Secondary battery and electronic device

Abstract

A secondary battery and an electronic device. The secondary battery comprises a negative pole piece and a diaphragm. The content of the silicon element in the negative electrode active layer is x, the puncture resistance strength of the diaphragm is r, and the hole closing temperature of the diaphragm is t. The capacity of the secondary battery is less than 1Ah, and the secondary battery satisfies one of the following conditions: (1) x is less than 3%, r is greater than or equal to 180 gf and less than 280 gf, and t is greater than or equal to 132 DEG C and less than 142 DEG C; (2) 3% < = x < 10%, 280 gf < = r < 460 gf, and 142 DEG C < = t < 150 DEG C; (3) 10% < = x < 25%, 460 gf < = r < 520 gf, 150 DEG C < = t < 153 DEG C; (4) x is greater than or equal to 25%, r is greater than or equal to 520 gf and less than 560 gf, and t is greater than or equal to 153 DEG C and less than 155 DEG C; or the capacity of the secondary battery is greater than or equal to 1Ah, and the secondary battery satisfies one of the following conditions: (1) x is less than 3%, r is greater than or equal to 120 gf and less than 220 gf, and t is greater than or equal to 130 DEG C and less than 140 DEG C; (2) 3% < = x < 10%, 220 gf < = r < 320 gf, 140 DEG C < = t < 145 DEG C; (3) 10% < = x < 25%, 320 gf < = r < 360 gf, and 145 DEG C < = t < 148 DEG C; and (4) x > = 25%, 360 < = r < 450, and 148 DEG C < = t < 152 DEG C.

Description

Secondary battery and electronic device TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a secondary battery and an electronic device. BACKGROUND

[0002] During storage, the capacity of a battery naturally decreases without an external circuit, which is called self-discharge. Self-discharge not only affects the capacity and internal resistance of the battery, but also brings insecurity in use.

[0003] With the wide application of lithium ion batteries in various electronic products, users have put forward higher and higher requirements for the energy density of lithium ion batteries. Silicon-based negative electrode materials have a significantly higher specific capacity than carbon-based negative electrode materials, and the application of silicon-based negative electrode materials is an important technical direction for the industry to develop high-energy-density lithium ion batteries. However, silicon-based negative electrode material particles are easy to pierce the separator and form micro-short circuit points, causing the problem of large self-discharge of the battery.

[0004] SUMMARY

[0005] One object of the present application is to provide a secondary battery that can improve the problem of self-discharge.

[0006] The first aspect of the present application provides a secondary battery comprising an electrode assembly. The electrode assembly comprises a negative electrode sheet, a positive electrode sheet, and a separator arranged between the negative electrode sheet and the positive electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer provided on at least one surface of the negative electrode current collector. The negative electrode active layer comprises silicon-based particles. The content of silicon elements in the negative electrode active layer is x, the puncture resistance of the separator is r, the closed pore temperature of the separator is t, the capacity of the secondary battery is less than 1 Ah, and the secondary battery satisfies one of the following conditions:

[0007] (1) x < 3%, 180 gf ≤ r < 280 gf, 132℃ ≤ t < 142℃;

[0008] (2) 3% ≤ x < 10%, 280 gf ≤ r < 460 gf, 142℃ ≤ t < 150℃;

[0009] (3) 10% ≤ x < 25%, 460 gf ≤ r < 520 gf, 150℃ ≤ t < 153℃;

[0010] (4) x ≥ 25%, 520 gf ≤ r < 560 gf, 153℃ ≤ t < 155℃;

[0011] Alternatively, the capacity of the secondary battery is greater than or equal to 1 Ah, and the secondary battery satisfies one of the following conditions:

[0012] (1) x < 3%, 120 gf ≤ r < 220 gf, 130℃ ≤ t < 140℃;

[0013] (2) 3%≤x<10%, 220 gf≤r<320 gf, 140℃≤t<145℃;

[0014] (3) 10%≤x<25%, 320 gf≤r<360 gf, 145℃≤t<150℃;

[0015] (4) x≥25%, 360≤r<450, 150℃≤t<155℃.

[0016] The secondary battery provided by the embodiments of the present application can have good self-discharge performance and thermal safety performance by regulating the puncture resistance r of the separator, the closed pore temperature t of the separator, and the content x of silicon in the negative active layer to satisfy the above conditions.

