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 including: a positive electrode, a negative electrode, and an electrolyte, the positive electrode including a positive electrode current collector and a positive electrode material disposed on the positive electrode current collector, the positive electrode material including lithium cobaltate, the electrolyte including methylene methanedisulfonate and propenyl-1,3-sultone, and the sum of the methylene methanedisulfonate and the propenyl-1,3-sultone being 0.02 to 3.5 parts by mass with respect to 100 parts by mass of the electrolyte. The present application can improve the overcurrent and overtemperature safety of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of energy storage, specifically to a secondary battery and electronic device. Background Technology

[0002] As one of the most commercially successful research directions, rechargeable batteries are facing increasing market demands for performance as electronic products and electric vehicles are updated and iterated.

[0003] Specifically, the diversification of product usage scenarios poses increasing challenges to the safety of secondary batteries. The fast pace of urban life has led to higher expectations for the over-temperature and over-current safety of secondary batteries. Therefore, the positive electrode, negative electrode, and electrolyte, as crucial components of secondary batteries, bear the responsibility of improving battery safety. Improving the materials of the positive electrode, negative electrode, and electrolyte, and exploring the compatibility between these components, has become a highly valuable research direction. Summary of the Invention

[0004] This application improves the overcurrent and overtemperature safety of a secondary battery by regulating the positive electrode material and electrolyte in the secondary battery. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The inventors of this application discovered that the positive electrode includes a positive electrode current collector and a positive electrode material disposed on the positive electrode current collector. The positive electrode material includes lithium cobalt oxide. The electrolyte includes methylene methane disulfonate and propylene-1,3-sulfonate lactone. Relative to 100 parts by mass of the electrolyte, the sum of methylene methane disulfonate and propylene-1,3-sulfonate lactone is 0.02 to 3.5 parts by mass, which can improve the overcurrent and overtemperature safety of the battery, thus completing this application.

[0005] In some embodiments, methylene methane disulfonate is 0.02 to 2 parts by weight and propylene-1,3-sulfonyl lactone is 0.02 to 1.5 parts by weight relative to 100 parts by weight of electrolyte.

[0006] In some embodiments, methylene methane disulfonate is present in amounts of 0.05 to 0.8 parts by weight relative to 100 parts by weight of electrolyte, and propylene-1,3-sulfonyl lactone is present in amounts of 0.02 to 0.7 parts by weight.

[0007] In some embodiments, the cathode material also includes molybdenum and iron.

[0008] In some embodiments, the molybdenum content is between 100 ppm and 2000 ppm by mass, and the iron content is between 100 ppm and 3000 ppm by mass, depending on the mass of the cathode material.

[0009] In some embodiments, the cathode material also includes antimony, with the antimony content ranging from 100 ppm to 2000 ppm based on the mass of the cathode material.

[0010] In some embodiments, the mass ratio of molybdenum, iron and antimony is (1-5):(0.1-1):1.

[0011] In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode material disposed on the negative electrode current collector, the negative electrode material including a silicon-based material.

[0012] In some embodiments, the silicon-based material includes a composite of silicon-based and carbon-based materials.

[0013] In another aspect of this application, an electronic device is provided that includes the secondary battery described in this application.

[0014] This application improves the overcurrent and overtemperature safety of secondary batteries through a specific combination of positive electrode and electrolyte.

[0015] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Detailed Implementation

[0016] The embodiments of this application will be described in detail below. These embodiments should not be construed as limiting the scope of this application.

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

[0018] This application improves the overcurrent and overtemperature safety of secondary batteries by using a preset positive electrode and a preset electrolyte.

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

[0020] electrolyte

[0021] This application relates to a secondary battery and an electronic device. Specifically, this application provides a secondary battery comprising: a positive electrode, a negative electrode, and an electrolyte. The electrolyte used in the secondary battery of this application comprises an electrolyte and a solvent for dissolving the electrolyte. The electrolyte comprises methylene methanedisulfonate and propylene-1,3-sulfonyl lactone, wherein the sum of methylene methanedisulfonate and propylene-1,3-sulfonyl lactone is 0.02 to 3.5 parts by mass relative to 100 parts by mass of the electrolyte. The positive electrode comprises a positive electrode current collector and a positive electrode material disposed on the positive electrode current collector, wherein the positive electrode material comprises lithium cobalt oxide.

