Lithium-ion battery and electric device

Abstract

A lithium-ion battery and an electric device. The lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer located on at least one surface of the positive electrode current collector; a positive electrode active material of the positive electrode active layer comprises a lithium-containing transition metal oxide, the lithium-containing transition metal oxide comprises a Ni element, and the molar amount of the Ni element accounts for 90% or more of the total molar amount of transition metal elements in the lithium-containing transition metal oxide; the residual lithium content of the positive electrode active material is less than or equal to 2000 ppm; the electrolyte comprises an electrolyte salt, and the electrolyte salt includes lithium bis(fluorosulfonyl)imide.

Description

Lithium-ion batteries and electrical devices

[0001] Related applications

[0002] This application claims priority to Chinese patent application filed on January 2, 2025, application number 2025100052964, entitled "Lithium-ion Battery and Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and more particularly to a lithium-ion battery and an electrical device. Background Technology

[0004] In recent years, lithium-ion batteries have been widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. With the continuous expansion of the application range of lithium-ion batteries and other batteries, correspondingly higher requirements are being placed on battery performance.

[0005] In the design of lithium-ion batteries, positive electrode active materials with high nickel content usually have high specific capacity, which is beneficial to improving the energy density of the battery, but it is difficult to make the battery achieve good cycle performance. Summary of the Invention

[0006] A first aspect of this application provides a lithium-ion battery. The lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte; the positive electrode includes a positive current collector and a positive active layer located on at least one surface of the positive current collector, the positive active material of the positive active layer comprising a lithium-containing transition metal oxide, the lithium-containing transition metal oxide including Ni element, the molar amount of Ni element accounting for more than 90% of the total molar amount of transition metal elements in the lithium-containing transition metal oxide; the amount of impure lithium in the positive active material is less than or equal to 2000 ppm; the electrolyte includes an electrolyte salt, the electrolyte salt including lithium bis(fluorosulfonyl)imide (LiFSI).

[0007] For cathode active materials with a lithium impurity content of 2000 ppm or less, the introduction of LiFSI, which is less reactive with water, can reduce the impact of the cathode active material's water absorption on battery cycle performance, thereby enabling the battery to achieve both high energy density and good cycle performance. However, when the lithium impurity content of the cathode active material exceeds 2000 ppm, since LiFSI is a Brønsted acid, the lithium impurities will react with LiFSI to form water, thus affecting the battery's cycle performance. Therefore, in this application, for cathode active materials with a lithium impurity content of 2000 ppm or less, the introduction of LiFSI, which is less reactive with water, can reduce the impact of the cathode active material's water absorption on battery cycle performance, thereby enabling the battery to achieve both high energy density and good cycle performance.

[0008] In some embodiments, the lithium bis(fluorosulfonyl)imide accounts for 9% to 17% of the mass percentage of the electrolyte. In lithium-ion batteries, the positive electrode current collector typically includes aluminum foil. LiFSI has a certain corrosive effect on aluminum foil. When the mass percentage of LiFSI in the electrolyte is in the range of 9% to 17%, the risk of aluminum foil corrosion can be reduced while improving the stability of the electrolyte, thereby further improving the cycle performance of the lithium-ion battery.

[0009] In some embodiments, the electrolyte salt further includes lithium hexafluorophosphate (LiPF6). In lithium-ion batteries, LiPF6 can passivate the aluminum foil, thereby reducing the risk of LiFSI corrosion of the aluminum foil and further improving the cycle performance of the lithium-ion battery.

[0010] In some embodiments, the lithium bis(fluorosulfonyl)imide constitutes a greater mass percentage of the electrolyte than the lithium hexafluorophosphate constitutes a greater mass percentage of the electrolyte. The mass percentage of LiFSI in the electrolyte is greater than that of LiPF6. LiFSI can compete with LiPF6 for contact with water, reducing the contact between LiPF6 and water and limiting the reaction between LiPF6 and water, while LiFSI does not readily react with water. Therefore, when the mass percentage of LiFSI in the electrolyte is greater than that of LiPF6, the reaction between the electrolyte salt and water in the electrolyte can be reduced, improving the stability of the electrolyte, thereby improving the cycle performance of the battery and enabling the battery to better balance higher energy density and better cycle performance.

[0011] In some embodiments, the lithium hexafluorophosphate accounts for 1.2% to 6.5% of the electrolyte by mass. A LiPF6 mass percentage within this range can further reduce the risk of LiPF6 reacting with water, which is beneficial for maintaining good battery cycle performance.

[0012] In some embodiments, the combined mass percentage of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate in the electrolyte is 11.5% to 22%. A combined mass percentage of LiFSI and LiPF6 within this range can result in lower polarization and lower impedance in the battery, while also allowing for a lower electrolyte viscosity, thereby enabling a higher lithium-ion transport rate and further improving the battery's cycle performance.

