A type of battery

Abstract

This invention provides a battery comprising an electrolyte and a negative electrode, wherein the negative electrode active material comprises a silicon-containing material; the electrolyte comprises a first additive and a second additive, the first additive comprising fluoroethylene carbonate, and the second additive comprising a compound having a structure of Formula 1, wherein R1-R3 are each independently selected from substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, or substituted or unsubstituted C2-C10 alkynyl groups, and at least one unsaturated group is included in R1-R3. The battery provided by this invention uses silicon material as the negative electrode and exhibits excellent room temperature and high temperature cycling performance, as well as high temperature storage performance.

Description

Technical Field

[0001] This invention relates to a battery, which belongs to the field of lithium-ion batteries. Background Technology

[0002] With technological advancements and diversified energy demands, traditional energy sources are being consumed at an accelerated pace, prompting countries to expedite their strategic deployments for new energy technologies. Among these, power batteries are rapidly emerging alongside the development of new energy vehicles, while energy storage batteries are also gaining momentum with the development of clean energy. Since 2017, competition in the new energy vehicle industry has intensified, with power battery companies continuously developing and updating their products to find chemical power systems that better suit the market, meeting users' demands for high specific energy and extended range, with the aim of comprehensively replacing traditional energy-powered passenger cars and buses.

[0003] Despite the numerous advantages of lithium-ion batteries, issues such as energy density and performance degradation at high and low temperatures continue to hinder their development. Traditional lithium-ion batteries use graphite anodes with a specific capacity of 372 mAh g⁻¹. -1 The current energy density of silicon is no longer sufficient to meet the higher specific energy requirements of lithium-ion batteries. As one of the most promising anode materials, silicon has attracted widespread attention from researchers at home and abroad. While the use of silicon-based materials can improve the energy density of batteries, the problem of rapid decline in battery life should also be taken seriously. Zhang et al. (jpowsour.2011, 196(1):13-24) proposed that silicon will experience huge volume expansion during charge-discharge cycles, which will lead to the continuous destruction of the interfacial film, continuous decomposition of the electrolyte, and ultimately a rapid increase in battery impedance, as well as problems such as reduced cycle life and increased battery gas production.

[0004] Therefore, those skilled in the art urgently need to develop a battery that uses silicon material as the negative electrode and has excellent room temperature and high temperature cycling performance as well as high temperature storage performance. Summary of the Invention

[0005] The present invention provides a battery in which the negative electrode is made of silicon material, and the battery exhibits excellent room temperature and high temperature cycling performance and high temperature storage performance.

[0006] The present invention provides a battery, wherein the battery includes an electrolyte and a negative electrode, and the negative electrode active material in the negative electrode includes a silicon-containing material;

[0007] The electrolyte includes a first additive and a second additive, wherein the first additive includes fluoroethylene carbonate and the second additive includes a compound represented by Formula 1.

[0008]

[0009] R1-R3 are each independently selected from substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, or substituted or unsubstituted C2-C10 alkynyl, and at least one unsaturated group is included in R1-R3.

[0010] The battery as described above, wherein the second additive comprises at least one of the compounds shown in Formulas 2-8:

[0011]

[0012] In the battery described above, the silicon-containing material includes at least one of nano-silicon, a composite system of silicon suboxide and carbon materials, and a composite system of chemical vapor deposition silicon and carbon materials; the carbon material includes at least one of artificial graphite, natural graphite, hard carbon, and soft carbon.

[0013] In the battery described above, the mass ratio of the fluoroethylene carbonate to the second additive is (10-100):1.

[0014] In the battery described above, the fluoroethylene carbonate has a mass percentage of 3-15% in the electrolyte;

[0015] And / or, the second additive has a mass percentage content of 0.01-0.5% in the electrolyte.

[0016] In the battery described above, the fluoroethylene carbonate has a mass percentage of 6-10% in the electrolyte;

[0017] And / or, the second additive has a mass percentage content of 0.1-0.3% in the electrolyte.

[0018] In the battery described above, the electrolyte further includes a third additive, which includes at least one of the following: vinylene carbonate, ethylene ethylene carbonate, ethylene ethylene sulfate, 1,3-propanesulfonyl lactone, 1,3-propenesulfonyl lactone, vinyl sulfite, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, lithium bis(oxalate)borate, lithium difluorooxalateborate, and lithium difluorodioxalate phosphate.

