Secondary battery and electronic device

Abstract

A secondary battery and an electronic device. The secondary battery comprises: a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode comprises a negative electrode current collector and a negative electrode material arranged on the negative electrode current collector, with the specific surface area of the negative electrode material being 1 m2 / g to 4 m2 / g, and the electrolyte comprises methyl ethyl carbonate and allyl-1,3-sultone. On the basis of 100 parts by mass of the electrolyte, the content of methyl ethyl carbonate is 65-85 parts by mass, and the content of allyl-1,3-sultone is 0.01-0.9 parts by mass. Therefore, the high- and low-temperature storage performance of the secondary battery can be improved, and the impedance thereof can be reduced.

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 storage performance of rechargeable batteries and reductions in impedance remain key issues that urgently need to be addressed.

[0003] Existing secondary batteries mainly consist of a positive electrode, a negative electrode, and an electrolyte. To meet increasingly demanding requirements, the electrolyte, as a crucial medium, wets the gaps between the active material particles on the positive and negative electrode plates. Innovative research on the electrolyte is of great significance for improving the performance of secondary batteries. Therefore, there is an urgent need to provide an electrolyte that can improve the storage performance of secondary batteries and reduce impedance. Summary of the Invention

[0004] This application improves storage performance and reduces impedance by controlling the negative electrode material and electrolyte in a secondary battery. The inventors of this application have discovered that the negative electrode includes a negative electrode current collector and a negative electrode material disposed on the negative electrode current collector, the specific surface area of ​​the negative electrode material being 1 m². 2 / g to 4m 2 / g, the electrolyte includes ethyl methyl carbonate and propylene-1,3-sulfonyl lactone, wherein relative to 100 parts by mass of the electrolyte, ethyl methyl carbonate is 65 to 85 parts by mass and propylene-1,3-sulfonyl lactone is 0.01 to 0.9 parts by mass, which not only improves the high and low temperature storage performance of the battery, but also reduces impedance, thereby completing this application.

[0005] In some embodiments, the mass ratio of ethyl methyl carbonate to propylene-1,3-sulfonyl lactone is (500~1000):1.

[0006] In some embodiments, the mass ratio of ethyl methyl carbonate to propylene-1,3-sulfonyl lactone is (600~900):1.

[0007] In some embodiments, the electrolyte comprises lithium tetrafluoroborate, wherein the amount of lithium tetrafluoroborate is from 0.01 parts by weight to 0.8 parts by weight relative to 100 parts by weight of the electrolyte.

[0008] In some embodiments, the electrolyte comprises lithium tetrafluoroborate, wherein the amount of lithium tetrafluoroborate is from 0.03 to 0.07 parts by weight relative to 100 parts by weight of the electrolyte.

[0009] In some embodiments, the electrolyte comprises tetramethylborate, wherein the tetramethylborate is 0.1 to 0.4 parts by weight relative to 100 parts by weight of the electrolyte.

[0010] In some embodiments, the mass ratio of methyl ethyl carbonate to tetramethyl borate is (400~700):(1~2).

[0011] In some embodiments, the negative electrode material includes silicon-based materials.

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

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

[0014] This application, by using a specific combination of negative electrode and electrolyte, can not only improve the high and low temperature storage performance of secondary batteries, but also reduce impedance.

[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, by using a specific combination of negative electrode and electrolyte, can not only improve the high and low temperature storage performance of secondary batteries, but also reduce impedance.

[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. Electrolyte

[0021] This application relates to a secondary battery and an electronic device. Specifically, this application provides a secondary battery comprising: a positive electrode, a negative electrode, and an electrolyte. The electrolyte used in the secondary battery of this application comprises an electrolyte and a solvent for dissolving the electrolyte. The electrolyte comprises ethyl methyl carbonate and propylene-1,3-sulfonyl lactone, wherein, relative to 100 parts by mass of the electrolyte, ethyl methyl carbonate comprises 65 to 85 parts by mass, and propylene-1,3-sulfonyl lactone comprises 0.01 to 0.9 parts by mass. The negative electrode comprises a negative electrode current collector and a negative electrode material disposed on the negative electrode current collector, the specific surface area of ​​the negative electrode material being 1 m². 2 / g to 4m 2 / g.

