Electrochemical device and electronic device

Abstract

An electrochemical device and an electronic device. The electrochemical device comprises a negative electrode sheet and an electrolyte; the negative electrode sheet comprises a negative electrode material layer, the negative electrode material layer comprises a silicon-carbon negative electrode material, the silicon-carbon negative electrode material comprises a doped element, and the doped element includes at least one of B, P, or S; the electrolyte comprises a compound of formula I and fluoroethylene carbonate. The electrolyte simultaneously comprising the compound of formula (I) and fluoroethylene carbonate is applied to the electrochemical device, thereby improving the cycle performance and energy density of the electrochemical device.

Description

An electrochemical device and an electronic device

[0001] This application claims priority to Chinese Patent Application No. 202411214633.2, filed on August 30, 2024, entitled "An Electrochemical Device and an Electronic Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemistry, and in particular to an electrochemical device and an electronic device. Background Technology

[0003] With the rapid development of electronic products, lithium-ion batteries, due to their advantages such as high energy density, miniaturization, and lightweight design, are widely used in mobile phones, laptops, tablets, drones, electric vehicles, power tools, and energy storage systems. Especially in the 3C product sector, consumer demand for extended battery life remains significant, thus placing higher demands on the energy density of lithium-ion batteries. To further improve the energy density of lithium-ion batteries, high-specific-capacity electrode materials are required. Silicon-based materials, as a type of alloyed anode material, can provide an ultra-high specific capacity of up to 4200 mAh / g, making them a highly promising material for improving energy density. However, the lithiation of silicon-based materials forms a lithium-silicon alloy, which is highly reactive and readily attacks solvent molecules in the electrolyte, leading to rapid electrolyte consumption and loss of active lithium, resulting in poor cycle performance. Summary of the Invention

[0004] The purpose of this application is to provide an electrochemical device and an electronic device to improve the cycle performance of the electrochemical device. The specific technical solution is as follows:

[0005] The first aspect of this application provides an electrochemical device comprising a negative electrode and an electrolyte, wherein the negative electrode comprises a negative electrode material layer, and the negative electrode material layer comprises a silicon-carbon negative electrode material;

[0006] The silicon-carbon anode material includes heterogeneous elements, which include at least one of B, P, or S elements. Based on the total mass of the silicon-carbon anode material, the mass percentage of heterogeneous elements is 0.1% to 2%.

[0007] The electrolyte comprises a compound of formula I and fluoroethylene carbonate;

[0008] Wherein, R is selected from fluorinated or unsubstituted C2 to C6 alkyl groups, fluorinated or unsubstituted C6 to C12 aryl groups, and the fluorine substitution can be full substitution or partial substitution.

[0009] In one embodiment of this application, the mass percentage of silicon element is 15% to 40% based on the total mass of the negative electrode material layer.

[0010] In one embodiment of this application, the mass percentage of silicon-carbon anode material is 30% to 85% based on the total mass of the anode material layer.

[0011] In one embodiment of this application, the compound of formula I includes at least one of the following compounds:

[0012] In one embodiment of this application, the mass percentage of the compound of formula I is 3% to 50%, preferably 3% to 20%, based on the total mass of the electrolyte.

[0013] In one embodiment of this application, the mass percentage of fluoroethylene carbonate is 5% to 30%, preferably 5% to 15%, based on the total mass of the electrolyte.

[0014] In one embodiment of this application, the electrolyte comprises a nitrile compound, which includes at least one of butadionitrile, adiponitrile, 1,3,6-hexanetrionitrile, glutaronitrile, methylglutaronitrile, heptacyanide, octadionitrile, anonadionitrile, or sebaconitrile, and the mass percentage of the nitrile compound is 0.1% to 5% based on the total mass of the electrolyte.

[0015] In one embodiment of this application, the electrolyte further includes a first component, which comprises at least one of dimethyl carbonate or diethyl carbonate; the first component has a mass percentage content of 5% to 35% based on the total mass of the electrolyte.

[0016] In one embodiment of this application, the electrolyte further includes a second component, which includes at least one of ethyl acetate, propyl acetate, propyl propionate, butyl acetate, ethyl butyrate, or ethyl isobutyrate; the mass percentage of the second component is 5% to 35% based on the total mass of the electrolyte.

[0017] A second aspect of this application provides an electronic device that includes the electrochemical device described in the first aspect of this application.

