Secondary batteries and electronic devices

Abstract

The present application relates to a secondary battery and an electronic device. Specifically, the present application provides a secondary battery, which includes: a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode includes a positive electrode current collector and an insulating layer and a positive electrode material layer disposed on the positive electrode current collector; the insulating layer includes boehmite, the positive electrode material layer includes a nickel-cobalt-manganese ternary material, and the electrolyte includes at least two dinitrile compounds. The present application can not only improve the short-circuit safety of the battery, but also reduce high-temperature gas production.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and in particular to a secondary battery and an electronic device. Background Art

[0002] Secondary batteries have been widely used in portable electronic devices, electric vehicles and other fields due to their high energy density and ability to be repeatedly charged and discharged, and are gaining more and more 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 positive electrodes, negative electrodes, separators, and electrolytes has been ongoing, and people have an increasing demand for the performance of secondary batteries, especially safety in special environments (e.g., high temperatures). Summary of the invention

[0003] The embodiments of the present application further improve safety by adjusting the composition of the positive electrode and electrolyte in the secondary battery. The inventors of the present application found that the positive electrode includes a positive electrode current collector and an insulating layer and a positive electrode material layer disposed on the positive electrode current collector; the insulating layer includes boehmite, the positive electrode material layer includes a nickel-cobalt-manganese ternary material, and the electrolyte includes at least two dinitrile compounds, which can not only improve the short-circuit safety of the battery, but also reduce high-temperature gas production, thereby completing the present application.

[0004] In some embodiments, the nickel-cobalt-manganese ternary material includes strontium and zirconium.

[0005] In some embodiments, the mass content ratio of strontium element to zirconium element is 1:(2000-3000).

[0006] In some embodiments, the dinitrile compound is selected from at least two of succinonitrile, adiponitrile, ethylene glycol di(propionitrile) ether, or 1,4-dicyano-2-butene.

[0007] In some embodiments, the dinitrile compound includes succinonitrile and adiponitrile, wherein the amount of succinonitrile is 0.1 to 1 parts by mass, and the amount of adiponitrile is 0.01 to 1.5 parts by mass relative to 100 parts by mass of the electrolyte.

[0008] In some embodiments, the electrolyte further includes a substance A, and the substance A includes at least one of vinylene carbonate, 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 ammonium perfluorooctanoate, and the amount of ammonium perfluorooctanoate 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 silver hexafluorophosphate, and the amount of silver hexafluorophosphate is 0.01 parts by mass to 3 parts by mass relative to 100 parts by mass of the electrolyte.

[0012] In another aspect of the present application, the present application provides an electronic device, which includes the secondary battery described in the present application.

[0013] The present application not only improves the short-circuit safety of the battery but also reduces high-temperature gas generation by using a combination of a specific positive electrode and an electrolyte.

[0014] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the subsequent description through implementation of the embodiments of the present application. DETAILED DESCRIPTION

[0015] 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.

[0016] Unless expressly stated otherwise, the following terms used in this application have the meanings indicated below.

[0017] The present application not only improves the short-circuit safety of the battery but also reduces high-temperature gas generation by using a specific combination of a positive electrode and an electrolyte.

[0018] In one embodiment, the present application provides a secondary battery, which includes a positive electrode, a negative electrode, and an electrolyte as described below.

[0019] I. Positive electrode

[0020] The present application relates to a secondary battery and an electronic device. Specifically, the present application provides a secondary battery, which includes: a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode includes a positive electrode current collector and an insulating layer and a positive electrode material layer disposed on the positive electrode current collector; the insulating layer includes boehmite, the positive electrode material layer includes a nickel-cobalt-manganese ternary material, and the electrolyte includes at least two dinitrile compounds. The present application can not only improve the short-circuit safety of the battery, but also reduce high-temperature gas production.

[0021] The positive electrode material layer contains nickel, cobalt and manganese ternary material, and the positive electrode material layer can be one layer or multiple layers.

[0022] The inventors of the present application unexpectedly discovered in experiments that the positive electrode material layer comprising the nickel-cobalt-manganese ternary material and the insulating layer comprising boehmite can cooperate with each other to produce a binding effect that is superior to that of a conventional positive electrode system. The inventors further discovered that the positive electrode system can improve the short-circuit safety of the battery and reduce high-temperature gas production in an electrolyte system containing at least two dinitrile compounds. It is speculated that the reason may be that the cyanide groups in the at least two dinitrile compounds are tightly combined with the positive electrode system in the presence of the orthorhombic crystal system of boehmite and the specific unit cell edge angles in the crystal structure of the nickel-cobalt-manganese ternary material, thereby enhancing the cohesion of the positive electrode material layer and the binding force with the current collector, which can not only improve the short-circuit safety of the battery, but also reduce high-temperature gas production.