[0022] The methane disulfonate and propylene-1,3-sulfonate lactone in the secondary battery of this application can stabilize the interface layer between the positive electrode and the electrolyte in the lithium cobalt oxide system, thereby improving the overcurrent and overtemperature safety of the secondary battery.

[0023] Specifically, from the perspective of improving the overcurrent and overtemperature safety of secondary batteries, the proportions of methylene methane disulfonate (Methylene ester) and propylene-1,3-sulfonyl lactone (MnO) are 0.02 to 2 parts by mass and 0.02 to 1.5 parts by mass, respectively, relative to 100 parts by mass of electrolyte. Meeting these conditions helps to further improve overcurrent and overtemperature safety.

[0024] Specifically, relative to 100 parts by weight of electrolyte, methylene methane disulfonate comprises 0.05 to 0.8 parts by weight, and propylene-1,3-sulfonyl lactone comprises 0.02 to 0.7 parts by weight. Meeting these conditions helps to further improve overcurrent and overtemperature safety.

[0025] In some embodiments, the electrolyte contains one or more of the following substances: 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, methyl fluorosulfonate, ethyl trifluoromethanesulfonate, methyl methanesulfonate, ethyl methanesulfonate, and dimethanesulfonic acid. Butyl acetate, methyl 2-(methanesulfonyloxy)propionate, ethyl 2-(methanesulfonyloxy)propionate, 1-fluoro-1,3-propanesulfonic acid lactone, 2-fluoro-1,3-propanesulfonic acid lactone, 3-fluoro-1,3-propanesulfonic acid lactone, 1-methyl-1,3-propanesulfonic acid lactone, 2-methyl-1,3-propanesulfonic acid lactone, 3-methyl-1,3-propanesulfonic acid lactone, 2-propene-1,3-sulfonic acid lactone, 1-fluoro-1-propene-1,3-sulfonic acid lactone, 2-fluoro-1-propene-1,3-sulfonic acid lactone, 3-fluoro-1-propene-1,3-sulfonic acid lactone, 1,3-Synolactone, 1-Fluoro-2-propen-1,3-Synolactone, 2-Fluoro-2-propen-1,3-Synolactone, 3-Fluoro-2-propen-1,3-Synolactone, 1-Methyl-1-propen-1,3-Synolactone, 2-Methyl-1-propen-1,3-Synolactone, 3-Methyl-1-propen-1,3-Synolactone, 1-Methyl-2-propen-1,3-Synolactone, 2-Methyl-2-propen-1,3-Synolactone, 3-Methyl-2-propen-1,3-Synolactone Oxylactone, 1,4-butyrolactone, 1,5-pentanesulfonate lactone, ethylene methanedisulfonate, dimethyl sulfite, methyl ethyl sulfite, lithium difluorophosphate, 1,2-ethylene glycol 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, and 1,5-pentanediol sulfite, etc.

[0026] In some embodiments, the electrolyte further includes an ionizable lithium salt, which includes at least one selected from LiPF6, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, CF3SO3Li, LiC(CF3SO2)3, and LiC4BO8. For example, the lithium salt used in the electrolyte of this application includes LiPF6, and the mass percentage of LiPF6 is 9% to 15%, preferably 9% to 13%, and more preferably 9% to 12%, based on the mass of the electrolyte. Meeting the above conditions can further improve the overcurrent and overtemperature safety of the secondary battery.

[0027] In some embodiments, the electrolyte further includes at least one of lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate borate) (LiBOB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0028] In some embodiments, the additives in the electrolyte also include at least one of fluoroether compounds, fluorocarbonate compounds and ether nitrile compounds, such as hydrofluoroether (HFE-458), fluoroethylene carbonate (FEC), etc.

[0029] In some embodiments, the electrolyte may also include a non-aqueous solvent. The non-aqueous solvent may be selected from carbonate compounds, carboxylic acid ester compounds, ether compounds, phosphate ester compounds, other organic solvents, or combinations thereof.

