A secondary battery and an electronic device

Abstract

The application provides a secondary battery, which comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprises a positive electrode current collector, a primer layer and a positive electrode active material layer, the primer layer is arranged between the positive electrode current collector and the positive electrode active material layer; the primer layer comprises an inorganic metal oxide, elements M in the inorganic metal oxide comprise at least one of Al, Ti, Sn, Sb or Mg, the mass percentage W1 of the inorganic metal oxide is 55% to 99%; a first compound in the electrolyte comprises at least one of fluoroethylene carbonate, difluoroethylene carbonate, formula (I), formula (II) or formula (III), the mass percentage of the first compound is a%, and 0.15 <= a <= 21. By regulating the element type, W1, the type and content of the first compound in the electrolyte included in the inorganic metal oxide within the scope of the application, the safety performance of the secondary battery can be improved while ensuring the cycle stability of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a secondary battery and electronic device. Background Technology

[0002] Secondary batteries (such as lithium-ion batteries) are widely used due to their high energy density and long cycle life. Currently, the additives that can improve cycle performance in the electrolyte of lithium-ion batteries include carbonate, sulfate, anhydride, phosphate, sulfonate, borate, and silicate esters.

[0003] When carbonate, sulfate, or anhydride additives are selected, some of these additives are prone to react with trace amounts of water in the electrolyte to generate acidic substances. Especially at high temperatures (e.g., temperatures greater than or equal to 45°C), the generated acidic substances can easily corrode the aluminum foil, leading to a decrease in the aluminum foil's toughness. At the same time, the acidic substances will corrode the surface of the positive electrode active material, causing the positive electrode active material particles to undergo a phase change, resulting in greater volume expansion and severe deformation of the aluminum foil. The decrease in the toughness or deformation of the aluminum foil will lead to a reduction in the safety performance of the lithium-ion battery. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and electronic device that improves the safety performance of the secondary battery while ensuring its cycle stability. The specific technical solution is as follows:

[0005] A first aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a base coating and a positive active material layer disposed on at least one surface of the positive current collector. The base coating is disposed between the positive current collector and the positive active material layer. The base coating comprises an inorganic metal oxide, which includes element M. Element M includes at least one of Al, Ti, Sn, Sb, or Mg. Preferably, element M includes at least one of Ti, Sn, or Sb. Based on the mass of the base coating, the mass percentage of the inorganic metal oxide is W1, where 55% ≤ W1 ≤ 99%, preferably 60% ≤ W1 ≤ 85%.

[0006] The electrolyte includes a first compound, which includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, the compound represented by formula (I), the compound represented by formula (II), or the compound represented by formula (III).

[0007]

[0008] Wherein, n and m are independently selected from integers 1 to 3, and R0, Rn and Rm are each independently selected from hydrogen, fluorine, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-C6 alkenyl; when substituted, the substituents of each group are halogens.

[0009] Based on the mass of the electrolyte, the mass percentage of the first compound is a%, 0.15≤a≤21, preferably 0.5≤a≤12. By adjusting the bottom coating of the positive electrode sheet to include inorganic metal oxides, the mass percentage of inorganic metal oxides, the types of elements included in the inorganic metal oxides, and the types and mass percentages of the first compound in the electrolyte within the scope of this application, the safety performance of the secondary battery can be improved while ensuring the cycle stability of the secondary battery.

[0010] In one embodiment of this application, the thickness of the base coating is A μm, where 2.1 ≤ A ≤ 15.5, and preferably, 2.5 ≤ A ≤ 9.5. By adjusting the value of A within the range of this application, the base coating can have a suitable thickness, effectively inhibiting the corrosion of the positive electrode current collector by acidic substances, and also ensuring the energy density of the secondary battery while improving its safety performance.

[0011] In one embodiment of this application, 0.02 ≤ a / A ≤ 5.1. By adjusting the value of a / A within the range of this application, the mass percentage content of the first compound can be matched with the thickness of the base coating, effectively suppressing the corrosion of the positive electrode current collector by acidic substances, and improving the safety performance of the secondary battery while ensuring the cycle stability of the secondary battery.

[0012] In one embodiment of this application, the compound represented by formula (I) includes at least one of succinic anhydride, glutaric anhydride, or adipic anhydride; the compound represented by formula (II) includes at least one of maleic anhydride, citrate anhydride, trifluoromethylmaleic anhydride, dimethylmaleic anhydride, 3-fluorofuran-2,5-dione, or 3,4-difluoromaleic anhydride; and the compound represented by formula (III) includes at least one of vinyl sulfate, propylene sulfate, butenyl sulfate, 1,3,2-dioxane-2,2-dioxide, or 2-methyl-1,3-propanedisulfite. By selecting the compounds represented by formula (I), formula (II), and formula (III), the safety performance of the secondary battery can be improved while ensuring the cycle stability of the secondary battery.

[0013] In one embodiment of this application, the inorganic metal oxide includes at least one selected from Al2O3, TiO2, SnO2, SnO, Sb2O3, Sb2O4, Sb2O5, or MgO. By selecting the above-mentioned inorganic metal oxide, it can react with acidic substances, reduce the content of acidic substances, and reduce the corrosion of the positive electrode current collector and positive electrode active material by acidic substances, thereby improving the safety performance of the secondary battery while ensuring the cycle stability of the secondary battery.

