Lithium-ion battery and electrical device

Abstract

Provided are a lithium-ion battery and an electrical device. The battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte; a positive electrode active material of the positive electrode sheet comprises a lithium-containing transition metal oxide, and the lithium-containing transition metal oxide comprises Ni, wherein the molar amount of Ni accounts for 90% or more of the total molar amount of transition metal elements in the lithium-containing transition metal oxide; the specific surface area of the positive electrode sheet is 0.6m2 / g-3m2 / g; the electrolyte comprises an electrolyte salt, and the electrolyte salt comprises 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 27, 2025, with application number 2025101264448, 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 lithium-ion batteries and electrical devices. 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, correspondingly higher requirements are being placed on battery performance.

[0005] In lithium-ion battery design, cathode active materials with high nickel content typically exhibit higher specific capacity, which is beneficial for improving battery energy density. However, cathode active materials with high nickel content generate significant heat, which may adversely affect the battery's thermal safety performance. Summary of the Invention

[0006] The 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 specific surface area of ​​the positive electrode is 0.6 m². 2 / g~3m 2 / g; the electrolyte comprises an electrolyte salt, which includes lithium bis(fluorosulfonyl)imide (LiFSI).

[0007] In lithium-ion batteries, the positive electrode has a large specific surface area, exhibiting good heat dissipation performance, promoting timely heat dissipation, and improving the battery's thermal safety. However, a large specific surface area of ​​the positive electrode may lead to more side reactions, resulting in a decrease in battery cycle performance. The use of LiFSI, which has good stability, can reduce the occurrence of side reactions in the positive electrode, allowing the battery to maintain good cycle performance. Therefore, in this embodiment, by combining a positive electrode with a large specific surface area with LiFSI, the battery can achieve both good thermal safety and good cycle performance while fully utilizing the high nickel content of the positive electrode active material to improve battery energy density.

[0008] In some embodiments, the porosity of the positive electrode active layer is 20% to 35%. A porosity within this range allows the electrolyte to fully wet the positive electrode sheet, further improving the battery's cycle performance.

[0009] In some embodiments, the compaction density of the positive electrode active layer is 3.4 g / cm³. 3 ~3.75g / cm 3 At this point, lithium-ion batteries can exhibit high energy density, while also promoting the wetting of the positive electrode by the electrolyte, further improving the battery's cycle performance.

[0010] In some embodiments, the specific surface area of ​​the positive electrode active material is 0.2 m². 2 / g~1m 2 / g. Within this range, the specific surface area of ​​the positive electrode active material allows the positive electrode sheet to have a suitable specific surface area, thereby promoting heat dissipation and further improving the thermal safety performance of the battery. Additionally, this specific surface area allows the electrolyte to fully wet the positive electrode active material, promoting lithium-ion transport and further improving the battery's cycle performance.

[0011] In some embodiments, the Dv50 of the positive electrode active material is 5 μm to 11 μm. A Dv50 within this range allows the positive electrode active material and the positive electrode sheet to have a suitable specific surface area, thereby promoting heat dissipation and improving the thermal safety performance of the battery.

[0012] 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 battery's thermal safety and cycle performance. 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, good thermal safety, and good cycle performance. Optionally, the mass ratio of the polycrystalline particles to the monocrystalline particles is 7:3 to 9:1.

[0013] In some embodiments, the specific surface area of ​​the single crystal particles is 0.85 m². 2 / g~1.5m 2 / g. The specific surface area of ​​the single crystal particles is greater than or equal to 0.85m². 2 / g can give the positive electrode active material and positive electrode sheet a suitable specific surface area, promoting heat dissipation. The specific surface area of ​​single crystal particles is less than or equal to 1.5m². 2 / g can reduce the gas generation rate during battery thermal runaway and further improve the battery's thermal safety performance.

[0014] In some embodiments, the Dv50 of the single crystal particles is 1.5 μm to 3 μm. A Dv50 within this range allows the positive electrode active material to have a suitable Dv50, resulting in a suitable specific surface area for both the positive electrode active material and the positive electrode sheet, thereby promoting heat dissipation and improving the thermal safety performance of the battery.