[0030] Optionally, the carbonate compound may be a chain 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.

[0031] Specifically, examples of chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene 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.

[0032] Specifically, examples of carboxylic acid ester compounds are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonic acid lactone, caprolactone, methyl formate, or combinations thereof.

[0033] Specifically, examples of ether compounds are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or combinations thereof.

[0034] Specifically, examples of phosphate ester compounds are trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or combinations thereof.

[0035] Specifically, examples of other organic solvents include dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methylpyrrolidone, formamide, dimethylformamide, acetonitrile, or combinations thereof.

[0036] positive electrode

[0037] The positive electrode includes a positive current collector and a positive electrode material disposed on the surface of the positive current collector. The positive electrode material includes lithium cobalt oxide.

[0038] The cathode material can be one or more layers. Each layer in a multilayer cathode material can contain the same or different cathode active materials. The cathode active material is any material capable of reversibly inserting and deintercalating lithium ions.

[0039] Specifically, from the perspective of improving the overcurrent and overtemperature safety of secondary batteries, cathode materials also include molybdenum and iron. Meeting these conditions can further improve the overcurrent and overtemperature safety of secondary batteries.

[0040] Specifically, from the perspective of improving the overcurrent and overtemperature safety of secondary batteries, based on the quality of the cathode material, the molybdenum content should be between 100 ppm and 2000 ppm, and the iron content should be between 100 ppm and 3000 ppm. Meeting these conditions can further improve the overcurrent and overtemperature safety of secondary batteries.

[0041] Specifically, from the perspective of improving the overcurrent and overtemperature safety of secondary batteries, the cathode material also includes antimony, with the antimony content ranging from 100 ppm to 2000 ppm based on the mass of the cathode material. Meeting these conditions can further improve the overcurrent and overtemperature safety of secondary batteries.

[0042] Specifically, from the perspective of improving the overcurrent and overtemperature safety of secondary batteries, the mass ratio of molybdenum, iron, and antimony should be (1–5):(0.1–1):1. Meeting this condition can further improve the overcurrent and overtemperature safety of secondary batteries.

[0043] In some embodiments, 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 include, but are not limited to, acetylene black, carbon black such as Super-P, amorphous carbon such as needle coke, carbon nanotubes, and graphene. The above-mentioned positive electrode conductive materials can be used alone or in any combination.

[0044] There are no particular restrictions on the type of positive electrode binder used in the manufacture of positive electrode materials. In the case of coating method, any material that can be dissolved or dispersed in the liquid medium used in electrode manufacturing is acceptable. Examples of positive electrode adhesives may include, but are not limited to, one or more of the following: resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; thermoplastic elastomer-like polymers such as styrene-butadiene-styrene block copolymers or their hydrides, ethylene-propylene-diene terpolymers (EPDM), styrene-ethylene-butadiene-ethylene copolymers, and styrene-isoprene-styrene block copolymers or their hydrides; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymer compositions with ion conductivity of alkali metal ions (especially lithium ions). The above-mentioned positive electrode adhesive can be used alone or in any combination.

[0045] There are no restrictions on the type of solvent used to form the positive electrode slurry, as long as it can dissolve or disperse the positive electrode active material, conductive material, positive electrode binder, and thickener used as needed. Examples of solvents used to form the positive electrode slurry can include any of aqueous solvents and organic solvents. Examples of aqueous media include, but are not limited to, mixtures of alcohol and water or water. Examples of organic media 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 (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide.

[0046] Thickeners are typically used to adjust the viscosity of slurries. In the case of aqueous media, thickeners and styrene-butadiene rubber (SBR) latex can be used for slurry preparation. There are no particular limitations on the types of thickeners, and examples include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts. The above thickeners can be used alone or in any combination.

[0047] There are no particular limitations on the type of positive electrode current collector; it can be any material known to be suitable for use as a positive electrode current collector. Examples of positive electrode current collectors include, but are not limited to, metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metallic material. In some embodiments, the positive electrode current collector is aluminum.

