the test is lower, and the temperature reached after failure is higher, so the high temperature safety performance is poor.
  • the Ni/Cu atomic ratio is within an appropriate range, which can improve the first-time performance of the battery. Discharge capacity, and can improve the high temperature cycle performance and high temperature storage performance of the battery.
  • the lithium-rich metal oxide is added to the positive electrode active material layer of the NCM battery as the positive electrode lithium supplement material, and the lithium-rich metal oxide contains Ni, One or more elements in Co, Fe, Mn, Cu, and at the same time make the electrolyte meet ⁇ 14%, which can make the battery have a high initial discharge capacity and at the same time significantly increase the failure temperature of the battery in a high temperature environment , so that the battery has high high temperature safety performance.
  • the amount of metal ions dissolved in the battery is significantly reduced, which is also conducive to improving the first discharge capacity of the battery, while enabling the battery to obtain higher high-temperature cycle performance and high-temperature storage performance.
  • the Ni/Cu atomic number ratio is in an appropriate range, which can improve the first time of the battery. Discharge capacity, and can improve the high temperature cycle performance and high temperature storage performance of the battery.

Abstract

本申请公开了一种锂离子二次电池及其制备方法、电池模块、电池包和装置。锂离子二次电池包括正极极片、负极极片和电解液，其中，正极极片包含正极活性材料和正极补锂材料，正极补锂材料包括富锂金属氧化物，富锂金属氧化物中含有Ni、Co、Fe、Mn、Cu中的一种或多种元素；电解液包含电解质锂盐和溶剂，且电解质锂盐的阴离子中氟元素的总质量相对于电解液的总质量的占比ε＜14％。

Description

锂离子二次电池及其制备方法、电池模块、电池包和装置 技术领域
本申请涉及电池技术领域，具体涉及一种锂离子二次电池及其制备方法、电池模块、电池包和装置。
背景技术
锂离子二次电池是一种可充电电池，其在放电后可通过充电的方式使活性物质激活而继续使用。具体来说，锂离子二次电池依靠锂离子在正极和负极之间往复脱嵌来实现充电和放电。由于具有能量密度高、循环寿命长，以及无污染、无记忆效应等突出特点，锂离子二次电池被广泛应用于各类电子产品，并快速普及到电动车辆和储能系统等大型装置领域。
在大型装置中，通常将多个锂离子二次电池组成电池模块或电池包，来满足对高容量的需求。此时，任意一个或几个锂离子二次电池发生热失控，将带来重大的安全隐患。为了推动电动汽车和储能系统等的进一步发展，需要使锂离子二次电池具有较高能量密度的前提下，提高安全性能。
发明内容
本申请第一方面提供一种锂离子二次电池，包括正极极片、负极极片和电解液，其中，正极极片包含正极活性材料和正极补锂材料，正极补锂材料包括富锂金属氧化物，富锂金属氧化物中含有Ni、Co、Fe、Mn、Cu中的一种或多种元素；电解液包含电解质锂盐和溶剂，且电解质锂盐的阴离子中氟元素的总质量相对于电解液的总质量的占比ε＜14％。可选地，1.5％≤ε≤9.5％。
富锂金属氧化物中含有Ni、Co、Fe、Mn、Cu中的一种或多种，能提高自身嵌锂量，从而能在电池充电过程中释放更多的活性锂，由此能更有效地弥补锂的不可逆损耗，从而使电池具有较高的高温循环寿命或高温存储寿命。并且，正极采用诸如磷酸铁锂等库伦效率较高活性材料的电池还可以具有提升的首次放电容量。
在正极极片添加正极补锂材料，同时使电解液满足电解质锂盐的阴离子中氟元素的总质量相对于电解液的总质量的占比在适当范围内，能显著减少金属离子溶出。因此，在提升电池体积能量密度的同时，保证电池的自放电率较低，从而能进一步提升电池的放电容量。尤其是，负极表面的金属沉积量明显减少，由此不仅进一步减少电解液副反应，降低产气量，还能减小沉积的金属在电池受热过程中刺穿隔离膜引发电池内短路的风险，从而有效改善电池的高温安全性能。
在本申请任意实施方式中，电解质锂盐的阴离子中氟元素的总质量相对于电解液 的总质量的占比2％≤ε≤9.3％。可选地，ε为2.5％～9.2％。电解质锂盐的阴离子中氟元素的总质量相对于电解液的总质量的占比在上述范围内，能进一步减少金属离子溶出，并且有利于电解液获得较高的离子电导率，从而能使电池获得较高的高温安全性能的同时，还兼具较高的高温循环性能和高温存储性能。
在本申请任一实施方式中，富锂金属氧化物可选自Li xM 1O 0.5(2+x)、Li 2M 2O 3、Li 2M 3O 4、Li 3M 4O 4、Li 5M 5O 4、Li 5M 6O 6中的一种或几种，其中，x≥1，M 1选自Ni、Co、Fe、Mn、Zn、Mg、Ca、Cu、Sn中的一种或几种，M 2选自Ni、Co、Fe、Mn、Sn、Cr中的一种或几种，M 3选自Ni、Co、Fe、Mn、Sn、Cr、V、Nb中的一种或几种，M 4选自Ni、Co、Fe、Mn、Sn、Cr、V、Mo、Nb中的一种或几种，M 5选自Ni、Co、Fe、Mn、Sn、Cr、Mo中的一种或几种，M 6选自Ni、Co、Mn中的一种或几种，M 1、M 2、M 3、M 4、M 5、M 6中每种元素的价态分别低于其自身的最高氧化价态。
在本申请任一实施方式中，富锂金属氧化物可包括Li 2MnO 2、Li 5FeO 4、Li 6CoO 4、Li 2NiO 2、Li 2Cu x1Ni 1-x1-y1M y1O 2中的一种或几种，以及任选的包括Li 3VO 4、Li 3NbO 4中的一种或几种，其中，0＜x1≤1，0≤y1＜0.1，M选自Zn、Sn、Mg、Fe和Mn中的一种或几种。可选地，0.2≤x1≤0.8，或0.4≤x1≤0.6。上述富锂金属氧化物具有较高的脱锂容量和合适的首次脱锂电压，由此可以具有较好的补锂效果，从而有助于提高电池能量密度。并且，适当的富锂金属氧化物还有助于提升电池的高温循环寿命或高温存储性能。
在本申请任一实施方式中，富锂金属氧化物中可含有游离锂，游离锂包括LiOH、LiHCO 3和Li 2CO 3中的一种或几种，且游离锂在富锂金属氧化物中的质量占比ω≤5wt％。可选地，ω≤3wt％。进一步可选地，0.3wt％≤ω≤0.7wt％。富锂金属氧化物中的游离锂可以消耗HF，从而进一步减少金属离子溶出。游离锂的含量在适当范围内，不仅能减少极片中的电化学惰性材料，使电池具有较高的能量密度，还能减少游离锂的分解产气，使电池获得较高的高温循环性能和高温存储性能。
在本申请任一实施方式中，富锂金属氧化物的至少一部分外表面可具有包覆层。包覆层包括金属氟化物、氧化物、金属磷酸盐、碳材料、导电聚合物中的一种或几种。
在本申请任一实施方式中，金属氟化物可选自AlF 3。氧化物可选自V 2O 5、Al 2O 3、ZrO 2、TiO 2、ZnO、SiO 2、B 2O 3中的一种或几种。金属磷酸盐可选自AlPO 4、FePO 4、Co 3(PO 4) 2、Ni 3(PO 4) 2中的一种或几种。包覆层能隔离富锂金属氧化物与外界环境的接触，从而能有效缓解富锂金属氧化物因吸水造成的自身容量损失或电池内的副反应，并且能减少金属离子溶出。因此，采用包覆层改性的富锂金属氧化物，可以进一步改善电池的高温安全性能，并且能改善高温循环性能和高温存储性能。
