WO2025213971A1 - 正极极片、二次电池和电子设备 - Google Patents

正极极片、二次电池和电子设备

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Publication number
WO2025213971A1
WO2025213971A1 PCT/CN2025/078995 CN2025078995W WO2025213971A1 WO 2025213971 A1 WO2025213971 A1 WO 2025213971A1 CN 2025078995 W CN2025078995 W CN 2025078995W WO 2025213971 A1 WO2025213971 A1 WO 2025213971A1
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WO
WIPO (PCT)
Prior art keywords
positive electrode
ratio
lithium
material layer
secondary battery
Prior art date
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Pending
Application number
PCT/CN2025/078995
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English (en)
French (fr)
Inventor
陈敏晶
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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Publication date
Application filed by Ningde Amperex Technology Ltd filed Critical Ningde Amperex Technology Ltd
Publication of WO2025213971A1 publication Critical patent/WO2025213971A1/zh
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes

Definitions

  • the present application relates to the field of electrochemical energy storage technology, and in particular to a positive electrode sheet, a secondary battery, and an electronic device.
  • lithium-ion electrochemical devices which are widely used in portable electronic devices, electric bicycles, electric vehicles and energy storage equipment, are constantly pursuing high charge cut-off voltage and high energy density as well as more diversified usage scenarios.
  • Lithium-ion battery cathode materials are prone to structural instability under high-temperature and high-pressure conditions. Side reactions can generate large amounts of gas, severely impacting the high-temperature performance of assembled secondary batteries and electrochemical devices. In more serious cases, dropping a secondary battery or electrochemical device under high-temperature conditions can easily cause fire and explosion, posing a serious safety hazard to users.
  • the present application provides a positive electrode plate, a secondary battery and an electronic device, which can improve the high temperature performance and thermal safety performance of the secondary battery.
  • the present application provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode material layer contains Co and Al, and the ratio of the atomic percentage of Al to the atomic percentage of Co based on the total number of atoms in the positive electrode material layer is T, 0.008 ⁇ T ⁇ 0.032, and the ratio of the atomic percentage of Al to the atomic percentage of Co based on the total number of atoms in the positive electrode active material is T', 0.005 ⁇ T' ⁇ 0.03, preferably, 0.008 ⁇ T ⁇ 0.025, 0.012 ⁇ T' ⁇ 0.02.
  • the atomic number refers to the number of atoms, as measured by X-ray photoelectron spectroscopy (XPS).
  • XPS X-ray photoelectron spectroscopy
  • the inventors speculate that when the ratio of the atomic percentages of Co and Al in the positive electrode material layer is within the above range, and the ratio of the atomic percentages of Co and Al in the positive electrode active material is also within the above range, the positive electrode active material can obtain an aluminum-containing coating layer with an appropriate proportion.
  • the coating layer can stabilize the internal structure of the positive electrode active material of the corresponding proportion under high temperature and high pressure, thereby inhibiting the migration of transition metals on the positive electrode active material into the electrolyte, thereby improving the charge and discharge performance of the assembled battery after 500 cycles at 45°C, reducing the occurrence of interfacial side reactions, reducing the generation of gas at the interface, and even inhibiting the generation of interfacial gas at higher temperatures (65°C).
  • the positive electrode material layer further contains C and O, and the ratio of the number of Co atoms in the positive electrode material layer to the sum of the number of Co, C, O, and Al atoms is t, and 17.5 ⁇ t ⁇ 25.
  • the present application regulates the ratio of the number of Co atoms in the positive electrode material layer (based on the ratio of the sum of the number of Co, C, O, and Al atoms) within the above range, which is beneficial to stabilizing the structure of the positive electrode active material, further improving the charge and discharge performance of the lithium-ion battery after 500 cycles at 45°C, and better suppressing the generation of interfacial gas at high temperatures.
  • the ratio of the number of Al atoms in the positive electrode material layer to the total number of Co, C, O, and Al atoms is t', and 0.31 ⁇ t' ⁇ 0.35.
  • the present application further regulates the ratio of the number of Al atoms in the positive electrode material layer (based on the ratio of the sum of the number of Co, C, O, and Al atoms) within the above range, which is more conducive to improving the charge and discharge performance of the lithium-ion battery over 500 cycles at 45°C and further suppressing the generation of interfacial gas at high temperatures.
  • the apparent concentration ratio of Co to Al in a longitudinal cross-section along the thickness direction of the positive electrode material layer is C0, 80 ⁇ C0 ⁇ 155.
  • the present application further regulates the apparent concentration ratio C0 of Co to Al in a longitudinal cross-section along the thickness direction of the positive electrode material layer to be within the above range, which is conducive to further improving the overall structural stability of the electrode piece and ensuring that the overall levels of various material elements on the electrode piece meet reasonable levels, thereby further controlling the thickness expansion of the battery at high temperature, and improving the low-temperature performance of the lithium-ion battery while taking into account the high-temperature performance of the lithium-ion battery.
  • D D1/D2, 3 ⁇ D ⁇ 8, and 20 ⁇ D1 ⁇ 27.
  • the positive electrode material on the positive electrode sheet has a powder resistivity of 120-430 ⁇ /cm at a pressure of 12 MPa.
  • the positive electrode material on the positive electrode sheet meets this powder resistivity, the movement of electrons on the positive electrode sheet and the movement of lithium ions between the positive and negative electrodes can be maintained at appropriate rates, thereby reducing the risk of local overheating, further improving the thermal safety performance of the battery, better passing thermal safety tests, and improving the battery's high-temperature and long-cycle performance.
  • the present application provides a secondary battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, and the positive electrode sheet is any one of the positive electrode sheets of the first aspect above.
  • the average pore size of the separator is in the range of 0.02 ⁇ m to 0.05 ⁇ m, which allows the separator in the lithium-ion battery to cooperate with the above-mentioned positive electrode plate to achieve high-temperature closed pores more quickly, thereby improving the hot box test pass rate and high-temperature drop test pass rate of the lithium-ion battery at high temperatures.
  • the electrolyte at high temperature includes propylene carbonate and a trinitrile compound. Based on the total mass of the electrolyte, the mass proportion of propylene carbonate and the trinitrile compound is Q%, and 2 ⁇ Q ⁇ 5.
  • the combination of the separator with the above-mentioned pore size and the electrolyte containing propylene carbonate and the trinitrile compound is conducive to the circulation of the electrolyte, and the electron migration inside the positive electrode material will not be hindered, thereby improving the thermal safety performance of the lithium-ion battery and better passing the thermal safety test.
  • the electrolyte contains the above-mentioned content of propylene carbonate and trinitrile compounds
  • observations under electrochemical atomic force microscopy show that a relatively stable and uniform CEI film can be formed on the positive electrode material through synergistic action, thereby improving high-temperature cycle performance.
  • the CEI film will further hinder the movement of electrons between the positive and negative electrodes by thickening, thereby preventing explosions, fires, and the like under conditions of thermal abuse, and further improving its thermal safety performance.
  • the separator includes filler particles and a binder, wherein the filler particles include organic particles having an aspect ratio of (1.1-1.4):1.
  • the aspect ratio of the organic particles on the separator falls within this range, electrolyte flow is more facilitated.
  • the aspect ratio of the organic particles is too large or too small, lithium ion movement may be too fast in some areas of the battery, while lithium ion movement may be too slow in other areas, which may easily cause local overheating. This further improves the thermal safety performance of the battery, allowing it to better pass thermal safety tests, while also improving the battery's high-temperature, long-cycle performance.
  • the electrolyte further comprises lithium 3-(diphenylphosphino)benzenesulfonate, with the mass percentage of lithium 3-(diphenylphosphino)benzenesulfonate being 1% to 4% based on the total mass of the electrolyte.
  • the present application provides an electronic device, which includes the secondary battery according to any one of the second aspects above.
  • the positive electrode provided in the first aspect of the present application has good heat resistance, so that the secondary battery provided in the second aspect of the present application has better high-temperature performance, better thermal safety and improved low-temperature performance, and the electronic device provided in the third aspect of the present application also takes into account improved high-temperature performance, thermal safety performance and low-temperature performance.
  • a list of items connected by the terms “one or more of,” “one or more of,” “at least one of,” or other similar terms may mean any combination of the listed items.
  • the phrase “at least one of A or B” means only A; only B; or A and B.
  • the phrase “at least one of A, B, or C” means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C.
  • Item A may contain a single element or multiple elements.
  • Item B may contain a single element or multiple elements.
  • Item C may contain a single element or multiple elements.
  • an embodiment of the present application provides a positive electrode sheet comprising a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector.
  • the positive electrode material layer contains Co and Al.
  • the ratio of the atomic percentage of Al to the atomic percentage of Co, based on the total number of atoms in the positive electrode material layer, is T, and 0.008 ⁇ T ⁇ 0.032.