[0017] According to some embodiments of the present application, the capacity of the secondary battery is less than 1 Ah, and the secondary battery satisfies one of the following conditions: (1) x<3%, 250 gf≤r<280 gf, 140℃≤t<142℃; (2) 3%≤x<10%, 300 gf≤r<460 gf, 142℃≤t<147℃; or the capacity of the secondary battery is greater than or equal to 1 Ah, and the secondary battery satisfies one of the following conditions: (1) x<3%, 190 gf≤r<220 gf, 135℃≤t<140℃; (2) 3%≤x<10%, 250 gf≤r<320 gf, 140℃≤t<142℃. In this way, the self-discharge performance and the thermal safety performance can be improved.

[0018] According to some embodiments of the present application, the separator comprises a substrate and an inorganic coating layer disposed on at least one surface of the substrate, and the inorganic coating layer comprises an inorganic filler and a binder. By disposing the inorganic coating layer, the heat resistance and the puncture resistance of the separator can be improved.

[0019] According to some embodiments of the present application, the thickness of the substrate is 3-7 μm, and the thickness h of the inorganic coating layer is 1-3 μm, so that the separator has appropriate puncture resistance and closed pore temperature while ensuring the energy density of the secondary battery.

[0020] According to some embodiments of the present application, the separator further comprises an organic coating layer disposed on the surface of the inorganic coating layer. The organic coating layer bonds the separator to the electrode sheet, thereby reducing the risk of delamination of the separator from the electrode sheet.

[0021] According to some embodiments of the present application, the organic coating layer comprises polymer particles selected from at least one of homopolymers or copolymers of vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, chloropropylene, acrylic acid, acrylate, styrene, butadiene, acrylonitrile. The gaps between the polymer particles reserve space for electrolyte transmission, improve the transmission capacity of the electrolyte, improve the electrolyte infiltration effect, and at the same time increase the storage capacity of the electrolyte, which is beneficial to improve the cycle performance.

[0022] According to some embodiments of the present application, the inorganic filler comprises at least one of boehmite, alumina, zirconia, titania, magnesia, mullite, silicon carbide, silicon nitride, boron nitride, or aluminum nitride.

[0023] According to some embodiments of the present application, the substrate comprises one or more of polyethylene, polypropylene, non-woven fabric, polyethylene terephthalate, polyimide, polypropylene-polyethylene-polypropylene composite film.

[0024] According to some embodiments of the present application, the silicon-based particles comprise one or more of silicon element, silicon-carbon, silicon-oxygen, silicon-oxygen-carbon, or silicon alloy.

[0025] The second aspect of the present application provides an electronic device comprising the secondary battery of any of the above embodiments. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application are described below clearly and in detail. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments. Unless otherwise defined, all the technical and scientific terms used herein have the same meanings as those commonly understood by the person skilled in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments and are not intended to limit the present application.

[0027] Further, when describing the embodiments of the present application, "may" means "one or more embodiments of the present application".

[0028] The professional terms used herein are for the purpose of describing the specific embodiments and are not intended to limit the present application. As used herein, the singular form is intended to include the plural form, unless the context clearly indicates otherwise. It should be further understood that the term "comprising" when used in the present specification means that the stated features, numbers, steps, operations, elements, and / or components are present, but does not exclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, and / or combinations thereof.

[0029] One embodiment of the present application provides a secondary battery including a housing and an electrode assembly and an electrolyte contained in the housing. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet. The housing can be a packaging bag obtained by packaging with a packaging film, or can be a metal housing, which is not limited by the present application. The positive electrode sheet, the separator, and the negative electrode sheet can be alternately stacked to form a stacked structure, or the positive electrode sheet, the separator, and the negative electrode sheet can be stacked and then wound to form a wound structure, which is not limited by the present application.

[0030] Negative electrode sheet

[0031] The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector. The negative active material of the negative active layer includes silicon-based particles. In some embodiments, the silicon-based particles include one or more of silicon elemental particles, silicon-carbon particles, silicon-oxygen particles, silicon-oxygen-carbon particles, or silicon alloy particles. The silicon-oxygen particles refer to silicon oxide particles, and the silicon oxide is represented by the general formula SiO x wherein 0 < x < 2. The silicon-oxygen-carbon particles refer to carbon-coated silicon oxide particles. The silicon-carbon particles refer to particulate materials composed of silicon and carbon. The silicon alloy particles refer to alloy composition particles formed by silicon and at least one metal, including but not limited to silicon-iron alloy, silicon-aluminum alloy, silicon-nickel alloy, or silicon-iron-aluminum alloy, etc.

[0032] In some embodiments, the negative active material of the negative active layer further includes carbon-based materials. The expansion rate of the carbon-based materials is lower than that of the silicon-based materials during the charging and discharging process of the secondary battery. The carbon-based materials include, but are not limited to, graphite, graphene, soft carbon, hard carbon, or mixtures thereof.

