Lithium ion battery

Abstract

The invention relates to the technical field of electrochemistry, and provides a lithium ion battery which comprises an electrolyte, a positive pole piece and a negative pole piece, the electrolyte comprises a first additive and a second additive, the first additive is lithium bis (trifluoromethane sulfonimide), and the second additive is N-phenyl imino disulfuryl fluoride; based on the mass of the electrolyte, the mass percentage content of the first additive is W1, 0.01% < = W1 < = 5%, the mass percentage content of the second additive is W2, 0.01% < = W2 < = 5%; the positive pole piece comprises a positive active material, and the positive active material is selected from x > = 0.80, ygt; 0, 1-x-ygt; 0. The synergistic effect of the first additive and the second additive can effectively improve the high-temperature cycle performance, cycle life and safety of the high-nickel ternary battery under the conditions of high temperature, high voltage and fast charge.

Description

Technical Field

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

[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 (NCMs) have become a key technological direction for achieving breakthroughs in battery energy density due to their high specific capacity (>200mAh / g) and low cost. However, in actual use, the crystal structure of high-nickel cathode materials is prone to change during the battery charge and discharge cycle, resulting in an unstable interface between the electrode and the electrolyte. This instability can lead to a series of adverse consequences: on the one hand, a large number of side reactions occur, the active materials and electrolyte are consumed in large quantities, and the battery capacity decays rapidly; on the other hand, a high-impedance passivation layer is formed at the interface, which hinders the transmission of lithium ions, resulting in a significant reduction in battery charge and discharge efficiency and a significant shortening of the cycle life.

[0003] In addition, gas production is another major problem of high nickel system lithium batteries. Gas production mainly comes from two aspects: one is the residual lithium on the surface of the material, such as etc. This is due to Unstable in air, The first is the reaction with the positive electrode, which leads to the formation of a layer of residual lithium and rock salt NiO. Secondly, the oxidative decomposition of the electrolyte produces a large amount of gas. This gas accumulates inside the battery, increasing the internal pressure. In severe cases, it can cause safety accidents such as battery bulging, fire, or even explosion, greatly limiting the promotion and application of high-nickel lithium batteries.

[0004] To address these issues, existing technologies attempt to improve battery performance by adding various electrolyte additives. For example, the use of certain lithium salt additives can inhibit battery gas production to a certain extent, but this can reduce the battery's room-temperature and high-temperature cycling performance. While some functional additives can optimize interfacial film performance, they cannot effectively address the problem of electrolyte oxidation and decomposition, and they also present problems such as insufficient electrochemical window and conductivity defects. Therefore, how to achieve high voltage stability, improve high-temperature cycling performance, cycle life, and safety while ensuring high conductivity and anode compatibility is a technical challenge that urgently needs to be addressed 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 interfacial stability of high-nickel lithium-ion batteries while also improving the high-temperature cycling performance, cycle life, and safety of lithium-ion batteries. The specific technical solution is as follows:

[0006] The application 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-trifluoromethanesulfonimide, 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 material layer, the positive electrode material layer comprises a positive electrode active material, and the positive electrode active material is selected from at least one of wherein x≥0.80, y>0, >0; the negative electrode sheet comprises a negative electrode material layer, the negative electrode material layer comprises a negative electrode active material, and the negative electrode active material is selected from at least one of graphite, hard carbon, mesocarbon microbeads, a silicon-based negative electrode material and a lithium-containing metal composite oxide material.

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

[0008] In an embodiment of the application, 0.05%≤W1≤3.5%.

[0009] In an embodiment of the application, 0.05%≤W2≤3.5%.

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

[0011] In an embodiment of the application, the electrolyte comprises a third additive, the third additive is vinyl sulfate, and the mass percentage of the third additive is W3, 0.01%≤W3≤1%, based on the mass of the electrolyte.

[0012] In an embodiment of the application, the electrolyte comprises a solvent, and the solvent is selected from at least one of vinyl carbonate, diethyl carbonate, dimethyl carbonate and methyl ethyl carbonate.

[0013] In an embodiment of the application, the electrolyte comprises a lithium salt, and the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluoro(oxalato)borate, lithium difluorophosphate and lithium difluorosulfuryl imide, and the mass percentage of the lithium salt is 10%-18%, based on the mass of the electrolyte.

