Secondary battery and electronic device

Abstract

The present application relates to a secondary battery and an electronic device. Specifically, the present application provides a secondary battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises a positive electrode current collector, and an insulating layer and a positive electrode material layer which are provided 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 present application can not only improve the short-circuit safety of the battery, but also reduce gas production at high temperature.

Description

Secondary battery and electronic device TECHNICAL FIELD

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

[0002] Secondary batteries have been widely used in portable electronic devices, electric vehicles and other fields due to their high energy density, repeated charging and discharging and other advantages, and are increasingly attracting attention. With the development of technology and the improvement of living standards, the use of secondary batteries in daily life is more diverse, and research on materials such as positive electrodes, negative electrodes, separators and electrolytes for secondary batteries has been ongoing. People's demand for the performance of secondary batteries, especially their safety in special environments (e.g., high temperatures), is increasing. SUMMARY

[0003] The present application adjusts the composition of the positive electrode and the electrolyte in the secondary battery to further improve the safety. The present inventors have 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 not only improves the short circuit safety of the battery, but also reduces high-temperature gas production, thereby completing the present application.

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

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

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

[0007] In some embodiments, the dinitrile compound includes butanedinitrile and hexanedinitrile, wherein the butanedinitrile is 0.1-1 parts by mass and the hexanedinitrile is 0.01-1.5 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 fluorosulfate, 1,3-propane sultone or ethylene 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 ammonium perfluorooctanoate is 0.03-0.7 parts by mass, relative to 100 parts by mass of the electrolyte.

[0011] In some embodiments, the electrolyte includes silver hexafluorophosphate, and the silver hexafluorophosphate is 0.01-3 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 including the secondary battery described in the present application.

[0013] The present application can not only improve the short circuit safety of the battery, but also reduce the high-temperature gas generation by using the combination of the specific positive electrode and the electrolyte.

[0014] Additional aspects and advantages of the embodiments of the present application will be described in part in the description that follows, will be apparent through the description, and will be learned from the practice of the embodiments of the present application. Embodiments of the present application

[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] The following terms used in the present application have the meanings indicated below, unless explicitly stated otherwise.

[0017] The present application can not only improve the short circuit safety of the battery, but also reduce the high-temperature gas generation by using the combination of the specific positive electrode and the electrolyte.

[0018] In one embodiment, the present application provides a secondary battery including 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 including a positive electrode, a negative electrode, and an electrolyte, the positive electrode including 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 including boehmite, the positive electrode material layer including a nickel-cobalt-manganese ternary material, and the electrolyte including at least two dinitrile compounds. The present application can not only improve the short circuit safety of the battery, but also reduce the high-temperature gas generation.

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

[0022] The inventors of the present application have unexpectedly found that the positive electrode material layer containing a nickel-cobalt-manganese ternary material and the insulating layer containing boehmite can cooperate with each other to produce a better combination than a conventional positive electrode system, and further found 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, which is presumably because the cyanide groups in the at least two dinitrile compounds are closely combined with the positive electrode system in the case that the specific intercellular edge angle exists in the orthorhombic system of boehmite and the crystal structure of the nickel-cobalt-manganese ternary material, thereby enhancing the cohesion of the positive electrode material layer and the bonding force with the current collector, which not only can improve the short-circuit safety of the battery, but also can reduce high-temperature gas production.

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

[0024] Specifically, from the perspective of improving the short-circuit safety of the battery and reducing high-temperature gas production, in some embodiments, the mass content of strontium is 1 ppm to 500 ppm based on the mass of the positive electrode material layer, 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 within a range consisting of any two of them. In some embodiments, from the perspective of improving the short-circuit safety of the battery and reducing high-temperature gas production, the mass content of zirconium is 500 ppm to 25000 ppm based on the mass of the positive electrode material layer, 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 within a range consisting of any two of them.