[0018] The beneficial effects of this application are:

[0019] This application provides an electrochemical device and an electronic device. The electrochemical device includes a negative electrode and an electrolyte. The electrolyte includes a compound of formula I and fluoroethylene carbonate (FEC). The negative electrode includes a negative electrode material layer, which includes a silicon-carbon negative electrode material. The silicon-carbon negative electrode material includes heterogeneous elements, including at least one of B, P, or S. The silicon-carbon negative electrode material is an excellent high-capacity negative electrode material. The heterogeneous elements coated on its surface can suppress the side reactions between silicon and the electrolyte to a certain extent. However, during long-term cycling, silicon will still come into contact with the electrolyte and undergo side reactions, leading to the continuous formation of a solid electrolyte interphase (SEI) film, which consumes the active lithium element in the battery. Fluorinated ethylene carbonate (FEC) is an excellent electrolyte additive for electrochemical devices. During battery formation, FEC in the electrolyte can form a cross-linked, highly tough polymer protective layer at the electrode interface, thereby greatly improving the cycle performance of the electrochemical device. However, FEC is consumed relatively quickly in the battery, resulting in a thick polymer layer that can hinder lithium-ion transport to some extent. Adding compound I can form a passivation layer at the positive and negative electrode interfaces rich in lithium-containing inorganic compounds with S and F elements, thereby preventing the excessive polymerization of FEC. Thus, a thinner SEI / cathode electrolyte interface (CEI) layer is synergistically formed, improving battery interface performance while enhancing cycle performance.

[0020] 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. Detailed Implementation

[0021] The technical solutions in the embodiments of this application will be clearly and completely described below. 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.

[0022] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries.

[0023] FEC (Fluoro Ethylene Carbonate) is an excellent film-forming additive used to repair damage to the SEI (Solid Electrolyte Interface) film on the surface of silicon particles. However, FEC is consumed rapidly, and excessive FEC addition can lead to poor cycle performance of lithium-ion batteries. Therefore, this invention adds substances containing -SO2F- groups to form an interface film rich in inorganic substances such as LiF and Li2S on the positive and negative electrode surfaces. This reduces damage to the SEI film on the surface of silicon particles and the CEI (Chemical Electrochemical Interface) film on the positive electrode surface, thereby reducing the consumption of FEC and electrolyte solvent and improving the long-term cycle stability of the battery.

[0024] The first aspect of this application provides an electrochemical device comprising a negative electrode and an electrolyte, wherein the negative electrode comprises a negative electrode material layer, and the negative electrode material layer comprises a silicon-carbon negative electrode material;

[0025] The silicon-carbon anode material includes a silicon-carbon composite, and the silicon-carbon composite includes heterogeneous elements, including at least one of B, P, or S elements. Based on the total mass of the silicon-carbon anode material, the mass percentage content of the heterogeneous elements is from 0.1% to 2%; for example, based on the total mass of the silicon-carbon anode material, the mass percentage content of the heterogeneous elements can be 0.1%, 0.2%, 0.3%, 0.5%, 1.0%, 1.5%, 2.0%, or a range of any two of these values. Without being limited to any theory, the inventors of this application have discovered that when heterogeneous elements are coated on the surface of the silicon-carbon anode material, and the mass percentage content of the heterogeneous elements is from 0.1% to 2%, it is beneficial to improve the lithium-ion transport efficiency of the silicon-carbon composite at high rates, thereby further improving the cycle performance of the lithium-ion battery.

[0026] The electrolyte comprises a compound of formula I and fluoroethylene carbonate;

[0027] Wherein, R is selected from fluorinated or unsubstituted C2 to C6 alkyl groups and fluorinated or unsubstituted C6 to C12 aryl groups, and the fluorine substitution can be complete or partial substitution. Without being limited to any particular theory, the inventors of this application have discovered that fluoroethylene carbonate is a good film-forming additive for the negative electrode surface, but its oxidative stability on the positive electrode side is insufficient. When fluoroethylene carbonate is used in combination with the compound of Formula I, a passivation layer can be formed on the positive electrode surface, which retains the good film-forming properties of fluoroethylene carbonate on the negative electrode surface while reducing the oxidative decomposition of fluoroethylene carbonate at the positive electrode interface. The combined use of the compound of Formula I and fluoroethylene carbonate enables lithium-ion batteries to have a higher cycle capacity retention rate, thereby improving the cycle performance of lithium-ion batteries.

