A lithium-ion battery

Abstract

The application relates to the field of electrochemistry, and provides a lithium ion battery, which comprises an electrolyte, a positive electrode sheet and a negative electrode sheet, the electrolyte comprises a first additive and a second additive, the first additive is lithium bis(trifluoromethanesulfonyl)imide, and the second additive is N-phenylimino disulfuryl fluoride; the mass percentage of the first additive is W1, 0.01%<=W1<=5%, and the mass percentage of the second additive is W2, 0.01%<=W2<=5%, based on the mass of the electrolyte; the positive electrode sheet comprises a positive electrode active material, and the positive electrode active material is selected from the group consisting of LiCoO2, LiNi0.8Mn0.1Co0.1O2, LiNi0.9Co0.05Al0.05O2, LiNi0.8Co0.1Al0.1O2 and LiNi0.5Mn1.5O4, wherein, x>=0.80, y>0, and 1-x-y>0. The first additive and the second additive can synergistically improve the high-temperature cycle performance, cycle life and safety of a high-nickel ternary battery under the conditions of high temperature, high voltage and fast charging.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to a lithium-ion battery. Background Technology

[0002] With the rapid development of new energy vehicles, energy storage power stations, and other fields, the demand for high-energy-density lithium-ion batteries is becoming increasingly urgent. High-nickel ternary cathode materials (NCM) have become a key technological direction for achieving breakthroughs in battery energy density due to their advantages of high specific capacity (>200mAh / g) and low cost. However, in practical applications, the crystal structure of high-nickel cathode materials is prone to change during battery charge-discharge cycles, leading to instability at the interface between the electrode and the electrolyte. This instability can trigger a series of adverse consequences: on the one hand, numerous side reactions occur, resulting in significant consumption of active materials and electrolyte, and rapid capacity decay; on the other hand, a high-resistance passivation layer forms at the interface, hindering lithium-ion transport, leading to a significant reduction in battery charge-discharge efficiency and a markedly shortened cycle life.

[0003] In addition, gas generation is another major problem in high-nickel lithium-ion batteries. Gas generation mainly originates from two sources: one is residual lithium on the material surface, such as… Decomposition of, etc. This is due to It is unstable in air. The reaction with the positive electrode promotes the formation of residual lithium and rock salt NiO layers. Secondly, the oxidative decomposition reaction of the electrolyte produces a large amount of gas. These gases accumulate inside the battery, increasing the internal pressure and potentially leading to battery bulging, fire, or even explosion, severely limiting the widespread application of high-nickel lithium-ion batteries.

[0004] To address these issues, existing technologies attempt to improve battery performance by adding various electrolyte additives. For example, using certain lithium salt additives can suppress battery gas production to some extent, but it reduces the battery's room temperature and high-temperature cycling performance. While some functional additives can optimize interfacial film performance, they cannot effectively solve the problem of electrolyte oxidation and decomposition, and they also suffer from insufficient electrochemical windows and conductivity defects. Therefore, how to achieve high voltage stability, improved high-temperature cycling performance, cycle life, and safety while ensuring high conductivity and negative electrode compatibility is a pressing technical challenge in the current high-nickel ternary battery field. Summary of the Invention

[0005] The purpose of this application is to provide a lithium-ion battery that improves the interface stability of high-nickel lithium-ion batteries, while also enhancing their high-temperature cycle performance, cycle life, and safety. The specific technical solution is as follows:

[0006] This application provides a lithium-ion battery comprising an electrolyte, a positive electrode, and a negative electrode. The electrolyte includes a first additive and a second additive. The first additive is lithium bis(trifluoromethanesulfonyl)imide, and the second additive is N-phenyliminodithiofluoride. Based on the mass of the electrolyte, the mass percentage of the first additive is W1, 0.01% ≤ W1 ≤ 5%, and the mass percentage of the second additive is W2, 0.01% ≤ W2 ≤ 5%. The positive electrode includes a positive electrode material layer, and the positive electrode material layer includes a positive electrode active material selected from... Where x ≥ 0.80, y > 0, >0; The negative electrode sheet includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material is selected from at least one of graphite, hard carbon, mesophase carbon microspheres, silicon-based negative electrode materials and lithium-containing metal composite oxide materials.