[0014] The application has the following beneficial effects:

[0015] The application 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-trifluoromethanesulfonimide, and the second additive is N-phenyliminodisulfuryl fluoride (CAS number: 1622206-83-0); 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 material layer, the positive electrode material layer comprises a positive electrode active material, and the positive electrode active material is selected from wherein x≥0.80, y>0, >0; the negative electrode sheet comprises a negative electrode material layer, the negative electrode material layer comprises a negative electrode active material, and the negative electrode active material is selected from at least one of graphite, hard carbon, mesocarbon microbeads, a silicon-based negative electrode material and a lithium-containing metal composite oxide material. The ion conductive layer of lithium bis-trifluoromethanesulfonimide (LiTFSI) and the mechanical protection layer of N-phenyliminodisulfuryl fluoride form a composite interface, and the synergistic effect of the two realizes the complementary advantages, forming a three-dimensional synergistic system of “electrochemical stability-interface mechanical strength-ion transport efficiency”. This multi-component synergistic design strategy can significantly improve the room temperature and high temperature cycle performance, fast charging performance and impedance growth rate of high-nickel ternary lithium batteries through the dual regulation and kinetic optimization of the interface film, thereby effectively improving the comprehensive performance and service life of the lithium battery.

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

[0017] The technical solutions in the application will be clearly and completely described below with reference to the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. All other embodiments obtained by a person skilled in the art based on the application belong to the protection scope of the application.

[0018] The application 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-trifluoromethanesulfonimide, and the second additive is N-phenylimino disulfuryl fluoride; the mass percentage of the first additive is W1, 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%, 3.5%, 4%, 4.5%, 5% or a range formed by any two of them; the mass percentage 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 a range formed by any two of them; the positive electrode sheet comprises a positive electrode material layer, the positive electrode material layer comprises a positive electrode active material, and the positive electrode active material is selected from wherein x≥0.80, y>0, >0; the negative electrode sheet comprises a negative electrode material layer, the negative electrode material layer comprises a negative electrode active material, and the negative electrode active material is selected from at least one of graphite, hard carbon, mesocarbon microbeads, a silicon-based negative electrode material and a lithium-containing metal composite oxide material.

[0019] The high-nickel ternary NCM battery system faces two major problems of poor interface stability and large gas production when the nickel content exceeds 80 mol% and high energy density (the theoretical specific capacity can reach 200-220 mAh / g) is achieved. The main reasons are as follows: on the one hand, the surface of the positive electrode material is prone to lattice distortion at high voltage (≥4.3 V), leading to the dissolution of transition metal ions, which in turn causes the repeated growth of the negative electrode SEI film, so that the battery interface impedance increases from the initial 50 Ω / cm² to more than 300 Ω / cm²; on the other hand, the oxidative decomposition reaction of the carbonate solvent in the electrolyte on the surface of the positive electrode and the side reaction of the negative electrode lithium metal and the electrolyte lead to a rapid increase in the volume of gas inside the battery, which seriously affects the safety and cycle life of the battery.

[0020] The inventors found that LiTFSI decomposes on the surface of the electrode: The LiF (lattice constant a=0.402 nm) produced by the decomposition can form a 0.5-1 nm thick dense passivation layer on the surface of the negative electrode, and the ionic conductivity thereof is about which is significantly higher than that of the lithium carbonate component (ionic conductivity ). At the same time, the strong electron-withdrawing groups of LiTFSI Can reduce the free Concentration, inhibition It reacts with water to generate HF, which effectively inhibits gas production. However, the strong Lewis acidity of LiTFSI will form a stable solvation structure with solvent molecules. , which increases the energy barrier for lithium ion desolvation, making the desolvation process more difficult and hindering the dynamics of lithium ion insertion and extraction on the electrode surface, affecting the battery's charge and discharge efficiency and capacity retention. At high temperatures, LiTFSI may also react with other components in the electrolyte, accelerating battery aging and leading to a decrease in cycle performance.

[0021] The second additive, N-phenyliminodisulfonyl fluoride, has a fluorine atom in its molecular structure. Forming a weak coordination effect can weaken Solvation structure, the desolvation energy barrier of lithium ions is reduced, thereby solving the problem of lithium ion desolvation caused by the introduction of LiTFSI; and N-phenyliminodisulfonyl fluoride reacts with trace water in the electrolyte to consume the water in the system, which can further inhibit the decomposition and gas production of the electrolyte. At the same time, N-phenyliminodisulfonyl fluoride undergoes oxidative polymerization on the surface of the positive electrode to generate The polymer membrane has excellent mechanical strength (Young's modulus of 1.2-1.5GPa), which can effectively block the diffusion of transition metal ions. The dissolution amount is reduced to 5-8ppm. However, when N-phenyliminodisulfonyl fluoride is used alone, it cannot independently form a stable SEI film and CEI film on the electrode surface, and it is difficult to prevent the side reaction between the electrode and the electrolyte.