[0025] As the voltage during charging, from the perspective of high-voltage, the positive electrode potential is preferably 4.4 V (vs. Li / Li + ) or more, more preferably 4.5 V (vs. Li / Li + ) or more, and particularly preferably 4.6 V (vs. Li / Li + ) or more.

[0026] The kind of the positive electrode conductive material is not limited, and any known conductive material can be used. Examples of the positive electrode conductive material can include, but are not limited to, carbon black such as acetylene black; amorphous carbon such as needle coke; and carbon materials; carbon nanotubes; graphene; and the like. The above-mentioned positive electrode conductive material can be used alone or in any combination.

[0027] The kind of the solvent used for forming the positive electrode slurry is not limited, as long as it is a solvent capable of dissolving or dispersing the positive electrode material, the conductive material, and the positive electrode binder. Examples of the solvent used for forming the positive electrode slurry can include any one of an aqueous solvent and an organic solvent. Examples of the aqueous medium can include, but are not limited to, water and a mixed medium composed of alcohol and water, and the like. Examples of the organic medium can 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.

[0028] The density of the active material layer of the positive electrode other than the current collector is generally 3.5 g / cm3or more, and preferably 4.0 g / cm3or more. 3 In order to further increase the capacity of the battery, it is preferable that the density of the active material layer of the positive electrode other than the current collector be 4.0 g / cm3or more. 3 In order to further increase the capacity of the battery, it is preferable that the density of the active material layer of the positive electrode other than the current collector be 4.0 g / cm3or more. 3 In order to further increase the capacity of the battery, it is preferable that the density of the active material layer of the positive electrode other than the current collector be 4.0 g / cm3or more.

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

[0030] In order to reduce the electronic contact resistance of the positive electrode current collector and the positive electrode material layer, the surface of the positive electrode current collector can include a conductive aid or a conductive coating. Examples of the conductive aid can include, but are not limited to, carbon and noble metals such as gold, platinum, and silver. Examples of the conductive coating can include a mixture layer containing inorganic oxides, a conductive agent, and a binder.

[0031] From the viewpoint of improving the safety of the battery against short circuit and reducing gas generation at high temperatures, the insulating layer contains boehmite.

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

[0033] The positive electrode is produced by:

[0034] Boehmite, polyvinylidene fluoride, N-methylpyrrolidone were mixed, deionized water was added thereto and mixed uniformly to prepare slurry 1.

[0035] The above positive electrode material, a conductive agent such as acetylene black, carbon black, and a binder such as polyvinylidene fluoride or polyacrylonitrile were mixed, a high-boiling solvent such as 1-methyl-2-pyrrolidone was added thereto and mixed to prepare slurry 2.

[0036] Slurry 1 and slurry 2 were applied in parallel on an aluminum foil or the like as 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 in which the electrolyte is dissolved. 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 containing a hydrocarbon group and two cyano groups (-CN) connected by a carbon atom. When at least two dinitrile compounds are used in the secondary battery in the present application, the inventors found that it not only improves the short circuit safety of the battery, but also reduces the high-temperature gas production under the addition of positive electrode nickel-cobalt-manganese ternary material and boehmite.

[0040] Specifically, from the point of view of improving the short circuit safety of the secondary battery and reducing the high-temperature gas production, the dinitrile compound is selected from at least two of succinonitrile, adiponitrile, ethylene glycol bis (propionitrile) ether or 1,4-dicyano-2-butene. Among them, 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, with respect to 100 parts by mass of electrolyte. In addition, from the point of view of improving the short circuit safety of the secondary battery and reducing the 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 the high-temperature gas generation, the dinitrile compound includes succinonitrile, wherein the succinonitrile is 0.1 parts by mass or more, preferably 0.15 parts by mass or more, and more preferably 0.18 parts by mass or more, with respect to 100 parts by mass of the electrolyte solution. In addition, from the viewpoint of improving the battery short circuit safety of the secondary battery and reducing the high-temperature gas generation, the upper limit of the content of the 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 it is within the above range, it is helpful to further improve the battery short circuit safety of the secondary battery and reduce the high-temperature gas generation. The dinitrile compound also includes adiponitrile, wherein the adiponitrile 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, with respect to 100 parts by mass of the electrolyte solution. In addition, from the viewpoint of improving the battery short circuit safety of the secondary battery and reducing the high-temperature gas generation, the upper limit of the content of the 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 it is within the above range, it is helpful to further improve the battery short circuit safety of the secondary battery and reduce the high-temperature gas generation.