[0014] In one embodiment of this application, the base coating further includes a binder and a conductive agent. Based on the mass of the base coating, the mass percentage of the binder is W2, and the mass percentage of the conductive agent is W3, with 0.5% ≤ W2 ≤ 25% and 0.5% ≤ W3 ≤ 20%. By adjusting the values ​​of W2 and W3 within the range of this application, the mass percentages of the binder and the conductive agent can be appropriately ranged, resulting in a suitable mass percentage of inorganic metal oxide, which is beneficial for effectively protecting the positive electrode current collector. Furthermore, it enables the inorganic metal oxide to bond well with the positive electrode current collector, giving the positive electrode sheet a high conductivity, thereby improving the safety performance of the secondary battery while ensuring its cycle stability.

[0015] In one embodiment of this application, the adhesive satisfies at least one of the following characteristics:

[0016] (1) The adhesive comprises a polymer formed from at least one monomer selected from acrylic acid, acrylamide, lithium acrylate, sodium acrylate, acrylonitrile, methyl acrylate, ethyl acrylate, methyl 2-methacrylate or ethyl 2-methacrylate;

[0017] (2) The adhesive includes at least one of sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, or nitrile rubber;

[0018] (3) The weight average molecular weight of the adhesive is between 150,000 and 1,950,000.

[0019] In one embodiment of this application, the conductive agent includes at least one of graphene, graphite fiber, carbon nanotubes, or conductive carbon black. By selecting the above-mentioned conductive agent, the positive electrode sheet can have a high conductivity, which is beneficial to improving the cycle performance of the secondary battery.

[0020] In one embodiment of this application, the negative electrode sheet includes a negative electrode active material, which includes at least one of natural graphite, artificial graphite, mesophase microcarbon spheres, hard carbon, soft carbon, silicon, or silicon-based composite materials. When the negative electrode sheet includes the above-mentioned negative electrode active material, the secondary battery exhibits high cycle stability and good safety performance.

[0021] A second aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good performance characteristics.

[0022] The beneficial effects of this application are:

[0023] This application provides a secondary battery and an electronic device. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a base coating and a positive active material layer disposed on at least one surface of the positive current collector. The base coating is disposed between the positive current collector and the positive active material layer. The base coating includes an inorganic metal oxide, which includes element M, and element M includes at least one of Al, Ti, Sn, Sb, or Mg. Based on the mass of the base coating, the mass percentage of the inorganic metal oxide is W1, 55% ≤ W1 ≤ 99%. The electrolyte includes a first compound, which includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, the compound shown in formula (I), the compound shown in formula (II), or the compound shown in formula (III). Based on the mass of the electrolyte, the mass percentage of the first compound is a%, 0.15 ≤ a ≤ 21. By adjusting the bottom coating of the positive electrode sheet, including inorganic metal oxides, the mass percentage of inorganic metal oxides, the types of elements included in the inorganic metal oxides, and the types and mass percentage of the first compound in the electrolyte, within the scope of this application, the safety performance of the secondary battery can be improved while ensuring the cycle stability of the secondary battery.

[0024] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0026] Figure 1 This is a schematic diagram of the positive electrode sheet of one embodiment of this application. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0028] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0029] This application provides a secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector, a base coating layer disposed on at least one surface of the positive current collector, and a positive active material layer. The base coating layer is disposed between the positive current collector and the positive active material layer. Figure 1 As shown, the positive electrode 10 includes a positive current collector 11, and a base coating layer 12 and a positive active material layer 13 are sequentially disposed on two surfaces of the positive current collector 11. The base coating includes an inorganic metal oxide, which includes element M. Element M includes at least one of Al, Ti, Sn, Sb, or Mg, preferably at least one of Ti, Sn, or Sb. Based on the mass of the base coating, the mass percentage content of the inorganic metal oxide is W1, 55% ≤ W1 ≤ 99%, preferably 60% ≤ W1 ≤ 85%. Exemplarily, W1 can be 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or a range consisting of any two of the above values.

[0030] The electrolyte includes a first compound, which includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, the compound shown in formula (I), the compound shown in formula (II), or the compound shown in formula (III).

[0031]

[0032] Wherein, n and m are independently selected from integers 1 to 3, and R0, Rn and Rm are each independently selected from hydrogen, fluorine, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-C6 alkenyl; when substituted, the substituents of each group are halogens.

[0033] Based on the mass of the electrolyte, the mass percentage of the first compound is a%, 0.15 ≤ a ≤ 21, preferably 0.5 ≤ a ≤ 12. Exemplarily, a can be 0.15, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, or a range of any two of the above values. In this application, the first compound is an additive.

[0034] In this application, when the first compound includes two or more compounds, there is no particular limitation on the mass percentage of each compound, as long as the total mass percentage of the first compounds meets the scope of this application.

[0035] The inventors discovered that when carbonate, sulfate, or anhydride additives are used in the electrolyte of secondary batteries, some of these additives readily react with trace amounts of water in the electrolyte at high temperatures or during cycling to generate acidic substances. These acidic substances easily corrode the positive electrode current collector and cause expansion of the positive electrode active material, leading to a decrease in the safety performance of the secondary battery. By applying a base coating to the positive electrode current collector, including inorganic metal oxides, the inventors found that these oxides can react with acidic substances, acting as a self-sacrificing agent to reduce the content of acidic substances. This reduces the corrosion of the positive electrode current collector and positive electrode active material by acidic substances, mitigating the deformation of the positive electrode current collector caused by the expansion of the positive electrode active material and the reduction in the toughness of the positive electrode current collector caused by corrosion. Simultaneously, the base coating also reduces direct contact between the electrolyte and the positive electrode current collector, providing protection and improving the safety performance of the secondary battery while ensuring its cycle stability. By adjusting the bottom coating of the positive electrode sheet, including inorganic metal oxides, the mass percentage of inorganic metal oxides, the types of elements included in the inorganic metal oxides, and the types and mass percentage of the first compound in the electrolyte, within the scope of this application, the safety performance of the secondary battery can be improved while ensuring the cycle stability of the secondary battery.