[0013] In some embodiments, the electrolyte further includes fluorosulfonates. Fluorosulfonates are beneficial for improving the stability of the solid electrolyte interphase (SEI) membrane, thereby improving the cycle performance of the battery. Furthermore, fluorosulfonates can promote the formation of more inorganic components in the SEI membrane. When hydrofluoric acid is generated inside the battery due to side reactions, the inorganic components have good tolerance to hydrofluoric acid, thus further improving the stability of the SEI membrane and further enhancing the cycle performance of the battery.

[0014] In some embodiments, the fluorosulfonate constitutes 0.01% to 0.5% of the electrolyte by mass. Within this range, the fluorosulfonate's mass percentage in the electrolyte can promote improved SEI film stability while maintaining good SEI film toughness. When the battery's electrode materials undergo volume changes due to expansion and contraction during cycling, the tougher SEI film has a lower risk of breakage, thus further improving the battery's cycle performance.

[0015] In some embodiments, the fluorosulfonate includes one or more of lithium fluorosulfonate, sodium fluorosulfonate, potassium fluorosulfonate, rubidium fluorosulfonate, cesium fluorosulfonate, magnesium fluorosulfonate, calcium fluorosulfonate, barium fluorosulfonate, aluminum fluorosulfonate, iron fluorosulfonate, and nickel fluorosulfonate.

[0016] In some embodiments, the hydrofluoric acid content in the electrolyte is less than or equal to 200 ppm. A lower hydrofluoric acid content in the electrolyte can reduce corrosion of the SEI film and the positive electrode-electrolyte interface film (CEI film), which is beneficial for improving the stability of the SEI film and CEI film, thereby enabling the battery to maintain better cycle performance.

[0017] In some embodiments, the positive electrode active material includes polycrystalline particles and monocrystalline particles. Polycrystalline particles have better compaction properties, which is beneficial for increasing the compaction density of the positive electrode, while monocrystalline particles have better stability, which is beneficial for improving the cycle stability of the battery. The combination of polycrystalline and monocrystalline particles allows the positive electrode sheet to achieve both high compaction density and good stability, thereby enabling the battery to achieve both high energy density and good cycle performance. Optionally, the mass ratio of the polycrystalline particles to the monocrystalline particles is 7:3 to 9:1.

[0018] In some embodiments, the porosity of the positive electrode active layer is 25% to 32%. Within this range, the porosity of the positive electrode active layer reduces the water absorption of the positive electrode active material, decreases the water content of the positive electrode sheet, reduces the adverse effects of moisture introduction on the battery, and further improves the battery's cycle performance. Simultaneously, this porosity allows the electrolyte to fully wet the positive electrode sheet, maximizing the capacity of the positive electrode active material and enabling the battery to maintain a high energy density.

[0019] In some embodiments, the moisture content of the positive electrode is less than or equal to 300 ppm. A lower moisture content in the positive electrode can further reduce the adverse effects of moisture introduction on the battery and further improve the battery's cycle performance.

[0020] In some embodiments, the water content of the negative electrode is less than or equal to 200 ppm. A lower water content in the negative electrode can further reduce the adverse effects of moisture introduction on the battery and further improve the battery's cycle performance.

[0021] A second aspect of this application provides an electrical device including the lithium-ion battery. Attached Figure Description

[0022] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0023] Figure 1 is a schematic diagram of a lithium-ion battery according to an embodiment of this application.

[0024] Figure 2 is an exploded view of a lithium-ion battery according to an embodiment of this application, as shown in Figure 1.

[0025] Figure 3 is a schematic diagram of an electrical device using a lithium-ion battery as a power source according to an embodiment of this application.

[0026] Explanation of reference numerals in the attached drawings: 1. Lithium-ion battery; 11. Casing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. Detailed Implementation

[0027] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0029] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be included or excluded independently, and they can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are also listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0030] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0031] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0032] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0033] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0034] In this application, unless otherwise stated, A (e.g., B) means that B is a non-limiting example of A, and it is understood that A is not limited to B.

[0035] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0036] In this application, unless otherwise specified, "lithium-ion battery" refers to a basic unit capable of converting chemical energy into electrical energy, and more generally includes a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrode. The electrolyte acts as a conductor for the active ions between the positive and negative electrode.

[0037] In lithium-ion batteries, the use of cathode active materials with high nickel content can improve the battery's energy density. However, cathode active materials with high nickel content often have a high amount of impure lithium, which can affect the battery's cycle performance.

[0038] Based on this, one embodiment of this application provides a lithium-ion battery. The lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte; the positive electrode includes a positive current collector and a positive active layer located on at least one surface of the positive current collector; the positive active material of the positive active layer includes a lithium-containing transition metal oxide, which includes Ni element, and the molar amount of Ni element accounts for more than 90% of the total molar amount of transition metal elements in the lithium-containing transition metal oxide; the amount of impure lithium in the positive active material is less than or equal to 2000 ppm; the electrolyte includes an electrolyte salt, which includes lithium bis(fluorosulfonyl)imide (LiFSI).