[0042] Specifically, in some embodiments, the electrolyte solution further includes a substance A, the substance A including at least one of vinyl carbonate, lithium fluorosulfate (LiSO3F), 1,3-propane sultone, or ethylene sulfate. The 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, with respect to 100 parts by mass of the electrolyte solution. In addition, from the viewpoint of improving the battery short circuit safety of the secondary battery and reducing the high-temperature gas generation, the 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 viewpoint of improving the battery short circuit safety of the secondary battery and reducing the high-temperature gas generation, the electrolyte solution includes ammonium perfluorooctanoate. In some embodiments, the ammonium perfluorooctanoate is a parts by mass with respect to 100 parts by mass of the electrolyte solution, a is in the range of 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 within a range defined by any two of them. When the mass fraction of the ammonium perfluorooctanoate in the electrolyte solution is regulated to satisfy the above range, the battery short circuit safety of the secondary battery and the reduction of the high-temperature gas generation can be further improved.

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

[0045] In some embodiments, the additive in the electrolyte includes one or more of the following: ethylene glycol sulfate, 1,2-propanediol sulfate, 1,3-propanediol 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, methyl ethyl sulfate, diethyl sulfate, methyl fluorosulfonate, ethyl trifluoromethanesulfonate, methyl methanesulfonate, ethyl methanesulfonate, butyl dimethylsulfonate, methyl 2-(methylsulfonyloxy)propionate, ethyl 2-(methylsulfonyloxy)propionate, 1-fluoro-1,3-propanesultone, 2-fluoro-1,3-propanesultone, 3-fluoro-1,3-propanesultone, 1-methyl-1,3-propanesultone, 2-methyl-1,3-propanesultone, 3-methyl-1,3-propanesultone, 1-propenyl-1,3-propanesultone, 2-propenyl-1,3-propanesultone, 1-fluoro-1-propenyl-1,3-propanesultone, 2-fluoro-1-propenyl-1,3-propanesultone, 3-fluoro-1-propenyl-1,3-propanesultone, 1-fluoro-2-propenyl-1,3-propanesultone, 2-fluoro-2-propenyl-1,3-propanesultone, 3-fluoro-2-propenyl-1,3-propanesultone, 1-methyl-1-propenyl-1,3-propanesultone, 2-methyl-1-propenyl-1,3-propanesultone, 3-methyl-1-propenyl-1,3-propanesultone, 1-methyl-2-propenyl-1,3-propanesultone, 2-methyl-2-propenyl-1,3-propanesultone, 3-methyl-2-propenyl-1,3-propanesultone, 1,4-butanesultone, 1,5-pentanesultone, methanedisulfonate methylene, methanedisulfonate ethylene, dimethyl sulfite, methyl ethyl sulfite, diethyl sulfite, 1,2-ethanediol sulfite, 1,2-propanediol sulfite, 1,3-propanediol 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, and the like.

[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 LiPF6is 9 to 15 mass%, preferably 9 to 13 mass%, and more preferably 9 to 12 mass% based on the mass of the electrolyte. By setting the content within the above range, the effects of improving the short circuit safety of the battery and reducing the gas generation at high temperatures can be more balanced.

[0047] In some embodiments, the electrolyte further includes at least one of lithium difluorophosphate (LiPO2F2), lithium difluoro-oxalato-borate (LiDFOB), lithium bis-oxalato-borate (LiBOB), lithium tetrafluoroborate (LiBF4), lithium bis-trifluoromethanesulfonimide (LiTFSI), lithium bis-fluorosulfonimide (LiFSI).

