Secondary battery and electronic device

Abstract

The invention relates to a secondary battery and an electronic device. Specifically, the secondary battery comprises a positive electrode, a negative electrode and an electrolyte, the positive electrode comprises a positive electrode current collector and a positive electrode material arranged on the positive electrode current collector, the positive electrode material comprises a nickel element, a cobalt element, a manganese element, an aluminum element and an iron element, and based on the content of metal elements except lithium in the positive electrode material, the content of the metal elements except lithium in the positive electrode material is calculated. The mass content of the iron element is 100 ppm to 2000 ppm, and the specific surface area of the positive electrode material is 1.2 m < 2 > / g to 1.7 m < 2 > / g; the electrolyte comprises ethylene sulfate and lithium difluorophosphate. According to the invention, the cycle performance of the battery can be improved, and the safety can be improved.

Description

Technical Field

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

[0002] As a current application and research hotspot, secondary batteries have been widely commercialized in portable electronic devices, electric vehicles and other fields. However, with the updating and iteration of various products and the continuous improvement of consumers' requirements for product performance, the further improvement of the cycle performance and safety of secondary batteries is still a focus issue that needs to be solved urgently.

[0003] Existing secondary batteries are mainly composed of positive electrodes, negative electrodes and electrolytes or electrolytes. Among them, the positive electrode materials are mainly composed of positive electrode active substances, conductive agents, lithium salts and binders. With the growing demand for various performance of secondary batteries, ternary materials have attracted attention due to their advantages such as high energy density. Conductive agents are usually carbon materials such as graphite, carbon black, and carbon fiber. Binders mainly play a bonding role between active material layers and are used for bonding between active material layers and current collectors. Summary of the invention

[0004] The present application improves the cycle and safety by regulating the positive electrode and electrolyte in the secondary battery. The inventor of the present application found that the positive electrode includes a positive electrode current collector and a positive electrode material disposed on the positive electrode current collector, and 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 100ppm to 2000ppm, and the specific surface area of ​​the positive electrode material is 1.2m 2 / g to 1.7m 2 / g; the electrolyte includes vinyl sulfate and lithium difluorophosphate, which can not only improve the battery cycle performance but also improve the safety, thereby completing the present application.

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

[0006] In some embodiments, the electrolyte includes ethylene glycol (bis) propionitrile ether, and the amount of ethylene glycol (bis) propionitrile ether is 0.01 parts by mass to 1.5 parts by mass relative to 100 parts by mass of the electrolyte.

[0007] In some embodiments, the electrolyte includes diethoxyphosphonic isocyanate, and the amount of diethoxyphosphonic isocyanate is 0.01 parts by mass to 0.5 parts by mass relative to 100 parts by mass of the electrolyte.

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

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

[0010] In some embodiments, the positive electrode 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 1 m 2 / g to 4m 2 / g.

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

[0014] The present application can not only improve the battery cycle performance but also improve the safety by using a combination of a specific positive electrode and an electrolyte.

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

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

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

[0018] The present application can improve not only the battery cycle performance but also the safety by using a specific combination of positive electrode and electrolyte.

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

[0020] I. Positive electrode

[0021] The present application relates to a secondary battery and an electronic device. Specifically, the present application provides a secondary battery, which includes: a positive electrode, a negative electrode and an electrolyte, 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 the iron element is 100 ppm to 2000 ppm, and the specific surface area of ​​the positive electrode material is 1.2 m 2 / g to 1.7m 2 / g; the electrolyte includes vinyl sulfate and lithium difluorophosphate. The present application can not only improve the battery cycle performance, but also enhance safety.