[0019] The third additive has a mass percentage of 0.5-5% in the electrolyte.

[0020] In the battery described above, the electrolyte further includes a lithium salt, which includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalateborate), and lithium di(fluorooxalateborate); the lithium salt has a mass content of 12-17%.

[0021] And / or, the electrolyte further includes an organic solvent, which includes at least one of propylene carbonate, methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, sulfolane, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate; the organic solvent has a mass percentage content of 10-80%.

[0022] In the battery described above, the electrolyte comprises, by mass percentage: 12.5-14% lithium salt, 8-10% fluoroethylene carbonate, 0.5-1% second additive, and 0.5-2% third additive; and / or, the ratio of the mass percentage of silicon in the negative electrode active material to the mass percentage of fluoroethylene carbonate in the electrolyte is (0.6-1.2):1.

[0023] The battery as described above further includes a positive electrode sheet, wherein the positive electrode active material in the positive electrode sheet includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide ternary material, lithium nickel manganese oxide, and lithium-rich manganese-based material, wherein the mass content of nickel or manganese in the positive electrode active material is greater than 65%.

[0024] The battery of this invention, by controlling the selection of the negative electrode active material and the first and second additives in the electrolyte, enables the silicon-containing material to work synergistically with the first and second additives. Not only can the silicon-containing material significantly improve the energy density of the lithium-ion battery, but the unsaturated bonds of fluoroethylene carbonate and the second additive jointly participate in the construction of the SEI film, making the SEI film highly elastic, dense, and heat-resistant. This protects the silicon-containing material from the significant volume expansion that occurs during charging and discharging, improving the battery's room temperature and high temperature cycle performance. Furthermore, the high temperature resistance of the SEI film prevents a decrease in its stability under high-temperature conditions, avoiding a sharp increase in battery impedance, thereby improving the battery's high-temperature cycle performance and high-temperature storage performance. The second additive can construct a stable, low-impedance CEI film, inhibit electrolyte decomposition, and prevent the dissolution of transition metal ions. Moreover, the boron atoms in the second additive can capture the released transition metal ions, thereby improving the battery's room temperature and high-temperature cycle performance and high-temperature storage performance. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0026] This invention provides a battery comprising an electrolyte and a negative electrode, wherein the negative electrode active material comprises a silicon-containing material.

[0027] The electrolyte includes a first additive and a second additive. The first additive includes fluoroethylene carbonate, and the second additive includes a compound shown in Formula 1.

[0028]

[0029] R1-R3 are each independently selected from substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, or substituted or unsubstituted C2-C10 alkynyl, and at least one unsaturated group is included in R1-R3.

[0030] The battery of the present invention includes a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode active layer disposed on the surface of the negative electrode current collector. The negative electrode active layer comprises a negative electrode active material, a conductive agent, and a binder, wherein the negative electrode current collector is generally copper foil. The negative electrode active material of the present invention includes silicon-containing materials, which refer to active materials containing silicon, such as elemental silicon, silicates, silicon compounds, etc. The conductive agent and binder in the negative electrode active layer of the present invention can be selected from conventional materials in the art.

[0031] The battery of the present invention includes an electrolyte comprising a first additive and a second additive. The first additive comprises fluoroethylene carbonate, and the second additive comprises a compound having the structural formula of Formula 1. The substituted or unsubstituted C1-C10 alkyl groups of the present invention refer to alkyl groups having 1-10 carbon atoms and having substituents or unsubstituted groups, or cycloalkyl groups having 3-10 carbon atoms and having substituents or unsubstituted groups; the substituted or unsubstituted C2-C10 alkenyl groups refer to alkenyl groups having 2-10 carbon atoms and having substituents or unsubstituted groups, or cycloalkenyl groups having 3-10 carbon atoms and having substituents or unsubstituted groups; the substituted or unsubstituted C2-C10 alkynyl groups refer to alynyl groups having 2-10 carbon atoms and having substituents or unsubstituted groups, or cycloalynyl groups having 3-10 carbon atoms and having substituents or unsubstituted groups. When R1, R2, and R3 are specified as hydrocarbon groups having a specific number of carbon atoms, all geometric isomers having that number of carbon atoms are included. The substituents of R1, R2, and R3 in this invention include phenyl and cyano groups, meaning that R1-R3 can each be independently selected from -CH3, -CH2CH3, -CH=C-CH3, -C≡C-CH3, -CH2CN, -C6H5, -CH2-C6H5, etc. Furthermore, including at least one unsaturated group in R1-R3 means that R1, R2, and R3 are not simultaneously alkyl groups, and at least one of R1, R2, and R3 is an alkenyl or alkynyl group.

