Lithium ion battery

Abstract

The application relates to the technical field of batteries, and particularly discloses a lithium ion battery, which comprises a negative electrode sheet and an electrolyte, the negative electrode sheet comprises a negative electrode active material, the negative electrode active material contains silicon elements, the electrolyte comprises a first additive and a second additive, the two additives are subjected to electro-polymerization during battery operation and are attached to the surfaces of the positive electrode and the negative electrode together, the stability and interface flatness of an electrode interface film are maintained, and the stable circulation of a silicon-based battery is promoted.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a lithium-ion battery. Background Technology

[0002] Graphite anodes currently possess high stability, capable of withstanding tens of thousands of charge-discharge cycles in lithium-ion batteries; however, their relatively low theoretical specific capacity limits their further application in high-energy-density systems. Silicon, on the other hand, boasts extremely high theoretical specific capacity (4200 mAh / g) and low lithium intercalation potential, and can provide Li+ in multiple directions. + While silicon-based lithium-ion batteries have deintercalation / intercalation channels, they also suffer from poor conductivity, easy particle breakage, unstable growth of the SEI film (solid electrolyte interface film), and volume expansion. These problems ultimately lead to poor fast-charging cycle capability of silicon-based lithium-ion batteries. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one object of this invention is to provide a lithium-ion battery that exhibits good fast-charge cycle performance.

[0004] Specifically, the present invention provides a lithium-ion battery, comprising a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises a negative electrode active material, and the negative electrode active material comprises silicon; the electrolyte comprises a first additive and a second additive.

[0005] The first additive has the structure shown in Formula 1:

[0006]

[0007] The second additive is selected from at least one of the following substances:

[0008] , .

[0009] To address the issues of electrode interface damage and poor fast-charge cycle performance in existing silicon-based lithium-ion batteries during cycling, this invention improves the electrolyte. The electrolyte includes a first additive and a second additive. These two additives undergo electropolymerization during battery operation and adhere together to the positive and negative electrode surfaces, maintaining the stability and smoothness of the electrode interface film, thereby promoting stable cycling of the silicon-based battery. The underlying principle is as follows.

[0010] The second additive has unsaturated hydrocarbon groups at both ends. During polymerization, long-chain polymers are formed at the unsaturated C=C polymerization points at both ends. In actual charge and discharge processes, the C=C at one end of the second additive is tightly anchored to the positive and negative electrode surfaces before polymerization occurs. This maintains interface flatness, improves the volume expansion and breakage issues of the negative electrode, and thus promotes battery cycle stability. However, the second additive cannot undergo double bond polymerization entirely on its own. The adsorption mode of some of the second additive changes from horizontal adsorption to vertical adsorption, hindering lithium ion migration and reducing the uniformity of the interface film, resulting in the negative electrode surface being easily broken. To solve this problem, a first additive is introduced. The byproduct of the first additive has the ability to oxidize other unsaturated groups (such as C=C), thereby promoting the polymerization reaction of the first additive. The byproduct of the polymerization reaction of the first additive is PO3F2. - The second additive oxidizes the C=C in its structure, promoting bond-breaking polymerization. Simultaneously, the reaction products adsorb onto the interface, reducing the probability of vertical adsorption of the second additive. This mitigates the adverse effects of the second additive on the negative electrode structure, maintaining interface flatness, mitigating the volume expansion and breakage issues of the negative electrode, and improving the fast-charging cycle stability of the battery. Furthermore, the combined use of the second and first additives addresses the issue of insufficient formation of the SEI film's organic cross-linked framework when the first additive is used alone. The second additive can tightly anchor itself to the positive and negative electrode surfaces via C=C and then polymerize. The resulting long-chain polymers are horizontally adsorbed on the electrode interface, and the different long-chain polymers intertwine to form an organic network structure. Together with the Si-O network structure formed by the polymerization of the first additive, this fully forms the SEI film's organic cross-linked framework, further maintaining interface flatness.