在本申请任一实施方式中，电解质锂盐可包括选自二氟草酸硼酸锂(LiDFOB)、双草酸硼酸锂(LiBOB)、二氟磷酸锂(LiDFP)、二氟二草酸磷酸锂(LiDFOP)、四氟草酸磷酸锂(LiTFOP)、双氟磺酰亚胺锂(LiFSI)、双三氟甲烷磺酰亚胺锂(LiTFSI)、四氟硼酸锂(LiBF 4)、三氟甲磺酸锂(LiCF 3SO 3)、二(三氟甲基磺酰)甲基锂(LiCH(CF 3SO 2) 2)、三(三氟甲基磺酰)甲基锂(LiC(CF 3SO 2) 3)中的一种或几种，且任选地包括六氟磷酸锂(LiPF 6)。采用合适的电解质锂盐，有利于使电解液的氟含量在所需范围内，同时还可以使电解液具有较高的热稳定性和电化学稳定性，从而能进一步改善电池的高温安全性能，并且可提升高温循环寿命和高温存储性能。
在本申请任一实施方式中，电解质锂盐可包括双草酸硼酸锂(LiBOB)、二氟二草酸磷酸锂(LiDFOP)、双氟磺酰亚胺锂(LiFSI)中的一种或几种。
在本申请任一实施方式中，电解质锂盐在电解液中的浓度为0.7mol/L～4mol/L，可选地为0.7mol/L～3mol/L。电解质锂盐的含量适当，能使电解液获得较高的离子电导率，从而改善电池能量密度和循环性能。
在本申请任一实施方式中，LiPF 6在电解液中的浓度≤0.4mol/L。由于LiPF 6在电解液中极易电离形成F ﹣、PF 5、PF 6 ﹣等含氟粒子，这些含氟粒子在电解液中易造成金属离子溶出。电解液中的LiPF 6含量较小，有利于减小上述问题。此外，控制LiPF 6在电解液中的浓度在上述范围内，可以进一步控制电解液的ε值，从而进一步降低自放电率。
在本申请任一实施方式中，正极活性材料可选自Li zCoO 2、Li zNiO 2、Li zMnO 2、Li zMn 2O 4、Li zNi aCo bMn cM’ dO 2、Li zNi 1-uCo uO 2、Li zCo 1-uMn uO 2、Li zNi 1-uMn uO 2、Li zNi αCo βMn γO 4、Li zMn 2-ηNi ηO 4、Li zMn 2-ηCo ηO 4、Li zFePO 4、Li zCoPO 4、Li zMnPO 4、以及它们的改性材料中的一种或几种，其中，M’选自Al、Mo、Nd、Zn中的一种或几种，z独立地满足0.5≤z≤1.3，0＜a＜1，0＜b＜1，0＜c＜1，0≤d＜1，a+b+c+d＝1，u独立地满足0＜u＜1，0＜α＜2，0＜β＜2，0＜γ＜2，α+β+γ＝2，η独立地满足0＜η＜2。
在本申请任一实施方式中，正极活性材料可包括Li zFePO 4及其改性材料中的一种或几种，其中0.5≤z≤1.3。可选地，0.9≤z≤1.2，或z＝1。采用Li zFePO 4及其改性材料有利于电池获得更高的高温安全性能。
正极活性材料包含于正极极片的正极活性材料层中。在一些实施例中，正极活性材料层的面密度≥18mg/cm 2，进一步可选地为18mg/cm 2～21mg/cm 2。设计较大的正极活性材料层面密度，能提高电池的能量密度。
在本申请任一实施方式中，正极活性材料可包括Li zNi aCo bMn cM’ dO 2及其改性材料中的一种或几种，其中0.5≤z≤1.3，0.5≤a＜1，0＜b≤0.2，0＜c≤0.3，0≤d＜1，M’选自Al、Mo、Nd、Zn中的一种或几种。采用该正极活性材料能使电池获得更高的能量密度。
在本申请任一实施方式中，正极极片包括正极集流体以及设置于正极集流体上的正极活性材料层，正极活性材料层包含正极活性材料；其中，正极补锂材料均匀分布于正极活性材料层中，和/或，正极补锂材料以补锂膜层的形式设置于正极集流体与正极活性材料层之间，和/或，正极补锂材料以补锂膜层的形式设置于正极活性材料层背离正极集流体的表面。采用补锂膜层的形式，可以进一步提升电池的安全性能。
在本申请任一实施方式中，在正极集流体的至少一侧，正极活性材料与正极补锂材料的质量比为99.9:0.1～85:15，可选地为98.5:1.5～93:7，进一步可选地为98:2～95:5。在正极极片中，正极活性材料与正极补锂材料的比例在适当范围内，能提供充足的锂，从而有助于提高电池的高温循环性能和高温存储性能，并且还能提升电池的过充性能。正极极片还可兼具较高的活性材料占比，有助于使电池具有较高的能量密度。
本申请第二方面提供一种锂离子二次电池的制备方法，包括以下步骤：提供正极极片，所述正极极片包含正极活性材料和正极补锂材料，正极补锂材料包括富锂金属氧化物，富锂金属氧化物中含有Ni、Co、Fe、Mn、Cu中的一种或多种元素；提供电解液，所述电解液包含电解质锂盐和溶剂，且电解质锂盐的阴离子中氟元素的总质量相对于电 解液的总质量的占比ε＜14％，可选地，1.5％≤ε≤9.5％；将正极极片、负极极片和电解液进行组装，得到锂离子二次电池。
本申请第三方面提供一种电池模块，包括根据本申请的锂离子二次电池。
本申请第四方面提供一种电池包，包括根据本申请的电池模块。
本申请第五方面提供一种装置，包括根据本申请的锂离子二次电池、电池模块、或电池包中的至少一种。
本申请提供的电池模块、电池包和装置包含根据本申请的锂离子二次电池，因而能具有相应的有益效果。
附图说明
图1是本申请的二次电池的一实施方式的示意图。
图2是本申请的二次电池的一实施方式的分解示意图。
图3是本申请的电池模块的一实施方式的示意图。
图4是本申请的电池包的一实施方式的示意图。
图5是图4的分解图。
图6是本申请的二次电池用作电源的装置的一实施方式的示意图。
在本申请中，附图并未按照实际的比例绘制。
具体实施方式
为了使本申请的发明目的、技术方案和有益技术效果更加清晰，以下结合实施例对本申请进行进一步详细说明。应当理解的是，本说明书中描述的实施例仅仅是为了解释本申请，并非为了限定本申请。
为了简便，本文仅明确地公开了一些数值范围。然而，任意下限可以与任何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，尽管未明确记载，但是范围端点间的每个点或单个数值都包含在该范围内。因而，每个点或单个数值可以作为自身的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。
在本文的描述中，需要说明的是，除非另有说明，“以上”、“以下”为包含本数，“一种或几种”中“几种”的含义是两种或两种以上。
本申请的上述发明内容并不意欲描述本申请中的每个公开的实施方式或每种实现方式。如下描述更具体地举例说明示例性实施方式。在整篇申请中的多处，通过一系列实施例提供了指导，这些实施例可以以各种组合形式使用。在各个实例中，列举仅作为代表性组，不应解释为穷举。
通常情况下，锂离子二次电池包括正极极片、负极极片、隔离膜及电解液。在电池充放电过程中，活性离子(锂离子)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，主要起到防止正负极短路的作用，同时可使锂离子通过。电解液在正极极片和负极极片之间，主要起到传导离子的作用。
在电池首次充电过程中，锂离子从正极活性材料脱出，经过电解液传导，嵌入到负极活性材料中。在此过程中，部分锂离子参与负极活性材料表面形成固态电解质界面(SEI)膜的反应，造成活性锂损失。并且，在电池后续循环充放电过程和存储过程中还可能发生SEI膜的修复与生长、以及电解液在嵌锂态负极表面的副反应，都会不可逆地消耗锂离子。活性锂的消耗会导致电池的循环性能和/或存储性能较低。同时，锂消耗反应还会增加电池内部产气，造成安全性能较差。上述影响在高温(例如45℃以上，如45℃～80℃或45℃～60℃等)条件下更为严重。
此外，首次充电形成SEI膜的活性锂损失还会造成首次放电容量较低，从而不利于电池能量密度的提升。
通过预补锂方案可以提供额外的活性锂，由此能弥补活性锂损失。预补锂的手段主要有负极补锂和正极补锂。负极补锂通常是采用金属锂粉或锂带对负极活性材料进行预锂化。但是，由于金属锂活性高，对环境及设备都有很高的要求，因而使负极补锂的工艺复杂、成本较高，不利于规模化应用。正极补锂方案可以是在正极添加富锂化合物作为补锂材料，避免了使用金属锂。富锂化合物在电池充电时释放锂，可以补偿活性锂在电池首次充电形成SEI膜以及后续循环过程和存储过程中的不可逆损失，从而能提高电池在循环和/或存储后的放电容量保持率。然而发明人发现，采用正极补锂的电池仍然存在高温安全性能较低的问题。
为了使电池同时兼顾较高的能量密度和高温安全性能，发明人进一步进行了大量研究发现，通过在正极极片添加合适的正极补锂材料，且使电解液中电解质锂盐的阴离子中氟元素的总质量相对于电解液的总质量的占比ε＜14％，能实现上述发明目的。电解质锂盐的阴离子中氟元素的总质量相对于电解液的总质量的占比ε可采用离子色谱法测得。
因此，本申请第一方面提供一种锂离子二次电池。该锂离子二次电池中，正极极片包含正极活性材料和正极补锂材料，正极补锂材料包括富锂金属氧化物，富锂金属氧化物中含有Ni、Co、Fe、Mn、Cu中的一种或多种元素；并且电解液包含电解质锂盐和溶剂，且电解质锂盐的阴离子中氟元素的总质量相对于电解液的总质量的占比ε＜14％。