[0022] The inventor of this application unexpectedly discovered in the experiment that the positive electrode material and electrolyte that meet the specific requirements of this application can improve the cycle performance and safety. It is speculated that the reason is that nickel, cobalt, manganese, aluminum and iron elements coexist in the positive electrode material. Based on the content of metal elements other than lithium in the positive electrode material, the mass content of iron is 100ppm to 2000ppm, and the specific surface area of ​​the positive electrode material is 1.2m 2 / g to 1.7m 2 / g, and the electrolyte includes vinyl sulfate and lithium difluorophosphate, which can reduce the structural disorder or instability caused by doping elements in conventional positive electrode materials to improve cycle performance. Therefore, the present application can not only improve the battery cycle performance, but also improve safety.

[0023] Specifically, from the perspective of improving battery cycle performance and safety, lithium cobalt oxide includes zirconium. From the perspective of improving battery cycle performance and safety, the mass content 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 content ratio of aluminum, iron and zirconium meets the above range, the 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 positive electrode material, the mass content of strontium is 50ppm to 100ppm. Unless otherwise specified in this application, the content of doping elements in the positive electrode material is measured relative to the mass content of metal elements other than lithium in the positive electrode material.

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

[0026] There is no limitation on the type of solvent used to form the positive electrode slurry, as long as it is a solvent that can dissolve or disperse the positive electrode material, the conductive material, and the positive electrode binder. Examples of solvents used to form the positive electrode slurry may include any of aqueous solvents and organic solvents. Examples of aqueous media may include, but are not limited to, water and mixed media consisting of alcohol and water. Examples of organic media may include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran; amides such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide; non-protonic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide, etc.

[0027] The type of positive electrode current collector is not particularly limited, and it can be any material known to be suitable for use as a positive electrode current collector. Examples of positive electrode current collectors may include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, and carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metal material. In some embodiments, the positive electrode current collector is aluminum.

[0028] In order to reduce the electronic contact resistance between the positive electrode current collector and the positive electrode material layer, the surface of the positive electrode current collector may include a conductive additive or a conductive coating. Examples of conductive additives may include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. Examples of conductive coatings may include a mixture layer containing an inorganic oxide, a conductive agent, and a binder.

[0029] II. Electrolyte

[0030] The electrolyte used in the secondary battery of the present application includes an electrolyte and a solvent that dissolves the electrolyte. In some embodiments, the electrolyte includes vinyl sulfate and lithium difluorophosphate (LiPO 2 F 2 ).

[0031] When vinyl sulfate and lithium difluorophosphate are used in the secondary battery of the present application, the inventors have found that the synergistic effect of the vinyl sulfate and lithium difluorophosphate with the positive electrode material of the present application can not only enhance the battery cycle performance but also improve the safety.

[0032] Specifically, from the viewpoint of improving the cycle performance and safety of the secondary battery, the amount of vinyl sulfate is 0.01 to 4 parts by mass, and the amount of 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 the secondary battery, the electrolyte includes ethylene glycol (bis) propionitrile ether, and relative to 100 parts by mass of the electrolyte, ethylene glycol (bis) propionitrile ether is 0.01 parts by mass to 1.5 parts by mass. When the above conditions are met, it helps to further improve the cycle performance and safety of the secondary battery.