[0033] In some embodiments, the negative active layer further includes a conductive agent. The conductive agent is used to improve the conductivity of the negative electrode sheet. The conductive agent can include any electrically conductive material that does not cause chemical changes. Examples of the conductive agent include, but are not limited to, carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, etc.), metal-based materials (such as metal powder or metal fibers, including copper, nickel, aluminum, silver, etc.), conductive polymers (such as polyphenylene derivatives, etc.), or mixtures thereof.

[0034] In some embodiments, the negative active layer further includes a binder. The binder can improve the binding between the negative active material particles and each other, and can improve the binding between the negative active material and the negative current collector. The binder can include any adhesive polymer. Examples of the binder include, but are not limited to, polyacrylic acid, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, nylon, or mixtures thereof.

[0035] In some embodiments, the negative current collector includes, but is not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, polymer substrate coated with a conductive metal, and any combination thereof. In some embodiments, the negative current collector is copper foil.

[0036] In some embodiments, the method of preparing the negative electrode tab is a method of preparing a negative electrode tab for a secondary battery known in the art. For example, the negative electrode tab can be obtained by mixing the negative active material, the conductive agent, and the binder in a solvent, and a thickening agent can be added as needed to prepare an active material composition, and the active material composition is coated on the negative current collector. In some embodiments, the solvent can include, but is not limited to, water, N-methylpyrrolidone.

[0037] Separator

[0038] The separator includes a substrate. The substrate is formed of an electrically insulating porous body. The material of the substrate is not particularly limited, and a known separator material can be used. Examples of the electrically insulating porous body include, but are not limited to, a film monolayer, a laminate, or an extended film of a mixture of the above resins composed of polyethylene, polypropylene, or a polyolefin, or a fiber nonwoven fabric made of at least one material selected from the group consisting of cellulose, polyester, and polypropylene. In some embodiments, the substrate includes one or more of polyethylene, polypropylene, nonwoven fabric, polyethylene terephthalate, polyimide, polypropylene-polyethylene-polypropylene composite film.

[0039] In some embodiments, the thickness of the substrate is 3 to 7 μm, and the separator has good mechanical properties while maintaining a good energy density. In some embodiments, the separator is provided with suitable puncture resistance and closed pore temperature by adjusting the material, thickness, stretching process, and the like of the substrate.

[0040] In some embodiments, the separator further comprises an inorganic coating layer disposed on at least one surface of the substrate. The inorganic coating layer comprises an inorganic filler. The inorganic filler can comprise any inorganic material that does not cause chemical change. Examples of the inorganic filler include, but are not limited to, boehmite, alumina, zirconia, titania, magnesia, mullite, silicon carbide, silicon nitride, boron nitride, aluminum nitride, or a mixture thereof. By disposing the inorganic coating layer, the heat resistance and the puncture strength of the separator can be improved.

[0041] In some embodiments, the inorganic coating layer further comprises a binder. The binder can improve the binding between the inorganic fillers and can improve the binding between the inorganic coating layer and the substrate. The binder can comprise any adhesive polymer. Examples of the binder include, but are not limited to, polyacrylate, polybutadiene-styrene copolymer, polyacrylic acid, polyacrylonitrile-acrylic acid copolymer, polytetrafluoroethylene, polyvinylidene fluoride, polymethyl methacrylate, polyvinylidene fluoride-hexafluoropropylene copolymer, or a mixture thereof.

[0042] In some embodiments, the inorganic coating layer has a thickness of 1 to 3 μm.

[0043] In some embodiments, the separator further comprises an organic coating layer. The organic coating layer is disposed on the surface of the inorganic coating layer facing away from the substrate. The organic coating layer comprises a polymer. The polymer can comprise any organic material that does not cause chemical change. Examples of the polymer include, but are not limited to, polyacrylic acid resin, aramid, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, or a mixture thereof.

[0044] In some embodiments, the polymer of the organic coating layer is in a particulate form, i.e., the organic coating layer comprises polymer particles selected from at least one of homopolymers or copolymers of vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, chloropropylene, acrylic acid, acrylate, styrene, butadiene, acrylonitrile. In some embodiments, the polymer particles are preferably polyvinylidene fluoride. In other embodiments, the polymer of the organic coating layer is in a non-particulate form.