[0011] According to some embodiments of the present invention, the mass ratio of the first additive to the second additive is 1:(0.01-5).

[0012] According to some embodiments of the present invention, the mass ratio of the first additive to the second additive is 1:(0.1-2).

[0013] According to some embodiments of the present invention, the mass ratio of the first additive to the second additive is 1:(0.1-1).

[0014] According to some embodiments of the present invention, the mass percentage of the first additive is 0.01%-5% based on the total mass of the electrolyte.

[0015] According to some embodiments of the present invention, the mass percentage of the first additive is 0.1%-2% based on the total mass of the electrolyte.

[0016] According to some embodiments of the present invention, the mass percentage of the second additive is 0.01%-2% based on the total mass of the electrolyte.

[0017] According to some embodiments of the present invention, the mass percentage of the second additive is 0.1%-1% based on the total mass of the electrolyte.

[0018] According to some embodiments of the present invention, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, wherein the negative active material layer includes the negative active material, and the mass percentage of silicon element in the negative active material layer is 1%-15%.

[0019] According to some embodiments of the present invention, the lithium-ion battery further includes a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material being LiNi. x M 1-x O material, wherein M includes at least one of Co and Mn, and 0.3≤x≤0.98.

[0020] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0021] Figure 1 These are SEM images of the negative electrode interface of the present invention with different degrees of flatness. L1 represents the flatness of the negative electrode interface of Example 1, which is excellent; L2 represents the flatness of the negative electrode interface of Example 5, which is good; L3 represents the flatness of the negative electrode interface of Example 7, which is medium; and L4 represents the flatness of the negative electrode interface of Comparative Example 1, which is poor. Detailed Implementation

[0022] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0023] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0024] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] To facilitate understanding of the invention, certain technical and scientific terms are specifically defined below. Unless otherwise expressly defined elsewhere in this document, all other technical and scientific terms used herein have the meaning commonly understood by one of ordinary skill in the art to which this invention pertains.

[0026] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this invention, but do not exclude other aspects.

[0027] In this document, the terms “optionally,” “optionally,” or “optionally” generally refer to an event or condition that may, but may not, occur, and the description includes both cases in which the event or condition occurs and cases in which the event or condition does not occur.

[0028] Graphite anodes currently possess high stability, capable of withstanding tens of thousands of charge-discharge cycles in lithium-ion batteries; however, their relatively low theoretical specific capacity limits their further application in high-energy-density systems. Silicon, on the other hand, boasts extremely high theoretical specific capacity (4200 mAh / g) and low lithium intercalation potential, and can provide Li+ in multiple directions. + While silicon-based lithium-ion batteries have deintercalation / intercalation channels, they also suffer from poor conductivity, easy particle breakage, unstable growth of the SEI film (solid electrolyte interface film), and volume expansion. These problems ultimately lead to poor fast-charging cycle capability of silicon-based lithium-ion batteries.

[0029] Although electrolyte additives account for only a small portion of the electrolyte in lithium-ion batteries, appropriate amounts of additives can form an SEI film (also referred to as an interface film in this application) on the surface of the negative electrode active material layer, reducing the problem of side reactions occurring after the negative electrode material comes into direct contact with the electrolyte. Therefore, improving the stability of the SEI film by controlling the electrolyte composition is crucial for enhancing the electrochemical performance of silicon-based lithium-ion batteries.

[0030] In view of this, the present invention proposes a lithium-ion battery, comprising a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises a negative electrode active material, and the negative electrode active material contains silicon; the electrolyte comprises a first additive and a second additive.

[0031] The first additive has the structure shown in Formula 1:

[0032]

[0033] The second additive is selected from at least one of the following substances:

[0034] , .