[0034] Specifically, in some embodiments, the electrolyte further includes diethoxy phosphonoisocyanate, and the diethoxy phosphonoisocyanate is 0.01 to 0.5 parts by mass relative to 100 parts by mass 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 additive in the electrolyte includes one or more of the following: 1,2-propylene glycol sulfate, 1,3-propylene glycol sulfate, 1,2-butylene glycol sulfate, 1,3-butylene glycol sulfate, 1,4-butylene glycol sulfate, 1,2-pentanediol sulfate, 1,3-pentanediol sulfate, 1,4-pentanediol sulfate, 1,5-pentanediol sulfate, dimethyl sulfate, ethyl methyl sulfate, methyl fluorosulfonate, ethyl trifluoromethanesulfonate, methyl methanesulfonate, ethyl methanesulfonate, butyl dimethanesulfonate, 2-(methylsulfonyloxy) 1-Fluoro-1,3-propane sultone, 2-Fluoro-1,3-propane sultone, 3-Fluoro-1,3-propane sultone, 1-Methyl-1,3-propane sultone, 2-Methyl-1,3-propane sultone, 3-Methyl-1,3-propane sultone, 1-Propene-1,3-sultone, 2-Propene-1,3-sultone, 1-Fluoro-1-propene-1,3-sultone, 2-Fluoro-1-propene-1,3-sultone, 3-Fluoro-1-propene-1,3-sultone, 1,3-sultone, 1-fluoro-2-propylene-1,3-sultone, 2-fluoro-2-propylene-1,3-sultone, 3-fluoro-2-propylene-1,3-sultone, 1-methyl-1-propylene-1,3-sultone, 2-methyl-1-propylene-1,3-sultone, 3-methyl-1-propylene-1,3-sultone, 1-methyl-2-propylene-1,3-sultone, 2-methyl-2-propylene-1,3-sultone, 3-methyl-2-propylene-1,3-sultone, 1,4-Butane sultone, 1,5-pentane sultone, methylene methanedisulfonate, ethylene methanedisulfonate, dimethyl sulfite, ethyl methyl sulfite, lithium difluorophosphate, 1,2-ethylene glycol sulfite, 1,2-propylene glycol sulfite, 1,3-propylene glycol sulfite, 1,2-butylene glycol sulfite, 1,3-butylene glycol sulfite, 1,4-butylene glycol sulfite, 1,2-pentanediol sulfite, 1,3-pentanediol sulfite, 1,4-pentanediol sulfite, 1,5-pentanediol sulfite, etc.

[0036] In some embodiments, the electrolyte further comprises an ionizable lithium salt, wherein the ionizable lithium salt comprises LiPF 6 、LiSbF 6 、LiAsF 6 、LiClO 4 、LiN(C 2 F 5 SO 2 ) 2 CF 3 SO 3 Li、LiC(CF 3 SO 2 ) 3 or LiC 4 BO 8 For example, the lithium salt used in the electrolyte of the present application includes LiPF 6 , based on electrolyte mass, LiPF 6 The content of is 9 to 15% by mass, preferably 9 to 13% by mass, and more preferably 9 to 12% by mass. 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 lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium tetrafluoroborate (LiBF 4 ), at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0038] In some embodiments, the additive in the electrolyte further includes at least one of a fluoroether compound, a fluorocarbonate compound, and an ether nitrile compound, such as hydrofluoroether (HFE-458), fluoroethylene carbonate (FEC), and the like.

[0039] In some embodiments, the electrolyte may further include a non-aqueous solvent. The non-aqueous solvent may be selected from carbonate compounds, carboxylate compounds, ether compounds, phosphate compounds, other organic solvents, or combinations thereof.

[0040] Optionally, the carbonate compound may be a linear carbonate compound, a cyclic carbonate compound or a combination thereof. On the other hand, the carbonate compound may also be a fluorinated carbonate compound, a non-fluorinated carbonate compound or a combination thereof.

[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), butylene carbonate (BC), vinyl ethylene carbonate (VEC) or combinations thereof. Examples of fluorocarbonate 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 the carboxylate compound are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, methyl formate, or a combination thereof.

[0043] Specifically, examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.

[0044] Specifically, examples of the phosphate compound are trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or a combination thereof.

[0045] Specifically, examples of other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methylpyrrolidone, formamide, dimethylformamide, acetonitrile, or a combination thereof.

[0046] III. Negative electrode

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

[0048] In some embodiments, the charge capacity of the negative electrode material is greater than the discharge capacity of the positive electrode material to prevent unintentional precipitation of lithium metal on the negative electrode during charging.

[0049] In some embodiments, the negative electrode material includes a carbon-based negative electrode material, a metal-based negative electrode material, and a negative electrode material combining the carbon-based negative electrode material and the like.

[0050] Carbon-based negative electrode materials

[0051] Here, the carbon-based negative electrode material refers to an active material having a carbon-based skeleton into which lithium can be inserted, and examples of the carbon-based negative electrode material include carbonaceous materials and graphite materials.

