Secondary battery and electric device

Abstract

Provided in the embodiments of the present application are a secondary battery and an electric device. In the secondary battery provided in the embodiments of the present application, the thickness Hc of a positive membrane layer of a battery, the contact angle θ of an electrolyte on a positive current collector, the weighted value a of a dielectric constant of an organic solvent in the electrolyte, and the total lithium-ion concentration M in the electrolyte are controlled, and the following relational expression is satisfied: 0.450≤(cosθ×a) / (M×Hc)≤0.792, so that the prepared secondary battery has lower self-discharge performance and better kinetic performance and cycle performance while meeting the requirement of high energy density.

Description

Secondary battery and electrical equipment

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on November 21, 2023, with application number 202311563142.4 and titled “A Secondary Battery and Electrical Equipment,” the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery manufacturing technology, and in particular to a secondary battery and electrical equipment. Background Art

[0003] Currently, lithium-ion batteries are widely used in portable electronic products and new energy vehicles due to their advantages such as high operating voltage, long cycle life, high energy density, low self-discharge and no memory effect.

[0004] In the existing technology, in order to obtain high energy density, lithium-ion battery electrodes need to be set with a larger coating weight or compaction density, but this also brings about the problems of difficulty in the electrode being infiltrated by the electrolyte, increased battery polarization, and deterioration of dynamic performance; and in order to obtain better dynamic performance, setting the electrode to have a smaller coating weight or compaction density will lead to increased side reactions, resulting in increased self-discharge, rapid decay of cycle performance and other consequences.

[0005] Therefore, existing lithium-ion batteries cannot effectively achieve both high energy density and good dynamic performance.

[0006] Summary of the Invention

[0007] The technical problem to be solved by the present application is to provide a secondary battery and an electrical device to solve the problem that existing lithium-ion batteries cannot effectively achieve both high energy density and good dynamic performance.

[0008] In order to solve the above problems, this application is implemented through the following technical solutions:

[0009] The present application proposes a secondary battery, comprising a positive electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector; the electrolyte comprises a lithium salt, an organic solvent, and an additive; the secondary battery satisfies the following formula (1): 0.450≤(cosθ×a) / (M×Hc)≤0.792 Formula (1)

[0010] Wherein, θ° is the contact angle of the electrolyte on the positive electrode current collector; a is the weighted value of the dielectric constant of the organic solvent in the electrolyte, satisfying formula (2); M mol / L is the total lithium ion concentration in the electrolyte; Hcμm is the thickness of the positive electrode membrane layer on one surface of the positive electrode current collector;

[0011] Wherein, n is the amount of organic solvent in the electrolyte; x i is the ratio of the mass of the i-th organic solvent to the total mass of all organic solvents; y i is the dielectric constant of the i-th organic solvent.

[0012] Furthermore, the secondary battery satisfies at least one of the following conditions: 1) 26.0°<θ<48.0°; 2) 21.0 <a<38.0;3)0.8≤M≤1.3;4)36.5≤Hc≤54.0。

[0013] Furthermore, in the secondary battery, the lithium salt includes lithium hexafluorophosphate, and at least one of lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, lithium fluorosulfonate, lithium trifluoromethanesulfonate, lithium difluorobis(oxalatophosphate), lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

[0014] Furthermore, in the secondary battery, the organic solvent includes acetonitrile and at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, methyl trifluoroethyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, ethyl difluoroacetate, 2,2-difluoroethyl acetate, cyclopentane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0015] Furthermore, in the secondary battery, the organic solvent includes acetonitrile, and at least one of fluoroethylene carbonate and sulfolane.

[0016] Furthermore, in the secondary battery, the organic solvent includes fluoroethylene carbonate, acetonitrile and sulfolane. Based on the total mass of the organic solvent, fluoroethylene carbonate accounts for 2% to 15%, acetonitrile accounts for 2% to 20%, and sulfolane accounts for 2% to 10%.

[0017] Furthermore, in the secondary battery, the additive includes at least one of vinylene carbonate, erythritol bis(carbonate), ethylene sulfate, pentaerythritol bicyclic sulfate, 1,3-propane sultone, 1,4-butane sultone, methylene disulfonate, 1-propylene-1,3-sultone, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, and tripropargyl phosphate.

[0018] Furthermore, in the secondary battery, the additive includes vinylene carbonate and at least one of erythritol bis(carbonate), 1,3-propane sultone, and pentaerythritol bicyclic sulfate.

[0019] Furthermore, in the secondary battery, the electrolyte additives include vinylene carbonate, erythritol bis(carbonate), 1,3-propane sultone and pentaerythritol bicyclic sulfate.

[0020] Furthermore, in the secondary battery, based on the total mass of the electrolyte, vinylene carbonate accounts for 0.01% to 1.5%, erythritol bis(carbonate) accounts for 0.01% to 1%, 1,3-propane sultone accounts for 0.1% to 2%, and pentaerythritol bicyclic sulfate accounts for 0.1% to 2%.

[0021] Furthermore, in the secondary battery, the positive electrode current collector includes a polymer substrate layer and metal layers arranged on both surfaces of the polymer substrate layer, and the positive electrode membrane layer is arranged on the metal layer.

[0022] Furthermore, in the secondary battery, the polymer substrate layer comprises an organic polymer material, and the organic polymer material includes at least one of polyamide, polyterephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, poly(p-phenylene terephthalamide), polypropylene, polyoxymethylene, epoxy resin, phenolic resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber or polycarbonate.

[0023] Furthermore, in the secondary battery, the thickness of the polymer substrate layer is 6 to 10 μm.

[0024] Furthermore, in the secondary battery, the metal layer is an aluminum layer.

[0025] Furthermore, in the secondary battery, the thickness of the aluminum layer is 0.5 to 1.5 μm.

[0026] Furthermore, in the secondary battery, the positive electrode film layer contains a positive electrode active material; the positive electrode active material includes Li x Ni a1 Co b M c A dO2, where M includes one or both of Mn and Al, A includes at least one of W, B, Mg, Y, V, F, P, Zr, Bi, and Ti, 0.95 ≤ x ≤ 1.2, 0.8 < a1 ≤ 0.95, 0 < b < 0.1, 0 < c < 0.1, 0 ≤ d < 0.1 and a1 + b + c + d = 1.