[0032] According to the above-described solution provided by the present invention, after applying the negative electrode sheet and electrolyte to a lithium-ion battery, the lithium-ion battery exhibits excellent room temperature and high temperature cycle performance, as well as high temperature storage performance. The inventors analyzed the principle behind this and believe the reason may lie in the synergistic effect of the silicon-containing material with the first and second additives. On one hand, the silicon-containing material can significantly improve the energy density of the lithium-ion battery. The unsaturated bonds of fluoroethylene carbonate and the second additive can decompose on the negative electrode surface, jointly participating in the construction of the SEI film. This results in a highly elastic, dense, and high-temperature resistant SEI film, thereby protecting the silicon-containing material from the significant volume expansion during charging and discharging, preventing the pulverization of the negative electrode active material layer, reducing the risk of exposure of the negative electrode active material layer in the electrolyte, reducing the occurrence of battery side reactions, and improving the room temperature and high temperature cycle performance of the battery. Furthermore, the high-temperature resistance of the SEI film can prevent the instability of the SEI film under high-temperature conditions. The additive prevents the SEI film from decomposing excessively, reducing gas production, and avoids the continuous decomposition and polymerization of fluoroethylene carbonate on the negative electrode surface, which could lead to an excessively thick SEI film and a sharp increase in battery impedance. This improves the battery's high-temperature cycle performance and high-temperature storage performance. On the other hand, the second additive can form a stable, low-resistance CEI film on the positive electrode surface, inhibiting electrolyte decomposition, reducing battery gas production, and preventing HF generated by fluoroethylene carbonate from attacking the positive electrode material and causing the dissolution of transition metal ions under high-temperature conditions. Furthermore, the boron atoms in the second additive can capture transition metal ions released from the positive electrode material, preventing the transition metal ions from catalytically decomposing the electrolyte. This improves the battery's room temperature and high-temperature cycle performance and high-temperature storage performance.

[0033] In one specific embodiment, the second additive comprises at least one of the compounds represented by formulas 2-8:

[0034]

[0035] When the above-mentioned compounds are selected as the second additive, the second additive can have a better synergistic effect with fluoroethylene carbonate to generate a denser and more stable SEI film, which can better protect silicon-containing materials, improve the battery's room temperature and high temperature cycle performance, and the second additive can better inhibit the decomposition of fluoroethylene carbonate at high temperature and its attack on the cathode material, reduce gas production and the dissolution of transition metals, and reduce the battery's impedance growth rate, thereby further improving the battery's room temperature and high temperature cycle performance and high temperature storage performance.

[0036] In one specific embodiment, the silicon-containing material includes at least one of nano-silicon, a composite system of silicon suboxide and carbon materials, and a composite system of chemical vapor deposition silicon and carbon materials; the carbon material includes at least one of artificial graphite, natural graphite, hard carbon, and soft carbon. When the above-mentioned materials are selected as the negative electrode active material, the negative electrode active material can better exert its performance and improve the energy density of the battery. At the same time, the SEI film and CEI film generated by the synergistic effect of fluoroethylene carbonate and the second additive can better protect the silicon-containing material, avoid the pulverization of the negative electrode active material layer, and reduce the exposure risk of the silicon-containing material in the electrolyte, thereby further improving the battery's room temperature and high temperature cycle performance and high temperature storage performance.

[0037] Specifically, chemical vapor deposition silicon (CVD silicon) is a silicon material formed by chemical vapor deposition (CVD). The composite system of chemical vapor deposition silicon and carbon material (CVD silicon@porous carbon) is formed by depositing silicon on the surface of carbon material by CVD. The carbon material is porous carbon, and silicon is deposited on the surface and in the pores of the porous carbon. The conductivity of the carbon material can give CVD silicon@porous carbon good conductivity, while the porous carbon can also inhibit silicon expansion.