[0028] In one embodiment of this application, the impurity element is introduced by coating the surface of the silicon-carbon anode material with an inorganic material, including B2O3 and Na5P3O. 10 Or at least one of Li2S.

[0029] In one embodiment of this application, the mass percentage of silicon element is 15% to 40% based on the total mass of the negative electrode material layer. For example, the mass percentage of silicon element can be 15%, 20%, 25%, 30%, 35%, 40%, or a range of any two of these values, and the silicon element is introduced from silicon-carbon negative electrode material. The mass percentage of silicon element is adjusted by adding silicon-carbon negative electrode material during the preparation of the negative electrode sheet. Without being limited to any theory, the inventors of this application have discovered that when the mass percentage of silicon element is 15% to 40%, the high energy density characteristic of silicon can be utilized, and at this ratio, it is more conducive to extending the lifespan of the lithium-ion battery, thereby improving the overall performance of the lithium-ion battery.

[0030] In one embodiment of this application, the mass percentage of silicon-carbon anode material is 30% to 85% based on the total mass of the anode material layer. The mass percentage of silicon-carbon anode material can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or a range of any two values ​​therein. Without being limited to any theory, the inventors of this application have discovered that when the mass percentage of silicon-carbon anode material is 30% to 85%, the high energy density characteristic of silicon-carbon anode material can be fully utilized, which is beneficial to improving the energy density of lithium-ion batteries, and does not lead to performance degradation caused by excessive silicon-carbon material.

[0031] The negative electrode material layer of this application may further include carbon material, which may be selected from at least one of natural graphite, artificial graphite, mesophase microcarbon spheres, hard carbon, or soft carbon. Based on the total mass of the negative electrode material layer, the carbon material content may range from 15% to 70%.

[0032] In one embodiment of this application, the compound of formula I includes at least one of the following compounds:

[0033] In one embodiment of this application, the compound of formula I can be prepared using methods known in the art or can be purchased commercially.

[0034] In one embodiment of this application, the mass percentage of compound I is 3% to 50%, preferably 3% to 20%, based on the total mass of the electrolyte. For example, the mass percentage of compound I can be 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or a range of any two of these values. Without being limited to any theory, by controlling the mass percentage of compound I within the range of 3% to 50%, a passivation interface can be formed on the electrode surface in conjunction with FEC, which is beneficial for improving the cycle performance of lithium-ion batteries.

[0035] In one embodiment of this application, the electrolyte comprises fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate is 5% to 30%, preferably 5% to 15%, based on the total mass of the electrolyte. For example, the mass percentage of fluoroethylene carbonate can be 5%, 10%, 15%, 20%, 25%, 30%, or a range of any two of these values. Without being limited to any particular theory, controlling the mass percentage of fluoroethylene carbonate within the range of 5% to 40% is beneficial for the formation of a complete SEI film layer by FEC, improving the cycle performance of the lithium-ion battery, while preventing the formation of an excessively thick SEI film layer, which would hinder interfacial ion transport and reduce the battery's low-temperature and rate discharge performance. Furthermore, it prevents excessive decomposition of FEC on the positive electrode side, resulting in excessive gas production, thus balancing cycle stability.

[0036] In one embodiment of this application, the electrolyte includes a nitrile compound, which includes at least one selected from butadionitrile, adiponitrile, 1,3,6-hexanetrionitrile, glutaronitrile, methylglutaronitrile, heptacyanide, octadionitrile, azelonitrile, or sebacate. Based on the total mass of the electrolyte, the mass percentage of the nitrile compound is from 0.1% to 5%. For example, the mass percentage of the nitrile compound can be 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or a range consisting of any two of these values. Without being limited to any particular theory, nitrile compounds can effectively stabilize transition metal elements, thereby improving the stability of the positive electrode interface and enhancing the cycle performance of lithium-ion batteries.

[0037] In one embodiment of this application, the electrolyte further includes a first component, which comprises at least one of dimethyl carbonate or diethyl carbonate; the mass percentage of the first component is 5% to 35% based on the total mass of the electrolyte. For example, the mass percentage of the first component can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, or a range of any two of these values. Without being limited to any theory, dimethyl carbonate and diethyl carbonate have low viscosity, which is beneficial for reducing the viscosity and bulk impedance of the electrolyte, improving the ion transport capacity of the electrolyte, and, when introduced into the electrolyte simultaneously with the compound of Formula I, further improving the cycle performance of the lithium-ion battery.

