Secondary battery and electronic device

Abstract

The invention relates to a secondary battery and an electronic device. Specifically, the secondary battery provided by the invention comprises a positive electrode, a negative electrode and an electrolyte, the positive electrode comprises a positive electrode current collector, and an insulating layer and a positive electrode material layer which are arranged on the positive electrode current collector; the insulating layer comprises boehmite, the positive electrode material layer comprises lithium cobalt oxide, the lithium cobalt oxide comprises tungsten element and tin element, and the electrolyte comprises vinylene carbonate. According to the invention, the short-circuit safety of the battery can be improved, and the high-rate discharge characteristic can also be improved.

Description

[0001] This application is a divisional application of a patent application with an application date of September 4, 2024, application number 202411236400.2, and invention name “Secondary Battery and Electronic Device”. Technical Field

[0002] The present application relates to the field of energy storage, and in particular to a secondary battery and an electronic device. Background Art

[0003] Secondary batteries, due to their high energy density and ability to be repeatedly charged and discharged, have been widely used in portable electronic devices, electric vehicles, and other fields, and are gaining increasing attention. With the development of science and technology and the improvement of living standards, the use of secondary batteries in daily life has become more diverse. Research on materials such as secondary battery cathodes, anodes, separators, and electrolytes is ongoing, and people are increasingly demanding their safety and rate performance. Summary of the Invention

[0004] The present invention further improves safety and rate performance by adjusting the composition of the positive electrode and electrolyte in a secondary battery. The inventors discovered that a positive electrode comprising a positive electrode current collector, an insulating layer disposed thereon, and a positive electrode material layer; the insulating layer comprising boehmite, the positive electrode material layer comprising lithium cobalt oxide, the lithium cobalt oxide comprising tungsten and tin, and the electrolyte comprising vinylene carbonate, can improve both short-circuit safety and high-rate discharge characteristics, thereby completing the present invention.

[0005] In some embodiments, the mass content ratio of tungsten element to tin element is 1:(0.5-0.9).

[0006] In some embodiments, the electrolyte includes 1,3,6-hexanetricarboxylic acid nitrile, wherein the amount of 1,3,6-hexanetricarboxylic acid nitrile is 0.1 parts by mass to 1 part by mass relative to 100 parts by mass of the electrolyte.

[0007] In some embodiments, the electrolyte includes 1,2,3-tris(2-cyanoethoxy)propane, wherein the amount of 1,2,3-tris(2-cyanoethoxy)propane is 0.01 parts by mass to 1.5 parts by mass relative to 100 parts by mass of the electrolyte.

[0008] In some embodiments, the electrolyte further includes substance A, which includes at least one of succinonitrile, adiponitrile, ethylene glycol bis(propionitrile) ether, lithium monofluorophosphate, 1,2-bis(difluorophosphine oxide)ethane, 1,2-bis(difluorophosphine oxide)propane, 1,2-bis(difluorophosphine oxide)butane, lithium fluorosulfonate, 1,3-propane sultone, or vinyl sulfate.

[0009] In some embodiments, the insulating layer includes polyvinylidene fluoride and N-methylpyrrolidone.

[0010] In some embodiments, the electrolyte includes 4-bromophenyl isocyanate, and the amount of 4-bromophenyl isocyanate is 0.03 parts by mass to 0.7 parts by mass relative to 100 parts by mass of the electrolyte.

[0011] In some embodiments, the electrolyte includes diethoxyphosphonoisocyanate, and the amount of diethoxyphosphonoisocyanate is 0.01 parts by mass to 3 parts by mass relative to 100 parts by mass of the electrolyte.

[0012] In some embodiments, the electrolyte includes 4-bromophenyl isocyanate and diethoxyphosphonoisocyanate. Relative to 100 parts by mass of the electrolyte, 4-bromophenyl isocyanate is a parts by mass, diethoxyphosphonoisocyanate is b parts by mass, and 0.01≤a / b≤0.95.

[0013] In another aspect of the present application, the present application provides an electronic device, which includes the secondary battery described in the present application.

[0014] The present application uses a combination of a specific positive electrode and an electrolyte to not only improve the short-circuit safety of the battery, but also improve the high-rate discharge characteristics.

[0015] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the following description through implementation of the embodiments of the present application. DETAILED DESCRIPTION

[0016] The embodiments of the present application will be described in detail below. The embodiments of the present application should not be interpreted as limiting the present application.

[0017] Unless expressly stated otherwise, the following terms used in this application have the meanings indicated below.

[0018] The present application uses a specific combination of positive electrode and electrolyte to not only improve the short-circuit safety of the battery, but also improve the high-rate discharge characteristics.

[0019] In one embodiment, the present application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte as described below.