[0027] Further, in the secondary battery, 0.9 ≤ a1 ≤ 0.95.

[0028] Further, the secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes at least one of a silicon oxide material, a carbon-silicon material, a metal silicide, and elemental silicon.

[0029] Further, the energy density of the secondary battery is 230 - 330 Wh / kg.

[0030] This application also provides an electrical device, which includes the lithium-ion secondary battery as described in any one of the foregoing, and the lithium-ion secondary battery serves as the power supply of the electrical device.

[0031] Compared with the prior art, the embodiments of this application have the following advantages:

[0032] In the embodiments of this application, the thickness Hc of the battery positive electrode film layer, the contact angle θ of the electrolyte on the positive electrode current collector, the weighted value a of the dielectric constant of the organic solvent in the electrolyte, and the total lithium ion concentration M in the electrolyte are controlled to satisfy the following relational expression: 0.450 ≤ (cosθ × a) / (M × Hc) ≤ 0.792, so that the prepared secondary battery has smaller self-discharge performance, better kinetic performance, and cycling performance while meeting the high energy density.

[0033] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit this application. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of this application, the drawings required for the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of this application, and those of ordinary skill in the art can also obtain other drawings without creative efforts based on these drawings.

[0035] FIG. 1 is a comparison diagram of the 45°C cycling performance of the lithium-ion secondary batteries prepared in Comparative Example 1, Example 1, and Example 2 of this application.

[0036] Explanation of the accompanying figures: 1- cycle-capacity curve of the lithium ion battery prepared in Comparative Example 1, 2- cycle-capacity curve of the lithium ion battery prepared in Example 1, 3- cycle-capacity curve of the lithium ion battery prepared in Example 2. Specific embodiments

[0037] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0038] The applicant of the present application has found that the existing battery design technology is unable to produce a lithium-ion battery that has high energy density, low self-discharge, good kinetic performance and cycle performance.

[0039] In order to solve the above-mentioned problem, the embodiment of the present application provides a secondary battery, comprising a positive electrode plate and an electrolyte, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector; the electrolyte comprises a lithium salt, an organic solvent, and an additive; the secondary battery satisfies the following formula (1): 0.450≤(cosθ×a) / (M×Hc)≤0.792 Formula (1)

[0040] Where θ° is the contact angle of the electrolyte on the positive electrode current collector; a is the weighted value of the dielectric constant of the organic solvent in the electrolyte, which satisfies formula (2); M mol / L is the total lithium ion concentration in the electrolyte; Hcμm is the thickness of the positive electrode film layer on one surface of the positive electrode current collector;

[0041] Where n is the amount of organic solvent in the electrolyte; x i is the ratio of the mass of the i-th organic solvent to the total mass of all organic solvents; y i is the dielectric constant of the i-th organic solvent.

[0042] In this application, the amount of organic solvent in the electrolyte refers to the number of types of organic solvents present in the electrolyte. The above formula (1) and formula (2) establish a quantitative relationship between the electrolyte parameters and the positive electrode plate parameters, so that the prepared secondary battery has a smaller self-discharge, better dynamic performance and cycle performance while meeting high energy density. Optionally, the value of formula (1) can be a range of one or any two of 0.45, 0.48, 0.56, 0.68, 0.72, 0.75, 0.78, and 0.792.

[0043] Optionally, the positive electrode current collector includes a polymer substrate layer and metal layers arranged on both surfaces of the polymer substrate layer, and the positive electrode membrane layer is arranged on the metal layer.

[0044] Optionally, the polymer substrate layer comprises an organic polymer material, and the organic polymer material includes at least one of polyamide, polyterephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, poly(p-phenylene terephthalamide), polypropylene, polyoxymethylene, epoxy resin, phenolic resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber or polycarbonate.

[0045] Optionally, the metal layer may be an aluminum layer.

[0046] Optionally, the thickness of the polymer substrate layer is 6-10 μm, and the thickness of the aluminum layer is 0.5-1.5 μm. The use of composite aluminum foil can improve the flexibility of the positive electrode current collector. The positive electrode current collector surface is stable and uniform, with minimal impact on the liquid. The contact angle θ of the electrolyte on the aluminum foil is an important parameter for measuring the electrolyte's wetting performance. Good electrolyte wetting performance can effectively increase ion transfer rate, reduce battery impedance, and enhance battery rate performance.

[0047] Alternatively, in one embodiment, the contact angle θ of the electrolyte on the positive electrode current collector satisfies 26.0°<θ<48.0°, which can effectively ensure high kinetic performance and long cycle stability of the electrolyte. The contact angle θ can be in the range of one or any two of 27°, 30°, 35°, 40°, 45°, and 47°.

[0048] The contact angle of the electrolyte on the positive electrode current collector can be measured in the following way: 4 μL of electrolyte is dropped on the surface of the positive electrode current collector with a thickness of 8 μm, and the contact angle of the electrolyte on the surface of the positive electrode current collector is measured using a contact angle meter, and the value of the contact time of 10 s is used as the test result of the contact angle.

[0049] Optionally, in one embodiment, the weighted value a of the dielectric constant of the organic solvent in the electrolyte satisfies: 21.0 <a<38.0。

[0050] The weighted dielectric constant of the organic solvent in the electrolyte can comprehensively reflect the dielectric constant level of the electrolyte. When the weighted dielectric constant of the organic solvent is controlled within the above range, it can effectively take into account the electrolyte viscosity and organic solvent stability, thereby ensuring low self-discharge, high dynamic performance, and long-term cycle stability of the electrolyte.

[0051] Optionally, in some embodiments, the weighted value a of the dielectric constant of the organic solvent in the electrolyte may be in the range of one or any two of 21.1, 22, 25, 27, 30, 32, 35, and 37.9.