[0015] In some embodiments, the specific surface area of ​​the polycrystalline particles is 0.1 m². 2 / g~0.7m 2 / g. The specific surface area of ​​the polycrystalline particles is greater than or equal to 0.1m². 2 / g can give the positive electrode active material and positive electrode sheet a suitable specific surface area, promoting heat dissipation. The specific surface area of ​​polycrystalline particles is less than or equal to 0.7m². 2 / g can reduce the gas generation rate during battery thermal runaway and further improve the battery's thermal safety performance.

[0016] In some embodiments, the Dv50 of the polycrystalline particles is 7.5 μm to 11 μm. A Dv50 within this range allows the positive electrode active material to have a suitable Dv50, resulting in a suitable specific surface area for both the positive electrode active material and the positive electrode sheet, thereby promoting heat dissipation and improving the thermal safety performance of the battery.

[0017] In some embodiments, the positive electrode active layer comprises a conductive carbon material. The conductive carbon material has good conductivity, which can improve the conductivity of the positive electrode sheet, thereby improving the electrical performance of the battery.

[0018] In some embodiments, the conductive carbon material accounts for 0.3% to 2% of the mass percentage of the positive electrode active layer. Conductive carbon materials typically have a large specific surface area. A mass percentage of less than or equal to 2% in the positive electrode active layer can reduce side reactions on the positive electrode side and reduce heat generation. Conversely, a mass percentage of greater than or equal to 0.3% can fully utilize the conductivity of the conductive carbon material and improve the conductivity of the positive electrode sheet.

[0019] In some embodiments, the thickness of the positive electrode current collector is 8 μm to 16 μm. In lithium-ion batteries, the positive electrode current collector typically comprises aluminum foil, which provides good heat dissipation. LiFSI has a certain corrosive effect on aluminum foil. A positive electrode current collector with a thickness in the range of 8 μm to 16 μm exhibits good corrosion resistance, maintaining a relatively stable structure and thus ensuring good heat dissipation, further improving the thermal safety performance of the lithium-ion battery. Simultaneously, a positive electrode current collector with a thickness in the range of 8 μm to 16 μm can result in lower internal resistance, reducing the heat generated inside the battery and further improving its thermal safety performance.

[0020] In some embodiments, the lithium bisfluorosulfonylimide accounts for 9% to 17% of the mass percentage of the electrolyte. When the mass percentage of LiFSI in the electrolyte is in the range of 9% to 17%, the risk of corrosion of the positive electrode current collector can be reduced while improving the stability of the electrolyte, thus maintaining a good heat dissipation effect of the positive electrode current collector and further improving the thermal safety performance of the lithium-ion battery.

[0021] 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 positive electrode current collector, maintaining good heat dissipation of the positive electrode current collector, and further improving the thermal safety performance of the lithium-ion battery.

[0022] 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. Since LiFSI does not readily react with water, the combination of LiFSI and LiPF6 can reduce the reaction between electrolyte salts and water in the electrolyte, improve the stability of the electrolyte, and reduce the risk of corrosion of the positive electrode current collector, further improving the thermal safety and cycle performance of the lithium-ion battery.

[0023] In some embodiments, the lithium hexafluorophosphate accounts for 1% to 8% of the mass percentage of the electrolyte. 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.

[0024] 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 the battery to exhibit lower polarization and lower impedance, while also resulting in a lower electrolyte viscosity. This, in turn, enables a higher lithium-ion transport rate, further improving the battery's thermal safety and 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, increased heat generation, and slower lithium-ion transport, thus affecting the battery's thermal safety and 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 affecting the battery's cycle performance.

[0025] 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 lithium-ion 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 lithium-ion battery.

[0026] 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 allows the SEI film to maintain good toughness while fully leveraging its ability to improve SEI film stability. When the electrode materials of a lithium-ion battery undergo volume changes due to expansion and contraction during cycling, the relatively tough SEI film has a lower risk of breakage, thus further improving the battery's cycle performance.

[0027] 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.

