Secondary battery and electronic apparatus

Abstract

A secondary battery and an electronic apparatus. Specifically, the secondary battery comprises: a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive electrode current collector and a positive electrode material arranged on the positive electrode current collector, and the positive electrode material comprises nickel, cobalt, manganese, aluminum, and iron, wherein based on the content of metallic elements other than lithium in the positive electrode material, the mass content of iron is 100 ppm to 2000 ppm, and a specific surface area of the positive electrode material is 1.2 m2 / g to 1.7 m2 / g; and the electrolyte comprises ethylene sulfate and lithium difluorophosphate. This not only improves battery cycle performance, but also improves safety.

Description

Secondary batteries and electronic devices Technical Field

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

[0002] Rechargeable batteries, a current hot topic in application and research, have been widely commercialized in portable electronic devices, electric vehicles, and other fields. However, with the continuous upgrading of various products and the increasing demands of consumers for product performance, further improvements in the cycle performance and safety of rechargeable batteries remain a key issue that urgently needs to be addressed.

[0003] Existing secondary batteries mainly consist of a positive electrode, a negative electrode, and an electrolyte or electrolyte solution. The positive electrode material mainly consists of positive electrode active material, conductive agent, lithium salt, and binder. With the increasing demand for various performance aspects of secondary batteries, ternary materials have attracted attention due to their advantages such as high energy density. The conductive agent is usually a carbon material such as graphite, carbon black, or carbon fiber. The binder mainly plays a role in bonding between the active material layers and is used for bonding between the active material layer and the current collector. Summary of the Invention

[0004] This application improves cycle life and safety by regulating the positive electrode and electrolyte in a secondary battery. The inventors of this application discovered that the positive electrode includes a positive electrode current collector and a positive electrode material disposed on the current collector. The positive electrode material includes nickel, cobalt, manganese, aluminum, and iron. Based on the content of metal elements other than lithium in the positive electrode material, the iron content is between 100 ppm and 2000 ppm by mass, and the specific surface area of ​​the positive electrode material is 1.2 m². 2 / g to 1.7m 2 / g; The electrolyte includes ethylene sulfate and lithium difluorophosphate, which can not only improve battery cycle performance but also improve safety, thus completing this application.

[0005] In some embodiments, the amount of vinyl sulfate is from 0.01 to 4 parts by weight and the amount of lithium difluorophosphate is from 0.3 to 3 parts by weight relative to 100 parts by weight of the electrolyte.

[0006] In some embodiments, the electrolyte comprises ethylene glycol (bis)propionitrile ether, wherein the amount of ethylene glycol (bis)propionitrile ether is from 0.01 parts by weight to 1.5 parts by weight relative to 100 parts by weight of electrolyte.

[0007] In some embodiments, the electrolyte comprises phosphonodiesterate diethoxyisocyanate, wherein the amount of diethoxyisocyanate is from 0.01 to 0.5 parts by weight relative to 100 parts by weight of the electrolyte.

[0008] In some embodiments, the cathode material includes zirconium.

[0009] In some embodiments, the mass ratio of aluminum, iron and zirconium is (2~6):(0.001~0.1):(1~3).

[0010] In some embodiments, the cathode material includes strontium.

[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 current collector is a composite current collector, and the negative electrode material includes a silicon-based negative electrode material.

[0012] In some embodiments, the specific surface area of ​​the negative electrode material is 1m². 2 / g to 4m 2 / g.

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

[0014] This application, by using a specific combination of positive electrode and electrolyte, can not only improve battery cycle performance but also enhance safety.

[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. Embodiments of the present invention

[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 not only battery cycle performance but also safety by using a specific combination of positive electrode and 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] I. Positive electrode

[0021] This application relates to a secondary battery and an electronic device. Specifically, this application provides a secondary battery comprising: a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode material disposed on the positive electrode current collector. The positive electrode material includes nickel, cobalt, manganese, aluminum, and iron. Based on the content of metal elements other than lithium in the positive electrode material, the mass content of iron is from 100 ppm to 2000 ppm, and the specific surface area of ​​the positive electrode material is 1.2 m². 2 / g to 1.7m 2 / g; the electrolyte includes ethylene sulfate and lithium difluorophosphate. This application not only improves battery cycle performance but also enhances safety.