[0052] The weighted value of the dielectric constant can be determined in the following way:

[0053] The obtained electrolyte was first filtered through an organic syringe filter with a pore size of 0.22 μm, and then directly placed on a gas chromatograph-mass spectrometer (GC-MS) for testing. The composition of the organic solvent can be determined by matching the peak position of the substance to the corresponding substance structure in the mass spectrometer;

[0054] After determining the composition of the organic solvent, the dielectric constant (y) of the corresponding organic solvent can be found in public literature or books. i : the dielectric constant of the i-th organic solvent), such as Lang's Handbook of Chemistry, Solvents and Solutes in Lithium-ion Batteries, etc.; at the same time, the mass fraction of each organic solvent in the electrolyte can be determined using the standard curve method based on the intensity of the peak;

[0055] First calculate the ratio of the mass fraction of the i-th organic solvent to the sum of the mass fractions of all organic solvents as the mass fraction ratio of the i-th organic solvent (x i ), and then calculate the weighted value of the dielectric constant of the organic solvent of the electrolyte a=x1×y1+x2×y2+x3×y3+……+x i ×y i .

[0056] Alternatively, in one embodiment, the total lithium ion concentration M in the electrolyte satisfies 0.8≤M≤1.3, in mol / L, that is, an interface film with a sufficient number of inorganic components can be formed, making the long-cycle performance of the battery more stable, and allowing the electrolyte to have a sufficient amount of transferred charge, ensuring the ion conductivity of the electrolyte and effectively suppressing self-discharge, while preventing the electrolyte from deteriorating the battery's kinetic performance due to excessive viscosity. Alternatively, in some embodiments, the lithium ion concentration M can be a range of one or any two of 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, and 1.3 mol / L.

[0057] Optionally, in one embodiment, the thickness Hc of the positive electrode membrane layer on one surface of the positive electrode current collector satisfies 36.5≤Hc≤54.0, and the unit is μm. The thickness of the positive electrode membrane layer is within the above range, which is suitable for electrolyte infiltration, thereby ensuring the dynamic performance of the battery, and makes the battery have a higher energy density.

[0058] In some embodiments, the thickness Hc of the positive electrode film layer is the thickness of the positive electrode film layer on either the upper or lower surface of the positive electrode current collector.

[0059] In some embodiments, the thickness Hc of the positive electrode film layer may be in the range of one or any two of 36.5 μm, 37.5 μm, 40 μm, 42 μm, 46.5 μm, 48.5 μm, 50 μm, 52.5 μm, and 54 μm.

[0060] The thickness of the positive electrode membrane layer can be measured by taking a small piece of the positive electrode sheet and using argon ion polishing to obtain a flat cross-section perpendicular to the positive electrode sheet surface. The cross-section of the positive electrode sheet is then photographed using a scanning electron microscope (SEM) to measure the thickness of the positive electrode membrane layer. The thickness of the positive electrode sheet can also be considered Hc when the battery is fully discharged to 0% SOC and the cell is disassembled.

[0061] Optionally, the energy density of the secondary battery in the present application is 230 to 330 Wh / kg. Within the above energy density range, by systematically optimizing the thickness of the positive electrode membrane layer, the concentration of lithium ions in the electrolyte, the dielectric constant of the organic solvent, and the contact angle of the electrolyte, the lithium-ion secondary battery can have low self-discharge, high dynamic performance and long cycle stability while meeting high energy density.

[0062] Optionally, in one embodiment, the lithium salt includes lithium hexafluorophosphate (LiPF6), and at least one of lithium tetrafluoroborate (LiBF4), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium difluorophosphate (LiPO2F2), lithium fluorosulfonate (LiOF), lithium trifluoromethanesulfonate (LiOTF), lithium difluorobis(oxalatophosphate) (LiDFOP), lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0063] Alternatively, in one embodiment, the organic solvent includes acetonitrile (AN), and at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), methyl trifluoroethyl carbonate, ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), ethyl difluoroacetate, 2,2-difluoroethyl acetate, cyclopentane (TMS), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE). Among them, acetonitrile has a low viscosity, which makes the transfer rate of lithium ions in the electrolyte faster, thereby reducing the internal resistance of the battery and improving the dynamic performance.

[0064] Optionally, in some embodiments, the organic solvent includes acetonitrile and at least one of fluoroethylene carbonate and sulfolane. That is, the organic solvent of the electrolyte in the embodiments of the present application is composed of acetonitrile, fluoroethylene carbonate, and / or sulfolane, which results in a high oxidation potential of the electrolyte, making it less susceptible to oxidation and decomposition, thereby improving the oxidation resistance of the electrolyte and the cycle performance of the battery.

[0065] Optionally, in some embodiments, the organic solvent includes acetonitrile, fluoroethylene carbonate and sulfolane, that is, the organic solvent in the electrolyte is composed of acetonitrile, fluoroethylene carbonate and sulfolane.

[0066] Optionally, in some embodiments, based on the total mass of the organic solvent, fluoroethylene carbonate accounts for 2% to 15%, acetonitrile accounts for 2% to 20%, and sulfolane accounts for 2% to 10%, which can more significantly improve the oxidation resistance of the electrolyte and the cycle performance of the battery.

[0067] Optionally, in one embodiment, the above-mentioned additives include at least one of vinylene carbonate (VC), erythritol bis(carbonate) (EBC), ethylene sulfate (DTD), pentaerythritol bicyclic sulfate, 1,3-propane sultone (PS), 1,4-butane sultone (BS), methylene methanedisulfonate (MMDS), 1-propylene-1,3-sultone (PST), tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate (TMSB), and tripropargyl phosphate (TPP).

[0068] Optionally, in some embodiments, the above-mentioned additives include vinylene carbonate, and at least one of erythritol bis(carbonate), 1,3-propane sultone and pentaerythritol bicyclic sulfate. Not only are the positive and negative electrodes used to form the film, but the above-mentioned additive components are stable at high temperatures and are not easily decomposed to produce acidic substances, thereby improving the high-temperature stability of the electrolyte, the battery cycle performance and the high-temperature storage performance.

[0069] Optionally, in some embodiments, the additives specifically include vinylene carbonate, erythritol bis(carbonate), 1,3-propane sultone and pentaerythritol bicyclic sulfate.

[0070] Optionally, in some embodiments, based on the total mass of the electrolyte, vinylene carbonate accounts for 0.01% to 1.5%, erythritol bis(carbonate) accounts for 0.01% to 1%, 1,3-propane sultone accounts for 0.1% to 2%, and pentaerythritol bicyclic sulfate accounts for 0.1% to 2%, which can more significantly improve the high temperature stability of the electrolyte, battery cycle performance and high temperature storage performance.