[0036] In one embodiment of this application, such as Figure 1 As shown, the thickness of the base coating 12 is A μm, where 2.1 ≤ A ≤ 15.5, and preferably, 2.5 ≤ A ≤ 9.5. Exemplarily, A can be 2.1, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, or a range consisting of any two of the above values. By adjusting the value of A within the range of this application, the base coating can have a suitable thickness, effectively inhibiting the corrosion of the positive electrode current collector by acidic substances, and also improving the safety performance of the secondary battery while ensuring its energy density.

[0037] In one embodiment of this application, 0.02 ≤ a / A ≤ 5.1. Exemplarily, a / A can be 0.02, 0.05, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.1, or a range consisting of any two of the above values. By adjusting the value of a / A within the range of this application, the mass percentage content of the first compound can be matched with the thickness of the base coating, effectively suppressing the corrosion of the positive electrode current collector by acidic substances, and improving the safety performance of the secondary battery while ensuring its cycle stability.

[0038] In one embodiment of this application, the compound represented by formula (I) includes at least one of succinic anhydride, glutaric anhydride, or adipic anhydride; the compound represented by formula (II) includes at least one of maleic anhydride, citrate anhydride, trifluoromethylmaleic anhydride, dimethylmaleic anhydride, 3-fluorofuran-2,5-dione, or 3,4-difluoromaleic anhydride; and the compound represented by formula (III) includes at least one of vinyl sulfate, propylene sulfate, butenyl sulfate, 1,3,2-dioxane-2,2-dioxide, or 2-methyl-1,3-propanedisulfite. By selecting the compounds represented by formula (I), formula (II), and formula (III), the safety performance of the secondary battery can be improved while ensuring the cycle stability of the secondary battery.

[0039] In one embodiment of this application, the inorganic metal oxide includes at least one selected from Al2O3, TiO2, SnO2, SnO, Sb2O3, Sb2O4, Sb2O5, or MgO. By selecting the above-mentioned inorganic metal oxide, it can react with acidic substances, reduce the content of acidic substances, and reduce the corrosion of the positive electrode current collector and positive electrode active material by acidic substances, thereby improving the safety performance of the secondary battery while ensuring the cycle stability of the secondary battery.

[0040] In one embodiment of this application, the primer layer further includes an adhesive and a conductive agent. Based on the mass of the primer layer, the mass percentage of the adhesive is W2, and the mass percentage of the conductive agent is W3, with 0.5% ≤ W2 ≤ 25%. For example, W2 can be 0.5%, 1%, 3%, 5%, 7%, 9%, 10%, 11%, 13%, 15%, 17%, 19%, 20%, 21%, 23%, 25%, or a range of any two of the above values; with 0.5% ≤ W3 ≤ 20%. For example, W3 can be 0.5%, 1%, 3%, 5%, 7%, 9%, 10%, 11%, 13%, 15%, 17%, 19%, 20%, or a range of any two of the above values. By adjusting the values ​​of W2 and W3 within the range of this application, the mass percentage content of the binder and the mass percentage content of the conductive agent can be appropriately ranged, thereby ensuring that the inorganic metal oxide has a suitable mass percentage content, which is beneficial for effectively protecting the positive electrode current collector; and it can also enable the inorganic metal oxide to bond well with the positive electrode current collector, so that the positive electrode sheet has a high conductivity, thereby improving the safety performance of the secondary battery while ensuring the cycle stability of the secondary battery.

[0041] In one embodiment of this application, the binder comprises a polymer formed from at least one monomer selected from acrylic acid, acrylamide, lithium acrylate, sodium acrylate, acrylonitrile, methyl acrylate, ethyl acrylate, methyl 2-methacrylate, or ethyl 2-methacrylate. By selecting the above-mentioned binder, the inorganic metal oxide can be better bonded to the positive electrode current collector, giving the positive electrode sheet higher electronic conductivity and improving the cycle performance of the secondary battery.

[0042] In one embodiment of this application, the binder includes at least one of sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, or nitrile rubber. By selecting the above-mentioned binder, the inorganic metal oxide can be better bonded to the positive electrode current collector, giving the positive electrode sheet higher conductivity and improving the cycle performance of the secondary battery.

[0043] In one embodiment of this application, the weight-average molecular weight of the binder is between 150,000 and 1,950,000. Exemplarily, the weight-average molecular weight of the binder can be 150,000, 160,000, 350,000, 550,000, 750,000, 950,000, 1,150,000, 1,350,000, 1,550,000, 1,750,000, 1,950,000, or a range consisting of any two of the above values. By controlling the weight-average molecular weight of the binder within the range of this application, both the film-forming properties and adhesion of the base coating can be considered, improving the uniformity and stability of the base coating, effectively inhibiting the corrosion of the positive electrode current collector by acidic substances, and enhancing the safety performance of the secondary battery while ensuring its cycle stability.

[0044] In one embodiment of this application, the conductive agent includes at least one of graphene, graphite fiber, carbon nanotubes, or conductive carbon black. By selecting the above-mentioned conductive agent, the positive electrode sheet can have a high conductivity, which is beneficial to improving the cycle performance of the secondary battery.