发明人发现，富锂金属氧化物中含有Ni、Co、Fe、Mn、Cu中的一种或多种，能提高自身嵌锂量。相应地，富锂金属氧化物具有较高的脱锂容量，能在电池充电过程中释放更多的活性锂，由此能更有效地弥补锂的不可逆损耗，从而使电池在高温条件下能具有较高的循环寿命或存储寿命。并且，诸如磷酸铁锂/石墨电池等正极首次效率较高的电池还可以具有提升的首次放电容量。
本申请的效果的解释不期望受到任何理论限制。所述富锂金属氧化物在脱锂过程中会发生晶格的剧烈变化，此时使电解液满足电解质锂盐的阴离子中氟元素的总质量相对于电解液的总质量的占比在适当范围内，能有效缓解金属离子溶出问题。金属离子的溶出量显著减少，能减少负极表面的金属沉积量，由此不仅进一步减少电解液副反应，降低产气量，还能减小沉积的金属在电池受热过程中刺穿隔离膜引发电池内短路的风险，从而进一步改善电池的高温安全性能。
此外，由于富锂金属氧化物溶出的金属离子大幅度减少，还能显著降低金属离子的穿梭效应或在负极表面沉积引发的电池自放电，由此能提高电池的容量发挥，从而进 一步提升电池的放电容量。而且，负极表面发生的金属离子还原反应减少，因而对SEI膜的破坏减小，由此能降低因SEI膜不断修复而造成的电解液和活性锂消耗，从而能使电池在高温下循环或存储的过程中具有较高的放电容量保持率。因此，电池的高温循环性能或高温存储性能进一步改善。
在一些实施方式中，在电解液中，电解质锂盐的阴离子中氟元素的总质量相对于电解液的总质量的占比ε为≤13.8％，≤13.5％，≤13％，≤12.5％，≤12％，≤11.5％，≤11％，≤10.5％，≤10％，≤9.5％，≤9.3％，≤9％，≤8.5％，≤8％，≤7.5％，≤7％，≤6.5％，≤6％，≤5.5％，≤5％，≤4.5％，≤4％，≤3.5％，≤3％，或≤2.5％。电解液的ε值在适当范围内，能进一步减少金属离子溶出，更有利于改善电池的高温安全性能。并且，电池的高温存储性能或高温循环性能也可进一步提升。
在一些实施方式中，电解液的ε为≥0％，≥0.5％，≥0.8％，≥1％，≥1.1％，≥1.2％，≥1.3％，≥1.4％，≥1.5％，≥1.6％，≥1.8％，≥2％，≥2.3％，或≥2.5％。电解液中含有适量的氟，有利于电解液获得较高的离子电导率，从而有利于提升电池的首次放电容量、高温循环性能和高温存储性能。另外，电池还可以具有较高的功率性能。
在一些实施方式中，电解液的ε为0～10％，0～9.3％，1％～9.5％，1.5％～9.5％，2％～9.3％，2.5％～9.2％，0.5％～8.5％，1％～8％，1％～7.5％，1.2％～7％，1.3％～6.5％，1.5％～5％，或2％～5％等。
[正极极片]
正极极片通常包括正极集流体和设置在正极集流体至少一侧表面的正极活性材料层。作为示例，正极集流体具有在自身厚度方向相对的两个表面，正极活性材料层设置于正极集流体的两个表面的任意一者或两者上。
正极集流体可采用金属箔片或复合集流体(可以将金属材料设置在高分子材料层上形成复合集流体)。作为示例，正极集流体可采用铝箔。
正极活性材料层包含正极活性材料。正极活性材料可采用本领域已知的用于锂离子二次电池正极、且能可逆地嵌入和脱出锂离子的材料。在一些实施方式中，正极活性材料可选自Li zCoO 2、Li zNiO 2、Li zMnO 2、Li zMn 2O 4、Li zNi aCo bMn cM’ dO 2、Li zNi 1- uCo uO 2、Li zCo 1-uMn uO 2、Li zNi 1-uMn uO 2、Li zNi αCo βMn γO 4、Li zMn 2-ηNi ηO 4、Li zMn 2- ηCo ηO 4、Li zFePO 4、Li zCoPO 4、Li zMnPO 4、以及它们的改性材料中的一种或几种，其中，M’选自Al、Mo、Nd、Zn中的一种或几种，z独立地满足0.5≤z≤1.3，0＜a＜1，0＜b＜1，0＜c＜1，0≤d＜1，a+b+c+d＝1，u独立地满足0＜u＜1，0＜α＜2，0＜β＜2，0＜γ＜2，α+β+γ＝2，η独立地满足0＜η＜2。
在本文中，改性材料中的改性可以是掺杂改性和包覆改性中的一种以上。
在一些实施方式中，正极活性材料可包括Li zFePO 4及其改性材料中的一种或几种，其中0.5≤z≤1.3。可选地，0.8≤z≤1.3，0.9≤z≤1.2，或0.95≤z≤1.1。在一些实施例中，z＝1。Li zFePO 4及其改性材料具有较高的热稳定性，因而有利于电池获得更高的高温安全性能。并且，电池还可兼具较长的高温循环寿命和较高的高温存储性能。
在一些实施方式中，Li zFePO 4的改性材料可以是其中的Fe被诸如Sc、V、Cr、Mn、Ti、Al、Co、Ni、Cu、Zn等Fe以外的且与Fe的原子半径相近的金属元素部分地取代。Li zFePO 4的改性材料的示例包括，Li zFe 1-kMe kPO 4，其中Me选自Sc、V、Cr、Mn、 Ti、Al、Co、Ni、Cu、Zn中的一种或几种，0＜k≤0.5。可选地，0.01≤k≤0.2。可选地，Me选自Mn、Ti、Al、Ni、Cu、Zn中的一种或几种。
发明人进一步发现，当正极活性材料包括Li zFePO 4及其改性材料中的一种或几种，若正极极片同时满足如下条件中的一个以上，能进一步改善电池的性能。
在一些实施例中，正极活性材料层的面密度≥18mg/cm 2。可选地，正极活性材料层的面密度为18mg/cm 2～26mg/cm 2，进一步可选地为18mg/cm 2～25mg/cm 2，18mg/cm 2～23mg/cm 2，18mg/cm 2～21mg/cm 2，19mg/cm 2～22mg/cm 2，或20mg/cm 2～25mg/cm 2。在本申请的锂离子二次电池中，可以设计较大的正极活性材料层面密度，由此能进一步提高电池的能量密度。
在这些实施例中，正极活性材料层的压实密度可以为2.0g/cm 3～2.6g/cm 3，例如2.2g/cm 3～2.4g/cm 3。正极活性材料层的压实密度在适当范围内，可以保证正极极片良好的电子传输性能，同时具有适于电解液浸润的孔隙率，从而有利于电池获得较高的循环性能。
在一些实施方式中，正极活性材料可包括Li zNi aCo bMn cM’ dO 2及其改性材料中的一种或几种，其中0.5≤z≤1.3，0.5≤a＜1，0＜b≤0.2，0＜c≤0.3，0≤d＜1，M’选自Al、Mo、Nd、Zn中的一种或几种。可选地，0.8≤z≤1.2。可选地，0.5≤a≤0.9，0.6≤a≤0.85，或0.65≤a≤0.8。作为示例，正极活性材料可选自LiNi 0.5Co 0.2Mn 0.3O 2、LiNi 0.6Co 0.2Mn 0.2O 2、LiNi 0.8Co 0.1Mn 0.1O 2、上述材料的改性材料等。采用上述的正极活性材料能使电池获得更高的能量密度。
在一些实施方式中，富锂金属氧化物可选自Li xM 1O 0.5(2+x)、Li 2M 2O 3、Li 2M 3O 4、Li 3M 4O 4、Li 5M 5O 4、Li 5M 6O 6中的一种或几种，其中，x≥1，M 1选自Ni、Co、Fe、Mn、Zn、Mg、Ca、Cu、Sn中的一种或几种，M 2选自Ni、Co、Fe、Mn、Sn、Cr中的一种或几种，M 3选自Ni、Co、Fe、Mn、Sn、Cr、V、Nb中的一种或几种，M 4选自Ni、Co、Fe、Mn、Sn、Cr、V、Mo、Nb中的一种或几种，M 5选自Ni、Co、Fe、Mn、Sn、Cr、Mo中的一种或几种，M 6选自Ni、Co、Mn中的一种或几种，M 1、M 2、M 3、M 4、M 5、M 6中每种元素的价态分别低于其自身的最高氧化价态。
在一些实施方式中，富锂金属氧化物可包括Li 2MnO 2、Li 5FeO 4、Li 6CoO 4、Li 2NiO 2、Li 2Cu x1Ni 1-x1-y1M y1O 2中的一种或几种，以及任选的包括Li 3VO 4、Li 3NbO 4中的一种或几种。可选地，富锂金属氧化物可包括Li 2MnO 2、Li 5FeO 4、Li 6CoO 4、Li 2NiO 2、Li 2Cu x1Ni 1-x1-y1M y1O 2中的一种或几种。进一步可选地，富锂金属氧化物可包括Li 5FeO 4、Li 6CoO 4、Li 2Cu x1Ni 1-x1-y1M y1O 2中的一种或几种。Li 2Cu x1Ni 1-x1-y1M y1O 2中，0＜x1≤1，0≤y1＜0.1，M选自Zn、Sn、Mg、Fe和Mn中的一种或几种。可选地，0.2≤x1≤0.8，0.2≤x1≤0.6，0.3≤x1≤0.7，0.3≤x1≤0.6，或0.4≤x1≤0.6。
上述富锂金属氧化物具有较高的脱锂容量的同时，还具有合适的首次脱锂电压，从而可以与正极活性材料的充电电位相匹配，更好地发挥补锂效果，因此能进一步提高电池能量密度。并且，适当的富锂金属氧化物还有助于提升高温循环寿命或高温存储性能。