[0020] I. Positive electrode

[0021] This application relates to a secondary battery and an electronic device. Specifically, this application provides a secondary battery comprising: a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises a positive electrode current collector, an insulating layer disposed thereon, and a positive electrode material layer. The insulating layer comprises boehmite, the positive electrode material layer comprises lithium cobalt oxide, and the lithium cobalt oxide comprises tungsten and tin. The electrolyte comprises vinylene carbonate. This application not only improves the battery's short-circuit safety but also enhances its high-rate discharge characteristics.

[0022] The positive electrode material layer contains lithium cobalt oxide, which includes tungsten and tin elements. The positive electrode material layer can be one layer or multiple layers.

[0023] The inventors of the present application unexpectedly discovered in experiments that when a positive electrode material layer comprising the above-mentioned lithium cobalt oxide is present on the positive electrode current collector, if an insulating layer comprising boehmite is also present and an electrolyte system containing vinylene carbonate is used, the short-circuit safety and high-rate discharge characteristics of the battery can be improved. It is speculated that the reason may be that vinylene carbonate is tightly combined with the positive electrode system in the presence of the orthorhombic crystal system of boehmite and the specific unit cell edge angle in the crystal structure of lithium cobalt oxide, which not only improves the short-circuit safety of the battery, but also improves the high-rate discharge characteristics.

[0024] Specifically, from the perspective of improving battery short-circuit safety and high-rate discharge characteristics, lithium cobalt oxide includes tungsten and tin. From the perspective of improving battery short-circuit safety, the mass content ratio of tungsten to tin is 1:(0.5-0.9), preferably 1:(0.6-0.8), for example, 1:0.7. When the mass content ratio of tungsten to tin falls within the above range, the battery short-circuit safety and high-rate discharge characteristics can be further improved.

[0025] Specifically, from the perspective of improving battery short-circuit safety and high-rate discharge characteristics, in some embodiments, based on the mass of the positive electrode material layer, the mass content of tungsten is 500 ppm to 2000 ppm, for example, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, or a value within the range of any two thereof. In some embodiments, from the perspective of improving battery short-circuit safety and high-rate discharge characteristics, based on the mass of the positive electrode material layer, the mass content of tin is 100 ppm to 1000 ppm, for example, 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, or a value within the range of any two thereof.

[0026] As the voltage during charging, from the viewpoint of increasing the voltage, the positive electrode potential is preferably 4.4 V (vs. Li / Li + ) or more, more preferably 4.5V (vs.Li / Li + ) or more, particularly preferably 4.6 V (vs. Li / Li + )above.

[0027] There are no restrictions on the type of positive electrode conductive material; any known conductive material may be used. Examples of positive electrode conductive materials include, but are not limited to, carbon black such as acetylene black; carbon materials such as amorphous carbon such as needle coke; carbon nanotubes; and graphene. These positive electrode conductive materials may be used alone or in any combination.

[0028] There is no limitation on the type of solvent used to form the positive electrode slurry, as long as it is a solvent that can dissolve or disperse the positive electrode material, conductive material, and positive electrode binder. Examples of solvents used to form the positive electrode slurry may include any of aqueous solvents and organic solvents. Examples of aqueous media may include, but are not limited to, water and mixed media consisting of alcohol and water. Examples of organic media may include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran; amides such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide.

[0029] The density of the active material layer of the positive electrode excluding the current collector is usually 3.5 g / cm 3 In order to further increase the capacity of the battery, it is preferably 4g / cm 3 In addition, as its upper limit, it is preferably 4.6 g / cm 3 the following.

[0030] The type of positive electrode current collector is not particularly limited and can be any known material suitable for use as a positive electrode current collector. Examples of positive electrode current collectors include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metal material. In some embodiments, the positive electrode current collector is aluminum.

[0031] To reduce the electronic contact resistance between the positive electrode current collector and the positive electrode material layer, the surface of the positive electrode current collector may include a conductive additive or a conductive coating. Examples of conductive additives include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. Examples of conductive coatings include a mixture layer containing an inorganic oxide, a conductive agent, and a binder.

[0032] From the viewpoint of improving battery short-circuit safety and high-rate discharge characteristics, boehmite is contained in the insulating layer.

[0033] Specifically, from the viewpoint of improving the short-circuit safety and high-rate discharge characteristics of the battery, the insulating layer includes polyvinylidene fluoride and N-methylpyrrolidone.

[0034] The positive electrode is made as follows:

[0035] Boehmite, polyvinylidene fluoride, and N-methylpyrrolidone were mixed, and deionized water was added thereto and mixed evenly to prepare slurry 1.