[0038] In this embodiment of the invention, CVD silicon@porous carbon can be obtained by conventional methods in the art, such as commercially available silicon or self-made silicon using conventional methods in the art. In this embodiment of the invention, CVD silicon can be obtained by conventional CVD methods in the art, or silicon can be deposited on carbon materials to form CVD silicon@porous carbon using conventional CVD methods in the art. There are no particular limitations on this.

[0039] In one specific embodiment, the mass ratio of fluoroethylene carbonate to the second additive is (10-100):1, for example, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, or 100:1. When the mass ratio of fluoroethylene carbonate to the second additive is within the above range, the fluoroethylene carbonate and the second additive can work synergistically better, resulting in SEI and CEI films with superior elasticity, density, and high-temperature resistance. Furthermore, it can reduce the individual film formation of fluoroethylene carbonate or the second additive, suppressing the negative effects of fluoroethylene carbonate at high temperatures, thereby improving the battery's room temperature and high-temperature cycle performance and high-temperature storage performance.

[0040] In one specific embodiment, the mass percentage of fluoroethylene carbonate in the electrolyte is 3-15%, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%. When the mass percentage of fluoroethylene carbonate is within the above range, the elasticity and density of the SEI film of the battery are sufficiently high, which can better protect the silicon-containing materials, avoid the pulverization of the negative electrode active material layer, and reduce the direct contact between the silicon-containing materials and the electrolyte, thereby further reducing the generation of battery side reactions. As a result, the battery exhibits better room temperature and high temperature cycle performance and high temperature storage performance.

[0041] In one specific embodiment, the second additive has a mass percentage content of 0.01-0.5% in the electrolyte, for example, 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, or 0.5%. When the mass percentage content of the second additive is within the above range, the second additive can better synergize with fluoroethylene carbonate to generate a higher performance SEI film and CEI film, which can better protect silicon-containing materials and inhibit electrolyte decomposition and dissolution of transition metal ions to a greater extent, resulting in better battery cycling performance at room temperature and high temperature, as well as high temperature storage performance. Preferably, the mass percentage content of the second additive in the electrolyte is 0.1-0.3%.

[0042] In one specific embodiment, the mass percentage of fluoroethylene carbonate in the electrolyte is 6-10%, for example, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%. When the mass percentage of fluoroethylene carbonate is within the above range, the SEI film of the battery provides higher protection for silicon-containing materials, and can reduce the generation of battery side reactions to a greater extent, thereby improving the battery's room temperature and high temperature cycle performance and high temperature storage performance.

[0043] In one specific embodiment, the second additive has a mass percentage content of 0.1-0.3% in the electrolyte, for example, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.26%, 0.28%, or 0.3%. When the mass percentage content of the second additive is within the above range, the second additive can have a better synergistic effect with fluoroethylene carbonate, resulting in the formation of a higher-performance SEI film and CEI film, providing better protection for silicon-containing materials. At the same time, the possibility of electrolyte decomposition and dissolution of transition metal ions is reduced, resulting in better room temperature and high temperature cycle performance and high temperature storage performance of the battery.

[0044] In one specific embodiment, the electrolyte further includes a third additive, which includes at least one of vinylene carbonate, ethylene ethylene carbonate, ethylene ethylene sulfate, 1,3-propanesulfonyl lactone, 1,3-propenesulfonate lactone, vinyl sulfite, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, lithium bis(oxalato)borate, lithium difluorooxalatoborate, and lithium difluorodioxalatophosphate. When the above-mentioned third additive is further added to the electrolyte, the third additive can further synergize with fluoroethylene carbonate and the second additive, participate in the construction of the SEI film and CEI film, making the elasticity, density and high temperature resistance of the SEI film and CEI film better, further inhibiting the decomposition of the electrolyte and the dissolution of transition metal ions, thereby improving the room temperature and high temperature cycle performance and high temperature storage performance of the battery to a greater extent.