[0045] In some embodiments, the organic coating layer further comprises a binder. The binder can improve the binding between the polymer particles and can improve the binding between the organic coating layer and the inorganic coating layer. The binder can comprise any adhesive polymer. Examples of the binder include, but are not limited to, polyacrylate, polybutadiene-styrene copolymer, polyacrylic acid, polyacrylonitrile-acrylic acid copolymer, polytetrafluoroethylene, polyvinylidene fluoride, polymethyl methacrylate, polyvinylidene fluoride-hexafluoropropylene copolymer, or a mixture thereof.

[0046] The puncture resistance of the separator is r, the closed pore temperature of the separator is t, and the content of silicon elements in the negative active layer is x. The inventors have found through research that the more the content of silicon elements in the negative active layer, the higher the risk of the separator being punctured by silicon-based particles. By adjusting the content of silicon elements and the puncture resistance of the separator, the self-discharge safety of the secondary battery can be ensured. However, the higher the puncture resistance of the separator, the higher the closed pore temperature of the separator, resulting in poor thermal safety performance. By adjusting the puncture resistance r of the separator, the closed pore temperature t of the separator, and the content x of silicon elements in the negative active layer, the secondary battery can have good self-discharge performance (K≤0.08 mV / h) and good thermal safety performance.

[0047] In some embodiments, the capacity of the secondary battery is less than 1 Ah, and the secondary battery satisfies the following conditions: x < 3%, 180 gf≤ r < 280 gf, 132℃≤ t < 142℃. When the secondary battery satisfies the above conditions, the secondary battery has good self-discharge characteristics K≤ 0.08 mV / h. Preferably, 250 gf≤ r < 280 gf, 140℃≤ t < 142℃.

[0048] In some embodiments, the capacity of the secondary battery is less than 1 Ah, and the secondary battery satisfies the following conditions: 3%≤ x < 10%, 280 gf≤ r < 460 gf, 142℃≤ t < 150℃. When the secondary battery satisfies the above conditions, the secondary battery has good self-discharge characteristics K≤ 0.08 mV / h and good thermal safety performance. Preferably, 300 gf≤ r < 460 gf, 142℃≤ t < 147℃.

[0049] In some embodiments, the capacity of the secondary battery is less than 1 Ah, and the secondary battery satisfies the following conditions: 10%≤ x < 25%, 460 gf≤ r < 520 gf, 150℃≤ t < 153℃.

[0050] In some embodiments, the capacity of the secondary battery is less than 1 Ah, and the secondary battery satisfies the following conditions: x≥ 25%, 520 gf≤ r < 560 gf, 153℃≤ t < 155℃. When the secondary battery satisfies the above conditions, the secondary battery has good self-discharge characteristics K≤ 0.08 mV / h and good thermal safety performance.

[0051] In some embodiments, the capacity of the secondary battery is greater than or equal to 1 Ah, and the secondary battery satisfies the following conditions: x < 3%, 120 gf≤ r < 220 gf, 130℃≤ t < 140℃. When the secondary battery satisfies the above conditions, the secondary battery has good self-discharge characteristics K≤ 0.08 mV / h and good safety performance. Preferably, 190 gf≤ r < 220 gf, 135℃≤ t < 140℃.

[0052] In some embodiments, the capacity of the secondary battery is greater than or equal to 1 Ah, and the secondary battery satisfies the following conditions: 3%≤x<10%, 220 gf≤r<320 gf, 140 °C≤t<145 °C. When the secondary battery satisfies the above conditions, the secondary battery has a good self-discharge characteristic K≤0.08 mV / h, and has good safety performance. Preferably, 250 gf≤r<320 gf, 140 °C≤t<142 °C.

[0053] In some embodiments, the capacity of the secondary battery is greater than or equal to 1 Ah, and the secondary battery satisfies the following conditions: 10%≤x<25%, 320 gf≤r<360 gf, 145 °C≤t<148 °C. When the secondary battery satisfies the above conditions, the secondary battery has a good self-discharge characteristic K≤0.08 mV / h, and has good safety performance.

[0054] In some embodiments, the capacity of the secondary battery is greater than or equal to 1 Ah, and the secondary battery satisfies the following conditions: x≥25%, 360≤r<450, 148 °C≤t<152 °C. When the secondary battery satisfies the above conditions, the secondary battery has a good self-discharge characteristic K≤0.08 mV / h, and has good safety performance.

[0055] Positive electrode sheet

[0056] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector. The positive active layer includes a positive active material, and the specific type of the positive active material is not particularly limited and can be selected as needed. In some embodiments, the positive active material includes a compound that reversibly intercalates and deintercalates lithium ions (i.e., lithiated intercalation compound). In some embodiments, the positive active material can include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive active material is selected from at least one of lithium cobaltate (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganate (LiMn2O4), lithium nickel manganate (LiNi 0.5 Mn 1.5 O4), or lithium iron phosphate (LiFePO4).