[0036] The above-mentioned positive electrode material is mixed with a conductive agent such as acetylene black or carbon black, and a binder such as polyvinylidene fluoride or polyacrylonitrile, and a high-boiling-point solvent such as N-methylpyrrolidone is added thereto and kneaded to prepare a slurry 2 .

[0037] Slurry 1 and slurry 2 are applied in parallel on an aluminum foil or the like of a current collector, dried, and pressed to form a positive electrode.

[0038] II. Electrolyte

[0039] The electrolyte used in the secondary battery of the present application includes an electrolyte and a solvent for dissolving the electrolyte. In some embodiments, the electrolyte of the present application includes vinylene carbonate.

[0040] When vinylene carbonate is used in the secondary battery of the present application, the inventors have found that the addition of vinylene carbonate to the positive electrode lithium cobalt oxide and boehmite can not only improve the short-circuit safety of the battery, but also improve the high-rate discharge characteristics.

[0041] Specifically, from the viewpoint of improving the battery short-circuit safety and high-rate discharge characteristics of the secondary battery, the vinylene carbonate is 0.01 mass parts or more, preferably 0.07 mass parts or more, and more preferably 0.15 mass parts or more relative to 100 mass parts of electrolyte. In addition, from the viewpoint of improving the battery short-circuit safety and high-rate discharge characteristics of the secondary battery, the vinylene carbonate is 2 mass parts or less, preferably 1.4 mass parts or less, more preferably 0.8 mass parts or less, further preferably 0.6 mass parts or less, and particularly preferably 0.5 mass parts or less.

[0042] Specifically, from the viewpoint of improving the battery short-circuit safety and high-rate discharge characteristics of the secondary battery, the electrolyte includes 1,3,6-hexane tricarbonitrile, wherein relative to 100 parts by mass of the electrolyte, 1,3,6-hexane tricarbonitrile is 0.1 parts by mass or more, preferably 1,3,6-hexane tricarbonitrile is 0.15 parts by mass or more, more preferably 0.18 parts by mass or more. In addition, as the upper limit of the content of 1,3,6-hexane tricarbonitrile, from the viewpoint of improving the battery short-circuit safety and high-rate discharge characteristics of the secondary battery, 1,3,6-hexane tricarbonitrile is 1 part by mass or less, preferably 0.8 parts by mass or less, more preferably 0.7 parts by mass or less, further preferably 0.6 parts by mass or less, particularly preferably 0.5 parts by mass or less. When within the above range, it helps to further improve the battery short-circuit safety and high-rate discharge characteristics of the secondary battery.

[0043] Specifically, from the viewpoint of improving the battery short-circuit safety and high-rate discharge characteristics of the secondary battery, the electrolyte includes 1,2,3-tris(2-cyanoethoxy)propane, wherein relative to 100 parts by mass of the electrolyte, 1,2,3-tris(2-cyanoethoxy)propane is 0.01 parts by mass or more, preferably 1,2,3-tris(2-cyanoethoxy)propane is 0.07 parts by mass or more, and more preferably 0.15 parts by mass or more. In addition, as the upper limit of the content of 1,2,3-tris(2-cyanoethoxy)propane, from the viewpoint of improving the battery short-circuit safety and high-rate discharge characteristics of the secondary battery, 1,2,3-tris(2-cyanoethoxy)propane is 1.5 parts by mass or less, preferably 1.2 parts by mass or less, more preferably 1.1 parts by mass or less, further preferably 0.9 parts by mass or less, and particularly preferably 0.8 parts by mass or less. When within the above range, it helps to further improve the battery short-circuit safety and high-rate discharge characteristics of the secondary battery.

[0044] Specifically, in some embodiments, the electrolyte further includes substance A, which includes at least one of succinonitrile, adiponitrile, ethylene glycol di(propionitrile) ether, monofluorolithium phosphate, 1,2-bis(difluorophosphorus oxide) ethane, 1,2-bis(difluorophosphorus oxide) propane, 1,2-bis(difluorophosphorus oxide) butane, lithium fluorosulfonate (LiSO3F), 1,3-propane sultone or vinyl sulfate. Wherein, relative to 100 parts by mass of the electrolyte, substance A is 0.01 parts by mass or more, preferably 0.07 parts by mass or more, and more preferably 0.15 parts by mass or more. In addition, from the viewpoint of improving the battery short-circuit safety and high-rate discharge characteristics of the secondary battery, substance A is 1 part by mass or less, preferably 0.8 parts by mass or less, more preferably 0.7 parts by mass or less, further preferably 0.6 parts by mass or less, and particularly preferably 0.5 parts by mass or less.