[0035] The second additive has unsaturated hydrocarbon groups at both ends. During polymerization, long-chain polymers are formed at the unsaturated C=C polymerization points at both ends. In actual charge and discharge processes, the C=C at one end of the second additive is tightly anchored to the positive and negative electrode surfaces before polymerization occurs. This maintains interface flatness, improves the volume expansion and breakage issues of the negative electrode, and thus promotes battery cycle stability. However, the second additive cannot undergo double bond polymerization entirely on its own. The adsorption mode of some of the second additive changes from horizontal adsorption to vertical adsorption, hindering lithium ion migration and reducing the uniformity of the interface film, resulting in the negative electrode surface being easily broken. To solve this problem, a first additive is introduced. The byproduct of the first additive has the ability to oxidize other unsaturated groups (such as C=C), thereby promoting the polymerization reaction of the first additive. The byproduct of the polymerization reaction of the first additive is PO3F2. - The second additive oxidizes the C=C in its structure, promoting bond-breaking polymerization. Simultaneously, the reaction products adsorb onto the interface, reducing the probability of vertical adsorption of the second additive. This mitigates the adverse effects of the second additive on the negative electrode structure, maintaining interface flatness, mitigating the volume expansion and breakage issues of the negative electrode, and improving the fast-charging cycle stability of the battery. Furthermore, the combined use of the second and first additives addresses the issue of insufficient formation of the SEI film's organic cross-linked framework when the first additive is used alone. The second additive can tightly anchor itself to the positive and negative electrode surfaces via C=C and then polymerize. The resulting long-chain polymers are horizontally adsorbed on the electrode interface, and the different long-chain polymers intertwine to form an organic network structure. Together with the Si-O network structure formed by the polymerization of the first additive, this fully forms the SEI film's organic cross-linked framework, further maintaining interface flatness.

[0036] In addition to achieving the above-mentioned effects, this invention also offers the following advantages:

[0037] 1. During the decomposition and polymerization of the first additive, byproducts Li3PO4 and LiF are formed. These substances can not only form more Li + Vacancies, and the space charge layer formed between interface defects, further enhance the conductivity of the interface, ultimately establishing SEI and CEI films, which are excellent lithium-ion conductors.

[0038] 2. The carbon-carbon double bond of the second additive is easily attacked by F in the electrolyte on the positive electrode side, losing electrons to form a covalent bond, breaking the π bond structure of the carbon-carbon double bond, and generating an interface film of the -CO-(Si)- three-dimensional topological structure polymer layer, which covers the positive electrode active site, thereby improving the quality of the CEI film and increasing its stability.

[0039] 3. The alkenyl group carried by the second additive will be attacked by free radicals in the electrolyte, thereby breaking bonds and polymerizing to form a carbon-containing organic chain. Furthermore, the introduction of Si-containing groups or carbonate groups on the alkenyl group will further enhance the polarity of the film, improve the desolvation ability of lithium ions, and increase the migration rate of lithium ions.

[0040] 4. The interfacial film formed by the combination of the first additive and the second additive has the following advantages, namely, improved high-temperature stability, electrochemical stability, low-temperature performance and cycling performance, as shown in Table 1.

[0041] Table 1

[0042]

[0043] In some embodiments, the mass ratio of the first additive to the second additive is 1:(0.01-5). This can improve the flatness of the battery interface, thereby enhancing the fast-charging cycle performance of the battery. When there is too much of the first additive, the inorganic salt content inside the battery is relatively high, which can lead to easy rupture of the SEI film and severe gas generation when the electrolyte contacts the negative electrode. When there is too much of the second additive, the probability of it forming vertical adsorption directly at the electrode interface is greatly increased, thereby affecting the desolvation and migration of lithium ions, and is not conducive to the stability of the negative electrode interface structure.

[0044] In some embodiments, the mass ratio of the first additive to the second additive can be 1:0.01, 1:0.05, 1:0.1, 1:0.2, 1:0.4, 1:0.6, 1:0.8, 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, or 1:5. The ratio can be selected according to actual needs. As some specific examples, the mass ratio of the first additive to the second additive can be 1:(0.1-2), preferably 1:(0.1-1). This can improve the flatness of the battery interface, thereby improving the fast-charging cycle performance of the battery.