[0022] The combination of LiTFSI and N-phenyliminodisulfonyl fluoride is not a simple superposition, but LiTFSI relies on the anion The SEI film and CEI film are constructed on the surface of the electrode to establish chemical stability; N-phenyliminodisulfonyl fluoride combines with the interface film formed by LiTFSI through the fluorine-containing group to increase the LiF content and utilize the benzene ring The accumulation effect enhances the density and mechanical strength of the membrane, effectively preventing At the same time, the special molecular structure of N-phenyliminodisulfonyl fluoride can interact with solvent molecules, weakening Solvation structure, solve the problem of lithium ion desolvation caused by LiTFSI, and accelerate ion migration. In addition, the sulfuryl fluoride group of N-phenyliminodisulfonyl fluoride can react with the decomposition of LiPF6 The Lewis acid reaction of equal strength further inhibits the electrolyte oxidation gas production, and the LiTFSI improves the system stability. The synergistic effect of the two realizes the complementary advantages, forming a three-dimensional synergistic system of "electrochemical stability-interface mechanical strength-ion transport efficiency". This multi-component synergistic design strategy, through the dual regulation and kinetic optimization of the interface film, can significantly improve the room temperature and high temperature cycle performance of high-nickel ternary lithium batteries and reduce the impedance growth rate, thereby effectively improving the overall performance and service life of lithium batteries. Within the scope of the present application, the mass percentage of the first additive and the second additive can fully exert the synergistic effect of the two, and will not have a negative impact on other properties of the electrolyte.

[0023] In an embodiment of the present application, 0.01:1≤W1 / W2≤25:1, preferably 2.5:1≤W1 / W2≤20:1. By limiting the mass ratio of the first additive and the second additive within the scope of the present application, the synergistic effect of the two can be better exerted, while forming a good interface film, low gas production, and reducing the risk of low lithium ion conductivity.

[0024] In an embodiment of the present application, the electrolyte comprises a third additive, the third additive is vinyl sulfate, and the mass percentage of the third additive is W3 based on the mass of the electrolyte, 0.01%≤W3≤1%. The third additive vinyl sulfate With the high reactivity of the five-membered ring structure, a structure-complementary synergistic system can be formed with the first additive and the second additive. The fragments such as sulfite and carbonate produced by decomposition interact with the thick LiF layer formed by the first additive on the positive electrode surface: the sulfur-containing compound fills the pores of the LiF layer, improving the density, and the organic carbonate salt enhances the flexibility of the interface film, reducing the risk of film rupture caused by positive electrode volume change. Small molecule fragments can also regulate the pore distribution of the film and optimize the lithium ion transport channel, thereby improving the conductivity of the interface film. And, The decomposition products of the first additive form a thick high-modulus polymer film with the second additive through chemical bonds The functional groups can enhance their adhesion to the positive electrode surface. In terms of gas inhibition, The sulfur atom in reacts with HF to consume acidic substances, and cooperates with the first additive to reduce The concentration of the second additive can further reduce the electrolyte decomposition gas. The three additives construct a stable and efficient interface system through structure complementation, further improving the performance of high-nickel ternary batteries.

[0025] In an embodiment of the present application, the electrolyte comprises a solvent selected from at least one of ethylene carbonate, diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate. The solvent within the scope of the present application has good solubility and electrochemical stability, and can form a stable electrolyte system with lithium salt and additives.

[0026] In an embodiment of the present application, the electrolyte comprises a lithium salt selected from at least one of lithium hexafluorophosphate, lithium difluoro(oxalato)borate, lithium difluorophosphate and lithium difluorosulfone imide, and the mass percentage of the lithium salt in the electrolyte is 10%-18%, for example, the mass percentage of the lithium salt can be 10%, 12%, 14%, 16%, 18% or a range defined by any two of the numbers. Limiting the mass percentage of the lithium salt within the scope of the present application can ensure that the electrolyte has appropriate ionic conductivity to meet the ion transmission requirements of lithium ion batteries during charging and discharging.