[0045] Specifically, from the viewpoint of improving the battery short-circuit safety and high-rate discharge characteristics of the secondary battery, the electrolyte includes 4-bromophenyl isocyanate. In some embodiments, relative to 100 parts by mass of the electrolyte, the 4-bromophenyl isocyanate is a part by mass, and the value of a ranges from 0.03 to 0.7, for example, a is 0.03, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or a value within the range consisting of any two thereof. When the mass fraction of 4-bromophenyl isocyanate in the electrolyte is regulated to meet the above range, the battery short-circuit safety and high-rate discharge characteristics of the secondary battery can be further improved.

[0046] Specifically, from the viewpoint of improving the battery short-circuit safety and high-rate discharge characteristics of the secondary battery, the electrolyte includes diethoxy phosphonoisocyanate. In some embodiments, relative to 100 parts by mass of the electrolyte, the diethoxy phosphonoisocyanate is b parts by mass, and the value range of b is 0.01 to 3, for example, b is 0.01, 0.1, 0.2, 0.3, 0.7, 0.8, 1.1, 1.3, 1.6, 1.7, 2.0, 2.1, 2.4, 2.6, 3.0 or a value within the range consisting of any two of them. When the mass fraction of diethoxy phosphonoisocyanate in the electrolyte is regulated to meet the above range, the battery short-circuit safety and high-rate discharge characteristics of the secondary battery can be further improved.

[0047] Specifically, from the perspective of improving the battery short-circuit safety and high-rate discharge characteristics of the secondary battery, the electrolyte includes 4-bromophenyl isocyanate and diethoxy phosphonoisocyanate. In some embodiments, 0.01≤a / b≤0.95, for example, the value of a / b is 0.01, 0.06, 0.13, 0.19, 0.27, 0.37, 0.42, 0.46, 0.52, 0.63, 0.67, 0.75, 0.87, 0.88, 0.95 or a value within the range of any two thereof. When the mass fractions of 4-bromophenyl isocyanate and diethoxy phosphonoisocyanate in the electrolyte are regulated to meet the above relationship, the interaction and close cooperation between the two can be promoted, thereby better improving the battery short-circuit safety and high-rate discharge characteristics of the secondary battery.

[0048] In some embodiments, the additive in the electrolyte comprises one or more of the following: ethylene glycol sulfate, 1,2-propylene glycol sulfate, 1,3-propylene glycol sulfate, 1,2-butanediol sulfate, 1,3-butanediol sulfate, 1,4-butanediol sulfate, 1,2-pentanediol sulfate, 1,3-pentanediol sulfate, 1,4-pentanediol sulfate, 1,5-pentanediol sulfate, dimethyl sulfate, ethyl methyl sulfate, diethyl sulfate, methyl fluorosulfonate, ethyl trifluoromethanesulfonate, methyl methanesulfonate, ethyl methanesulfonate, dimethyl sulfonate. Butyl ester, methyl 2-(methylsulfonyloxy)propionate, ethyl 2-(methylsulfonyloxy)propionate, 1-fluoro-1,3-propane sultone, 2-fluoro-1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1-methyl-1,3-propane sultone, 2-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1-propylene-1,3-sultone, 2-propylene-1,3-sultone, 1-fluoro-1-propylene-1,3-sultone, 2-fluoro-1-propylene-1,3-sultone, 3-fluoro-1-propylene-1,3-sultone -1-Fluoro-1-propene-1,3-sultone, 1-Fluoro-2-propene-1,3-sultone, 2-Fluoro-2-propene-1,3-sultone, 3-Fluoro-2-propene-1,3-sultone, 1-Methyl-1-propene-1,3-sultone, 2-Methyl-1-propene-1,3-sultone, 3-Methyl-1-propene-1,3-sultone, 1-Methyl-2-propene-1,3-sultone, 2-Methyl-2-propene-1,3-sultone, 3-Methyl-2-propene-1,3-sultone Lactone, 1,4-butane sultone, 1,5-pentane sultone, methylene methanedisulfonate, ethylene methanedisulfonate, dimethyl sulfite, ethyl methyl sulfite, diethyl sulfite, 1,2-ethylene glycol sulfite, 1,2-propylene glycol sulfite, 1,3-propylene glycol sulfite, 1,2-butanediol sulfite, 1,3-butanediol sulfite, 1,4-butanediol sulfite, 1,2-pentanediol sulfite, 1,3-pentanediol sulfite, 1,4-pentanediol sulfite, 1,5-pentanediol sulfite, etc. In some embodiments, the electrolyte further includes an ionizable lithium salt, and the ionizable lithium salt includes at least one of LiPF6, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, CF3SO3Li, LiC(CF3SO2)3, or LiC4BO8. For example, the lithium salt used in the electrolyte of the present application includes LiPF6. The content of LiPF6 is 9% to 15% by mass, preferably 9% to 13% by mass, and more preferably 9% to 12% by mass, based on the mass of the electrolyte. By setting the content within the above range, the effects of improving the short-circuit safety and high-rate discharge characteristics of the battery can be more balanced.