[0048] To reduce the electronic contact resistance between the positive current collector and the positive electrode material, the surface of the positive current collector may include a conductive additive or a conductive coating. Examples of conductive additives include, but are not limited to, noble metals such as carbon, gold, platinum, and silver. Examples of conductive coatings may include a mixture layer containing inorganic oxides, conductive agents, and binders.

[0049] The positive electrode can be manufactured by forming a positive electrode material containing a positive electrode active material and a binder on a current collector. The manufacture of a positive electrode using a positive electrode active material can be carried out by conventional methods, namely, dry mixing the positive electrode active material, binder, and conductive materials and thickeners as needed, forming a sheet, and pressing the resulting sheet onto the positive electrode current collector; or dissolving or dispersing these materials in a liquid medium to form a slurry, coating the slurry onto the positive electrode current collector and drying it, thereby forming the positive electrode material on the current collector, thus obtaining the positive electrode.

[0050] negative electrode

[0051] The negative electrode includes a negative electrode current collector and a negative electrode material disposed on the surface of the negative electrode current collector.

[0052] In some embodiments, the rechargeable capacity of the negative electrode material is greater than the discharge capacity of the positive electrode material to prevent unintentional deposition of lithium metal on the negative electrode during charging.

[0053] In some embodiments, the anode material includes carbon-based anode materials, metal-based anode materials, and anode materials combining these.

[0054] Here, carbon-based anode materials refer to active materials with carbon as the main framework that can insert lithium. Examples of carbon-based anode materials include carbonaceous materials and graphitic materials.

[0055] Examples of carbonaceous materials include easily graphitized carbon and difficult-to-graphitize carbon. Among easily graphitized carbons are carbon materials derived from petroleum or coal using tar pitch as a raw material; specific examples include coke, mesophase carbon microspheres (MCMB), mesophase pitch-based carbon fibers, and pyrolysis-grown carbon fibers. Furthermore, examples of difficult-to-graphitize carbons include carbon materials with amorphous structures, such as glassy carbon; specific examples include phenolic resin sintered bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin sintered bodies (PFA), and hard carbon.

[0056] Further, examples of the graphite material include natural graphite and artificial graphite. Among them, examples of the artificial graphite include artificial graphite obtained by subjecting carbon containing graphitizable carbon to heat treatment mainly at 2800°C or higher, graphitic MCMB obtained by subjecting MCMB to heat treatment at 2000°C or higher, and graphitic mesophase pitch-based carbon fiber obtained by subjecting mesophase pitch-based carbon fiber to heat treatment at 2000°C or higher. In addition, in the present application, as the carbon-based negative electrode material, natural graphite with at least a part of its surface coated with amorphous carbon (amorphous-coated natural graphite) can be used.

[0057] In addition, the metal-based negative electrode material is an active material containing a metal, and generally refers to an active material that contains an element capable of intercalating lithium or alloying with lithium in its structure, and has a theoretical current capacity per unit mass of 500 mAh / g or more when intercalating lithium or alloying with lithium. As the metal-based negative electrode material, for example, lithium metal, elemental metals capable of forming lithium alloys (such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, and Ti) and their alloys, as well as their oxides, sulfides, nitrides, silicides, carbides, phosphides and the like can be used. Among them, as the metal-based negative electrode material, an active material containing silicon (silicon-based negative electrode material) is preferred. This is because the use of the silicon-based negative electrode material can increase the capacity of the secondary battery.

[0058] In some embodiments, the negative electrode material includes a silicon-based material.

[0059] In some embodiments, the silicon-based material includes at least one of a composite of a silicon-based substance and a carbon-based substance, and silicon oxide (SiOₓ, 0<x≤2). The silicon-based substance may be silicon particles, silicon alloy particles, and the like. The negative electrode material may further include a carbon material, and the carbon material may be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be graphite, such as amorphous, platy, flaky, spherical or fibrous natural graphite and / or artificial graphite, and the amorphous carbon may be soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0060] The composite of the silicon-based substance and the carbon-based substance may be a composite having a structure in which silicon nanoparticles are disposed on the carbon-based substance, a composite in which the silicon particles are included on the surface and inside of the carbon-based substance, and a composite in which the silicon particles are coated with the carbon-based substance and included in the carbon-based substance. In the composite of the silicon-based substance and the carbon-based substance, the carbon-based substance may be graphite, graphene, graphene oxide, or a combination thereof.