[0028] In some embodiments, the electrolyte includes a solvent; ethylene carbonate (EC) constitutes less than or equal to 35% of the solvent by mass. The coordination between lithium ions and bis(fluorosulfonyl)imide ions in the electrolyte allows LiFSI to improve the battery's thermal safety and cycle performance. However, under solvation, EC competes with bis(fluorosulfonyl)imide ions for coordination with lithium ions, disrupting the coordination between them and thus affecting the effectiveness of LiFSI and hindering the improvement of battery thermal safety and cycle performance. Simultaneously, the oxidative decomposition of EC itself deteriorates the battery's thermal safety performance. Therefore, a lower mass percentage of EC in the solvent is beneficial for improving the thermal safety and cycle performance of lithium-ion batteries.

[0029] In some embodiments, the specific surface area of ​​the negative electrode is 0.5 m². 2 / g~3m 2 / g. The specific surface area of ​​the negative electrode sheet within this range can achieve good heat dissipation, while keeping the side reactions at the negative electrode sheet at a low level, further improving the thermal safety performance and cycle performance of the battery.

[0030] A second aspect of this application provides an electrical device including the lithium-ion battery described in the first aspect. Attached Figure Description

[0031] 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:

[0032] Figure 1 is a schematic diagram of a lithium-ion battery according to an embodiment of this application.

[0033] Figure 2 is an exploded view of a lithium-ion battery according to an embodiment of this application, as shown in Figure 1.

[0034] 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.

[0035] 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

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0041] 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.

[0042] 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.

[0043] In this application, unless otherwise specified, 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.

[0044] 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.

[0045] 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.

[0046] In lithium-ion batteries, using cathode active materials with a high nickel content can result in higher energy density. However, cathode active materials with a high nickel content generate significant heat, making the battery prone to thermal runaway and negatively impacting its safety performance.

[0047] 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 specific surface area of ​​the positive electrode is 0.6 m². 2 / g~3m 2 / g. The electrolyte includes an electrolyte salt, which includes lithium bis(fluorosulfonyl)imide.

[0048] In this embodiment, the positive electrode has a large specific surface area, exhibiting good heat dissipation performance, promoting timely heat dissipation of the battery, and improving the battery's thermal safety performance. However, a large specific surface area of ​​the positive electrode may lead to more side reactions, resulting in a decrease in the battery's cycle performance. Therefore, by using LiFSI, which has good stability, the occurrence of side reactions of the positive electrode can be reduced, allowing the battery to maintain good cycle performance. Thus, in this embodiment, the combination of a positive electrode with a large specific surface area and LiFSI can fully utilize the high nickel content of the positive electrode active material to improve the battery's energy density, while simultaneously achieving good thermal safety and good cycle performance.

[0049] Furthermore, LiFSI exhibits good thermal stability. When the battery temperature rises, the use of LiFSI can help maintain the stability of the electrolyte, thereby further improving the thermal safety performance of the battery.

[0050] Furthermore, the specific surface area of ​​the positive electrode is less than or equal to 3m². 2 / g can reduce the gas production rate when the battery experiences thermal runaway, further improving the battery's thermal safety performance.

[0051] In this application, the specific surface area of ​​the positive electrode sheet can be tested using a gas adsorption method. Specifically, the positive electrode sheet to be tested is subjected to vacuum degassing, and the degassed positive electrode sheet is placed in a liquid nitrogen atmosphere. The amount of liquid nitrogen adsorbed on the surface of the positive electrode sheet under different adsorption pressures is tested, and the specific surface area of ​​the positive electrode sheet is calculated according to the BET multilayer adsorption theory. Optionally, the different adsorption pressures can be 0.05 MPa, 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, or 0.3 MPa.

[0052] The lithium-ion battery in this application will be further described below.

[0053] [Positive electrode plate]

[0054] The positive electrode includes a positive current collector and a positive active layer located on at least one surface of the positive current collector.