[0039] In their research on batteries containing cathode active materials with high nickel content, the inventors discovered that a higher amount of impure lithium results in greater water absorption and a higher water content in the cathode active material, thus affecting the battery's cycle performance. For example, the water in the cathode active material may react with electrolyte salts in the electrolyte, impacting the battery's cycle performance. For cathode active materials with an impure lithium content of 2000 ppm or less, the impact of water absorption on battery cycle performance can be reduced by introducing LiFSI, which is less reactive with water, thereby enabling the battery to achieve both high energy density and good cycle performance. However, when the impure lithium content in the cathode active material exceeds 2000 ppm, because LiFSI is a Brønsted acid, the impure lithium will react with LiFSI to form water, further affecting the battery's cycle performance. Therefore, in this embodiment, for positive electrode active materials with a mixed lithium content of less than or equal to 2000 ppm, the influence of the water absorption of the positive electrode active material on the battery cycle performance can be reduced by introducing LiFSI, which is not easily reactive with water, thereby enabling the battery to achieve both high energy density and good cycle performance.

[0040] Optionally, the molar amount of Ni accounts for more than 90% of the total molar amount of transition metal elements in the lithium-containing transition metal oxide. The percentage of the molar amount of Ni in the total molar amount of transition metal elements in the lithium-containing transition metal oxide can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, or any value within the range of any two of the above values.

[0041] Impure lithium content refers to the amount of lithium in a cathode active material that exists in non-ideal forms other than the lithium that normally occupies lattice positions in an ideal crystal structure. These non-ideal forms include lithium compounds adsorbed on the surface, lithium impurities at grain boundaries, or unreacted residual lithium sources.

[0042] The amount of impure lithium can be tested as follows: Disassemble the battery, scrape off the positive electrode active layer from the positive electrode sheet and grind it into powder. Weigh 30g of powder of any particle size, add 100ml of pure water and stir for 30min. Let it stand for 10min, filter it, and transfer a certain amount of filtrate. Use 0.05mol / L hydrochloric acid standard solution, drain the liquid to remove air bubbles from the burette, and start the automatic detection using a potentiometric titrator to read the corresponding result.

[0043] Optionally, the amount of impure lithium in the positive electrode active material can be 2000ppm, 1900ppm, 1800ppm, 1700ppm, 1600ppm, 1500ppm, 1400ppm, 1300ppm, 1200ppm, 1100ppm, 1000ppm, 900ppm, 800ppm, 700ppm, or any value within the range of any two of the above values.

[0044] In some embodiments, lithium bisfluorosulfonylimide (LiFSI) comprises 9% to 17% of the electrolyte by mass. In lithium-ion batteries, the positive electrode current collector typically includes aluminum foil. LiFSI has a certain corrosive effect on aluminum foil. When the mass percentage of LiFSI in the electrolyte is within this range, the risk of aluminum foil corrosion can be reduced while improving electrolyte stability, thereby further improving the cycle performance of the lithium-ion battery. Optionally, the mass percentage of LiFSI in the electrolyte can be 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, or any value within the range of any two of the above values.

[0045] In some embodiments, the electrolyte salt also includes lithium hexafluorophosphate (LiPF6). In lithium-ion batteries, LiPF6 can passivate the aluminum foil, thereby reducing the risk of LiFSI corrosion of the aluminum foil and further improving the cycle performance of the lithium-ion battery.

[0046] In some embodiments, the mass percentage of lithium bis(fluorosulfonyl)imide in the electrolyte is greater than that of lithium hexafluorophosphate. The mass percentage of LiFSI in the electrolyte is greater than that of LiPF6. LiFSI can compete with LiPF6 for contact with water, reducing the contact between LiPF6 and water and inhibiting the reaction between LiPF6 and water, while LiFSI does not readily react with water. Therefore, when the mass percentage of LiFSI in the electrolyte is greater than that of LiPF6, the reaction between the electrolyte salt and water in the electrolyte can be reduced, improving the stability of the electrolyte, thereby improving the cycle performance of the battery and enabling the battery to better balance higher energy density and better cycle performance.

[0047] In some embodiments, lithium hexafluorophosphate accounts for 1.2% to 6.5% of the electrolyte by mass. A LiPF6 mass percentage within this range can further reduce the risk of LiPF6 reacting with water, which is beneficial for maintaining good battery cycle performance. Optionally, the LiPF6 mass percentage of the electrolyte can be 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, 5.2%, 5.5%, 5.8%, 6%, 6.2%, 6.5%, or any value within the range of any two of the above values.

[0048] In some embodiments, the combined mass percentage of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate in the electrolyte is 11.5% to 22%. Within this range, the combined mass percentage of LiFSI and LiPF6 in the electrolyte allows for lower polarization and lower impedance in the battery, while also resulting in lower electrolyte viscosity, thereby enabling higher lithium-ion transport rates and further improving battery cycle performance. For example, when the combined mass percentage of LiFSI and LiPF6 in the electrolyte is low, the electrolyte conductivity is low, and the charge transfer impedance is high, leading to greater battery polarization and slower lithium-ion transport, which in turn affects battery cycle performance. Conversely, when the combined mass percentage of LiFSI and LiPF6 in the electrolyte is high, the electrolyte viscosity is high, increasing the obstacle to lithium-ion transport and also affecting battery cycle performance. Optionally, the sum of the mass percentages of LiFSI and LiPF6 in the electrolyte can be 11.5%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any value within the range of any two of the above values.

