Electrolyte, secondary battery and electronic device

Abstract

The invention relates to an electrolyte, a secondary battery and an electronic device. Specifically, the present application provides an electrolyte solution including ethyl 2, 2-difluoroacetate, 1, 2, 3-tri (2-cyanoxy) propane, and 1, 3-propane sultone, with respect to 100 parts by mass of the electrolyte solution, the amount of ethyl 2, 2-difluoroacetate being 1.5-6 parts by mass, the amount of 1, 2, 3-tri (2-cyanoxy) propane being 0.5-4 parts by mass, the amount of 1, 3-propane sultone being 0.5-5 parts by mass, and the amount of 1, 3-propane sultone being 0.5-5 parts by mass. The content of the 1, 3-propane sultone is 1 to 5.5 parts by mass. According to the invention, the over-current and over-temperature safety of the secondary battery can be improved.

Description

Technical Field

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

[0002] Secondary batteries are one of the most successful research directions in commercialization today. With the updating of products such as electronic products and electric vehicles, the market demand for their performance is getting higher and higher.

[0003] Specifically, the diversification of commodity usage scenarios poses an increasing challenge to the safety of secondary batteries. The fast-paced urban life has made people have more expectations for the over-temperature and over-current safety of secondary batteries. Therefore, as an important component of secondary batteries, electrolytes are responsible for improving the safety of secondary batteries. How to improve electrolytes has become a very valuable research direction. Summary of the invention

[0004] The present application improves the overcurrent and overtemperature safety of secondary batteries by regulating the electrolyte. The inventors of the present application found that the electrolyte includes ethyl 2,2-difluoroacetate, 1,2,3-tris(2-cyano)propane and 1,3-propane sultone. Relative to 100 parts by mass of the electrolyte, ethyl 2,2-difluoroacetate is 1.5 to 6 parts by mass, 1,2,3-tris(2-cyano)propane is 0.5 to 4 parts by mass, and 1,3-propane sultone is 1 to 5.5 parts by mass, which can improve the overcurrent and overtemperature safety of the battery, thereby completing the present application.

[0005] In some embodiments, the mass ratio of ethyl 2,2-difluoroacetate, 1,2,3-tris(2-cyano)propane and 1,3-propane sultone is (2-5):(0.6-3):(2-5).

[0006] In some embodiments, the electrolyte further includes vinylene carbonate and ethyl propionate, and the sum of the contents of vinylene carbonate and ethyl propionate is 40 parts by mass to 55 parts by mass relative to 100 parts by mass of the electrolyte.

[0007] In some embodiments, the electrolyte further includes fluoride ions, and the fluoride ions are in an amount of 0.5 parts by mass to 2 parts by mass relative to 100 parts by mass of the electrolyte.

[0008] In some embodiments, the sum of the contents of ethyl 2,2-difluoroacetate, 1,2,3-tris(2-cyano)propane, 1,3-propane sultone and fluoride ion is 7.7 to 11.5 parts by mass relative to 100 parts by mass of the electrolyte.

[0009] In some embodiments, the electrolyte further comprises ethylene carbonate, lithium difluorophosphate and fluoroethylene carbonate, and the sum of the contents of ethylene carbonate, lithium difluorophosphate and fluoroethylene carbonate is 12 to 21 parts by mass relative to 100 parts by mass of the electrolyte.

[0010] In some embodiments, the electrolyte further comprises propylene carbonate and adiponitrile, and the sum of the contents of propylene carbonate and adiponitrile is 20 parts by mass to 40 parts by mass relative to 100 parts by mass of the electrolyte.

[0011] In some embodiments, relative to 100 parts by mass of the electrolyte, the sum of the contents of ethylene carbonate, lithium difluorophosphate and fluoroethylene carbonate is A parts by mass, the sum of the contents of propylene carbonate and adiponitrile is B parts by mass, and the ratio of B to A, i.e., B / A, is in the range of 1.35 to 1.79.

[0012] In another aspect of the present application, the present application provides a secondary battery, which includes the electrolyte described in the present application.