[0071] Optionally, in one embodiment, the above-mentioned positive electrode film layer contains a positive electrode active material; the positive electrode active material includes Li x Ni a1 Co b M c A d O2, where M includes one or both of Mn and Al, A includes at least one of W, B, Mg, Y, V, F, P, Zr, Bi, and Ti, 0.95 ≤ x ≤ 1.2, 0.8 < a1 ≤ 0.95, 0 < b < 0.1, 0 < c < 0.1, 0 ≤ d < 0.1, and a1 + b + c + d = 1.

[0072] In this embodiment, the positive electrode active material can be obtained by doping and modifying lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide with at least one of W, B, Mg, V, F, P, Zr, Bi, and Ti. The above elements are beneficial to improving the stability and energy density of the positive electrode material. Moreover, the nickel content of the positive electrode active material used in this application is greater than 80% and less than or equal to 95%, which can further improve the energy density. Using this positive electrode active material to make the positive electrode film layer in the embodiments of this application can further improve the energy density, kinetic performance, and cycling performance of the secondary battery.

[0073] Optionally, in one embodiment, 0.9 ≤ a1 ≤ 0.95. When the content of Ni is within the above range, the energy density of the secondary battery can be further improved.

[0074] Optionally, in one embodiment, the positive electrode active material includes a first particle and a second particle, and the nickel contents in the first particle and the second particle are different.

[0075] Optionally, in one embodiment, the positive electrode active material includes a first particle and a second particle, and the particle sizes of the first particle and the second particle are different. Mixing particles of different sizes can optimize the distribution of the positive electrode active material particles in the positive electrode film and can further improve the energy density, kinetic performance, and cycling performance of the secondary battery. Optionally, in one embodiment, the above-mentioned positive electrode sheet further includes a conductive agent, and the conductive agent can include at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, hard carbon, carbon fiber, and carbon microspheres.

[0076] In some embodiments, the positive electrode sheet is prepared as follows: Disperse the components for preparing the positive electrode sheet, such as the positive electrode active material including the above-mentioned positive electrode material, the binder, and the conductive agent, in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; coat the positive electrode slurry on a positive electrode current collector such as aluminum foil; after processes such as drying, rolling, and die-cutting, the positive electrode sheet can be obtained.

[0077] The secondary battery provided in the embodiment of the present application further includes a negative electrode plate and a separator.

[0078] Optionally, in one embodiment, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material.

[0079] Optionally, in a specific embodiment, the negative electrode active material includes at least one of a silicon-oxygen material, a carbon-silicon material, a metal silicide, or elemental silicon.

[0080] Optionally, in a specific embodiment, the negative electrode active material comprises silicon oxide material and graphite.

[0081] Optionally, in a specific embodiment, the silicon oxide material comprises SiO x (1 <x<2)。

[0082] In the secondary battery provided in the embodiment of the present application, the negative electrode plate also includes a conductive agent and a binder; optionally, the conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene, and the binder includes a carboxymethyl cellulose-based binder and a resin binder.

[0083] Optionally, in one embodiment, the carboxymethyl cellulose-based binder includes one or more of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose; and / or the resin binder includes one or more of styrene-butadiene rubber, polyacrylic acid, and polyacrylonitrile.

[0084] In some embodiments, the negative electrode sheet is prepared as follows: the components for preparing the negative electrode sheet, such as the negative electrode active material, binder and conductive agent, are dispersed in a solvent such as deionized water to form a negative electrode slurry; the negative electrode slurry is coated on both sides of a negative electrode current collector such as copper foil; and after baking, rolling, cutting and other processes, the negative electrode sheet can be obtained.

[0085] Among them, the electrolyte plays the role of conducting ions between the positive electrode and the negative electrode.

[0086] In practical applications, the negative electrode sheet, the positive electrode sheet and the separator are wound to obtain a core, the core is packaged to obtain a dry cell, and the dry cell is baked and then injected with liquid, formed, sealed and sorted to obtain the above-mentioned secondary battery.

[0087] The present application also proposes an electrical device, which includes the above-mentioned secondary battery, and the secondary battery serves as a power supply for the electrical device.

[0088] For the above-mentioned electrical equipment embodiment, it includes the above-mentioned secondary battery and can achieve the same technical effect. In order to avoid repetition, it will not be described here. For relevant matters, please refer to the partial description of the secondary battery embodiment.

[0089] In order to make the invention purpose, technical solution and beneficial effects of this application clearer, the present application is further described below in conjunction with examples. It should be understood that these examples are only used to illustrate this application and are not used to limit the scope of this application.

[0090] The present application is described in detail below through examples.

[0091] Test method: (The lower cut-off voltage involved below is 2.8V and the upper cut-off voltage is 4.2V)

[0092] (1) Electrolyte contact angle test:

[0093] 4 μL of electrolyte was dropped onto the surface of an 8 μm thick aluminum foil (the aluminum foil structure was: 1 μm aluminum layer + 6 μm polymer substrate layer + 1 μm aluminum layer). The contact angle of the electrolyte on the aluminum foil surface was measured using a contact angle meter. The value after a contact time of 10 s was used as the contact angle test result.

[0094] (2) Weighted value test of dielectric constant:

[0095] The obtained electrolyte was first filtered through an organic syringe filter with a pore size of 0.22 μm, and then directly placed on a gas chromatograph-mass spectrometer (GC-MS) for testing. The composition of the organic solvent can be determined by matching the peak position of the substance to the corresponding substance structure in the mass spectrometer;

[0096] After determining the composition of the organic solvent, the dielectric constant (y) of the corresponding organic solvent was found in Lang's Handbook of Chemistry. i : dielectric constant of the i-th organic solvent); at the same time, the mass fraction of each organic solvent in the electrolyte can be determined using the standard curve method according to the intensity of the peak;

[0097] First calculate the ratio of the mass fraction of the i-th organic solvent to the sum of the mass fractions of all organic solvents as the mass fraction ratio of the i-th organic solvent (x i ), and then calculate the weighted value of the dielectric constant of the organic solvent of the electrolyte a=x1×y1+x2×y2+x3×y3+……+x i ×y i .