[0022] The inventors of this application unexpectedly discovered during experiments that cathode materials and electrolytes meeting the specific requirements of this application can improve cycle performance and safety. The reason for this is speculated to be the coexistence of nickel, cobalt, manganese, aluminum, and iron in the cathode material. Based on the content of metals other than lithium in the cathode material, the iron content ranges from 100 ppm to 2000 ppm by mass, and the specific surface area of ​​the cathode material is 1.2 m². 2 / g to 1.7m 2 The electrolyte, comprising ethylene sulfate and lithium difluorophosphate, can mitigate the structural disorder or instability caused by doping elements in conventional cathode materials to improve cycle performance. Therefore, this application not only improves battery cycle performance but also enhances safety.

[0023] Specifically, from the viewpoint of improving battery cycle performance and safety, lithium cobalt oxide includes zirconium. Furthermore, from the viewpoint of improving battery cycle performance and safety, the mass ratio of aluminum, iron, and zirconium is (2~6):(0.001~0.1):(1~3), preferably (2~6):(0.005~0.05):(1~3). When the mass ratio of aluminum, iron, and zirconium meets the above range, battery cycle performance and safety can be further improved.

[0024] Specifically, from the perspective of improving battery cycle performance and safety, lithium cobalt oxide includes strontium. Based on the content of metal elements other than lithium in the cathode material, the mass content of strontium is 50 ppm to 100 ppm. Unless otherwise specified in this application, the content of doping elements in the cathode material is relative to the mass content of metal elements other than lithium in the cathode material.

[0025] There are no restrictions on the type of positive electrode conductive material; any known conductive material can be used. Examples of positive electrode conductive materials include, but are not limited to, carbon black such as acetylene black; carbon materials such as amorphous carbon such as needle coke; carbon nanotubes; graphene, etc. The above-mentioned positive electrode conductive materials can be used alone or in any combination.

[0026] 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 material, conductive material, and positive electrode binder. Examples of solvents used to form the positive electrode slurry can include any of aqueous solvents and organic solvents. Examples of aqueous media can include, but are not limited to, water and mixed media composed of alcohol and water. Examples of organic media 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.

[0027] 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 may include, but are not limited to, metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metallic material. In some embodiments, the positive electrode current collector is aluminum.

[0028] To reduce the electronic contact resistance between the positive current collector and the positive electrode material layer, 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, carbon and precious metals such as gold, platinum, and silver. Examples of conductive coatings may include a mixture layer containing inorganic oxides, conductive agents, and binders.

[0029] II. Electrolyte

[0030] The electrolyte used in the secondary battery of this application includes an electrolyte and a solvent for dissolving the electrolyte. In some embodiments, the electrolyte includes vinyl sulfate and lithium difluorophosphate (LiPO2F2).

[0031] When vinyl sulfate and lithium difluorophosphate are used in the secondary battery of this application, the inventors have found that, in synergy with the cathode material of this application, they can not only improve the battery cycle performance, but also improve safety.

[0032] Specifically, from the viewpoint of improving the cycle performance and safety of secondary batteries, the amount of vinyl sulfate is 0.01 to 4 parts by mass and lithium difluorophosphate is 0.3 to 3 parts by mass relative to 100 parts by mass of the electrolyte, preferably 0.01 to 1 part by mass of vinyl sulfate and 0.3 to 1 part by mass of lithium difluorophosphate.

[0033] Specifically, from the viewpoint of improving the cycle performance and safety of secondary batteries, the electrolyte includes ethylene glycol (bis)propionitrile ether, with ethylene glycol (bis)propionitrile ether comprising 0.01 to 1.5 parts by weight relative to 100 parts by weight of the electrolyte. Meeting the above conditions helps to further improve the cycle performance and safety of secondary batteries.

[0034] Specifically, in some embodiments, the electrolyte further comprises phosphonium diethoxyisocyanate, wherein the phosphonium diethoxyisocyanate is present in amounts of 0.01 to 0.5 parts by weight relative to 100 parts by weight of the electrolyte. When the above conditions are met, it helps to further improve the cycle performance and safety of the secondary battery.

[0035] In some embodiments, the additives in the electrolyte comprise one or more of the following: 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, butyl dimethanesulfonate, 2-(methanesulfonyloxy) methyl 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, 1-propene-1,3-sulfonic 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 1,4-Butylsulfonyl lactone, 1,5-pentanesulfonyl lactone, methanedisulfonate, 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, 1,5-pentanediol sulfite, etc.

[0036] 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, or LiC4BO8. For example, the lithium salt used in the electrolyte of this 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 within the above range, the cycle performance and safety of the secondary battery can be further improved.