[0057] In some embodiments, the positive electrode active layer further includes a binder, and optionally, a conductive material. The binder can improve the binding between the positive electrode active material particles, and can improve the binding between the positive electrode active material and the positive electrode current collector. In some embodiments, the binder includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, butadiene-styrene rubber, acrylated butadiene-styrene rubber, epoxy resins, and nylon, etc.

[0058] In some embodiments, the positive electrode active layer includes a conductive material, thereby imparting electrical conductivity to the positive electrode plate. The conductive material can include any conductive material, as long as it does not cause chemical changes. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, etc.), metal-based materials (e.g., metal powder, metal fibers, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0059] In some embodiments, the positive electrode current collector is a metal, including, but not limited to, aluminum foil.

[0060] In some embodiments, the method of preparing the positive electrode is a method of preparing a positive electrode for an electrochemical device known in the art. For example, the positive electrode can be obtained by mixing the active material, the conductive material, and the binder in a solvent to prepare an active material composition, and coating the active material composition on the current collector. In some embodiments, the solvent can include water, N-methyl pyrrolidone, etc., but is not limited thereto.

[0061] Electrolyte

[0062] The electrolyte used in the embodiments of the present application can be an electrolyte known in the art. The electrolyte can be classified into an aqueous electrolyte and a non-aqueous electrolyte, wherein the electrochemical device using the non-aqueous electrolyte can operate at a wider voltage window compared to the aqueous electrolyte, thereby achieving a higher energy density. In some embodiments, the non-aqueous electrolyte includes an organic solvent, an electrolyte, and an additive.

[0063] Electrolytes that can be used in the electrolyte of embodiments of the present application include, but are not limited to, inorganic lithium salts such as LiC104, LiAsF6, LiPF6, LiBF4, LiSbF6, LiSO3F, LiN(FSO2)2, and the like; fluorine-containing organic lithium salts such as LiCF3SO3, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,3-hexafluoropropanedisulfonimide lithium, cyclic 1,2-tetrafluoroethane disulfonimide lithium, LiPF4(CF3)2, LiN(CF3SO2)(C4F9SO2), LiC(CF3SO2)3, LiPF4(CF3SO2)2, LiPF4(C2F5)2, LiPF4(C2F5SO2)2, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2; dicarboxylic acid complex-containing lithium salts such as lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, and the like. Additionally, the above electrolytes can be used singly, or two or more kinds can be used simultaneously. For example, in some embodiments, the electrolyte includes a combination of LiPF6and LiBF4. In some embodiments, the electrolyte includes LiPF6.

[0064] In some embodiments, the concentration of the electrolyte is in the range of 0.8 mol / L to 3 mol / L, such as in the range of 0.8 mol / L to 2.5 mol / L, in the range of 0.8 mol / L to 2 mol / L, in the range of 1 mol / L to 2 mol / L, and for example, 1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.5 mol / L, 2 mol / L, or 2.5 mol / L.

[0065] The additive that can be used in the electrolyte of embodiments of the present application can be any additive known in the art that can be used to improve the electrochemical performance of the battery. In some embodiments, the additive includes, but is not limited to, at least one of a polycarbonitrile compound, a sulfur-containing additive, fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), 1,4 butane sultone.

[0066] The organic solvent that can be used in the electrolyte of embodiments of the present application can be any organic solvent known in the art. In some embodiments, the organic solvent includes, but is not limited to, a carbonate compound, an ester-based compound, an ether-based compound, a ketone-based compound, an alcohol-based compound, an aprotic solvent, or a combination thereof. Among them, examples of the carbonate compound include, but are not limited to, a chain carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound, or a combination thereof.

[0067] In some embodiments, the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, methyl acetate, or ethyl propionate.

[0068] The preparation method of the electrolyte of the embodiments of the present application is not limited and can be prepared in a conventional manner of electrolyte. In some embodiments, the electrolyte of the present application can be prepared by mixing the components.

[0069] The embodiments of the present application also provide an electronic device including the secondary battery as above. The electronic device of the present application can be, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, an illuminating appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0070] Some specific examples are listed below to better illustrate the present application, in which lithium ion batteries are taken as examples.