[0098] (3) Positive electrode film thickness test

[0099] The battery is fully discharged to 0% SOC state, then the battery cell is disassembled, the positive electrode sheet, separator, and negative electrode sheet are taken out and placed separately; a small piece of the positive electrode sheet is taken, and argon ion polishing technology is used to obtain a flat positive electrode sheet cross-section perpendicular to the surface of the positive electrode sheet, and a scanning electron microscope (SEM) is used to take a picture of the positive electrode sheet cross-section to measure the thickness of the positive electrode membrane layer.

[0100] (4) Energy density test

[0101] a. At 25±2℃, discharge the secondary battery at 1C constant current to the lower cut-off voltage, and then let it stand for 30 minutes;

[0102] b. Charge at 1C constant current and constant voltage to the upper cut-off voltage. The cut-off condition for constant voltage charging is that the current drops to less than or equal to 0.05C, and then let it stand for 30 minutes.

[0103] c. Repeat step a and measure the discharge energy E (unit: Wh).

[0104] d. Repeat steps b to c twice and take the average value Ea of the three discharge energies.

[0105] e. Use a balance to weigh the mass M of a single battery (unit: kg). The energy density of a secondary battery is the ratio of the average value Ea of the three discharge energies to the mass of a single battery (unit: Wh / kg).

[0106] (5) Fast charging cycle performance test

[0107] a. Place the secondary battery in a 45±2℃ environment for 5 minutes.

[0108] b. Charge at a constant current rate of 1.2C to the upper cut-off voltage, then charge at a constant voltage rate until the current is less than or equal to 0.05C.

[0109] c. Let it stand for 5 minutes, then discharge it at a constant current of 1C to the lower cut-off voltage, and record the discharge capacity C1.

[0110] d. Repeat steps a to c until the discharge capacity is less than or equal to 80% of the initial discharge capacity. Record the number of cycles to characterize the cycle performance of the battery. The unit is cycle.

[0111] (6) Normal temperature DCR test

[0112] At 25±2°C, charge the secondary battery at 1C constant current and constant voltage to the upper cut-off voltage, then discharge at 1C constant current for 30 minutes. After adjusting to 50% SOC, let it stand for 30 minutes, and then discharge at 5C constant current pulse for 10 seconds. Record the voltage values ​​before and after the pulse, and calculate DCR = (voltage before pulse discharge - voltage after pulse discharge) / discharge current * 100%.

[0113] (7) Self-discharge test (storage performance test)

[0114] a. At 25±2°C, charge the secondary battery at 1C constant current and constant voltage to the upper cut-off voltage. The constant voltage charge cut-off condition is that the current is reduced to less than or equal to 0.05C. Then let it stand for 10 minutes, and then discharge it at 1C constant current to the lower cut-off voltage. Record the initial discharge capacity C0.

[0115] b. At 25±2℃, let it stand for 10 minutes, then charge at a constant current and constant voltage rate of 1C to the upper cut-off voltage. The constant voltage charge cut-off condition is when the current drops to less than or equal to 0.05C;

[0116] c. Place the fully charged lithium-ion secondary battery in a 60±2°C environment and store it for 15 days.

[0117] d. After 15 days, remove the battery and cool it naturally to 25±2℃. Then let it stand for 10 minutes and discharge it at a constant current of 1C to the lower cut-off voltage. Record the discharge capacity Cs and calculate the residual capacity retention rate (%) which is equal to the ratio of Cs to C0. This is used to characterize the self-discharge of the secondary battery.

[0118] Example 1

[0119] (1) Preparation of positive electrode sheet:

[0120] The positive electrode active material LiNi 0.92 Co 0.07 Mn 0.01 O2, conductive agent SP, and binder polyvinylidene fluoride (PVDF) are uniformly dispersed in solvent N-methylpyrrolidone (NMP) in a mass ratio of 96:2:2 to obtain a positive electrode slurry;

[0121] The positive electrode slurry was evenly coated on the upper and lower surfaces of 8μm aluminum foil (the aluminum foil structure was: 1μm aluminum layer + 6μm polymer substrate layer + 1μm aluminum layer) to form a positive electrode film layer with a thickness of 40.8um to obtain a positive electrode sheet.

[0122] (2) Preparation of negative electrode sheet:

[0123] The negative electrode active material graphite, the conductive agent SP, the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene latex (SBR) were dispersed in the solvent deionized water at a mass ratio of 96.5:1:1:1.5 and uniformly mixed to obtain a negative electrode slurry;

[0124] The negative electrode slurry is evenly coated on the upper and lower surfaces of the negative electrode current collector copper foil, and then dried, cold pressed, slit and cut into pieces to obtain the negative electrode sheet.

[0125] (3) Preparation of electrolyte:

[0126] EC, EMC, and DEC are mixed uniformly in a mass ratio of 30:50:20 to obtain a mixed solvent; the temperature is then controlled at ≤20°C, and fully dried lithium salts LiPF6 and LiBF4 are dissolved in the mixed organic solvent, fully dissolved and stirred, and the temperature is again controlled at ≤20°C and additives vinylene carbonate and ethylene sulfate are added. The final electrolyte has a lithium ion concentration M of 0.8 mol / L and contains 2% by mass of ethylene sulfate and 0.5% by mass of vinylene carbonate.

[0127] (4) Preparation of lithium-ion batteries:

[0128] The positive electrode sheets, separators and negative electrode sheets are stacked in sequence so that each positive electrode membrane layer and negative electrode membrane layer are covered with a separator. Then they are stacked into battery cells, hot pressed, the tabs are welded and placed in an outer packaging shell. After baking and drying, the above-mentioned electrolyte is injected. Then, after standing, formation, aging and capacity separation, a lithium-ion battery is made.

[0129] Example 2

[0130] The difference between Example 2 and Example 1 is that in the electrolyte preparation step (3), the amount of lithium salt LiPF6 added is adjusted, and the total lithium ion concentration M in the final prepared electrolyte is 1.0 mol / L.

[0131] Example 3

[0132] The difference between Example 3 and Example 1 is that in the electrolyte preparation step (3), the amount of lithium salt LiPF6 added is adjusted, and the total lithium ion concentration M in the final prepared electrolyte is 1.3 mol / L.