  • the ratio of the atomic percentage of Al to the atomic percentage of Co, based on the total number of atoms in the positive electrode active material, is T', and 0.005 ⁇ T' ⁇ 0.03.
  • the positive electrode material layer can be located on one or both sides of the positive electrode current collector.
  • the positive electrode current collector can be aluminum foil, although other common positive electrode current collectors in the art can also be used.
  • the thickness of the positive electrode current collector can be 1 ⁇ m to 200 ⁇ m.
  • the positive electrode active material layer can be coated only on a portion of the positive electrode current collector.
  • the thickness of the positive electrode active material layer can be 10 ⁇ m to 500 ⁇ m. It should be understood that these are merely exemplary, and other suitable thicknesses can be used.
  • the positive electrode active material may include at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide. These positive electrode active materials may be doped and/or coated.
  • the positive electrode material is lithium nickel cobalt aluminum oxide
  • the ratio of aluminum to cobalt in the positive electrode sheet/on the positive electrode material is the ratio that takes into account the total amount of cobalt atoms and aluminum atoms in both the positive electrode material matrix and the coating layer.
  • a covering layer containing lithium phosphate and lithium niobate may be further provided on the surface of the positive electrode material, wherein the mass ratio of lithium phosphate to lithium niobate is 1:5 to 1:1, and the thickness of the covering layer is 2 to 3 ⁇ m.
  • the positive electrode active material layer further includes a positive electrode binder and a positive electrode conductor.
  • the positive electrode binder may include at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene, or polyhexafluoropropylene.
  • the positive electrode conductor may include at least one of conductive carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, or carbon fibers.
  • the inventors adjusted the ratio of the atomic percentages of Co and Al in the positive electrode material layer within the above range, and at the same time, coordinated the ratio of the atomic percentages of Co and Al in the positive electrode active material to be appropriate, so that the high-temperature cycle performance of the lithium-ion battery can be improved, and the amount of interface gas generated in the lithium-ion battery at high temperature can be suppressed.
  • the inventors speculate that when the ratio of the atomic percentages of Co and Al in the positive electrode material layer is within the above range, and the ratio of the atomic percentages of Co and Al in the positive electrode active material is also within the above range, the positive electrode active material can obtain an aluminum-containing coating layer with a suitable ratio, which can stabilize the internal structure of the corresponding proportion of the positive electrode active material under high temperature and high pressure, thereby suppressing the migration of transition metals on the positive electrode active material into the electrolyte, thereby improving the charge and discharge performance of the assembled battery for 500 cycles at 45°C, reducing the generation of interfacial side reactions, reducing the generation of gas at the interface, and even suppressing the generation of interface gas at higher temperatures (65°C).
  • the atomic percentage of Co is greater than or equal to 12 atomic percent and less than or equal to 30 atomic percent based on the total atomic number of the positive electrode material layer.
  • the atomic percentage of Co is greater than or equal to 15 atomic percent based on the total atomic percentage of the positive electrode active material.
  • the positive electrode material layer also contains C and O, and the ratio of the number of Co atoms in the positive electrode material layer to the sum of the number of Co, C, O, and Al atoms is t, 17.5 ⁇ t ⁇ 25. Regulating the proportion of the number of Co atoms in the positive electrode material layer within the above range is conducive to stabilizing the structure of the positive electrode active material, further improving the charge and discharge performance of the lithium-ion battery after 500 cycles at 45°C, and better suppressing the generation of interface gas at high temperatures. Specifically, in some embodiments, 17.5 ⁇ t ⁇ 24. In some embodiments, 17.5 ⁇ t ⁇ 22. In some embodiments, 17.5 ⁇ t ⁇ 21.8.
  • the ratio of the number of Al atoms in the positive electrode material layer to the total number of Co, C, O, and Al atoms is t', and 0.31 ⁇ t' ⁇ 0.35. Specifically, in some embodiments, 0.32 ⁇ t' ⁇ 0.35. In some embodiments, 0.33 ⁇ t' ⁇ 0.35. In some embodiments, 0.34 ⁇ t' ⁇ 0.35.
  • the apparent concentration ratio of Co and Al is C0, 80 ⁇ C0 ⁇ 155.
  • the ratio C0 of the apparent concentrations of Co and Al is 80, 90, 100, 105, 115, 125, 135, 145, 155, or a range consisting of any two of the foregoing values.
  • the apparent concentration of Al in a longitudinal cross-section of the positive electrode material layer along the thickness direction is 0.89 to 1.8.
  • the apparent concentration of Al is 0.89, 0.9, 1.1, 1.3, 1.5, 1.6, 1.8, or a range consisting of any two of the above values.
  • D the value of D is 3, 4, 5, 6, 7, 8, or a range consisting of any two of the above values.
  • the particle size Dv90 of the positive electrode material is 20 ⁇ m, 21 ⁇ m, 22 ⁇ m, 23 ⁇ m, 24 ⁇ m, 25 ⁇ m, 26 ⁇ m, 27 ⁇ m, or a range consisting of any two of the above values.
  • the specific surface area of the positive electrode active material is 0.11-0.15 m 2 g -1 .
  • the specific surface area of the positive electrode active material is 0.11 m 2 g -1 , 0.12 m 2 g -1 , 0.13 m 2 g -1 , 0.14 m 2 g -1 , 0.15 m 2 g -1 , or a range consisting of any two of the foregoing values.
  • the powder resistivity of the positive electrode material on the positive electrode sheet at a pressure of 12 MPa is 120-430 ⁇ /cm.
  • the powder resistivity of the positive electrode material on the positive electrode sheet at a pressure of 12 MPa may be 120 ⁇ /cm, 150 ⁇ /cm, 200 ⁇ /cm, 250 ⁇ /cm, 300 ⁇ /cm, 350 ⁇ /cm, 400 ⁇ /cm, 430 ⁇ /cm, or a range consisting of any two of the foregoing values.
  • the secondary battery of the present application includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.
  • the separator is arranged between the positive electrode sheet and the negative electrode sheet.
  • the positive electrode sheet is any one of the positive electrode sheets mentioned above.
  • the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid.
  • the polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene.
  • Polyethylene and polypropylene are particularly effective in preventing short circuits and can improve battery safety through a shutdown effect.
  • the separator has a thickness ranging from approximately 3 ⁇ m to 480 ⁇ m.
  • the isolation membrane has a porous layer
  • the binder of the porous layer is selected from at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene or polyhexafluoropropylene.
  • the porous layer on the surface of the isolation membrane can improve the heat resistance, oxidation resistance and electrolyte wetting performance of the isolation membrane, and enhance the adhesion between the isolation membrane and the electrode.
  • the diaphragm can also include a high-melting-point crystalline polymer or a high-temperature resistant amorphous polymer, and the high-temperature resistant resin includes at least one of polypropylene, poly4-methylpentene, polytetrafluoroethylene, polyvinylidene fluoride and cycloolefin copolymers.
  • the high-melting-point crystalline polymer includes at least one of polypropylene, poly4-methylpentene, polytetrafluoroethylene or polyvinylidene fluoride, and the high-temperature resistant amorphous polymer includes cycloolefin copolymers.
  • the mass percentage z of the high-temperature resistant resin is 2% to 10%.
  • the mass percentage z of the high-temperature resistant resin is 2%, 3%, 5%, 7%, 8%, 10%, or a range consisting of any two of these values.
  • the average pore size of the isolation membrane is in the range of 0.02 ⁇ m to 0.05 ⁇ m.
  • the isolation membrane of the above pore size is combined with an electrolyte containing propylene carbonate and a trinitrile compound, which is conducive to the circulation of the electrolyte and does not hinder the electron migration inside the positive electrode material, thereby improving the thermal safety performance of the lithium-ion battery and better passing the thermal safety test.
  • the average pore size of the isolation membrane is in the range of 0.02 ⁇ m, 0.025 ⁇ m, 0.03 ⁇ m, 0.035 ⁇ m, 0.04 ⁇ m, 0.045 ⁇ m, 0.05 ⁇ m or a range consisting of any two of the above values.
  • the isolation film includes filler particles and a binder
  • the filler particles include organic particles
  • the aspect ratio of the organic particles is (1.1-1.4): 1.
  • the aspect ratio of the organic particles can be 1.1:1, 1.2:1, 1.3:1, or 1.4:1.
  • the electrolyte includes a lithium salt and a non-aqueous solvent.
  • the lithium salt may include, but is not limited to, at least one of LiPF6 , LiBF4 , LiClO4 , LiB (C6H5 ) 4 , LiCH3SO3 , LiCF3SO3 , LiN( SO2CF3 ) 2 , LiC( SO2CF3 ) 3 , Li2SiF6 , lithium bis(oxalatoborate) (LiBOB), or lithium difluoroborate.