[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 improve the over-current and over-temperature safety of secondary batteries by improving the composition of the electrolyte and regulating the content relationship between the various components.

[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 the over-current and over-temperature safety of the secondary battery by using a preset 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] Electrolyte

[0021] The present application relates to a secondary battery and an electronic device. Specifically, the present application provides a secondary battery comprising: a positive electrode, a negative electrode and an electrolyte. The electrolyte used in the secondary battery of the present application comprises an electrolyte and a solvent for dissolving the electrolyte. The electrolyte comprises ethyl 2,2-difluoroacetate, 1,2,3-tris(2-cyano)propane and 1,3-propane sultone, and relative to 100 parts by mass of the electrolyte, ethyl 2,2-difluoroacetate is 1.5 to 6 parts by mass, 1,2,3-tris(2-cyano)propane is 0.5 to 4 parts by mass, and 1,3-propane sultone is 1 to 5.5 parts by mass.

[0022] When a preset content of ethyl 2,2-difluoroacetate, 1,2,3-tris(2-cyano)propane and 1,3-propane sultone is used in the secondary battery of the present application, the inventors found that it can improve the overcurrent and overtemperature safety of the secondary battery. It is speculated that the reason may be that ethyl 2,2-difluoroacetate, 1,2,3-tris(2-cyano)propane and 1,3-propane sultone can synergistically improve the stability of ion migration under different conditions within the content range specified in the present application, thereby improving the safety of the secondary battery under some overload conditions such as overcurrent and overtemperature conditions.

[0023] Specifically, from the perspective of improving the overcurrent and overtemperature safety of the secondary battery, the mass content ratio of ethyl 2,2-difluoroacetate, 1,2,3-tris(2-cyano)propane and 1,3-propane sultone is (2-5):(0.6-3):(2-5). When the above conditions are met, it helps to further improve the overcurrent and overtemperature safety.

[0024] Specifically, from the perspective of improving the overcurrent and overtemperature safety of the secondary battery, the electrolyte further includes vinylene carbonate and ethyl propionate, and the sum of the contents of vinylene carbonate and ethyl propionate is 40 to 55 parts by mass relative to 100 parts by mass of the electrolyte. When the above conditions are met, it helps to further improve the overcurrent and overtemperature safety.

[0025] Specifically, the mass content ratio of vinylene carbonate to ethyl propionate is 1:(450-550).

[0026] Specifically, the amount of vinylene carbonate is 0.05 to 0.5 parts by mass relative to 100 parts by mass of the electrolyte solution.

[0027] Specifically, the amount of ethyl propionate is 45 parts by mass to 55 parts by mass relative to 100 parts by mass of the electrolyte solution.

[0028] Specifically, in some embodiments, the electrolyte further includes fluoride ions, and the fluoride ions are 0.5 to 2 parts by mass relative to 100 parts by mass of the electrolyte. When the above conditions are met, it helps to further improve the overcurrent and overtemperature safety of the secondary battery.

[0029] Specifically, from the viewpoint of further improving the overcurrent and overtemperature safety of the secondary battery, the sum of the contents of ethyl 2,2-difluoroacetate, 1,2,3-tris(2-cyanato)propane, 1,3-propane sultone and fluoride ions is 7.7 to 11.5 parts by mass relative to 100 parts by mass of the electrolyte.

[0030] Specifically, from the viewpoint of further improving the overcurrent and overtemperature safety of the secondary battery, the electrolyte also includes ethylene carbonate, lithium difluorophosphate and fluoroethylene carbonate, and the sum of the contents of ethylene carbonate, lithium difluorophosphate and fluoroethylene carbonate is 12 to 21 parts by mass relative to 100 parts by mass of the electrolyte.

[0031] Specifically, the mass content ratio of ethylene carbonate, lithium difluorophosphate and fluoroethylene carbonate is (50-150):(1-3):(50-70).

[0032] Specifically, from the perspective of further improving the overcurrent and overtemperature safety of the secondary battery, the electrolyte further includes propylene carbonate and adiponitrile, and the sum of the contents of propylene carbonate and adiponitrile is 20 to 40 parts by mass relative to 100 parts by mass of the electrolyte.