[0007] In one embodiment of this application, 0.01:1 ≤ W1 / W2 ≤ 25:1.

[0008] In one embodiment of this application, 0.05% ≤ W1 ≤ 3.5%.

[0009] In one embodiment of this application, 0.05% ≤ W2 ≤ 3.5%.

[0010] In one embodiment of this application, 2.5:1 ≤ W1 / W2 ≤ 20:1.

[0011] In one embodiment of this application, the electrolyte includes a third additive, which is vinyl sulfate, and the mass percentage of the third additive is W3 based on the mass of the electrolyte, where 0.01% ≤ W3 ≤ 1%.

[0012] In one embodiment of this application, the electrolyte includes a solvent selected from at least one of ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0013] In one embodiment of this application, the electrolyte includes a lithium salt selected from at least one of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium difluorosulfonylimide, wherein the lithium salt has a mass percentage content of 10%-18% based on the mass of the electrolyte.

[0014] The beneficial effects of this application are:

[0015] This application provides a lithium-ion battery comprising an electrolyte, a positive electrode, and a negative electrode. The electrolyte includes a first additive and a second additive. The first additive is lithium bis(trifluoromethanesulfonyl)imide, and the second additive is N-phenyliminodithioyl fluoride (CAS No.: 1622206-83-0). Based on the mass of the electrolyte, the mass percentage of the first additive is W1, 0.01% ≤ W1 ≤ 5%, and the mass percentage of the second additive is W2, 0.01% ≤ W2 ≤ 5%. The positive electrode includes a positive electrode material layer, and the positive electrode material layer includes a positive electrode active material selected from... Where x ≥ 0.80, y > 0, >0; The negative electrode sheet includes a negative electrode material layer, which includes a negative electrode active material. The negative electrode active material is selected from at least one of graphite, hard carbon, mesophase carbon microspheres, silicon-based negative electrode materials, and lithium-containing metal composite oxide materials. The ion-conducting layer of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and the mechanically protective layer of N-phenyliminodithioyl fluoride form a composite interface. Their synergistic effect achieves complementary advantages, forming a three-dimensional synergistic system of "electrochemical stability - interfacial mechanical strength - ion transport efficiency". This multi-component synergistic design strategy, through dual regulation and kinetic optimization of the interfacial film, can significantly improve the room temperature and high temperature cycle performance, fast charging performance, and reduce the impedance growth rate of high-nickel ternary lithium batteries, thereby effectively improving the overall performance and lifespan of lithium batteries.

[0016] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Detailed Implementation

[0017] The technical solutions of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0018] This application provides a lithium-ion battery comprising an electrolyte, a positive electrode, and a negative electrode. The electrolyte includes a first additive and a second additive. The first additive is lithium bis(trifluoromethanesulfonyl)imide, and the second additive is N-phenyliminodithioyl fluoride. Based on the mass of the electrolyte, the mass percentage of the first additive is W1, where 0.01% ≤ W1 ≤ 5%, preferably 0.05% ≤ W1 ≤ 3.5%. For example, W1 can be 0.01%, 0.05%, 0.5%, 1%, 2%, 2.5%, 3%, or 3%. The content of the second additive is W2, 0.01% ≤ W2 ≤ 5%, preferably 0.05% ≤ W2 ≤ 3.5%. For example, W2 can be 0.01%, 0.05%, 0.5%, 1%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any two of these values. The positive electrode includes a positive electrode material layer, which includes a positive electrode active material selected from... Where x ≥ 0.80, y > 0, >0; The negative electrode sheet includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material is selected from at least one of graphite, hard carbon, mesophase carbon microspheres, silicon-based negative electrode materials and lithium-containing metal composite oxide materials.