[0038] In one embodiment of this application, the electrolyte further includes a second component, which comprises at least one selected from ethyl acetate, propyl acetate, propyl propionate, butyl acetate, ethyl butyrate, or ethyl isobutyrate; the mass percentage of the second component is 5% to 35% based on the total mass of the electrolyte. For example, the mass percentage of the second component can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, or a range of any two of these values. Without being limited to any theory, the lower viscosity of the second component is beneficial for reducing the viscosity and bulk impedance of the electrolyte, improving the ion transport capacity of the electrolyte, and, when introduced into the electrolyte simultaneously with the compound of Formula I, further improving the cycle performance of the lithium-ion battery.

[0039] In this application, the electrolyte also includes a lithium salt. There are no particular limitations on the lithium salt; any lithium salt known in the art can be used, as long as it achieves the purpose of this application. For example, the lithium salt can be selected from at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, and LiPO2F2. For example, LiPF6 can be used as the lithium salt. Based on the mass of the electrolyte, the mass percentage of the lithium salt can be from 8% to 20%, for example, the mass percentage of the lithium salt can be 8%, 10%, 12%, 13%, 15%, 18%, 20%, or a range consisting of any two of these values.

[0040] This application does not impose any particular restrictions on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents.

[0041] 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 dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates 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). Fluorinated carbonate 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, methyl propionate, ethyl 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 aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 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 content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved.

[0042] This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved. For example, based on the mass of the electrolyte, the mass percentage of non-aqueous solvents can range from 0% to 73.9%.

[0043] In one embodiment of this application, the mass percentage of silicon-carbon anode material is 30% to 85% based on the total mass of the anode material layer. The mass percentage of silicon-carbon anode material can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or any range thereof. Without being limited to any theory, the inventors of this application have discovered that when the mass percentage of silicon-carbon anode material is 30% to 85%, the high energy density characteristic of silicon can be utilized, which is beneficial to improving the energy density of lithium-ion batteries, and does not lead to performance degradation caused by excessive silicon-carbon material.

[0044] In this application, the electrochemical device further includes a positive electrode sheet, which comprises a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode 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 term "surface" here can refer to the entire surface area of ​​the positive current collector, or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0045] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0046] The positive electrode material layer includes a positive electrode active material. This application does not impose any particular restrictions on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include, but is not limited to, at least one of lithium nickel cobalt manganese oxide (e.g., 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.

[0047] The positive electrode material layer may also include a conductive agent and a binder. This application does not impose any particular restrictions on the types of conductive agents and binders, as long as they can achieve the purpose of this application. This application does not impose any particular restrictions on the mass ratio of positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0048] This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector can be 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer can be 30 μm to 120 μm.

[0049] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0050] In this application, the electrochemical device also includes a diaphragm. This application does not impose any particular limitation on the diaphragm, as long as it achieves the purpose of this application. For example, the diaphragm material may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of diaphragm may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0051] In some embodiments of this application, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer 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.

[0052] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0053] In some embodiments of this application, the inorganic layer comprises inorganic particles and a binder. This application does not particularly limit the inorganic particles; for example, the inorganic particles may include at least one selected from 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 particularly limit the binder; for example, the binder may be at least one of the binders described above. In some embodiments of this application, the polymer layer comprises a polymer, the polymer material of which includes at least one selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0054] In some embodiments of this application, the inorganic layer may also include a thickener and a wetting agent. This application does not have any particular restrictions on the types of thickeners and wetting agents, as long as they can achieve the purpose of this application. For example, the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose; the wetting agent may include, but is not limited to, at least one of dimethylsiloxane, sodium dodecyl sulfate, trialkyl phosphate, methyl decanoate, and dodecyl acetate.

[0055] In this application, there is no particular limitation on the thickness of the diaphragm, as long as it can achieve the purpose of this application. For example, the thickness of the diaphragm can be from 4 μm to 30 μm.

[0056] In this application, the electrochemical device further includes a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The phrase "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the term "surface" here can refer to the entire surface area of ​​the negative electrode current collector, or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0057] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.

[0058] In some embodiments of this application, the negative electrode material layer may further include a conductive agent, a binder, and / or a thickener. This application does not particularly limit the types of conductive agents and thickeners, as long as they achieve the purpose of this application. For example, the conductive agent and binder may be at least one of the aforementioned conductive agents and binders. The thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. This application does not particularly limit the mass ratio of the negative electrode material, conductive agent, binder, and thickener in the negative electrode material layer; those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.

