Secondary batteries and electrical devices

Abstract

The present application discloses a secondary battery and an electric device, belonging to the field of battery technology. The present application controls the material parameters of the negative electrode plate, the plate parameters, the contact angle of the electrolyte and the additives to satisfy the following relationship: 105≤(S BET ×Cosθ×Y) / (W×Z)≤325, which is beneficial to improving the wettability of the electrolyte, can effectively increase the infiltration speed, promote the formation of a uniform and dense interface film at the negative electrode, reduce the gas production of the secondary battery, reduce the impedance, enhance the ion conductivity of the SEI film, and effectively improve the cycle performance.

Description

Technical Field

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

[0002] Secondary batteries are widely used in various fields due to their advantages such as long life, high specific energy and no memory effect. At the same time, due to the increasingly severe environmental situation and the shortage of fossil fuels in recent years, secondary batteries, as an alternative clean energy to provide power for transportation, have further entered all aspects of people's lives and entered a stage of rapid development. However, existing secondary batteries are difficult to balance cycle performance and expansion performance.

[0003] In view of this, this application is filed. Summary of the invention

[0004] The purpose of the present application is to overcome the deficiencies of the prior art and provide a secondary battery and an electrical device, wherein the secondary battery has excellent cycle stability.

[0005] To achieve the above-mentioned object, the first aspect of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material; the electrolyte comprises an additive, wherein the additive comprises a first additive, wherein the first additive comprises at least two of vinylene carbonate, fluoroethylene carbonate and vinyl sulfate;

[0006] The secondary battery satisfies: 105≤(S BET ×Cosθ×Y) / (W×Z)≤325;

[0007] Among them, S BET m 2 / g is the specific surface area of ​​the negative electrode active material;

[0008] θ is the contact angle of the electrolyte;

[0009] Y% is the mass percentage of the first additive in the electrolyte;

[0010] W g / mm 2 is the single-sided surface density of the negative electrode plate;

[0011] Z mm is the thickness of the negative electrode plate.

[0012] As an implementation scheme of the present application, at least one of the following (a) to (e) is satisfied:

[0013] (a) 1≤S BET ≤1.7;

[0014] (b) 20°≤θ≤60°;

[0015] (c) 2.0≤Y≤5.5;

[0016] (d) 0.12 ≤ W ≤ 1.7;

[0017] (e) 0.13≤Z≤0.2.

[0018] As an embodiment of the present application, the additive further includes a second additive, wherein the second additive includes at least one of methylene disulfonate, 1,3-propane sultone, and propenyl-1,3-sultone;

[0019] The mass percentage of the second additive in the electrolyte is 0.1% to 4%.

[0020] As an embodiment of the present application, the second additive includes methylene disulfonate and 1,3-propane sultone, satisfying: 0.4≤A1+A2≤2;

[0021] The A1% is the mass percentage of methylene disulfonate in the electrolyte,

[0022] The A2% is the mass percentage of 1,3-propane sultone in the electrolyte.

[0023] As an embodiment of the present application, 0.2≤A1≤1; and / or 0.2≤A2≤1.

[0024] As an embodiment of the present application, the electrolyte further includes an organic solvent, the organic solvent includes a chain carboxylate, and the mass percentage of the chain carboxylate in the organic solvent is 10% to 60%.

[0025] As an embodiment of the present application, the chain carboxylic acid ester includes at least one of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0026] As an embodiment of the present application, the organic solvent further includes at least one of a cyclic carbonate and a chain carbonate.

[0027] As an embodiment of the present application, the cyclic carbonate includes at least one of propylene carbonate and ethylene carbonate;

[0028] As an embodiment of the present application, the linear carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0029] As an implementation scheme of the present application, at least one of the following (1) to (2) is satisfied:

[0030] (1) The mass percentage of the cyclic carbonate in the electrolyte is 30% to 40%;

[0031] (2) The mass percentage of the linear carbonate in the organic solvent is 10% to 50%.

[0032] As an embodiment of the present application, the first additive comprises vinylene carbonate and fluoroethylene carbonate, the mass percentage of the vinylene carbonate in the electrolyte is B1%, the mass percentage of the fluoroethylene carbonate in the electrolyte is B2%, and B1 / B2≥4.5.

[0033] A second aspect of the present application provides an electrical device, comprising the secondary battery described above.