[0027] In the present application, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode sheet. The "positive electrode material layer arranged on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be arranged on one surface of the positive electrode current collector along the thickness direction of the positive electrode current collector, or can be arranged on two surfaces of the positive electrode current collector along the thickness direction of the positive electrode current collector. It should be noted that the "surface" herein can be the entire area of the surface of the positive electrode current collector, or can be part of the area of the surface of the positive electrode current collector, which is not particularly limited in the present application as long as the purpose of the present application can be achieved. The positive electrode current collector is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the positive electrode current collector can be an aluminum foil, an aluminum alloy foil or a composite positive electrode current collector. The 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, and the material of the polymer material base layer can include but is not limited to at least one of polypropylene (PP), polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), and the material of the metal layer can include but is not limited to at least one of aluminum, aluminum alloy, nickel or nickel alloy. The thickness of the positive electrode material layer and the positive electrode current collector is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the thickness of the single-sided positive electrode material layer is 50 μm to 250 μm, and the thickness of the positive electrode current collector is 7 μm to 20 μm.

[0028] The positive electrode material layer can further include a positive electrode conductive agent and a positive electrode binder. The present application does not have a particular limitation on the type of positive electrode conductive agent and positive electrode binder as long as the purpose of the present application can be achieved. For example, the positive electrode conductive agent can include, but is not limited to, at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, or carbon fibers. For example, the positive electrode binder can include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer. The present application does not have a particular limitation on the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode material layer, and a person skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0029] In the present application, the negative electrode tab 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 above-mentioned "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 the thickness direction of the negative electrode current collector, or can be disposed on both surfaces of the negative electrode current collector along the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector, or can be part of the area of the surface of the negative electrode current collector, and the present application does not have a particular limitation as long as the purpose of the present application can be achieved. The present application does not have a particular limitation on the negative electrode current collector as long as the purpose of the present application can be achieved. For example, the negative electrode current collector can be a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam or a copper foam, an aluminum foil, or a composite negative electrode current collector. The above-mentioned 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 above-mentioned polymer material base layer can include, but is not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET), or polybutylene terephthalate (PBT). The material of the above-mentioned metal layer can include, but is not limited to, at least one of copper, copper alloy, nickel, or nickel alloy. The present application does not have a particular limitation on the thickness of the negative electrode material layer and the negative electrode current collector as long as the purpose of the present application can be achieved. For example, the thickness of the single-sided negative electrode material layer is 50 μm to 180 μm, and the thickness of the negative electrode current collector is 3 μm to 10 μm.

[0030] In the present application, the negative electrode material layer can further comprise a negative electrode conductive agent, a negative electrode binder and a negative electrode thickening agent. The present application does not have a particular limitation on the types of the negative electrode conductive agent, the negative electrode binder and the negative electrode thickening agent, as long as the purpose of the present application can be achieved. For example, the negative electrode conductive agent can include, but is not limited to, at least one of super P, acetylene black, carbon black, graphene. For example, the negative electrode binder can include, but is not limited to, at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), polyacrylamide (PAM). For example, the negative electrode thickening agent can include, but is not limited to, sodium carboxymethyl cellulose (CMC-Na). The present application does not have a particular limitation on the mass ratio of the negative electrode conductive agent and the negative electrode binder in the negative electrode material layer, and those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0031] In the present application, the lithium ion battery further comprises a separator. The present application does not have a particular limitation on the separator, and a porous structure separator with good stability can be selected, for example, the material of the separator can include, but is not limited to, at least one of polyethylene separator, polypropylene separator, PE ceramic coated separator. In the present application, the thickness of the separator does not have a particular limitation, as long as the purpose of the present application can be achieved, for example, the thickness of the separator can be 4 μm to 20 μm.

[0032] In the present application, the lithium ion battery further comprises a shell for accommodating the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte, and other components known in the battery field, and the present application does not limit the above-mentioned other components. The present application does not have a particular limitation on the shell, which can be a shell known in the art, as long as the purpose of the present application can be achieved. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal, and the present application does not limit the type of metal, and a metal hard shell known in the art can be used, as long as the purpose of the present application can be achieved. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0033] The preparation process of the lithium ion battery of the present application is well known to those skilled in the art, and the present application does not have a particular limitation. For example, the preparation process of the lithium ion battery can include, but is not limited to, the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding, etc. according to the needs to obtain a wound structure electrode assembly, placing the electrode assembly into the shell, injecting the electrolyte into the shell and sealing to obtain the lithium ion battery. Alternatively, the positive electrode sheet, the separator and the negative electrode sheet are stacked in order, and then the four corners of the entire stack structure are fixed with adhesive tape to obtain a stack structure electrode assembly, the electrode assembly is placed into the shell, the electrolyte is injected into the shell and sealed to obtain the lithium ion battery. In addition, the anti-overcurrent element, the guide plate, etc. can also be placed in the shell according to the needs, so as to prevent the pressure rise in the battery and overcharge and discharge.