[0022] When specific amounts of methyl ethyl carbonate and propylene-1,3-sulfonyl lactone are used in the secondary battery described in this application, the inventors have discovered that, in synergy with the negative electrode material having a specific surface area, they not only improve the high and low temperature storage performance of the secondary battery but also reduce impedance. It is speculated that this is because the specific amounts of methyl ethyl carbonate and propylene-1,3-sulfonyl lactone, within the content range defined in this application, can better wet the negative electrode material with its specific surface area and synergistically form a negative electrode interface film, thereby improving the high and low temperature storage performance of the secondary battery and reducing impedance.

[0023] Specifically, from the viewpoint of improving the high and low temperature storage performance of secondary batteries and reducing impedance, the mass ratio of ethyl methyl carbonate to propylene-1,3-sulfonyl lactone is (500~1000):1, preferably (600~900):1.

[0024] Specifically, from the viewpoint of improving the high and low temperature storage performance of secondary batteries and reducing impedance, the electrolyte includes lithium tetrafluoroborate (LiBF4), wherein the lithium tetrafluoroborate comprises 0.01 to 0.8 parts by mass, preferably 0.03 to 0.07 parts by mass, relative to 100 parts by mass of the electrolyte. Meeting the above conditions helps to further improve the high and low temperature storage performance and reduce impedance.

[0025] Specifically, in some embodiments, the electrolyte further comprises tetramethylborate, wherein the tetramethylborate content is 0.1 to 0.4 parts by weight relative to 100 parts by weight of the electrolyte. When the above conditions are met, it helps to further improve the high and low temperature storage performance of the secondary battery and reduce impedance.

[0026] Specifically, from the perspective of improving the high and low temperature storage performance of secondary batteries and reducing impedance, the mass ratio of methyl ethyl carbonate to tetramethyl borate is (400~700):(1~2).

[0027] In some embodiments, the electrolyte contains one or more of the following substances: ethylene glycol sulfate, 1,2-propanediol sulfate, 1,3-propanediol sulfate, 1,2-butanediol sulfate, 1,3-butanediol sulfate, 1,4-butanediol sulfate, 1,2-pentanediol sulfate, 1,3-pentanediol sulfate, 1,4-pentanediol sulfate, 1,5-pentanediol sulfate, dimethyl sulfate, methyl ethyl sulfate, methyl fluorosulfonate, ethyl trifluoromethanesulfonate, methyl methanesulfonate, ethyl methanesulfonate, butyl dimethanesulfonate. 2-(methanesulfonyloxy)propionate methyl ester, 2-(methanesulfonyloxy)propionate ethyl ester, 1-fluoro-1,3-propanesulfonate lactone, 2-fluoro-1,3-propanesulfonate lactone, 3-fluoro-1,3-propanesulfonate lactone, 1-methyl-1,3-propanesulfonate lactone, 2-methyl-1,3-propanesulfonate lactone, 3-methyl-1,3-propanesulfonate lactone, 2-propene-1,3-sulfonate lactone, 1-fluoro-1-propene-1,3-sulfonate lactone, 2-fluoro-1-propene-1,3-sulfonate lactone, 3-fluoro-1-propene-1,3-sulfonate lactone 1-Sulfonyl lactone, 1-fluoro-2-propen-1,3-sulfonyl lactone, 2-fluoro-2-propen-1,3-sulfonyl lactone, 3-fluoro-2-propen-1,3-sulfonyl lactone, 1-methyl-1-propen-1,3-sulfonyl lactone, 2-methyl-1-propen-1,3-sulfonyl lactone, 3-methyl-1-propen-1,3-sulfonyl lactone, 1-methyl-2-propen-1,3-sulfonyl lactone, 2-methyl-2-propen-1,3-sulfonyl lactone, 3-methyl-2-propen-1,3-sulfonyl lactone, 1,4 -Butyl butyrate lactone, 1,5-pentanesulfonate lactone, methanedisulfonate methylene, ethylene methanedisulfonate methylene, 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.

[0028] 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.

[0029] In some embodiments, the electrolyte further includes at least one of lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate borate) (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0030] 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.

