Lithium ion battery

Abstract

The present invention relates to the technical field of batteries, and particularly discloses a lithium ion battery, the lithium ion battery comprises a negative electrode plate and an electrolyte, the negative electrode plate comprises a negative electrode active material, and the negative electrode active material comprises a silicon element; the electrolyte comprises a first additive and a second additive, the first additive and the second additive are electrically polymerized during operation of the battery and jointly attached to the surfaces of a positive electrode and a negative electrode, the stability and the interface flatness of an electrode interface film are maintained, and therefore stable circulation of the silicon-based battery is promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a lithium-ion battery. Background Art

[0002] Today, graphite anodes have high stability and can meet the needs of lithium-ion batteries for thousands of charge and discharge cycles, but their low theoretical specific capacity limits their further application in high energy density systems. Silicon has an extremely high theoretical specific capacity (4200 mAh / g) and low lithium insertion potential, which can provide Li + However, there are problems such as poor conductivity, easy crushing of particles, unstable growth of SEI film (solid electrolyte interface film), and volume expansion. These problems ultimately lead to poor fast charging and cycling capabilities of silicon-based lithium-ion batteries. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, one object of the present invention is to provide a lithium-ion battery having good fast charge and cycle performance.

[0004] Specifically, the present invention provides a lithium-ion battery comprising a negative electrode plate and an electrolyte, wherein the negative electrode plate comprises a negative electrode active material, wherein the negative electrode active material comprises silicon; and the electrolyte comprises a first additive and a second additive. Wherein, the first additive has a structure shown in Formula 1:

[0005] The second additive is selected from at least one of the following substances: 、 .

[0006] In response to the problems that the electrode interface of existing silicon-based lithium-ion batteries is easily damaged during the cycle and the fast charging cycle performance is poor, the present invention improves the electrolyte. The electrolyte includes a first additive and a second additive. These two additives undergo electropolymerization during battery operation and adhere to the positive and negative electrode surfaces together, maintaining the stability and interface flatness of the electrode interface film, thereby promoting the stable cycle of silicon-based batteries. The inferred principle is as follows.

[0007] The second additive structure contains unsaturated hydrocarbon groups at both ends. When polymerization occurs, long-chain polymers are formed at the unsaturated C=C polymerization points at both ends. During the actual charge and discharge process, the C=C at one end of the second additive is tightly anchored on the surface of the positive and negative electrodes and then polymerizes. This can maintain the smoothness of the interface, improve the volume expansion and breakage problems of the negative electrode, and thus promote the stability of the battery cycle. However, the second additive cannot actively undergo double bond polymerization. The adsorption mode of some second additives will change from horizontal adsorption to vertical adsorption, hindering the migration of lithium ions and reducing the uniformity of the interface film, resulting in the negative electrode surface being easily broken. In order to solve this problem, the first additive is introduced. The by-product of the first additive has the ability to oxidize other unsaturated groups (such as C=C), which can promote the polymerization reaction of the first additive. The by-product PO3F2 produced by the polymerization reaction of the first additive - It will oxidize the C=C in the structure of the second additive, promote bond breaking polymerization, and at the same time, the reaction product is adsorbed at the interface, reducing the probability of vertical adsorption of the second additive, thereby improving the adverse effects of the second additive on the negative electrode structure, maintaining the smoothness of the interface, improving the volume expansion and breakage problems of the negative electrode, and achieving the effect of improving the fast charging cycle stability of the battery. At the same time, the second additive used in combination with the first additive can also solve the problem that the first additive alone is not enough to fully form the organic cross-linked skeleton of the SEI film: the second additive can be tightly anchored on the surface of the positive and negative electrodes through C=C and then polymerized. The long-chain polymers formed are horizontally adsorbed on the electrode interface. Different long-chain polymers are interwoven to form an organic network structure, which together with the Si-O network structure polymerized by the first additive fully forms the organic cross-linked skeleton of the SEI film, thereby further maintaining the smoothness of the interface.

[0008] According to some embodiments of the present invention, the mass ratio of the first additive to the second additive is 1:(0.01-5).

[0009] According to some embodiments of the present invention, the mass ratio of the first additive to the second additive is 1:(0.1-2).