  • LiPF6 LiBF4 , LiClO4 , LiB (C6H5 ) 4
  • LiCH3SO3 , LiCF3SO3 LiN( SO2CF3 ) 2 , LiC( SO2CF3 ) 3
  • Li2SiF6 lithium bis(oxalatoborate) (LiBOB), or lithium difluoroborate.
  • LiBOB lithium bis(oxalatoborate)
  • the mass percentage of the lithium salt is 5% to 23%.
  • the concentration of the lithium salt in the electrolyte can be 5%, 8%, 12%, 16%, 20%, 23%, or a range consisting of any two of the above values.
  • non-aqueous solvents may include but are not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents.
  • the above-mentioned carbonate compounds may include but are not limited to at least one of linear carbonate compounds, cyclic carbonate compounds or fluorinated carbonate compounds.
  • the above-mentioned linear carbonate compounds may include but are not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or methyl ethyl carbonate (MEC).
  • the above-mentioned cyclic carbonate, except propylene carbonate (PC) may also include but are not limited to at least one of ethylene carbonate (EC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC).
  • the fluorinated carbonate compound may include, but is not limited to, at least one of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate.
  • the above-mentioned carboxylate compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, ⁇ -butyrolactone, decanoic acid lactone, valerolactone, or caprolactone.
  • the above-mentioned ether compound may include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran.
  • the above-mentioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.
  • the electrolyte comprises propylene carbonate and a trinitrile compound, wherein the mass ratio of propylene carbonate to the trinitrile compound is Q%, based on the total mass of the electrolyte, and 2 ⁇ Q ⁇ 5. Preferably, 3 ⁇ Q ⁇ 5. Based on the total mass of the electrolyte, the propylene carbonate content is 8.18% to 8.31%, and the trinitrile content is 1.66% to 2.73%.
  • the trinitrile compound includes 1,3,6-hexanetrinitrile and/or 1,2,3-tris(2-cyanoethoxy)propane.
  • the electrolyte further comprises lithium 3-(diphenylphosphino)benzenesulfonate, and the mass percentage of lithium 3-(diphenylphosphino)benzenesulfonate is 1% to 4% based on the total mass of the electrolyte.
  • the electrolyte contains the above-mentioned content of propylene carbonate and trinitrile compound, through observation by electrochemical atomic force microscopy, a relatively stable and uniform CEI film can be formed on the positive electrode material through synergistic action, thereby improving high-temperature cycle performance, and further improving its thermal safety performance and anti-drop performance at high temperatures.
  • the mass percentage of lithium 3-(diphenylphosphino)benzenesulfonate is 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% or a range consisting of any two of the above values.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector.
  • the present application does not particularly limit the thickness of the negative electrode active layer, as long as the objectives of the present application can be achieved.
  • the thickness of the negative electrode active layer is 30 ⁇ m to 120 ⁇ m.
  • the negative electrode active material may include at least one of a carbon material or a silicon-based material.
  • the carbon material includes but is not limited to at least one of natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, or soft carbon.
  • the silicon-based material includes but is not limited to at least one of silicon, a silicon-oxygen composite material, or a silicon-carbon composite material.
  • the present application does not particularly limit the thickness of the negative electrode current collector, as long as the objectives of the present application can be achieved.
  • it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector (e.g., a composite current collector with a metal layer disposed on the surface of a polymer layer).
  • the present application does not particularly limit the thickness of the negative electrode current collector, as long as the objectives of the present application can be achieved.
  • the thickness of the negative electrode current collector is 5 ⁇ m to 12 ⁇ m.
  • the negative electrode active layer may also include a binder and a thickener. This application does not specifically limit the types of binder and thickener, as long as they can achieve the objectives of this application.
  • the binder may include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber;
  • the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.
  • the negative electrode active layer may also include a conductive agent. This application does not specifically limit the type of conductive agent, as long as it can achieve the objectives of this application.
  • the conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, Ketjen black, graphene, a metallic material, or a conductive polymer.
  • CNTs carbon nanotubes
  • the negative electrode plate may also include a conductive layer, which is located between the negative electrode current collector and the negative electrode active layer. The present application does not particularly limit the composition of the conductive layer, and it may be any conductive layer commonly used in the art.
  • the conductive layer may include a conductive agent and a binder.
  • the present application does not particularly limit the conductive agent and binder in the conductive layer, and for example, it may be at least one of the conductive agent and binder used in the negative electrode active layer described above.
  • Secondary batteries can be prepared according to conventional methods in the art.
  • the aforementioned positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrode sheets to provide isolation, to form an electrode assembly.
  • the electrode assembly can be wound together. The electrode assembly is then placed in a packaging case, injected with electrolyte, and sealed to form a secondary battery.
  • lithium battery there is no particular limitation on the structure of the lithium battery, and coin-type batteries, cylindrical batteries, square batteries, or soft-pack batteries with single-layer or multi-layer separators can be used.
  • the use of the lithium-ion battery of the present application is not particularly limited, and it can be used in any electronic device known in the prior art.
  • the lithium-ion battery of the present application can be used for, but not limited to, laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.
  • the electronic device of the present application includes any of the above-mentioned secondary batteries.
  • the electronic device of the present application includes, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.
  • aluminum isopropoxide is selected as the aluminum source, and the amount of aluminum isopropoxide is calculated according to the required amount of aluminum oxide.
  • 100g of lithium cobaltate and 6.4g of aluminum isopropoxide are placed in a converter and heated to 140°C to vaporize the aluminum isopropoxide therein. The temperature is kept for 2 hours, and then water vapor (about 450ml) is slowly introduced. The converter is rotated for another hour, and the temperature is continued to be raised to 300°C and kept at this temperature for 3 hours. Then, the converter is naturally cooled to room temperature to obtain a product of alumina-coated LiCoO2, which is recorded as the first product.
  • the first product (Dv90 of 20 ⁇ m, BET of 0.15 m 2 g -1 ), conductive carbon black and binder polyvinylidene fluoride (PVDF) were stirred into a uniform slurry at a mass ratio of 82:9:9. The slurry was stirred, coated, dried, rolled and spot-welded to obtain a positive electrode for the battery.
  • PVDF polyvinylidene fluoride
  • the amount of aluminum isopropoxide can also be obtained by referring to the above calculation method in the remaining embodiments, and the rest are the same as in Example 1-1.
  • negative electrode active material artificial graphite with a particle size of 12 ⁇ m
  • conductive agent carbon black
  • binder styrene-butadiene rubber, SBR
  • ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate were mixed in a mass ratio of 1:2:1:2, and 3-(diphenylphosphino)benzenesulfonate lithium accounting for 1% of the total mass of the electrolyte and a certain mass of 1,3,6-hexanetrinitrile were added.
  • a certain amount of lithium salt was added so that the final concentration of the lithium salt in the electrolyte was 8%, and the mass ratio of propylene carbonate to 1,3,6-hexanetrinitrile to the total mass of the electrolyte was 2.
  • Boehmite with a volume average particle size Dv90 of 1.8 ⁇ m and a binder polyacrylate were dispersed in deionized water at a mass ratio of 86:14 to form an inorganic coating slurry with a solid content of 48%.
  • the predetermined slurry was applied to both surfaces of the negative electrode ring by gravure roller coating at a speed of 0.6 m/min, and dried by blowing hot air at 120° C. at a wind speed of 0.5 m/sec, thereby forming an inorganic coating with a thickness of 3 ⁇ m adhered to the surface of the PE substrate;
  • the first coating slurry was evenly applied onto the inorganic coating and dried in an oven to obtain a first coating.
  • the coating weight of the first coating slurry was 1.8 mg/5000 mm2 , and the thickness of the first coating was 2 ⁇ m.
  • the mass ratio of the first polymer, the second polymer, sodium carboxymethyl cellulose, and dimethylsiloxane was 75:20:0.7:4.3.
  • the regulation of the average pore size of the isolation membrane it can be achieved by adjusting the mass ratio of boehmite and adhesive or the solid content of the inorganic coating, or by adjusting the viscosity and solid content of the slurry.
  • the above methods can all achieve the regulation of the average pore size of the isolation membrane.
  • the positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator placed between the positive and negative electrode sheets to act as an insulator.
  • the cells are then wound into bare cells, which are then placed in an aluminum-plastic film. After dehydration at 80°C, the electrolyte is injected and sealed. The cells then undergo a standing, formation, and shaping process to obtain a lithium-ion battery.
  • Example 1-1 Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-1.
  • Example 1-1 Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-1.
  • Example 1-1 Except for adjusting the relevant preparation parameters according to Table 1 and Table 3, the rest is the same as Example 1-1.
  • Example 1-1 Except for adjusting the relevant preparation parameters according to Table 4, the rest is the same as Example 1-1.
  • Example 1-1 Except for adjusting the relevant preparation parameters according to Table 5, the rest is the same as Example 1-1.
  • the lithium ion batteries of the embodiments and comparative examples were repeatedly charged and discharged by the following steps, and the discharge capacity retention rates of the lithium ion batteries were calculated.