[0055] The positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0056] In some implementations, the specific surface area of ​​the positive electrode is 0.6 m². 2 / g~3m 2 / g. Optionally, the specific surface area of ​​the positive electrode can be 0.6m. 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g、2m 2 / g、2.1m 2 / g, 2.2m 2 / g, 2.3m 2 / g, 2.4m 2 / g, 2.5m 2 / g, 2.6m 2 / g, 2.7m 2 / g, 2.8m 2 / g, 2.9m 2 / g、3m 2 / g and any value within the range consisting of any two of the above values.

[0057] 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.

[0058] In some embodiments, the specific surface area of ​​the positive electrode active material is 0.2 m². 2 / g~1m 2 / g. Within this range, the specific surface area of ​​the positive electrode active material allows the positive electrode sheet to have a suitable specific surface area, thereby promoting heat dissipation and further improving the thermal safety performance of the battery. Additionally, within this range, the specific surface area of ​​the positive electrode active material allows the electrolyte to fully wet the positive electrode active material, promoting lithium-ion transport and further improving the battery's cycle performance. Optionally, the specific surface area of ​​the positive electrode active material can be 0.2m². 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1m 2 / g and any value within the range consisting of any two of the above values.

[0059] In this application, the specific surface area of ​​the material can be tested using methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc., USA.

[0060] In some embodiments, the Dv50 of the positive electrode active material is 5 μm to 11 μm. A Dv50 within this range allows the positive electrode active material and the positive electrode sheet to have a suitable specific surface area, thereby promoting heat dissipation and improving the thermal safety performance of the battery. Optionally, the Dv50 of the positive electrode active material can be 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, or any value within the range of any two of the above values.

[0061] In this application, Dv50 represents the particle size corresponding to a cumulative volumetric distribution percentage of 50%. It can be determined according to standard GB / T19077-2016 using a laser particle size analyzer (such as a Malvern Master Size 3000).

[0062] In some embodiments, the porosity of the positive electrode active layer is 20% to 35%. A porosity within this range allows the electrolyte to fully wet the positive electrode sheet, further improving the battery's cycle performance. Optionally, the porosity of the positive electrode active layer can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or any value within the range of any two of the above values.

[0063] 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%.

[0064] In some embodiments, the compaction density of the positive electrode active layer is 3.4 g / cm³. 3 ~3.75g / cm 3 At this point, the lithium-ion battery exhibits a high energy density, while simultaneously promoting the wetting of the positive electrode by the electrolyte, further improving the battery's cycle performance. Optionally, the compaction density of the positive electrode active layer can be 3.4 g / cm³. 3 3.42 g / cm 3 3.45g / cm 3 3.48 g / cm 3 3.5g / cm 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.

[0065] 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 the electrode sheet, 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).

[0066] 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 thermal safety and cycle performance 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, good thermal safety, 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.

[0067] In some implementations, the specific surface area of ​​the single-crystal particles is 0.85 m². 2 / g~1.5m 2 / g. The specific surface area of ​​the single crystal particles is greater than or equal to 0.85m². 2 / g can give the positive electrode active material and positive electrode sheet a suitable specific surface area, promoting heat dissipation. The specific surface area of ​​single crystal particles is less than or equal to 1.5m². 2 / g can reduce the gas generation rate during battery thermal runaway, further improving the battery's thermal safety performance. Optionally, the specific surface area of ​​the single crystal particles can be 0.85m². 2 / g, 0.88m 2 / g, 0.9m 2 / g, 0.92m 2 / g, 0.95m 2 / g, 0.98m 2 / g, 1m 2 / g, 1.2m 2 / g, 1.5m 2 / g and any value within the range consisting of any two of the above values.

[0068] In some embodiments, the Dv50 of the single-crystal particles is 1.5 μm to 3 μm. A Dv50 within this range allows the positive electrode active material to have a suitable Dv50, resulting in a suitable specific surface area for both the positive electrode active material and the positive electrode sheet, thereby promoting heat dissipation and improving the thermal safety performance of the battery. Optionally, the Dv50 of the single-crystal particles can be 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, or any value within the range of any two of the above values.