[0034] The beneficial effect of the present application is that the present application controls the material parameters of the negative electrode plate, the plate parameters, the contact angle of the electrolyte and the additives to satisfy the following relationship: 105≤(S BET ×Cosθ×Y) / (W×Z)≤325, which is beneficial to improving the wettability of the electrolyte, can effectively increase the infiltration speed, promote the formation of a uniform and dense interface film at the negative electrode, reduce the gas production of the secondary battery, reduce the impedance, enhance the ion conductivity of the SEI film, and effectively improve the cycle performance. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0036] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0037] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0038] The reagents or instruments used in this application without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0039] The embodiment of the present application provides a secondary battery, including a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material; the electrolyte includes an additive, wherein the additive includes a first additive, wherein the first additive includes at least two of vinylene carbonate, fluoroethylene carbonate and vinyl sulfate;

[0040] The secondary battery satisfies: 105≤(S BET × Cosθ × Y) / (W × Z) ≤ 325, for example, it can be 105, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 325 or a range consisting of any two of the values;

[0041] Among them, S BET m 2 / g is the specific surface area of ​​the negative electrode active material;

[0042] θ is the contact angle of the electrolyte;

[0043] Y% is the mass percentage of the first additive in the electrolyte;

[0044] W g / mm 2 is the single-sided surface density of the negative electrode plate;

[0045] Z mm is the thickness of the negative electrode plate.

[0046] The inventors of the present application have found that the performance of the secondary battery has a significant correlation with the material parameters of the negative electrode plate, the plate parameters, the contact angle of the electrolyte and the additives. The present application controls the material parameters of the negative electrode plate, the plate parameters, the contact angle of the electrolyte and the additives to satisfy the following relationship: 105≤(S BET ×Cosθ×Y) / (W×Z)≤325, which is beneficial to improving the wettability of the electrolyte, can effectively increase the infiltration speed, promote the formation of a uniform and dense interface film at the negative electrode, reduce the gas production of the secondary battery, reduce the impedance, enhance the ion conductivity of the SEI film, and effectively improve the cycle performance.

[0047] In one embodiment, the secondary battery satisfies: 190≤(S BET ×Cosθ×Y) / (W×Z)≤300.

[0048] In one embodiment, the secondary battery satisfies: 210≤(SBET ×Cosθ×Y) / (W×Z)≤300.

[0049] In one embodiment, 1≤S BET ≤1.7, for example, it can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7 or a range consisting of any two of these values. Controlling the specific surface area of ​​the negative electrode active material within this range can reduce the occurrence of side reactions of the negative electrode active material, better promote the embedding and extraction of active ions, increase the transmission rate of active ions, improve the stability of the SEI film, further reduce the gas production of the secondary battery, and improve the cycle performance.

[0050] It should be noted that in the present application, a specific surface area and pore size distribution measuring instrument is used to test the specific surface area of ​​the negative electrode active material, and the test standard is GB / T 19587-2017 gas adsorption BET method.

[0051] In one embodiment, 20°≤θ≤60°, for example, it can be 20°, 22°, 25°, 28°, 30°, 32°, 35°, 38°, 40°, 42°, 45°, 46°, 48°, 50°, 52°, 55°, 56°, 58°, 60° or a range consisting of any two of these values. By controlling the contact angle of the electrolyte within this range, the wettability of the electrolyte can be effectively improved, which is conducive to the transfer of charges between the electrode and the electrolyte and the diffusion of ions in the electrolyte, and promotes the formation of a uniform and dense interface film at the negative electrode, thereby avoiding an increase in the interface resistance between the electrolyte and the electrode surface, avoiding an increase in the internal resistance, and further reducing the gas production of the secondary battery and improving the cycle performance.

[0052] This application uses a surface contact angle tester to test the contact angle of the electrolyte on the diaphragm (7μm PE base film + 2μm boehmite layer + double-sided 5μm PVDF), and the test standard is GB / T 30693-2014.

[0053] In one embodiment, 2.0≤Y≤5.5, for example, it can be 2.0, 2.4, 2.6, 2.8, 3.0, 3.2, 3.5, 3.6, 3.8, 4, 4.2, 4.5, 4.6, 4.8, 5, 5.2, 5.4, 5.5 or a range consisting of any two of the values. By controlling the mass percentage of the first additive in the electrolyte to be within this range, the ion transfer rate and conductivity are effectively improved, the formation of a uniform and dense interface film at the negative electrode is promoted, the embedding of solvent molecules is effectively reduced, the gas production of the secondary battery is further reduced, and the cycle performance is improved.