[0019] High-nickel ternary NCM battery systems, with nickel content exceeding 80 mol%, face two major challenges in achieving high energy density (theoretical specific capacity of 200-220 mAh / g): poor interface stability and high gas production. The main reasons are: firstly, the surface of the cathode material... At high voltages (≥4.3V), lattice distortion easily occurs, leading to the dissolution of transition metal ions. This triggers repeated growth of the SEI film on the negative electrode, increasing the battery interface impedance from the initial 50Ω / cm² to over 300Ω / cm². On the other hand, the oxidative decomposition reaction of the carbonate solvent in the electrolyte on the positive electrode surface... And the side reactions between the negative electrode lithium metal and the electrolyte. This causes the gas volume inside the battery to increase rapidly, seriously affecting battery safety and cycle life.

[0020] The inventors discovered that LiTFSI undergoes a decomposition reaction on the electrode surface: The LiF produced by decomposition (lattice constant a = 0.402 nm) can form a dense passivation layer of 0.5-1 nm thickness on the negative electrode surface, with an ionic conductivity of approximately The lithium carbonate content (ionic conductivity) is significantly higher than that in traditional solid electrolyte interphase (SEI) membranes. Meanwhile, LiTFSI has strong electron-withdrawing groups. It can reduce the free electrolyte. Concentration, inhibition It reacts with water to generate HF, thus effectively suppressing gas production. However, the strong Lewis acidity of LiTFSI allows it to form a stable solvation structure with solvent molecules. This leads to an increased desolvation energy barrier for lithium ions, making the desolvation process more difficult. Consequently, the kinetics of lithium ion insertion and extraction at the electrode surface are hindered, affecting the battery's charge / discharge efficiency and capacity retention. At high temperatures, LiTFSI may also react with other components in the electrolyte, accelerating battery aging and causing a decline in cycle performance.

[0021] The second additive, N-phenyliminodithioyl fluoride, has fluorine atoms in its molecular structure that are... Forming a weak coordination can weaken The solvation structure lowers the desolvation energy barrier for lithium ions, thus solving the problem of difficult desolvation of lithium ions caused by the introduction of LiTFSI. Furthermore, N-phenyliminodithioyl fluoride reacts with trace amounts of water in the electrolyte, consuming the water in the system and further suppressing electrolyte decomposition and gas generation. Simultaneously, N-phenyliminodithioyl fluoride undergoes oxidative polymerization on the positive electrode surface, generating a product containing… Polymer membranes with various functional groups exhibit excellent mechanical strength (Young's modulus of 1.2-1.5 GPa) and can effectively block the diffusion of transition metal ions. The leaching amount is reduced to 5-8 ppm. However, when N-phenyliminodithioyl fluoride is used alone, it cannot independently form a stable SEI film and CEI film on the electrode surface, making it difficult to prevent side reactions between the electrode and the electrolyte.

[0022] The combination of LiTFSI and N-phenyliminodithioyl fluoride is not a simple additive process, but rather LiTFSI utilizes its anionic properties... Basic SEI and CEI films are constructed on the electrode surface to establish chemical stability; N-phenyliminodithioyl fluoride increases the LiF content by binding to the interfacial film formed by LiTFSI through fluorine-containing groups, and utilizes the benzene ring... Stacking enhances the membrane's density and mechanical strength, effectively blocking... Transition metal ions diffuse. Simultaneously, the unique molecular structure of N-phenyliminodithioyl fluoride allows it to interact with solvent molecules, weakening... The solvation structure addresses the difficulty of desolvation of lithium ions caused by LiTFSI, accelerating ion migration. Furthermore, the thioacryl fluoride group of N-phenyliminodithioyl fluoride can react with the thioacryl fluoride produced by the decomposition of LiPF6. The equal-strength Lewis acid reaction further suppresses electrolyte oxidation and gas production, and together with LiTFSI, enhances system stability. The synergistic effect of these two additives achieves complementary advantages, forming a three-dimensional synergistic system of "electrochemical stability - interfacial mechanical strength - ion transport efficiency". This multi-component synergistic design strategy, through dual regulation and kinetic optimization of the interfacial film, can significantly improve the room-temperature and high-temperature cycling performance of high-nickel ternary lithium batteries and reduce the impedance growth rate, thereby effectively improving the overall performance and lifespan of lithium batteries. Limiting the mass percentage of the first and second additives within the scope of this application allows for the full utilization of their synergistic effect without negatively impacting other electrolyte properties.