  • Cycle capacity retention rate (discharge capacity at the 600th cycle/discharge capacity at the first cycle)*100%.
  • the battery passes the test. 15 lithium-ion secondary batteries are tested in each group, and the pass rate of the lithium-ion secondary battery drop test is recorded.
  • the lithium ion batteries of the embodiments and comparative examples were repeatedly charged and discharged by the following steps, and the discharge capacity retention rates of the lithium ion batteries were calculated.
  • Cycle capacity retention rate (discharge capacity at the 500th cycle/discharge capacity at the first cycle)*100%.
  • Cycle capacity retention rate (discharge capacity at the 500th cycle/discharge capacity at the first cycle)*100%.
  • Step 1 Charge the prepared battery at a constant current of 0.5C to a cut-off voltage of 4.2V, then charge it at a constant voltage to a cut-off current of 200mA, and let it stand for 5 minutes;
  • Step 2 Attach the temperature-sensing wire to the fully charged battery between the two tabs, connect the two tabs to monitor the voltage, and hang the battery cell vertically in the box;
  • Step 3 Heat the hot box to 145°C at a rate of 5°C and maintain for 60 minutes.
  • the powder volume resistivity ⁇ of the positive electrode active material under a pressure of 12 MPa can be measured using a powder volume resistivity test method.
  • the four-probe method can be used.
  • the test method includes: adding 2 g of positive electrode active material powder to a sample table, applying a pressure of 12 MPa to the powder using a press, and then reading the powder volume resistivity ⁇ under a pressure of 12 MPa using a resistivity meter after the pressure stabilizes.
  • the ratio of the atomic percentage of Co and Al in the positive electrode material layer of Comparative Examples 1-1 to Comparative Examples 1-3 is not within the scope of the present application, and the ratio of the atomic percentage of Co and Al in the positive electrode active material is not within the scope of the present application.
  • the capacity retention rate after 500 cycles at 45°C is not higher than 70%, and the gas production at 65°C is higher than 3.5ml.
  • the ratio of the atomic percentage of Co and Al in the positive electrode material layer of Example 1-1 and the ratio of the atomic percentage of Co and Al in the positive electrode active material are both within the appropriate range, the capacity retention rate after 500 cycles at 45°C is significantly improved, and the gas production at 65°C is significantly reduced.
  • the ratio of the atomic percentages of Co and Al in the positive electrode material layer to be within the preferred range, and at the same time, synergistically regulating the ratio of the atomic percentages of Co and Al in the positive electrode active material to be within the preferred range, the high-temperature cycle performance and high-temperature gas production of the lithium-ion battery are improved.
  • the ratios of the number of atoms of Co and Al in the positive electrode material layer to the sum of the number of atoms of Co, C, O, and Al are also appropriate, the effects of improving the high-temperature cycle performance and high-temperature gas production of the lithium-ion battery are better.
  • the pass rate of the hot box test at 145°C and the pass rate of the drop performance test at 45°C for electrochemical devices can be improved, thereby enhancing the thermal safety performance and high-temperature drop resistance of electrochemical devices and electronic devices.
  • the pass rate of the hot box test at 145°C and the pass rate of the drop performance test at 45°C for electrochemical devices can also be significantly improved.
  • lithium 3-(diphenylphosphino)benzenesulfonate is added thereto in an amount of 1% to 4%, the thermal safety performance and anti-drop performance at high temperature of the assembled lithium ion battery can be significantly improved.