[0045] In this application, the carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes; the conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black.

[0046] In one embodiment of this application, the negative electrode sheet includes a negative electrode active material, which includes at least one of natural graphite, artificial graphite, mesophase microcarbon spheres, hard carbon, soft carbon, silicon, or silicon-based composite materials. When the negative electrode sheet includes the aforementioned negative electrode active material, the secondary battery exhibits high cycle stability and good safety performance. In this application, the silicon-based composite material may include SiO.

[0047] This application does not impose any particular limitation on the preparation method of the positive electrode sheet, as long as it achieves the purpose of this application. Exemplarily, the preparation method of the positive electrode sheet may include the following steps: mixing an inorganic metal oxide, a binder, and a conductive agent in a certain proportion, adding a solvent, and mixing evenly to obtain an inorganic slurry; uniformly coating the inorganic slurry onto one side surface of the positive current collector, and drying to obtain a positive electrode sheet with a single-sided base coating; mixing a positive active material, a positive binder, and a positive conductive agent in a certain proportion, adding a solvent, and mixing evenly to obtain a positive slurry; uniformly coating the positive slurry onto the base coating, and drying to obtain a positive electrode sheet with a single-sided base coating and a positive active material layer; then repeating the above steps on the other side surface of the positive current collector to obtain the positive electrode sheet. This application does not impose any particular limitation on the solvent, as long as it achieves the purpose of this application; for example, the solvent can be N-methylpyrrolidone (NMP). This application does not impose any particular limitation on the solid content of the inorganic slurry, as long as the purpose of this application can be achieved. For example, the solid content of the inorganic slurry can be from 20 wt% to 50 wt%. This application does not impose any particular limitation on the solid content of the cathode slurry, as long as the purpose of this application can be achieved. For example, the solid content of the cathode slurry can be from 60 wt% to 80 wt%.

[0048] In this application, the positive electrode sheet includes a positive current collector and a base coating and a positive active material layer disposed on at least one surface of the positive current collector. The aforementioned "base coating and positive active material layer disposed on at least one surface of the positive current collector" means that the base coating and positive active material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the positive current collector or only a part of it; this application has no particular limitation, as long as the purpose of this application is achieved. This application has no particular limitation on the positive current collector, as long as the purpose of this application is achieved; for example, it can include aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector).

[0049] The positive electrode active material layer of this application includes a positive electrode active material. This application does not impose any particular limitation on the positive electrode active material, as long as it achieves the purpose of this application. For example, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide (e.g., common NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate. The positive electrode active material layer of this application also includes a positive electrode conductive agent and a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode conductive agent, as long as it achieves the purpose of this application. For example, the positive electrode conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. The aforementioned conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation on the positive electrode binder, as long as it achieves the purpose of this application. For example, the positive electrode binder may include, but is not limited to, at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride (PVDF), polystyrene-butadiene copolymer (styrene-butadiene rubber), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium carboxymethyl cellulose, or potassium carboxymethyl cellulose. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode active material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0050] This application does not impose any particular limitation on the thickness of the positive electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode current collector can be 5 μm to 20 μm. This application also does not impose any particular limitation on the thickness of the positive electrode active material layer, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode active material layer before cold pressing can be 30 μm to 250 μm, and the thickness of the positive electrode active material layer after cold pressing can be 15 μm to 150 μm. This application also does not impose any particular limitation on the thickness of the positive electrode sheet, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode sheet can be 50 μm to 500 μm.

[0051] In this application, the electrolyte also includes lithium salts and non-aqueous solvents. The lithium salts may include various lithium salts commonly used in the art, such as at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the non-aqueous solvents, as long as they can achieve the purpose of this application. For example, they may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (EMC). The aforementioned cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). The aforementioned fluorocarbonate compounds may include, but are not limited to, at least one of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvents mentioned above may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the mass percentage of lithium salt and non-aqueous solvent, as long as the purpose of this application is achieved. For example, based on the mass of the electrolyte, the mass percentage of lithium salt may be 10% to 30%, and the mass percentage of non-aqueous solvent may be 49% to 89%.

[0052] In this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The aforementioned "negative electrode active material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode active material layer can be disposed on one surface of the negative electrode current collector along its own thickness direction, or on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or only a part of it; this application has no particular limitation, as long as the purpose of this application is achieved. This application has no particular limitation on the negative electrode current collector, as long as the purpose of this application is achieved, for example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collectors, etc.

[0053] The negative electrode active material layer of this application includes a negative electrode active material. The negative electrode active material layer of this application also includes a negative electrode binder. This application does not have any particular limitation on the negative electrode binder, as long as it can achieve the purpose of this application. For example, the negative electrode binder can be at least one of the aforementioned positive electrode binders. The negative electrode active material layer of this application also includes a negative electrode conductive agent. This application does not have any particular limitation on the negative electrode conductive agent, as long as it can achieve the purpose of this application. For example, the negative electrode conductive agent can be at least one of the aforementioned positive electrode conductive agents. This application does not have any particular limitation on the mass ratio of the negative electrode active material, negative electrode binder, and negative electrode conductive agent in the negative electrode active material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0054] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector can be 5 μm to 15 μm. This application also does not impose any particular limitation on the thickness of the negative electrode active material layer, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode active material layer before cold pressing can be 30 μm to 250 μm, and the thickness of the negative electrode active material layer after cold pressing can be 15 μm to 150 μm. This application also does not impose any particular limitation on the thickness of the negative electrode sheet, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode sheet can be 50 μm to 500 μm.