[0054] In one embodiment, 0.12≤W≤1.7, for example, it can be 0.12, 0.15, 0.18, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7 or a range consisting of any two of these values. By having the single-sided surface density of the negative electrode pole piece within this range, the internal resistance of the secondary battery can be effectively reduced, the uniform distribution of the negative electrode active material on the negative electrode pole piece can be promoted, the migration and diffusion pathways of the active ions in the negative electrode active material can be reduced, the gas production of the secondary battery can be further reduced, and the cycle performance can be improved.

[0055] Among them, in this application, the single-sided surface density test method of the negative electrode sheet is to cut the negative electrode sheet into a sheet with an area of ​​1540.25mm 2 The mass of the small disc is weighed with a high-precision balance, and the mass of the small disc is deducted, divided by the area of ​​the disc and then divided by 2 to calculate the single-sided surface density of the negative electrode.

[0056] In one embodiment, 0.13≤Z≤0.2, for example, it can be 0.13, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2 or a range consisting of any two of these values. By controlling the thickness of the negative electrode plate within this range, the ability to store electrons can be improved, the stability of the negative electrode plate can be improved, deformation and damage can be avoided, the wettability of the negative electrode plate can be improved, better electron conduction and ion diffusion channels can be provided, the gas production of the secondary battery can be further reduced, and the cycle performance can be improved.

[0057] In one embodiment, the first additive comprises vinylene carbonate and fluoroethylene carbonate, the mass percentage of the vinylene carbonate in the electrolyte is B1%, the mass percentage of the fluoroethylene carbonate in the electrolyte is B2%, and B1 / B2≥4.5. Exemplarily, B1 / B2 can be 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10 or a range consisting of any two of the values. In one embodiment, 4.5≤B1 / B2≤9. The mass ratio of vinylene carbonate to fluoroethylene carbonate is within the above range, which can further improve the cycle performance and storage performance of the secondary battery.

[0058] In one embodiment, the additive further includes a second additive, and the second additive includes at least one of methylene disulfonate, 1,3-propane sultone, and propenyl-1,3-sultone;

[0059] The mass percentage of the second additive in the electrolyte is 0.1% to 4%, for example, it can be 0.1%, 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.6%, 3.8%, 4% or a range consisting of any two of these values. By adding the above-mentioned second additive, it is possible to promote the formation of a stable SEI film, prevent the solvent molecules of the electrolyte from being embedded in the electrode material, thereby slowing down the structural damage of the electrode material and improving the flatulence problem generated by the battery during the charging and discharging process.

[0060] In one embodiment, the second additive includes methylene disulfonate and 1,3-propane sultone, satisfying: 0.4≤A1+A2≤2; for example, it can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.5, 1.6, 1.8, 2 or a range consisting of any two of the values. By controlling the sum of the addition amounts of the two to meet this range, the high temperature stability can be effectively improved.

[0061] The A1% is the mass percentage of methylene disulfonate in the electrolyte, and the A2% is the mass percentage of 1,3-propane sultone in the electrolyte.

[0062] In one embodiment, 0.2≤A1≤1, for example, it can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range consisting of any two values ​​therein.

[0063] In one embodiment, 0.2≤A2≤1, for example, it can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range consisting of any two of these values.

[0064] In one embodiment, the electrolyte further includes an organic solvent, and the organic solvent includes a chain carboxylate, and the mass percentage of the chain carboxylate in the organic solvent is 10% to 60%, for example, it can be 10%, 20%, 30%, 40%, 50%, 60% or a range consisting of any two values ​​therein.

[0065] In one embodiment, the chain carboxylic acid ester includes at least one of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0066] In one embodiment, the chain carboxylic acid ester includes ethyl acetate. When the secondary battery further includes ethyl acetate, it can effectively improve the wettability of the electrode, provide better electron conduction and ion diffusion channels, reduce internal resistance, and improve cycle performance.

[0067] In one embodiment, the organic solvent further comprises at least one of a cyclic carbonate and a chain carbonate.

[0068] In one embodiment, the cyclic carbonate includes at least one of propylene carbonate and ethylene carbonate.

[0069] In one embodiment, the cyclic carbonate comprises ethylene carbonate.