[0061] The composite of silicon-based and carbon-based materials can be an active material obtained by dispersing silicon nanoparticles with an average particle size of 200 nm or smaller on carbon-based material particles, and then coating them with carbon, active materials in which silicon (Si) particles exist on and inside graphite.

[0062] From the perspective of improving battery capacity, silicon-carbon materials are preferred, such as porous carbon-supported silicon composites.

[0063] In addition, a single negative electrode material can be used alone, or two or more materials can be used in any ratio.

[0064] The negative electrode material layer may also include a negative electrode binder. The negative electrode binder improves the bonding between negative electrode material particles and the bonding between the negative electrode material and the current collector. There are no particular limitations on the type of negative electrode binder, as long as it is a material stable to the electrolyte or the solvent used in electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluoropolymers, polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. When using an aqueous solvent to prepare the negative electrode slurry, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salts, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, and polyvinyl alcohol.

[0065] As the current collector for retaining the negative electrode material, any known current collector can be used. Examples of negative electrode current collectors include, but are not limited to, metallic materials such as copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode current collector is copper. In some embodiments, the negative electrode current collector is a composite current collector, namely a 12μm composite copper foil (commercially available, a composite current collector made by depositing metallic copper layers on both sides of polyethylene terephthalate (PET) as the base material using an advanced vacuum deposition process).

[0066] The negative electrode can be prepared by coating a negative electrode slurry containing negative electrode material, resin binder, etc. onto a negative electrode current collector, drying it, and then calendering it to form a negative electrode material layer on both sides of the negative electrode current collector, thereby obtaining the negative electrode.

[0067] Separating membrane

[0068] To prevent short circuits, a separator is typically placed between the positive and negative electrodes. In this case, the electrolyte of this application is typically used after penetrating into the separator.

[0069] There are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. The separator can be a resin, glass fiber, inorganic material, etc., formed from a material that stabilizes the electrolyte of this application. In some embodiments, the separator includes porous sheets with excellent liquid retention properties and non-woven fabric-like materials. Examples of materials for resin or glass fiber separators include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, and polyethersulfone. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned separator materials can be used alone or in any combination.

[0070] The separator can also be a material formed by laminating the above-mentioned materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in that order.

[0071] Examples of inorganic materials include, but are not limited to, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.). Inorganic materials may be in the form of, but are not limited to, particulates and fibrous materials.

[0072] The separator can be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, and microporous membranes. In the thin film form, the pore size of the separator is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In addition to the above-mentioned independent thin film separators, the following separators can also be used: separators formed by using a resin-based adhesive to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive and / or negative electrodes. For example, a separator formed by using fluororesin as an adhesive to form a porous layer of alumina particles with a particle size of less than 1 μm on both sides of the positive electrode.

[0073] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator is within the above ranges, insulation and mechanical strength can be ensured, as well as the DC resistance characteristics and energy density of the secondary battery.

[0074] This application also provides an electronic device that includes a secondary battery as described in this application.

[0075] The application of the secondary battery in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the secondary battery of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0076] The following examples illustrate embodiments of the secondary battery of this application, but this application is not limited to these embodiments. Unless otherwise stated, reagents, software, and instruments involved in the following examples that are not specifically described are all conventional commercially available products or open-source products.

[0077] Preparation of secondary batteries

[0078] 1. Positive Electrode Fabrication: The positive electrode material (97 wt%), conductive carbon black (1.5 wt%), and polyvinylidene fluoride (1.5 wt%) shown in Table 1 were dissolved in N-methylpyrrolidone and mixed to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil used as a positive electrode current collector. The aluminum foil was dried at 120°C to obtain a positive electrode sheet with an 80 μm thick positive electrode material layer coated on one side. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode material layer. The coated aluminum foil was dried, pressurized, and then cut to the specified size to fabricate the positive electrode.

[0079] 2. Separating membrane: A 12μm thick polyethylene (PE) microporous membrane is selected as the separating membrane.