[0059] This application does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it can achieve the purpose of this application. For example, the thickness of the single-sided negative electrode material layer is 30 μm to 120 μm.

[0060] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0061] This application does not impose any particular limitation on the conductive agent, as long as it can achieve the purpose of this application. For example, the 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. 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 polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0062] This application does not impose any particular limitation on the adhesive, as long as it can achieve the purpose of this application. For example, the adhesive may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride.

[0063] The electrochemical device also includes a housing for accommodating the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of electrochemical devices. This application does not limit the scope of these other components. This application does not impose any particular limitation on the housing; it can be a housing known in the art, as long as it achieves the purpose of this application. For example, the housing can be a rigid housing or a flexible housing. The material of the rigid housing can be metal; this application does not limit the type of metal and can use known metal rigid housings, as long as they achieve the purpose of this application. The flexible housing can be a metal-plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0064] The preparation process of the electrochemical device described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the preparation process of the electrochemical device 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 into a housing; injecting electrolyte into the housing and sealing it to obtain the electrochemical device. Alternatively, 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 into a housing; injecting electrolyte into the housing and sealing it to obtain the electrochemical device. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the electrochemical device.

[0065] A second aspect of this application provides an electronic device, including the electrochemical device in any of the foregoing embodiments of this application.

[0066] The electronic device described in this application is not particularly limited and 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-based 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.

[0067] Example

[0068] 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.

[0069] Test methods and equipment

[0070] Cyclic performance test:

[0071] Place the lithium-ion battery in a 25°C constant temperature test chamber and let it stand for 30 minutes to allow it to reach a constant temperature. Charge it at a constant current of 0.5C to 4.45V, then charge it at a constant voltage to a current of 0.025C. Let it stand for 5 minutes, then discharge it at a constant current of 0.5C to 3.0V. Record this as the initial discharge capacity C1. Repeat this process for 200 cycles and record the discharge capacity C2 after 200 cycles. Calculate the cycle capacity retention rate of the lithium-ion battery. Cycle capacity retention rate = C2 / C1 × 100%.

[0072] Cyclic thickness growth rate

[0073] Charge the battery to 4.45V at a constant current of 0.5C, then charge it to 0.025C at a constant voltage. Let it stand for 5 minutes and measure the thickness. This thickness is recorded as the thickness of the battery after the first full charge. Use the same charge and discharge process as in the above cycle capacity retention test, cycle 500 times, and measure the thickness. This thickness is recorded as the battery thickness after the 500th cycle.

[0074] The difference between the battery thickness after the 500th cycle and the thickness at the first full charge is divided by the thickness at the first full charge. The battery thickness is measured using a micrometer, and the average value is taken from five different locations. This average value is the cycle thickness growth rate. The smaller the cycle thickness growth rate, the better.

[0075] Testing of B, P, and S element content:

[0076] The mass percentages of B, P, and S elements in silicon-carbon anode materials were determined using an ICP (Inductively Coupled Plasma) analyzer.

[0077] Test for silicon elemental mass percentage:

[0078] A lithium-ion battery discharged at 0.5C to 3.0V was disassembled, and the negative electrode sheet was removed. It was then soaked in dimethyl carbonate (DMC) for 20 minutes, followed by rinsing with DMC and acetone respectively. The negative electrode sheet was then placed in an oven and baked at 80℃ for 12 hours to obtain the negative electrode sheet. The negative electrode sheet was then placed in a vacuum oven and dried at 100℃ for 24 hours. One gram of powdered negative electrode material layer was scraped off the negative electrode sheet with a blade, and the mass percentage of silicon in the negative electrode material layer was determined using an ICP (Inductively Coupled Plasma) analyzer.

[0079] Example 1-1

[0080] (1) Preparation of positive electrode sheet

[0081] LiCoO2 (positive electrode active material), Super-P (conductive agent), and PVDF (binder) were mixed in a mass ratio of 96:2.0:2.0. N-methylpyrrolidone (NMP) was added, and the mixture was stirred until homogeneous to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was uniformly coated onto one surface of a 12 μm thick aluminum foil used as a positive electrode current collector and dried at 120 °C to obtain a positive electrode sheet with a 100 μm thick positive electrode material layer coated on one side. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material layers. The sheet was dried under vacuum at 120 °C, and then cold-pressed, cut, and slit to obtain a positive electrode sheet with dimensions of 74 mm × 867 mm.