[0010] According to some embodiments of the present invention, the mass ratio of the first additive to the second additive is 1:(0.1-1).

[0011] According to some embodiments of the present invention, based on the total mass of the electrolyte, the mass proportion of the first additive is 0.01%-5%.

[0012] According to some embodiments of the present invention, based on the total mass of the electrolyte, the mass of the first additive accounts for 0.1%-2%.

[0013] According to some embodiments of the present invention, based on the total mass of the electrolyte, the mass proportion of the second additive is 0.01%-2%.

[0014] According to some embodiments of the present invention, based on the total mass of the electrolyte, the mass proportion of the second additive is 0.1%-1%.

[0015] According to some embodiments of the present invention, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer arranged on at least one side of the negative electrode current collector, the negative electrode active material layer includes the negative electrode active material, and the mass proportion of silicon element in the negative electrode active material layer is 1%-15%.

[0016] According to some embodiments of the present invention, the lithium-ion battery further comprises a positive electrode plate, wherein the positive electrode plate 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.

[0017] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 These are SEM images of different flatnesses of the negative electrode interface of the present invention, 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; L4 represents the flatness of the negative electrode interface of Comparative Example 1, which is poor. DETAILED DESCRIPTION

[0019] 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 understood as limiting the present invention.

[0020] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features defined as "first" or "second" may explicitly or implicitly include one or more of such features. Furthermore, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0021] The endpoints of the ranges and any values ​​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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0022] In order to make the present invention more easily understood, certain technical and scientific terms are specifically defined below. Unless otherwise clearly defined elsewhere in this document, all other technical and scientific terms used herein have the meaning commonly understood by those skilled in the art to which the present invention belongs.

[0023] In this document, the terms “include” or “comprising” are open expressions, that is, including the contents specified in the present invention, but not excluding other contents.

[0024] As used herein, the terms "optionally," "optional," or "optionally" generally mean that the subsequently described event or circumstance may but need not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0025] Today, graphite anodes have high stability and can meet the needs of lithium-ion batteries for thousands of charge and discharge cycles, but their low theoretical specific capacity limits their further application in high energy density systems. Silicon has an extremely high theoretical specific capacity (4200 mAh / g) and low lithium insertion potential, which can provide Li + However, there are problems such as poor conductivity, easy crushing of particles, unstable growth of SEI film (solid electrolyte interface film), and volume expansion. These problems ultimately lead to poor fast charging and cycling capabilities of silicon-based lithium-ion batteries.

[0026] Electrolyte additives only account for a small fraction of the electrolyte in lithium-ion batteries. However, an appropriate amount of these additives can form an SEI film (also referred to herein as an interfacial film) on the surface of the anode active material layer, mitigating side reactions that can occur when the anode material comes into direct contact with the electrolyte. Therefore, improving the stability of the SEI film by regulating the electrolyte composition is crucial for enhancing the electrochemical performance of silicon-based lithium-ion batteries.

[0027] In view of this, the present invention proposes a lithium-ion battery comprising a negative electrode plate and an electrolyte, wherein the negative electrode plate comprises a negative electrode active material, and the negative electrode active material comprises silicon; the electrolyte comprises a first additive and a second additive, Wherein, the first additive has a structure shown in Formula 1:

[0028] The second additive is selected from at least one of the following: 、 .

[0029] The second additive structure contains unsaturated hydrocarbon groups at both ends, and when polymerization occurs, long-chain polymers are formed at the unsaturated C=C polymerization points at both ends. In the actual charging and discharging process, the C=C at one end of the second additive is tightly anchored to the positive and negative electrode surfaces and then polymerizes again, which can maintain the interface flat, improve the volume expansion and crushing problem of the negative electrode, and thus promote the cycle stability of the battery. However, the second additive cannot actively undergo double bond polymerization, and part of the second additive changes from horizontal adsorption to vertical adsorption, which hinders the migration of lithium ions and reduces the uniformity of the interface film, resulting in the negative electrode surface being easily crushed. In order to solve this problem, the first additive is introduced, and the byproduct of the first additive has the ability to oxidize other unsaturated groups (such as C=C), which can promote the polymerization of the first additive, and the byproduct PO3F2 - produced by the polymerization of the first additive can oxidize the C=C in the structure of the second additive, promote the occurrence of bond-breaking polymerization, and the reaction product is adsorbed on the interface, reducing the probability of vertical adsorption of the second additive, thereby improving the adverse effects of the second additive on the negative electrode structure, maintaining the interface flat, improving the volume expansion and crushing problem of the negative electrode, and achieving the effect of improving the fast-charging cycle stability of the battery. At the same time, the combination of the second additive and the first additive can also solve the problem that the first additive alone is not enough to form an organic cross-linked skeleton of the SEI film: the second additive can be tightly anchored to the positive and negative electrode surfaces and then polymerize, and the long-chain polymers formed are horizontally adsorbed on the electrode interface, and different long-chain polymers interweave to form an organic network structure, together with the Si-O network structure formed by the polymerization of the first additive, to fully form an organic cross-linked skeleton of the SEI film, thereby further maintaining the interface flat.