[0133] Example 4

[0134] The difference between Example 4 and Example 2 is that in the electrolyte preparation step (3), EC and EMC are mixed uniformly in a mass ratio of 35:65 to obtain a mixed solvent, and the lithium salt is adjusted to consist of 11.5 parts of LiPF6 and 1.5 parts of LiFSI in parts by mass, and the total lithium ion concentration M in the final prepared electrolyte is 1.0 mol / L.

[0135] Example 5

[0136] The difference between Example 5 and Example 4 is that in the electrolyte preparation step (3), EC and EMC are mixed uniformly at a mass ratio of 40:60 to obtain a mixed solvent.

[0137] Example 6

[0138] The difference between Example 6 and Example 2 is that in the electrolyte preparation step (1), the thickness Hc of the positive electrode membrane layer is adjusted to 54.0 μm.

[0139] Example 7

[0140] The difference between Example 7 and Example 1 is that in the electrolyte preparation step (3), EC, EMC and EDC are evenly mixed in a mass ratio of 30:30:40 to obtain a mixed solvent, and the lithium salt is adjusted to consist of 12.7 parts of LiPF6 and 0.9 parts of LiPO2F2 in parts by mass, and the total lithium ion concentration M in the final prepared electrolyte is 1.1 mol / L.

[0141] Example 8

[0142] The difference between Example 8 and Example 7 is that in the electrolyte preparation step (3), EC and EMC are uniformly mixed in a mass ratio of 30:70 to obtain a mixed solvent.

[0143] Example 9

[0144] The difference between Example 9 and Example 7 is that, in the electrolyte preparation step (3), ethylene carbonate, ethyl methyl carbonate, acetonitrile, fluoroethylene carbonate, and cyclopentane sulfone are uniformly mixed in a mass ratio of 10:45:20:15:10 to obtain a mixed solvent, and in the negative electrode preparation step (2), the negative electrode active material is adjusted to a composite material of silicon oxide (SiO) and graphite, wherein the mass ratio of silicon oxide (SiO) to graphite is 5:95.

[0145] Example 10

[0146] The difference between Example 10 and Example 9 is that in the electrolyte preparation step (3), ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, fluoroethylene carbonate, and sulfolane are uniformly mixed in a mass ratio of 20:35:20:15:10 to obtain a mixed solvent.

[0147] Example 11

[0148] The difference between Example 11 and Example 10 is that in the preparation step (3) of the electrolyte, the additives are adjusted to vinylene carbonate, erythritol bis(carbonate), 1,3-propane sultone and pentaerythritol bicyclic sulfate, and the final electrolyte contains 0.2% by mass of erythritol bis(carbonate), 0.5% by mass of 1,3-propane sultone, 1.0% by mass of pentaerythritol bicyclic sulfate and 0.5% by mass of vinylene carbonate.

[0149] Example 12

[0150] The difference between Example 12 and Example 10 is that in the preparation step (3) of the electrolyte, the additives are adjusted to vinylene carbonate, erythritol bis(carbonate), 1,3-propane sultone and pentaerythritol bicyclic sulfate, and the final electrolyte contains erythritol bis(carbonate) with a mass fraction of 0.01%, 1,3-propane sultone with a mass fraction of 0.1%, pentaerythritol bicyclic sulfate with a mass fraction of 0.1% and vinylene carbonate with a mass fraction of 0.01%. In the preparation step (1) of the positive electrode sheet, the positive electrode active material is adjusted to LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0151] Example 13

[0152] The difference between Example 13 and Example 10 is that in the preparation step (3) of the electrolyte, the additives are adjusted to vinylene carbonate, erythritol bis(carbonate), 1,3-propane sultone and pentaerythritol bicyclic sulfate, and the final electrolyte contains erythritol bis(carbonate) with a mass fraction of 1.0%, 1,3-propane sultone with a mass fraction of 2.0%, pentaerythritol bicyclic sulfate with a mass fraction of 2.0% and vinylene carbonate with a mass fraction of 1.5%. In the preparation step (1) of the positive electrode sheet, the positive electrode active material is adjusted to LiNi 0.85 Co 0.1 Mn 0.05 O2.

[0153] Example 14

[0154] The difference between Example 14 and Example 11 is that in the preparation step (1) of the positive electrode sheet, the positive electrode active material is adjusted to LiNi 0.9 Co 0.08 Mn 0.01 Zr 0.01 O2.

[0155] Example 15

[0156] The difference between Example 15 and Example 11 is that in the preparation step (1) of the positive electrode sheet, the positive electrode active material is adjusted to LiNi 0.9 Co 0.08 Mn 0.01 Ti 0.01 O2.

[0157] Example 16

[0158] The difference between Example 16 and Example 11 is that in the preparation step (1) of the positive electrode sheet, the positive electrode active material is adjusted to LiNi 0.95 Co 0.02 Al0.02 Ti 0.01 O2.

[0159] Example 17

[0160] The difference between Example 17 and Example 1 is that in the electrolyte preparation step (3), the amount of lithium salt LiBF4 added is adjusted, and the total lithium ion concentration M in the final prepared electrolyte is 0.79 mol / L, and the thickness Hc of the positive electrode membrane layer is adjusted to 40.3 μm.

[0161] Comparative Example 1

[0162] The difference between Comparative Example 1 and Example 1 is that in the electrolyte preparation step (3), the amount of lithium salt LiPF6 added is adjusted, and the total lithium ion concentration M in the final prepared electrolyte is 0.7 mol / L.

[0163] Comparative Example 2

[0164] The difference between Comparative Example 2 and Example 4 is that in the electrolyte preparation step (3), EC and EMC are uniformly mixed in a mass ratio of 20:80 to obtain a mixed solvent.

[0165] Comparative Example 3

[0166] The difference between Comparative Example 3 and Example 9 is that in the electrolyte preparation step (3), EC, EMC, EDC and FEC are uniformly mixed in a mass ratio of 10:60:20:10 to obtain a mixed solvent.

[0167] The contact angle of the electrolyte and the weighted value a of the dielectric constant of the organic solvent in each embodiment were measured, and the components and parameters of the battery structure in each embodiment were obtained as shown in Table 1.