[0023] Specifically, from the perspective of improving battery short-circuit safety and reducing high-temperature gas production, lithium cobalt oxide includes strontium and zirconium. From the perspective of improving battery short-circuit safety, the mass content ratio of strontium and zirconium is 1:(2000-3000), preferably 1:(2200-2700), and more preferably 1:2500. When the mass content ratio of strontium and zirconium meets the above range, the battery short-circuit safety and high-temperature gas production can be further improved.

[0024] Specifically, from the perspective of improving battery short circuit safety and reducing high temperature gas production, in some embodiments, based on the mass of the positive electrode material layer, the mass content of strontium element is 1 ppm to 500 ppm, such as 1 ppm, 2 ppm, 3 ppm, 4 ppm, 5 ppm, 6 ppm, 7 ppm, 8 ppm, 9 ppm, 10 ppm, 80 ppm, 170 ppm, 240 ppm, 330 ppm, 390 ppm, 500 ppm or a value in the range of any two thereof. In some embodiments, from the perspective of improving battery short circuit safety and reducing high temperature gas production, based on the mass of the positive electrode material layer, the mass content of zirconium element is 500 ppm to 25000 ppm, such as 500 ppm, 2000 ppm, 2700 ppm, 4100 ppm, 7200 ppm, 8200 ppm, 10600 ppm, 12600 ppm, 14700 ppm, 17700 ppm, 19400 ppm, 20200 ppm, 25000 ppm or a value in the range of any two thereof.

[0025] 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 4.6V (vs.Li / Li + )above.

[0026] There is no limitation on the type of positive electrode conductive material, and any known conductive material can be used. Examples of positive electrode conductive materials may include, but are not limited to, carbon black such as acetylene black; carbon materials such as amorphous carbon such as needle coke; carbon nanotubes; graphene, etc. The above positive electrode conductive materials may be used alone or in any combination.

[0027] 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, the conductive material, and the 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; non-protonic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide, etc.

[0028] 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 4 g / cm 3 In addition, the upper limit is preferably 4.6 g / cm 3 the following.

[0029] The type of positive electrode current collector is not particularly limited, and it can be any material known to be suitable for use as a positive electrode current collector. Examples of positive electrode current collectors may include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, 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.

[0030] In order 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 may include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. Examples of conductive coatings may include a mixture layer containing an inorganic oxide, a conductive agent, and a binder.

[0031] From the viewpoint of improving the short-circuit safety of the battery and reducing high-temperature gas generation, boehmite is contained in the insulating layer.

[0032] Specifically, from the viewpoint of improving the short-circuit safety of the battery and reducing high-temperature gas generation, the insulating layer includes polyvinylidene fluoride and N-methylpyrrolidone.

[0033] The positive electrode is made as follows:

[0034] Boehmite, polyvinylidene fluoride and N-methylpyrrolidone are mixed, and deionized water is added thereto and mixed evenly to prepare slurry 1.

[0035] 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 1-methyl-2-pyrrolidone is added thereto and kneaded to prepare a slurry 2 .

[0036] Slurry 1 and slurry 2 are applied in parallel on an aluminum foil or the like of a current collector, and then dried and pressed to form a positive electrode.

[0037] II. Electrolyte

[0038] 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 at least two dinitrile compounds.

[0039] In the present application, a dinitrile compound refers to an organic compound formed by connecting carbon atoms containing a hydrocarbon group and two cyano groups (-CN). When at least two dinitrile compounds are used in the secondary battery in the present application, the inventors found that the addition of the positive electrode nickel-cobalt-manganese ternary material and boehmite can not only improve the short-circuit safety of the battery, but also reduce high-temperature gas production.

[0040] Specifically, from the viewpoint of improving the battery short-circuit safety of the secondary battery and reducing high-temperature gas production, the dinitrile compound is selected from at least two of succinonitrile, adiponitrile, ethylene glycol di(propionitrile) ether or 1,4-dicyano-2-butene. Among them, relative to 100 parts by mass of the electrolyte, each dinitrile compound is 0.01 parts by mass or more, preferably 0.06 parts by mass or more, more preferably 0.13 parts by mass or more, and particularly preferably 0.5 parts by mass or more. In addition, from the viewpoint of improving the battery short-circuit safety of the secondary battery and reducing high-temperature gas production, each dinitrile compound is 2 parts by mass or less, preferably 1.6 parts by mass or less, more preferably 1.1 parts by mass or less, and further preferably 0.7 parts by mass or less.