[0030] In addition to the above-mentioned effects, the present application can also bring the following advantages: 1. The byproducts Li3PO4 and LiF formed during the decomposition and polymerization of the first additive can not only establish more Li + vacancies, but also form a space charge layer between the interface defects, which can further improve the electrical conductivity of the interface, and ultimately establish an SEI film and a CEI film that are excellent lithium ion conductors.

[0031] 2. The carbon-carbon double bond of the second additive is easily attacked by F in the electrolyte, loses electrons to form a covalent bond, breaks the pi bond structure of the carbon-carbon double bond, and generates a -C-O-(Si) three-dimensional topological structure polymerization layer interface film that covers the positive active sites, thereby improving the quality of the CEI film and improving its stability.

[0032] 3. The olefinic groups carried by the second additive itself will be attacked by free radicals in the electrolyte, thereby breaking bonds and polymerizing to form carbon-containing organic chains, and introducing Si-containing groups or carbonate groups on the olefinic groups to further enhance the polarity of the membrane, enhance the desolvation ability of lithium ions, and increase the migration rate of lithium ions.

[0033] 4. The interfacial film formed by the composite of the first additive and the second additive has the following advantages, namely, improved high temperature stability, electrochemical stability, low temperature performance and cycle performance, as shown in Table 1.

[0034] Table 1

[0035] 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 battery's fast-charge cycle performance. When the first additive is excessive, the inorganic salt content inside the battery is relatively high, which can easily cause the SEI membrane to rupture and cause severe gas production when the electrolyte contacts the negative electrode. When the second additive is excessive, the probability of it directly forming vertical adsorption at the electrode interface is greatly increased, thereby affecting the desolvation and migration of lithium ions, etc., and is not conducive to the stability of the negative electrode interface structure.

[0036] In some embodiments, the mass ratio of the first additive to the second additive may 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 based on actual needs. As some specific examples, the mass ratio of the first additive to the second additive may be 1:(0.1-2), preferably 1:(0.1-1). This can improve the flatness of the battery interface and thereby enhance the fast charge cycle performance of the battery.

[0037] In some embodiments, based on the total mass of the electrolyte, the mass proportion of the first additive is 0.01%-5%. This can improve the flatness of the battery interface, thereby improving the fast charge cycle performance of the battery. When the amount of the first additive is too small, the effect on improving the flatness of the battery interface is limited; when the amount of the first additive is too much, the inorganic salt content inside the battery is relatively high, and the SEI film is easily ruptured.

[0038] In some specific embodiments, based on the total mass of the electrolyte, the mass proportion 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%.

[0039] In some specific embodiments, based on the total mass of the electrolyte, the mass proportion of the first additive is 0.1%-2%.

[0040] In some embodiments, based on the total mass of the electrolyte, the mass proportion of the second additive is 0.01%-2%. In this way, the flatness of the battery interface can be improved, thereby improving the fast charge cycle performance of the battery. When the amount of the second additive is too small, it has little effect on the full formation of the SEI organic cross-linked skeleton, and its synergistic effect with the first additive is not obvious; when the amount of the second additive is too much, the probability of vertical adsorption at the electrode interface is greatly increased, which is not conducive to the stability of the negative electrode interface structure.

[0041] In some specific embodiments, based on the total mass of the electrolyte, the mass proportion 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%.