[0023] In one embodiment of this application, 0.01:1 ≤ W1 / W2 ≤ 25:1, preferably, 2.5:1 ≤ W1 / W2 ≤ 20:1. Limiting the mass ratio of the first additive to the second additive within the scope of this application can better leverage their synergistic effect, achieving a good interfacial film formation and low gas production while reducing the risk of low lithium-ion conductivity.

[0024] In one embodiment of this application, the electrolyte includes a third additive, which is vinyl sulfate. Based on the mass of the electrolyte, the mass percentage of the third additive is W3, where 0.01% ≤ W3 ≤ 1%. The third additive is vinyl sulfate. Due to the high reactivity of the five-membered ring structure, it can form a synergistic system with the first and second additives that have complementary structures. The sulfite and carbonate fragments generated during decomposition interact with the thick LiF layer formed on the cathode surface by the first additive: sulfur-containing compounds fill the pores of the LiF layer, improving its density; organic carbonate salts enhance the flexibility of the interfacial film, reducing the risk of film rupture caused by changes in cathode volume. Small molecule fragments, acting as templates, can also regulate the film pore distribution, optimize lithium-ion transport channels, and thus improve the interfacial film conductivity. Furthermore, The decomposition products are chemically bonded to the second additive to form a thick, high-modulus polymer film. The binding of functional groups can enhance its adhesion to the positive electrode surface. Regarding gas generation suppression, The sulfur atoms in the middle react with HF to consume acidic substances, and together with the first additive, reduce... The concentration and the water-consuming effect of the second additive can further reduce the gas production from electrolyte decomposition. The three additives, through structural complementarity, construct a stable and efficient interfacial system, further improving the performance of high-nickel ternary batteries.

[0025] In one embodiment of this application, the electrolyte includes a solvent selected from at least one of ethylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate. Solvents within the scope of this application exhibit good solubility and electrochemical stability, and can form stable electrolyte systems in combination with lithium salts and additives.

[0026] In one embodiment of this application, the electrolyte includes a lithium salt selected from at least one of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium difluorosulfonylimide. Based on the mass of the electrolyte, the mass percentage of the lithium salt is 10%-18%, for example, it can be 10%, 12%, 14%, 16%, 18%, or a range of any two of these values. Limiting the mass percentage of the lithium salt within the scope of this application ensures that the electrolyte has suitable ionic conductivity, meeting the ion transport requirements of lithium-ion batteries during charging and discharging.

[0027] In this application, the positive electrode sheet includes a positive current collector and a positive active material layer located on at least one surface of the positive electrode sheet. The aforementioned "positive material layer disposed on at least one surface of the positive current collector" means that the positive material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the positive current collector, or only a portion of the surface area; this application has no particular limitation, as long as the purpose of this application is achieved. This application has no particular limitation on the positive current collector, as long as the purpose of this application is achieved; for example, the positive current collector can be an aluminum foil, an aluminum alloy foil, or a composite positive current collector. The aforementioned composite positive electrode current collector can be a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The material of the polymer material base layer can be, but is not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET), or polybutylene terephthalate (PBT). The material of the metal layer can be, but is not limited to, at least one of aluminum, aluminum alloy, nickel, or nickel alloy. This application does not impose any particular limitation on the thickness of the positive electrode material layer and the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the single-sided positive electrode material layer can be from 50 μm to 250 μm, and the thickness of the positive electrode current collector can be from 7 μm to 20 μm.

[0028] The positive electrode material layer may further include a positive electrode conductive agent and a positive electrode binder. This application does not impose any particular limitation on the types of positive electrode conductive agents and positive electrode binders, as long as they achieve the purpose of this application. For example, the positive electrode conductive agent may include, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon fiber. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or a terpolymer of PVDF-PTFE-propylene. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0029] In this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The phrase "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the negative electrode current collector, or only a portion of the surface area; this application has no particular limitation, as long as the purpose of this application is achieved. This application has no particular limitation on the negative electrode current collector, as long as the purpose of this application is achieved; for example, the negative electrode current collector can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel or foamed copper, aluminum foil, or a composite negative electrode current collector. The aforementioned composite negative electrode current collector can be a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The material of the polymer material base layer can be, but is not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET), or polybutylene terephthalate (PBT). The material of the metal layer can be, but is not limited to, at least one of copper, copper alloy, nickel, or nickel alloy. This application does not impose any particular limitation on the thickness of the negative electrode material layer and the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the single-sided negative electrode material layer can be from 50 μm to 180 μm, and the thickness of the negative electrode current collector can be from 3 μm to 10 μm.