[0049] In some embodiments, the electrolyte further includes at least one of lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI), and lithium bis(fluorosulfonyl imide) (LiFSI).

[0050] In some embodiments, the additive in the electrolyte further includes at least one of a fluoroether compound, a fluorocarbonate compound, and an ether nitrile compound, such as hydrofluoroether (HFE-458), fluoroethylene carbonate (FEC), ethylene glycol bis(propionitrile) ether (DENE), and the like.

[0051] In some embodiments, the electrolyte may further include a non-aqueous solvent. The non-aqueous solvent may be selected from carbonate compounds, carboxylate compounds, ether compounds, phosphate compounds, other organic solvents, or combinations thereof.

[0052] Alternatively, the carbonate compound may be a linear carbonate compound, a cyclic carbonate compound, or a combination thereof. Alternatively, the carbonate compound may be a fluorinated carbonate compound, a non-fluorinated carbonate compound, or a combination thereof.

[0053] The example of chain carbonate compound is diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) and its combination. The example of cyclic carbonate compound is ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC) or its combination. The example of fluorocarbonate compound is fluoroethylene carbonate (FEC), 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, trifluoromethylethylene carbonate or its combination.

[0054] Specifically, examples of the carboxylate compound are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, methyl formate, or a combination thereof.

[0055] Specifically, examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.

[0056] Specifically, examples of the phosphate compound are trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or a combination thereof.

[0057] Specifically, examples of other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methylpyrrolidone, formamide, dimethylformamide, acetonitrile, or a combination thereof.

[0058] III. Negative electrode

[0059] The negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on a surface of the negative electrode current collector, wherein the negative electrode material layer comprises a negative electrode material. In some embodiments, the charge capacity of the negative electrode material is greater than the discharge capacity of the positive electrode material to prevent unintentional deposition of lithium metal on the negative electrode during charging.

[0060] The negative electrode material is not particularly limited, and examples thereof include carbon-based negative electrode materials, metal-based negative electrode materials, silicon-based negative electrode materials, and negative electrode materials obtained by combining these.

[0061] Carbon-based negative electrode materials

[0062] Here, the carbon-based negative electrode material refers to an active material having a carbon-based skeleton that can insert lithium. Examples of the carbon-based negative electrode material include carbonaceous materials and graphite materials.

[0063] Examples of carbonaceous materials include easily graphitized carbon and non-graphitizable carbon having an amorphous structure, such as glassy carbon. Examples of easily graphitized carbon include carbon materials obtained from petroleum or coal using tar pitch as a raw material. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, and pyrolysis vapor-grown carbon fibers. Examples of non-graphitizable carbon include phenolic resin sintered bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin sintered bodies (PFA), and hard carbon.

[0064] Furthermore, examples of graphite materials include natural graphite and artificial graphite. Examples of artificial graphite include artificial graphite obtained by heat-treating carbon containing graphitized carbon at 2800°C or higher, graphite MCMB obtained by heat-treating MCMB at 2000°C or higher, and graphite mesophase pitch-based carbon fibers obtained by heat-treating mesophase pitch-based carbon fibers at 2000°C or higher. Furthermore, in the present application, natural graphite (amorphous-coated natural graphite) at least a portion of its surface is coated with amorphous carbon as a carbon-based negative electrode material.

[0065] In addition, the metal-based negative electrode material is an active material comprising a metal, generally referring to an active material having an element capable of inserting lithium or alloying with lithium in the structure, an element inserted into lithium or alloyed with lithium, and a theoretical current capacity of 500 mAh / g or more per unit mass. As a metal-based negative electrode material, for example, lithium metal, a single metal (such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) that can form a lithium alloy and its alloy, and their oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. can be used. Among them, as a metal-based negative electrode material, an active material (silicon-based negative electrode material) comprising silicon is preferably used. This is because the secondary battery can be high-capacitated by using a silicon-based negative electrode material.

[0066] Examples of silicon-based negative electrode materials include silicon (Si), alloys containing silicon, SiO, SiO 2 , and composites of silicon-containing materials and conductive carbon (silicon-carbon materials) in which a silicon-containing material is coated with conductive carbon or composited with conductive carbon.

[0067] From the viewpoint of improving battery capacity, silicon-carbon materials, for example, porous carbon-supported silicon composite materials are preferred.

[0068] The negative electrode material may be used alone or in combination of two or more at any ratio.