在一些实施方式中，富锂金属氧化物可包括或是Li 2Cu x1Ni 1-x1-y1M y1O 2。式中，Ni/Cu原子数量比为0.1～4。可选地，Ni/Cu原子数量比为1:4～4:1，1:2～4:1，2:3～4:1， 3:7～7:3，4:6～7:3，或4:6～6:4。采用该富锂金属氧化物，能进一步改善电池的能量密度，并且能提升电池的高温循环性能、高温存储性能和高温安全性能。发明人还发现，采用该正极补锂材料还能进一步提升电池的过充窗口，使电池获得较高的过充性能。
在一些实施方式中，富锂金属氧化物的首次脱锂容量≥250mAh/g。可选地，富锂金属氧化物的首次脱锂容量≥300mAh/g，≥350mAh/g，≥400mAh/g，或≥450mAh/g。富锂金属氧化物的首次脱锂容量较高，应用于电池中能释放更多的活性锂，从而有助于提升电池的能量密度。进一步地，电池还可获得较长的循环寿命或存储寿命。
在一些实施方式中，富锂金属氧化物的首次脱锂平台电压为2.0V～4.5V(相对于Li/Li +)。可选地，富锂金属氧化物的首次脱锂平台电压为2.5V～4.2V，3V～4.2V，2.8V～4V，3.0V～3.75V，3.2V～3.6V，或3.4V～4.1V等(相对于Li/Li +)。富锂金属氧化物具有较低的脱锂平台电压，能够与正极活性材料的脱锂电位相匹配，从而能更好地发挥补锂材料和活性材料的容量发挥，提高补锂效果。
在一些实施方式中，富锂金属氧化物中可含有游离锂，游离锂包括LiOH、LiHCO 3和Li 2CO 3中的一种或几种。富锂金属氧化物中的游离锂可以消耗HF，从而进一步减少金属离子溶出。
在一些实施方式中，游离锂在富锂金属氧化物中的质量占比ω≤5wt％。可选地，ω≤3wt％。进一步可选地，0.1wt％≤ω≤3wt％，0.1wt％≤ω≤2wt％，0.2wt％≤ω≤1wt％，或0.3wt％≤ω≤0.7wt％。富锂金属氧化物中游离锂的含量在适当范围内，能减少游离锂的分解产气，使极片保持良好的反应界面，从而使电池获得较高的高温循环性能和高温存储性能。此外，游离锂为电化学惰性材料，减少正极中的游离锂含量有利于电池获得较高的能量密度。
在一些实施方式中，富锂金属氧化物的至少一部分外表面具有包覆层。包覆层可包括金属氟化物、氧化物、金属磷酸盐、碳材料、导电聚合物中的一种或几种。氧化物选自元素周期表第IB族至第VIIB族、第VIII族、第IIIA族、第IV族除C外的元素的氧化物或锂复合氧化物。可选地，包覆层可包括金属氟化物、氧化物、金属磷酸盐中的一种或几种。
富锂金属氧化物通常呈碱性，尤其当碱性较高(例如pH约为12)时，更容易吸收环境中的水分。富锂金属氧化物将水分引入电池内会引发一系列的副反应等问题，影响电池的容量发挥和循环寿命的进一步提升。包覆层可以起到隔离作用，减少富锂金属氧化物与外界环境的接触，从而减少吸水量，因此能有效缓解因吸水造成的容量损失，使电池获得较高的能量密度和循环容量保持率。另外，包覆层还可以隔离富锂金属氧化物与电解液的直接接触，由此有利于进一步减少金属离子溶出，从而能进一步改善电池的高温安全性能、高温循环性能和高温存储性能。
在一些实施例中，金属氟化物可选自AlF 3。
在一些实施例中，氧化物可选自V 2O 5、Al 2O 3、ZrO 2、TiO 2、ZnO、SiO 2、Co 3O 4、B 2O 3、Li 2MnO 3、LiAlO 2、Li 2TiO 3、Li 2ZrO 3中的一种或几种。可选地，氧化物可选自V 2O 5、Al 2O 3、ZrO 2、TiO 2、ZnO、SiO 2、B 2O 3中的一种或几种。适当的氧化物可以提升包覆层的稳定性，有助于更好地隔离富锂金属氧化物与外界环境或电解液的接触，从而进一步减少吸水量和金属离子溶出。
在一些实施例中，磷酸盐可选自Li 3PO 4、AlPO 4、FePO 4、Co 3(PO 4) 2、Ni 3(PO 4) 2中的一种或几种。可选地，磷酸盐可选自AlPO 4、FePO 4、Co 3(PO 4) 2、Ni 3(PO 4) 2中的一种或几种。适当的磷酸盐可以提升包覆层的稳定性，有助于更好地隔离富锂金属氧化物与外界环境或电解液的接触，从而进一步减少吸水量和金属离子溶出。
在一些实施例中，碳材料可选自石墨烯、碳纳米管、碳纤维中的一种或几种。
在一些实施例中，导电聚合物可选自聚噻吩类、聚吡咯类、聚苯胺类、聚吡啶类、上述材料的改性聚合物中的一种或几种。作为示例，改性聚合物可以是聚乙二醇修饰改性的聚合物。聚噻吩类的示例可选自聚噻吩、聚3,4-乙烯二氧噻吩等。
在一些实施例中，包覆层包含金属氟化物、氧化物、磷酸盐中的一种或几种和导电聚合物。作为一个示例，包覆层包含Al 2O 3和聚乙二醇修饰的聚3,4-乙烯二氧噻吩。作为另一示例，包覆层包含Li 3PO 4和聚吡咯。
在任意实施例中，包覆层可以为单层或多层复合包覆层。
在正极极片中，正极补锂材料可以以任意能释放锂至电解液中的形式负载到正极集流体上。在一些实施方式中，正极补锂材料可均匀分布于正极活性材料层中。即，正极活性材料层包含正极活性材料和正极补锂材料。
在一些实施方式中，正极补锂材料均匀分布于正极活性材料层中，且基于正极活性材料层的总重量，正极补锂材料的含量W为0.1％～10％。可选地，W≥0.5％，≥1％，≥1.5％，≥2％，≥3％，或≥4％。正极极片中正极补锂材料的含量在适当范围内，能提供充足的锂来弥补SEI膜或副反应消耗的活性锂，从而提高电池高温循环或高温存储过程中的容量保持率。发明人还发现，当正极极片中含有适当多的正极补锂材料时，还能进一步提升电池的过充窗口，使电池获得较高的过充性能。可选地，W≤10％，≤8％，≤7％，或≤6％。使正极极片中正极补锂材料的含量在上述范围内，还能确保正极具有较高的活性材料占比，有助于电池获得较高的能量密度。
在一些实施例中，W为1％～10％，1％～8％，1％～6％，2％～6％，3％～6％，1％～5％，1.5％～3％，2％～5％，2％～4％，4％～10％，6％～10％，或8％～10％。
在一些实施方式中，正极补锂材料以补锂膜层的形式设置于正极集流体。补锂膜层是包含正极补锂材料的薄膜层。在一些实施例中，补锂膜层可以与正极活性材料层层叠设置于正极集流体的表面。
作为一个示例，补锂膜层设置于正极集流体与正极活性材料层之间。当电池发生穿钉等异常情况时，由于在正极集流体与正极活性材料层之间具有补锂膜层，可以降低正极集流体的毛刺与负极接触的风险，还有助于提升短路电阻，从而提高电池的安全性能。
作为另一个示例，补锂膜层设置于正极活性材料层背离正极集流体的表面。发明人发现，当隔离膜发生熔融或刺穿等情况引发电池内短路时，由于正极活性材料层背离正极集流体的表面设置有补锂膜层，能提升短路电阻，并且可以降低短路时的反应剧烈程度，从而可以进一步提高电池的高温安全性能。另外，补锂膜层位于正极活性材料层的外表面，还有助于提升电池过充性能。
在正极极片中，补锂膜层与正极活性材料层可以彼此接触或不接触。
在一些实施方式中，在正极集流体的至少一侧，正极活性材料与正极补锂材料的 质量比为99.9:0.1～85:15，可选地为99.5:0.5～90:10，99.5:0.5～92:8，99:1～89:11，99:1～93:7，98.5:1.5～93:7，98.5:1.5～94:6，98:2～94:6，98:2～95:5，或98:2～96:4。正极极片中正极补锂材料的含量在适当范围内，能提供充足的锂，从而有助于提高电池的高温循环性能和高温存储性能，并且还能提升电池的过充性能。此外，正极极片还可以具有较高的活性材料占比，从而有助于电池具有较高的能量密度。
在本申请的正极极片中，正极活性材料层和/或补锂膜层还可选地包含粘结剂。粘结剂的示例可包括聚偏氟乙烯(PVDF)和聚四氟乙烯(PTFE)中的一种或几种。
在本申请的正极极片中，正极活性材料层和/或补锂膜层还可选地包含导电剂。导电剂的示例可包括超导碳、炭黑(例如，乙炔黑、科琴黑)、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种或几种。
需要说明的是，正极活性材料层和任选的补锂膜层可设置于正极集流体的一侧表面或两侧表面。正极集流体任意一侧的膜层或材料的参数满足本申请，即认为落入本申请的保护范围内。且本申请所述的正极活性材料层的压实密度、面密度等范围均是指经冷压压实后并可用于组装电池的正极极片中正极活性材料层的参数。
在本申请中，富锂金属氧化物的化学组成、Ni/Cu原子数量比均可以采用本领域已知的方法测试。例如，电感耦合等离子体发射光谱法。富锂金属氧化物的Ni/Cu原子数量比的示例性测试方法如下：在25℃下，取0.5g富锂金属氧化物，于100mL 0.1mol/L的HCl溶液中消解30min。消解可在搅拌(例如磁力搅拌、机械搅拌或微波搅拌等)下进行。将消解后的溶液放入电感耦合等离子体发射光谱仪(例如，美国Thermo Fisher scientific ICAP7400)中，选择测试Cu、Ni元素的含量。测试条件为：清洗泵为40～60rpm(转每分)，射频功率为950W～1150W，雾化器压力为24～32Psi(磅力/平方英寸)，辅助器流量设为0.5L/min。根据Cu、Ni元素的含量计算得到Ni/Cu原子数之比。富锂金属氧化物的化学组成可参照上述的方法测定。