[0080] 3. Anode Fabrication: The anode material shown in Table 1 (96 wt%) and styrene-butadiene rubber (2 wt%) are mixed and added to a solution obtained by dissolving lithium carboxymethyl cellulose (2 wt%) in deionized water. This mixture is then used to prepare the anode slurry. The anode slurry is coated onto one side of a copper foil, dried, pressure-treated, and then cut to the specified size to fabricate the anode. This application does not impose any particular limitations on the method for controlling the particle size of the anode material, as long as it achieves the purpose of this application. For example, anode materials of different particle sizes can be obtained through mechanical crushing, grinding, sieving, etc.

[0081] 4. Electrolyte preparation: In an argon atmosphere glove box with a water content of less than 10 ppm, fluoroethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate (dimethyl carbonate and methyl ethyl carbonate in a mass ratio of 1:0.5:4) are mixed to obtain a basic solvent. Then, lithium salt LiPF6 and methanedisulfonate and propylene-1,3-sulfonyl lactone in the amounts shown in Table 1 are added to the above basic solvent. After mixing evenly, the electrolyte is obtained. The mass content of LiPF6 is 15% based on the mass of the electrolyte.

[0082] 5. Battery Fabrication: The positive electrode, separator, and negative electrode are stacked sequentially, with the separator acting as a barrier between the positive and negative electrodes. The electrode assembly is then wound up. After welding the tabs, the electrode assembly is placed in an outer aluminum-plastic film package. Moisture is removed at 80°C, and the electrolyte is injected. Following vacuum sealing, settling, formation, shaping, and capacity testing, a lithium-ion battery is obtained. This secondary battery is a pouch-shaped device measuring 30mm wide, 45mm high, and 5mm thick.

[0083] Test methods

[0084] 1. Test method for over-temperature safety:

[0085] The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. The battery was then charged at a constant current of 0.7C to a voltage of 4.3V, followed by constant voltage charging at 4.3V to a current of 82.5mA. The thickness of the lithium-ion battery was measured and recorded as T0. The battery was then placed in a 60°C oven for 10 hours, removed from the oven, and cooled for 1 hour. The thickness of the lithium-ion battery was measured again and recorded as T1. The thickness of the lithium-ion battery in the oven was monitored in real time.

[0086] The over-temperature safety assessment is performed using the value X calculated by the following formula:

[0087] X = (T1 - T0) / T0 × 100%.

[0088] In the above formula, the smaller the value of X, the better the over-temperature safety of the secondary battery in this application. The batteries are graded (A to D) based on the test results of X, with the following grading criteria:

[0089] A: X is less than 12%;

[0090] B: X is 12% or more but less than 15%;

[0091] C: X is 15% or more but less than 20%;

[0092] D: X is greater than 20%.

[0093] 2. Overcurrent safety test method:

[0094] At a room temperature of 25°C, the secondary battery was charged with a constant current of 1C, increasing the state of charge (SOC) from 10% to 30%. Then, it was charged with a constant current of 1.5C, increasing the SOC from 30% to 60%. Finally, it was charged with a constant current of 2C, increasing the SOC from 60% to 90%. The temperature of the secondary battery was then monitored using a temperature measuring instrument.

[0095] The lower the measured temperature of the secondary battery, the better its performance. The secondary batteries are graded (A to D) based on their temperature test results, with the following grading criteria:

[0096] A: Temperature is less than 50℃;

[0097] B: The temperature is above 50℃ and below 55℃;

[0098] C: Temperature is above 55℃ and below 60℃;

[0099] D: Temperature greater than 60℃.

[0100] Test Results

[0101] Please refer to Table 1 for the above test results. In Table 1, " / " indicates that the substance was not added.

[0102] As shown in Table 1, the positive electrode of this application includes a positive electrode current collector and a positive electrode material disposed on the positive electrode current collector. The positive electrode material includes lithium cobalt oxide, and the electrolyte includes methylene disulfonate and propylene-1,3-sulfonyl lactone. Relative to 100 parts by mass of electrolyte, the sum of methylene disulfonate and propylene-1,3-sulfonyl lactone is 0.02 to 3.5 parts by mass, which can improve the overcurrent and overtemperature safety of the battery.