[0037] In some embodiments, the electrolyte further includes at least one of lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate borate) (LiBOB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0038] 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.

[0039] 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.

[0040] 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.

[0041] Specifically, examples of chain carbonate compounds 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 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.

[0042] 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.

[0043] 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.

[0044] Specifically, examples of phosphate ester compounds are trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or combinations thereof.

[0045] 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.

[0046] III. Negative electrode

[0047] The negative electrode includes a negative electrode current collector and a negative electrode material disposed on the surface of the negative electrode current collector.

[0048] 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.

[0049] In some embodiments, the anode material includes carbon-based anode materials, metal-based anode materials, and anode materials combining these.

[0050] Carbon-based anode materials

[0051] 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.

[0052] Examples of carbonaceous materials include easily graphitized carbon and difficult-to-graphitize carbon with a similar amorphous structure, such as glassy carbon. Among easily graphitized carbons, examples include 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 phenolic resin sintered bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin sintered bodies (PFA), and hard carbon.

[0053] Furthermore, examples of graphitic materials include natural graphite and artificial graphite. Among these, examples of artificial graphite include: artificial graphite formed by heat-treating carbon containing easily graphitizable carbon primarily at temperatures above 2800°C; graphitic MCMB formed by heat-treating MCMB at temperatures above 2000°C; and graphitic mesophase pitch-based carbon fiber formed by heat-treating mesophase pitch-based carbon fiber at temperatures above 2000°C. Additionally, in this invention application, as a carbon-based negative electrode material, natural graphite whose surface is at least partially coated with amorphous carbon (amorphously coated natural graphite) can be used.

[0054] Furthermore, metal-based anode materials are active materials containing metals, typically referring to active materials whose structure contains elements capable of intercalating into or alloying with lithium, and whose theoretical current capacity per unit mass is 500 mAh / g or higher when intercalated into or alloyed with lithium. Examples of metal-based anode materials that can be used include: lithium metal, elemental metals capable of forming lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) and their alloys, as well as their oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. Among these, active materials containing silicon (silicon-based anode materials) are preferred as metal-based anode materials. This is because using silicon-based anode materials enables high-capacity secondary batteries.

[0055] In some embodiments, the anode material includes a silicon-based anode material.

[0056] Examples of silicon-based anode materials include: silicon (Si), silicon-containing alloys, SiO, SiO2, and silicon-containing materials coated or composited with conductive carbon (silicon-carbon materials).

[0057] From the perspective of improving battery capacity, silicon-carbon materials are preferred, such as porous carbon-supported silicon composites.

[0058] In addition, a single negative electrode material can be used alone, or two or more materials can be used in any ratio.

[0059] In some embodiments, the specific surface area of ​​the negative electrode material is 1m². 2 / g to 4m 2 / g.

[0060] Here, the volume average particle size of the negative electrode material is preferably 1 μm or more, more preferably 5 μm or more, 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-mentioned lower limit, the heat generation during internal short circuit can be effectively suppressed. In addition, if the volume average particle size of the negative electrode material is below the above-mentioned upper limit, the increase in the initial resistance of the resulting battery can be effectively suppressed.

[0061] 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, polyolefin resins, etc. When a negative electrode slurry is prepared using an aqueous solvent, 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, polyvinyl alcohol, etc.

[0062] 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 12 μm 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).

[0063] 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.

[0064] IV. Separating membrane

[0065] 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.

[0066] 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 may be a resin, glass fiber, inorganic material, or other material formed from a material stable to the electrolyte of this application. In some embodiments, the separator includes a porous sheet or non-woven fabric-like material with excellent liquid retention properties. Examples of materials for resin or glass fiber separators may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned separator materials can be used alone or in any combination.

[0067] 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.

[0068] Examples of inorganic materials may 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, but are not limited to, particulate or fibrous forms.

[0069] The separator can be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, microporous membranes, etc. 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 separator, the following separator can also be used: a separator 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 electrode and / or negative electrode, 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.

[0070] 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.

[0071] This application also provides an electronic device that includes a secondary battery as described in this application.

[0072] 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.

[0073] Example

[0074] The following are embodiments of the secondary battery of this application, but this application is not limited to these embodiments.