[0052] As carbonaceous materials, for example, graphitizable carbon, non-graphitizable carbon having a structure similar to an amorphous structure represented by glassy carbon, etc. can be cited. Here, as graphitizable carbon, for example, carbon materials obtained from petroleum or coal using tar pitch as a raw material can be cited. When giving specific examples, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, and pyrolysis vapor-grown carbon fibers can be cited. In addition, as non-graphitizable carbon, for example, phenolic resin sintered bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin sintered bodies (PFA), hard carbon, etc. can be cited.

[0053] Furthermore, as graphite materials, for example, natural graphite, artificial graphite, etc. can be cited. Among them, as artificial graphite, for example: artificial graphite obtained by heat-treating carbon containing graphitized carbon mainly at 2800°C or above, graphite MCMB obtained by heat-treating MCMB at 2000°C or above, graphite mesophase pitch-based carbon fiber obtained by heat-treating mesophase pitch-based carbon fiber at 2000°C or above, etc. can be cited. In addition, in the present application, as a carbon-based negative electrode material, natural graphite (amorphous coated natural graphite) in which at least a portion of its surface is coated with amorphous carbon can be used.

[0054] In addition, the metal-based negative electrode material is an active material containing a metal, generally referring to an active material having an element capable of inserting lithium or alloying with lithium in the structure, an element capable of inserting lithium or alloying with lithium, and a theoretical current capacity of 500 mAh / g or more per unit mass. As a metal-based negative electrode material, for example, lithium metal, a single metal capable of forming a lithium alloy (such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) and its alloy, and their oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. can be used. Among them, as a metal-based negative electrode material, an active material (silicon-based negative electrode material) containing silicon is preferably used. This is because the use of a silicon-based negative electrode material can increase the capacity of a secondary battery.

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

[0056] Examples of silicon-based negative electrode materials include silicon (Si), alloys containing silicon, SiO, SiO 2 , a composite of a silicon-containing material and conductive carbon (silicon-carbon material) in which a silicon-containing material is coated or composited with conductive carbon.

[0057] From the viewpoint of improving battery capacity, a silicon-carbon material, for example, a porous carbon-supported silicon composite material is preferred.

[0058] The negative electrode material may be used alone or in combination of two or more at any ratio.

[0059] In some embodiments, the specific surface area of ​​the negative electrode material is 1 m 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, preferably 30 μm or less, and more preferably 20 μm or less. If the volume average particle size of the negative electrode material is above the above lower limit, the heat generation during the internal short circuit can be effectively suppressed. In addition, if the volume average particle size of the negative electrode material is below the above upper limit, the increase in the initial resistance of the obtained battery can be effectively suppressed.

[0061] The negative electrode material layer may further include a negative electrode binder. The negative electrode binder can improve the bonding between the negative electrode material particles and the bonding between the negative electrode material and the current collector. The type of negative electrode binder is not particularly limited, as long as it is a material that is stable to the solvent used in the electrolyte or electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluororesins, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, and the like. When an aqueous solvent is used to prepare the negative electrode mixture slurry, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salt, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salt, polyvinyl alcohol, and the like.

[0062] As a current collector for maintaining the negative electrode material, any known current collector can be used. Examples of negative electrode current collectors include, but are not limited to, metal materials such as copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode current collector is copper. In some embodiments, the negative electrode current collector is a composite current collector, i.e., a 12 μm composite copper foil (commercially available, a composite current collector made of polyethylene terephthalate (PET) as a base material and depositing a metal copper layer on both sides thereof using an advanced vacuum coating process).

[0063] The negative electrode can be prepared by applying a negative electrode mixture slurry containing a negative electrode material, a resin binder, etc. on a negative electrode current collector, drying it, and then rolling it to form a negative electrode material layer on both sides of the negative electrode current collector, thereby obtaining a negative electrode.

[0064] IV. Isolation membrane

[0065] In order to prevent short circuit, a separator is usually provided between the positive electrode and the negative electrode. In this case, the electrolyte of the present application is usually used by infiltrating the separator.