[0055] In this application, the secondary battery also includes a separator. The separator is used to separate the positive electrode and the negative electrode, prevent internal short circuits in the secondary battery, allow electrolyte ions to pass freely, and does not affect the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator, as long as it can achieve the purpose of this application. For example, the material of the separator may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the type of separator may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0056] In this application, the separator may include a substrate and a surface treatment layer. The substrate may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a separator binder. This application does not have any particular limitation on the inorganic particles, and may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not have any particular limitation on the separator binder, and may include at least one of the aforementioned positive electrode binders. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0057] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not have any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0058] In this application, the secondary battery may include, but is not limited to: lithium metal secondary battery, lithium-ion secondary battery (lithium-ion battery), lithium polymer secondary battery or lithium-ion polymer secondary battery, etc.

[0059] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent the internal pressure of the secondary battery from rising and overcharging / discharging. The packaging bag is any packaging bag known in the art, and this application does not limit its use.

[0060] A second aspect of this application provides an electronic device that includes a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good performance characteristics.

[0061] This application does not specifically limit the type of electronic device, which can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0062] Example

[0063] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0064] Test methods and equipment:

[0065] Tests on the types and contents of elements, and the mass percentage of inorganic metal oxides:

[0066] The lithium-ion battery was disassembled, and the positive electrode was separated. The positive active material layer on the surface of the positive electrode was peeled off with tape to expose the undercoat. The undercoat was scraped off with a knife to obtain a solid powder sample. Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to detect the types and contents of elements in the solid powder sample. 0.2g of the above solid powder sample was weighed and dissolved in a 42% nitric acid solution. The nitric acid solution containing the dissolved solid powder sample was then analyzed to obtain the types and contents of elements in the solid powder sample. The mass percentage of the corresponding inorganic metal oxide was calculated based on the types and contents of the metal elements.

[0067] Test of the mass percentage content of the first compound:

[0068] The mass percentage of the first compound was determined using gas chromatography. After discharging the lithium-ion battery to 3V, the packaging bag at the battery tabs was cut open, and the open end of the lithium-ion battery was inserted into a centrifuge tube for centrifugation to obtain the electrolyte. The mass percentage of the first compound in the centrifuged electrolyte was determined using gas chromatography.

[0069] Weight average molecular weight test:

[0070] The weight-average molecular weight of the adhesive was determined using gel permeation chromatography (GPC). 0.01 g of the adhesive was dissolved in 5 mL of solvent (N-methylpyrrolidone) to obtain a solution. After complete dissolution, impurities in the solution were filtered out using a filter head. The weight-average molecular weight of the adhesive was then determined using a GPC (PL-GPC220) gel permeation chromatography instrument.

[0071] Cyclic performance test:

[0072] At 45℃, the lithium-ion battery was charged to 4.3V at a constant current of 0.5C, left to rest for 30 minutes, and then discharged to 3.0V at a constant current of 0.5C. This constitutes one charge-discharge cycle. The initial discharge capacity was recorded as C1. This process was repeated 200 times, and the discharge capacity after the 200th cycle was recorded as C. 200 .

[0073] The cycle capacity retention rate of a lithium-ion battery = (C 200 / C1)×100%.

[0074] Drop test:

[0075] Take the lithium-ion battery that has undergone 200 cycles at 45℃ (at which point the lithium-ion battery is discharged to 3.0V), and charge it at a constant current of 0.5C to 4.45V at 25℃. Then, charge it at a constant voltage of 0.025C at 4.45V. In a test environment of 20±5℃, use a concrete drop floor to drop the lithium-ion battery from a height of 2m (based on the concrete drop floor) along three sides, three edges, and eight corners once, for a total of one round of testing. The drop order is: once on each of the three sides → once on each of the three edges → once on each of the eight corners. The lithium-ion battery that does not smoke, leak, catch fire, or explode is considered to have passed. Each group of tests consists of 50 lithium-ion batteries. The lithium-ion battery is a soft-pack lithium-ion battery, which is a cuboid with six faces: top, bottom, left, right, front, and back. The three faces mentioned above refer to one face from each of the top, bottom, left, right, and front / back. It also has twelve edges, namely four lengths, four widths, and four heights. The three edges mentioned above refer to one edge from each of the lengths, widths, and heights.

[0076] Example 1-1

[0077] <Preparation of the positive electrode>

[0078] Inorganic metal oxide TiO2, binder nitrile rubber, and conductive agent carbon nanotubes were mixed at a mass ratio of 58:22:20. N-methylpyrrolidone (NMP) was then added as a solvent, and the mixture was stirred uniformly under vacuum to obtain an inorganic slurry with a solid content of 30 wt%. This inorganic slurry was uniformly coated onto one side of a 12 μm thick aluminum foil used as a positive electrode current collector. The aluminum foil was then dried at 90 °C for 1 h to obtain a single-sided positive electrode with a base coating thickness of 2.15 μm. The base coating consisted of inorganic metal oxide TiO2, which included element M, specifically Ti. Lithium cobalt oxide (LiCoO2), a positive electrode active material, polyvinylidene fluoride (PVDF), a positive electrode binder, and conductive carbon black (Super P), a positive electrode conductive agent, were mixed in a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was uniformly coated onto the surface of a base coating layer and dried at 120°C for 1 hour to obtain a positive electrode sheet with a single-sided base coating layer and a positive electrode active material layer (230 μm thick). The above steps were repeated on the other side of an aluminum foil to obtain a positive electrode sheet with a double-sided base coating layer and a positive electrode active material layer. After cold pressing and slitting, a positive electrode sheet with a size of 74 mm × 867 mm was obtained. The thickness of the positive electrode active material layer after cold pressing was 102 μm.