[0045] In one specific embodiment, the mass percentage of the third additive in the electrolyte is 0.5-5%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%. When the mass percentage of the third additive is within the above range, the SEI and CEI films constructed with the third additive exhibit better elasticity, density, and high-temperature resistance. This avoids excessive thickness of the SEI and CEI films due to excessive addition of the third additive, thereby better reducing the battery impedance growth rate and improving the battery's room temperature and high-temperature cycle performance, as well as its high-temperature storage performance.

[0046] In one specific embodiment, the electrolyte further includes a lithium salt, which includes at least one selected from lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate-borate), and lithium di(fluorooxalate-borate). The mass content of the lithium salt is 12-17%, for example, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, or 17%. When the above-mentioned lithium salt is selected and the mass percentage of the lithium salt is controlled within the above range, the addition of the lithium salt can improve the conductivity and stability of the electrolyte, thereby improving the battery's room temperature and high temperature cycle performance and high temperature storage performance.

[0047] In one specific embodiment, the electrolyte further includes an organic solvent, which includes at least one of the following: propylene carbonate, ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, sulfolane, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate; the mass percentage of the organic solvent is 10-80%. When the organic solvent of the present invention includes the above-mentioned solvents and the mass percentage of the organic solvent is within the above range, the electrolyte has a lower viscosity and a higher ionic conductivity, which is beneficial to improving the migration rate of lithium ions, thereby improving the battery's room temperature and high temperature cycle performance and high temperature storage performance.

[0048] In one specific embodiment, the electrolyte comprises, by mass percentage: 12.5-14%, organic solvent 73.8-78.9%, fluoroethylene carbonate 8-10%, second additive 0.1-0.2%, and third additive 0.5-2%; the mass percentage ratio of silicon in the negative electrode active material to that of fluoroethylene carbonate in the electrolyte is (0.6-1.2):1. When the mass percentages of each component in the electrolyte and the ratio of silicon to fluoroethylene carbonate are within the above ranges, the SEI and CEI films of the battery exhibit superior elasticity, density, and high-temperature resistance, providing sufficient protection for the negative electrode active material layer and further improving the battery's room temperature and high-temperature cycle performance and high-temperature storage performance.

[0049] In one specific embodiment, the battery further includes a positive electrode sheet, wherein the positive electrode active material in the positive electrode sheet includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide ternary materials, lithium nickel manganese oxide, and lithium-rich manganese-based materials, wherein the mass content of nickel or manganese in the positive electrode active material is greater than 65%. When the above-mentioned compounds are selected as the positive electrode active material, the positive electrode active material can better exert its energy, thereby further improving the energy density of the battery.

[0050] In one specific embodiment, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector, the positive active material layer including the aforementioned positive active material. The positive current collector may include a metal foil or a composite positive current collector; for example, the metal foil may be aluminum foil. The composite positive current collector may include a polymer material substrate and a metal layer formed on at least one side surface of the polymer material substrate. For example, the composite negative current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0051] In one specific embodiment, the positive electrode active material layer may optionally include a conductive agent, for example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0052] In one specific embodiment, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0053] In one specific embodiment, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive electrode active material, conductive agent, and binder, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes.

[0054] In one specific embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0055] In one specific embodiment, the negative electrode current collector can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0056] In one embodiment, the negative electrode active material layer may optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0057] In one embodiment, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0058] In one specific embodiment, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0059] In one specific embodiment, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0060] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0061] In one specific embodiment, the material of the separator may include at least one of glass fiber, non-woven fabric, polyolefin membrane, aromatic polyamide membrane, polytetrafluoroethylene membrane, and polyethersulfone membrane.

[0062] The present invention will be further described in detail below through specific embodiments.

[0063] Example 1

[0064] 1. Electrolyte preparation: The solvent (ethylene carbonate EC: propylene carbonate PC: diethyl carbonate DEC: methyl ethyl carbonate EMC in a mass ratio of 1.5:1.5:5:2), lithium salt (LiPF6), first additive (fluoroethylene carbonate FEC), and second additive (Formula 2) are mixed evenly according to the mass fraction of each component to obtain the electrolyte. Among them, based on the total mass of the electrolyte, the mass ratio of lithium salt is 12%, the mass ratio of first additive is 10%, the mass ratio of second additive is 0.3%, and the remainder is solvent.