[0034] Examples

[0035] Hereinafter, the embodiments of the present application will be described more specifically by citing examples and comparative examples. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0036] Test methods and apparatus:

[0037] 25℃ cycle performance test

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

[0039] High-temperature cycle performance test

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

[0041] Gas production

[0042] The thickness of the battery was measured and recorded as m1. The battery was left to stand for 24 h at an ambient temperature of 45℃, and then charged at 0.1C (240mA) to 4.0V under a pressure of 3kg. After standing for 2 days (to fully activate the battery), the thickness of the battery was measured and recorded as m2, and the gassing amount during the formation was recorded as G wherein ρ is the density of liquid water.

[0043] Battery impedance test

[0044] The battery was left to stand for 5 min at an ambient temperature of 25℃, and then discharged at a constant current of 1C to a cut-off voltage of 2.5V. The battery was charged at a constant current and constant voltage of 1C to an upper limit voltage of 4.25V, with a cut-off current of 0.05C. The battery was then discharged at a constant current of 1C for 30 min, and adjusted to a state of charge (SOC) of 50%. The voltage value of the battery was recorded as V0. The battery was left to stand for 5 min at 25℃, and then discharged at a constant current of 2C for 30 s. The discharge current at 2C was recorded as I 2C, record the voltage after discharging for 30s as V1. The formula for calculating the discharge DC resistance at 50% SOC is as follows: DCR (mΩ) = (V0-V1) / I 2C ×100%.

[0045] Select several lithium ion soft package batteries with consistent electrical properties from the same batch. After being fully charged, record the initial DCR value. Then, store the battery in a high-temperature oven at 60±2℃ for 60 days, keeping it fully charged during the period and checking the temperature stability regularly. On the 60th day of storage, remove the battery from the high-temperature oven and restore it to room temperature. Discharge it at a current of 2C for 30s, record the voltage change, and calculate the DCR value after storage. 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 <10 ppm, oxygen <1 ppm), the solvent ethylene carbonate (EC) and methyl ethyl carbonate (EMC) were mixed in 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 solvent and mixed uniformly to obtain an 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-phenylimino disulfuryl fluoride was 2.5%, and the remaining amount was the base solvent.

[0049] <Preparation of positive electrode sheet>

[0050] The positive active material lithium nickel cobalt manganese oxide (LiNi 0.88 Co 0.06 Mn 0.06 O2), conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96.8:2.0:1.2 with the solvent N-methyl pyrrolidone (NMP) to form a positive electrode slurry with a certain viscosity, which was coated on both surfaces of the positive current collector aluminum foil with a coating amount of 0.033g / cm 2 . Subsequently, after drying at 85℃, cold pressing, edge cutting, sheet cutting, and striping were performed, followed by drying at 85℃ under vacuum conditions for 4h, and welding of the tabs to form a positive electrode sheet that meets the requirements of a lithium ion battery.

[0051] <Preparation of negative electrode sheet>

[0052] The graphite, conductive agent Super P, thickening agent CMC (carboxymethyl cellulose), binder SBR (styrene-butadiene rubber, wherein styrene: butadiene = 1:1) were dissolved in the solvent deionized water in a mass ratio of 95:1.5:1.5:2, mixed uniformly to prepare a negative electrode slurry, and then the negative electrode slurry was uniformly coated on the current collector copper foil, with a coating amount of 0.0228 g / cm 2 , followed by drying at 85°C, cold pressing, edge cutting, piece cutting, striping, and then drying at 110°C under vacuum for 4h, welding the tab, to prepare a negative electrode sheet for a lithium ion battery meeting the requirements

[0053] <Preparation of a separator>

[0054] The separator was a polyethylene separator with a thickness of 8 pm (purchased from Shenzhen Xingyuan Material Technology Co., Ltd. SP312J3020H).

[0055] <Preparation of a lithium ion battery>

[0056] The prepared positive electrode sheet, negative electrode sheet and separator were stacked in order, with a thickness of 12 pm of the rubber-coated separator / ceramic separator being selected as the separator, the separator was placed between the positive electrode sheet and the negative electrode sheet, the cell was placed in an aluminum plastic film after winding, dried, and a lithium ion battery with a thickness of 5.6 mm, a width of 5.5 mm and a length of 100 mm was prepared. After vacuum baking at 75°C for 10 hours, the electrolyte prepared in the foregoing was injected, and the lithium ion battery was obtained after vacuum packaging, standing, formation, shaping, sorting and other processes.