[0082] (2) Preparation of negative electrode sheet

[0083] Microporous carbon material with a carbon content of 50% loaded with nano-silicon and inorganic coating material sodium tripolyphosphate Na5P3O 10 The mixture is added to an ethanol solvent to form a suspension, then ball-milled and mixed to achieve uniform dispersion. After filtration and drying, a silicon-carbon anode material with an inorganic coating layer on its surface is obtained.

[0084] The silicon-carbon anode material prepared according to the above scheme, artificial graphite, conductive agent Super-P, thickener CMC, and binder SBR were dissolved in deionized water at a mass ratio of 50:46.5:1.0:1.0:1.5 and mixed evenly to form an anode slurry. The anode slurry was then uniformly coated onto the copper foil of the anode current collector, with a coating amount of 1.85 g / cm³. 2 After drying at 85℃, the material is cold-pressed, trimmed, cut into sheets, and slit. Then, it is dried under vacuum at 110℃ for 4 hours, and the negative electrode tabs are welded to produce a negative electrode sheet that meets the requirements.

[0085] Based on the total mass of the negative electrode material layer, the silicon content is shown in Table 1 below, and based on the total mass of the silicon-carbon negative electrode material, the impurity element content is shown in Table 1 below.

[0086] (3) Preparation of electrolyte

[0087] In an argon-atmospheric glove box with a water content of <10ppm, ethyl propionate, propylene carbonate, and ethyl methyl carbonate are mixed in a ratio of 3:4:3 to obtain a base solvent. Compound I-1, fluoroethylene carbonate, and lithium salt LiPF6 are then added, dissolved, and mixed evenly to obtain an electrolyte. Based on the total mass of the electrolyte, the mass percentage of lithium salt LiPF6 is 12.5%, the mass percentage of fluoroethylene carbonate is 20%, the mass percentage of the first compound I-1 is 25%, and the remainder is the base solvent.

[0088] (4) Diaphragm

[0089] A porous polyethylene film with a thickness of 7μm (provided by Shanghai Enjie Co., Ltd.) was used as the separator.

[0090] (5) Preparation of lithium-ion batteries

[0091] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as a separator. They are then wound, with the positive tab connected to the positive electrode and the negative tab connected to the negative electrode, thus obtaining the electrode assembly. The electrode assembly is placed in an aluminum foil packaging bag, with the positive and negative tabs extended from the inside to the outside of the bag. Moisture is removed at 80°C, and the electrolyte prepared above is injected. After vacuum sealing, settling, formation, degassing, and shaping, a lithium-ion battery is obtained.

[0092] Examples 1-2 to Examples 1-30

[0093] Except for adjusting the type of inorganic material used for coating, the mass percentage of impurities in the silicon-carbon anode material, and the mass percentage of silicon in the anode material layer according to Table 1 in the preparation of the anode electrode sheet, and adjusting the type and mass percentage of compound I, the mass percentage of fluoroethylene carbonate, and the mass percentage of the base solvent according to Table 1 in the preparation of the electrolyte, while keeping the mass percentage of lithium salt LiPF6 unchanged, the rest is the same as in Example 1-1.

[0094] Examples 2-1 to 2-7

[0095] Except for the addition of nitrile compounds according to Table 2 in the preparation of the electrolyte, and the adjustment of the type and mass percentage of nitrile compounds, the mass percentage of the base solvent is changed accordingly, and the mass percentage of lithium salt LiPF6 remains unchanged, the rest is the same as in Example 1-1.

[0096] Examples 3-1 to 3-15

[0097] Except for adding the first and second components according to Table 3 in the preparation of the electrolyte, and adjusting the types and mass percentages of the first and second components, while keeping the mass percentage of lithium salt LiPF6 unchanged, the rest is the same as the corresponding Examples 2-3 in the table.

[0098] Comparative Example 1

[0099] Except that no compound of formula I is added in the preparation of the electrolyte, the mass percentage of the base solvent is changed accordingly, and the mass percentage of the lithium salt remains unchanged, the rest is the same as in Example 1-1.

[0100] Comparative Example 2

[0101] Except that fluoroethylene carbonate is not added in the preparation of the electrolyte, the mass percentage of the base solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Example 1-1.