[0049] In some embodiments, the electrolyte salt may also include one or more of lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0050] In some embodiments, the electrolyte also includes fluorosulfonates. Fluorosulfonates are beneficial for improving the stability of the solid electrolyte interphase (SEI) membrane, thereby improving the cycle performance of the battery. Furthermore, fluorosulfonates can promote the formation of more inorganic components in the SEI membrane. When hydrofluoric acid is generated inside the battery due to side reactions, the inorganic components have good tolerance to hydrofluoric acid, thus further improving the stability of the SEI membrane and further enhancing the cycle performance of the battery.

[0051] Optionally, the fluorosulfonate constitutes 0.01% to 0.5% of the electrolyte by mass. Within this range, the fluorosulfonate's mass percentage in the electrolyte allows the SEI film to maintain good toughness while fully leveraging its ability to improve SEI film stability. When the battery's electrode materials undergo volume changes due to expansion and contraction during cycling, the SEI film, with its better toughness, has a lower risk of breakage, thus further improving the battery's cycle performance. As some optional examples, the fluorosulfonate's mass percentage in the electrolyte can be 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or any value within the range of any two of the above values.

[0052] In some embodiments, fluorosulfonates include one or more of lithium fluorosulfonate, sodium fluorosulfonate, potassium fluorosulfonate, rubidium fluorosulfonate, cesium fluorosulfonate, magnesium fluorosulfonate, calcium fluorosulfonate, barium fluorosulfonate, aluminum fluorosulfonate, iron fluorosulfonate, and nickel fluorosulfonate.

[0053] In some embodiments, the electrolyte further includes film-forming additives. Film-forming additives can improve the film-forming performance of the interfacial film inside the battery, further improving the battery's cycle performance. Optionally, the film-forming additive accounts for 0.2% to 3% of the electrolyte by mass. More preferably, the film-forming additive accounts for 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or any value within the range of any two of the above values.

[0054] In some embodiments, the film-forming additive includes one or more of the negative electrode film-forming additive and the positive electrode film-forming additive.

[0055] Negative electrode film-forming additives are beneficial for promoting the formation of the solid electrolyte interphase (SEI) film, reducing side reactions at the negative electrode, and improving the cycle performance of the battery. Optionally, the negative electrode film-forming additive accounts for 0.5% to 3% of the electrolyte by mass. For example, the mass percentage of the negative electrode film-forming additive in the electrolyte can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or any value within the range of any two of the above values. Further optionally, the negative electrode film-forming additive includes one or more of vinylene carbonate, ethylene carbonate, and fluoroethylene carbonate.

[0056] Positive electrode film-forming additives promote the formation of the positive electrode-electrolyte interface film (CEI film), reduce side reactions at the positive electrode, and improve the cycle performance of the battery. Optionally, the positive electrode film-forming additive accounts for 0.2% to 1% of the electrolyte by mass. For example, the positive electrode film-forming additive can account for 0.2%, 0.5%, 0.8%, 1%, or any value within the range of any two of the above values. Further optionally, the positive electrode film-forming additive includes 1,3-propanesulfonyl lactone (PS).

[0057] In some implementations, the electrolyte may also include other functional additives, such as additives that improve battery overcharge performance or additives that improve battery high-temperature or low-temperature performance.

[0058] Understandably, the electrolyte also includes a solvent. Optionally, the solvent includes at least one of cyclic carbonates and chain carbonates. Cyclic carbonates include ethylene carbonate (EC). ), fluoroethylene carbonate (FEC), propylene carbonate (PC), ) and butylene carbonate One or more of the following. Chain carbonates include one or more of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0059] In some embodiments, the solvent includes cyclic carbonates and chain carbonates. The cyclic carbonates constitute 10% to 25% of the solvent by mass. Optionally, the cyclic carbonates may constitute 10%, 12%, 15%, 18%, 20%, 22%, 25%, or any value within the range of any two of the above values. The chain carbonates constitute 75% to 90% of the solvent by mass. Optionally, the chain carbonates may constitute 75%, 78%, 80%, 82%, 85%, 88%, 90%, or any value within the range of any two of the above values.

[0060] In some embodiments, the hydrofluoric acid content in the electrolyte is less than or equal to 200 ppm. A lower hydrofluoric acid content in the electrolyte can reduce corrosion of the SEI and CEI films inside the battery, reduce side reactions between the active materials and the electrolyte, and thus maintain better cycle performance of the battery.

[0061] The hydrofluoric acid content in this application can be tested as follows: The battery is fully discharged and disassembled, the electrolyte is poured into a container, and the container is placed at an ice-water mixing temperature. The mass of the electrolyte, m1, is recorded in grams, and the volume of the electrolyte, V1, is recorded in liters. An indicator is added to the electrolyte. 0.01 mol / L NaOH is added dropwise to the electrolyte until the electrolyte changes color; the volume of the electrolyte at this point, V2, is recorded. The volume of NaOH added is then V2 - V1. The hydrofluoric acid content in the electrolyte (ppm) = (V2 - V1) × 200 / m.