[0071] Example 1-1

[0072] (1) Preparation of the negative electrode sheet

[0073] A copper foil is used as the negative current collector, and a mixed slurry of graphite and silicon carbon is coated on the surface of the copper foil. The composition of the slurry is 97.6wt% negative active material (87.84wt% graphite and 9.76wt% silicon carbon (SiC)), 0.5wt% carboxymethyl cellulose (CMC), 1.7wt% polyacrylic acid (PAA), and 0.2% carbon nanotubes. Then, drying, cold pressing, cutting, and welding of the tabs are performed to prepare the negative electrode sheet.

[0074] (2) Preparation of the positive electrode sheet

[0075] An aluminum foil is used as the positive current collector, and a layer of lithium cobaltate slurry is uniformly coated on both sides of the aluminum foil. The composition of the lithium cobaltate slurry is 97.8wt% LiCoO2(LCO), 0.8wt% polyvinylidene fluoride (PVDF), and 1.4wt% conductive carbon black. Then, drying, cold pressing, cutting, and welding of the tabs are performed to prepare the positive electrode sheet.

[0076] (3) Preparation of the electrolyte

[0077] An electrolyte was prepared by adding LiPF6 into a solvent mixed from propylene carbonate (PC), ethylene carbonate (EC) and diethyl carbonate (DEC) (weight ratio 1:1:1) under dry argon atmosphere, wherein the concentration of LiPF6 was 1.15 mol / L.

[0078] (4) Preparation of the separator

[0079] A polyethylene porous film with a thickness of 4.5 μm was selected as the base material. An inorganic coating layer was formed on the surface of the base material, and an organic coating layer was formed on the surface of the inorganic coating layer. The inorganic filler of the inorganic coating layer was boehmite, and the polymer particles of the organic coating layer were polyvinylidene fluoride. The thickness of the inorganic coating layer was 2 μm.

[0080] (5) Preparation of the lithium ion battery

[0081] The positive electrode sheet and the negative electrode sheet were wound after slitting, and the positive electrode sheet and the negative electrode sheet were separated by the separator, so that the separator played a role of isolation. The electrode assembly was obtained by winding. The electrode assembly was placed in an aluminum plastic film, injected with electrolyte, and formed to obtain a lithium ion battery with a capacity of 0.8 Ah.

[0082] Examples 1-2 to 1-22 and Comparative Examples 1-1 to 1-6

[0083] The difference from Example 1-1 was that at least one of the type of silicon-based material, the content of silicon-based material in the negative active layer, the content x of silicon element in the negative active layer, the puncture resistance r of the separator, the closed pore temperature t of the separator, and the thickness of the inorganic coating layer was different. In each example and comparative example, the content of the negative active material in the negative active layer was the same. The silicon oxide was SiO. See Table 1 for details.

[0084] The test methods of the various parameters of the present application are described below.

[0085] Puncture resistance test of the separator:

[0086] The separator sample was fixed in a clamp, and a needle with a diameter of 1.0 mm was used to puncture at a speed of 100 mm / min on a puncture resistance tester. The puncture resistance of the separator when punctured was measured (unit: gf).

[0087] Closed pore temperature test of the separator:

[0088] The separator sample immersed in the electrolyte was fixed in a clamp and placed in an oven. The temperature of the oven was set to 155℃. The temperature was raised from room temperature, and the temperature-resistance change of the separator sample was monitored simultaneously using an electrochemical workstation. When the resistance suddenly rose to 3000Ω, the corresponding temperature was the closed pore temperature of the separator.

[0089] Test of silicon element content:

[0090] The lithium ion battery was disassembled to obtain a negative electrode sheet, which was soaked in a dimethyl carbonate (DMC) solution for 15 min and then dried for standby use. The negative electrode active layer was scraped to form a powder, and the silicon element content was tested by inductively coupled plasma technology (ICP).

[0091] Test of lithium ion battery self-discharge rate (K value):

[0092] The lithium ion battery was charged at room temperature according to the standard process to the vicinity of the platform voltage (for example, the battery nominal capacity is C, the platform voltage is 3.85 V, 0.2C CC to 3.9 V, CV to 0.02C), then placed in a 45°C environment for 1 day and in a 25°C environment for 1 day, and the voltage at this time was recorded as U1. Then, it was placed in a 25°C environment for 2 days, and the voltage at this time was recorded as U2. The K value was obtained by the following formula: K (mV / h) = (U1-U2) / (2x24h).

[0093] Test of lithium ion thermal safety performance:

[0094] The lithium ion battery was charged at room temperature according to the standard process to the upper limit voltage, for example, the battery nominal capacity of 3-4.5 V system is C, and the process of 0.2C CC to 4.5 V, CV to 0.02C is full charged after; 5 samples were placed in a heating box and heated to the target temperature at a heating rate of 5±2°C and kept for 60 min, the sample did not catch fire or explode, and was considered to pass the thermal safety test of the target temperature, and the highest temperature without fire or explosion was the upper limit temperature of the thermal failure passing.