在本申请中，游离锂在富锂金属氧化物中的质量占比可采用本领域已知的方法测定，例如滴定法。测试可参考标准：GB/T 9725-2007化学试剂电位滴定法通则。示例性测试方法如下：采用905 Titrando电位滴定仪，搭配复合pH电极；取30g富锂金属氧化物于碘量瓶中，加入100mL去离子水，在25℃、以360r/min的速度分散30min，静置10min，用0.45μm的微孔滤膜真空抽滤，得到分散液；之后用0.05mol/L的HCl溶液对分散液进行滴定；依据滴定量，计算游离锂含量及游离锂在富锂金属氧化物中的质量占比。
在本申请中，正极活性材料层的面密度为本领域公知的含义，可采用本领域已知的方法测试。例如取单面涂布且经冷压后的正极极片(若是双面涂布的正极极片，可先擦拭掉其中一面的正极活性材料层)，冲切成面积为S1的小圆片，称其重量，记录为M1。然后将上述称重后的正极极片的正极活性材料层擦拭掉，称量正极集流体的重量，记录为M0，正极活性材料层的面密度＝(正极极片的重量M1－正极集流体的重量M0)/S1。
在本申请中，正极活性材料层的压实密度为本领域公知的含义，可采用本领域已知的方法测试。正极活性材料层的压实密度＝正极活性材料层的面密度/正极活性材料层的厚度。其中正极活性材料层的厚度可采用本领域已知的方法测试，例如万分尺(例如Mitutoyo293-100型，精度为0.1μm)。
[电解液]
电解液包含电解质锂盐和溶剂，且电解质锂盐的阴离子中氟元素的总质量相对于电解液的总质量的占比ε＜14％。在一些实施例中，ε为≤13.8％，≤13.5％，≤13％，≤12.5％，≤12％，≤11.5％，≤11％，≤10.5％，≤10％，≤9.5％，≤9.3％，≤9％，≤8.5％，≤8％，≤7.5％，≤7％，≤6.5％，≤6％，≤5.5％，≤5％，≤4.5％，≤4％，≤3.5％，≤3％，或≤2.5％。在一些实施例中，ε为≥0％，≥0.5％，≥0.8％，≥1％，≥1.1％，≥1.2％，≥1.3％，≥1.4％，≥1.5％，≥1.6％，≥1.8％，≥2％，≥2.3％，或≥2.5％。可选地，ε为0～10％，0～9.3％，1％～9.5％，1.5％～9.5％，2％～9.3％，2.5％～9.2％，0.5％～8.5％，1％～8％，1％～7.5％，1.2％～7％，1.3％～6.5％，1.5％～5％，或2％～5％等。
可采用离子色谱法测定电解质锂盐的阴离子中氟元素的总质量相对于电解液的总质量的占比ε。示例性测试方法如下：使用离子色谱仪(例如ICS-900)；色谱柱为阴离子分离柱(例如Shodex IC SI-90 4E，4.6×250mm)；抑制器使用阴离子抑制器(例如ACRS 500，4mm)；检测器使用电导检测器；淋洗液使用含1.8mmol/L Na 2CO 3+1.8mmol/L NaHCO 3+20％乙腈(体积/体积)的水溶液，流量为1.0mL/min。测试可参照JY/T 020-1996《离子色谱分析方法通则》进行。测出的所有电解质锂盐的阴离子种类及其各自在电解液中的含量，再将每种阴离子的含量与该阴离子中氟元素占该阴离子的质量百分比相乘，并求和，计算电解液中电解质锂盐的阴离子中氟元素的总质量，进而计算得到ε。
需要说明的是，针对电解液的测试，可以直接取电解液样品(注入电池前)测试，也可以从循环充放电圈数在200圈以内的二次电池中取样测试。
在一些实施方式中，电解质锂盐可选自LiPF 6和有机锂盐的组合、LiBF 4、LiBF 4和有机锂盐的组合、有机锂盐中的一种或几种。可选地，电解质锂盐可选自LiBF 4、LiBF 4和有机锂盐的组合、有机锂盐中的一种或几种。进一步可选地，电解质锂盐可选自有机锂盐。
有机锂盐的有机阴离子可以是含氟或不含氟的。在一些实施例中，有机锂盐可选自二氟草酸硼酸锂(LiDFOB)、双草酸硼酸锂(LiBOB)、二氟磷酸锂(LiDFP)、二氟二草酸磷酸锂(LiDFOP)、四氟草酸磷酸锂(LiTFOP)、双氟磺酰亚胺锂(LiFSI)、双三氟甲烷磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiCF 3SO 3)、二(三氟甲基磺酰)甲基锂(LiCH(CF 3SO 2) 2)、三(三氟甲基磺酰)甲基锂(LiC(CF 3SO 2) 3)中的一种或几种。可选地，有机锂盐可包括LiDFOB、LiBOB、LiTFOP、LiTFSI、LiDFOP、LiFSI中的一种或几种。进一步可选地，有机锂盐可包括LiDFOB、LiBOB、LiTFOP、LiDFOP、LiFSI中的一种或几种。更进一步可选地，有机锂盐可包括LiBOB、LiDFOP、LiFSI中的一种或几种。
采用合适的电解质锂盐，有利于使电解液的氟含量在所需范围内，同时还能使电解液具有较高的离子电导率，由此能改善电池的容量发挥以及在循环过程中的容量保持率，从而进一步提高首次放电容量和循环寿命。合适的电解质锂盐还可以具有较高的热稳定性和电化学稳定性，从而可进一步提升电池的高温循环寿命和高温存储性能，并且能改善电池的高温安全性能。其中，电池的热扩散性能或热箱性能得到明显提升。
在一些实施方式中，电解质锂盐在电解液中的浓度为0.7mol/L～4mol/L。可选 地，电解质锂盐在电解液中的浓度为0.7mol/L～3mol/L，0.9mol/L～2mol/L，1mol/L～1.5mol/L，1mol/L～4mol/L，或2mol/L～4mol/L。电解质锂盐的含量适当，能使电解液获得较高的离子电导率，进一步提升正极补锂材料的容量发挥，提高电池能量密度。
在一些实施方式中，电解液中包含LiPF 6，且LiPF 6在电解液中的浓度≤0.4mol/L。可选地，LiPF 6在电解液中的浓度≤0.3mol/L，≤0.2mol/L，或≤0.1mol/L。在一些实施例中，LiPF 6在电解液中的浓度为0～0.4mol/L，0.05mol/L～0.3mol/L，或0.1mol/L～0.2mol/L等。由于LiPF 6在电解液中极易电离形成F ﹣、PF 5、PF 6 ﹣等的含氟粒子，这些含氟粒子在电解液中易造成金属离子溶出。电解液中的LiPF 6含量较小，有利于减小上述问题。此外，通过控制LiPF 6在电解液中的浓度在上述范围内，可以进一步控制电解液的ε值，从而进一步降低自放电率。
在一些实施方式中，电解液的溶剂可包含碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸甲乙酯(EMC)、甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯和丁酸甲酯中的一种或几种。
在一些实施例中，溶剂包括EC和PC中的一种或几种，并且包括DEC、DMC、EMC中的一种或几种。作为示例，溶剂包括EC、EMC和任选的PC。可选地，在该溶剂中，EC的体积占比为20％～40％，PC的体积占比为0％～20％，EMC的体积占比为60％～80％。例如，EC、PC和EMC的体积比为1:1:3，或3:0:7等。
在一些实施方式中，电解液的溶剂还可选地包括γ-丁内酯(GBL)和甲基膦酸二甲酯(DMMP)中的一种或几种。这样有利于降低电解液的密度，使电池的重量降低，从而能提升能量密度。
在一些实施方式中，溶剂中还包含可选的添加剂。添加剂可选自本领域已知的用于二次电池电解液的添加剂。作为示例，添加剂可包括第一添加剂、第二添加剂和第三添加剂中的一种或几种。
第一添加剂的示例可包括七甲基二硅氮烷(HEMDS)、乙醇胺(MEA)、1,3-丙磺酸内酯(1,3-PS)、丁二腈(SN)中的一种或几种。使用第一添加剂能消耗电解液中副产的HF，从而能进一步抑制金属离子的溶出，有助于提升电池的高温安全性能。
第二添加剂的示例可包括三(三甲基硅烷)磷酸酯(TMSP)、三(三甲基硅烷)硼酸酯(TMSB)中的一种或几种。第二添加剂能够在正极氧化形成保护膜，可以起到减少金属离子溶出和保护正极活性材料的作用，由此能进一步改善电池的高温安全性能，并且还能改善高温循环寿命或高温存储性能。
第三添加剂的示例可包括聚酒石酸硼酸锂盐(PLTB)、聚双(三羟甲基丙烷)硼酸锂盐(PLDB)、聚季戊四醇硼酸锂盐(PLPB)中的一种或几种。第三添加剂具有较高的热稳定性，有助于提升电池高温安全性能。
[负极极片]
用于与本申请的正极极片配合使用的负极极片可以选用本领域常用的各种常规负极极片，其构成和制备方法是本领域公知的。例如，负极极片可以包括负极集流体和设置于负极集流体上负极活性材料层。负极活性材料层可以包括负极活性材料以及可选地粘结剂、可选地导电剂和其它可选添加剂。负极活性材料例如为诸如石墨(人造石墨或 天然石墨)、导电炭黑、碳纤维等的碳质材料，例如Si、Sn、Ge、Bi、Sn、In等金属或半金属材料或其合金，含锂氮化物或含锂氧化物，锂金属或锂铝合金等。
作为示例，导电剂可包括超导碳、炭黑(例如乙炔黑、科琴黑等)、碳点、碳纳米管、石墨烯及碳纳米纤维中一种或几种。粘结剂可包括丁苯橡胶(SBR)、水溶性不饱和树脂SR-1B、水性丙烯酸树脂、聚乙烯醇(PVA)、海藻酸钠(SA)及羧甲基壳聚糖(CMCS)中的一种或几种。其它可选添加剂如是增稠剂(如羧甲基纤维素钠CMC-Na)、PTC热敏电阻材料等。