[0075] Preparation of secondary batteries

[0076] The production of the positive electrode:

[0077] A ternary cathode material (97 wt%) containing the doping elements listed in Table 1 (Ni:Co:Mn atomic ratio of 54:3:5), conductive carbon black (1.5 wt%), and polyvinylidene fluoride (1.5 wt%) were dissolved in N-methylpyrrolidone and mixed to prepare a cathode slurry. The cathode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil used as a cathode current collector. The aluminum foil was dried at 120˚C to obtain a cathode sheet with a single-sided coating of 80 μm thick cathode material. The above steps were repeated on the other surface of the aluminum foil to obtain a cathode sheet with a double-sided coating of cathode material. The coated aluminum foil was dried, pressurized, and then cut to the specified size to fabricate the cathode.

[0078] This application does not impose any particular limitation on the method for controlling the specific surface area of ​​the cathode material, as long as it can achieve the purpose of this application. For example, cathode materials with different specific surface areas can be obtained by mechanical crushing, grinding, sieving, etc. Exemplarily, cathode materials with different specific surface areas can be obtained by ball milling in mechanical crushing. Generally, extending the ball milling time increases the specific surface area; shortening the ball milling time decreases the specific surface area.

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

[0080] Making the negative electrode:

[0081] A negative electrode slurry was prepared by mixing 96 wt% negative electrode material and 2 wt% styrene-butadiene rubber, adding the mixture to a solution obtained by dissolving 2 wt% lithium carboxymethyl cellulose in deionized water, and mixing the mixture. This negative electrode slurry was then coated onto one side of a copper foil (except for composite copper foil used in Examples 11 and 12, all other examples used conventional copper foil), dried, pressure-treated, and then cut to the specified size.

[0082] This application does not impose any particular limitation on the method for controlling the specific surface area of ​​the negative electrode material, as long as it can achieve the purpose of this application. For example, negative electrode materials with different specific surface areas can be obtained by mechanical crushing, grinding, sieving, etc. Exemplarily, negative electrode materials with different specific surface areas can be obtained by ball milling in mechanical crushing. Generally, extending the ball milling time increases the specific surface area; shortening the ball milling time decreases the specific surface area.

[0083] Preparation of electrolyte: In an argon atmosphere glove box with a water content of less than 10 ppm, methyl ethyl carbonate, dimethyl carbonate, and ethylene carbonate were mixed in a mass ratio of 4:0.5:1 to obtain a basic solvent. Then, lithium salt LiPF6 and the substances shown in Table 1 were added to the above basic solvent and mixed evenly to obtain the electrolyte. The mass content of LiPF6 was 12% based on the mass of the electrolyte.

[0084] Battery making:

[0085] 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 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 battery with dimensions of 30mm wide, 45mm high, and 5mm thick.

[0086] Table 1

[0087]

[0088]

[0089] Test methods

[0090] Specific surface area

[0091] The testing method is as follows:

[0092] The specific surface area of ​​the cathode materials in each embodiment and comparative example was measured using a Tristar II 3020M surface area analyzer via nitrogen adsorption. The specific tests were conducted according to the national standard GB / T 19587-2017, "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method".

[0093] Battery short circuit safety

[0094] The testing method is as follows:

[0095] The prepared secondary battery was charged under the following conditions:

[0096] (1) Constant current charging: the charging current is 1400mA (the charging termination voltage is 4.3V); and (2) Constant voltage charging: the charging voltage is 4.3V (the charging termination current is 100mA).

[0097] At 25°C, a 2.5mm diameter round iron nail was used to puncture one side of a charged battery at a speed of 5mm / sec. Then, the temperature T at the short circuit (where the nail passed) was measured 1 hour after the puncture.

[0098] The following benchmark is used for evaluation: the smaller the temperature T value, the better the safety.

[0099] A: The value of temperature T is less than 80℃.

[0100] B: The temperature T is above 80℃ and below 100℃.

[0101] C: The value of temperature T is above 100℃ and below 130℃.

[0102] D: The value of temperature T is above 130℃.

[0103] High temperature cycling performance

[0104] The testing method is as follows:

[0105] The lithium-ion battery was placed in a 45˚C constant temperature chamber and left to stand for 20 minutes to allow it to reach a constant temperature. The first charge and discharge cycle was then performed. First, a constant current charge of 0.5C was used to charge the battery to 4.3V, followed by a constant voltage charge. Then, a constant current discharge of 1C was used to discharge the battery to 2.8V. The discharge capacity of the first cycle was recorded. This charge and discharge cycle was then repeated, and the discharge capacity of the 300th cycle was recorded.