[0030] In this application, the negative electrode material layer may further include a negative electrode conductive agent, a negative electrode binder, and a negative electrode thickener. This application does not impose any particular limitation on the types of negative electrode conductive agents, negative electrode binders, and negative electrode thickeners, as long as they achieve the purpose of this application. For example, the negative electrode conductive agent may include, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, and graphene. For example, the negative electrode binder may include, but is not limited to, at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), and polyacrylamide (PAM). For example, the negative electrode thickener may include, but is not limited to, sodium carboxymethyl cellulose (CMC-Na). This application does not impose any particular limitation on the mass ratio of the negative electrode conductive agent and the negative electrode binder in the negative electrode material layer; those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.

[0031] In this application, the lithium-ion battery also includes a separator. This application does not impose any particular limitations on the separator; a porous structure separator with good stability can be selected. For example, the separator material can be at least one of polyethylene separator, polypropylene separator, and PE ceramic-coated separator. In this application, the thickness of the separator is not particularly limited, as long as it achieves the purpose of this application; for example, the separator thickness can be from 4 μm to 20 μm.

[0032] In this application, the lithium-ion battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the battery field. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0033] The manufacturing process of the lithium-ion battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the manufacturing process of a lithium-ion battery may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain a lithium-ion battery. Alternatively, stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain a lithium-ion battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent the internal pressure of the battery from rising and causing overcharging and over-discharging.

[0034] Example

[0035] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0036] Test methods and equipment:

[0037] 25℃ Cyclic Performance Test

[0038] The lithium-ion battery was left to stand for 4 hours at an ambient temperature of 25℃, and then subjected to 1162 charge-discharge cycles at a 1C current. The test voltage window was 2.75V-4.25V. The discharge capacity of the first cycle was recorded as C1, and the discharge capacity of the 1162nd cycle was recorded as C2. 1162 Record the capacity retention rate η1=C after 1162 cycles at 25℃. 1162 / C1×100%.

[0039] High-temperature cycling performance test

[0040] The lithium-ion battery was left to stand for 4 hours at an ambient temperature of 45℃, and then subjected to 558 charge-discharge cycles at a 1C current. The test voltage window was 2.75V-4.25V. The discharge capacity of the first cycle was recorded as C2, and the discharge capacity of the 558th cycle was recorded as C. 558 High-temperature cycling capacity retention rate η2=C 558 / C2×100%

[0041] Gas production

[0042] The thickness of the battery is recorded as m1. After placing the battery in an environment of 45°C and letting it stand for 24 hours, a pressure of 3 kg is applied, and it is charged to 4.0V at 0.1C (240mA). After standing for 2 days (to fully activate the battery), the thickness of the battery is recorded as m2. The amount of gas produced during the formation process is also recorded. , where ρ is the density of liquid water.

[0043] Battery impedance test

[0044] The battery was placed in a 25°C environment and discharged at a constant current of 1C to a cutoff voltage of 2.5V. After resting for 5 minutes, it was charged at a constant current and constant voltage of 1C to the upper limit voltage of 4.25V, with a cutoff current of 0.05C. It was then discharged at a constant current of 1C for 30 minutes, and the battery was adjusted to 50% state of charge (SOC). The battery voltage value V0 was recorded. At 25°C, the battery was allowed to rest for 5 minutes, and then discharged at a constant current of 2C for 30 seconds. The discharge current during 2C discharge was I. 2CRecord the voltage V1 after 30 seconds of discharge. The formula for calculating the DC internal resistance of discharge at 50% SOC is as follows: DCR (mΩ) = (V0 - V1) / I 2C ×100%.