[隔离膜]
本申请可以选用本领域常用的各种常规隔离膜。在一些实施方式中，隔离膜可选自玻璃纤维、无纺布、聚乙烯膜、聚丙烯膜、聚偏二氟乙烯膜、以及它们中两种以上的多层复合薄膜。
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，二次电池可包括外包装。外包装可用于封装上述电极组件及电解液。
在一些实施方式中，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。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，如聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)、聚丁二酸丁二醇酯(PBS)等中的一种或几种。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。如图1是作为一个示例的方形结构的二次电池5。
在一些实施方式中，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用于盖设所述开口，以封闭容纳腔。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封装于容纳腔。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或几个，可根据需求来调节。
在一些实施方式中，二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。
图3是作为一个示例的电池模块4。参照图3，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
图4和图5是作为一个示例的电池包1。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用于盖设下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任 意的方式排布于电池箱中。
制备方法
本申请还提供一种锂离子二次电池的制备方法，包括如下步骤：提供正极极片，所述正极极片包含正极活性材料和正极补锂材料，正极补锂材料包括富锂金属氧化物，富锂金属氧化物中含有Ni、Co、Fe、Mn、Cu中的一种或多种元素；提供电解液，所述电解液包含电解质锂盐和溶剂，且电解质锂盐的阴离子中氟元素的总质量相对于电解液的总质量的占比ε<14％，可选地，1.5％≤ε≤9.5％；将正极极片、负极极片和电解液进行组装，得到锂离子二次电池。
在一些实施方式中，可以通过如下步骤制备正极极片：将正极活性材料和正极补锂材料以及可选地粘结剂和可选地导电剂分散于溶剂中并搅拌均匀，形成正极浆料；将正极浆料涂布到正极集流体上，并经干燥、冷压，形成正极活性材料层。溶剂可以是N-甲基吡咯烷酮(NMP)。
在一些实施方式中，制备正极极片的步骤还可包括：将正极补锂材料以及可选地粘结剂和可选地导电剂分散于溶剂中并搅拌均匀，形成补锂浆料；将补锂浆料涂布到正极集流体上，并经干燥、冷压，形成补锂膜层。溶剂可以是NMP。补锂浆料和正极浆料可以同时涂布或分别涂布。补锂涂层和正极涂层可以同时干燥或分别干燥，可以同时冷压或分别冷压。
值得注意的是，当制备正极极片的步骤包括补锂膜层的制备步骤时，在正极浆料中可以省去正极补锂材料。
本申请所使用的材料可以通过商业途径获得或本领域已知的方法制备得到。本领域技术人员可以根据实际使用环境做出恰当选择。
在一些实施方式中，正极补锂材料可采用如下的方法制备得到：将氧化锂、各金属的前驱体混合，在非氧化性气体气氛下烧结，得到富锂金属氧化物。金属的前驱体可以选自金属氧化物、金属氢氧化物等。非氧化性气体气氛例如为惰性气体气氛或氮气气氛等。烧结的温度可以为600℃～800℃。烧结的时间可以为5h～15h，或10h～20h等。
在烧结之后还可选地包括破碎分级步骤，以获得具有适当粒径分布的富锂金属氧化物。在一些实施例中，富锂金属氧化物的体积平均粒径D v50为3μm～7μm，可选地为3μm～5μm，或4μm～6μm。
在烧结之后还可选地包括洗涤步骤。通过洗涤步骤洗去颗粒表面的杂质，有助于提升电池的能量密度、循环性能和存储性能中的一者以上。在洗涤步骤中，可采用无水乙醇进行洗涤。洗涤的时间可以为0.5h～1h。洗涤后对颗粒进行干燥。干燥的温度可以为80℃～200℃，例如120℃～160℃。干燥的时间可以为5h～15h，例如8h～12h。在一些实施例中，洗涤步骤在破碎分级步骤之后进行。这样有助于更充分地洗去杂质，提升富锂金属氧化物的纯度。
以Li 2Cu x1Ni 1-x1-y1M y1O 2为例对制备方法进行具体示例说明：
S1：称取Li 2O、NiO、CuO和任选的金属M的氧化物粉体，球磨混合均匀。在S1中，Li 2O可以适当过量。例如，在混合粉体中，Li的摩尔含量与除Li外的金属元素的总摩尔含量的比值为2:05:1～2.12:1。作为一个示例，在混合粉体中，Li、Ni、Cu元素的摩尔比为2.05:0.4:0.6。
S2：在非氧化性气体气氛(例如氮气气氛)下对混合粉体进行烧结。在S2，烧结的温度可以为600℃～800℃，可选地为650℃～750℃。烧结的时间可以为5h～15h，可选地为8h～10h。烧结结束后自然冷却至室温，即可得到富锂金属氧化物。也可以将烧结产物经后续破碎分级步骤和/或洗涤步骤的处理，来得到富锂金属氧化物。
在一些实施例中，可以以1℃/min～10℃/min的升温速率升温至烧结温度。可选地，升温速率为1℃/min～5℃/min，3℃/min～8℃/min，或3℃/min～5℃/min。
S3：对烧结产物进行破碎分级，得到分级产物。在S3，分级产物的体积平均粒径D v50可选为3μm～7μm，进一步可选地为3μm～5μm，或4μm～6μm。
S4：对分级产物进行洗涤，经干燥，得到富锂金属氧化物最终产品。在S4，洗涤可以用无水乙醇。进行洗涤的时间可以为0.5h～1h。干燥的温度可以为80℃～200℃，例如120℃～160℃。
除了本申请正极极片的制备方法外，本申请的锂离子二次电池的其它构造和制备方法是公知的。例如负极极片可以按如下制备方法：将负极活性材料以及可选地导电剂和可选地粘结剂等分散于溶剂(如NMP或去离子水)中，搅拌均匀后涂覆在负极集流体上，经干燥、冷压后，得到负极极片。
在一些实施方式中，可将正极极片、隔离膜、负极极片经卷绕工艺或叠片工艺形成电极组件；将电极组件置于外包装中，注入电解液，经过真空封装、静置、化成、整形等工序，得到锂离子二次电池。
本申请的锂离子二次电池的可选技术特征也同样适用于本申请的制备方法中。
装置
本申请还提供一种装置，所述装置包括本申请的锂离子二次电池、电池模块、或电池包中的至少一种。锂离子二次电池、电池模块或电池包可以用作装置的电源，也可以用作装置的能量存储单元。装置的示例可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
所述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。该装置可以根据实际使用需求，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
下述实施例更具体地描述了本申请公开的内容，这些实施例仅仅用于阐述性说明，因为在本申请公开内容的范围内进行各种修改和变化对本领域技术人员来说是明显的。除非另有声明，以下实施例中所报道的所有份、百分比、和比值都是基于重量计，而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
一、电池的制备
(一)正极补锂材料Li 2Cu 0.6Ni 0.4O 2的制备：
(1)称取Li 2O、NiO、CuO粉体，球磨混合均匀。混合粉体中，Li、Ni、Cu元素的摩尔比为2.05:0.4:0.6。
(2)在氮气气氛下，以3℃/min的升温速率升温至680℃，保温10h，对混合粉体进行烧结。烧结后自然降温。
(3)对烧结产物进行破碎分级，得到D v50为5μm的分级产物。
(4)对分级产物用无水乙醇进行洗涤0.5h，之后在160℃的鼓风烘箱中干燥12h，得到Li 2Cu 0.6Ni 0.4O 2。
其它Ni/Cu比的Li 2Cu x1Ni 1-x1O 2正极补锂材料可参照上述方法制备得到。
(二)正极补锂材料Li 2NiO 2的制备：
(1)通过共沉淀法合成得到的镍基前驱体Ni(OH) 2；
(2)将前驱体Ni(OH) 2和氧化锂Li 2O(纯度>97％，Aldrich)按摩尔比为Li/Ni＝3:1的比例球磨混合，混合时间为5h，转速为500rpm，得到混合粉体；
(3)将混合粉体在氮气气氛下，在250℃烧结2h，450℃烧结2h，再在升温速率为1℃/min升温至700℃烧结10h，得到Li 2NiO 2。
(三)正极补锂材料Li 5FeO 4的制备：