[0066] There is no particular restriction on the material and shape of the isolation membrane, as long as the effect of the present application is not significantly impaired. The isolation membrane may be a resin, glass fiber, inorganic substance, etc. formed of a material that is stable to the electrolyte of the present application. In some embodiments, the isolation membrane includes a porous sheet or a non-woven fabric-like material with excellent liquid retention. Examples of materials for resin or glass fiber isolation membranes may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyether sulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above isolation membranes may be used alone or in any combination.

[0067] The isolation film may also be a material formed by laminating the above materials, and examples thereof include, but are not limited to, a three-layer isolation film formed by laminating polypropylene, polyethylene, and polypropylene in this order.

[0068] Examples of inorganic materials may include, but are not limited to, oxides such as aluminum oxide and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.) The form of the inorganic material may include, but is not limited to, granular or fibrous.

[0069] The separator may be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, microporous films, etc. In the thin film form, the separator has a pore size of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the above-mentioned independent thin film separators, the following separators may also be used: a separator formed by forming a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or the negative electrode using a resin-based adhesive, for example, a separator formed by using a fluororesin as an adhesive to form a porous layer on both sides of the positive electrode with aluminum oxide particles having a particle size of 90% less than 1 μm.

[0070] The thickness of the isolation film is arbitrary. In some embodiments, the thickness of the isolation film is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the isolation film is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the isolation film is within the above range, the insulation and mechanical strength can be ensured, and the DC resistance characteristics and energy density of the secondary battery can be ensured.

[0071] The present application further provides an electronic device, which includes the secondary battery described in the present application.

[0072] The use of the secondary battery of the present application is not particularly limited, and it can be used for any electronic device known in the prior art. In some embodiments, the secondary battery of the present application can be used for, but not limited to, laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

[0073] Example

[0074] Examples of the secondary battery of the present application are shown below, but the present application is not limited to these examples.

[0075] Preparation of secondary batteries

[0076] Production of positive electrode:

[0077] The ternary positive electrode material (97wt%) containing the doping elements in Table 1 (the atomic number ratio of nickel, cobalt and manganese is Ni:Co:Mn is 54:3:5), conductive carbon black (1.5wt%), and polyvinylidene fluoride (1.5wt%) are dissolved in N-methylpyrrolidone and mixed to prepare a positive electrode slurry. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm, and the aluminum foil is dried at 120C to obtain a positive electrode sheet coated with a positive electrode material layer with a thickness of 80μm on one side. Repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode material layer on both sides. The coated aluminum foil is dried and pressurized and then cut into a specified size to make a positive electrode.

[0078] The present application does not particularly limit the method for regulating the specific surface area of ​​the positive electrode material, as long as the purpose of the present application can be achieved. For example, positive electrode materials with different specific surface areas can be obtained by mechanical crushing, grinding, screening, etc. Exemplarily, positive electrode materials with different specific surface areas can be obtained by ball milling in mechanical crushing. Generally, the specific surface area increases when the ball milling time is extended, and the specific surface area decreases when the ball milling time is shortened.

[0079] Isolation film: A 12 μm thick polyethylene (PE) microporous membrane was selected as the isolation membrane.

[0080] Negative electrode production:

[0081] A negative electrode material (96 wt%) and styrene-butadiene rubber (2 wt%) were mixed and added to a solution prepared by dissolving 2 wt% of lithium carboxymethyl cellulose in deionized water and mixed to prepare a negative electrode slurry. The negative electrode slurry was coated on one side of a copper foil (except for the composite copper foil used in Examples 11 and 12, the rest were conventional copper foils), dried, pressurized, and then cut into a specified size to prepare a negative electrode.