[0079] <Preparation of Negative Electrode Sheets>

[0080] The negative electrode active material, sodium carboxymethyl cellulose (CMC-Na) negative electrode binder, and styrene-butadiene rubber (SBR) negative electrode binder were mixed at a mass ratio of 85:2:13. Deionized water was added, and the mixture was stirred evenly under vacuum to obtain a negative electrode slurry with a solid content of 30 wt%. The negative electrode slurry was uniformly coated on one side of a 12 μm thick copper foil negative electrode current collector and dried at 120°C for 1 hour to obtain a negative electrode sheet with a single-sided coating of negative electrode active material layer with a coating thickness of 143 μm. The above steps were repeated on the other side of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode active material layer. After cold pressing and slitting, a negative electrode sheet with a size of 78 mm × 875 mm was obtained. The negative electrode active material was obtained by mixing SiO and artificial graphite, with a SiO to artificial graphite mass ratio of 20:80 based on the mass of the negative electrode active material. The thickness of the single-sided negative electrode active material layer after cold pressing was 80 μm.

[0081] <Preparation of the diaphragm>

[0082] A porous polypropylene film with a thickness of 12 μm (supplied by Celgard) was used.

[0083] <Preparation of Electrolyte>

[0084] In an argon-atmospheric glove box with a water content of <10ppm, ethylene carbonate and diethyl carbonate were mixed at a mass ratio of 3:7 to obtain an organic solvent. Lithium salt LiPF6 and the first compound, fluoroethylene carbonate, were then added to the organic solvent and stirred until homogeneous to obtain an electrolyte. Based on the total mass of the electrolyte, the mass percentage (a%) of the first compound was 0.15%, the mass percentage of the lithium salt was 13%, and the remainder was the organic solvent.

[0085] <Preparation of Lithium-ion Batteries>

[0086] The positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to isolate them. They are then wound, with the positive electrode tab connected to the positive electrode and the negative electrode tab connected to the negative electrode, thus obtaining the electrode assembly. The electrode assembly is then placed inside an aluminum foil bag, with the positive and negative electrode tabs extended from the inside to the outside of the outer packaging. After baking at 80°C for 10 hours to remove moisture, electrolyte is injected into the inner space of the outer packaging. Following vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained.

[0087] Examples 1-2 to 1-26

[0088] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-1. Specifically, as the mass percentage content W1 of the inorganic metal oxide changes, the sum of the mass percentage contents of the binder and conductive agent also changes, while the mass ratio of the binder to the conductive agent remains constant. When the mass percentage content of the first compound added changes, the mass percentage content of the organic solvent changes accordingly, while the mass ratio of ethylene carbonate and diethyl carbonate and the mass percentage content of the lithium salt remain unchanged.

[0089] Examples 1-27

[0090] Except for the section on "Preparation of Negative Electrode Sheet", where the negative electrode active material is artificial graphite, the rest is the same as in Example 1-1.

[0091] Examples 2-1 to 2-12

[0092] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as in Examples 1-5. Specifically, when the mass percentage of the first compound added changes, the mass percentage of the organic solvent changes accordingly, while the mass ratio of ethylene carbonate and diethyl carbonate and the mass percentage of lithium salt remain unchanged.

[0093] Examples 3-1 to 3-20

[0094] Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as in Examples 2-3. Specifically, as the mass percentage content W2 of the binder and the mass percentage content W3 of the conductive agent change, the mass percentage content W1 of the inorganic metal oxide also changes accordingly.

[0095] Comparative Example 1

[0096] Except for preparing the positive electrode sheet according to the following method and adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0097] <Preparation of the positive electrode>

[0098] Lithium cobalt oxide (LiCoO2), a positive electrode active material, polyvinylidene fluoride (PVDF), a positive electrode binder, and conductive carbon black (Super P), a positive electrode conductive agent, were mixed in a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was uniformly coated onto one side of a 12 μm thick aluminum foil used as a positive electrode current collector. The foil was then dried at 120°C for 1 hour to obtain a single-sided positive electrode sheet with a coating thickness of 227.8 μm. The same steps were repeated on the other side of the aluminum foil to obtain a double-sided positive electrode sheet with a coating layer of positive active material. After cold pressing and slitting, a positive electrode sheet with a size of 74 mm × 867 mm was obtained. The thickness of the positive electrode active material layer after cold pressing was 102 μm.

[0099] Comparative Examples 2 to 5

[0100] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Examples 1-1. Specifically, as the mass percentage content W1 of the inorganic metal oxide changes, the sum of the mass percentage contents of the binder and conductive agent also changes, while the mass ratio of the binder to the conductive agent remains constant. When the mass percentage content of the first compound added changes, the mass percentage content of the organic solvent changes accordingly, while the mass ratio of ethylene carbonate and diethyl carbonate and the mass percentage content of the lithium salt remain unchanged.