[0070] In one embodiment, the cyclic carbonate includes ethylene carbonate, the linear carboxylic acid ester includes ethyl acetate, and the total mass of the ethylene carbonate and the ethyl acetate accounts for greater than or equal to 50% of the mass percentage of the organic solvent, for example, it can be at least one of 50%, 51%, 54%, 55%, 58%, 60%, 63%, 65%, 68%, 70%, 75%, 80%, 85%, 90% or a range consisting of any two of the values. When the contents of the two are within this range, the solvent system of the electrolyte is in a better condition, which can make the battery performance better.

[0071] In one embodiment, the cyclic carbonate includes ethylene carbonate, the linear carboxylic acid ester includes ethyl acetate, and the total mass of the ethylene carbonate and the ethyl acetate accounts for greater than or equal to 70% of the mass percentage of the organic solvent.

[0072] In one embodiment, the linear carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0073] In one embodiment, the linear carbonate includes ethyl methyl carbonate and dimethyl carbonate.

[0074] In one embodiment, the organic solvent comprises at least one of dimethyl carbonate and ethyl methyl carbonate, ethylene carbonate and ethyl acetate. When the solvent system comprises the above substances, the overall performance of the electrolyte can be more compatible with the battery system.

[0075] In one embodiment, the organic solvent comprises ethyl methyl carbonate, ethylene carbonate and ethyl acetate.

[0076] In one embodiment, the organic solvent includes ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and ethyl acetate.

[0077] In one embodiment, the mass percentage of the cyclic carbonate in the organic solvent is 10% to 40%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40% or a range consisting of any two values ​​therein.

[0078] In one embodiment, the mass percentage of the cyclic carbonate in the organic solvent is 30% to 40%.

[0079] In one embodiment, the mass percentage of the linear carbonate in the organic solvent is 10% to 50%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or a range consisting of any two of these values.

[0080] In one embodiment, the electrolyte further includes a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalatoborate, and lithium bis(oxalatoborate).

[0081] In one embodiment, the mass percentage of the lithium salt in the electrolyte is 5-20%, for example, it can be 5%, 6%, 8%, 10%, 12%, 15%, 16%, 18%, 20% or a range consisting of any two of these values.

[0082] In one embodiment, the negative electrode active material can be natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithium titanate Li4Ti5O 12 , at least one of Li-Al alloy and metallic lithium.

[0083] In one embodiment, the negative electrode active material includes at least one of natural graphite and artificial graphite.

[0084] In the present application, there is no particular limitation on the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector.

[0085] In one embodiment, the negative electrode active material layer further includes a conductive agent and a binder.

[0086] In one embodiment, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0087] In one embodiment, the positive electrode active material can be selected from sodium iron composite oxide, sodium cobalt composite oxide, sodium manganese composite oxide, sodium nickel composite oxide, sodium nickel titanium composite oxide, sodium nickel manganese composite oxide, sodium iron manganese composite oxide, sodium nickel cobalt manganese composite oxide, sodium iron phosphate, sodium manganese phosphate, sodium cobalt phosphate, nickel cobalt manganese lithium and nickel cobalt aluminum lithium. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries can also be used. These positive electrode active materials can be used alone or in combination of two or more.

[0088] In one embodiment, the positive electrode active material includes a chemical formula of Li a Fe 1-b M b PO4 compound, wherein 0.8≤a≤1.2, 0≤b≤0.9, and M is selected from at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, and Ti.

[0089] The embodiment of the present application provides a secondary battery, including a positive electrode plate, a negative electrode plate, an electrolyte and a separator, wherein the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material, wherein the positive electrode active material includes a lithium iron phosphate compound; the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material; the electrolyte includes an additive, wherein the additive includes a first additive, wherein the first additive includes at least two of vinylene carbonate, fluoroethylene carbonate and vinyl sulfate;

[0090] The secondary battery satisfies: 105≤(S BET ×Cosθ×Y) / (W×Z)≤325;

[0091] Among them, S BET m 2 / g is the specific surface area of ​​the negative electrode active material;

[0092] θ is the contact angle of the electrolyte;

[0093] Y% is the mass percentage of the first additive in the electrolyte;

[0094] W g / mm 2 is the single-sided surface density of the negative electrode plate;

[0095] Z mm is the thickness of the negative electrode plate.

[0096] When the positive electrode active material includes a lithium iron phosphate compound, the electrolyte and the negative electrode plate meet the above conditions, which can make the secondary battery system better compatible and the overall performance of the battery better.