[0082] The present application has no particular restrictions on the method for regulating the specific surface area of ​​the negative electrode material, as long as the purpose of the present application can be achieved. For example, negative electrode materials with different specific surface areas can be obtained by mechanical crushing, grinding, screening, etc. Exemplarily, negative electrode materials with different specific surface areas can be obtained by ball milling in mechanical crushing. Generally, the specific surface area increases with the extension of ball milling time, and the specific surface area decreases with the shortening of ball milling time.

[0083] Preparation of electrolyte: In an argon atmosphere glove box with a water content of less than 10 ppm, ethyl methyl carbonate, dimethyl carbonate, and ethylene carbonate were mixed in a mass ratio of 4:0.5:1 to obtain a base solvent, and then lithium salt LiPF was added to the base solvent. 6 and the substances shown in Table 1, and mixed evenly to obtain an electrolyte, wherein, based on the mass of the electrolyte, LiPF 6 The mass content is 12%.

[0084] Battery production:

[0085] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and the electrode assembly is wound, and the electrode assembly is placed in the outer packaging aluminum plastic film after welding the pole ear, and the water is removed at 80°C, and the above electrolyte is injected, and the lithium ion battery is obtained after vacuum packaging, standing, formation, shaping, capacity testing and other processes. The secondary battery is a bag-shaped battery with a width of 30mm, a height of 45mm, and a thickness of 5mm.

[0086] Table 1

[0087]

[0088]

[0089]

[0090] Test Method

[0091] Specific surface area

[0092] The test method is as follows:

[0093] The specific surface area of ​​the positive electrode materials of each embodiment and comparative example was tested by nitrogen adsorption using a specific surface area analyzer (Tristar II 3020M). The specific test was performed in accordance with the national standard GB / T19587-2017 "Determination of the specific surface area of ​​solid substances by gas adsorption BET method".

[0094] Battery short circuit safety

[0095] The test method is as follows:

[0096] The prepared secondary battery was charged according to the following conditions:

[0097] (1) Constant current charging: charging current is 1400mA (charging termination voltage is 4.3V); and (2) Constant voltage charging: charging voltage is 4.3V (charging termination current is 100mA).

[0098] In an environment of 25° C., a round iron nail with a diameter of 2.5 mm was used to pierce one side of the charged battery at a speed of 5 mm / sec. Then, the temperature T of the short-circuit (nail pierced) position was measured 1 hour after the nail piercing.

[0099] The evaluation was performed based on the following criteria: the smaller the value of the temperature T, the better the safety.

[0100] A: The value of temperature T is less than 80°C.

[0101] B: The value of the temperature T is 80°C or more and less than 100°C.

[0102] C: The value of the temperature T is 100°C or more and less than 130°C.

[0103] D: The value of the temperature T is 130° C. or higher.

[0104] High temperature cycle performance

[0105] The test method is as follows:

[0106] Place the lithium-ion battery in a 45°C constant temperature box and let it stand for 20 minutes to allow the lithium-ion battery to reach a constant temperature. Perform the first charge and discharge, first use a 0.5C current for constant current charging, charge to 4.3V, then perform constant voltage charging, then perform constant current discharge at a 1C current, discharge to 2.8V, and record the discharge capacity of the first cycle; then perform charge and discharge cycles, and record the discharge capacity of the 300th cycle.

[0107] 45° C. cycle capacity retention rate=(discharge capacity at the 300th cycle / discharge capacity at the first cycle)×100%. Evaluation was performed based on the following criteria: a larger capacity retention rate indicates better high temperature cycle performance of the secondary battery.

[0108] A: The capacity retention rate is greater than 90%.

[0109] B: The capacity retention rate is 85% or more and less than 90%.

[0110] C: The capacity retention rate is 80% or more and less than 85%.

[0111] D: The capacity retention rate is less than 80%.

[0112] Test Results

[0113] In Table 1, “ / ” indicates that the substance was not added;

[0114] As shown in Table 1, the positive electrode of the present 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. The specific surface area of ​​the positive electrode material is 1.2 m 2 / g to 1.7m 2 / g; the electrolyte includes vinyl sulfate and lithium difluorophosphate, which can not only improve the battery cycle performance but also improve safety.