[0031] 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.

[0032] 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.

[0033] Specifically, examples of chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), or combinations thereof. Examples of fluorinated carbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or combinations thereof.

[0034] 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.

[0035] 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.

[0036] Specifically, examples of phosphate ester compounds are trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or combinations thereof.

[0037] 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.

[0038] II. Negative electrode

[0039] The negative electrode includes a negative electrode current collector and a negative electrode material disposed on the surface of the negative electrode current collector. The negative electrode material in this application has a specific surface area of ​​1 m². 2 / g to 4m 2 / g.

[0040] 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.

[0041] In some embodiments, the anode material includes carbon-based anode materials, metal-based anode materials, and anode materials combining these.

[0042] Carbon-based anode materials

[0043] 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.

[0044] 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.

[0045] 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.

[0046] In addition, the metal-based negative electrode material is an active material containing a metal, and generally refers to an active material containing an element capable of inserting lithium or alloying with lithium in its structure, and having a theoretical current capacity of 500 mAh / g or more per unit mass when lithium is inserted or alloyed with lithium. As the metal-based negative electrode material, for example, lithium metal, elemental metals 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.), 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 a silicon-based negative electrode material can increase the capacity of the secondary battery.

[0047] In some embodiments, the negative electrode material includes a silicon-based material.

[0048] In some embodiments, the silicon-based material includes at least one of a composite of a silicon-based substance and a carbon-based substance or silicon oxide (SiO x , 0 < x ≤ 2). The silicon-based substance can be silicon particles, silicon alloy particles, or silicon oxide (SiO x , 0 < x ≤ 2), etc. The negative electrode material may 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-like, 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.

[0049] 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 and inside 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.

[0050] The silicon- and carbon-based composite can be an active material obtained by dispersing silicon nanoparticles with an average particle size of 200 nm or less on carbon-based particles, and then coating them with carbon, an active material in which silicon (Si) particles are present on and within graphite, etc. The average particle size of the secondary particles in the silicon- and carbon-based composite can be from 5 μm to 20 μm. The average particle size of the silicon nanoparticles can be 5 nm or more, for example, 10 nm or more, for example, 20 nm or more, for example, 50 nm or more, for example, 70 nm or more. The average particle size of the silicon nanoparticles can be 200 nm or less, 150 nm or less, 100 nm or less, 50 nm or less, 20 nm or less, or 10 nm or less. For example, the average particle size of the silicon nanoparticles can be from 100 nm to 150 nm.

[0051] The average particle size of the secondary particles of the silicon-based and carbon-based composite material can be from 5 μm to 20 μm, for example, from 7 μm to 15 μm, for example, from 10 μm to 13 μm.

[0052] From the perspective of improving battery capacity, silicon-carbon materials are preferred, such as porous carbon-supported silicon composites.

[0053] In addition, a single negative electrode material can be used alone, or two or more materials can be used in any ratio.

[0054] In some embodiments, the specific surface area of ​​the negative electrode material is 1m². 2 / g to 4m 2 / g.

[0055] 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.

[0056] 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.

[0057] 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).

[0058] 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.

[0059] III. Positive electrode

[0060] The positive electrode includes a positive current collector and a positive electrode material disposed on the surface of the positive current collector.

[0061] The cathode material can be one or more layers. Each layer in a multilayer cathode material can contain the same or different cathode active materials. The cathode active material is any material capable of reversibly inserting and deintercalating lithium ions.

[0062] The positive electrode active material includes lithium transition metal oxides containing nickel and other transition metals. In lithium transition metal oxides containing nickel and other transition metals, the amount of nickel 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, relative to the total moles of transition metals.

[0063] For example, lithium transition metal oxides can be compounds represented by the following formula 1:

[0064] Formula 1: Li a Ni x Co y M z O 2-b A b ,

[0065] In Formula 1, 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 can 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.

[0066] For example, the lithium transition metal oxide can be at least one compound represented by Formula 2 or Formula 3 below:

[0067] Formula 2: LiNi x Co y Mn z O2,

[0068] where in Formula 2, 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.

[0069] Formula 3: LiNi x Co y Al z O2,

[0070] where in Formula 3, 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.