[0168] Table 1

[0169] According to Table 1, the Y value corresponding to the battery in each embodiment is calculated according to formula (1): Y = (cosθ×a) / (M×Hc), and the batteries prepared in each embodiment are subjected to energy density test, 45°C fast charge cycle performance test, room temperature DCR test and self-discharge test. The test results are shown in Table 2.

[0170] Table 2

[0171] As can be seen from Table 2, the batteries prepared in Examples 1 to 17 of the present application can simultaneously meet the requirements of DCR ≤ 14.5 mOhm at room temperature, number of cycles ≥ 1000 cls at 45°C, and residual capacity retention rate ≥ 82.0% after storage for 15 days at 60°C.

[0172] Specifically, as can be seen from Table 2 by comparing Examples 1 to 3 and Comparative Example 1, by adjusting the mass fraction of the lithium salt LiPF6 in the electrolyte to change the total lithium ion concentration M in the electrolyte, the electrolyte composition changes, and the contact angle θ of the electrolyte also changes accordingly. As shown in Fig. 1, in the comparison diagram of the 45°C cycling performance of the lithium-ion secondary batteries prepared in Examples 1 to 3 and Comparative Example 1, the lithium-ion secondary battery prepared in Example 3 has the most 45°C cycling cycles, and the lithium-ion secondary battery prepared in Comparative Example 1 has the fewest 45°C cycling cycles. In the electrolyte of Comparative Example 1, the total lithium ion concentration M < 0.8 mol / L, and (cosθ × a) / (M × Hc) > 0.792. The room-temperature DCR of the prepared lithium-ion secondary battery is significantly greater than that of Examples 1 to 3, and the 45°C cycling performance deteriorates significantly.

[0173] Therefore, the total lithium ion concentration M in the electrolyte should be controlled within a suitable range. By adjusting the lithium ion concentration in the electrolyte within the range of 0.8 ≤ M ≤ 1.3 in this application and satisfying formula (1), the prepared lithium-ion secondary battery can have low self-discharge, high kinetic performance, and stable long-cycle performance simultaneously.

[0174] As can be seen from Table 2 by comparing Example 2, Examples 4 to 5 and Comparative Example 2, by adjusting the composition and content ratio of the organic solvent, the weighted value a of the dielectric constant of the organic solvent is changed; the contact angle θ of the electrolyte also changes accordingly. Specifically, for Comparative Example 2, the weighted value a of the dielectric constant of the organic solvent < 21.0, and (cosθ × a) / (M × Hc) < 0.450. Although the prepared lithium-ion secondary battery has a lower room-temperature DCR, the 45°C cycling cycles and the residual capacity retention rate after storage at 60°C for 15 days are significantly lower than those of Example 2, Examples 4, and Example 5.

[0175] Therefore, the weighted value a of the dielectric constant of the organic solvent in the electrolyte should be controlled within a suitable range. By adjusting the weighted value of the dielectric constant of the organic solvent in the electrolyte within the range of 21.0 < a < 38.0 in this application and satisfying formula (1), the prepared lithium-ion secondary battery has more excellent comprehensive performance.

[0176] As can be seen from Table 2 by comparing Example 2 and Example 6, the thickness Hc of the positive electrode film layer on one surface of the positive electrode current collector of the prepared lithium-ion secondary battery is adjusted. Specifically, for the lithium-ion secondary battery prepared in Example 6, the thickness Hc of the positive electrode film layer = 54.0 μm, and (cosθ × a) / (M × Hc) = 0.462. The battery energy density is increased from 276 Wh / kg to 282 Wh / kg, and at the same time, the 45°C cycling performance of the battery and the residual capacity retention rate after storage at 60°C for 15 days still remain at a relatively high level.

[0177] Therefore, the thickness Hc of the positive electrode membrane layer of the prepared lithium ion secondary battery is within the range of 36.5≤Hc≤54.0 in this application and satisfies formula (1), so that the prepared lithium ion secondary battery can obtain high energy density and excellent comprehensive performance.

[0178] According to Table 2, comparing Examples 7 to 8 with Comparative Example 3, it can be seen that the contact angle of the electrolyte can be changed by adjusting the composition of the organic solvent, and the dielectric constant weighted value a of the organic solvent in the electrolyte will also change accordingly. Specifically, the contact angle θ of the electrolyte in Comparative Example 3 is less than 26.0°, (cosθ×a) / (M×Hc) is less than 0.450, the stability of the electrolyte deteriorates, and the 45°C cycle performance and residual capacity retention rate of the prepared lithium-ion secondary battery after storage at 60°C for 15 days are significantly deteriorated.

[0179] Therefore, the contact angle θ of the electrolyte should be controlled within an appropriate range. Adjusting the contact angle θ of the electrolyte within the range of 26.0°<θ<48.0° in this application and satisfying formula (1) enables the prepared lithium-ion secondary battery to have better comprehensive performance.

[0180] According to Table 2, comparing Example 9 with Example 8, Example 9 uses a mixed solvent of acetonitrile, fluoroethylene carbonate, and sulfolane, and has the lowest room temperature DCR, indicating that it has excellent kinetic performance. At the same time, the battery energy density is increased from 275Wh / kg to 302Wh / kg, and stable cycle performance and storage performance can still be obtained, indicating that the solvent combination of Example 9 has good electrochemical stability.

[0181] According to Table 2, when comparing Example 10 with Example 7, the energy density of the battery in Example 10 is increased from 274Wh / kg to 305Wh / kg. Since a mixed solvent of fluoroethylene carbonate and sulfolane is used, the battery has excellent storage performance and cycle performance, but the DCR at room temperature is large.

[0182] According to Table 2, comparing Example 9 and Example 10, the addition of acetonitrile in Example 9 can improve the problem of large DCR at room temperature in Example 10, while also taking into account good storage performance and cycle performance.

[0183] According to Table 2, by comparing Examples 11 to 13 with Example 10, it can be seen that the additives used in Example 11 are vinylene carbonate, erythritol bis(carbonate), 1,3-propane sultone and pentaerythritol bicyclic sulfate, and the room temperature DCR, cycle performance and storage performance of the battery are all improved; at the same time, it can be seen from Examples 11 to 13 that by adding 0.01% to 1.5% of vinylene carbonate, 0.01% to 1% of erythritol bis(carbonate), 0.1% to 2% of 1,3-propane sultone and 0.1% to 2% of pentaerythritol bicyclic sulfate to the electrolyte, the batteries can obtain good room temperature DCR, cycle performance and storage performance.