[0065] 2. Preparation of the positive electrode sheet: The positive electrode active material lithium nickel cobalt manganese oxide (NCM811), binder PVDF (polyvinylidene fluoride), and conductive agent acetylene black were added to N-methylpyrrolidone (NMP) at a mass ratio of 96.5:2:1.5. The mixture was vacuum stirred until it reached a certain viscosity and uniform flowability. This slurry was then uniformly coated onto aluminum foil. The coated aluminum foil was baked in ovens at three different temperature gradients (90°C, 100°C, and 85°C), and then dried in an oven at 120°C for 8 hours. Finally, the positive electrode sheet was rolled to achieve a compaction density of 3.5 g / cm³. 3 The positive electrode is obtained by cutting.

[0066] 3. Preparation of the negative electrode sheet: The negative electrode active material, thickener CMC (sodium carboxymethyl cellulose), binder SBR (styrene-butadiene rubber latex), conductive agent SuperP (conductive carbon black), and conductive agent single-walled carbon nanotubes (SWCNTs) are added to deionized water in a mass ratio of 95.9:1:2:1:0.1, and a negative electrode slurry is obtained under vacuum stirring. The negative electrode slurry is uniformly coated onto a copper foil with a thickness of 6 μm. After drying (85℃, 5h) and rolling, the compaction density of the negative electrode sheet is controlled to be 1.65 g / cm³. 3 The negative electrode sheet is obtained by die cutting;

[0067] The negative electrode active material includes 84% ​​artificial graphite by mass and 16% CVD silicon@porous carbon by mass; in CVD silicon@porous carbon, the mass ratio of silicon to porous carbon is 1:1.

[0068] The ratio of the mass percentage of silicon in the negative electrode active material to the mass percentage of fluoroethylene carbonate in the electrolyte is 0.82:1.

[0069] 4. Separator: 8μm thick polyethylene diaphragm.

[0070] 5. Battery fabrication:

[0071] The above-mentioned positive electrode, separator, and negative electrode are stacked in sequence and then wound to obtain a bare cell without electrolyte filling. The bare cell is placed in an outer packaging foil, and the prepared electrolyte is injected into the dried bare cell. After vacuum sealing, standing, formation, shaping, and sorting, a lithium-ion battery is obtained.

[0072] Examples 2 to 46, and Comparative Examples 1 to 9: The differences from Example 1 are as follows: the mass percentage of the first additive in the electrolyte (the content of the first additive in Table 1), the type and mass percentage of the second additive in the electrolyte (the content of the second additive in Table 1), the mass ratio of the first additive to the second additive, the type and mass percentage of the third additive in the electrolyte (the content of the third additive in Table 1), the type and mass percentage of the lithium salt in the electrolyte (the lithium salt content in Table 1), the composition of the negative electrode active material in the negative electrode sheet, the ratio of the mass percentage of silicon in the negative electrode active material to the mass percentage of fluoroethylene carbonate in the electrolyte (the ratio of silicon to FEC in Table 2), and the positive electrode active material are different. See Tables 1 and 2 for details. Except for the differences shown in Tables 1 and 2, the other conditions are the same.

[0073] Test case

[0074] The lithium-ion batteries prepared in the examples and comparative examples were tested for the following performance, and the results are shown in Table 3. During the following tests, the charging cutoff voltage A of the batteries in Examples 1-41, Examples 44-46, Comparative Examples 1-3, and Comparative Example 8 (positive electrode active material was NCM811) was 4.2V; the charging cutoff voltage A of the batteries in Example 42 and Comparative Examples 4-5 (positive electrode active material was lithium cobalt oxide) was 4.4V; and the charging cutoff voltage A of the batteries in Example 43, Comparative Examples 6, and Comparative Example 7 (positive electrode active material was lithium nickel manganese oxide) was 4.8V.

[0075] 1. Capacity retention after 500 cycles at 25°C

[0076] Test method: At 25℃, the battery is charged at a constant current of 1C to the cutoff voltage A, then charged at a constant voltage of A to the cutoff current of 0.05C, and then discharged at 1C to 2.75V. This charge-discharge cycle is repeated for 500 cycles. The discharge capacity Q1 of the first cycle and the discharge capacity Q of the 500th cycle are recorded. 500 via Q 500 / Q1×100% calculates the capacity retention rate after 500 cycles at 25℃.