[0045] In some embodiments, the first additive accounts for 0.01%-5% of the total mass of the electrolyte. This improves the smoothness of the battery interface, thereby enhancing the battery's fast-charging cycle performance. Insufficient dosage of the first additive has limited effect on improving the smoothness of the battery interface; while excessive dosage leads to a relatively high content of inorganic salts inside the battery, making the SEI film prone to rupture.

[0046] In some specific embodiments, based on the total mass of the electrolyte, the mass percentage of the first additive may be 0.01%, 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%.

[0047] In some specific embodiments, the mass percentage of the first additive is 0.1%-2% based on the total mass of the electrolyte.

[0048] In some embodiments, the second additive accounts for 0.01%-2% of the total mass of the electrolyte. This improves the smoothness of the battery interface, thereby enhancing the battery's fast-charging cycle performance. When the amount of the second additive is too small, it has little effect on the full formation of the SEI organic cross-linked framework, and its synergistic effect with the first additive is not significant. Conversely, when the amount of the second additive is too large, the probability of it forming vertical adsorption at the electrode interface increases significantly, which is detrimental to the stability of the negative electrode interface structure.

[0049] In some specific embodiments, based on the total mass of the electrolyte, the mass percentage of the second additive may be 0.01%, 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, or 2%.

[0050] In some specific embodiments, the mass percentage of the second additive is 0.1%-1% based on the total mass of the electrolyte.

[0051] In some embodiments, the electrolyte further includes a lithium salt. The lithium salt includes at least one of lithium hexafluorophosphate and lithium bisfluorosulfonylimide (LiFSI). This can reduce battery gas production and improve battery cycle performance.

[0052] In some embodiments, the lithium salt accounts for 6%-20% of the total mass of the electrolyte. Controlling the lithium salt content in the electrolyte can achieve an optimal balance between conductivity, safety, interface stability, thermal stability, and cost, ensuring the overall performance and economy of the battery.

[0053] In some specific embodiments, the lithium salt accounts for 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 6%, 7%, 8%, 19%, or 20% of the total mass of the electrolyte.

[0054] In some embodiments, the lithium salt comprises lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. The mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is (2-15):(0-2). This can reduce battery gas production and improve battery cycle performance.

[0055] In some specific embodiments, the mass ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide can be 2:0, 2:1, 2:2, 3:0, 3:1, 3:2, 4:0, 4:1, 4:2, 5:0, 5:1 or 5:2.

[0056] In some embodiments, the electrolyte may further include other conventional additives selected from at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), tris(trimethylsilane) phosphate (TMSP), and lithium difluorodioxane phosphate (LiODFP). The conventional additives constitute 0.1%-5% of the electrolyte by mass, for example, 0.5%-4.9%, 1%-4%, 2%-3%, etc. It should be noted that the conventional additives are types commonly used in the art, and those skilled in the art can select them according to actual needs; further details are omitted here. The features and advantages described above regarding the electrolyte additives also apply to this electrolyte, and will not be repeated here.

[0057] In some embodiments, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector. The negative active material layer includes the negative active material, and the mass percentage of silicon in the negative active material layer is 1%-15%. Adding silicon to the negative active material layer is beneficial to improving battery capacity; however, the amount of silicon added should not be excessive. Excessive silicon can amplify problems such as unstable SEI growth and volume expansion. Even when using the electrolyte of the present invention, these problems are not easily resolved effectively.

[0058] In some specific embodiments, the mass percentage of silicon in the negative electrode active material layer may be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%.

[0059] In some embodiments, the lithium-ion battery further includes a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material being LiNi. x M 1-xThe material is O, wherein M includes at least one of Co and Mn, and 0.3 ≤ x ≤ 0.98. Using positive electrode active materials containing Co and / or Mn is beneficial for improving the electrochemical performance of the battery; however, these transition metal elements pose a risk of dissolution, and the decomposition byproduct of the first additive in this invention is PO3F2. - It has the ability to bind transition metal ions, preventing them from diffusing to the negative electrode and damaging the SEI film, thereby overcoming the dissolution defects of positive electrode active materials containing Co and / or Mn.