[0048] In some embodiments, the additive in the electrolyte further includes at least one of a fluoro-ether compound, a fluoro-carbonate compound, an ether-nitrile compound, such as hydrofluoro-ether (HFE-458), fluoro-ethylene carbonate (FEC), ethylene glycol bis (propionitrile) ether (DENE), and the like.

[0049] In some embodiments, the electrolyte can further include a non-aqueous solvent. The non-aqueous solvent can be selected from a carbonate compound, a carboxylic acid ester compound, an ether compound, a phosphate compound, other organic solvents, or a combination thereof.

[0050] Alternatively, the carbonate compound can be a chain carbonate compound, a cyclic carbonate compound, or a combination thereof. On the other hand, the carbonate compound can also be a fluoro-carbonate compound, a non-fluoro-carbonate compound, or a combination thereof.

[0051] Specifically, examples of the chain carbonate compound are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), or combinations thereof. Examples of the fluoro carbonate compound 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-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, trifluoromethyl ethylene carbonate, or combinations thereof.

[0052] Specifically, examples of the carboxylic acid ester compound are methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decalactone, valerolactone, methylvaleronolactone, caprolactone, methyl formate, or combinations thereof.

[0053] Specifically, examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or combinations thereof.

[0054] Specifically, examples of the phosphoric acid ester compound are trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or combinations thereof.

[0055] Specifically, examples of the other organic solvent are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methylpyrrolidinone, formamide, dimethylformamide, acetonitrile, or combinations thereof.

[0056] III. Negative electrode

[0057] 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, the negative electrode material layer including 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 inadvertently depositing on the negative electrode during charging.

[0058] Further, as the negative electrode material, there are no particular limitations, and carbon-based negative electrode materials, metal-based negative electrode materials, silicon-based negative electrode materials, and negative electrode materials combining them, and the like can be cited.

[0059] Carbon-based negative electrode material

[0060] Here, the carbon-based negative electrode material refers to an active material that can intercalate lithium with a carbon-based skeleton, and as the carbon-based negative electrode material, for example, carbonaceous materials and graphitic materials can be given.

[0061] As the carbonaceous material, for example, easy graphitizable carbon, difficult graphitizable carbon having a structure similar to an amorphous structure represented by glassy carbon, and the like can be given. Here, as the easy graphitizable carbon, for example, carbon materials obtained from tar pitch as a raw material from petroleum or coal can be given. When a specific example is given, for example, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, and pyrolytic vapor grown carbon fibers can be given. Further, as the difficult graphitizable carbon, for example, phenol resin sintered bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin sintered bodies (PFA), hard carbon, and the like can be given.

[0062] Further, as the graphitic material, for example, natural graphite, artificial graphite, and the like can be given. Among them, as the artificial graphite, for example, artificial graphite obtained by heat-treating carbon containing easy graphitizable carbon at 2800°C or higher, graphitic MCMB obtained by heat-treating MCMB at 2000°C or higher, graphitic mesophase pitch-based carbon fibers obtained by heat-treating mesophase pitch-based carbon fibers at 2000°C or higher, and the like can be given. In addition, in the present application, as the carbon-based negative electrode material, natural graphite in which at least a part of the surface is covered with amorphous carbon (amorphous-coated natural graphite) can be used.

[0063] Further, the metal-based negative electrode material is an active material containing a metal, and generally refers to an active material containing an element capable of intercalating lithium or alloying with lithium in the structure, and having a theoretical current capacity of 500 mAh / g or more per unit mass in the case of intercalating lithium or alloying with lithium. As the metal-based negative electrode material, for example, lithium metal, elemental metals that can form lithium alloys (for example, Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, and the like), alloys thereof, and oxides, sulfides, nitrides, silicides, carbides, phosphides, and the like thereof can be used. Among them, as the metal-based negative electrode material, an active material containing silicon (silicon-based negative electrode material) is preferable. This is because the use of the silicon-based negative electrode material can allow the secondary battery to be high in capacity.