[0062] It is understandable that hydrofluoric acid is mainly generated by the reaction between the electrolyte and residual moisture in the electrode plates. During the manufacturing process of lithium-ion batteries, the hydrofluoric acid content in the electrolyte can be reduced by minimizing the water content in the electrode plates.

[0063] In some embodiments, the positive electrode active material includes polycrystalline particles and monocrystalline particles. Polycrystalline particles have better compaction properties, which is beneficial for increasing the compaction density of the positive electrode, while monocrystalline particles have better stability, which is beneficial for improving the cycle stability of the battery. The combination of polycrystalline and monocrystalline particles allows the positive electrode sheet to achieve both high compaction density and good stability, thereby enabling the battery to achieve both high energy density and good cycle performance. Optionally, the mass of the polycrystalline particles is greater than the mass of the monocrystalline particles. More preferably, the mass ratio of polycrystalline particles to monocrystalline particles is 7:3 to 9:1. For example, the mass ratio of polycrystalline particles to monocrystalline particles is 9:1, 8.5:1.5, 8:2, 7.5:2.5, 7:3, or any value within the range of any two of the above values.

[0064] In some embodiments, the porosity of the positive electrode active layer is 25% to 32%. A porosity within this range reduces the water absorption of the positive electrode active material, decreases the water content of the positive electrode sheet, reduces the adverse effects of moisture introduction on the battery, and further improves the battery's cycle performance. Simultaneously, a porosity within this range allows the electrolyte to fully wet the positive electrode sheet, maximizing the capacity of the positive electrode active material and enabling the battery to maintain a high energy density. Optionally, the porosity of the positive electrode active layer can be 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, or any value within the range of any two of the above values.

[0065] The porosity of the positive electrode active layer in this application can be tested according to GB / T 24586-2009. The battery is fully discharged, disassembled, and the positive electrode is removed. The apparent volume of the positive electrode to be tested is measured. After cleaning by immersing the positive electrode in ethyl methyl carbonate (EMC), it is placed in a true density analyzer. The testing system is sealed, and helium gas is introduced according to the procedure. By detecting the gas pressure in the sample chamber and expansion chamber, and then calculating the true volume according to Bohr's law, the porosity of the sample is obtained. Porosity = 1 - (True Volume / Apparent Volume) × 100%.

[0066] In some implementations, the moisture content of the positive electrode is less than or equal to 300 ppm. A lower moisture content in the positive electrode can further reduce the adverse effects of moisture introduction on the battery and further improve the battery's cycle performance. It is understood that moisture in the positive electrode is difficult to completely remove; therefore, during the preparation of the positive electrode, its moisture content can be minimized through drying.

[0067] The moisture content of the positive electrode in this application can be tested using the following method: Fully fill the battery, disassemble the battery, remove the positive electrode, and soak it thoroughly in DMC for at least 2 hours. Pour out the DMC and allow the electrode to air dry naturally. Test the moisture content of the positive electrode using a fully automated moisture content analyzer. Optionally, the fully automated moisture content analyzer can be a Metrohm 874+831.

[0068] In some embodiments, the compaction density of the positive electrode active layer is 3.5 g / cm³. 3 ~3.75g / cm 3 Optionally, the compaction density of the positive electrode active layer can be 3.5 g / cm³. 3 3.52g / cm 3 3.55g / cm 3 3.58g / cm 3 3.6g / cm 3 3.62g / cm 3 3.65g / cm 3 3.68g / cm 3 3.7g / cm 3 3.72g / cm 3 3.75g / cm 3 And any value within the range consisting of any two of the above values.

[0069] The compaction density of the active layer of the electrode sheet in this application can be tested by the following method: Disassemble the battery, take a single-sided coated electrode sheet (if it is a double-sided coated electrode sheet, the active layer on one side can be wiped off first), cut it into a small circular piece with an area of ​​S1, weigh it, and record its weight as M1; measure the thickness of the active layer and record it as T; then wipe off the above-weighed active layer, weigh the current collector, and record it as M0. The compaction density of the active layer PD = (M1 - M0) / (S1 × T).

[0070] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0071] For example, lithium-containing transition metal oxides include those with the chemical formula Li x (Ni a Co b Mn c ) 1- d M d O 2-y A y The material has the following properties: 0.2≤x≤1.2, 0.9≤a≤1, 0≤b≤0.1, 0≤c≤0.1, a+b+c=1, 0≤d<1, 0≤y<2, M includes one or more of Zr, Sr, B, Sn, Al, Mg, Fe, Cu, V, Ti, W, Sb, Dy and Te, and A includes one or more of N, P, S and halogen elements.

[0072] Understandably, in Li x (Ni a Co b Mn c ) 1-d M d O 2-y A yIn the materials, when 0.9 ≤ a ≤ 1, the positive electrode active material has a higher nickel content and a higher specific capacity, which is beneficial for maintaining a high energy density in the battery. Optionally, a can be 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, or any value within the range of any two of the above values. Further optionally, 0.9 ≤ a ≤ 0.96. Further optionally, Li x (Ni a Co b Mn c ) 1-d M d O 2-y A y It could be LiNi 0.9 Co 0.09 Mn 0.01 O2, LiNi 0.92 Co 0.05 Mn 0.03 O2, LiNi 0.96 Co 0.02 Mn 0.02 O2, etc.