将氧化锂(纯度>97％，Aldrich)和氧化铁(纯度>99％，Aldrich)以Li/Fe原子摩尔比5:1混合均匀后，在氩气气氛下，在450℃温度下预处理8h，然后研磨均匀，再以5℃/min的速度升温至750℃，在此温度下烧结18h，最后自然冷却至室温，得到Li 5FeO 4正极补锂材料。
(四)正极补锂材料Li 6CoO 4的制备：
在干燥房中，将氧化锂(纯度>97％，Aldrich)和氧化钴(纯度>99％，Aldrich)以Li/Co原子摩尔比6:1球磨12h，混合均匀后，在氩气气氛下，700℃温度下加热12h，最后自然冷却至室温，得到Li 6CoO 4正极补锂材料。
(五)锂离子二次电池的制备
实施例1
正极极片的制备
将正极活性材料LiFePO 4(简写为LFP)、导电剂乙炔黑、粘结剂聚偏二氟乙烯(PVDF)、正极补锂材料Li 2Cu x1Ni 1-x1O 2(x1＝0.6)按重量比(98×0.97):(98×0.01):(98×0.02):2，在溶剂NMP中充分搅拌混合均匀，得到正极浆料。将正极浆料涂覆于正极集流体铝箔的相对两个表面，经烘干、冷压后，得到正极极片。其中，正极活性材料层的面密度为19.5mg/cm 2，压实密度为2.4g/cm 3。
负极极片的制备
将负极活性材料人造石墨、导电剂乙炔黑、粘结剂丁苯橡胶(SBR)及增稠剂羧甲基纤维素钠(CMC-Na)按照重量比96.5:0.7:1.8:1分散于溶剂去离子水中，充分搅拌混合均匀后，得到负极浆料。将负极浆料涂覆在负极集流体铜箔的相对两个表面，经烘干、冷压后，得到负极极片。其中，负极活性材料层的面密度为9.7mg/cm 2，压实密度为1.7g/cm 3。
电解液的制备
将碳酸亚乙酯EC、碳酸甲乙酯EMC按体积比3:7混合均匀，得到溶剂；再将电 解质锂盐LiTFSI和LiDFOP溶解于上述溶剂中，混合均匀，得到电解液。电解液中LiTFSI的浓度为0.8M(mol/L)，LiDFOP的浓度为0.2M。
锂离子二次电池的制备
将正极极片、聚乙烯PE/聚丙烯PP多孔复合隔离膜、负极极片按顺序层叠好，然后卷绕得到电极组件；将电极组件装入外包装中，注入电解液并封装，得到锂离子二次电池。
实施例2～27及对比例1～2
锂离子二次电池的制备与实施例1类似，不同的是，调整正极极片和电解液的相关制备参数，详见表1。以及，实施例27中，正极补锂材料是以补锂膜层的形式设置于正极活性材料层背离正极集流体的表面。补锂膜层以PVDF作为粘结剂。
实施例28～48及对比例3～4
锂离子二次电池的制备与实施例1类似，不同的是，调整正极极片和电解液的相关制备参数，其中，正极活性材料为LiNi 0.5Co 0.2Mn 0.3O 2(简写为NCM523)；正极活性材料层的面密度为18mg/cm 2，压实密度为3.4g/cm 3；负极活性材料层的面密度为10.7mg/cm 2，压实密度为1.7g/cm 3；其余参数详见表3。以及，实施例48中，正极补锂材料是以补锂膜层的形式设置于正极活性材料层背离正极集流体的表面。补锂膜层以PVDF作为粘结剂。
在表1和表3中，游离锂质量占比指的是在富锂金属氧化物中的质量占比。正极补锂材料含量指的是在正极活性材料层中的质量百分含量。氟占比ε指的是电解液中，电解质锂盐的阴离子中氟元素的总质量相对于电解液的总质量的占比。
二、电池的性能测试：
1、取注入电池前的电解液样品，采用前文所述方法测试氟占比ε。
2、首次充放电比容量测试
在常温(25℃)下，将电池以1C倍率恒流充电至充电终止电压(LFP电池为4.25V，NCM电池为4.35V)，然后恒压充电至电流为0.05C，记录此时的充电容量，即为第1圈充电容量；再以1C恒流放电至放电终止电压(LFP电池为2.5V，NCM电池为2.8V)，记录此时的放电容量，即为第1圈放电容量。
首次充电比容量(mAh/g)＝第1圈充电容量/正极活性物质质量
首次放电比容量(mAh/g)＝第1圈放电容量/正极活性物质质量
3、高温循环性能测试
在45℃下，将电池以1C倍率恒流充电至充电终止电压，然后恒压充电至电流为0.05C；再以1C恒流放电至放电终止电压，之后静置5min，此为一个循环充放电过程，记录此时的放电容量，即为第1圈放电容量。将电池按照上述方法进行循环充放电测试，记录每圈的放电容量。
电池第X圈循环容量保持率(％)＝第X圈放电容量/第1圈放电容量×100％
4、负极极片的金属离子沉积量测试
将进行高温循环性能测试3后的电池进行拆解，取出负极极片；将负极极片的负极活性材料层剥离，取2g负极活性材料层加入酸溶液(例如王水)中消解，消解可以在搅拌(例如机械搅拌或微波搅拌等)下进行，消解时间可以为30min；将消解后的溶液加 入ICAP 7400光谱仪中，即可定量分析负极极片的金属离子沉积量。
5、过充性能测试
a)电池满充：在常温(25℃)下，将电池以1C倍率恒流充电至充电终止电压，然后恒压充电至电流为0.05C，此时电池为满充状态(100％SOC)。
b)以1C倍率对满充状态的电池恒流充电，直至电池失效(电池失效标准可参考EUCAR电池滥用标准等级，当电池达到HL3等级(电池开始冒烟)以上时判断为失效)，停止充电。记录电池此时的SOC。
6、高温安全性能测试
可参照GB/T 31485-2015标准进行测试。具体步骤为：
a)按照测试4步骤a)的方法将电池满充。
b)将满充状态的正极为NCM的电池放入热箱(正极为LFP的电池采用四周设置加热板)，以5℃/min的升温速率加热至80℃；之后将热箱按照5℃/min的速率升温5℃，并保温30min；若电池未失效，继续按照上述方式升温、保温，直至电池失效(电池失效标准可参考EUCAR电池滥用标准等级，当电池达到HL3等级(电池开始冒烟)以上是判断为失效)。记录电池发生失效时热箱的温度。失效温度越高，则电池的高温安全性能越好。还可以根据需要记录电池失效后所达到的最高温度。电池失效后所达到的最高温度越低，则电池的高温安全性能越好。
7、高温存储性能测试
将电池各取5支，在常温(25℃)下以1C倍率恒流充电至充电终止电压，再恒压充电至0.05C；然后以1C倍率恒流放电至放电终止电压，测得放电容量为E 0。再将满充状态的电池置于60℃烘箱中30天；然后将电池取出，立即在常温(25℃)下测试其放电容量并记为E n。
电池在60℃下存储30天后的容量保持率＝(E n-E 0)/E 0×100％。取5支电池的高温存储容量保持率的平均值。
以上测试3-7中，LiFePO 4电池的充电终止电压为3.65V，放电终止电压为2.5V；LiNi 0.5Co 0.2Mn 0.3O 2电池的充电终止电压为4.35V，放电终止电压为2.8V。
实施例1～27和对比例1～2的电池简称为LFP电池，测试结果示于表2。实施例28～48和对比例3～4的电池简称为NCM电池，测试结果示于表4。
表1：LFP电池制备参数
Figure PCTCN2020139106-appb-000001
表2：LFP电池测试结果
Figure PCTCN2020139106-appb-000002
由实施例1～13与对比例1～2的数据可以看出，通过在LFP电池的正极活性材料层添加富锂金属氧化物作为正极补锂材料，且该富锂金属氧化物中含有Ni、Co、Fe、Mn、Cu中的一种或多种元素，同时使电解液满足ε＜14％，能有效弥补SEI膜成膜以及副 反应消耗的活性锂，并且使电池内具有较少的金属离子溶出量。因此，LFP电池既能获得较高的首次放电容量、高温循环性能和高温存储性能，同时电池在高温安全试验中的失效温度明显提高，因此还获得较高的高温安全性能。此外，电池在热失效后所达到的最高温度也明显降低，进一步表明其具有改善的高温安全性能。
对比例1中未添加正极补锂材料，且电解液中电解质锂盐的阴离子的氟元素含量较高，使得电池的首次放电容量、高温循环性能和高温存储性能均较低，而且电池在高温安全试验中的失效温度较低，且失效后所达到的温度较高，因此高温安全性能较差。
对比例2中添加了正极补锂材料，尽管电池的首次放电容量、高温循环性能和高温存储性能提升，但是由于电解液中电解质锂盐的阴离子的氟元素含量较高，加重了正极补锂材料的金属溶出现象，使得电池的高温安全性能仍然较差。
由实施例11、14～19的结果可以看出，在正极活性材料层中添加适量的正极补锂材料，使得电池在具有较高的高温安全性能的同时，还能兼顾更高的首次放电容量、高温循环性能和高温存储性能。另外，正极补锂材料的添加量增加，能进一步提升电池的过充性能。
由实施例11、20～23的结果可以看出，正极补锂材料Li 2Cu x1Ni 1-x1-y1M y1O 2中，Ni/Cu原子数量比在适当范围内，能提升电池的首次放电容量，并且能提升电池的高温循环性能和高温存储性能。
表3：NCM电池制备参数
Figure PCTCN2020139106-appb-000003
表4：NCM电池测试结果
Figure PCTCN2020139106-appb-000004