[0045] Several lithium-ion pouch batteries with consistent electrical performance were selected from the same batch, and their initial DCR values ​​were recorded after full charging. Next, the batteries were stored in a high-temperature chamber at 60±2℃ for 60 days, maintaining a fully charged state and periodically checking temperature stability. On the 60th day of storage, the batteries were removed from the high-temperature chamber, allowed to return to room temperature, and then discharged at a 2C discharge current for 30 seconds. The voltage change was recorded, and the DCR value after storage was calculated. The formula for calculating the DCR growth rate after 60 days of storage at 60℃ is as follows: / Initial DCR value × 100%.

[0046] Example 1-1

[0047] <Preparation of Electrolyte>

[0048] In an argon-filled glove box (moisture <10ppm, oxygen <1ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly at a mass ratio of 3:7 to obtain a base solvent. Lithium hexafluorophosphate (LiPF6), a first additive, and a second additive were added to the base solvent and mixed uniformly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of LiPF6 was 10.5%, the mass percentage of the first additive LiTFSI was 2%, the mass percentage of the second additive N-phenyliminodithioyl fluoride was 2.5%, and the remainder was the base solvent.

[0049] <Preparation of the positive electrode>

[0050] Lithium nickel cobalt manganese oxide (LiNi) is used as the positive electrode active material. 0.88 Co 0.06 Mn 0.06 O2), conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were mixed with solvent N-methylpyrrolidone (NMP) at a mass ratio of 96.8:2.0:1.2 to prepare a positive electrode slurry of a certain viscosity. This slurry was then coated onto both surfaces of the positive electrode current collector aluminum foil, with a coating amount of 0.033 g / cm³. 2 After drying at 85°C, the material is cold-pressed, trimmed, cut into sheets, and slit. Then, it is dried under vacuum at 85°C for 4 hours, and the tabs are welded to produce the positive electrode sheet of a lithium-ion battery that meets the requirements.

[0051] <Preparation of Negative Electrode Sheets>

[0052] Graphite, conductive agent Super P, thickener CMC (carboxymethyl cellulose), and binder SBR (styrene-butadiene rubber, where styrene:butadiene = 1:1) were dissolved in deionized water at a mass ratio of 95:1.5:1.5:2 and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry was then uniformly coated onto the current collector copper foil with a coating amount of 0.0228 g / cm³. 2 After drying at 85℃, the material undergoes cold pressing, edge trimming, sheet cutting, and slitting. It is then dried under vacuum at 110℃ for 4 hours, and electrode tabs are welded on to produce the negative electrode sheet for a lithium-ion battery that meets the requirements.

[0053] <Preparation of the diaphragm>

[0054] The diaphragm is an 8μm polyethylene diaphragm (purchased from Shenzhen Xingyuan Material Technology Co., Ltd. SP312J3020H).

[0055] <Preparation of Lithium-ion Batteries>

[0056] The prepared positive electrode, negative electrode, and separator are stacked in sequence. The separator is a 12μm thick coated / ceramic separator. The separator is placed between the positive and negative electrode, and after winding, the cell is placed in an aluminum-plastic film for encapsulation and dried to produce a lithium-ion battery with a thickness of 5.6mm, a width of 5.5mm, and a length of 100mm. The battery is then vacuum baked at 75℃ for 10 hours, injected with the electrolyte prepared above, and subjected to vacuum encapsulation, settling, formation, shaping, and sorting processes to obtain the lithium-ion battery.

[0057] Examples 1-2 to Examples 1-15

[0058] Except for adjusting the mass percentages of the first and second additives according to Table 1 in the <Preparation of Electrolyte>, and changing the mass percentage of the base solvent accordingly, the rest is the same as in Examples 1-1.

[0059] Comparative Example 1 - Comparative Example 2

[0060] Except for the fact that in the <Preparation of Electrolyte>, the first additive is not added and the mass percentage of the second additive is adjusted according to Table 1, and the mass percentage of the base solvent is changed accordingly, the rest is the same as in Example 1-1.

[0061] Comparative Examples 3-4

[0062] Except for the fact that in the <Preparation of Electrolyte>, no second additive is added and the mass percentage of the first additive is adjusted according to Table 1, and the mass percentage of the base solvent is changed accordingly, the rest is the same as in Example 1-1.