[0033] Specifically, the mass content ratio of propylene carbonate to adiponitrile is (15-23):(3.5-5).

[0034] Specifically, from the viewpoint of further improving the overcurrent and overtemperature safety of the secondary battery, relative to 100 parts by mass of the electrolyte, the sum of the contents of ethylene carbonate, lithium difluorophosphate and fluoroethylene carbonate is A parts by mass, the sum of the contents of propylene carbonate and adiponitrile is B parts by mass, and the ratio of B to A ranges from 1.35 to 1.79.

[0035] In some embodiments, the electrolyte further includes an ionizable lithium salt, and the ionizable lithium salt includes at least one of LiPF6, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, CF3SO3Li, LiC(CF3SO2)3, and LiC4BO8. For example, the lithium salt used in the electrolyte of the present application includes LiPF6, and the mass proportion of LiPF6 is 9% to 15%, preferably 9% to 13%, and more preferably 9% to 12% based on the mass of the electrolyte. When the above conditions are met, the overcurrent and overtemperature safety of the secondary battery can be further improved.

[0036] negative electrode

[0037] The negative electrode includes a negative electrode current collector and a negative electrode material disposed on a surface of the negative electrode current collector.

[0038] In some embodiments, the charge capacity of the negative electrode material is greater than the discharge capacity of the positive electrode material to reduce unintentional precipitation of lithium metal on the negative electrode during charging.

[0039] 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.

[0040] 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.

[0041] Examples of carbonaceous materials include graphitizable carbon and non-graphitizable carbon. Here, graphitizable carbon includes, for example, carbon materials obtained from petroleum or coal using tar pitch as a raw material; specifically, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, and pyrolysis vapor-grown carbon fibers. In addition, non-graphitizable carbon includes, for example, carbon materials having amorphous structures such as glassy carbon; specifically, phenolic resin sintered bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin sintered bodies (PFA), and hard carbon.

[0042] Furthermore, as graphite materials, for example, natural graphite and artificial graphite 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.

[0043] In addition, the metal-based negative electrode material is an active material containing metal, and generally refers to an active material that contains an element capable of inserting lithium or alloying with lithium in its structure, and has a theoretical current capacity per unit mass of 500 mAh / g or more when inserting 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, etc.), their alloys, and their oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. 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.

[0044] In some embodiments, the negative electrode material includes a silicon-based material.

[0045] 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 can be silicon particles, silicon alloy particles, etc. The negative electrode material can further include a carbon material, and the carbon material can be crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon can be graphite, such as amorphous, plate-shaped, flaky, spherical, or fibrous natural graphite and / or artificial graphite, and the amorphous carbon can be soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, or calcined coke, etc.

[0046] The composite of the silicon-based substance and the carbon-based substance can be a composite having a structure in which silicon nanoparticles are arranged on the carbon-based substance, a composite in which silicon particles are included on the surface and inside of the carbon-based substance, and a composite in which 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 can be graphite, graphene, graphene oxide, or a combination thereof.

[0047] The composite of the silicon-based substance and the carbon-based substance can be an active material obtained by dispersing silicon nanoparticles with an average particle size of 200 nm or less on carbon-based substance particles, and then coating with carbon, an active material in which silicon (Si) particles are present on and inside graphite, etc.

[0048] From the viewpoint of improving the battery capacity, silicon-carbon materials, such as composites of porous carbon loaded with silicon, are preferred.

[0049] In addition, the negative electrode material can be used alone or two or more kinds can be used in any ratio combination.

[0050] 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 manufacture of the electrolyte or electrode. 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, and polyolefin resins. 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, and polyvinyl alcohol.

[0051] 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).

[0052] 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.

[0053] positive electrode

[0054] The positive electrode includes a positive electrode collector and a positive electrode material disposed on a surface of the positive electrode collector.

[0055] The positive electrode material can be one layer or multiple layers. Each layer of the multiple layers of positive electrode material can contain the same or different positive electrode active materials. The positive electrode active material is any material that can reversibly embed and de-embed lithium ions.