[0069] In some implementations, the specific surface area of ​​the polycrystalline particles is 0.1 m². 2 / g~0.7m 2 / g. The specific surface area of ​​the polycrystalline particles is greater than or equal to 0.1m². 2 / g can give the positive electrode active material and positive electrode sheet a suitable specific surface area, promoting heat dissipation. The specific surface area of ​​polycrystalline particles is less than or equal to 0.7m². 2 / g can reduce the gas generation rate during battery thermal runaway, further improving the battery's thermal safety performance. Optionally, the specific surface area of ​​the polycrystalline particles can be 0.1m². 2 / g, 0.15m 2 / g, 0.2m 2 / g, 0.25m 2 / g, 0.3m 2 / g, 0.35m 2 / g, 0.4m 2 / g, 0.45m 2 / g, 0.5m 2 / g, 0.55m 2 / g, 0.6m 2 / g, 0.65m 2 / g, 0.7m 2 / g and any value within the range consisting of any two of the above values.

[0070] In some embodiments, the Dv50 of the polycrystalline particles is 7.5 μm to 11 μm. A Dv50 within this range allows the positive electrode active material to have a suitable Dv50, resulting in a suitable specific surface area for both the positive electrode active material and the positive electrode sheet, thereby promoting heat dissipation and improving the thermal safety performance of the battery. Optionally, the Dv50 of the polycrystalline particles can be 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, or any value within the range of any two of the above values.

[0071] In some embodiments, the positive electrode active layer comprises a conductive carbon material. The conductive carbon material has good conductivity, which can improve the conductivity of the positive electrode sheet, thereby improving the electrical performance of the battery.

[0072] Optionally, the conductive carbon material accounts for 0.3% to 2% of the mass percentage of the positive electrode active layer. Conductive carbon materials typically have a large specific surface area. A mass percentage of conductive carbon material in the positive electrode active layer of less than or equal to 2% can reduce side reactions on the positive electrode side and reduce heat generation. Conversely, a mass percentage of conductive carbon material in the positive electrode active layer of greater than or equal to 0.3% can fully utilize the conductivity of the conductive carbon material and promote improved conductivity of the positive electrode sheet. Furthermore, the large specific surface area of ​​conductive carbon materials within this range allows the positive electrode sheet to have a suitable specific surface area.

[0073] Further optionally, the mass percentage of conductive carbon material in the positive electrode active layer can be 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%, 2%, or any value within the range of any two of the above values.

[0074] As a non-limiting example, conductive carbon materials may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0075] In some embodiments, the amount of impure lithium in the positive electrode active material is less than or equal to 2000 ppm. Positive electrode active materials with impure lithium in this range have low water absorption, which can reduce the water content of the positive electrode, reduce side reactions of the positive electrode, and further improve the cycle performance of the battery.

[0076] Impure lithium content refers to the mass content of lithium in positive electrode active materials 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.

[0077] The amount of impure lithium can be tested as follows: Disassemble the lithium-ion 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.

[0078] 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.

[0079] In some embodiments, the thickness of the positive electrode current collector is 8 μm to 16 μm. In lithium-ion batteries, the positive electrode current collector typically includes aluminum foil, which provides good heat dissipation. LiFSI has a certain corrosive effect on aluminum foil; therefore, a positive electrode current collector with a thickness in the range of 8 μm to 16 μm exhibits good corrosion resistance, maintaining a relatively stable structure and thus ensuring good heat dissipation, further improving the thermal safety performance of the lithium-ion battery. Simultaneously, a positive electrode current collector thickness in the range of 8 μm to 16 μm can result in lower internal resistance in the battery, reducing internal heat generation and further improving thermal safety. Optionally, the thickness of the positive electrode current collector can be, but is not limited to, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, or any value within the range of any two of the above values. Further optionally, the thickness of the positive electrode current collector is 10 μm to 14 μm.