[0064] As the silicon-based negative electrode material, for example, silicon (Si), alloys containing silicon, SiO, SiO2, a composite of a silicon-containing material and a conductive carbon obtained by coating or compounding a silicon-containing material with a conductive carbon (silicon-carbon material) can be given.

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

[0066] In addition, the negative electrode material can be used singly or in combination of two or more kinds at an arbitrary ratio.

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

[0068] The negative electrode material layer can further include a negative electrode binder. The negative electrode binder can improve the binding between the negative electrode material particles and the binding between the negative electrode material and the current collector. The kind of the negative electrode binder is not particularly limited as long as it is a material stable to the electrolyte or the solvent used at the time of electrode production. In some embodiments, the negative electrode binder includes a resin binder. Examples of the resin binder include, but are not limited to, a fluorine resin, a polyacrylonitrile (PAN), a polyimide resin, an acrylic resin, a polyolefin resin, and the like. When the negative electrode binder is prepared using an aqueous solvent, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or a salt thereof, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, and the like.

[0069] As the current collector that holds the negative electrode material, a publicly known current collector can be arbitrarily used. Examples of the negative electrode current collector include, but are not limited to, a metal material such as copper, nickel, stainless steel, nickel-plated steel, and the like. In some embodiments, the negative electrode current collector is copper.

[0070] The negative electrode can be produced by coating a negative electrode binder slurry including a negative electrode material, a resin binder, and the like on a negative electrode current collector, drying, and then performing calendering to form a negative electrode material layer on both sides of the negative electrode current collector, whereby the negative electrode can be obtained.

[0071] IV. Separator

[0072] In order to prevent short circuit, a separator is generally provided between the positive electrode and the negative electrode. In this case, the electrolyte of the present application is generally used by permeating into the separator.

[0073] The material and shape of the separator film are not particularly limited as long as they do not significantly impair the effects of the present application. The separator film can be a resin, a glass fiber, an inorganic substance, or the like formed of a material stable to the electrolyte of the present application. In some embodiments, the separator film includes a porous sheet or a nonwoven fabric-like substance, or the like, which is excellent in liquid retention. Examples of the material of the resin or glass fiber separator film can include, but are not limited to, polyolefin, aramid, polytetrafluoroethylene, polyether sulfone, or the like. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned materials of the separator film can be used alone or in any combination.

[0074] The separator film can also be a material in which the above-mentioned materials are layered, examples of which include, but are not limited to, a three-layer separator film in which polypropylene, polyethylene, and polypropylene are layered in this order, or the like.

[0075] Examples of the material of the inorganic substance can include, but are not limited to, oxides such as alumina and silica, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate. The form of the inorganic substance can include, but is not limited to, a granular or fibrous form.

[0076] The shape of the separator film can be a film shape, examples of which include, but are not limited to, a nonwoven fabric, a woven fabric, a microporous film, or the like. In the film shape, the separator film has a pore diameter of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the above-mentioned independent film-like separator film, a separator film formed by forming a composite porous layer containing the above-mentioned inorganic substance particles on the surface of the positive electrode and / or the negative electrode using a resin-based adhesive, for example, a separator film in which 90% of alumina particles having a particle size of less than 1 μm are formed into a porous layer on both surfaces of the positive electrode using a fluororesin as an adhesive, can also be used.

[0077] The thickness of the separator film is arbitrary. In some embodiments, the thickness of the separator film is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator film is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator film is within the above-mentioned range, the insulating property and the mechanical strength can be ensured, and the direct current resistance property and the energy density of the secondary battery can be ensured.

[0078] The present application also provides an electronic device including the secondary battery according to 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 art. In some embodiments, the secondary battery of the present application can be used for, but not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copying machines, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, hand-held cleaners, portable CD players, mini-disc players, transceivers, electronic organizers, calculators, memory cards, portable audio players, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting appliances, toys, game machines, timepieces, power tools, flashlights, cameras, home-use large storage batteries, and lithium-ion capacitors, etc.