[0106] 45℃ cycle capacity retention = (discharge capacity of the 300th cycle / discharge capacity of the first cycle) × 100%. Evaluation is based on the following benchmark: a higher capacity retention indicates better high-temperature cycle performance of the secondary battery.

[0107] A: Capacity retention rate is greater than 90%.

[0108] B: Capacity retention rate is above 85% and less than 90%.

[0109] C: Capacity retention rate is above 80% and less than 85%.

[0110] D: Capacity retention rate is less than 80%.

[0111] Test Results

[0112] In Table 1, " / " indicates that the substance was not added;

[0113] 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 nickel, cobalt, manganese, aluminum, and iron. Based on the content of metal elements other than lithium in the positive electrode material, the mass content of iron is 100 ppm to 2000 ppm, and the specific surface area of ​​the positive electrode material is 1.2 m². 2 / g to 1.7m 2 / g; The electrolyte includes ethylene sulfate and lithium difluorophosphate, which can not only improve battery cycle performance, but also improve safety.

[0114] Specifically, relative to 100 parts by weight of the electrolyte, the presence of 0.01 to 4 parts by weight of ethylene sulfate and 0.3 to 3 parts by weight of lithium difluorophosphate can further improve the battery's cycle performance and safety.

[0115] Specifically, the electrolyte includes ethylene glycol (bis)propionitrile ether, which is 0.01 to 1.5 parts by weight relative to 100 parts by weight of the electrolyte, which can further improve battery cycle performance and safety.

[0116] Specifically, the electrolyte includes phosphonium diethoxyisocyanate, which is present in amounts of 0.01 to 0.5 parts by weight relative to 100 parts by weight of the electrolyte, which can further improve battery cycle performance and safety.

[0117] In particular, the cathode material includes zirconium, which can further improve battery cycle performance and safety.

[0118] In particular, the mass ratio of aluminum, iron and zirconium is (2~6):(0.001~0.1):(1~3), which can further improve the battery cycle performance and safety.

[0119] In particular, the cathode material includes strontium, which can further improve battery cycle performance and safety.

[0120] Specifically, the specific surface area of ​​the negative electrode material is 1m².2 / g to 4m 2 / g can further improve battery cycle performance and safety.

[0121] Specifically, the negative electrode includes a negative electrode current collector and a negative electrode material disposed on the negative electrode current collector. The negative electrode current collector is a composite current collector, and the negative electrode material includes silicon-based negative electrode materials, which can further improve the battery cycle performance and safety.

[0122] 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 one 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.

[0123] 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: Positive electrode, negative electrode and 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 nickel, cobalt, manganese, aluminum, and iron. Based on the content of metal elements other than lithium in the positive electrode material, the mass content of iron is between 100 ppm and 2000 ppm, and the specific surface area of ​​the positive electrode material is 1.2 m². 2 / g to 1.7m 2 / g; The electrolyte comprises vinyl sulfate and lithium difluorophosphate.

2. The secondary battery according to claim 1, characterized in that, Relative to 100 parts by weight of the electrolyte, the ethylene sulfate is 0.01 to 4 parts by weight, and the lithium difluorophosphate is 0.3 to 3 parts by weight.

3. The secondary battery according to claim 1, characterized in that, The electrolyte comprises ethylene glycol (bis)propionitrile ether, wherein the ethylene glycol (bis)propionitrile ether is 0.01 to 1.5 parts by weight relative to 100 parts by weight of the electrolyte.

4. The secondary battery according to claim 1, characterized in that, The electrolyte comprises phosphonodiesterate diethoxyisocyanate, wherein the amount of diethoxyisocyanate is from 0.01 to 0.5 parts by weight relative to 100 parts by weight of the electrolyte.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The cathode material includes zirconium.

6. The secondary battery according to claim 5, characterized in that, The mass ratio of aluminum, iron and zirconium is (2~6):(0.001~0.1):(1~3).

7. The secondary battery according to any one of claims 1 to 4, characterized in that, The cathode material includes strontium.

8. The secondary battery according to any one of claims 1 to 4, characterized in that, The negative electrode includes a negative electrode current collector and a negative electrode material disposed on the negative electrode current collector. The negative electrode current collector is a composite current collector, and the negative electrode material includes a silicon-based negative electrode material.

9. The secondary battery according to claim 8, characterized in that, The specific surface area of ​​the negative electrode material is 1m². 2 / g to 4m 2 / g.

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

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