[0095] Table 1

[0096] As can be seen from Examples 1-1 to 1-22 and Comparative Examples 1-1 to 1-6, when the capacity of the secondary battery is less than 1 Ah, when x < 3%, 180 gf≤ r < 280 gf, 132℃≤ t < 142℃; and / or, 3%≤ x < 10%, 220 gf≤ r < 320 gf, 140℃≤ t < 145℃; and / or, 10%≤ x < 25%, 320 gf≤ r < 360 gf, 145℃≤ t < 150℃; and / or, x≥ 25%, 360≤ r < 450, 150℃≤ t < 155℃, the self-discharge of the secondary battery is significantly reduced, K≤ 0.08 mV / h, and the upper limit temperature of thermal failure passing is within an acceptable range, and good safety performance is achieved. When x < 3%, 250 gf≤ r < 280 gf, 140℃≤ t < 142℃; and / or, 3%≤ x < 10%, 300 gf≤ r < 460 gf, 142℃≤ t < 147℃, it is more conducive to improving the self-discharge and thermal safety performance.

[0097] Example 2-1

[0098] (1) Preparation of the negative electrode sheet

[0099] A copper foil was used as the negative electrode current collector, and a mixed slurry of graphite and silicon carbon was coated on the surface of the copper foil. The composition of the slurry was 97.6wt% negative electrode active material (87.84wt% graphite and 9.76wt% silicon carbon (SiC)), 0.5wt% carboxymethyl cellulose (CMC), 1.7wt% polyacrylic acid (PAA), and 0.2% carbon nanotubes. Subsequently, drying, cold pressing, and then cutting and welding the tabs were performed to prepare the negative electrode sheet.

[0100] (2) Preparation of the positive electrode sheet

[0101] An aluminum foil was used as the positive electrode current collector, and a layer of lithium cobalt oxide slurry was uniformly coated on both sides of the aluminum foil. The composition of the lithium cobalt oxide slurry was 97.8wt% LiCoO2(LCO), 0.8wt% polyvinylidene fluoride (PVDF), and 1.4wt% conductive carbon black. Subsequently, drying, cold pressing, and then cutting and welding the tabs were performed to prepare the positive electrode sheet.

[0102] (3) Preparation of the electrolyte

[0103] In a dry argon environment, LiPF6 was added to a solvent composed of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (weight ratio 1:1:1) and mixed uniformly to obtain an electrolyte, wherein the concentration of LiPF6 was 1.15 mol / L.

[0104] (4) Preparation of the separator

[0105] A polyethylene porous film with a thickness of 4.5 μm is selected as a base material. An inorganic coating layer is formed on the surface of the base material, and an organic coating layer is formed on the surface of the inorganic coating layer. The inorganic filler of the inorganic coating layer is boehmite, and the polymer particles of the organic coating layer are polyvinylidene fluoride. The thickness of the inorganic coating layer is 2 μm.

[0106] (5) Preparation of lithium ion battery

[0107] The positive electrode sheet and the negative electrode sheet are wound after slitting, and the positive electrode sheet and the negative electrode sheet are separated by a separator, so that the separator plays a role of isolation, and an electrode assembly is obtained by winding. The electrode assembly is placed in an aluminum plastic film, injected with electrolyte, and formed to obtain a lithium ion battery with a capacity of 2.7 Ah.

[0108] Examples 2-2 to 2-21 and Comparative Examples 2-1 to 2-6

[0109] The difference from Example 2-1 is that at least one of the type of silicon-based material, the content of silicon-based material in the negative active layer, the content x of silicon element in the negative active layer, the puncture resistance r of the separator, and the closed pore temperature t of the separator is different. The specific parameters are shown in Table 2.

[0110] The batteries of each example and comparative example are tested for K value and safety performance. The test results are shown in Table 2.