[0073] As some alternative examples of x, x can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, and any value within the range consisting of any two of the above values.

[0074] As some alternative examples of b, 0 ≤ b ≤ 0.1. Optionally, b can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, and any value within the range consisting of any two of the above values.

[0075] As some alternative examples of c, 0 ≤ c ≤ 0.1. c can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, and any value within the range of any two of the above values.

[0076] As some optional examples of d, d can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and any value within the range of any two of the above values. Optionally, 0 ≤ d ≤ 0.05.

[0077] As some optional examples of y, y can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and any value within the range of any two of the above values. Optionally, 0 ≤ y ≤ 0.05.

[0078] It is understandable that A includes one or more of N, P, S and halogen elements, where halogen elements can be F, Cl, Br, etc.

[0079] In some embodiments, the positive electrode active material may include, in addition to lithium-containing transition metal oxides with a high nickel content, positive electrode active materials known in the art for use in batteries.

[0080] Alternatively, the positive electrode active material may also include lithium-containing transition metal oxides with low nickel content. For example, non-limiting examples of nickel-containing lithium salt materials with low nickel content may include LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 LiNi 0.8 Co 0.15 Al 0.05 O2, etc. Further optionally, the positive electrode active material may also include a lithium-containing phosphate. The lithium-containing phosphate may include at least one of lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon. The lithium-containing phosphate may also include one or more of lithium manganese phosphate and a composite of lithium manganese phosphate and carbon.

[0081] Further optionally, the positive electrode active material may also include one or more of the following materials: lithium cobalt oxide (such as LiCoO2), lithium manganese oxide, lithium manganese cobalt oxide, and modified compounds thereof. Non-limiting examples of lithium cobalt oxide may include LiCoO2. Non-limiting examples of lithium manganese oxide may include LiMnO2, LiMn2O4, etc.

[0082] In some embodiments, the positive electrode active layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0083] In some embodiments, the positive electrode active layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0084] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents described in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector.

[0085] It is understood that the negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector, the negative active layer including a negative active material.

[0086] In some embodiments, the compaction density of the negative electrode active layer is 1.5 g / cm³. 3 ~1.8g / cm 3 Optionally, the compaction density of the negative electrode active layer can be 1.5 g / cm³. 3 1.55g / cm 3 1.6g / cm 3 1.65g / cm 3 1.7g / cm 3 1.75g / cm 3 1.8g / cm3 And any value within the range consisting of any two of the above values.

[0087] In some implementations, the moisture content of the negative electrode is less than or equal to 200 ppm. A lower moisture content in the negative electrode can further reduce the adverse effects of moisture introduction on the battery and further improve the battery's cycle performance. It is understood that moisture in the negative electrode is difficult to completely remove; therefore, during the preparation of the negative electrode, its moisture content can be minimized by drying.

[0088] Understandably, the moisture content of the negative electrode can be tested using the following method: Fully fill the battery, disassemble it, remove the negative electrode, and soak it thoroughly in DMC for at least 2 hours. Pour out the DMC and allow the electrode to air dry naturally. Test the moisture content of the positive electrode using a fully automated moisture content analyzer. Optionally, the fully automated moisture content analyzer can be a Metrohm 874+831.

[0089] In some embodiments, 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 current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0090] In some embodiments, the negative electrode active material includes graphite. Optionally, the graphite includes one or more of artificial graphite and natural graphite. Further optionally, the negative electrode active material may also employ negative electrode active materials known in the art for use in batteries. As a non-limiting example, the negative electrode active material may include one or more of the following materials: soft carbon, hard carbon, tin-based materials, and lithium titanate, etc. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0091] In some embodiments, the negative electrode active layer may optionally include a binder. The binder may include one or more 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).

[0092] In some embodiments, the negative electrode active layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0093] In some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0094] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of the negative electrode current collector, and then obtaining the negative electrode sheet after processes such as drying and cold pressing. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector.

[0095] It is understood that the battery also includes a separator. The separator is located between the positive electrode and the negative electrode. This application does not impose any particular restriction on the type of separator; any well-known porous separator with good chemical and mechanical stability can be selected.

[0096] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0097] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0098] In some embodiments, the battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0099] In some embodiments, the battery's outer packaging can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The battery's outer packaging can also be a soft pack, such as a pouch-type soft pack. The soft pack can be made of plastic; further, non-limiting examples of plastics may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0100] This application does not impose any particular limitation on the shape of the lithium-ion battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square-structured lithium-ion battery 1 as an example.

[0101] In some embodiments, referring to FIG2, the outer packaging may include a housing 11 and a cover plate 13. The housing 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The lithium-ion battery 1 may contain one or more electrode assemblies 12, which can be selected by those skilled in the art according to actual needs.

[0102] In some implementations, the lithium-ion battery can be a single cell, a battery module, or a battery pack.