[0101] The preparation parameters and electrical performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0102] Table 1

[0103]

[0104]

[0105] Note: (1) In Table 1, “ / ” indicates that there are no relevant preparation parameters; (2) Taking Examples 1-16 as an example, the first compound in Table 1 is “fluoroethylene carbonate + vinyl sulfate”, and the mass percentage a% of the first compound is “5% + 1%”, that is, the first compound added is two substances, fluoroethylene carbonate and vinyl sulfate. Based on the mass of the electrolyte, the mass percentage of fluoroethylene carbonate is 5% and the mass percentage of vinyl sulfate is 1%. Other examples and comparative examples are understood in the same way; (3) Taking Examples 1-21 as an example, the inorganic metal oxide in Table 1 is “TiO2 + Al2O3”, the element M is “Ti + Al”, and the mass percentage of the inorganic metal oxide is “Ti + Al”. The content W1 is “32%+35%”, that is, two inorganic metal oxides TiO2 and Al2O3 are added to the base coating. The element M includes Ti and Al. Based on the mass of the base coating, the mass percentage of inorganic metal oxide TiO2 is 32% and the mass percentage of inorganic metal oxide Al2O3 is 35%. Other examples and comparative examples are understood in the same way. (4) Taking Example 1-1 as an example, the number of drop test pass in Table 1 is “15 / 50”, which means that 50 lithium-ion batteries were drop tested. Among them, 15 lithium-ion batteries did not smoke, leak, catch fire or explode. 15 lithium-ion batteries passed the drop test. Other examples and comparative examples are understood in the same way.

[0106] Referring to Table 1, and as shown in Examples 1-1 to 1-27 and Comparative Examples 1 to 5, when the bottom coating of the positive electrode sheet includes inorganic metal oxides, and the mass percentage of the inorganic metal oxides, the types of elements included in the inorganic metal oxides, and the types and mass percentages of the first compound in the electrolyte are within the scope of this application, the lithium-ion battery exhibits a high cycle capacity retention rate and a high number of drop test pass rates, indicating good cycle stability and safety performance. In contrast, in Comparative Examples 1 to 5, the lithium-ion batteries exhibit low cycle capacity retention rates and a low number of drop test pass rates, indicating poor cycle stability and safety performance.

[0107] In Examples 1-1 to 1-8, by adjusting the mass percentage of the first compound, the cycle stability of the lithium-ion battery can be improved within a certain range. When the mass percentage of the first compound is low, the drop test pass rate is higher, and the safety performance of the lithium-ion battery is significantly improved. As the mass percentage of the first compound increases, the improvement in the safety performance of the lithium-ion battery decreases. When the mass percentage of the first compound is between 0.5% and 12%, a relatively stable solid electrolyte interface film can be formed on the surface of the negative electrode, while generating less acidic substances, resulting in less impact on the aluminum foil. Therefore, the lithium-ion battery has higher cycle stability and better safety performance.

[0108] In Examples 1-9 to 1-15, the inorganic metal oxide content in the base coating is within the scope of this application, resulting in a higher number of drop test pass rates and improved safety performance of the lithium-ion battery. Increasing the inorganic metal oxide content in the base coating reduces direct contact between the electrolyte and the aluminum foil, and allows the inorganic metal oxide to fully react with the acidic substances generated by the first compound, increasing the strength of the aluminum foil and enabling the lithium-ion battery to maintain strong impact resistance during drops. When the inorganic metal oxide content is between 60% and 85%, the improvement in safety performance is particularly significant.

[0109] In Examples 1-16 to 1-25, by adding multiple types of first compounds or adding multiple inorganic metal oxides to the undercoat, the lithium-ion battery exhibited higher cycle capacity retention and a higher number of drop test pass rates, indicating that both cycle stability and safety performance of the lithium-ion battery could be improved simultaneously. In Comparative Example 1, the positive electrode did not include the undercoat. Due to the presence of the first compound, the acidic substances generated during the lithium-ion battery cycle easily corroded the aluminum foil and the positive electrode active material, resulting in poor safety performance of the lithium-ion battery. Comparative Examples 2 and 5 show that a low mass percentage of inorganic metal oxides in the undercoat leads to poor safety performance of the lithium-ion battery; a high mass percentage of inorganic metal oxides in the undercoat cannot further improve the safety performance of the lithium-ion battery. As can be seen from Comparative Examples 3 and 4, if the mass percentage of the first compound is too low, the cycle stability of the lithium-ion battery will be poor. This is because if the content of the first compound is too low, it is difficult to form a stable solid electrolyte interface film on the surface of the negative electrode. The instability of the negative electrode will be detrimental to the cycle stability of the lithium-ion battery. If the mass percentage of the first compound is too high, it will not be able to further improve the cycle stability of the lithium-ion battery, and will also lead to poor safety performance of the lithium-ion battery.

[0110] Table 2

[0111]

[0112] The thickness A of the undercoat layer typically affects the cycle stability, safety performance, and energy density of lithium-ion batteries. As shown in Examples 1-5 and 2-1 to 2-8, increasing the thickness of the undercoat layer can improve the drop test pass rate within a certain range, which is beneficial for improving the safety performance of lithium-ion batteries. When the thickness of the undercoat layer is between 2.5 μm and 9.5 μm, the lithium-ion battery exhibits both good cycle stability and good safety performance. As shown in Examples 1-5 and 2-1 to 2-2, a relatively small undercoat layer thickness has a relatively limited effect on inhibiting the corrosion of the aluminum foil by the first compound, resulting in limited improvement in the safety performance of the lithium-ion battery. However, within the scope of this application, the thickness of the undercoat layer results in relatively good safety performance for the lithium-ion battery. As shown in Examples 2-6 to 2-8, a relatively large undercoat layer thickness cannot further improve the cycle performance of the lithium-ion battery and also affects its energy density.