[0184] Comparing Examples 14-16 with Example 11, Table 2 shows that the use of Zr or Ti in the positive electrode active materials of Examples 14-16 enhances the ion diffusion capacity of the active materials, resulting in a lower DCR at room temperature. This also improves the structural stability of the positive electrode active materials, enhancing both cycling and storage performance.

[0185] In summary, in this embodiment, by adjusting the electrolyte contact angle θ of the secondary battery, the total lithium ion concentration M in the electrolyte, the weighted value a of the dielectric constant of the organic solvent in the electrolyte, and the thickness Hc of the positive electrode membrane layer on one surface of the positive electrode current collector to satisfy a specific relationship, the lithium ion secondary battery can have low self-discharge, better kinetic performance and long cycle performance while meeting high energy density, thereby solving the problem that existing lithium ion batteries cannot effectively take into account both high energy density and good kinetic performance.

[0186] Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they become aware of the basic inventive concepts. Therefore, the claims are intended to include the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0187] The above is a detailed introduction to a secondary battery and electrical equipment provided by the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for those skilled in the art, according to the idea of ​​the present application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present application.

Claims

1. A secondary battery, comprising a positive electrode sheet and an electrolyte, wherein: The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector; the electrolyte includes a lithium salt, an organic solvent and an additive; the secondary battery satisfies formula (1): 0.450≤(cosθ×a) / (M×Hc)≤0.792 Formula (1) Wherein, θ° is the contact angle of the electrolyte on the positive electrode current collector; a is the weighted value of the dielectric constant of the organic solvent in the electrolyte, satisfying formula (2); M mol / L is the total lithium ion concentration in the electrolyte; Hcμm is the thickness of the positive electrode film layer on one surface of the positive electrode current collector; Wherein, n is the amount of organic solvent in the electrolyte; x i is the ratio of the mass of the ith organic solvent to the total mass of all organic solvents; y i is the dielectric constant of the ith organic solvent.

2. The secondary battery according to claim 1, wherein At least one of the following conditions is met: 1) 26.0°<θ<48.0°; 2)21.0<a<38.0； 3)0.8≤M≤1.3； 4)36.5≤Hc≤54.

0.

3. The secondary battery according to claim 1, wherein The lithium salt includes lithium hexafluorophosphate, and at least one of lithium tetrafluoroborate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium difluorophosphate, lithium fluorosulfonate, lithium trifluoromethanesulfonate, lithium difluorobisoxalatophosphate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

4. The secondary battery according to claim 1, wherein The organic solvent includes acetonitrile and at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, methyl trifluoroethyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, ethyl difluoroacetate, 2,2-difluoroethyl acetate, cyclopentane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

5. The secondary battery according to claim 4, wherein The organic solvent includes acetonitrile and at least one of fluoroethylene carbonate and sulfolane.

6. The secondary battery according to claim 5, wherein The organic solvent comprises fluoroethylene carbonate, acetonitrile and sulfolane. Based on the total mass of the organic solvent, fluoroethylene carbonate accounts for 2% to 15%, acetonitrile accounts for 2% to 20%, and sulfolane accounts for 2% to 10%.

7. The secondary battery according to claim 1, wherein The additive includes at least one of vinylene carbonate, erythritol bis(carbonate), ethylene sulfate, pentaerythritol bicyclic sulfate, 1,3-propane sultone, 1,4-butane sultone, methanedisulfonic acid methylene ester, 1-propylene-1,3-sultone, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, and tripropargyl phosphate.

8. The secondary battery according to claim 7, wherein The additive includes vinylene carbonate, and at least one of erythritol bis(carbonate), 1,3-propane sultone, and pentaerythritol bicyclic sulfate.

9. The secondary battery according to claim 7, wherein The additives include vinylene carbonate, erythritol bis(carbonate), 1,3-propane sultone and pentaerythritol bicyclic sulfate.

10. The secondary battery according to claim 8, wherein Based on the total mass of the electrolyte, vinylene carbonate accounts for 0.01% to 1.5%, erythritol bis(carbonate) accounts for 0.01% to 1%, 1,3-propane sultone accounts for 0.1% to 2%, and pentaerythritol bicyclic sulfate accounts for 0.1% to 2%.

11. The secondary battery according to claim 1, wherein The positive electrode current collector comprises a polymer substrate layer and a metal layer arranged on two surfaces of the polymer substrate layer, and the positive electrode film layer is arranged on the metal layer.

12. The secondary battery according to claim 11, wherein The polymer substrate layer comprises an organic polymer material, and the organic polymer material includes at least one of polyamide, polyterephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, poly(p-phenylene terephthalamide), polypropylene, polyoxymethylene, epoxy resin, phenolic resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber or polycarbonate.

13. The secondary battery according to claim 12, wherein: The thickness of the polymer substrate layer is 6 to 10 μm.

14. The secondary battery according to claim 11, wherein The metal layer is an aluminum layer.

15. The secondary battery according to claim 11, wherein The thickness of the aluminum layer is 0.5-1.5 μm.

16. The secondary battery according to any one of claims 1 to 15, wherein: The positive electrode film layer contains a positive electrode active material; the positive electrode active material includes Li x Ni a1 Co b M c A d O2, where M includes one or both of Mn and Al, A includes at least one of W, B, Mg, Y, V, F, P, Zr, Bi, and Ti, 0.95 ≤ x ≤ 1.2, 0.8 < a1 ≤ 0.95, 0 < b < 0.1, 0 < c < 0.1, 0 ≤ d < 0.1, and a1 + b + c + d = 1.

17. The secondary battery according to claim 16, wherein 0.9≤a1≤0.95。 18. The secondary battery according to claim 1, wherein The invention comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises at least one of silicon-oxygen material, carbon-silicon material, metal silicide and elemental silicon.

19. The secondary battery according to any one of claims 1 to 15, wherein: The energy density of the secondary battery is 230-330Wh / kg.

20. An electrical device, wherein: It comprises a secondary battery as claimed in any one of claims 1 to 19, wherein the secondary battery is used as a power supply for the electrical device.

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