[0077] 2. Capacity retention rate after 200 cycles at 45°C

[0078] Test method: At 45℃, the battery is charged at a constant current of 1C to the cutoff voltage A, then charged at a constant voltage of A to the cutoff current of 0.05C, and then discharged at 1C to 2.75V. This charge-discharge cycle is repeated 200 times. The discharge capacity Q1 of the first cycle and the discharge capacity Q of the 200th cycle are recorded. 200 via Q 200 / Q1×100% calculates the capacity retention rate after 200 cycles at 45℃.

[0079] 3. High-temperature storage performance

[0080] Test method: At 25℃, the battery is charged at a constant current of 1C to the cutoff voltage A, then charged at a constant voltage of A to the cutoff current of 0.05C. Then, the battery is discharged at a constant current of 0.5C to 2.75V, and the discharge capacity is recorded as C2. Next, the battery is charged at a constant current of 1C to A, and charged at a constant voltage of A to the cutoff current of 0.05C. Then, the battery is transferred to a high temperature of 60℃ and left for 7 days. Then, it is discharged at a constant current of 0.5C, and the discharge capacity is recorded as C3. The capacity retention rate of the battery after 7 days of storage at 60℃ is calculated by C3 / C2×100%.

[0081] The initial thickness of the battery after capacity testing is recorded as h1, and the thickness after being stored at 60℃ for 7 days is h2. The thickness expansion rate of the battery after 7 days of storage at 60℃ is calculated by (h2-h1) / h1×100%.

[0082] 4. DC internal resistance (DCIR) growth rate

[0083] Test method: At 25℃, charge the battery at a constant current of 1C to A, let it rest for 5 minutes, then discharge it at 1C for 30 minutes, let it rest for 1 hour, and then discharge it at 2C (I 2C Discharge for 10 seconds, record the voltage values ​​V1 and V2 before and after 2C discharge, and calculate the DCIR1 of the battery at 50% SOC (the formula for calculating DCIR is: DCIR = (V1 - V2) / I). 2C After storing the battery at 60℃ for 7 days, it was charged and discharged at 1C constant current for 3 weeks. Then, it was charged to A at 1C constant current, rested for 5 minutes, discharged at 1C for 30 minutes, rested for 1 hour, and then discharged at 2C (I). 2C Discharge for 10 seconds, record the voltage values ​​V3 and V4 before and after 2C discharge, and calculate the DCIR2 of the battery at 50% SOC. DC internal resistance (DCIR) growth rate = (DCIR2 - DCIR1) / DCIR1 × 100%.

[0084] Table 1

[0085]

[0086]

[0087] Note: The ratios in Table 1 represent mass ratios. For example, “DTD:VC:PS=1:1:1” means that the third additive is composed of DTD+VC+PS in a mass ratio of 1:1:1; “ / ” indicates that this component was not added to the electrolyte.

[0088] Table 2

[0089]

[0090]

[0091] Table 3

[0092]

[0093]

[0094] Furthermore, when a second additive is added to the electrolyte without FEC, the battery exhibits high internal resistance and poor performance in room temperature cycling and high-temperature storage. Specifically, without FEC, when the content of the second additive in the electrolyte is around 0.5%, the battery's capacity retention rate drops below 70% (between 70% and 60%) after 500 cycles at 25°C, and below 80% after 100 cycles at 45°C; when the content of the second additive in the electrolyte is 10.2%, the battery cannot operate normally.