[0102] Comparative Example 3

[0103] Except that the mass percentage of compound I in the preparation of the electrolyte is 1%, the mass percentage of fluoroethylene carbonate is 1%, the mass percentage of the base solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Examples 1-1.

[0104] Comparative Example 4

[0105] Except that the mass percentage of compound I in the preparation of the electrolyte is 1%, the mass percentage of fluoroethylene carbonate is 35%, the mass percentage of the base solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Example 1-1.

[0106] Comparative Example 5

[0107] Except that the mass percentage of compound I in the preparation of the electrolyte is 55%, the mass percentage of fluoroethylene carbonate is 1%, the mass percentage of the base solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Example 1-1.

[0108] Comparative Example 6

[0109] Besides directly using microporous carbon materials with a carbon content of 50% to support nano-silicon as silicon-carbon anode materials, the rest are related to...

[0110] Same as Example 1-1.

[0111] Table 1

[0112] As can be seen from Examples 1-1 to 1-30 and Comparative Examples 1 to 6, when the types and mass percentages of hetero-elements, the types and mass percentages of compounds of Formula I, the mass percentages of fluoroethylene carbonate, and the mass percentages of silicon are within the scope of this application, lithium-ion batteries have a high cycle capacity retention rate and a low cycle thickness growth rate.

[0113] Table 2

[0114] As can be seen from Examples 1-1, 2-1 to 2-7, when the types and mass percentages of nitrile compounds are within the scope of this application, lithium-ion batteries have higher cycle capacity retention and lower cycle thickness growth rate.

[0115] As can be seen from Examples 2-3 and 3-1 to 3-15, when the types and mass percentages of the first and second components are within the range of this application, the cycle capacity retention rate of the lithium-ion battery is higher, and the cycle thickness growth rate is further reduced. When the first and second components are used in combination, the cycle capacity retention rate can be further improved.

[0116] 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. An electrochemical device comprising a negative electrode and an electrolyte, wherein, The negative electrode sheet includes a negative electrode material layer, and the negative electrode material layer includes a silicon-carbon negative electrode material. The silicon-carbon anode material includes heterogeneous elements, which include at least one of B, P, or S elements. Based on the total mass of the silicon-carbon anode material, the mass percentage of the heterogeneous elements is 0.1% to 2%. The electrolyte comprises a compound of formula I and fluoroethylene carbonate; Wherein, R is selected from fluorinated or unsubstituted C2 to C6 alkyl groups, and fluorinated or unsubstituted C6 to C6 alkyl groups. 12 Aryl.

2. The electrochemical device according to claim 1, wherein, Based on the total mass of the negative electrode material layer, the mass percentage of silicon is between 15% and 40%.

3. The electrochemical device according to claim 1, wherein, Based on the total mass of the negative electrode material layer, the mass percentage of the silicon-carbon negative electrode material is 30% to 85%.

4. The electrochemical device according to claim 1, wherein, The compound of formula I includes at least one of the following compounds:

5. The electrochemical device according to claim 1, wherein, Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is 3% to 50%.

6. The electrochemical device according to claim 1, wherein, Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is 3% to 20%.

7. The electrochemical device according to claim 1, wherein, Based on the total mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is 5% to 30%.

8. The electrochemical device according to claim 1, wherein, Based on the total mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is 5% to 15%.

9. The electrochemical device according to any one of claims 1 to 8, wherein, The electrolyte comprises nitrile compounds, including at least one selected from succinic anionyl nitrile, adiponitrile, 1,3,6-hexanetrionitrile, glutaronitrile, methylglutaronitrile, heptanonitrile, octanoic anionyl nitrile, anonadionitrile, or sebacate; the mass percentage of the nitrile compounds is 0.1% to 5% based on the total mass of the electrolyte.

10. The electrochemical device according to any one of claims 1 to 8, wherein, The electrolyte further includes a first component, which comprises at least one of dimethyl carbonate or diethyl carbonate; the mass percentage of the first component is 5% to 35% based on the total mass of the electrolyte.

11. The electrochemical device according to any one of claims 1 to 8, wherein, The electrolyte further includes a second component, which comprises at least one of ethyl acetate, propyl acetate, propyl propionate, butyl acetate, ethyl butyrate, or ethyl isobutyrate; the second component has a mass percentage content of 5% to 35% based on the total mass of the electrolyte.

12. An electronic device comprising the electrochemical device according to any one of claims 1 to 11.

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