[0103] The battery module includes at least one lithium-ion battery. The battery module may contain one or more lithium-ion batteries, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0104] In a battery module, multiple lithium-ion batteries can be arranged sequentially along the length of the module. Of course, they can also be arranged in any other manner. Furthermore, these multiple lithium-ion batteries can be secured using fasteners.

[0105] Optionally, the battery module may also include a housing with a receiving space in which multiple lithium-ion batteries are housed.

[0106] In some embodiments, the battery modules can also be assembled into a battery pack, and the battery pack may contain one or more battery modules. Those skilled in the art can select an appropriate number based on the application and capacity of the battery pack.

[0107] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0108] In addition, this application also provides an electrical device, which includes the lithium-ion battery provided in this application. The battery can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0109] As an electrical device, lithium-ion batteries can be selected based on its usage requirements.

[0110] Figure 3 shows an example of an electrical device 2. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device, a battery pack or battery module can be used.

[0111] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a battery as their power source.

[0112] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0113] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0114] Example 1

[0115] (1) Positive electrode plate

[0116] LiNi, the positive electrode active material 0.9 Co 0.09 Mn 0.01O2, polyvinylidene fluoride (PVDF) binder, and super P conductive agent are mixed in a weight ratio of 96:2:2, and N-methylpyrrolidone (NMP) solvent is added. The mixture is stirred to form a positive electrode slurry. This slurry is then coated onto a current collector aluminum foil, dried, and subjected to cold pressing, slitting, and cutting to form the positive electrode sheet. The positive electrode active material contains 2000 ppm of impurity lithium and comprises polycrystalline and single-crystal particles in a mass ratio of 8:2. The compaction density of the positive electrode active layer is 3.7 g / cm³. 3 The porosity of the active layer in the positive electrode is 30%.

[0117] (2) Negative electrode plate

[0118] A negative electrode slurry was prepared by mixing graphite (anode active material), carbon black (conductive agent), sodium carboxymethyl cellulose (CMC-Na) (thickener), and styrene-butadiene rubber (SBR) (binder) in a weight ratio of 97:0.5:1:1.5, adding deionized water as a solvent, and stirring. The negative electrode slurry was then coated onto copper foil (current collector), dried, and subjected to cold pressing, slitting, and cutting to form the negative electrode sheet. The compaction density of the negative electrode active layer was 1.65 g / cm³. 3 .

[0119] (3) Separating membrane

[0120] Polyethylene (PE) film is used as the separator.

[0121] (4) Electrolyte

[0122] In an argon-atmospheric glove box with a water content <1 ppm and an oxygen content <1 ppm, ethylene carbonate and methyl ethyl carbonate were mixed at a mass ratio of 16:84 to obtain a mixed solvent. Positive electrode film-forming additive PS, negative electrode film-forming additive FEC, and LiFSO3 were added to the mixed solvent, followed by lithium salts LiFSI and LiPF6. The mixture was stirred until dissolved to obtain the electrolyte. Based on the total mass of the electrolyte, the mass percentages of LiFSO3, LiFSI, LiPF6, FEC, and PS were 0.5%. The hydrofluoric acid content in the electrolyte was 85 ppm.

[0123] (5) Lithium-ion batteries

[0124] The positive electrode, separator, and negative electrode are prepared in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then wound to obtain a bare cell, and tabs are welded on. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0125] Examples 2 to 10, Comparative Example 1

[0126] The differences between Examples 2 to 10 and Comparative Example 1 compared to Example 1 are shown in Table 1.

[0127] Comparative Example 2

[0128] Compared with Example 1, Comparative Example 2 differs in that the amount of impure lithium in the positive electrode active material is 2200 ppm.

[0129] Test case

[0130] The cycle capacity retention rate of the battery was tested using the following method:

[0131] At 25°C, the battery is charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage of 4.25V until the current is less than 0.05C. Finally, the battery is discharged at a constant current of 0.33C to 2.8V. This constitutes one charge-discharge cycle. This charging and discharging process is repeated, and the capacity retention rate of the lithium-ion battery after 1000 cycles is calculated.

[0132] The capacity retention rate (%) of a lithium-ion battery after 1000 cycles at 25°C = (discharge capacity of the 1000th cycle / discharge capacity of the first cycle) × 100%.

[0133] Table 1

[0134] In Table 1, "Polycrystalline:Monocrystalline" represents the mass ratio of polycrystalline particles to monocrystalline particles in the positive electrode active material. "LiFSI" represents the mass percentage of LiFSI in the electrolyte. "LiPF6" represents the mass percentage of LiPF6 in the electrolyte. "LiFSO3" represents the mass percentage of LiFSO3 in the electrolyte.

[0135] As can be seen from Example 1 and Comparative Example 1, the cycle capacity retention rate of the battery in Example 1 is higher than that in Comparative Example 1. This indicates that for batteries containing positive electrode active materials with high nickel content, when the amount of impure lithium in the positive electrode active material is less than or equal to 2000 ppm, the introduction of LiFSI into the electrolyte can enable the battery to have higher cycle performance.