[0095] In summary, based on the comparison of Examples 1-46 and Comparative Examples 1-8, it can be seen that when the electrolyte includes fluoroethylene carbonate and the compound of Formula 1, the electrolyte can enable the battery to exhibit better room temperature and high temperature cycling performance and high temperature storage performance. Comparisons of Examples 1-6, 23, and 24 show that when the mass percentage of fluoroethylene carbonate is 3-15%, the battery exhibits higher room temperature and high temperature cycling performance and higher temperature storage performance. Comparisons of Examples 1, 7-12, and 25-26 show that when the mass percentage of compound 1 in the electrolyte is 0.01-0.5%, the battery exhibits better room temperature and high temperature cycling performance and higher temperature storage performance. Comparisons of Examples 1 and 13-20 show that when at least one of compounds from Formulas 2 to 8 is used as compound 1, the battery exhibits better room temperature and high temperature cycling performance and higher temperature storage performance. Comparisons of Examples 1, 21, and 22, and Examples 27 and 39-41, show that when the mass percentage of silicon in the silicon material is equal to the mass percentage of fluoroethylene carbonate... When the value is (0.6-1.2):1, the battery exhibits better room temperature and high temperature cycling performance and high temperature storage performance. According to the comparison of Examples 1, 27-35, 44, and 45, when the electrolyte also includes a third additive and the mass percentage of the third additive in the electrolyte is 0.5-5%, the battery exhibits higher room temperature and high temperature cycling performance and high temperature storage performance. According to the comparison of Examples 27, 36-38, and 46, when the mass content of lithium salt is 12-17%, the battery exhibits higher room temperature and high temperature cycling performance and high temperature storage performance. According to the comparison of Examples 27, 42-43 and Comparative Examples 4-7, this electrolyte can be applied to batteries containing cathode materials such as ternary cathode materials, lithium cobalt oxide, and lithium nickel manganese oxide, enabling the battery to exhibit excellent room temperature and high temperature cycling performance and high temperature storage performance.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery, characterized in that, The battery includes an electrolyte and a negative electrode, wherein the negative electrode active material in the negative electrode includes a silicon-containing material; The electrolyte includes a first additive and a second additive, wherein the first additive includes fluoroethylene carbonate and the second additive includes a compound represented by Formula 1. R1-R3 are each independently selected from substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C2-C10 alkenyl, or substituted or unsubstituted C2-C10 alkynyl, and at least one unsaturated group is included in R1-R3.

2. The battery according to claim 1, characterized in that, The second additive includes at least one of the compounds shown in Formulas 2-8:

3. The battery according to claim 1 or 2, characterized in that, The silicon-containing material includes at least one of nano-silicon, a composite system of silicon suboxide and carbon materials, and a composite system of chemical vapor deposition silicon and carbon materials; the carbon material includes at least one of artificial graphite, natural graphite, hard carbon, and soft carbon.

4. The battery according to any one of claims 1-3, characterized in that, The mass ratio of the fluoroethylene carbonate to the second additive is (10-100):

1.

5. The battery according to any one of claims 1-4, characterized in that, The fluoroethylene carbonate has a mass percentage content of 3-15% in the electrolyte; And / or, the second additive has a mass percentage content of 0.01-0.5% in the electrolyte.

6. The battery according to claim 5, characterized in that, The fluoroethylene carbonate has a mass percentage of 6-10% in the electrolyte; And / or, the second additive has a mass percentage content of 0.1-0.3% in the electrolyte.

7. The battery according to any one of claims 1-6, characterized in that, The electrolyte further includes a third additive, which includes at least one of the following: vinylene carbonate, ethylene ethylene carbonate, ethylene ethylene sulfate, 1,3-propanesulfonyl lactone, 1,3-propenesulfonate lactone, vinyl sulfite, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, lithium bis(oxalate)borate, lithium difluorooxalateborate, and lithium difluorodioxalate phosphate. The third additive has a mass percentage of 0.5-5% in the electrolyte.

8. The battery according to any one of claims 1-7, characterized in that, The electrolyte further includes lithium salts, which include at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalateborate), and lithium di(fluorooxalateborate); the lithium salts have a mass content of 12-17%. And / or, the electrolyte further includes an organic solvent, which includes at least one of propylene carbonate, methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, sulfolane, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate; the organic solvent has a mass percentage content of 10-80%.

9. The battery according to claim 8, characterized in that, The electrolyte comprises, by weight percentage: 12.5-14% lithium salt, 8-10% fluoroethylene carbonate, 0.1-0.2% second additive, and 0.5-2% third additive; And / or, the ratio of the mass percentage of silicon in the negative electrode active material to the mass percentage of fluoroethylene carbonate in the electrolyte is (0.6-1.2):

1.

10. The battery according to any one of claims 1-9, characterized in that, The battery further includes a positive electrode sheet, wherein the positive electrode active material in the positive electrode sheet includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide ternary material, lithium nickel manganese oxide, and lithium-rich manganese-based material, wherein the mass content of nickel or manganese in the positive electrode active material is greater than 65%.

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