[0097] The embodiment of the present application provides a secondary battery, including a positive electrode plate, a negative electrode plate, an electrolyte and a separator, wherein the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material, wherein the positive electrode active material includes a lithium iron phosphate compound; the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material; the electrolyte includes a solvent and an additive, wherein the solvent includes a cyclic carbonate and a chain carboxylic acid ester; the additive includes a first additive, wherein the first additive includes at least two of vinylene carbonate, fluoroethylene carbonate and vinyl sulfate;

[0098] The secondary battery satisfies: 105≤(S BET ×Cosθ×Y) / (W×Z)≤325;

[0099] Among them, S BET m 2 / g is the specific surface area of ​​the negative electrode active material;

[0100] θ is the contact angle of the electrolyte;

[0101] Y% is the mass percentage of the first additive in the electrolyte;

[0102] W g / mm 2 is the single-sided surface density of the negative electrode plate;

[0103] Z mm is the thickness of the negative electrode plate.

[0104] In one embodiment, the cyclic carbonate comprises ethylene carbonate, and the linear carboxylic acid ester comprises ethyl acetate.

[0105] When the positive electrode active material includes a lithium iron phosphate compound, the electrolyte includes a cyclic carbonate, a chain carboxylate, and the electrolyte includes a first additive, which can further improve the wettability of the electrolyte, effectively increase the wetting speed, promote the formation of a protective film, reduce secondary battery gas production, reduce impedance, enhance the ion conductivity of the SEI film, and effectively improve the cycle performance.

[0106] In one embodiment, the type of the positive electrode current collector is not particularly limited, and it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, and carbon materials such as carbon cloth and carbon paper.

[0107] There is no particular restriction on the form of the positive electrode current collector. When the positive electrode current collector is a metal material, the positive electrode current collector may be in the form of metal foil, metal cylinder, metal strip roll, metal plate, metal foil, metal plate mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, the positive electrode current collector may include but is not limited to a carbon plate, a carbon film, a carbon cylinder, etc.

[0108] In one embodiment, the positive electrode active material layer further includes a conductive agent and a binder.

[0109] In one embodiment, the type of the conductive agent mentioned in the present application is not limited, and any known conductive agent can be used.

[0110] In one embodiment, the conductive agent includes at least one of carbon materials such as acetylene black, needle coke, carbon nanotubes, and graphene.

[0111] In one embodiment, the type of the binder mentioned in the present application is not limited, and any known positive electrode binder can be used.

[0112] In one embodiment, the binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber.

[0113] In the secondary battery mentioned in the present application, a separator is usually provided between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the separator are not particularly limited as long as the effect of the present application is not significantly impaired.

[0114] In one embodiment, the separator includes a porous sheet or non-woven fabric having excellent liquid retention. The materials of the resin or glass fiber separator include, but are not limited to, polyolefin, aromatic polyamide, polytetrafluoroethylene, polyethersulfone, and the like.

[0115] In one embodiment, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above-mentioned diaphragm can be used alone or in any combination.

[0116] In one embodiment, the secondary battery may include an outer package, which can be used to encapsulate the electrode assembly and the electrolyte.

[0117] In one embodiment, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0118] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape.

[0119] An embodiment of the present application provides an electrical device, comprising the secondary battery described above.

[0120] Exemplarily, the above-mentioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0121] The present application is further described below with specific embodiments:

[0122] Example 1

[0123] A method for preparing a secondary battery, wherein the rated capacity Cap. of the secondary battery is designed to be 5.0Ah, comprises the following steps:

[0124] Preparation of positive electrode

[0125] The positive electrode material LiFePO4, conductive agent SP, and binder PVDF were mixed in a mass ratio of 96:2:2, and NMP was added and stirred under vacuum until the system was uniform to obtain the positive electrode slurry; then the positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil, dried in an oven, and then cold pressed to obtain the positive electrode sheet. The compacted density of the positive electrode sheet is 2.45 g / cm 3 .

[0126] Preparation of negative electrode

[0127] After mixing the negative electrode active material graphite, conductive agent SP, thickener CMC, and binder SBR in a mass ratio of 96.2:1.2:1.2:1.4, deionized water is added as a solvent, and then stirred under vacuum until the system is uniform, the negative electrode slurry is obtained, and the negative electrode slurry is evenly coated on the copper foil current collector, dried in an oven, and then cold pressed to obtain the negative electrode sheet. The thickness of the negative electrode sheet is 0.15mm.