[0069] Here, the volume average particle size of the negative electrode material is preferably 1 μm or greater, more preferably 5 μm or greater, and preferably 30 μm or less, more preferably 20 μm or less. If the volume average particle size of the negative electrode material is above the lower limit, heat generation during internal short circuiting can be effectively suppressed. If the volume average particle size of the negative electrode material is below the upper limit, an increase in the initial resistance of the resulting battery can be effectively suppressed.

[0070] The negative electrode material layer may further include a negative electrode binder. The negative electrode binder can improve the bonding between the negative electrode material particles and the bonding between the negative electrode material and the current collector. The type of negative electrode binder is not particularly limited, as long as it is a material that is stable to the electrolyte or the solvent used in electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluororesins, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, and the like. When an aqueous solvent is used to prepare the negative electrode mixture slurry, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salt, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salt, polyvinyl alcohol, and the like.

[0071] As a current collector for holding the negative electrode material, any known current collector can be used. Examples of negative electrode current collectors include, but are not limited to, metal materials such as copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode current collector is copper.

[0072] The negative electrode can be prepared by applying a negative electrode mixture slurry containing a negative electrode material, a resin binder, etc. on a negative electrode current collector, drying it, and then rolling it to form a negative electrode material layer on both sides of the negative electrode current collector.

[0073] IV. Isolation membrane

[0074] To prevent short circuits, a separator is usually provided between the positive electrode and the negative electrode. In this case, the electrolyte of the present application is usually used by permeating the separator.

[0075] There is no particular restriction on the material and shape of the isolation membrane, as long as the effect of the present application is not significantly impaired. The isolation membrane may be a resin, glass fiber, inorganic substance, etc. formed of a material that is stable to the electrolyte of the present application. In some embodiments, the isolation membrane includes a porous sheet or a non-woven fabric-like material with excellent liquid retention. Examples of materials for resin or glass fiber isolation membranes may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above-mentioned isolation membranes can be used alone or in any combination.

[0076] The isolation film may also be a material formed by laminating the above materials, and examples thereof include, but are not limited to, a three-layer isolation film formed by laminating polypropylene, polyethylene, and polypropylene in this order.

[0077] Examples of inorganic materials include, but are not limited to, oxides such as aluminum oxide and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.) The inorganic material may be in the form of, but is not limited to, particles or fibers.

[0078] The separator may be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, and microporous films. In the thin film form, the separator has a pore size of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the above-mentioned independent thin film separators, separators may also be used: separators formed by forming a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or negative electrode using a resin-based binder. For example, a separator formed by forming a porous layer on both sides of the positive electrode using fluororesin as a binder with aluminum oxide particles having a particle size of 90% less than 1 μm.

[0079] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator is within the above range, insulation and mechanical strength can be ensured, and the DC resistance characteristics and energy density of the secondary battery can be ensured.

[0080] The present application further provides an electronic device, which includes the secondary battery according to the present application.

[0081] The use of the secondary battery of the present application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the secondary 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 televisions, 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.

[0082] Example

[0083] Examples of the secondary battery of the present application are shown below, but the present application is not limited to these examples.

[0084] Preparation of secondary batteries

[0085] Production of positive electrode:

[0086] 80 wt% of boehmite and 20 wt% of polyvinylidene fluoride were mixed and dissolved in N-methylpyrrolidone, and deionized water was added thereto and mixed evenly to prepare a positive electrode slurry 1.

[0087] Positive electrode slurry 2 was prepared by mixing the positive electrode materials (97 wt%) and conductive carbon black (1.5 wt%) listed in Table 1 with a solution of polyvinylidene fluoride (1.5 wt%) dissolved in N-methylpyrrolidone. Slurry 1 was applied to the tab side, and slurries 1 and 2 were applied parallel to the aluminum foil. The coated aluminum foil was dried, pressurized, and then cut to the desired size to produce the positive electrode.

[0088] Preparation of isolation membrane: A 12 μm thick polyethylene (PE) microporous membrane was selected as the isolation membrane.

[0089] Preparation of negative electrode:

[0090] A negative electrode slurry was prepared by mixing 96 wt% artificial graphite, SiO2 (mass ratio 90:10), and 2 wt% styrene-butadiene rubber. This mixture was then added to a solution of 2 wt% lithium carboxymethyl cellulose dissolved in deionized water. This slurry was then applied to one side of copper foil, dried, pressurized, and cut to the desired size to create the negative electrode.

[0091] Preparation of electrolyte: In an argon atmosphere glove box with a water content of less than 10 ppm, ethyl methyl carbonate, ethyl acetate, and ethylene carbonate were mixed in a mass ratio of 1:1:1 to obtain a base solvent, and then lithium salt LiPF6 and the additives shown in Table 1 were added to the above base solvent. After mixing evenly, an electrolyte was obtained, wherein the mass content of LiPF6 based on the mass of the electrolyte was 12%.