[0080] Embodiments

[0081] Hereinafter, embodiments of the secondary battery of the present application will be shown, but the present application is not limited to these embodiments.

[0082] Preparation of the secondary battery

[0083] Preparation of the positive electrode:

[0084] Boehmite 80 wt%, polyvinylidene fluoride 20 wt% were mixed and dissolved in N-methylpyrrolidone, deionized water was added thereto and mixed to prepare a positive electrode slurry 1.

[0085] The positive electrode material (97 wt%) in Table 1, conductive carbon black (1.5 wt%), and a solution obtained by dissolving polyvinylidene fluoride (1.5 wt%) in N-methylpyrrolidone were mixed to prepare a positive electrode slurry 2. The slurry 1 was coated on the tab side, and the slurry 1 and the slurry 2 were coated in parallel on an aluminum foil. The coated aluminum foil was dried, subjected to a pressure treatment, and then cut into a predetermined size to prepare a positive electrode.

[0086] Preparation of the separator: A 12 μm-thick polyethylene (PE) microporous membrane was used as a separator.

[0087] Preparation of the negative electrode:

[0088] Artificial graphite and SiO2 (mass ratio 90:10) 96 wt%, styrene-butadiene rubber 2 wt% were mixed, and added to a solution obtained by previously dissolving lithium carboxymethyl cellulose 2 wt% in deionized water and mixed to prepare a negative electrode slurry. The negative electrode slurry was coated on one side of a copper foil, dried, subjected to a pressure treatment, and then cut into a predetermined size to prepare a negative electrode.

[0089] Preparation of electrolyte: In an argon glove box with water content less than 10 ppm, methyl ethyl carbonate, ethyl acetate, propylene carbonate were mixed in a mass ratio of 1:1:1 to obtain a base solvent, then LiPF6 and the substances shown in Table 1 were added to the above base solvent, and the electrolyte was obtained after mixing uniformly, wherein the mass content of LiPF6 was 12% based on the mass of the electrolyte.

[0090] Battery preparation:

[0091] The positive electrode sheet, the separator, and the negative electrode sheet were sequentially stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, and the electrode assembly was obtained by winding. After welding the tab, the electrode assembly was placed in an outer packaging aluminum plastic film, and after removing the water at 80°C, the above electrolyte was injected. After vacuum packaging, standing, formation, shaping, capacity testing and other processes, a lithium ion battery was obtained. The secondary battery is a bag-shaped battery with a width of 30 mm, a height of 45 mm, and a thickness of 5 mm.

[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: the charging current was 1400 mA (the charging termination voltage was 4.3 V); and

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

[0100] At 25°C, a round iron nail with a diameter of 2.5 mm was used to puncture the charged battery from one side at a speed of 5 mm / sec. Then, the temperature T of the short-circuit (punctured by the nail) position was measured after 1 hour of puncture.

[0101] Evaluation was made by the following criteria. The smaller the value of temperature T, the more the insulating layer and the electrolyte system in the application can slow down the temperature fluctuation under extreme conditions (such as simulated short circuit), synergistically control the temperature rise of the secondary battery, help to reduce the thermal decomposition of the nickel-cobalt-manganese ternary material in the application, and improve the safety.

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

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

[0104] C: the value of the temperature T is 100°C or higher and lower than 130°C.