[0113] The a / A value typically affects the cycle stability and safety performance of lithium-ion batteries. As shown in Examples 2-1 to 2-12, by adjusting the a / A value within the range of this application, the lithium-ion battery exhibits a high cycle capacity retention rate and a high number of drop test pass rates, indicating that the lithium-ion battery has high cycle stability and good safety performance.

[0114] Table 3

[0115]

[0116] Note: (1) Taking Examples 3-19 as an example, the binder in Table 3 is "nitrile rubber + polyacrylamide", and the mass percentage W2 of the binder is "4% + 10%", that is, the binder added is two substances: nitrile rubber and polyacrylamide. Based on the mass of the base layer, the mass percentage of nitrile rubber is 4% and the mass percentage of polyacrylamide is 10%; the conductive agent in Table 3 is "graphene + acetylene black", and the mass percentage W3 of the conductive agent is "5% + 5%", that is, the conductive agent added is two substances: graphene and acetylene black. Based on the mass of the base layer, the mass percentage of graphene is 5% and the mass percentage of acetylene black is 5%. Other examples can be understood in the same way; (2) Taking Examples 3-17 as an example, the binder in Table 3 is "nitrile rubber + polyacrylamide", and the weight average molecular weight of the binder is "160,000 + 190,000", that is, the weight average molecular weight of the binder nitrile rubber is 160,000 and the weight average molecular weight of the binder polyacrylamide is 190,000. Other examples can be understood in the same way.

[0117] The mass percentage content of the binder (W2) and the mass percentage content of the conductive agent (W3) typically affect the cycle stability and safety performance of lithium-ion batteries. As shown in Examples 3-1 to 3-16, by adjusting the mass percentage content of the binder (W2) and the conductive agent (W3) within the scope of this application, the lithium-ion battery exhibits a high cycle capacity retention rate and a high number of drop test pass rates, indicating that the lithium-ion battery possesses good cycle stability and safety performance. When the mass percentage content of the conductive agent is relatively low, it affects the conductivity of the positive electrode, thereby impacting the cycle stability of the lithium-ion battery. However, within the scope of this application, the lithium-ion battery exhibits good cycle stability due to the relatively low mass percentage content of the conductive agent.

[0118] The type of binder, its weight-average molecular weight, and the type of conductive agent typically affect the cycle stability and safety performance of lithium-ion batteries. As shown in Examples 3-1 to 3-20, by selecting the aforementioned binder and controlling its weight-average molecular weight within the range of this application, and by selecting the aforementioned conductive agent, the lithium-ion battery exhibits a higher cycle capacity retention rate and a higher number of drop test pass rates, indicating that the lithium-ion battery possesses good cycle stability and safety performance.

[0119] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive current collector and a base coating and a positive active material layer disposed on at least one surface of the positive current collector, the base coating being disposed between the positive current collector and the positive active material layer; the base coating comprises an inorganic metal oxide, the inorganic metal oxide comprising element M, the element M comprising Al, Ti, and Sb, the inorganic metal oxide comprising Al2O3, TiO2, and at least one selected from Sb2O3, Sb2O4, or Sb2O5, and the mass percentage of the inorganic metal oxide, based on the mass of the base coating, is W1, 70% ≤ W1 ≤ 95%; The electrolyte includes a first compound, which includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, a compound represented by formula (I), or a compound represented by formula (III). ,in, n and m are independently selected from integers 1 to 3, and R0, Rn and Rm are each independently selected from hydrogen, fluorine, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C2-C6 alkenyl; when substituted, the substituents of each group are halogens. Based on the mass of the electrolyte, the mass percentage of the first compound is a%, 0.5≤a≤15.

2. The secondary battery according to claim 1, wherein, The secondary battery satisfies at least one of the following characteristics: （1）0.5≤a≤12； （2）70%≤W1≤85%。 3. The secondary battery according to claim 1, wherein, The thickness of the base coating is A μm, where 2.1 ≤ A ≤ 15.

5.

4. The secondary battery according to claim 1, wherein, The thickness of the base coating is A μm, where 2.5 ≤ A ≤ 9.

5.

5. The secondary battery according to claim 3, wherein, 0.02≤a / A≤5.

1.

6. The secondary battery according to claim 1, wherein, The compound represented by formula (I) includes at least one of succinic anhydride, glutaric anhydride or adipic anhydride, and the compound represented by formula (III) includes at least one of vinyl sulfate, propylene sulfate, butene sulfate or 2-methyl-1,3-propanedisulfite.

7. The secondary battery according to claim 1, wherein, The base coating also includes an adhesive and a conductive agent. Based on the mass of the base coating, the mass percentage of the adhesive is W2, the mass percentage of the conductive agent is W3, 0.5%≤W2≤25%, and 0.5%≤W3≤20%.

8. The secondary battery according to claim 7, wherein, The adhesive satisfies at least one of the following characteristics: (1) The adhesive comprises a polymer formed from at least one monomer selected from acrylic acid, acrylamide, lithium acrylate, sodium acrylate, acrylonitrile, methyl acrylate, ethyl acrylate, methyl 2-methacrylate or ethyl 2-methacrylate; (2) The adhesive includes at least one of sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, or nitrile rubber; (3) The weight average molecular weight of the adhesive is between 150,000 and 1,950,000.

9. The secondary battery according to claim 7, wherein, The conductive agent includes at least one of graphene, graphite fiber, carbon nanotubes, or conductive carbon black.

10. The secondary battery according to claim 1, wherein, The negative electrode sheet includes a negative electrode active material, which includes at least one of natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon, or silicon-based composite materials.

11. An electronic device comprising a secondary battery as described in any one of claims 1 to 10.

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