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Abstract

本申请公开了一种正极极片、二次电池和电子设备，正极极片包括正极集流体和设置于正极集流体至少一个表面上的正极材料层，正极材料层中含有Co和Al，基于正极材料层的原子总数，Al的原子数百分比和Co的原子数百分比的比值为T，0.008≤T≤0.032，基于正极活性材料的原子总数，Al的原子数百分比和Co的原子数百分比的比值为T'，0.012≤T'≤0.02，所述正极材料层中还含有C和O。本申请的二次电池具有较优的高温性能和热安全性能。

Description

正极极片、二次电池和电子设备 技术领域
本申请涉及电化学储能技术领域，尤其涉及一种正极极片、二次电池和电子设备。
背景技术
随着人们对锂离子电化学装置的需求越来越高，被广泛应用于便携式电子设备、电动自行车、电动汽车及储能设备等领域中的锂离子电化学装置在不断追求高充电截止电压和高能量密度以及更多元化的使用场景。
锂离子电池正极材料在高温高压条件下容易出现结构的不稳定性，副反应发生的同时会有大量气体的生成，严重影响组装的二次电池及电化学装置的高温使用性能。更严重的情况下，在高温条件下二次电池或电化学装置的跌落容易引起起火和爆炸，对使用者来说存在严重的安全隐患。
发明内容
本申请提供一种正极极片、二次电池和电子设备，能够改善二次电池的高温性能和热安全性能。
第一方面，本申请提供了一种正极极片，正极极片包括正极集流体和设置于正极集流体至少一个表面上的正极材料层，正极材料层中含有Co和Al，基于正极材料层的原子总数，Al的原子数百分比和Co的原子数百分比的比值为T，0.008≤T≤0.032，基于正极活性材料的原子总数，Al的原子数百分比和Co的原子数百分比的比值为T′，0.005≤T′≤0.03，优选地，0.008≤T≤0.025，0.012≤T′≤0.02。原子数是指原子数量，根据X射线光电子能谱(XPS)测量。发明人通过调整正极材料层中Co和Al的原子数百分比的比值在上述范围，同时，协同调控正极活性材料中Co和Al的原子数百分比的比值也合适，如此，能够实现改善锂离子电池的高温循环性能，还可以抑制锂离子电池在高温下界面气体的生成量。
发明人推测，正极材料层中Co和Al的原子数百分比的比值在上述范围，同时正极活性材料中Co和Al的原子数百分比的比值也在上述范围内时，正极活性材料可以获得具有合适比例的含铝包覆层，该包覆层可以在高温高压下对于对应比例的正极活性材料起到稳定内部结构的作用，从而抑制正极活性材料上的过渡金属迁移到电解液中，进而改善组装电池在45℃下循环500圈的充放电性能，减少界面副反应的产生，降低界面的气体生成，甚至可以在温度更高(65℃)条件下，抑制界面气体的生成量。
在一些实施方式中，正极材料层中还含有C和O，正极材料层中Co的原子数与Co、C、O、Al的原子数之和的比值为t，17.5≤t≤25。本申请调控正极材料层中Co的原子数占比(基于Co、C、O、Al四种原子数之和的占比)在上述范围内，利于稳定正极活性材料的结构，进一步改善锂离子电池在45℃下循环500圈的充放电性能，能够更好地抑制其在高温下界面气体的生成量。
在一些实施方式中，正极材料层中Al的原子数与Co、C、O、Al的原子总数之和的比值为t′，0.31≤t′≤0.35。本申请进一步调控正极材料层中Al的原子数占比(基于Co、C、O、Al四种原子数之和的占比)在上述范围内，更利于改善锂离子电池在45℃下循环500圈的充放电性能，进一步抑制高温下界面气体的生成量。
在一些实施方式中，正极材料层沿厚度方向的纵截面中，Co和Al的表观浓度之比为C0，80≤C0≤155。本申请进一步调控正极材料层沿厚度方向的纵截面中Co和Al的表观浓度之比C0在上述范围内，如此，利于进一步改善极片整体的结构稳定性，并使得极片上各物质元素整体满足合理的水平，从而进一步控制电池在高温下的厚度膨胀，在兼顾锂离子电池高温性能的同时还能够改善锂离子电池的低温性能。
在一些实施方式中，正极活性材料的颗粒粒径Dv90为D1μm，其比表面积为D2 m2g-1，D＝D1/D2，3≤D≤8，20≤D1≤27。正极活性材料的颗粒粒径Dv90与其比表面积BET的数值的比值D在上述范围内，能够改善极片上材料颗粒整体的平整度和结构的稳定性，通过合适的颗粒平整度带来极片的平整度，因此电子在材料表面的移动速率会更加合理，从而进一步降低因为局部电子速率不同导致的电池的厚度膨胀，还利于进一步提升锂离子电池的低温性能，尤其是低温循环性能。
在一些实施方式中，正极极片上的正极材料在12MPa压力下的粉体电阻率为120-430Ω/cm。当正极极片上的正极材料满足该粉体电阻率时，可以使得正极极片上的电子运动和正负极之间的锂离子运动均具有合适的速率，从而不易引发局部过热现象，进一步提升电池的热安全性能，更好地通过热安全测试，同时改善电池的高温长循环性能。
第二方面，本申请提供了一种二次电池，二次电池包括正极极片、负极极片、隔离膜和电解液，正极极片为上述第一方面任一种的正极极片。
在一些实施方式中，隔离膜的平均孔径范围为0.02μm～0.05μm，可以使得锂离子电池中的隔离膜配合上述正极极片能够更加快速的实现高温闭孔，从而提高高温下锂离子电池的热箱测试通过率和高温跌落测试通过率。在高温下的电解液包括碳酸丙烯酯和三腈化合物，基于电解液的总质量，碳酸丙烯酯和三腈化合物的质量占比为Q％，2≤Q≤5。上述孔径的隔离膜与含有碳酸丙烯酯、三腈化合物的电解液组合，利于电解液的流通，正极材料内部的电子迁移不会受到阻碍，从而提升锂离子电池的热安全性能，还能够更好地通过热安全测试。并且，电解液中含有上述含量碳酸丙烯酯和三腈化合物时，通过电化学原子力显微镜的观察，能够在正极材料通过协同作用形成相对稳定和均匀的CEI膜，从而改善高温循环性能，并且能够在更高的温度(大于100℃)时，该CEI膜会进一步通过增厚阻碍正负极之间的电子运动，从而阻止热滥用条件下的爆炸、起火等现象，进一步改善其热安全性能。
在一些实施方式中，隔离膜包括填料颗粒和粘结剂，填料颗粒包括有机颗粒，有机颗粒的长径比为(1.1-1.4):1。当隔离膜上的有机颗粒长径比满足该范围时，更有利于电解液的流通，当有机颗粒长径比过大或过小时，电池局部区域会出现锂离子运动速率过快，另外一些区域可能出现锂离子运动速率过慢，从而容易引发局部过热现象，从而进一步提升电池的热安全性能，更好地通过热安全测试，同时改善电池的高温长循环性能。
在一些实施方式中，电解液还包括3-(二苯基膦基)苯磺酸锂，基于电解液的总质量，3-(二苯基膦基)苯磺酸锂的质量百分含量为1％～4％。如此，在电池的高温充放电过程中，能够捕获正极界面产生的气体分子，从而降低界面副反应的发生，最终提升电池在高温下循环500圈的容量保持率，提升电池的高温循环性能。
第三方面，本申请提供了一种电子设备，电子设备包括上述第二方面任一项的二次电池。
本申请第一方面提供的正极极片具有较好的耐热性能，从而本申请第二方面提供的二次电池具有较优的高温性能、热安全性更好且兼顾低温性能的提升，而且本申请第三方面提供的电子设备也兼顾改善高温性能、热安全性能以及低温性能。
具体实施方式
本申请的实施例将会被详细的描示在下文中。本申请的实施例不应该被解释为对本申请的限制。
如本申请所用，术语“包括”、“含有”和“包含”以其开放、非限制性含义使用。
另外，有时在本文中以范围格式呈现量、比率和其它数值。应理解，此类范围格式是用于便利及简洁起见，且应灵活地理解，不仅包含明确地指定为范围限制的数值，而且包含涵盖于范围内的所有个别数值或子范围，如同明确地指定每一数值及子范围一般。
在具体实施方式及权利要求书中，由术语“中的一者或多者”、“中的一个或多个”、“中的至少一种”或其他相似术语所连接的项目的列表可意味着所列项目的任何组合。例如，如果列出项目A及B，那么短语“A或B中的至少一种”意味着仅A；仅B；或A及B。在另一实例中，如果列出项目A、B及C，那么短语“A、B或C中的至少一种”意味着仅A；或仅B；仅C；A及B(排除C)；A及C(排除B)；B及C(排除A)；或A、B及C的全部。项目A可包含单个元件或多个元件。项目B可包含单个元件或多个元件。项目C可包含单个元件或多个元件。
正极极片
本申请实施例第一方面提供一种正极极片，正极极片包括正极集流体和设置于正极集流体至少一个表面上的正极材料层，正极材料层中含有Co和Al，基于正极材料层的原子总数，Al的原子数百分比和Co的原子数百分比的比值为T，0.008≤T≤0.032，基于正极活性材料的原子总数，Al的原子数百分比和Co的原子数百分比的比值为T′，0.005≤T′≤0.03。正极材料层可以位于正极集流体一侧或两侧上。在一些实施例中，正极集流体可以采用铝箔，当然，也可以采用本领域常用的其他正极集流体。在一些实施例中，正极集流体的厚度可以为1μm至200μm。在一些实施例中，正极活性材料层可以仅涂覆在正极集流体的部分区域上。在一些实施例中，正极活性材料层的厚度可以为10μm至500μm。应该理解，这些仅是示例性的，可以采用其他合适的厚度。
在一些实施例中，正极活性材料可以包括钴酸锂、镍钴锰酸锂或镍钴铝酸锂中的至少一种，上述正极活性材料可以经过掺杂和/或包覆处理。当正极材料为镍钴铝酸锂时，的正极极片/正极材料上的铝和钴的比值则是考虑了正极材料基体和包覆层两者的钴原子和铝原子的量总和的比值。