[0042] In some specific embodiments, based on the total mass of the electrolyte, the mass proportion of the second additive is 0.1%-1%.

[0043] In some embodiments, the electrolyte further includes a lithium salt. The lithium salt includes at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide (LiFSI). This can reduce battery gas production and improve battery cycle performance.

[0044] In some embodiments, the lithium salt accounts for 6% to 20% of the total mass of the electrolyte. Controlling the lithium salt content in the electrolyte can achieve an optimal balance between conductivity, safety, interfacial stability, thermal stability, and cost, ensuring the overall performance and economic efficiency of the battery.

[0045] 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.

[0046] In some embodiments, the lithium salt includes 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 gassing and improve battery cycle performance.

[0047] In some specific embodiments, the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide may 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.

[0048] 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(trimethylsilyl) phosphate (TMSP), and lithium difluorobis(oxaloyl)phosphate (LiODFP), wherein the conventional additives account for 0.1%-5% of the mass of the electrolyte, for example, 0.5%-4.9%, 1%-4%, 2%-3%, etc. It should be noted that conventional additives are the types of additives commonly used in the art, and those skilled in the art can select them according to actual needs, which will not be repeated here. The features and advantages described for the above-mentioned electrolyte additives are also applicable to the electrolyte, which will not be repeated here.

[0049] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer includes the negative electrode active material, and the weight percentage of silicon in the negative electrode active material layer is 1%-15%. Adding silicon to the negative electrode active material layer can help increase battery capacity; however, excessive silicon additives should not be used. Excessive silicon can amplify problems such as unstable SEI growth and volume expansion. Even with the electrolyte of the present invention, these problems pose a risk of being difficult to effectively address.

[0050] In some specific embodiments, the mass proportion 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%.

[0051] In some embodiments, the lithium-ion battery further comprises a positive electrode plate, wherein the positive electrode plate 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, 0.3≤x≤0.98. The use of positive electrode active materials containing Co and / or Mn is beneficial to improving the electrochemical performance of the battery, but these transition metal elements have the risk of dissolution, and the decomposition byproduct PO3F2 of the first additive of the present invention is -It has the ability to bind transition metal ions, preventing them from diffusing to the negative electrode and destroying the SEI film, thereby overcoming the dissolution defects of the positive electrode active material containing Co and / or Mn.

[0052] In some specific embodiments, x may 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.

[0053] 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 O2, etc.

[0054] Typically, a lithium-ion battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0055] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on at least one side surface of the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode active material.

[0056] 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 base layer and a metal layer formed on at least one side of the polymer material base layer. 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 a substrate such as polypropylene (PP), polyethylene terephthalate (PET), or polybutylene terephthalate (PBT)).

[0057] In some embodiments of the present invention, the positive electrode active material layer may further 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.

[0058] In some embodiments of the present invention, the positive electrode active material layer may further include a binder. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0059] In some embodiments of the present invention, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, and the binder, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0060] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0061] 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 substrate and a metal layer formed on at least one surface of the polymer 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 substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0062] In some embodiments of the present invention, the negative electrode active material may be a silicon-containing active material commonly known in the art for use in batteries. For example, the negative electrode active material may include at least one of the following: elemental silicon, silicon oxides, silicon-carbon composites, and CVD silicon (i.e., silicon materials prepared by chemical vapor deposition), combined with at least one carbon material such as natural graphite, artificial graphite, soft carbon, hard carbon, mesocarbon microbeads, and nanocarbon. The weight percentage of silicon in the negative electrode active material layer is 1% to 15%.

[0063] 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).

[0064] In some embodiments of the present invention, the negative electrode active material layer may further include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0065] In some embodiments of the present invention, the negative electrode active material layer further includes other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0066] In some embodiments of the present invention, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0067] The present invention has no particular limitation on the type of separator, and any known separator with a porous structure having good chemical stability and mechanical stability can be selected.

[0068] In some embodiments of the present invention, the material of the isolation membrane may include at least one of glass fiber, non-woven fabric, polyolefin membrane, aromatic polyamide membrane, polytetrafluoroethylene membrane, and polyethersulfone membrane. In some embodiments of the present invention, the thickness of the isolation membrane may be 10 μm to 12 μm, for example, 10 μm, 11 μm, 12 μm, etc.