[0092] Battery production:

[0093] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrode sheets to provide insulation. The electrodes are then wound to form an electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging. After dehydration at 80°C, the aforementioned electrolyte is injected. The secondary battery is vacuum packaged, allowed to stand, formed, shaped, and then tested for capacity to obtain a pouch-shaped secondary battery. The pouch-shaped secondary battery is 30 mm wide, 45 mm high, and 5 mm thick.

[0094] Table 1

[0095]

[0096]

[0097]

[0098]

[0099] Test Method

[0100] Battery short circuit safety

[0101] The test method is as follows:

[0102] The prepared secondary battery was charged according to the following conditions:

[0103] (1) Constant current charging: charging current is 1400mA (charging termination voltage is 4.6V);

[0104] (2) Constant voltage charging: the charging voltage is 4.6V (the charging termination current is 100mA).

[0105] A 2.5 mm diameter round iron nail was used to pierce one side of a charged battery at a speed of 5 mm / sec in an environment of 25°C. The temperature T of the short-circuit position (where the nail pierced) was measured 1 hour after the nail piercing.

[0106] The evaluation was conducted using the following benchmarks: A smaller value for temperature T indicates that the insulating layer and electrolyte system in this application can mitigate temperature fluctuations under extreme conditions (such as simulated short circuits), synergistically control the temperature rise of the secondary battery, and help reduce the thermal decomposition of the lithium cobalt oxide in this application, thereby improving safety.

[0107] A: The value of temperature T is less than 80°C.

[0108] B: The value of the temperature T is 80°C or higher and lower than 100°C.

[0109] C: The value of the temperature T is 100°C or higher and lower than 130°C.

[0110] D: The value of the temperature T is 130° C. or higher.

[0111] High rate discharge characteristics

[0112] The prepared battery was subjected to charge / discharge in a constant temperature bath set at 25°C by the following steps:

[0113] (1) Constant current charging: charging current 0.2C (1C is 1 hour rate current), charging end voltage 4.6V;

[0114] (2) Constant voltage charging: charging voltage 4.6V, charging end current 0.01C;

[0115] (3) Constant current discharge: discharge current 0.2C, discharge end voltage 3V.

[0116] Subsequently, the prepared battery was subjected to charge / discharge through the following steps.

[0117] (4) Constant current charging: charging current 1C, charging end voltage 4.6V;

[0118] (5) Constant voltage charging: charging voltage 4.6V, charging end current 0.05C;

[0119] (6) Constant current discharge: discharge current 1C, discharge end voltage 3V.

[0120] Subsequently, the prepared battery was further subjected to charge / discharge through the following steps.

[0121] (7) Constant current charging: charging current 1C, charging end voltage 4.6V;

[0122] (8) Constant voltage charging: charging voltage 4.6V, charging end current 0.05C;

[0123] (9) Constant current discharge: discharge current 2.5C, discharge end voltage 3V.

[0124] The ratio of the discharge capacity at a discharge current of 1 C to the discharge capacity at a discharge current of 2.5 C was determined as a percentage and expressed as high-rate discharge characteristics (%).

[0125] The calculated high-rate discharge characteristics were evaluated according to the following criteria: A higher value indicates better high-rate discharge characteristics.

[0126] A: High-rate discharge characteristics (%) are 90 or higher.

[0127] B: High-rate discharge characteristics (%) are 80 or more and less than 90.

[0128] C: High-rate discharge characteristics (%) are 70 or more and less than 80.

[0129] D: High rate discharge characteristics (%) is less than 70.

[0130] Test results

[0131] In Table 1, “ / ” indicates that the substance was not added;

[0132] As can be seen from Table 1, the positive electrode of the present application includes a positive electrode current collector and an insulating layer and a positive electrode material layer arranged on the positive electrode current collector; the insulating layer includes boehmite, the positive electrode material layer includes lithium cobalt oxide, the lithium cobalt oxide is doped with tungsten and tin elements, and the electrolyte includes vinylene carbonate, which can not only improve the short-circuit safety of the battery, but also improve the high-rate discharge characteristics.

[0133] In particular, the mass content ratio of tungsten element to tin element is 1:(0.5-0.9), which can further improve the short-circuit safety and high-rate discharge characteristics of the battery.

[0134] In particular, the electrolyte includes 1,3,6-hexanetricarboxylonitrile, which can further improve the short-circuit safety and high-rate discharge characteristics of the battery.

[0135] In particular, the electrolyte includes 1,2,3-tris(2-cyanoethoxy)propane, which can further improve the short-circuit safety and high-rate discharge characteristics of the battery.

[0136] In particular, the electrolyte includes substance A, which can further improve the short-circuit safety and high-rate discharge characteristics of the battery.