[0071] For example, the lithium transition metal oxide can 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 Mn 0.1 O2 or LiNi 0.88 Co 0.1 Al 0.02 O2.

[0072] 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).

[0073] In some embodiments, there is no limitation on the type of positive electrode conductive material, and any known conductive material can be used. Examples of positive electrode conductive materials may include, but are not limited to, acetylene black, Super-P carbon black, 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.

[0074] There are no particular restrictions on the type of positive electrode binder used in the manufacture of positive electrode materials. In the case of coating methods, any material that can be dissolved or dispersed in the liquid medium used during electrode manufacturing is acceptable. Examples of positive electrode binders may include, but are not limited to, one or more of the following: resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; styrene-butadiene-styrene block copolymers or their hydrides, and ethylene-propylene-diene terpolymers (EPDM). The above-mentioned positive electrode adhesives include thermoplastic elastomers such as styrene-ethylene-butadiene-ethylene copolymers, styrene-isoprene-styrene block copolymers, or their hydrides; soft resinous polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymeric compositions with ion conductivity of alkali metal ions (especially lithium ions). These positive electrode adhesives can be used alone or in any combination.

[0075] There are no restrictions on the type of solvent used to form the positive electrode slurry, as long as it can dissolve or disperse the positive electrode active material, conductive material, positive electrode binder, and thickener used as needed. Examples of solvents used to form the positive electrode slurry can include any of aqueous solvents and organic solvents. Examples of aqueous media can include, but are not limited to, mixtures of alcohol and water or 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 (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide.

[0076] Thickeners are typically used to adjust the viscosity of slurries. In the case of aqueous media, thickeners and styrene-butadiene rubber (SBR) latex can be used for slurry preparation. There are no particular limitations on the types of thickeners; examples include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts. The above-mentioned thickeners can be used alone or in any combination.

[0077] There are no particular limitations on the type of positive electrode current collector; it can be any known material 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 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.

[0078] To reduce the electronic contact resistance between the positive current collector and the positive electrode material, the surface of the positive current collector may include a conductive additive or a conductive coating. Examples of conductive additives include, but are not limited to, 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.

[0079] The positive electrode can be manufactured by forming a positive electrode material containing a positive electrode active material and a binder on a current collector. The manufacture of a positive electrode using a positive electrode active material can be carried out by conventional methods, namely, dry mixing the positive electrode active material, binder, and conductive materials and thickeners as needed, forming a sheet, and pressing the resulting sheet onto the positive electrode current collector; or dissolving or dispersing these materials in a liquid medium to form a slurry, coating the slurry onto the positive electrode current collector and drying it, thereby forming the positive electrode material on the current collector, thus obtaining the positive electrode.

[0080] IV. Separating membrane

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] This application also provides an electronic device that includes a secondary battery as described in this application.

[0088] 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.

[0089] Example

[0090] The following are embodiments of the secondary battery of this application, but this application is not limited to these embodiments.

[0091] Preparation of secondary batteries

[0092] The production of the positive electrode:

[0093] LiNi 0.88 Co 0.08 Mn 0.04A solution of O2 cathode material (97wt%), conductive carbon black (1.5wt%), and polyvinylidene fluoride (1.5wt%) dissolved in N-methylpyrrolidone was prepared and mixed to form a cathode slurry. The cathode slurry was uniformly coated onto one surface of a 10μm thick aluminum foil used as a cathode current collector. The aluminum foil was dried at 120°C to obtain a cathode sheet with an 80μm thick cathode material layer coated on one side. The above steps were repeated on the other surface of the aluminum foil to obtain a cathode sheet with a double-sided cathode material layer. The coated aluminum foil was dried, pressurized, and then cut to the specified size to fabricate the cathode.

[0094] Separating membrane: A 12μm thick polyethylene (PE) microporous membrane is selected as the separating membrane.

[0095] Making the negative electrode:

[0096] 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.

[0097] 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.