[0060] In some specific embodiments, x can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 0.98. The value of x can be selected according to actual needs.

[0061] In some specific embodiments, LiNi x M 1-x O materials include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.90 Co 0.05 Mn 0.05 O2, LiNi 0.8 Co 0.2 O2, LiNi 0.5 Mn 0.5 One or more of the following: O2, etc.

[0062] Typically, a lithium-ion battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0063] 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, wherein the positive active material layer includes the aforementioned positive active material.

[0064] In some embodiments of the present invention, the positive electrode current collector may include a metal foil or a composite positive electrode current collector. For example, the metal foil may be aluminum foil. The composite positive electrode current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. For example, the composite positive electrode current collector may 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.).

[0065] In some embodiments of the present invention, the positive electrode active material layer may further include a conductive agent. As an example, 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.

[0066] In some embodiments of the present invention, the positive electrode active material layer may further 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.

[0067] In some embodiments of the present invention, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive 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 the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0068] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0069] In some embodiments of the present invention, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite negative electrode 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 negative electrode current collector may 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.).

[0070] In some embodiments of the present invention, the negative electrode active material may be a silicon-containing active material known in the art for use in batteries. As an example, it may include at least one of the following materials: elemental silicon, silicon oxide, silicon-carbon composite, CVD silicon (i.e., silicon material prepared by chemical vapor deposition), and at least one carbon material such as natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, and nanocarbon, wherein the mass percentage of silicon element in the negative electrode active material layer is 1%-15%.

[0071] In some embodiments of the present invention, the negative electrode active material layer may further 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).

[0072] In some embodiments of the present invention, the negative electrode active material layer may further 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.

[0073] In some embodiments of the present invention, the negative electrode active material layer also includes other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0074] In some embodiments of the present invention, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as 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 after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0075] This invention 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.

[0076] In some embodiments of the present invention, the material of the separator may include at least one of glass fiber, nonwoven fabric, polyolefin film, aromatic polyamide film, polytetrafluoroethylene film, and polyethersulfone film. In some embodiments of the present invention, the thickness of the separator may be 10μm-12μm, for example, 10μm, 11μm, 12μm, etc.

[0077] In some embodiments of the present invention, the battery includes the electrolyte, positive electrode active material and negative electrode active material described above.

[0078] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0079] Example 1

[0080] (1) Electrolyte preparation: Ethylene carbonate (EC) and dimethyl carbonate (DMC) in a mass ratio of 3:7 were used as solvents. After mixing, lithium salt (15wt% LiPF6 and 1wt% LiFSI), 0.2wt% first additive (compound of formula 1), 0.1wt% second additive (compound of formula 2-1), 0.5wt% vinylene carbonate (VC) and 10wt% fluoroethylene carbonate (FEC) were added according to the mass fraction of each component. After mixing evenly, the electrolyte was obtained. Here, the mass fraction refers to the proportion of the mass of each component in the total mass of the electrolyte.

[0081] (2) Preparation of positive electrode sheet: The positive electrode active material LiNi is prepared. 0.90 Co 0.05 Mn 0.05 O2, conductive agent SuperP (conductive carbon black), carbon nanotubes, and binder PVDF (polyvinylidene fluoride) are mixed evenly in a mass ratio of 94:2.5:1.5:2. This mixture is then added to N-methylpyrrolidone solvent and stirred under vacuum (solid content 50%). The resulting slurry is then evenly coated onto both sides of an aluminum foil. The foil is subsequently dried at 85°C, cold-pressed, edge-trimmed, cut into sheets, slit, and vacuum-dried at 85°C for 10 hours. After welding the tabs, a surface density of 30 mg / cm³ is achieved. 2 The positive electrode sheet.