[0115] In particular, relative to 100 parts by mass of the electrolyte, the amount of vinyl sulfate is 0.01 parts by mass to 4 parts by mass, and the amount of lithium difluorophosphate is 0.3 parts by mass to 3 parts by mass, which can further improve the battery cycle performance and safety.

[0116] In particular, the electrolyte includes ethylene glycol (bis) propionitrile ether, and the amount of ethylene glycol (bis) propionitrile ether is 0.01 to 1.5 parts by mass relative to 100 parts by mass of the electrolyte, which can further improve the battery cycle performance and safety.

[0117] In particular, the electrolyte includes diethoxyphosphonoisocyanate in an amount of 0.01 to 0.5 parts by mass relative to 100 parts by mass of the electrolyte, which can further improve the battery cycle performance and safety.

[0118] In particular, the positive electrode material includes zirconium element, which can further improve the battery cycle performance and safety.

[0119] In particular, the mass content ratio of aluminum element, iron element and zirconium element is (2-6):(0.001-0.1):(1-3), which can further improve the battery cycle performance and safety.

[0120] In particular, the positive electrode material includes strontium, which can further improve the battery cycle performance and safety.

[0121] In particular, the specific surface area of ​​the negative electrode material is 1m 2 / g to 4m 2 / g, which can further improve the battery cycle performance and safety.

[0122] In particular, 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, which can further improve the battery cycle performance and safety.

[0123] References to "embodiments", "partial embodiments", "one embodiment", "another example", "example", "specific example" or "partial example" throughout the specification mean that at least one embodiment or example in the present application includes the specific features, structures, materials or characteristics described in the embodiment or example. Therefore, descriptions appearing in various places throughout the specification, such as: "in some embodiments", "in an embodiment", "in one embodiment", "in another example", "in an example", "in a specific example" or "example", do not necessarily refer to the same embodiment or example in the present application. In addition, the specific features, structures, materials or characteristics in the present application may be combined in one or more embodiments or examples in any suitable manner.

[0124] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions and modifications may be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A secondary battery comprising: A positive electrode, a negative electrode and an electrolyte, characterized in that The positive electrode comprises a positive electrode current collector and a positive electrode material disposed on the positive electrode current collector, wherein the positive electrode material comprises nickel, cobalt, manganese, aluminum and iron, and based on the content of metal elements other than lithium in the positive electrode material, the mass content of the iron element is 100 ppm to 2000 ppm, and the specific surface area of ​​the positive electrode material is 1.2 m 2 / g to 1.7m 2 / g; The electrolyte includes vinyl sulfate and lithium difluorophosphate.

2. The secondary battery according to claim 1, characterized in that: The amount of the vinyl sulfate is 0.01 to 4 parts by mass, and the amount of the lithium difluorophosphate is 0.3 to 3 parts by mass, relative to 100 parts by mass of the electrolyte.

3. The secondary battery according to claim 1, characterized in that: The electrolyte solution includes ethylene glycol (bis) propionitrile ether, and the ethylene glycol (bis) propionitrile ether is in an amount of 0.01 parts by mass to 1.5 parts by mass relative to 100 parts by mass of the electrolyte solution.

4. The secondary battery according to claim 1, characterized in that: The electrolyte solution includes diethoxyphosphonic acid ester, and the diethoxyphosphonic acid ester is present in an amount of 0.01 parts by mass to 0.5 parts by mass relative to 100 parts by mass of the electrolyte solution.

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

6. The secondary battery according to claim 5, characterized in that: The mass content ratio of the aluminum element, the iron element and the zirconium element 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 positive electrode material includes strontium.

8. The secondary battery according to any one of claims 1 to 4, characterized in that: The negative electrode comprises a negative electrode current collector and a negative electrode material arranged on the negative electrode current collector. The negative electrode current collector is a composite current collector, and the negative electrode material comprises 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 1 m 2 / g to 4m 2 / g.

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

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