[0098] Preparation of electrolyte: In an argon atmosphere glove box with a water content of less than 10 ppm, methyl ethyl carbonate (content as shown in Table 1), dimethyl carbonate and ethylene carbonate (dimethyl carbonate and ethylene carbonate in a mass ratio of 0.5:1) are mixed to obtain a basic solvent. Then, lithium salt LiPF6 and propylene-1,3-sulfonyl lactone as shown in Table 1 are added to the above basic solvent (in some embodiments, lithium tetrafluoroborate and / or tetramethylborate are also added, as shown in Table 1). After mixing evenly, the electrolyte is obtained, wherein the mass content of LiPF6 is 12% based on the mass of the electrolyte.

[0099] Battery making:

[0100] 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.

[0101] Table 1

[0102]

[0103] Test methods

[0104] Specific surface area

[0105] The testing method is as follows:

[0106] The specific surface area of ​​the negative electrode materials in each embodiment and comparative example was measured using a Tristar II 3020M specific surface area analyzer via nitrogen adsorption. The specific testing was conducted in accordance with the national standard GB / T 19587-2017, "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method".

[0107] Battery storage performance

[0108] The testing method is as follows:

[0109] The lithium-ion battery was placed in a 15℃ constant temperature chamber and left to stand for 30 minutes to reach a constant temperature. The battery was then charged at a constant current of 0.7C to a voltage of 4.3V, followed by constant voltage charging at 4.3V to a current of 82.5mA. The thickness of the lithium-ion battery was measured and recorded as T0. The battery was then placed in a 45℃ oven for 10 hours, removed from the oven, and cooled for 1 hour. The thickness of the lithium-ion battery was measured again and recorded as T1. The thickness of the lithium-ion battery in the oven was monitored in real time.

[0110] The thickness expansion rate at 45℃ can be calculated using the following formula:

[0111] Thickness expansion rate at 45℃ = (T1-T0) / T0×100%.

[0112] The following criteria are used for evaluation: the smaller the thickness expansion rate, the better the high and low temperature storage performance of the secondary battery in this application.

[0113] A: Thickness expansion rate is less than 12%.

[0114] B: The thickness expansion rate is 12% or more but less than 15%.

[0115] C: Thickness expansion rate is 15% or more but less than 20%.

[0116] D: Thickness expansion rate is over 20%.

[0117] impedance

[0118] The testing method is as follows:

[0119] At 15℃, the lithium-ion battery was charged at a constant current of 0.7C to 4.3V, then charged at a constant voltage of 4.3V to a current of 82.5mA, and then discharged at a constant current of 0.2C for 4 hours, resulting in a state of charge (SOC) of 20%. Voltage V0 was obtained by discharging at 0.1C for 10 seconds; voltage V1 was obtained by discharging at 1C for 1 second. DCR (initial state at 15℃) = (V0 - V1) / 0.1C.

[0120] The lithium-ion battery was placed in a 45°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. The battery was then charged at a constant current of 0.7C to 4.3V at 45°C, followed by constant voltage charging at 4.3V to a current of 82.5mA, and then constant current discharging at 0.2C to 3.0V. This constitutes one charge-discharge cycle. After 800 such charge / discharge cycles, the battery was charged at a constant current of 0.7C to 4.3V, followed by constant voltage charging at 4.3V to a current of 82.5mA, and then constant current discharging at 0.2C for 4 hours, resulting in a state of charge (SOC) of 20%. Voltage V2 was obtained by discharging at 0.1C for 10 seconds; voltage V3 was obtained by discharging at 1C for 1 second. The discharge rate (DCR) (800 cycles at 45°C) = (V2 - V3) / 0.1C.

[0121] The rate of change of DCR during 45℃ cycling is calculated using the following formula:

[0122] Cyclic DCR change rate = (DCR (800 cycles at 45℃) / DCR (initial state at 15℃) - 1) × 100%.

[0123] The following criteria are used for evaluation: the lower the impedance, the better the performance of the secondary battery.

[0124] A: The DCR change rate is less than 25%.

[0125] B: The DCR change rate is above 25% and less than 29%.

[0126] C: The rate of change of DCR is above 29% and less than 35%.

[0127] D: The DCR change rate is above 35%.