[0103] Table 1. Composition and performance test results of the secondary batteries of Examples 1-10 and Comparative Examples 1-4 of this application.

[0104]

[0105] Specifically, relative to 100 parts by weight of electrolyte, the presence of 0.02 to 2 parts by weight of methylene disulfonate and 0.02 to 1.5 parts by weight of propylene-1,3-sulfonyl lactone can further improve the overcurrent and overtemperature safety of the secondary battery.

[0106] Specifically, relative to 100 parts by weight of electrolyte, the presence of 0.05 to 0.8 parts by weight of methylene disulfonate and 0.02 to 0.7 parts by weight of propylene-1,3-sulfonyl lactone can further improve the overcurrent and overtemperature safety of the secondary battery.

[0107] In particular, the cathode material also includes molybdenum and iron, which can further improve the overcurrent and overtemperature safety of the secondary battery.

[0108] Specifically, based on the quality of the cathode material, the molybdenum content is 100ppm to 2000ppm and the iron content is 100ppm to 3000ppm, which can further improve the overcurrent and overtemperature safety of the secondary battery.

[0109] In particular, the cathode material also includes antimony. Based on the mass of the cathode material, the antimony content ranges from 100 ppm to 2000 ppm, which can further improve the overcurrent and overtemperature safety of the secondary battery.

[0110] In particular, the mass ratio of molybdenum, iron and antimony is (1-5):(0.1-1):1, which can further improve the overcurrent and overtemperature safety of the secondary battery.

[0111] In particular, the negative electrode material includes silicon-based materials, which can further improve the overcurrent and overtemperature safety of the secondary battery.

[0112] In particular, silicon-based materials, including composites of silicon and carbon-based substances, can further improve the overcurrent and overtemperature safety of secondary batteries.

[0113] Throughout this specification, references to "embodiment," "partial embodiment," "one embodiment," "another example," "example," "specific example," or "partial example" mean that at least one embodiment or example in this application includes a specific feature, structure, material, or characteristic described in that embodiment or example. Therefore, descriptions appearing throughout this 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 embodiments or examples in this application. Furthermore, specific features, structures, materials, or characteristics in this application can be combined in any suitable manner in one or more embodiments or examples.

[0114] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can 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 includes a positive electrode current collector and a positive electrode material disposed on the positive electrode current collector. The positive electrode material includes lithium cobalt oxide, which is doped with molybdenum and iron. Based on the mass of the positive electrode material, the mass content of molybdenum is 100 ppm to 2000 ppm, and the mass content of iron is 100 ppm to 3000 ppm. The electrolyte comprises methylene methane disulfonate and propylene-1,3-sulfonyl lactone, wherein the sum of methylene methane disulfonate and propylene-1,3-sulfonyl lactone is 0.02 to 3.5 parts by mass relative to 100 parts by mass of the electrolyte.

2. The secondary battery according to claim 1, characterized in that, Relative to 100 parts by weight of the electrolyte, the methylene disulfonate is 0.02 to 2 parts by weight, and the propylene-1,3-sulfonyl lactone is 0.02 to 1.5 parts by weight.

3. The secondary battery according to claim 1, characterized in that, Relative to 100 parts by weight of the electrolyte, the methylene disulfonate is 0.05 to 0.8 parts by weight, and the propylene-1,3-sulfonyl lactone is 0.02 to 0.7 parts by weight.

4. The secondary battery according to claim 1, characterized in that, The cathode material also includes antimony, and the mass content of antimony is between 100 ppm and 2000 ppm, depending on the mass of the cathode material.

5. The secondary battery according to claim 4, characterized in that, The mass ratio of the molybdenum, iron, and antimony elements is (1~5):(0.1~1):

1.

6. The secondary battery according to any one of claims 1 to 3, characterized in that, The negative electrode includes a negative electrode current collector and a negative electrode material disposed on the negative electrode current collector, wherein the negative electrode material includes a silicon-based material.

7. The secondary battery according to claim 6, characterized in that, The silicon-based materials include composites of silicon-based substances and carbon-based substances.

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

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