[0041] Specifically, from the viewpoint of improving the battery short-circuit safety of the secondary battery and reducing high-temperature gas production, the dinitrile compound includes succinonitrile, wherein relative to 100 parts by mass of the electrolyte, succinonitrile is 0.1 parts by mass or more, preferably succinonitrile is 0.15 parts by mass or more, and more preferably 0.18 parts by mass or more. In addition, as the upper limit of the content of succinonitrile, from the viewpoint of improving the battery short-circuit safety of the secondary battery and reducing high-temperature gas production, succinonitrile 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. When within the above range, it helps to further improve the battery short-circuit safety of the secondary battery and reduce high-temperature gas production. The dinitrile compound also includes adiponitrile, wherein relative to 100 parts by mass of the electrolyte, adiponitrile is 0.01 parts by mass or more, preferably adiponitrile 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 adiponitrile, from the viewpoint of improving the battery short-circuit safety of the secondary battery and reducing high-temperature gas production, adiponitrile 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 of the secondary battery and reduce high-temperature gas production.

[0042] Specifically, in some embodiments, the electrolyte further includes substance A, and substance A includes at least one of vinylene carbonate, 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 perspective of improving the battery short-circuit safety of the secondary battery and reducing high-temperature gas production, 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.

[0043] Specifically, from the perspective of improving the battery short-circuit safety of the secondary battery and reducing high-temperature gas production, the electrolyte includes ammonium perfluorooctanoate. In some embodiments, relative to 100 parts by mass of the electrolyte, the ammonium perfluorooctanoate is a part by mass, and the value range of a is 0.01 to 2, for example, a is 0.01, 0.03, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1.1, 1.3, 1.6, 1.7, 2.0 or a value in the range composed of any two of them. When the mass fraction of ammonium perfluorooctanoate in the electrolyte is regulated to meet the above range, the battery short-circuit safety of the secondary battery can be further improved and high-temperature gas production can be reduced.

[0044] Specifically, from the perspective of improving the battery short-circuit safety of the secondary battery and reducing high-temperature gas production, the electrolyte includes silver hexafluorophosphate. In some embodiments, relative to 100 parts by mass of the electrolyte, the silver hexafluorophosphate 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 in the range composed of any two of them. When the mass fraction of silver hexafluorophosphate in the electrolyte is regulated to meet the above range, the battery short-circuit safety of the secondary battery can be further improved and high-temperature gas production can be reduced.

[0045] In some embodiments, the additive in the electrolyte includes one or more of the following: ethylene glycol sulfate, 1,2-propylene glycol sulfate, 1,3-propylene glycol sulfate, 1,2-butylene glycol sulfate, 1,3-butylene glycol sulfate, 1,4-butylene glycol 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 -1-fluoro-1-propylene-1,3-sultone, 1-fluoro-2-propylene-1,3-sultone, 2-fluoro-2-propylene-1,3-sultone, 3-fluoro-2-propylene-1,3-sultone, 1-methyl-1-propylene-1,3-sultone, 2-methyl-1-propylene-1,3-sultone, 3-methyl-1-propylene-1,3-sultone, 1-methyl-2-propylene-1,3-sultone, 2-methyl-2-propylene-1,3-sultone, 3-methyl-2-propylene-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-butylene glycol sulfite, 1,3-butylene glycol sulfite, 1,4-butylene glycol sulfite, 1,2-pentanediol sulfite, 1,3-pentanediol sulfite, 1,4-pentanediol sulfite, 1,5-pentanediol sulfite, etc.

[0046] 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, and the content of LiPF6 is 9-15% by mass, preferably 9-13% by mass, and more preferably 9-12% by mass based on the mass of the electrolyte. By setting the content range as above, the effects of improving the short-circuit safety of the battery and reducing high-temperature gas production can be more balanced.

[0047] 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).

[0048] 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.

[0049] 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.

[0050] Optionally, the carbonate compound may be a linear carbonate compound, a cyclic carbonate compound or a combination thereof. On the other hand, the carbonate compound may also be a fluorinated carbonate compound, a non-fluorinated carbonate compound or a combination thereof.