在一些实施例中，正极材料表面还可以进一步设置含有磷酸锂和铌酸锂的覆盖层，磷酸锂和铌酸锂的质量比为1:5～1:1，覆盖层的厚度为2～3μm。
在一些实施例中，正极活性材料层还包括正极粘结剂和正极导电剂。在一些实施例中，正极粘结剂可以包括聚偏氟乙烯、偏氟乙烯-六氟丙烯共聚物、苯乙烯-丙烯酸酯共聚物、苯乙烯-丁二烯共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、羧甲基纤维素钠、聚醋酸乙烯酯、聚乙烯呲咯烷酮、聚乙烯醚、聚四氟乙烯或聚六氟丙烯中的至少一种。在一些实施例中，正极导电剂可以包括导电炭黑、乙炔黑、科琴黑、石墨烯、碳纳米管或碳纤维中的至少一种。
发明人通过调整正极材料层中Co和Al的原子数百分比的比值在上述范围，同时，协同调控正极活性材料中Co和Al的原子数百分比的比值也合适，如此，能够实现改善锂离子电池的高温循环性能，还可以抑制锂离子电池在高温下界面气体的生成量。发明人推测，正极材料层中Co和Al的原子数百分比的比值在上述范围，同时正极活性材料中Co和Al的原子数百分比的比值也在上述范围内时，正极活性材料可以获得具有合适比例的含铝包覆层，该包覆层可以在高温高压下对于对应比例的正极活性材料起到稳定内部结构的作用，从而抑制正极活性材料上的过渡金属迁移到电解液中，进而改善组装电池在45℃下循环500圈的充放电性能，减少界面副反应的产生，降低界面的气体生成，甚至可以在温度更高(65℃)条件下，抑制界面气体的生成量。
具体地，在一些实施例中，0.008≤T≤0.03。在一些实施例中，0.008≤T≤0.028。在一些实施例中，0.008≤T≤0.025。在一些实施例中，0.01≤T≤0.02。在一些实施例中，0.012≤T≤0.016。
具体地，在一些实施例中，0.008≤T′≤0.028。在一些实施例中，0.01≤T′≤0.025。在一些实施例中，0.012≤T′≤0.02。在一些实施例中，0.015≤T′≤0.018。
在一些实施例中，基于正极材料层的原子总数，Co的原子数百分比为大于或等于12原子百分比且小于或等于30原子百分比。
在一些实施例中，基于正极活性材料的原子总数，Co的原子数百分比为大于或等于15原子百分比。
在一些实施例中，正极材料层中还含有C和O，正极材料层中Co的原子数与Co、C、O、Al的原子数之和的比值为t，17.5≤t≤25。调控正极材料层中Co的原子数占比在上述范围内，利于稳定正极活性材料的结构，进一步改善锂离子电池在45℃下循环500圈的充放电性能，能够更好地抑制其在高温下界面气体的生成量。具体地，在一些实施例中，17.5≤t≤24。在一些实施例中，17.5≤t≤22。在一些实施例中，17.5≤t≤21.8。
在一些实施例中，正极材料层中Al的原子数与Co、C、O、Al的原子总数之和的比值为t′，0.31≤t′≤0.35。具体地，在一些实施例中，0.32≤t′≤0.35。在一些实施例中，0.33≤t′≤0.35。在一些实施例中，0.34≤t′≤0.35。
在一些实施例中，正极材料层沿厚度方向的纵截面中，Co和Al的表观浓度之比为C0，80≤C0≤155。此时，利于进一步改善极片整体的结构稳定性，并使得极片上各物质元素整体满足合理的水平，从而进一步控制电池在高温下的厚度膨胀，在兼顾锂离子电池高温性能的同时还能够改善锂离子电池的低温性能。具体地，在一些实施例中，85≤C0≤140。在一些实施例中，90≤C0≤130。在一些实施例中，100≤C0≤120。在一些实施例中，105≤C0≤115。
示例性地，Co和Al的表观浓度之比C0为80、90、100、105、115、125、135、145、155或上述任意两个值组成的范围。
在一些实施例中，正极材料层沿厚度方向的纵截面中，Al的表观浓度为0.89～1.8。示例性地，Al的表观浓度为0.89、0.9、1.1、1.3、1.5、1.6、1.8或上述任意两个值组成的范围。
在一些实施例中，正极活性材料的颗粒粒径Dv90为D1μm，其比表面积为D2 m2g-1，D＝D1/D2，3≤D≤8，20≤D1≤27。如此，能够改善极片上材料颗粒整体的平整度和结构的稳定性，从而进一步降低因为局部电子速率不同导致的电池的厚度膨胀，还利于进一步提升锂离子电池的低温性能，尤其是低温循环性能。示例性地，D的取值为3、4、5、6、7、8或上述任意两个值组成的范围。示例性地，正极材料的粒径Dv90为20μm、21μm、22μm、23μm、24μm、25μm、26μm、27μm或上述任意两个值组成的范围。
在一些实施例中，正极活性材料的比表面积为0.11～0.15m2g-1。示例性地，正极活性材料的比表面积为0.11m2g-1、0.12m2g-1、0.13m2g-1、0.14m2g-1、0.15m2g-1或上述任意两个值组成的范围。
在一些实施例中，正极极片上的正极材料在12MPa压力下的粉体电阻率为120-430Ω/cm。示例性地，正极极片上的正极材料在12MPa压力下的粉体电阻率可以为120Ω/cm、150Ω/cm、200Ω/cm、250Ω/cm、300Ω/cm、350Ω/cm、400Ω/cm、430Ω/cm或上述任意两个值组成的范围。
二次电池
本申请的二次电池包括正极极片、负极极片、隔离膜和电解液，隔离膜设置在正极极片和负极极片之间，正极极片为上述任意一种的正极极片。
隔离膜包括聚乙烯、聚丙烯、聚偏氟乙烯、聚对苯二甲酸乙二醇酯、聚酰亚胺或芳纶中的至少一种。例如，聚乙烯包括选自高密度聚乙烯、低密度聚乙烯或超高分子量聚乙烯中的至少一种。尤其是聚乙烯和聚丙烯，它们对防止短路具有良好的作用，并可以通过关断效应改善电池的安全性。在一些实施例中，隔离膜的厚度在约3μm至480μm的范围内。
在一些实施例中，隔离膜具有多孔层，多孔层的粘结剂选自聚偏氟乙烯、偏氟乙烯-六氟丙烯共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、羧甲基纤维素钠、聚乙烯呲咯烷酮、聚乙烯醚、聚四氟乙烯或聚六氟丙烯中的至少一种。隔离膜表面的多孔层可以提升隔离膜的耐热性能、抗氧化性能和电解质浸润性能，增强隔离膜与极片之间的粘接性。隔膜还可以包括高熔点的结晶聚合物或耐高温的非晶聚合物中的一种，耐高温的树脂包括聚丙烯、聚4-甲基戊烯、聚四氟乙烯、聚偏氟乙烯和环烯烃类共聚物中的至少一种。高熔点的结晶聚合物包括聚丙烯、聚4-甲基戊烯、聚四氟乙烯或聚偏氟乙烯中的至少一种，耐高温的非晶聚合物包括环烯烃类共聚物。基于聚烯烃多孔基材的质量，耐高温的树脂的质量百分含量z为2％至10％。例如，耐高温的树脂的质量百分含量z为2％、3％、5％、7％、8％、10％或为其中任意两个数值组成的范围。当在聚烯烃多孔基材中添加上述种类的耐高温的树脂，并将耐高温的树脂的质量百分含量调控在上述范围内时，有利于提高隔膜的熔破温度，提高了强度和电化学装置的高温性能。
在一些实施例中，隔离膜的平均孔径范围为0.02μm～0.05μm。上述孔径的隔离膜与含有碳酸丙烯酯、三腈化合物的电解液组合，利于电解液的流通且使得正极材料内部的电子迁移不会受到阻碍，从而提升锂离子电池的热安全性能，还能够更好的通过热安全测试。示例性地，隔离膜的平均孔径的范围为0.02μm、0.025μm、0.03μm、0.035μm、0.04μm、0.045μm、0.05μm或上述任意两个值组成的范围。
在一些实施例中，隔离膜包括填料颗粒和粘结剂，填料颗粒包括有机颗粒，且有机颗粒的长径比为(1.1-1.4):1。示例性地，有机颗粒的长径比可以为1.1:1、1.2:1、1.3:1、1.4:1。
电解液包括锂盐和非水溶剂，本申请对锂盐没有特别限制，只要能实现本申请的目的即可。例如锂盐可以包括但不限于LiPF6、LiBF4、LiClO4、LiB(C6H5)4、LiCH3SO3、LiCF3SO3、LiN(SO2CF3)2、LiC(SO2CF3)3、Li2SiF6、双草酸硼酸锂(LiBOB)或二氟硼酸锂中的至少一种。本申请对锂盐在电解液中的含量没有特别限制，只要能实现本申请的目的即可。例如，基于电解液的质量，锂盐的质量百分含量为5％至23％的，例如，锂盐在电解液中的浓度可以为5％、8％、12％、16％、20％、23％或为上述任意两个数值组成的范围。本申请对非水溶剂没有特别限制，只要能实现本申请的目的即可，例如，非水溶剂可以包括但不限于碳酸酯化合物、羧酸酯化合物、醚化合物或其它有机溶剂中的至少一种。上述碳酸酯化合物可以包括但不限于链状碳酸酯化合物、环状碳酸酯化合物或氟代碳酸酯化合物中的至少一种。上述链状碳酸酯化合物可以包括但不限于碳酸二甲酯(DMC)、碳酸二乙酯(DEC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)或碳酸甲乙酯(MEC)中的至少一种。上述环状碳酸酯除了碳酸丙烯酯(PC)之外，还可以包括但不限于碳酸乙烯酯(EC)、碳酸亚丁酯(BC)或碳酸乙烯基亚乙酯(VEC)中的至少一种。氟代碳酸酯化合物可以包括但不限于碳酸1,2-二氟亚乙酯、碳酸1,1-二氟亚乙酯、碳酸1,1,2-三氟亚乙酯、碳酸1,1,2,2-四氟亚乙酯、碳酸1-氟-2-甲基亚乙酯、碳酸1-氟-1-甲基亚乙酯、碳酸1,2-二氟-1-甲基亚乙酯、碳酸1,1,2-三氟-2-甲基亚乙酯或碳酸三氟甲基亚乙酯中的至少一种。上述羧酸酯化合物可以包括但不限于甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸正丙酯、乙酸叔丁酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、γ-丁内酯、癸内酯、戊内酯或己内酯中的至少一种。上述醚化合物可以包括但不限于二丁醚、四甘醇二甲醚、二甘醇二甲醚、1,2-二甲氧基乙烷、1,2-二乙氧基乙烷、1-乙氧基-1-甲氧基乙烷、2-甲基四氢呋喃或四氢呋喃中的至少一种。上述其它有机溶剂可以包括但不限于二甲亚砜、1,2-二氧戊环、环丁砜、甲基环丁砜、1,3-二甲基-2-咪唑烷酮、N-甲基-2-吡咯烷酮、二甲基甲酰胺、乙腈、磷酸三甲酯、磷酸三乙酯或磷酸三辛酯中的至少一种。本申请对非水溶剂在电解液中的含量没有特别限制，只要能实现本申请的目的即可。其中，非水溶剂的含量＝100％-锂盐的含量。