[0056] Specifically, in some embodiments, the positive electrode active material includes a lithium transition metal oxide containing nickel and other transition metals. In the lithium transition metal oxide including nickel and other transition metals, the amount of nickel relative to the total molar number of the transition metal may be 60 mol% or more, for example, 75 mol% or more, for example, 80 mol% or more, for example, 85 mol% or more, or for example, 90 mol% or more.

[0057] For example, the lithium transition metal oxide may be a compound represented by the following Formula 1:

[0058] Formula 1: Li a Nix Co y M z O 2-b A b , wherein, 0.9 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0.6 ≤ x < 1, 0 < y ≤ 0.3, 0 < z ≤ 0.3, and x + y + z = 1, M is at least one selected from manganese (Mn), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al) or boron (B), and A is F, S, Cl, Br or a combination thereof. For example, the above subscripts may be 0.7 ≤ x < 1, 0 < y ≤ 0.3, and 0 < z ≤ 0.3; 0.8 ≤ x < 1, 0 < y ≤ 0.3, and 0 < z ≤ 0.3; 0.8 ≤ x < 1, 0 < y ≤ 0.2, and 0 < z ≤ 0.2; 0.83 ≤ x < 0.97, 0 < y ≤ 0.15, and 0 < z ≤ 0.15; or 0.85 ≤ x < 0.95, 0 < y ≤ 0.1, and 0 < z ≤ 0.1.

[0059] For example, the lithium transition metal oxide may be at least one compound represented by Formula 2 or Formula 3 below:

[0060] Formula 2: LiNi x Co y Mn z O2, wherein, 0.6 ≤ x ≤ 0.95, 0 < y ≤ 0.2, and 0 < z ≤ 0.1. For example, 0.7 ≤ x ≤ 0.95, 0 < y ≤ 0.3, and 0 < z ≤ 0.3.

[0061] Formula 3: LiNi x Co y Al z O2, wherein, 0.6 ≤ x ≤ 0.95, 0 < y ≤ 0.2, and 0 < z ≤ 0.1. For example, 0.7 ≤ x ≤ 0.95, 0 < y ≤ 0.3, and 0 < z ≤ 0.3. For example, 0.8 ≤ x ≤ 0.95, 0 < y ≤ 0.3, and 0 < z ≤ 0.3. For example, 0.82 ≤ x ≤ 0.95, 0 < y ≤ 0.15, and 0 < z ≤ 0.15. For example, 0.85 ≤ x ≤ 0.95, 0 < y ≤ 0.1, and 0 < z ≤ 0.1.

[0062] For example, the lithium transition metal oxide may be LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.88 Co 0.08 Mn 0.04 O2, LiNi 0.8 Co 0.15 Mn 0.05O2、LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.88 Co 0.1 Mn 0.02 O2、LiNi 0.8 Co 0.15 Al 0.05 O2、LiNi 0.8 Co 0.1 Al 0.1 O2 or LiNi 0.88 Co 0.1 Al 0.02 O2.

[0063] According to another embodiment, the positive electrode active material includes at least one active material selected from the group consisting of Li-Ni-Co-Al (NCA), Li-Ni-Co-Mn (NCM), lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMnO2), lithium nickel oxide (LiNiO2) and lithium iron phosphate (LiFePO4).

[0064] In some embodiments, the type of positive electrode conductive material is not limited, and any known conductive material can be used. Examples of positive electrode conductive materials may 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 positive electrode conductive materials can be used alone or in any combination.

[0065] The type of positive electrode binder used in the production of the positive electrode material is not particularly limited. In the case of a coating method, any material may be used as long as it is soluble or dispersible in a liquid medium used in the production of the electrode. Examples of positive electrode binders may include, but are not limited to, one or more of the following: resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose and nitrocellulose; rubber polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber and ethylene-propylene rubber; thermoplastic elastomer 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 polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers and propylene-α-olefin copolymers; fluorine-based polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride and polytetrafluoroethylene-ethylene copolymers; polymer compositions having ionic conductivity of alkali metal ions (especially lithium ions), etc. The above positive electrode binders may be used alone or in any combination.