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

[0106] High-temperature gas generation

[0107] The test method is as follows:

[0108] The lithium ion secondary battery was left to stand for 5 hours at a temperature of 20°C after the electrolyte was injected. Subsequently, the battery was charged to a battery cell voltage of 4.3V at a temperature of 20°C and a constant current of 0.2C, and then, an aging treatment was performed for 12 hours at a temperature of 45°C. Thereafter, the electrode portion (the stacked body portion of the positive electrode, the separator, and the negative electrode) of the battery cell was pressurized for 1 minute at 25 kPa, and then, the gas retention area on the electrode was measured using an ultrasonic inspection system (NAUT21 manufactured by JAPAN PROBE). The gas retention area ratio (%) was obtained by dividing the gas retention area by the electrode area, and the evaluation was performed according to the following criteria. The smaller the gas retention area ratio, the less the amount of residual gas of 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 is not added;

[0115] As can be seen from Table 1, the positive electrode of the application includes a positive electrode current collector and an insulating layer and a positive electrode material layer provided 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 a dinitrile compound, which not only can improve the short circuit safety of the battery but also can reduce high-temperature gas generation.

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

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

[0118] In particular, the dinitrile compound includes butanedinitrile, 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 battery short circuit safety and reduce high-temperature gas generation.

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

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

[0122] In particular, the electrolyte includes ammonium perfluorooctanoate, and the ammonium perfluorooctanoate is 0.03 to 0.7 parts by mass with respect to 100 parts by mass of the electrolyte, which can further improve the battery short circuit safety and reduce high-temperature gas generation.

[0123] In particular, the electrolyte includes silver hexafluorophosphate, and the silver hexafluorophosphate is 0.01 to 3 parts by mass with respect to 100 parts by mass of the electrolyte, which can further improve the battery short circuit safety and reduce high-temperature gas generation.

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

[0125] The terms “an embodiment,” “one embodiment,” “some embodiments,” “another embodiment,” “exemplary embodiment,” “in an embodiment,” “in another embodiment,” “in one embodiment,” “in a particular embodiment,” or “in some embodiments” as may occur in the specification, indicate that the particular feature, structure, material, or characteristic being described is included in at least one embodiment or example of the application. Thus, the appearance of the phrases “in an embodiment,” “in one embodiment,” “in another embodiment,” “in some embodiments,” “in some examples,” “in one example,” “in a particular example,” or “in some examples” in various places in the specification are not necessarily referring to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples.

[0126] While the illustrative embodiments have been described and illustrated, it will be understood by those skilled in the art that the above-described embodiments are not the only arrangements that will be capable of embodying the application and that numerous modifications can be made to the embodiments without departing from the spirit, principles and scope of the 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.

2. The secondary battery according to claim 1, characterized by The nickel-cobalt-manganese ternary material comprises strontium elements and zirconium elements.

3. The secondary battery according to claim 2, characterized by The mass content ratio of the strontium elements and the zirconium elements is 1: (2000-3000).

4. The secondary battery according to any one of claims 1 to 3, characterized by The dinitrile compounds are selected from at least two of butanedinitrile, hexanedinitrile, ethylene glycol bis (propionitrile) ether or 1,4-dicyano-2-butene.

5. The secondary battery according to any one of claims 1 to 3, characterized by The dinitrile compounds comprise butanedinitrile and hexanedinitrile, wherein the butanedinitrile is 0.1-1 parts by mass and the hexanedinitrile is 0.01-1.5 parts by mass relative to 100 parts by mass of the electrolyte.

6. The secondary battery according to any one of claims 1 to 3, characterized by The electrolyte further comprises at least one of vinylene carbonate, lithium fluorosulfate, 1,3-propane sultone or ethylene sulfate.

7. The secondary battery according to any one of claims 1 to 3, characterized by The insulating layer comprises polyvinylidene fluoride and N-methylpyrrolidone.

8. The secondary battery according to any one of claims 1 to 3, characterized by The electrolyte comprises ammonium perfluorooctanoate, and the ammonium perfluorooctanoate is 0.01-2 parts by mass relative to 100 parts by mass of the electrolyte.

9. The secondary battery according to any one of claims 1 to 3, characterized by The electrolyte comprises silver hexafluorophosphate, and the silver hexafluorophosphate is 0.01-3 parts by mass relative to 100 parts by mass of the electrolyte.

10. An electronic device, comprising: The secondary battery comprises the secondary battery according to any one of claims 1-9.

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