在一些实施例中，电解液包含碳酸丙烯酯和三腈化合物，基于电解液的总质量，碳酸丙烯酯与三腈化合物的质量占比为Q％，2≤Q≤5。优选地，3≤Q≤5。基于电解液的总质量，碳酸丙烯酯的含量为8.18％～8.31％，三腈化合物的含量为1.66％～2.73％，三腈化合物包括1,3,6-己烷三腈和/或1,2,3-三(2-氰基乙氧基)丙烷。
在一些实施例中，电解液还包括3-(二苯基膦基)苯磺酸锂，基于电解液的总质量，3-(二苯基膦基)苯磺酸锂的质量百分含量为1％～4％。电解液中含有上述含量碳酸丙烯酯和三腈化合物时，通过电化学原子力显微镜的观察，能够在正极材料通过协同作用形成相对稳定和均匀的CEI膜，从而改善高温循环性能，进一步改善其热安全性能和高温下的防跌落性能。示例性地，3-(二苯基膦基)苯磺酸锂的质量百分含量为1％、1.5％、2％、2.5％、3％、3.5％、4％或上述任意两个值组成的范围。
负极极片包括负极集流体和设置在负极集流体至少一个表面上的负极材料层，本申请对负极活性层的厚度没有特别限制，只要能够实现本申请目的即可，例如，负极活性层的厚度为30μm至120μm。在一些实施例中，负极活性材料可以包括碳材料或硅基材料中的至少一种。在一些实施例中，碳材料包括但不限于天然石墨、人造石墨、中间相微碳球、硬碳或软碳中的至少一种。在一些实施例中，硅基材料包括但不限于硅、硅氧复合材料或硅碳复合材料中的至少一种。本申请对负极集流体没有特别限制，只要能够实现本申请目的即可，例如，可以包含铜箔、铜合金箔、镍箔、不锈钢箔、钛箔、泡沫镍、泡沫铜或复合集流体(例如聚合物层表面设置金属层的复合集流体)等。本申请对负极集流体的厚度没有特别限制，只要能够实现本申请目的即可，例如，负极集流体的厚度为5μm至12μm。负极活性层还可以包括粘结剂和增稠剂，本申请对粘结剂和增稠剂的种类没有特别限制，只要能够实现本申请目的即可。例如，粘结剂可以包括但不限于聚乙烯醇、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、聚乙烯吡咯烷酮、聚氨酯、聚四氟乙烯、聚偏二氟乙烯、丁苯橡胶或丙烯酸(酯)化的丁苯橡胶中的至少一种；增稠剂可以包括但不限于羧甲基纤维素钠或羧甲基纤维素锂中的至少一种。负极活性层还可以包括导电剂，本申请对导电剂的种类没有特别限制，只要能够实现本申请目的即可。例如，导电剂可以包括但不限于导电炭黑、碳纳米管(CNTs)、碳纤维、科琴黑、石墨烯、金属材料或导电聚合物中的至少一种。本申请对负极活性层中负极活性材料、导电剂、粘结剂和增稠剂的质量比没有特别限制，本领域技术人员可以根据实际需要选择，只要能够实现本申请目的即可。可选地，负极极片还可以包含导电层，导电层位于负极集流体和负极活性层之间。本申请对导电层的组成没有特别限制，可以是本领域常用的导电层。例如，导电层包括导电剂和粘结剂。本申请对导电层中的导电剂和粘结剂没有特别限制，例如可以是上述负极活性层中的导电剂和粘结剂中的至少一种。
二次电池可以按照本领域常规方法制备。示例性地，将上述正极极片、隔离膜及负极极片按顺序堆叠好，使隔离膜处于正极极片与负极极片之间起到隔离的作用，得到电极组件，也可以是经卷绕后得到电极组件；将电极组件置于包装外壳中，注入电解液并封口，得到二次电池。
对于锂电池的结构没有特别限定，可以适用具有单层或者多层的隔膜的硬币型电池、圆筒型电池、方型电池、或软包电池等。本申请的锂离子电池的用途没有特别限定，其可用于现有技术中已知的任何电子装置。在一些实施例中，本申请的锂离子电池可用于，但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
电子设备
本申请的电子设备包括上述任意一种二次电池。本申请的电子设备包括，但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
以下，举出实施例及对比例来对本申请的实施方式进行更具体地说明。除非另有声明，以下所列的份、百分比和比值都是基于重量计，所使用的原料都可商购获得或是按照常规方法进行合成获得。
实施例1-1
(一)锂离子电池的制备
<正极极片的制备>
正极活性材料的制备
按质量比计算，即Al2O3:LiCoO2＝1:62.5的比例，选取异丙醇铝为铝源，按照所需氧化铝的量计算得到异丙醇铝的量，将100g钴酸锂、6.4g异丙醇铝放在转炉中加热至140℃，使其中的异丙醇铝汽化，保温2h，再缓慢通入水蒸气(约450ml)，再转动1h，继续升温至300℃并恒温3小时，然后自然冷却至室温，得到氧化铝包覆LiCoO2的产物记为第一产物。
将第一产物(Dv90为20μm，BET为0.15m2g-1)、导电碳黑和粘结剂聚偏二氟乙烯(PVDF)按质量比82:9:9搅拌成均一浆料，浆料经搅拌、涂布、烘干、辊压、点焊极耳后得到电池正极。
其余实施例中也可参照上述计算方法得到异丙醇铝的量，其他均与实施例1-1相同。
<负极极片的制备>
称取负极活性物质(粒径为12μm的人造石墨)100g、导电剂(炭黑)1g、粘结剂(丁苯橡胶，SBR)4g加入到3g的N-甲基吡咯烷酮中和110g水中形成负极浆料，负极浆料的固含量为80wt％，负极浆料经搅拌、涂布、烘干、辊压、点焊极耳后得到电池负极。
<电解液的制备>
在充满氩气的手套箱中，将碳酸乙烯酯、碳酸甲乙酯、碳酸二乙酯、碳酸丙烯酯按照质量比1：2：1：2混合，加入占电解液总质量1％的3-(二苯基膦基)苯磺酸锂和一定质量的1,3,6-己烷三腈，加入一定量的锂盐，使得最终锂盐在电解液中的浓度为8％，碳酸丙烯酯与1,3,6-己烷三腈的占电解液总质量比为2。
<隔膜>
将体积平均粒径Dv90为1.8μm的勃姆石与粘结剂聚丙烯酸酯按照质量比86:14分散在去离子水中形成固含量为48％的无机涂层浆料，通过凹版辊涂以0.6m/min的速度将预定的浆液涂覆到负极圈的两个表面上，并通过以0.5m/sec的风速吹120℃的热风将其干燥，由此形成粘附在PE基材的表面上形成厚度为3μm的无机涂层；
将熔指为5g/10min的第一聚合物以丙烯为基础单体的聚合物颗粒、将熔指为15g/10min的第二聚合物以偏氟乙烯为基础单体的聚合物颗粒以1：2的摩尔比加入搅拌器中，搅拌均匀；将羧甲基纤维素钠加入搅拌器中，搅拌均匀；将润湿剂二甲基硅氧烷加入搅拌器中，然后加入去离子水搅拌，调整浆料的粘度为42mPa·s、固含量为5％，得到第一涂层浆料；
将第一涂层浆料均匀涂布无机涂层上，在烘箱中干燥后，得到第一涂层。第一涂层浆料的涂布重量为1.8mg/5000mm2，第一涂层的厚度为2μm。第一聚合物、第二聚合物、羧甲基纤维素钠、二甲基硅氧烷的质量比为75:20:0.7:4.3。
关于隔离膜的平均孔径的调控，可以是通过调整勃姆石和粘合剂的质量比或者无机涂层的固含量，也可以是调整浆料的粘度和固含量，上述方法均可以实现隔离膜的平均孔径的调控，具体操作可参见现有技术的常规手段，根据实际情况具体选择，本申请并不限制。
<锂离子电池的制备>
将正极极片、隔离膜、负极极片依次层叠设置，使隔离膜处于正极极片和负极极片中间起到隔离的作用，然后卷绕成裸电芯，将裸电芯装入铝塑膜中，在80℃下脱去水分后，注入电解液并封口，之后经过静置、化成、整形等工序，得到锂离子电池。其中，化成工序如下：在45℃下，进行首圈充放电，流程如下：首先以0.1C倍率恒流充电10min，随后以0.5C倍率恒流充电至指定电压Q＝4.6V，再恒压充电至电流小于等于0.05C，接着以0.5C倍率恒流放电至2.5V。
实施例1-2至实施例1-7
除了按照表2调整相关制备参数以外，其余与实施例1-1相同。
对比例1-1至对比例1-3
除了按照表2调整相关制备参数以外，其余与实施例1-1相同。
实施例2-1至实施例2-12
除了按照表1和表3调整相关制备参数以外，其余与实施例1-1相同。
表1
实施例3-1至实施例3-17
除了按照表4调整相关制备参数以外，其余与实施例1-1相同。
实施例4-1至实施例4-6
除了按照表5调整相关制备参数以外，其余与实施例1-1相同。
(二)测试方法
(1)低温(-25℃)性能测试
通过以下步骤对各实施例和对比例的锂离子电池重复进行充电和放电，并计算锂离子电池的放电容量保持率。