[0063] Comparative Examples 5-6

[0064] Except for the adjustment of the mass percentages of the first and second additives according to Table 1 in the <Preparation of Electrolyte>, and the corresponding change in the mass percentage of the base solvent, the rest is the same as in Example 1-1.

[0065] Examples 2-1 to 2-3

[0066] Except for the addition of a third additive in the <Preparation of Electrolyte>, the mass percentage of the third additive was adjusted according to Table 2, and the mass percentage of the base solvent was changed accordingly, the rest was the same as in Example 1-1.

[0067] Examples 2-4 to 2-5

[0068] Except for adjusting the type of positive electrode active material according to Table 2 in the <Preparation of Positive Electrode Sheet>, the rest is the same as in Example 1-1.

[0069] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1 and 2.

[0070] Table 1

[0071]

[0072] Table 2

[0073]

[0074] When the first and second additives are used together as electrolyte additives, they can effectively suppress gas production, reduce the DCR growth rate during high-temperature storage, and improve the battery's capacity retention rate during both room temperature and high-temperature cycles. As can be seen from Examples 1-1 to 1-15 and Comparative Examples 1 to 6, the electrolyte, including the first and second additives within the scope of this application, exhibits a good synergistic effect, effectively suppressing gas production, reducing the DCR growth rate during high-temperature storage, and improving the high-temperature cycle performance, cycle life, and safety of lithium-ion batteries.

[0075] As can be seen from Comparative Examples 1 to 6, adding only one additive, or adding two additives with a mass percentage not within the scope of this application, results in increased gas production of lithium-ion batteries and decreased capacity retention rates at both room temperature and high temperature.

[0076] As can be seen from Examples 2-1 to 2-3, adding the first additive, the second additive, and the third additive and controlling the amount added within the scope of this application can further suppress battery gas production, reduce the high-temperature storage DCR growth rate, and improve high-temperature cycle performance, cycle life, and safety.

[0077] As can be seen from Examples 1-1, 2-4 to 2-5, the first additive and the second additive can exert a good synergistic effect in the NCM system with high nickel content (nickel content ≥80mol%).

[0078] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A lithium-ion battery comprising an electrolyte, a positive electrode, and a negative electrode, wherein the electrolyte comprises a first additive and a second additive, the first additive being lithium bis(trifluoromethanesulfonyl)imide, and the second additive being N-phenyliminodithiofluoride; based on the mass of the electrolyte, the mass percentage content of the first additive is W1, 0.01% ≤ W1 ≤ 5%, and the mass percentage content of the second additive is W2, 0.01% ≤ W2 ≤ 5%; The positive electrode sheet includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material is selected from... ,in, x≥0.80, y>0, 1-xy>0; The negative electrode sheet includes a negative electrode material layer, and the negative electrode material layer includes a negative electrode active material, wherein the negative electrode active material is selected from at least one of graphite, hard carbon, mesophase carbon microspheres, silicon-based negative electrode materials and lithium-containing metal composite oxide materials.

2. The lithium-ion battery according to claim 1, wherein, 0.01:1≤W1 / W2≤25:

1.

3. The lithium-ion battery according to claim 1, wherein, 0.05%≤W1≤3.5%。 4. The lithium-ion battery according to claim 1, wherein, 0.05%≤W2≤3.5%。 5. The lithium-ion battery according to claim 1, wherein, 2.5:1≤W1 / W2≤20:

1.

6. The lithium-ion battery according to claim 1, wherein, The electrolyte includes a third additive, which is vinyl sulfate. Based on the mass of the electrolyte, the mass percentage of the third additive is W3, where 0.01% ≤ W3 ≤ 1%.

7. The lithium-ion battery according to claim 1, wherein, The electrolyte includes a solvent selected from at least one of ethylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate.

8. The lithium-ion battery according to claim 1, wherein, The electrolyte includes a lithium salt selected from at least one of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium difluorosulfonylimide. The lithium salt has a mass percentage content of 10%-18% based on the mass of the electrolyte.

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