[0082] (3) Preparation of negative electrode sheet: CVD silicon (Jiangxi Zichen Technology Co., Ltd.), graphite material, conductive agent SuperP (conductive carbon black, SP), thickener CMC (sodium carboxymethyl cellulose), and binder SBR (styrene-butadiene rubber emulsion) are thoroughly mixed in a mass ratio of 5:90:2:1:2, added to solvent water, and stirred into a uniform slurry (solid content 50%). After coating both sides of copper foil, it is dried at 85°C, then cold-pressed, trimmed, cut, and slit. Finally, it is dried under vacuum at 85°C for 12 hours, and the electrode tabs are welded to obtain a surface density of 12 mg / cm³. 2 The negative electrode sheet; wherein, the mass ratio of silicon element in the negative electrode active material layer is the ratio of the mass of CVD silicon to the total mass of CVD silicon, graphite material, conductive agent SuperP, thickener and binder.

[0083] (4) Separating membrane: A 9μm thick porous polyethylene polymer film is used as the separating membrane.

[0084] (5) Lithium-ion battery preparation: The positive electrode, separator, and negative electrode are wound together to form a core. The separator is placed between the positive and negative electrode to provide isolation. The core is then placed in a casing (made of nickel-plated stainless steel), and the negative current collector is welded to the casing using laser welding. After drying, electrolyte is injected. After standing, the cell is charged to 4.25V at 0.1C at 45°C to complete the formation (forming a passivation layer) and capacity testing processes, thus completing the preparation of the lithium-ion battery.

[0085] Example 2-24

[0086] Lithium-ion batteries were prepared according to the method described in Example 1, with the differences shown in Table 2 below.

[0087] Example 25

[0088] A lithium-ion battery was prepared according to the method described in Example 1, except that LiNi was used as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 O2 replaces LiNi 0.90 Co 0.05 Mn 0.05 O2.

[0089] Example 26

[0090] A lithium-ion battery was prepared according to the method described in Example 1, except that LiNi was used as the positive electrode active material. 0.5 Co 0.2 Mn 0.3 O2 replaces LiNi 0.90 Co 0.05 Mn 0.05 O2.

[0091] Comparative Examples 1-4

[0092] Lithium-ion batteries were prepared according to the method described in Example 1, with the differences shown in Table 2 below.

[0093] Comparative Example 5

[0094] A lithium-ion battery was prepared according to the method described in Example 1, except that the first additive was used. Substitution compound 1.

[0095] Table 2

[0096]

[0097] In this context, " / " represents that it has not been added.

[0098] The fast-charge cycle performance and negative electrode interface of the lithium-ion batteries obtained in the examples and comparative examples were characterized, and the characterization results are shown in Table 3 below.

[0099] 1. Fast charging cycle test: Charge the battery at 3C constant current to 4.25V at 25℃, charge at 4.25V constant voltage to the cutoff current of 0.05C, and then discharge the battery at 1.0C constant current. Repeat the charge and discharge cycle for 1000 cycles. Record the discharge capacity of the 1000th cycle and the 1st cycle. Divide the two values ​​to obtain the capacity retention rate.

[0100] 2. Negative electrode interface characterization: The battery was charged at 25℃ with a constant current of 1.5C to 4.25V, then charged at a constant voltage of 4.25V to a cutoff current of 0.05C. The battery was then discharged with a constant current of 1.0C, repeating this charge-discharge cycle 100 times. The battery was disassembled after 100 cycles, and a portion of the negative electrode was selected for SEM testing. Based on the smoothness of the interface, it was ultimately classified into four levels: L1, L2, L3, and L4, as detailed below:

[0101] L1 (Superior): The electrode sheet remains flat overall, with uniform particle size and no obvious large cracks;

[0102] L2 (Good): The electrode sheet has good overall flatness and no obvious particle separation boundary, but there are obvious large cracks in some areas;

[0103] L3 (Medium): Particle boundaries are distinct but not dense;

[0104] L4 (Poor): The lithium plating on the electrode surface is obvious, and it is severely fragmented. Large-scale delamination and powdering occur during disassembly.