[0051] Specifically, examples of chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC) or combinations thereof. Examples of fluorinated carbonate compounds are 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 combinations thereof.

[0052] 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.

[0053] 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.

[0054] Specifically, examples of the phosphate compound are trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or a combination thereof.

[0055] 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.

[0056] III. Negative electrode

[0057] The negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on the surface of the negative electrode current collector, wherein the negative electrode material layer contains a negative electrode material. In some embodiments, the chargeable capacity of the negative electrode material is greater than the discharge capacity of the positive electrode material to prevent lithium metal from being accidentally precipitated on the negative electrode during charging.

[0058] 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 in combination thereof.

[0059] Carbon-based negative electrode materials

[0060] Here, the carbon-based negative electrode material refers to an active material having a carbon-based skeleton into which lithium can be inserted, and examples of the carbon-based negative electrode material include carbonaceous materials and graphite materials.

[0061] As carbonaceous materials, for example, graphitizable carbon, non-graphitizable carbon having a structure similar to an amorphous structure represented by glassy carbon, etc. can be cited. Here, as graphitizable carbon, for example, carbon materials obtained from petroleum or coal using tar pitch as a raw material can be cited. When giving specific examples, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, and pyrolysis vapor-grown carbon fibers can be cited. In addition, as non-graphitizable carbon, for example, phenolic resin sintered bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin sintered bodies (PFA), hard carbon, etc. can be cited.

[0062] Furthermore, as graphite materials, for example, natural graphite, artificial graphite, etc. can be cited. Among them, as artificial graphite, for example: artificial graphite obtained by heat-treating carbon containing graphitized carbon mainly at 2800°C or above, graphite MCMB obtained by heat-treating MCMB at 2000°C or above, graphite mesophase pitch-based carbon fiber obtained by heat-treating mesophase pitch-based carbon fiber at 2000°C or above, etc. can be cited. In addition, in the present application, as a carbon-based negative electrode material, natural graphite (amorphous coated natural graphite) in which at least a portion of its surface is coated with amorphous carbon can be used.

[0063] In addition, the metal-based negative electrode material is an active material containing a metal, generally referring to an active material having an element capable of inserting lithium or alloying with lithium in the structure, an element capable of inserting lithium or alloying 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 capable of forming a lithium alloy (such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) 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) containing silicon is preferably used. This is because the use of a silicon-based negative electrode material can increase the capacity of a secondary battery.

[0064] 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.

[0065] From the viewpoint of improving battery capacity, a silicon-carbon material, for example, a porous carbon-supported silicon composite material is preferred.

[0066] The negative electrode material may be used alone or in combination of two or more at any ratio.

[0067] Here, the volume average particle size of the negative electrode material is preferably 1 μm or more, more preferably 5 μm or more, preferably 30 μm or less, and more preferably 20 μm or less. If the volume average particle size of the negative electrode material is above the above lower limit, the heat generation during the internal short circuit can be effectively suppressed. In addition, if the volume average particle size of the negative electrode material is below the above upper limit, the increase in the initial resistance of the obtained battery can be effectively suppressed.

[0068] 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 solvent used in the electrolyte or 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.

[0069] 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.

[0070] 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, thereby obtaining a negative electrode.

[0071] IV. Isolation membrane

[0072] In order to prevent short circuit, 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 infiltrating the separator.

[0073] 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, polyether sulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above isolation membranes may be used alone or in any combination.

[0074] 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.

[0075] Examples of inorganic materials may include, but are not limited to, oxides such as aluminum oxide and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (eg, barium sulfate, calcium sulfate, etc.). The form of the inorganic material may include, but is not limited to, granular or fibrous.

[0076] The separator may be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, microporous films, etc. 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, the following separators can also be used: a separator formed by forming a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or the negative electrode using a resin-based adhesive, for example, a separator formed by using a fluororesin as an adhesive to form a porous layer on both sides of the positive electrode with alumina particles having a particle size of 90% less than 1 μm.

[0077] The thickness of the isolation film is arbitrary. In some embodiments, the thickness of the isolation film is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the isolation film is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the isolation film is within the above range, the insulation and mechanical strength can be ensured, and the DC resistance characteristics and energy density of the secondary battery can be ensured.

[0078] The present application further provides an electronic device, which includes the secondary battery described in the present application.

[0079] The use of the secondary battery of the present application is not particularly limited, and it can be used for 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 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.

[0080] Example

[0081] Examples of the secondary battery of the present application are shown below, but the present application is not limited to these examples.