[0069] In some embodiments of the present invention, a battery includes the above-mentioned electrolyte, a positive electrode active material, and a negative electrode active material.

[0070] Below, the scheme of the present invention will be explained in conjunction with embodiment.It will be understood by those skilled in the art that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.In the embodiment, if specific technology or conditions are not indicated, the technology or conditions described in the literature in this area or the product instructions are used.The reagents or instruments used are not indicated by the manufacturer, and are all conventional products that can be obtained by commercial purchase.

[0071] Example 1 (1) Preparation of electrolyte: Ethylene carbonate (EC) and dimethyl carbonate (DMC) with a mass ratio of 3:7 were used as solvents. After mixing, lithium salt (15 wt% LiPF6 and 1 wt% LiFSI), 0.2 wt% of the first additive (the compound of formula 1), 0.1 wt% of the second additive (the compound of formula 2-1), 0.5 wt% of vinylene carbonate (VC) and 10 wt% of fluoroethylene carbonate (FEC) were added according to the mass fraction of each component. After mixing evenly, the electrolyte was obtained. The mass fraction here refers to the proportion of the mass of each component in the total mass of the electrolyte.

[0072] (2) Preparation of positive electrode sheet: LiNi 0.90 Co 0.05 Mn 0.05 O2, conductive agent SuperP (conductive carbon black), carbon nanotubes, and adhesive PVDF (polyvinylidene fluoride) are mixed evenly in a mass ratio of 94:2.5:1.5:2, added to N-methylpyrrolidone solvent and stirred in a vacuum (solid content is 50%), and then the slurry is evenly coated on the front and back of the aluminum foil, dried at 85°C, cold pressed, trimmed, cut, slit, and vacuum dried at 85°C for 10 hours. After welding the tabs, the surface density is 30mg / cm 2 The positive electrode.

[0073] (3) Preparation of negative electrode: CVD silicon (Jiangxi Zichen Technology Co., Ltd.), graphite material, conductive agent SuperP (conductive carbon black, SP), thickener CMC (sodium carboxymethyl cellulose), adhesive SBR (styrene-butadiene rubber emulsion) were fully mixed in a mass ratio of 5:90:2:1:2, added to solvent water, stirred into a uniform slurry (solid content 50%), and after coating on both sides of the copper foil, dried at 85 ° C, and then cold pressed, trimmed, cut, and striped. Finally, dried under vacuum conditions at 85 ° C for 12 hours, and the welding tabs were obtained to obtain a surface density of 12 mg / cm 2 The negative electrode sheet is a negative electrode sheet; wherein the mass proportion of the 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 adhesive.

[0074] (4) Isolation membrane: A polyethylene porous polymer film with a thickness of 9 μm is used as the isolation membrane.

[0075] (5) Preparation of lithium-ion batteries: The positive electrode sheet, separator, and negative electrode sheet are wound to form a core, wherein the separator is placed between the positive and negative electrode sheets to play an isolating role. The core is placed in a shell (made of nickel-plated stainless steel) and the negative electrode current collector is welded to the shell by laser welding. After drying, the electrolyte is injected. After standing and charging the cell to 4.25V at 0.1C at 45°C, the formation (passivation layer) and capacity separation processes are completed to complete the preparation of the lithium-ion battery.

[0076] Examples 2-24 A lithium-ion battery was prepared according to the method described in Example 1, with the differences shown in Table 2 below.

[0077] Example 25 A lithium-ion battery was prepared according to the method described in Example 1, except that the positive electrode active material was LiNi 0.8 Co 0.1 Mn 0.1 O2 replaces LiNi 0.90 Co 0.05 Mn 0.05 O2.

[0078] Example 26 A lithium-ion battery was prepared according to the method described in Example 1, except that the positive electrode active material was LiNi 0.5 Co 0.2 Mn 0.3 O2 replaces LiNi 0.90 Co 0.05 Mn 0.05 O2.

[0079] Comparative Examples 1-4 A lithium-ion battery was prepared according to the method described in Example 1, with the differences shown in Table 2 below.

[0080] Comparative Example 5 A lithium ion battery was prepared according to the method described in Example 1, except that the first additive was Substitute the compound of formula 1.