[0066] There is no restriction 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 active material, the conductive material, the positive electrode binder and the thickener used as needed. 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, a mixed medium of alcohol and water or water, etc. 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 (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide and dimethylacetamide; aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide, etc.

[0067] Thickeners are usually used to adjust the viscosity of the slurry. In the case of using an aqueous medium, a thickener and a styrene-butadiene rubber (SBR) emulsion can be used for slurrying. The type of thickener is not particularly limited, and examples thereof may include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. The above-mentioned thickeners may be used alone or in any combination.

[0068] There is no particular limitation on the type of positive electrode current collector, which 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, and tantalum; 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.

[0069] In order to reduce the electronic contact resistance between the positive electrode current collector and the positive electrode material, 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, noble metals such as carbon, gold, platinum and silver. Examples of conductive coatings may include a mixture layer containing an inorganic oxide, a conductive agent and a binder.

[0070] The positive electrode can be made 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 a conventional method, that is, the positive electrode active material and the binder, as well as the conductive material and the thickener as required, are dry-mixed to form a sheet, and the obtained sheet is pressed onto the positive electrode current collector; or these materials are dissolved or dispersed in a liquid medium to form a slurry, and the slurry is applied to the positive electrode current collector and dried to form a positive electrode material on the current collector, thereby obtaining a positive electrode.

[0071] Isolation film

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

[0073] There is no particular restriction on the material and shape of the isolation membrane, as long as the effect of the present application is not significantly impaired. The isolation membrane may be a resin, glass fiber, inorganic substance, etc. formed of a material that is stable to the electrolyte of the present application. In some embodiments, the isolation membrane includes a porous sheet with excellent liquid retention and a non-woven fabric-like material. Examples of materials for resin or glass fiber isolation membranes may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, and polyether sulfone. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above isolation membranes may be used alone or in any combination.

[0074] The isolation film may also be a material formed by laminating the above materials, examples of which include but are not limited to a three-layer isolation film formed by laminating polypropylene, polyethylene, and polypropylene in this order.

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

[0076] The separator may be in the form of a thin film, examples of which include but are not limited to nonwoven fabrics, woven fabrics, and microporous films. In the thin film form, the separator has a pore size of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the above-mentioned independent thin film separators, the following separators can also be used: a separator formed by forming a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or the negative electrode using a resin-based adhesive, for example, a separator formed by using 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.

[0077] 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 range, insulation and mechanical strength can be ensured, and the DC resistance characteristics and energy density of the secondary battery can be ensured.

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

[0079] The purpose 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, notebook computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

[0080] The following are examples of the secondary battery of the present application, but the present application is not limited to these examples. Unless otherwise specified, the reagents, software and instruments involved in the following examples are all conventional commercial products or open source.

[0081] Preparation of secondary batteries

[0082] 1. Production of positive electrode: LiNi 0.6 Co 0.2 Mn 0.2O2 (97wt%), 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 120°C 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.

[0083] 2. Isolation membrane: A 12 μm thick polyethylene (PE) microporous membrane is used as the isolation membrane.

[0084] 3. Preparation of negative electrode: 96 wt% of artificial graphite and 2 wt% of styrene-butadiene rubber were mixed and added to a solution prepared by dissolving 2 wt% of lithium carboxymethyl cellulose in deionized water and mixed to prepare negative electrode slurry. The negative electrode slurry was coated on one side of a copper foil, dried, pressurized, and then cut into a specified size to prepare a negative electrode.

[0085] 4. Preparation of electrolyte: In an argon atmosphere glove box with a water content of less than 10 ppm, dimethyl carbonate and ethyl methyl carbonate are mixed in a mass ratio of 1:7 to obtain a basic solvent, and then lithium salt LiPF6 and other substances in the electrolyte shown in Table 1 are added to the above-mentioned base solvent, and the mixture is evenly mixed to obtain an electrolyte, wherein the mass content of LiPF6 is 14.5% based on the mass of the electrolyte.