[0111] Table 2

[0112] As can be seen from Examples 2-1 to 2-21, when the capacity of the secondary battery is greater than or equal to 1 Ah, when x < 3%, 120 gf ≤ r < 220 gf, 130 ℃ ≤ t < 140 ℃; and / or, 3% ≤ x < 10%, 220 gf ≤ r < 320 gf, 140 ℃ ≤ t < 145 ℃; and / or, 10% ≤ x < 25%, 320 gf ≤ r < 360 gf, 145 ℃ ≤ t < 148 ℃; and / or, x ≥ 25%, 360 ≤ r < 450, 148 ℃ ≤ t < 152 ℃, the self-discharge of the secondary battery is significantly reduced, K ≤ 0.08 mV / h, and the upper limit temperature of thermal failure is within an acceptable range, and has good safety performance. When x < 3%, 190 gf ≤ r < 220 gf, 135 ℃ ≤ t < 140 ℃; and / or 3% ≤ x < 10%, 250 gf ≤ r < 320 gf, 140 ℃ ≤ t < 142 ℃, it is more beneficial to improve the self-discharge and thermal safety performance.

[0113] The above disclosure is only the preferred embodiments of the present application, and of course cannot limit the scope of the rights of the present application, so the equivalent changes made according to the claims of the present application are still within the scope covered by the present application.

Claims

1. A secondary battery comprising an electrode assembly including a negative electrode sheet, a positive electrode sheet, and a separator disposed between the negative electrode sheet and the positive electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode active layer provided on at least one surface of the negative electrode current collector, characterized in that, The negative active layer includes silicon-based particles; The content of silicon element in the negative active layer is x, the puncture resistance of the separator is r, and the closed pore temperature of the separator is t; The capacity of the secondary battery is less than 1 Ah, and the secondary battery satisfies one of the following conditions: (1) x < 3%, 180 gf ≤ r < 280 gf, 132℃ ≤ t < 142℃; (2) 3% ≤ x < 10%, 280 gf ≤ r < 460 gf, 142℃ ≤ t < 150℃; (3) 10% ≤ x < 25%, 460 gf ≤ r < 520 gf, 150℃ ≤ t < 153℃; (4) x ≥ 25%, 520 gf ≤ r < 560 gf, 153℃ ≤ t < 155℃; Alternatively, the capacity of the secondary battery is greater than or equal to 1 Ah, and the secondary battery satisfies one of the following conditions: (1) x < 3%, 120 gf ≤ r < 220 gf, 130℃ ≤ t < 140℃; (2) 3% ≤ x < 10%, 220 gf ≤ r < 320 gf, 140℃ ≤ t < 145℃; (3) 10% ≤ x < 25%, 320 gf ≤ r < 360 gf, 145℃ ≤ t < 148℃; (4) x ≥ 25%, 360 ≤ r < 450, 148℃ ≤ t < 152℃.

2. The secondary battery according to claim 1, wherein The capacity of the secondary battery is less than 1 Ah, and the secondary battery satisfies one of the following conditions: (1) x < 3%, 250 gf ≤ r < 280 gf, 140℃ ≤ t < 142℃; (2) 3% ≤ x < 10%, 300 gf ≤ r < 460 gf, 142℃ ≤ t < 147℃.

3. The secondary battery according to claim 1, wherein The capacity of the secondary battery is greater than or equal to 1 Ah, and the secondary battery satisfies one of the following conditions: (1) x < 3%, 190 gf ≤ r < 220 gf, 135℃ ≤ t < 140℃; (2) 3% ≤ x < 10%, 250 gf ≤ r < 320 gf, 140℃ ≤ t < 142℃.

4. The secondary battery according to any one of claims 1 to 3, characterized by The separator includes a base material and an inorganic coating layer provided on at least one surface of the base material, and the inorganic coating layer includes an inorganic filler and a binder.

5. The secondary battery according to claim 4, wherein The thickness of the base material is 3 to 7 μm, and the thickness h of the inorganic coating layer is 1 to 3 μm.

6. The secondary battery according to claim 4, wherein The separator further includes an organic coating layer provided on a surface of the inorganic coating layer.

7. The secondary battery according to claim 6, wherein The organic coating layer includes polymer particles selected from at least one of homopolymers or copolymers of vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, chloropropylene, acrylic acid, acrylic ester, styrene, butadiene, and acrylonitrile.

8. The secondary battery according to claim 4, wherein The inorganic filler includes at least one of boehmite, alumina, zirconia, titania, magnesia, mullite, silicon carbide, silicon nitride, boron nitride, or aluminum nitride.

9. The secondary battery according to claim 4, wherein The base material includes one or more of polyethylene, polypropylene, non-woven fabric, polyethylene terephthalate, polyimide, and polypropylene-polyethylene-polypropylene composite film.

10. The secondary battery according to any one of claims 1 to 3, characterized by The silicon-based particles include one or more of silicon single substance, silicon-carbon, silicon-oxygen, silicon-oxygen-carbon, or silicon alloy.

11. An electronic device, comprising: A secondary battery including the secondary battery according to any one of claims 1 to 10.