[0137] In particular, the insulating layer includes polyvinylidene fluoride and N-methylpyrrolidone, which can further improve the short-circuit safety and high-rate discharge characteristics of the battery.

[0138] In particular, the electrolyte includes 4-bromophenyl isocyanate, and the amount of 4-bromophenyl isocyanate is 0.03 to 0.7 parts by mass relative to 100 parts by mass of the electrolyte, which can further improve the short circuit safety and high rate discharge characteristics of the battery.

[0139] In particular, the electrolyte includes diethoxyphosphonoisocyanate, and the amount of diethoxyphosphonoisocyanate is 0.01 to 3 parts by mass relative to 100 parts by mass of the electrolyte, which can further improve the short circuit safety and high rate discharge characteristics of the battery.

[0140] In particular, the electrolyte includes 4-bromophenyl isocyanate and diethoxyphosphonoisocyanate, relative to 100 parts by mass of the electrolyte, 4-bromophenyl isocyanate is a part by mass, diethoxyphosphonoisocyanate is b parts by mass, and 0.01≤a / b≤0.95 can further improve the battery short-circuit safety and high-rate discharge characteristics.

[0141] References throughout the specification to “an embodiment,” “some embodiments,” “one embodiment,” “another example,” “an example,” “a specific example,” or “a portion of an example” mean that at least one embodiment or example in the present application includes the specific features, structures, materials, or characteristics described in that embodiment or example. Therefore, descriptions appearing throughout the specification, such as, for example, “in some embodiments,” “in an embodiment,” “in one embodiment,” “in another example,” “in an example,” “in a specific example,” or “an example,” are not necessarily references to the same embodiment or example in the present application. In addition, the specific features, structures, materials, or characteristics in the present application may be combined in any suitable manner in one or more embodiments or examples.

[0142] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the present application.

Claims

1. A secondary battery comprising: A positive electrode, a negative electrode and an electrolyte, characterized in that the positive electrode comprises a positive electrode current collector and an insulating layer and a positive electrode material layer arranged on the positive electrode current collector; the insulating layer comprises boehmite, the positive electrode material layer comprises lithium cobalt oxide, and the electrolyte comprises vinylene carbonate; The electrolyte further includes substance A, and the substance A includes at least one of succinonitrile, adiponitrile, ethylene glycol di(propionitrile) ether, lithium monofluorophosphate, 1,2-bis(difluorophosphine oxide)ethane, 1,2-bis(difluorophosphine oxide)propane, 1,2-bis(difluorophosphine oxide)butane, lithium fluorosulfonate, 1,3-propane sultone or vinyl sulfate.

2. The secondary battery according to claim 1, characterized in that: The lithium cobalt oxide includes tungsten and tin.

3. The secondary battery according to claim 2, characterized in that: The mass content ratio of the tungsten element to the tin element is 1:(0.5-0.9).

4. The secondary battery according to any one of claims 1 to 3, characterized in that: The electrolyte includes 1,3,6-hexanetricarboxylonitrile, wherein the 1,3,6-hexanetricarboxylonitrile is in an amount of 0.1 to 1 parts by mass relative to 100 parts by mass of the electrolyte.

5. The secondary battery according to any one of claims 1 to 3, characterized in that: The electrolyte solution includes 1,2,3-tris(2-cyanoethoxy)propane, wherein the 1,2,3-tris(2-cyanoethoxy)propane is in an amount of 0.01 parts by mass to 1.5 parts by mass relative to 100 parts by mass of the electrolyte solution.

6. The secondary battery according to any one of claims 1 to 3, characterized in that: The insulating layer comprises polyvinylidene fluoride and N-methylpyrrolidone.

7. The secondary battery according to any one of claims 1 to 3, characterized in that: The electrolyte solution includes 4-bromophenyl isocyanate, and the amount of the 4-bromophenyl isocyanate is 0.03 parts by mass to 0.7 parts by mass relative to 100 parts by mass of the electrolyte solution.

8. The secondary battery according to any one of claims 1 to 3, characterized in that: The electrolyte solution includes diethoxyphosphonic acid ester, and the diethoxyphosphonic acid ester is present in an amount of 0.01 parts by mass to 3 parts by mass relative to 100 parts by mass of the electrolyte solution.

9. The secondary battery according to any one of claims 1 to 3, characterized in that: The electrolyte comprises 4-bromophenyl isocyanate and diethoxyphosphonic acid ester. Relative to 100 parts by mass of the electrolyte, the 4-bromophenyl isocyanate is a part by mass, the diethoxyphosphonic acid ester is b parts by mass, and 0.01≤a / b≤0.

95.

10. An electronic device, characterized in that: It includes the secondary battery according to any one of claims 1 to 9.

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