[0086] 5. Battery production: stack the positive electrode, separator and negative electrode in order, so that the separator is between the positive electrode and the negative electrode to play an isolating role, and wind to obtain the electrode assembly. After welding the pole ear, place the electrode assembly in the outer packaging aluminum plastic film, remove moisture at 80°C, inject the above electrolyte, and obtain a lithium-ion battery 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.

[0087] Table 1

[0088]

[0089]

[0090] Test Method

[0091] 1. Test method for over-temperature safety:

[0092] Place the lithium-ion battery in a 25℃ constant temperature box and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge the lithium-ion battery that has reached a constant temperature at a constant current of 0.7C to a voltage of 4.2V, and then charge it at a constant voltage of 4.2V to a current of 82.5mA. Test the thickness of the lithium-ion battery and record it as T0; place it in a 60℃ oven for 10 hours, take it out of the oven and cool it for 1 hour, test the thickness of the lithium-ion battery as T1, and monitor the thickness of the lithium-ion battery in the oven in real time.

[0093] The value X calculated by the following formula is used for over-temperature safety evaluation:

[0094] X=(T1-T0) / T0×100%.

[0095] In the above formula, the smaller the value of X is, the better the over-temperature safety of the secondary battery in this application is. It is graded (A to D) according to the test results of X, and the grading criteria are as follows:

[0096] A: X is less than 12%;

[0097] B: X is 12% or more and less than 15%;

[0098] C: X is 15% or more and less than 20%;

[0099] D:X is greater than 20%.

[0100] 2. Test method for overcurrent safety:

[0101] At room temperature of 25℃, the secondary battery is charged with a constant current of 1C, and the battery state of charge (SOC) is charged from 10% to 30%. The secondary battery is then charged with a constant current of 1.5C, and the battery state of charge (SOC) is charged from 30% to 60%. The secondary battery is then charged with a constant current of 2C, and the battery state of charge (SOC) is charged from 60% to 90%. The temperature of the secondary battery is then monitored with a temperature measuring instrument.

[0102] The lower the temperature of the secondary battery measured above, the better the performance of the secondary battery. The secondary battery is graded (A to D) according to the test results of the temperature, and the grading criteria are as follows:

[0103] A: Temperature is less than 50℃;

[0104] B: The temperature is above 50℃ and below 55℃;

[0105] C: The temperature is above 55℃ and below 60℃;

[0106] D: Temperature greater than 60°C.

[0107] Test Results

[0108] Please refer to Table 1 for the above test results. In Table 1, “ / ” means that the substance is not added.

[0109] It can be seen from Table 1 that the electrolyte of the present application includes ethyl 2,2-difluoroacetate, 1,2,3-tris(2-cyanoxy)propane and 1,3-propane sultone. Relative to 100 parts by mass of the electrolyte, ethyl 2,2-difluoroacetate is 1.5 to 6 parts by mass, 1,2,3-tris(2-cyanoxy)propane is 0.5 to 4 parts by mass, and 1,3-propane sultone is 1 to 5.5 parts by mass, which can improve the over-current and over-temperature safety of the battery.

[0110] In particular, the mass content ratio of ethyl 2,2-difluoroacetate, 1,2,3-tri(2-cyano)propane and 1,3-propane sultone is (2-5):(0.6-3):(2-5), which can further improve the over-current and over-temperature safety of the secondary battery.

[0111] Particularly, the electrolyte includes vinylene carbonate and ethyl propionate, and the sum of the contents of vinylene carbonate and ethyl propionate is 40 to 55 parts by mass relative to 100 parts by mass of the electrolyte, which can further improve the overcurrent and overtemperature safety of the secondary battery.

[0112] In particular, the electrolyte includes fluoride ions, and the fluoride ions are in an amount of 0.5 to 2 parts by mass relative to 100 parts by mass of the electrolyte, which can further improve the over-current and over-temperature safety of the secondary battery.