[0136] As can be seen from Example 1 and Comparative Example 2, when the amount of impure lithium in the positive electrode active material is greater than 2000 ppm, even with the introduction of LiFSI into the electrolyte, the cycle capacity retention rate of the battery remains low. Furthermore, as can be seen from Comparative Example 1 and Comparative Example 2, the cycle capacity retention rate of Comparative Example 2 is lower than that of Comparative Example 1, indicating that when the amount of impure lithium in the positive electrode active material is greater than 2000 ppm, the use of LiFSI is insufficient to balance the impact of the amount of impure lithium in the positive electrode active material on battery cycling, thus making it difficult to obtain a high cycle capacity retention rate.

[0137] As can be seen from Examples 1-3 and Example 4, the cycle capacity retention rate of the batteries in Examples 1-3 is higher than that in Example 4, indicating that a mass percentage of LiFSI in the electrolyte of 9%-17% is beneficial to further improve the cycle performance of the batteries.

[0138] As can be seen from Examples 1-4 and Example 5, the cycle capacity retention rate of the batteries in Examples 1-4 is higher than that in Example 5, indicating that when the mass percentage of LiFSI in the electrolyte is greater than the mass percentage of LiPF6, the cycle performance of the battery can be further improved.

[0139] As can be seen from Examples 2 and 6, the cycle capacity retention rate of the battery in Example 2 is higher than that in Example 6, indicating that adding LiFSO3 to the electrolyte is beneficial to further improve the cycle performance of the battery.

[0140] As can be seen from Examples 2 and 7-8, the cycle capacity retention rate of the batteries in Examples 2 and 7 is higher than that in Example 8, indicating that a porosity of 25% to 32% in the positive electrode active layer is beneficial to further improve the cycle performance of the battery.

[0141] As can be seen from Examples 2 and 9, the cycle capacity retention rate of the battery in Example 2 is higher than that in Example 9, indicating that the combination of polycrystalline particles and monocrystalline particles is beneficial to further improve the cycle performance of the battery.

[0142] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0143] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte; the positive electrode comprises a positive current collector and a positive active layer located on at least one surface of the positive current collector, the positive active material of the positive active layer comprising a lithium-containing transition metal oxide, the lithium-containing transition metal oxide comprising Ni element, the molar amount of Ni element accounting for more than 90% of the total molar amount of transition metal elements in the lithium-containing transition metal oxide; the amount of impure lithium in the positive active material is less than or equal to 2000 ppm; the electrolyte comprises an electrolyte salt, the electrolyte salt comprising lithium bis(fluorosulfonyl)imide.

2. The lithium-ion battery according to claim 1, wherein, The lithium difluorosulfonylimide accounts for 9% to 17% of the mass of the electrolyte.

3. The lithium-ion battery according to any one of claims 1 to 2, wherein, The electrolyte salt also includes lithium hexafluorophosphate.

4. The lithium-ion battery according to claim 3, wherein, The mass percentage of lithium difluorosulfonylimide in the electrolyte is greater than the mass percentage of lithium hexafluorophosphate in the electrolyte.

5. The lithium-ion battery according to any one of claims 3 to 4, wherein, The lithium hexafluorophosphate accounts for 1.2% to 6.5% of the mass of the electrolyte.

6. The lithium-ion battery according to any one of claims 3 to 5, wherein, The sum of the mass percentages of lithium difluorosulfonylimide and lithium hexafluorophosphate in the electrolyte is 11.5% to 22%.

7. The lithium-ion battery according to any one of claims 1 to 6, wherein, The electrolyte also includes fluorosulfonate.

8. The lithium-ion battery according to claim 7, wherein, The fluorosulfonate accounts for 0.01% to 0.5% of the mass of the electrolyte.

9. The lithium-ion battery according to any one of claims 7 to 8, wherein, The fluorosulfonates include one or more of lithium fluorosulfonate, sodium fluorosulfonate, potassium fluorosulfonate, rubidium fluorosulfonate, cesium fluorosulfonate, magnesium fluorosulfonate, calcium fluorosulfonate, barium fluorosulfonate, aluminum fluorosulfonate, iron fluorosulfonate, and nickel fluorosulfonate.

10. The lithium-ion battery according to any one of claims 1 to 9, wherein, The electrolyte contains less than or equal to 200 ppm of hydrofluoric acid.

11. The lithium-ion battery according to any one of claims 1 to 10, wherein, The positive electrode active material includes polycrystalline particles and single-crystal particles.

12. The lithium-ion battery according to claim 11, wherein, The mass ratio of the polycrystalline particles to the single-crystal particles is 7:3 to 9:

1.

13. The lithium-ion battery according to any one of claims 1 to 12, wherein, The porosity of the positive electrode active layer is 25% to 32%.

14. The lithium-ion battery according to any one of claims 1 to 13, wherein, The water content of the positive electrode sheet is less than or equal to 300 ppm.

15. The lithium-ion battery according to any one of claims 1 to 14, wherein, The water content of the negative electrode sheet is less than or equal to 200 ppm.

16. An electrical device comprising a lithium-ion battery according to any one of claims 1 to 15.

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