[0105] The interface smoothness of the negative electrode sheet after 100 cycles of the battery in Example 1 is as follows: Figure 1 As shown in L1. The interface smoothness of the negative electrode sheet after 100 cycles of the battery in Example 5 is as follows. Figure 1 As shown in L2. The interface smoothness of the negative electrode sheet after 100 cycles of the battery in Example 7 is as follows. Figure 1 As shown in L3 in the figure. The interface smoothness of the negative electrode plate of the battery in Comparative Example 1 after 100 cycles is as follows. Figure 1 As shown in L4.

[0106] Table 3

[0107]

[0108] Results and Discussion

[0109] By comparing Example 1 with Comparative Examples 1-4, it can be seen that the combined use of the first additive and the second additive has a significant effect on improving the smoothness of the battery interface and the fast-charging cycle performance; the absence of either one will lead to a significant deterioration in the fast-charging cycle performance, even if the amount of additive is the same, it will also lead to a significant deterioration in the fast-charging cycle performance; thus, it can be seen that the two additives have a synergistic effect in improving cycle performance.

[0110] By comparing Example 1 and Comparative Example 5, it can be seen that, compared with tris(trimethylsilyl)phosphate, the compound of Formula 1, when used in combination with the second additive, is more beneficial to improving the fast-charging cycle performance of the battery. This may be because the decomposition byproduct PO3F2 of the compound of Formula 1... - It can reduce the probability of vertical adsorption of the second additive and effectively improve the stability of the electrode interface.

[0111] By comparing Examples 1-8, it can be seen that the mass ratio of the first additive and the second additive has a significant impact on the fast-charging cycle performance of the battery.

[0112] By comparing Examples 9-14, it can be seen that the amount of the first additive within the scope of the present invention is beneficial to improving the fast charging cycle performance of the battery, while too much or too little additive will have an adverse effect on the fast charging cycle performance.

[0113] By comparing Examples 15-20, it can be seen that the amount of the second additive within the scope of the present invention is beneficial to improving the fast charging cycle performance of the battery, while too much or too little additive will have an adverse effect on the fast charging cycle performance.

[0114] By comparing Example 1 and Examples 21-23, it can be seen that excessive silicon in the negative electrode active material layer has an adverse effect on fast charging cycle performance.

[0115] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0116] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, The device includes a negative electrode sheet and an electrolyte. The negative electrode sheet includes a negative electrode active material, which contains silicon. The electrolyte includes a first additive and a second additive. The first additive has the structure shown in Formula 1: The second additive is selected from at least one of the following substances: 、 。 2. The lithium-ion battery according to claim 1, characterized in that, The mass ratio of the first additive to the second additive is 1:(0.01-5).

3. The lithium-ion battery according to claim 2, characterized in that, The mass ratio of the first additive to the second additive is 1:(0.1-2).

4. The lithium-ion battery according to claim 3, characterized in that, The mass ratio of the first additive to the second additive is 1:(0.1-1).

5. The lithium-ion battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the first additive is 0.01%-5%.

6. The lithium-ion battery according to claim 5, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the first additive is 0.1%-2%.

7. The lithium-ion battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the second additive is 0.01%-2%.

8. The lithium-ion battery according to claim 7, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the second additive is 0.1%-1%.

9. The lithium-ion battery according to claim 1, characterized in that, The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector. The negative active material layer includes the negative active material, and the mass percentage of silicon in the negative active material layer is 1%-15%.

10. The lithium-ion battery according to claim 1, characterized in that, It also includes a positive electrode sheet, which comprises a positive electrode active material, wherein the positive electrode active material is LiNi. x M 1-x O material, wherein M includes at least one of Co and Mn, and 0.3≤x≤0.98.

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