[0057] Examples 1-2 to 1-15

[0058] Except that in the <Preparation of an electrolyte> the mass percentage content of the first additive and the second additive was adjusted according to Table 1, and the mass percentage content of the base solvent changed accordingly, the rest was the same as Example 1-1.

[0059] Comparative Examples 1-2

[0060] Except that in the <Preparation of an electrolyte> no first additive was added and the mass percentage content of the second additive was adjusted according to Table 1, and the mass percentage content of the base solvent changed accordingly, the rest was the same as Example 1-1.

[0061] Comparative Examples 3-4

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

[0063] Comparative Examples 5-6

[0064] The same as Example 1-1 except that in the preparation of the electrolyte, the mass percentage of the first additive and the second additive is adjusted according to Table 1, and the mass percentage of the base solvent is changed accordingly.

[0065] Examples 2-1 to 2-3

[0066] The same as Example 1-1 except that in the preparation of the electrolyte, the third additive is added, the mass percentage of the third additive is adjusted according to Table 2, and the mass percentage of the base solvent is changed accordingly.

[0067] Examples 2-4 to 2-5

[0068] The same as Example 1-1 except that in the preparation of the positive electrode sheet, the type of the positive active material is adjusted according to Table 2.

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

[0070] Table 1

[0071] Table 2

[0072] When the first additive and the second additive are used as electrolyte additives in combination, they can effectively inhibit gas generation, reduce the high-temperature storage DCR growth rate, and improve the room-temperature and high-temperature cycle capacity retention rate of the battery. As can be seen from Examples 1-1 to 1-15 and Comparative Examples 1 to 6, the electrolyte including the first additive and the second additive within the scope of the present application has a good synergistic effect, can effectively inhibit gas generation, reduce the high-temperature storage DCR growth rate, and improve the high-temperature cycle performance, cycle life, and safety of the lithium ion battery.

[0073] As can be seen from Comparative Examples 1 to 6, the lithium ion battery obtained by adding only one kind of additive or two kinds of additives with a mass percentage not within the scope of the present application has increased gas generation, and the room-temperature and high-temperature cycle capacity retention rates are both poor.

[0074] 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 addition amount within the scope of the present application can further inhibit gas generation of the battery, reduce the high-temperature storage DCR growth rate, and improve the high-temperature cycle performance, cycle life, and safety.

[0075] As can be seen from Examples 1-1, 2-4, and 2-5, the first additive and the second additive can have a good synergistic effect in the NCM (nickel content ≥ 80 mol%) system with high nickel content.

[0076] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. A lithium ion battery, comprising an electrolyte, a positive electrode sheet and a negative electrode sheet, the electrolyte comprising a first additive and a second additive, the first additive being lithium bis-trifluoromethanesulfonimide, the second additive being N-phenyliminodisulfuryl fluoride; a mass percentage content of the first additive being W1, 0.01%≤W1≤5%, a mass percentage content of the second additive being W2, 0.01%≤W2≤5%, based on a mass of the electrolyte; The positive electrode sheet includes a positive electrode material layer including a positive electrode active material selected from wherein x≥0.80, y>0, 1-x-y>0; the negative electrode sheet comprising a negative electrode material layer, the negative electrode material layer comprising a negative electrode active material, the negative electrode active material being selected from at least one of graphite, hard carbon, mesocarbon microbead, silicon-based negative electrode material and lithium-containing metal complex oxide material.

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

1.

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

1.

6. The lithium-ion battery according to claim 1, wherein the electrolyte comprising a third additive, the third additive being vinyl sulfate, a mass percentage content of the third additive being W3, 0.01%≤W3≤1%, based on a mass of the electrolyte.

7. The lithium-ion battery of claim 1, wherein, the electrolyte comprising a solvent, the solvent being selected from at least one of vinyl carbonate, diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate.

8. The lithium-ion battery of claim 1, wherein, the electrolyte comprising a lithium salt, the lithium salt being selected from at least one of lithium hexafluorophosphate, lithium difluoro(oxalato)borate, lithium difluorophosphate and lithium difluorosulfurylimide, a mass percentage content of the lithium salt being 10%-18%, based on a mass of the electrolyte.

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