[0128] Test Results

[0129] In Table 1, " / " indicates that the substance was not added;

[0130] As shown in Table 1, the negative electrode of this application includes a negative electrode current collector and a negative electrode material disposed on the negative electrode current collector. The specific surface area of ​​the negative electrode material is 1 m². 2 / g to 4m 2 / g, the electrolyte includes ethyl methyl carbonate and propylene-1,3-sulfonyl lactone, wherein ethyl methyl carbonate is 65 to 85 parts by mass and propylene-1,3-sulfonyl lactone is 0.01 to 0.9 parts by mass relative to 100 parts by mass of the electrolyte, which can not only improve the high and low temperature storage performance of the battery, but also reduce impedance.

[0131] In particular, the mass ratio of ethyl methyl carbonate to propylene-1,3-sulfonyl lactone is (500~1000):1, which can further improve the high and low temperature storage performance of the secondary battery and reduce impedance.

[0132] In particular, the mass ratio of ethyl methyl carbonate to propylene-1,3-sulfonyl lactone is (600~900):1, which can further improve the high and low temperature storage performance of secondary batteries and reduce impedance.

[0133] Specifically, the electrolyte includes lithium tetrafluoroborate, which is 0.01 to 0.8 parts by mass relative to 100 parts by mass of the electrolyte, which can further improve the high and low temperature storage performance of the secondary battery and reduce impedance.

[0134] Specifically, the electrolyte includes lithium tetrafluoroborate, which is 0.03 to 0.07 parts by mass relative to 100 parts by mass of the electrolyte, which can further improve the high and low temperature storage performance of the secondary battery and reduce impedance.

[0135] Specifically, the electrolyte includes tetramethylborate, which is 0.1 to 0.4 parts by mass relative to 100 parts by mass of the electrolyte, which can further improve the high and low temperature storage performance of the secondary battery and reduce impedance.

[0136] In particular, the mass ratio of ethyl methyl carbonate to tetramethyl borate is (400~700):(1~2), which can further improve the high and low temperature storage performance of the secondary battery and reduce impedance.

[0137] In particular, the negative electrode material includes silicon-based materials, which can further improve the high and low temperature storage performance of the secondary battery and reduce impedance.

[0138] In particular, silicon-based materials, including composites of silicon and carbon materials, can further improve the high and low temperature storage performance of secondary batteries and reduce impedance.

[0139] 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.

[0140] 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 negative electrode includes a negative electrode current collector and a negative electrode material disposed on the negative electrode current collector. The specific surface area of ​​the negative electrode material is 1 m². 2 / g to 4m 2 / g; The electrolyte comprises ethyl methyl carbonate and propylene-1,3-sulfonyl lactone, wherein the ethyl methyl carbonate comprises 65 to 85 parts by mass and the propylene-1,3-sulfonyl lactone comprises 0.01 to 0.9 parts by mass relative to 100 parts by mass of the electrolyte.

2. The secondary battery according to claim 1, characterized in that, The mass ratio of methyl ethyl carbonate to propenyl-1,3-sulfonyl lactone is (500~1000):

1.

3. The secondary battery according to claim 1, characterized in that, The mass ratio of methyl ethyl carbonate to propenyl-1,3-sulfonyl lactone is (600~900):

1.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The electrolyte comprises lithium tetrafluoroborate, wherein the lithium tetrafluoroborate comprises 0.01 to 0.8 parts by weight relative to 100 parts by weight of the electrolyte.

5. The secondary battery according to any one of claims 1 to 3, characterized in that, The electrolyte comprises lithium tetrafluoroborate, wherein the lithium tetrafluoroborate comprises 0.03 to 0.07 parts by weight relative to 100 parts by weight of the electrolyte.

6. The secondary battery according to any one of claims 1 to 3, characterized in that, The electrolyte comprises tetramethylboronic acid ester, wherein the tetramethylboronic acid ester comprises 0.1 to 0.4 parts by weight relative to 100 parts by weight of the electrolyte.

7. The secondary battery according to claim 6, characterized in that, The mass ratio of methyl ethyl carbonate to tetramethyl borate is (400~700):(1~2).

8. The secondary battery according to any one of claims 1 to 3, characterized in that, The negative electrode material includes silicon-based materials.

9. The secondary battery according to claim 8, characterized in that, The silicon-based materials include composites of silicon-based substances and carbon-based substances.

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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