[0128] Preparation of electrolyte

[0129] Solvent system (based on total solvent mass): EC (ethylene carbonate), EMC (ethyl methyl carbonate), DMC (dimethyl carbonate) and EA (ethyl acetate), with a mass ratio of 30:5:5:60;

[0130] Additives: MMDS (recorded as A1 in Table 1, methylene disulfonate): 0.5%, first additive (two combinations of VC (vinyl carbonate) 4.5%, FEC (fluoroethylene carbonate) 0.5%): 5%, PS (recorded as A2 in Table 1, 1,3-propane sultone): 0.4%;

[0131] Lithium salt: LiPF6 (lithium hexafluorophosphate): 12.5%. (The above percentages are all mass percentages of the total electrolyte).

[0132] Assembly of secondary batteries

[0133] The positive electrode sheet, isolation film (7μm PE base film + 2μm boehmite layer + double-sided 5μm PVDF), and negative electrode sheet are stacked in order, so that the isolation film is between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a core, and the core is packaged in an aluminum-plastic film. After drying, 19g of the prepared electrolyte is injected, and then vacuum packaging, standing, formation, and hot pressing processes are carried out to obtain a secondary battery.

[0134] Example 1 The specific material parameters of the negative electrode plate, the plate parameters, the contact angle of the electrolyte and the parameters of the additives are shown in Table 1.

[0135] Examples 2-6, Comparative Examples 1-2

[0136] The difference between Examples 2 to 6 and Comparative Examples 1 to 2 and Example 1 is that Examples 2 to 6 and Comparative Examples 1 to 2 change the composition and / or content of the organic solvent, thereby changing the contact angle.

[0137] In Example 2, the mass ratio of EC, EMC, DMC and EA is 30:10:10:50.

[0138] In Example 3, the mass ratio of EC, EMC, DMC and EA is 40:5:15:40.

[0139] In Example 4, the mass ratio of EC, EMC, DMC and EA is 40:5:25:30.

[0140] In Example 5, the mass ratio of EC, EMC, DMC and EA is 40:5:35:20.

[0141] In Example 6, the mass ratio of EC, EMC, DMC and EA is 40:20:30:10.

[0142] In Comparative Example 1, the organic solvents are EC, EMC and EA, and the mass ratio of the three is 30:5:65.

[0143] In Comparative Example 2, the mass ratio of EC, EMC, DMC and EA is 40:20:35:5.

[0144] Examples 7-9, Comparative Examples 3-4

[0145] Embodiments 7-9 and Comparative Examples 3-4 Compared with Embodiment 3, Embodiments 7-9 and Comparative Examples 3-4 change the type of the first additive and / or the mass percentage of the first additive in the electrolyte.

[0146] Among them, the first additives in Example 7 are VC and FEC, with mass percentages of 4.5% and 1% respectively;

[0147] In Example 8, the first additives are VC and FEC, with mass percentages of 3.5% and 0.5% respectively;

[0148] In Example 9, the first additive is DTD (vinyl sulfate) and VC, with mass percentages of 0.5% and 1.5% respectively;

[0149] In Comparative Example 3, the first additives are VC and FEC, with mass percentages of 4.5% and 2%, respectively;

[0150] In Comparative Example 4, the first additives are VC and FEC, with the mass percentages being 1% and 0.5% respectively.

[0151] Examples 10-12, Comparative Examples 5-6

[0152] Examples 10-12 and Comparative Examples 5-6 Compared with Example 3, Examples 10-12 and Comparative Examples 5-6 change the specific surface area of ​​the negative electrode active material, as shown in Table 1.

[0153] Examples 13-15, Comparative Examples 7-8

[0154] Compared with Example 3, Examples 13-15 and Comparative Examples 7-8 change the thickness of the negative electrode sheet and the surface density of the negative electrode sheet by adjusting the coating amount of the negative electrode slurry on the current collector and / or adjusting the cold pressing pressure, as shown in Table 1.

[0155] Embodiments 16 to 19

[0156] Compared with Example 3, Examples 16 to 19 change the addition amounts of A1 and A2, as shown in Table 1.

[0157] Table 1

[0158]

[0159] Performance Testing

[0160] 1. Cycle performance test: At 25°C, charge with 1C charging current to 3.65V, discharge with 1C discharging current to 2.5V, repeat charging and discharging at 1C / 1C to the upper and lower limit voltages, and test the percentage of 500-cycle discharge capacity to the initial discharge capacity.