[0080] In some implementations, the water content of the positive electrode is less than or equal to 300 ppm. Positive electrode active materials with high nickel content have a certain water content. The presence of water in the positive electrode active material affects the thermal safety performance of lithium-ion batteries. For example, water may react with electrolyte salts in the electrolyte to produce hydrofluoric acid. The generation of hydrofluoric acid damages the solid electrolyte interphase (SEI) film and the positive electrode-electrolyte interphase (CEI) film inside the battery, increasing side reactions between the active material and the electrolyte and affecting the battery's cycle performance. When the water content of the positive electrode is less than or equal to 300 ppm, the adverse effects of water introduction on the battery can be reduced, internal side reactions can be decreased, and the battery's cycle performance can be further improved. It is understood that water in the positive electrode is difficult to completely remove; therefore, during the preparation of the positive electrode, the water content can be minimized by drying.

[0081] 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.

[0082] It is understandable that the presence of moisture in cathode active materials with high nickel content can affect the cycle performance of lithium-ion batteries. For example, moisture may react with electrolyte salts in the electrolyte, leading not only to electrolyte salt consumption but also to gas generation, thus affecting the cycle performance of the lithium-ion battery. In the lithium-ion battery of this application, LiFSI does not readily react with water, thereby improving the stability of the electrolyte and thus enhancing the cycle performance of the lithium-ion battery.

[0083] 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).

[0084] In some embodiments, the lithium-containing transition metal oxide includes 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.

[0085] 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 0.06 Mn 0.02 O2, LiNi 0.95 Co 0.04 Mn 0.01 O2, etc.

[0086] As some alternative examples of b, b can be 0, 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.

[0087] As some alternative examples of c, c can be 0, 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.

[0088] 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.

[0089] 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.

[0090] 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, 1.91, 1.92, 1.93, 1.94, 1.95, 1.96, 1.97, 1.98, 1.99, and any value within the range of any two of the above values. Optionally, 0 ≤ y ≤ 0.05.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] Electrolyte

[0099] The electrolyte plays a role in conducting lithium ions between the positive and negative electrode plates.

[0100] In some embodiments, lithium bisfluorosulfonylimide accounts for 9% to 17% of the electrolyte by mass. When the mass percentage of LiFSI in the electrolyte is in the range of 9% to 17%, the risk of corrosion of the positive electrode current collector can be reduced while improving the stability of the electrolyte, thus maintaining good heat dissipation of the positive electrode current collector and further improving the thermal safety 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%, 17.5%, or any value within the range of any two of the above values.

[0101] In some embodiments, the electrolyte salt also includes lithium hexafluorophosphate (LiPF6). In lithium-ion batteries, LiPF6 can passivate the aluminum foil to a certain extent, thereby reducing the risk of the positive electrode current collector being corroded by LiFSI, maintaining good heat dissipation of the positive electrode current collector, and further improving the thermal safety performance of lithium-ion batteries.

[0102] Optionally, 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 limiting the reaction between LiPF6 and water. Since LiFSI does not readily react with water, the combination of LiFSI and LiPF6 can reduce the reaction between electrolyte salts and water in the electrolyte, improve electrolyte stability, and simultaneously reduce the risk of corrosion of the positive electrode current collector, further improving the thermal safety and cycle performance of the lithium-ion battery.

[0103] Optionally, the mass percentage of lithium hexafluorophosphate in the electrolyte is 1% to 8%. A mass percentage of LiPF6 in the electrolyte within this range can further reduce the risk of LiPF6 reacting with water, which is beneficial for maintaining good battery cycle performance. More preferably, the mass percentage of LiPF6 in the electrolyte can be 1%, 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%, 6.8%, 7%, 7.2%, 7.5%, 8%, or any value within the range of any two of the above values.

[0104] 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. This, in turn, enables higher lithium-ion transport rates, further improving the battery's thermal safety and 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, increased heat generation, and slower lithium-ion transport, thus affecting the battery's thermal safety and 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 negatively impacting the battery's 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.

[0105] 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).

[0106] 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 lithium-ion 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 lithium-ion battery.

[0107] Optionally, the fluorosulfonate constitutes 0.01% to 0.5% of the electrolyte by mass. Within this range, the fluorosulfonate content allows the SEI film to maintain good toughness while fully leveraging its ability to improve SEI film stability. When the electrode materials of the lithium-ion battery 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 content 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.

[0108] 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.

[0109] In some embodiments, the electrolyte may further include film-forming additives. Film-forming additives can improve the film-forming performance of the interfacial film inside the lithium-ion 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.