[0082] Preparation of secondary batteries

[0083] Production of positive electrode:

[0084] 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.

[0085] The positive electrode material (97wt%) and conductive carbon black (1.5wt%) in Table 1 were mixed, and polyvinylidene fluoride (1.5wt%) was dissolved in N-methylpyrrolidone to obtain a solution and mixed to prepare positive electrode slurry 2. Among them, slurry 1 was applied on the ear side, and slurry 1 and slurry 2 were applied on the aluminum foil in parallel. The coated aluminum foil was dried, pressurized, and cut into a specified size to make a positive electrode.

[0086] Preparation of isolation membrane: A 12 μm thick polyethylene (PE) microporous membrane was selected as the isolation membrane.

[0087] Negative electrode production:

[0088] The negative electrode material artificial graphite and SiO2 (mass ratio 90:10): 96wt%, styrene-butadiene rubber: 2wt% are mixed, added to a solution obtained by dissolving carboxymethyl cellulose lithium: 2wt% in deionized water in advance and mixed to prepare a negative electrode slurry. The negative electrode slurry is coated on one side of a copper foil, dried, pressurized, and then cut into a specified size to make a negative electrode.

[0089] Preparation of electrolyte: In an argon atmosphere glove box with a water content of less than 10 ppm, ethyl methyl carbonate, ethyl acetate, and propylene carbonate are mixed in a mass ratio of 1:1:1 to obtain a basic solvent, and then lithium salt LiPF6 and the substances shown in Table 1 are added to the above-mentioned base solvent, and the mixture is evenly mixed to obtain an electrolyte, wherein the mass content of LiPF6 is 12% based on the mass of the electrolyte.

[0090] Battery production:

[0091] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and the electrode assembly is wound, and the electrode assembly is placed in the outer packaging aluminum plastic film after welding the pole ear, and the water is removed at 80°C, and the above electrolyte is injected, and the lithium ion battery is obtained after vacuum packaging, standing, formation, shaping, capacity testing and other processes. The secondary battery is a bag-shaped battery with a width of 30mm, a height of 45mm, and a thickness of 5mm.

[0092] Table 1

[0093]

[0094] Test Method

[0095] Battery short circuit safety

[0096] The test method is as follows:

[0097] The prepared secondary battery was charged according to the following conditions:

[0098] (1) Constant current charging: charging current is 1400mA (charging termination voltage is 4.3V); and

[0099] (2) Constant voltage charging: charging voltage is 4.3V (charging termination current is 100mA).

[0100] In an environment of 25°C, a round iron nail with a diameter of 2.5 mm was used to pierce one side of the charged battery at a speed of 5 mm / sec. Then, the temperature T of the short-circuit (nail pierced) position was measured 1 hour after the nail piercing.

[0101] The evaluation is performed using the following benchmarks. The smaller the value of temperature T, the more the insulating layer and electrolyte system in the present 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 nickel-cobalt-manganese ternary material in the present application and improve safety.

[0102] A: The value of temperature T is less than 80°C.

[0103] B: The value of the temperature T is 80°C or more and less than 100°C.

[0104] C: The value of the temperature T is 100°C or more and less than 130°C.

[0105] D: The value of the temperature T is 130° C. or higher.

[0106] High temperature gas production

[0107] The test method is as follows:

[0108] After the electrolyte is injected into the lithium-ion secondary battery, it is left to stand at a temperature of 20°C for 5 hours. Next, the battery cell voltage is charged to 4.3V by a constant current method at a temperature of 20°C and 0.2C, and then an aging treatment is performed at a temperature of 45°C for 12 hours. Afterwards, the electrode part of the battery cell (the laminated part of the positive electrode, separator and negative electrode) is pressurized at 25kPa for 1 minute, and then the gas retention area on the electrode is measured using an ultrasonic inspection system (JAPANPROBE. "NAUT21"). The gas retention area ratio (%) is obtained by dividing the gas retention area by the electrode area, and the evaluation is performed according to the following criteria. The smaller the gas retention area ratio, the less residual gas in the secondary battery.

[0109] A: The gas retention area ratio is less than 8%.

[0110] B: The gas retention area ratio is 8% or more and less than 20%.

[0111] C: The gas retention area ratio is 20% or more and less than 30%.

[0112] D: The gas retention area ratio is 30% or more.