在-25℃的环境中，进行第一次充电和放电，在2C的充电电流下进行恒流充电到满充电压4.2V(针对镍钴锰酸锂材料或者是镍钴铝酸锂材料则采用充电到4.5V)，然后在最大电压下进行恒压充电，直到电流为0.02C，然后在0.5C的放电电流下进行恒流放电，直到最终电压为3V，记录首次循环的放电容量；之后重复上述步骤进行400次的充电和放电循环，记录第600次循环的放电容量。
循环容量保持率＝(第600次循环的放电容量/首次循环的放电容量)*100％。
(2)45℃下的跌落测试
将组装的电池用双面胶固定在跌落测试夹具中，将夹具的6个面依次编号1、2、3、4、5、6，将夹具的四个角依次编号C1、C2、C3、C4。
在45℃下，将夹具置于1.5m高的测试台上，按照编号1-6的顺序依次跌落锂离子二次电池，然后再按照编号C1-C4的顺序依次跌落锂离子二次电池，循环6次，完成跌落测试，静置1h后，观察锂离子二次电池的包装壳是否破损或顶封冲开；
A.拆开锂离子二次电池观察电芯的极耳是否有断裂；
B.拆开锂离子二次电池观察电芯的宽度方向上的两侧隔离膜是否有移位或起皱；
C.拆开锂离子二次电池观察正极片与负极片是否有接触内短路；
无上述情况出现即为通过，每组测试15个锂离子二次电池，记录锂离子二次电池跌落测试的通过率。
(3)电池50℃循环500圈后的厚度膨胀测试
通过以下步骤对各实施例和对比例的锂离子电池重复进行充电和放电，并计算锂离子电池的放电容量保持率。
在40℃的环境中，进行第一次充电和放电，在2C的充电电流下进行恒流充电到满充电压4.2V(针对镍钴锰酸锂材料或者是镍钴铝酸锂材料则可充电到4.5V)，然后在最大电压下进行恒压充电，直到电流为0.02C，然后在0.5C的放电电流下进行恒流放电，直到最终电压为3.0V，记录首次循环的放电容量；之后重复上述步骤进行500次的充电和放电循环，记录第500次循环的放电容量。
循环容量保持率＝(第500次循环的放电容量/首次循环的放电容量)*100％。
(4)50℃循环性能测试
在50℃的环境中，进行第一次充电和放电，在2C的充电电流下进行恒流充电到满充电压4.2V(针对镍钴锰酸锂材料或者是镍钴铝酸锂材料则可充电到4.5V)，然后在最大电压下进行恒压充电，直到电流为0.02C，然后在0.5C的放电电流下进行恒流放电，直到最终电压为3.0V，记录首次循环的放电容量；之后重复上述步骤进行500次的充电和放电循环，记录第500次循环的放电容量。
循环容量保持率＝(第500次循环的放电容量/首次循环的放电容量)*100％。
(5)电池65℃下气体产生量测试
在65℃下以0.2C的电流值进行恒电流充电直至达到4.2V后(针对镍钴锰酸锂材料或者是镍钴铝酸锂材料则可充电到4.5V)，在4.2V下进行1小时的恒电压充电。然后，将该充电后的电池在65℃的恒温槽内贮藏。经过200小时后，将电池从恒温槽取出，恢复至室温后，测定各电池的气体产生量，通过这样的方法来评价电池的4.2V贮藏特性。气体产生量使用如下的阿基米德法：在装有超纯水的容器中投入测试电池，由其前后的重量变化测定单层层压电池的体积。作为由重量变化测定体积的装置，使用AlphaMirage Corp制的比重计MDS-300。
(6)145℃热箱测试
步骤1：将制备得到的电池以0.5C恒流充电到截止电压4.2V，再恒压充电到截止电流为200mA，再静置5分钟；
步骤2：将满充的电池贴上感温线，贴在两极耳之间，两极耳接线监控电压，将电芯竖直悬挂在箱体内；
步骤3：热箱按照5℃升温速度升温至145℃并保持60min。
评判标准：电池不起火、不爆炸即为通过。计算通过热箱测试的电池数量。
(7)正极材料的粉体电阻率测试
正极活性物质在12MPa压力下的粉体体积电阻率ρ可以采用的粉体体积电阻率测试方法。例如，采用四探针法进行测试。测试方法包括：取2g正极活性物质粉体加入样品台中，通过压力机对粉体施加12MPa的压力，待压力稳定后，通过电阻率仪读取正极活性物质在12MPa压力下的粉体体积电阻率ρ。
表2
结合表2，对比例1-1至对比例1-3与实施例1-1相比，对比例1-1至对比例1-3的正极材料层中的Co和Al的原子数百分比的比值不在本申请的范围内，且其正极活性材料中的Co和Al的原子数百分比的比值不在本申请的范围内，其在45℃下循环500圈的容量保持率均不高于超过70％，且在65℃下产气量均高于3.5ml。实施例1-1的正极材料层中的Co和Al的原子数百分比的比值以及正极活性材料中的Co和Al的原子数百分比的比值均在合适范围，其在45℃下循环500圈的容量保持率明显提升，在65℃下的产气量明显下降。
特别地，进一步调整正极材料层中的Co和Al的原子数百分比的比值在优选范围，同时，协同调控正极活性材料中的Co和Al的原子数百分比的比值也在优选范围时，改善锂离子电池的高温循环性能以及高温产气的效果更好。
特别地，进一步正极材料层中Co和Al的原子数分别与Co、C、O、Al的原子数之和的比值也合适时，改善锂离子电池的高温循环性能以及高温产气的效果更优。
表3
结合表3可以看出，进一步调整正极材料层沿厚度方向的纵截面中钴原子与铝原子的表观浓度之比在合适范围，同时，调控正极活性材料的颗粒粒径Dv90与其比表面积的比值也合适时，能够兼顾改善锂离子电池的高温性能以及其低温性能。
表4
结合表4可以看出，进一步调整隔离膜的平均孔径满足本申请的范围，可以改善锂离子电池在145℃下热箱测试的通过率和45℃下的跌落性能测试通过率，提升锂离子电池及电子装置的热安全性能和高温下的防跌落性能。当使得碳酸丙烯酯的含量满足本申请的范围，可以改善电化学装置及电子装置的热安全性能和高温下的防跌落性能。进一步的，通过限制三腈化合物的种类及种类满足本申请的范围，可以改善电化学装置在145℃下热箱测试的通过率和45℃下的跌落性能测试通过率，提升电化学装置及电子装置的热安全性能和高温下的防跌落性能。当限制碳酸丙烯酯与三腈化合物的质量比值满足本申请的范围，也可以明显的改善电化学装置在145℃下热箱测试的通过率和45℃下的跌落性能测试通过率。当向其中加入含量为1％至4％的3-(二苯基膦基)苯磺酸锂时，可以显著地改善组装的锂离子电池的热安全性能和高温下的防跌落性能。
表5
结合表5可以看出，当隔离膜上的有机颗粒的长径比满足本申请的1.1:1至1.4:1时，可以显著地提升锂离子电池的热安全性能和高温下的长循环性能。
以上仅为本申请的较佳实施例而已，并不用以限制本申请，凡在本申请的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本申请的保护范围之内。

Claims (12)

  1. 一种正极极片，其特征在于，所述正极极片包括正极集流体和设置于所述正极集流体至少一个表面上的正极材料层，所述正极材料层中含有Co和Al；
    基于所述正极材料层的原子总数，Al的原子数百分比和Co的原子数百分比的比值为T，0.008≤T≤0.032；
    基于正极活性材料的原子总数，Al的原子数百分比和Co的原子数百分比的比值为T′，0.012≤T′≤0.02；
    所述正极材料层中还含有C和O。
  2. 根据权利要求1所述的正极极片，其特征在于，0.008≤T≤0.025。
  3. 根据权利要求1或2所述的正极极片，其特征在于，
    所述正极材料层中Co的原子数与Co、C、O、Al的原子数之和的比值为t，17.5≤t≤25；和/或，
    所述正极材料层中Al的原子数与Co、C、O、Al的原子总数之和的比值为t′，0.32≤t′≤0.35。
  4. 根据权利要求1或2所述的正极极片，其特征在于，所述正极材料层沿厚度方向的纵截面中，Co和Al的表观浓度之比为C0，80≤C0≤155。
  5. 根据权利要求4所述的正极极片，其特征在于，所述正极活性材料的颗粒粒径Dv90为D1μm，其比表面积为D2 m2g-1，D＝D1/D2，130≤D≤250，20≤D1≤27。
  6. 根据权利要求1或2所述的正极极片，其特征在于，所述正极极片上的正极材料在12MPa压力下的粉体电阻率为120-430Ω/cm。
  7. 一种二次电池，其特征在于，所述二次电池包括正极极片、负极极片、隔离膜和电解液；
    所述正极极片为权利要求1～6中任一项所述的正极极片。
  8. 根据权利要求7所述的二次电池，其特征在于，所述隔离膜的平均孔径范围为0.02μm～0.05μm。
  9. 根据权利要求7所述的二次电池，其特征在于，所述隔离膜包括填料颗粒和粘结剂；
    所述填料颗粒包括有机颗粒，所述有机颗粒的长径比为(1.1-1.4):1。
  10. 根据权利要求7～9任一项所述的二次电池，其特征在于，所述电解液包括碳酸丙烯酯和三腈化合物，所述碳酸丙烯酯和所述三腈化合物的质量比为Q％，2≤Q≤5。
  11. 根据权利要求10所述的二次电池，其特征在于，所述电解液还包括3-(二苯基膦基)苯磺酸锂，基于电解液的总质量，所述3-(二苯基膦基)苯磺酸锂的质量百分含量为1％～4％。
  12. 一种电子设备，其特征在于，所述电子设备包括权利要求7～11中任一项所述的二次电池。
PCT/CN2025/078995 2024-04-09 2025-02-25 正极极片、二次电池和电子设备 Pending WO2025213971A1 (zh)

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