[0161] 2. Low temperature lithium precipitation test: adjust the temperature to -10℃, charge to 3.65V with 0.23C charging current, discharge to 2.5V with 1C discharge current, cycle 10 times, adjust the temperature to 25℃, charge to 3.65V with 1C charging current, and disassemble and observe the interface.

[0162] 3. High temperature gas generation test: The secondary battery is tested at volume V0, then the secondary battery is charged to 3.65V and placed in a 70℃ environment for 60 days to test the secondary battery volume V 60 , compare the volume change of the secondary battery over 60 days to determine the gas production.

[0163] Table 2

[0164]

[0165] As can be seen from Tables 1 and 2, the present application satisfies the following relationship by controlling the material parameters of the negative electrode plate, the plate parameters, the contact angle of the electrolyte, and the additives: 105≤(S BET ×Cosθ×Y) / (W×Z)≤325, which is beneficial to improving the wettability of the electrolyte, can effectively increase the infiltration speed, promote the formation of a uniform and dense interface film at the negative electrode, reduce the gas production of the secondary battery, reduce the impedance, enhance the ion conductivity of the SEI film, and effectively improve the cycle performance.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, ordinary technicians in this field should understand that the technical solution of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present application.

Claims

1. A secondary battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, characterized in that: The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material; the electrolyte includes an additive, wherein the additive includes a first additive, wherein the first additive includes at least two of vinylene carbonate, fluoroethylene carbonate, and vinyl sulfate; The secondary battery satisfies: 105≤(S BET ×Cosθ×Y) / (W×Z)≤325; Among them, S BET m 2 / g is the specific surface area of ​​the negative electrode active material; BET Satisfy: 1≤S BET ≤1.7; θ is the contact angle of the electrolyte; θ satisfies: 20°≤θ≤60°; Y% is the mass percentage of the first additive in the electrolyte; Y satisfies: 2.0≤Y≤5.5; Wg / mm 2 is the single-sided surface density of the negative electrode plate; W satisfies: 0.12≤W≤0.17; Zmm is the thickness of the negative electrode plate; Z satisfies: 0.13≤Z≤0.2; The contact angle of the electrolyte is the contact angle of the electrolyte on the separator.

2. The secondary battery according to claim 1, characterized in that: The secondary battery meets the following requirements: 190≤(S BET ×Cosθ×Y) / (W×Z)≤300.

3. The secondary battery according to claim 2, characterized in that: The secondary battery satisfies: 210≤(S BET ×Cosθ×Y) / (W×Z)≤300.

4. The secondary battery according to any one of claims 1 to 3, characterized in that: The additive further includes a second additive, wherein the second additive includes at least one of methylene methane disulfonate, 1,3-propane sultone, and propenyl-1,3-sultone; The mass percentage of the second additive in the electrolyte is 0.1% to 4%.

5. The secondary battery according to claim 4, characterized in that: The second additive includes methylene disulfonate and 1,3-propane sultone, A1% is the mass percentage of methylene disulfonate in the electrolyte, and A2% is the mass percentage of 1,3-propane sultone in the electrolyte, satisfying: 0.4≤A1+A2≤2.

6. The secondary battery according to claim 5, characterized in that: 0.2≤A1≤1; and / or 0.2≤A2≤1。 7. The secondary battery according to any one of claims 1 to 3, characterized in that: The electrolyte further includes an organic solvent, and the organic solvent includes a chain carboxylate, wherein the mass percentage of the chain carboxylate in the organic solvent is 10% to 60%.

8. The secondary battery according to claim 7, characterized in that: The chain carboxylic acid ester includes at least one of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

9. The secondary battery according to claim 7, characterized in that: The organic solvent further comprises at least one of a cyclic carbonate and a chain carbonate; The cyclic carbonate includes at least one of propylene carbonate and ethylene carbonate; The chain carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate and dipropyl carbonate.

10. The secondary battery according to claim 9, characterized in that: Satisfy at least one of the following (1) to (2): (1) The mass percentage of the cyclic carbonate in the organic solvent is 30% to 40%; (2) The mass percentage of the linear carbonate in the organic solvent is 10% to 50%.

11. The secondary battery according to any one of claims 1 to 3, characterized in that: The first additive comprises vinylene carbonate and fluoroethylene carbonate, the mass percentage of the vinylene carbonate in the electrolyte is B1%, the mass percentage of the fluoroethylene carbonate in the electrolyte is B2%, and B1 / B2≥4.

5.

12. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 11.

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