[0113] In particular, relative to 100 parts by mass of the electrolyte, the sum of the contents of ethyl 2,2-difluoroacetate, 1,2,3-tris(2-cyano)propane, 1,3-propane sultone and fluoride ions is 7.7 parts by mass to 11.5 parts by mass, which can further improve the overcurrent and overtemperature safety of the secondary battery.

[0114] In particular, the electrolyte also includes ethylene carbonate, lithium difluorophosphate and fluoroethylene carbonate. Relative to 100 parts by mass of the electrolyte, the sum of the contents of ethylene carbonate, lithium difluorophosphate and fluoroethylene carbonate is 12 parts by mass to 21 parts by mass, which can further improve the over-current and over-temperature safety of the secondary battery.

[0115] Particularly, the electrolyte further comprises propylene carbonate and adiponitrile, and the sum of the contents of propylene carbonate and adiponitrile is 20 to 40 parts by mass relative to 100 parts by mass of the electrolyte, which can further improve the overcurrent and overtemperature safety of the secondary battery.

[0116] In particular, relative to 100 parts by mass of the electrolyte, the sum of the contents of ethylene carbonate, lithium difluorophosphate and fluoroethylene carbonate is A parts by mass, the sum of the contents of propylene carbonate and adiponitrile is B parts by mass, and the ratio of B to A ranges from 1.35 to 1.79, which can further improve the over-current and over-temperature safety of the secondary battery.

[0117] 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.

[0118] 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. An electrolyte, characterized in that: The electrolyte includes ethyl 2,2-difluoroacetate, 1,2,3-tris(2-cyano)propane and 1,3-propane sultone. Relative to 100 parts by mass of the electrolyte, the ethyl 2,2-difluoroacetate is 1.5 parts by mass to 6 parts by mass, the 1,2,3-tris(2-cyano)propane is 0.5 parts by mass to 4 parts by mass, and the 1,3-propane sultone is 1 parts by mass to 5.5 parts by mass.

2. The electrolyte according to claim 1, characterized in that The mass content ratio of the ethyl 2,2-difluoroacetate, the 1,2,3-tris(2-cyano)propane and the 1,3-propane sultone is (2-5):(0.6-3):(2-5).

3. The electrolyte according to claim 1, characterized in that The electrolyte further includes vinylene carbonate and ethyl propionate, and the sum of the contents of vinylene carbonate and ethyl propionate is 40 parts by mass to 55 parts by mass relative to 100 parts by mass of the electrolyte.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The electrolyte solution further includes fluoride ions, and the fluoride ions are present in an amount of 0.5 parts by mass to 2 parts by mass relative to 100 parts by mass of the electrolyte solution.

5. The electrolyte according to claim 4, characterized in that The total content of the ethyl 2,2-difluoroacetate, the 1,2,3-tris(2-cyano)propane, the 1,3-propane sultone and the fluoride ion is 7.7 to 11.5 parts by mass relative to 100 parts by mass of the electrolyte.

6. The electrolyte according to any one of claims 1 to 3, characterized in that The electrolyte further comprises ethylene carbonate, lithium difluorophosphate and fluoroethylene carbonate. The sum of the contents of ethylene carbonate, lithium difluorophosphate and fluoroethylene carbonate is 12 to 21 parts by mass relative to 100 parts by mass of the electrolyte.

7. The electrolyte according to claim 6, characterized in that The electrolyte further comprises propylene carbonate and adiponitrile, and the sum of the contents of propylene carbonate and adiponitrile is 20 parts by mass to 40 parts by mass relative to 100 parts by mass of the electrolyte.

8. The electrolyte according to claim 7, characterized in that Relative to 100 parts by mass of the electrolyte, the sum of the contents of ethylene carbonate, lithium difluorophosphate and fluoroethylene carbonate is A parts by mass, the sum of the contents of propylene carbonate and adiponitrile is B parts by mass, and the ratio of B to A ranges from 1.35 to 1.

79.

9. A secondary battery, characterized in that: It comprises the electrolyte according to any one of claims 1 to 8.

10. An electronic device, characterized in that: It comprises the secondary battery according to claim 9.

Images