由实施例28～40和对比例3～4的比较可以看出，通过在NCM电池的正极活性材料层添加富锂金属氧化物作为正极补锂材料，且该富锂金属氧化物中含有Ni、Co、Fe、Mn、Cu中的一种或多种元素，同时使电解液满足ε＜14％，能使电池在具有较高的首次放电容量的同时，明显提升电池在高温环境下的失效温度，使得电池具有较高的高温安全性能。并且，电池内的金属离子溶出量显著减少，还有利于提升电池的首次放电容量，同时使电池获得更高的高温循环性能和高温存储性能。
对比例3中未添加正极补锂材料，且电解液中电解质锂盐的阴离子的氟元素含量较高，使得电池的高温循环性能和高温存储性能均较低，而且电池在高温安全试验中的失效温度较低，因此高温安全性能较差。
对比例4中添加了正极补锂材料，尽管电池的高温循环性能和高温存储性能提 升，但是由于电解液中电解质锂盐的阴离子的氟含量较高，加重了正极补锂材料的金属溶出现象，使得电池的高温安全性能仍然较差。
由实施例38、41～44的结果可以看出，正极补锂材料Li 2Cu x1Ni 1-x1-y1M y1O 2中，Ni/Cu原子数量比在适当范围内，能提升电池的首次放电容量，并且能提升电池的高温循环性能和高温存储性能。
以上所述，仅为本申请的具体实施方式，但本申请的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可轻易想到各种等效的修改或替换，这些修改或替换都应涵盖在本申请的保护范围之内。因此，本申请的保护范围应以权利要求的保护范围为准。

Claims (17)

  1. 一种锂离子二次电池，包括正极极片、负极极片和电解液，其中，
    所述正极极片包含正极活性材料和正极补锂材料，所述正极补锂材料包括富锂金属氧化物，所述富锂金属氧化物中含有Ni、Co、Fe、Mn、Cu中的一种或多种元素；
    所述电解液包含电解质锂盐和溶剂，且所述电解质锂盐的阴离子中氟元素的总质量相对于所述电解液的总质量的占比ε＜14％，可选地，1.5％≤ε≤9.5％。
  2. 根据权利要求1所述的锂离子二次电池，其中，2％≤ε≤9.3％；可选地，2.5％≤ε≤9.2％。
  3. 根据权利要求1或2所述的锂离子二次电池，其中，所述富锂金属氧化物选自Li xM 1O 0.5(2+x)、Li 2M 2O 3、Li 2M 3O 4、Li 3M 4O 4、Li 5M 5O 4、Li 5M 6O 6中的一种或几种，
    其中，x≥1，
    M 1选自Ni、Co、Fe、Mn、Zn、Mg、Ca、Cu、Sn中的一种或几种，
    M 2选自Ni、Co、Fe、Mn、Sn、Cr中的一种或几种，
    M 3选自Ni、Co、Fe、Mn、Sn、Cr、V、Nb中的一种或几种，
    M 4选自Ni、Co、Fe、Mn、Sn、Cr、V、Mo、Nb中的一种或几种，
    M 5选自Ni、Co、Fe、Mn、Sn、Cr、Mo中的一种或几种，
    M 6选自Ni、Co、Mn中的一种或几种，
    M 1、M 2、M 3、M 4、M 5、M 6中每种元素的价态分别低于其自身的最高氧化价态。
  4. 根据权利要求1或2所述的锂离子二次电池，其中，所述富锂金属氧化物包括Li 2MnO 2、Li 5FeO 4、Li 6CoO 4、Li 2NiO 2、Li 2Cu x1Ni 1-x1-y1M y1O 2中的一种或几种，以及任选地包括Li 3VO 4、Li 3NbO 4中的一种或几种，其中，0＜x1≤1，0≤y1＜0.1，M选自Zn、Sn、Mg、Fe和Mn中的一种或几种；可选地，0.2≤x1≤0.8，或0.4≤x1≤0.6。
  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，所述富锂金属氧化物中含有游离锂，所述游离锂包括LiOH、LiHCO 3和Li 2CO 3中的一种或几种，且所述游离锂在所述富锂金属氧化物中的质量占比ω≤5wt％；可选地，ω≤3wt％；进一步可选地，0.3wt％≤ω≤0.7wt％。
  6. 根据权利要求1-5任一项所述的锂离子二次电池，其中，所述富锂金属氧化物的至少一部分外表面具有包覆层，所述包覆层包括金属氟化物、氧化物、金属磷酸盐、碳材料、导电聚合物中的一种或几种；
    可选地，所述金属氟化物选自AlF 3；所述氧化物选自V 2O 5、Al 2O 3、ZrO 2、TiO 2、ZnO、SiO 2、B 2O 3中的一种或几种；所述金属磷酸盐选自AlPO 4、FePO 4、Co 3(PO 4) 2、Ni 3(PO 4) 2中的一种或几种。
  7. 根据权利要求1-6任一项所述的锂离子二次电池，其中，所述电解质锂盐包括选自二氟草酸硼酸锂(LiDFOB)、双草酸硼酸锂(LiBOB)、二氟磷酸锂(LiDFP)、二氟二草酸磷酸锂(LiDFOP)、四氟草酸磷酸锂(LiTFOP)、双氟磺酰亚胺锂(LiFSI)、双三氟甲烷磺酰亚胺锂(LiTFSI)、四氟硼酸锂(LiBF 4)、三氟甲 磺酸锂(LiCF 3SO 3)、二(三氟甲基磺酰)甲基锂(LiCH(CF 3SO 2) 2)、三(三氟甲基磺酰)甲基锂(LiC(CF 3SO 2) 3)中的一种或几种，且任选地包括六氟磷酸锂(LiPF 6)；
    可选地，所述电解质锂盐包括双草酸硼酸锂(LiBOB)、二氟二草酸磷酸锂(LiDFOP)、双氟磺酰亚胺锂(LiFSI)中的一种或几种。
  8. 根据权利要求1-7任一项所述的锂离子二次电池，其中，所述电解液还满足：
    所述电解质锂盐在所述电解液中的浓度为0.7mol/L～4mol/L，可选地为0.7mol/L～3mol/L；可选地，LiPF 6在所述电解液中的浓度≤0.4mol/L。
  9. 根据权利要求1-8任一项所述的锂离子二次电池，其中，所述正极活性材料选自Li zCoO 2、Li zNiO 2、Li zMnO 2、Li zMn 2O 4、Li zNi aCo bMn cM’ dO 2、Li zNi 1-uCo uO 2、Li zCo 1-uMn uO 2、Li zNi 1-uMn uO 2、Li zNi αCo βMn γO 4、Li zMn 2-ηNi ηO 4、Li zMn 2-ηCo ηO 4、Li zFePO 4、Li zCoPO 4、Li zMnPO 4、以及它们的改性材料中的一种或几种，其中，M’选自Al、Mo、Nd、Zn中的一种或几种，z独立地满足0.5≤z≤1.3，0＜a＜1，0＜b＜1，0＜c＜1，0≤d＜1，a+b+c+d＝1，u独立地满足0＜u＜1，0＜α＜2，0＜β＜2，0＜γ＜2，α+β+γ＝2，η独立地满足0＜η＜2。
  10. 根据权利要求1-9任一项所述的锂离子二次电池，其中，所述正极活性材料包括Li zFePO 4及其改性材料中的一种或几种，其中0.5≤z≤1.3，可选地，0.9≤z≤1.2，或z＝1；
    可选地，所述正极活性材料包含于所述正极极片的正极活性材料层中，所述正极活性材料层的面密度≥18mg/cm 2，进一步可选地为18mg/cm 2～21mg/cm 2。
  11. 根据权利要求1-10任一项所述的锂离子二次电池，其中，所述正极活性材料包括Li zNi aCo bMn cM’ dO 2及其改性材料中的一种或几种，其中0.5≤z≤1.3，0.5≤a＜1，0＜b≤0.2，0＜c≤0.3，0≤d＜1，M’选自Al、Mo、Nd、Zn中的一种或几种。
  12. 根据权利要求1-10任一项所述的锂离子二次电池，其中，所述正极极片包括正极集流体以及设置于所述正极集流体上的正极活性材料层，所述正极活性材料层包含所述正极活性材料；其中，
    所述正极补锂材料均匀分布于所述正极活性材料层中，和/或，
    所述正极补锂材料以补锂膜层的形式设置于所述正极集流体与所述正极活性材料层之间，和/或，
    所述正极补锂材料以补锂膜层的形式设置于所述正极活性材料层背离所述正极集流体的表面。
  13. 根据权利要求12所述的锂离子二次电池，其中，在所述正极集流体的至少一侧，所述正极活性材料与所述正极补锂材料的质量比为99.9:0.1～85:15，可选地为98.5:1.5～93:7，进一步可选地为98:2～95:5。
  14. 一种锂离子二次电池的制备方法，包括以下步骤：
    提供正极极片，所述正极极片包含正极活性材料和正极补锂材料，所述正极补锂材料包括富锂金属氧化物，所述富锂金属氧化物中含有Ni、Co、Fe、Mn、Cu中的一种或多种元素；
    提供电解液，所述电解液包含电解质锂盐和溶剂，且所述电解质锂盐的阴离子中 氟元素的总质量相对于所述电解液的总质量的占比ε＜14％，可选地，1.5％≤ε≤9.5％；
    将所述正极极片、负极极片和所述电解液进行组装，得到锂离子二次电池。
  15. 一种电池模块，包括根据权利要求1-13任一项所述的锂离子二次电池或根据权利要求14所述制备方法得到的锂离子二次电池。
  16. 一种电池包，包括根据权利要求15所述的电池模块。
  17. 一种装置，包括根据权利要求1-13任一项所述的锂离子二次电池、根据权利要求14所述制备方法得到的锂离子二次电池、根据权利要求15所述的电池模块、或根据权利要求16所述的电池包中的至少一种。
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