[0081] Table 2

[0082] Among them, “ / ” means not added.

[0083] 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.

[0084] 1. Fast charge cycle test: Charge the battery to 4.25V at 3C constant current at 25℃, charge it to 0.05C at 4.25V constant voltage, and then discharge it at 1.0C constant current. Repeat the charge and discharge steps for 1000 cycles. The discharge capacity of the 1000th cycle and the discharge capacity of the 1st cycle are recorded and the capacity retention rate is obtained by dividing the two.

[0085] 2. Characterization of the negative electrode interface: Charge the battery at 1.5C constant current to 4.25V at 25°C, charge it at 4.25V constant voltage to a cut-off current of 0.05C, and then discharge it at 1.0C constant current. Repeat the charge and discharge steps for 100 cycles. The battery after 100 cycles was disassembled, and SEM tests were performed on selected areas of the negative electrode sheet. The interface flatness was finally divided into four levels: L1, L2, L3, and L4, as follows: L1 (excellent): The pole piece remains flat as a whole, the particle size is uniform, and there are no obvious large cracks; L2 (good): The overall flatness of the electrode is good, with no obvious particle separation boundary, but there are obvious large cracks in some parts; L3 (middle): the particle boundaries are clear and not tight; L4 (poor): The surface of the electrode is obviously lithium-plated, severely fragmented, and large-scale peeling and powdering occurs during disassembly.

[0086] The interface flatness of the negative electrode sheet after 100 cycles of the battery in Example 1 is as follows: Figure 1 The interface flatness of the negative electrode sheet of the battery of Example 5 after 100 cycles is shown as Figure 1 The interface flatness of the negative electrode sheet of the battery of Example 7 after 100 cycles is shown as Figure 1 The interface flatness of the negative electrode sheet of the battery of Comparative Example 1 after 100 cycles is shown as Figure 1 As shown in L4.

[0087] Table 3

[0088] Results and Discussion 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 battery interface flatness and fast charge cycle performance; the lack of any one of them will lead to a significant deterioration in the fast charge cycle performance, even if the amount of additives is the same; it can be seen that the two additives have a synergistic effect in improving the cycle performance.

[0089] By comparing Example 1 with Comparative Example 5, it can be seen that the compound of Formula 1 is more conducive to improving the fast charge cycle performance of the battery when used in combination with the second additive compared to tris(trimethylsilyl)phosphate. 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.

[0090] By comparing Examples 1-8, it can be seen that the mass ratio of the first additive to the second additive has a significant effect on the fast charge cycle performance of the battery.

[0091] By comparing Examples 9-14, it can be seen that the amount of the first additive used within the scope of the present invention is beneficial to improving the fast charge cycle performance of the battery, and too much or too little of the first additive used will have an adverse effect on the fast charge cycle performance.

[0092] By comparing Examples 15-20, it can be seen that the amount of the second additive used within the scope of the present invention is beneficial to improving the fast charge cycle performance of the battery, and too much or too little of the second additive used will have an adverse effect on the fast charge cycle performance.

[0093] By comparing Example 1 with Examples 21-23, it can be seen that excessive silicon elements in the negative electrode active material layer have an adverse effect on the fast charge cycle performance.

[0094] In the description of this specification, reference to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification, as well as features of different embodiments or examples, unless they are mutually inconsistent.

[0095] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that: The invention comprises a negative electrode plate and an electrolyte, wherein the negative electrode plate comprises a negative electrode active material, and the negative electrode active material comprises silicon; the electrolyte comprises a first additive and a second additive, Wherein, the first additive has a 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, wherein 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, wherein 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, wherein 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, wherein Based on the total mass of the electrolyte, the mass proportion 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 proportion of the first additive is 0.1%-2%.

7. The lithium-ion battery according to claim 1, wherein Based on the total mass of the electrolyte, the mass proportion 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 proportion of the second additive is 0.1%-1%.

9. The lithium-ion battery according to claim 1, wherein The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer arranged on at least one side of the negative electrode current collector. The negative electrode active material layer includes the negative electrode active material, and the mass proportion of silicon element in the negative electrode active material layer is 1%-15%.

10. The lithium-ion battery according to claim 1, wherein It also includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material, 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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