[0113] Test Results

[0114] In Table 1, “ / ” indicates that the substance was not added;

[0115] It can be seen from Table 1 that the positive electrode of the present application includes a positive electrode collector and an insulating layer and a positive electrode material layer arranged on the positive electrode collector; the insulating layer includes boehmite, the positive electrode material layer includes a nickel-cobalt-manganese ternary material, and the electrolyte includes a dinitrile compound, which can not only improve the short-circuit safety of the battery, but also reduce high-temperature gas production.

[0116] In particular, the present application dopes strontium and zirconium into the nickel-cobalt-manganese ternary material, which can further improve the short-circuit safety of the battery and reduce high-temperature gas production.

[0117] In particular, the mass content ratio of strontium and zirconium is 1:(2000~3000), which can further improve the short-circuit safety of the battery and reduce high-temperature gas production.

[0118] In particular, the dinitrile compounds include succinonitrile, which can further improve the short-circuit safety of the battery and reduce high-temperature gas generation.

[0119] In particular, the dinitrile compound includes adiponitrile, which can further improve the short-circuit safety of the battery and reduce high-temperature gas generation.

[0120] In particular, the electrolyte includes substance A, which can further improve the short-circuit safety of the battery and reduce high-temperature gas generation.

[0121] In particular, the insulating layer includes polyvinylidene fluoride and N-methylpyrrolidone, which can further improve the short-circuit safety of the battery and reduce high-temperature gas generation.

[0122] In particular, the electrolyte includes ammonium perfluorooctanoate, and the amount of ammonium perfluorooctanoate 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 of the battery and reduce high temperature gas generation.

[0123] In particular, the electrolyte includes silver hexafluorophosphate, and the amount of silver hexafluorophosphate 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 of the battery and reduce high temperature gas generation.

[0124] In particular, the electrolyte includes ammonium perfluorooctanoate and silver hexafluorophosphate, relative to 100 parts by mass of the electrolyte, the ammonium perfluorooctanoate is a part by mass, the silver hexafluorophosphate is b parts by mass, and 0.01≤a / b≤0.95 can further improve the short circuit safety of the battery and reduce high temperature gas generation.

[0125] References to "embodiments", "partial embodiments", "one embodiment", "another example", "example", "specific example" or "partial example" throughout the specification mean that at least one embodiment or example in the present application includes the specific features, structures, materials or characteristics described in the embodiment or example. Therefore, descriptions appearing in various places throughout the specification, such as: "in some embodiments", "in an embodiment", "in one embodiment", "in another example", "in an example", "in a specific example" or "example", do not necessarily refer 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 one or more embodiments or examples in any suitable manner.

[0126] Although illustrative embodiments have been demonstrated 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 a nickel-cobalt-manganese ternary material, and the electrolyte comprises at least two dinitrile compounds; The doping elements of the nickel-cobalt-manganese ternary material include strontium and zirconium; the mass content ratio of the strontium element to the zirconium element is 1:(2000-3000); based on the mass of the positive electrode material layer, the mass content of the strontium element is 1ppm to 500ppm, and the mass content of the zirconium element is 500ppm to 25000ppm; Relative to 100 parts by mass of the electrolyte, each of the dinitrile compounds is 0.01 parts by mass to 2 parts by mass; The dinitrile compound is selected from at least two of succinonitrile, adiponitrile, ethylene glycol di(propionitrile) ether or 1,4-dicyano-2-butene.

2. The secondary battery according to claim 1, characterized in that: The dinitrile compound includes succinonitrile and adiponitrile, wherein the succinonitrile is in an amount of 0.1 to 1 parts by mass, and the adiponitrile is in an amount of 0.01 to 1.5 parts by mass relative to 100 parts by mass of the electrolyte.

3. The secondary battery according to claim 1, characterized in that: The electrolyte further comprises at least one of vinylene carbonate, lithium fluorosulfonate, 1,3-propane sultone or vinyl sulfate.

4. The secondary battery according to claim 1, characterized in that: The insulating layer comprises polyvinylidene fluoride and N-methylpyrrolidone.

5. The secondary battery according to claim 1, characterized in that: The electrolyte solution includes ammonium perfluorooctanoate, and the ammonium perfluorooctanoate is in an amount of 0.01 parts by mass to 2 parts by mass relative to 100 parts by mass of the electrolyte solution.

6. The secondary battery according to claim 1, characterized in that: The electrolyte solution includes silver hexafluorophosphate, and the silver hexafluorophosphate is present in an amount of 0.01 to 3 parts by mass relative to 100 parts by mass of the electrolyte solution.

7. An electronic device, characterized in that: It includes the secondary battery according to any one of claims 1 to 6.

Images