[0110] 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.

[0111] Negative electrode film-forming additives are beneficial for promoting the formation of the 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.

[0112] 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).

[0113] In some embodiments, the electrolyte may also include other functional additives, such as additives that improve the overcharge performance of lithium-ion batteries, additives that improve the high-temperature or low-temperature performance of batteries, etc.

[0114] 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).

[0115] In some embodiments, ethylene carbonate constitutes less than or equal to 35% of the solvent by mass. The coordination between lithium ions and bis(fluorosulfonyl)imide ions in the electrolyte allows LiFSI to improve battery thermal safety and cycle performance. However, under solvation, EC competes with bis(fluorosulfonyl)imide ions for coordination with lithium ions, disrupting the coordination between them and thus affecting the effectiveness of LiFSI and hindering the improvement of battery thermal safety and cycle performance. Simultaneously, the oxidative decomposition of EC itself deteriorates battery thermal safety. Therefore, a lower percentage of EC in the solvent by mass is beneficial for improving the thermal safety and cycle performance of lithium-ion batteries.

[0116] 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.

[0117] 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 reduce the heat generated inside the battery due to side reactions, thereby maintaining better thermal safety and cycle performance of the battery.

[0118] 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, in grams, and the volume of the electrolyte, V1, in liters, are recorded. An indicator is added to the electrolyte. 0.01 mol / L NaOH is added dropwise until the electrolyte is full, and the volume of the electrolyte at this point, V2, is recorded. The volume of NaOH added is V2 - V1. The hydrofluoric acid content in the electrolyte (ppm) = (V2 - V1) × 200 / m.

[0119] 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.

[0120] [Negative electrode plate]

[0121] The negative electrode sheet includes a negative current collector and a positive active layer located on at least one surface of the negative current collector.

[0122] The negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0123] In some implementations, the specific surface area of ​​the negative electrode is 0.5 m². 2 / g~3m 2 / g. Within this range, the specific surface area of ​​the negative electrode sheet can provide good heat dissipation while keeping side reactions at the negative electrode sheet at a low level, further improving the battery's thermal safety and cycle performance. Optionally, the specific surface area of ​​the negative electrode sheet can be 0.5 μm. 2 / g, 0.8m 2 / g, 1m 2 / g, 1.3m 2 / g, 1.5m 2 / g, 1.8m 2 / g、2m 2 / g, 2.3m 2 / g, 2.5m 2 / g, 2.8m 2 / g、3m 2 / g and any value within the range consisting of any two of the above values.

[0124] Understandably, the specific surface area of ​​the negative electrode can be tested using the same method described above for testing the specific surface area of ​​the positive electrode.

[0125] In some embodiments, the compaction density of the negative electrode active layer is 1.5 g / cm³. 3 ~1.8g / cm 3 At this point, the lithium-ion battery exhibits a high energy density, while simultaneously promoting the wetting of the negative electrode by the electrolyte, further improving the battery's cycle performance. 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 / cm 3 And any value within the range consisting of any two of the above values.

[0126] In some implementations, the moisture content of the negative electrode is less than or equal to 200 ppm. When the moisture content of the negative electrode is less than or equal to 200 ppm, the adverse effects of moisture introduction on the battery can be reduced, internal side reactions can be decreased, and the battery's cycle performance can be further improved. 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 through drying.

[0127] 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.

[0128] 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).

[0129] 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.

[0130] 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).

[0131] 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.

[0132] In some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0133] 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.

[0134] [Isolation membrane]

[0135] It is understood that lithium-ion batteries may also include 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.

[0136] 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.

[0137] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0138] In some embodiments, the lithium-ion battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0139] In some embodiments, the outer packaging of the lithium-ion battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the lithium-ion battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0140] 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.

[0141] 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.

[0142] In some implementations, the lithium-ion battery can be a single cell, a battery module, or a battery pack.

[0143] 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.

[0144] 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.

[0145] Optionally, the battery module may also include a housing with a receiving space in which multiple lithium-ion batteries are housed.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] As an electrical device, lithium-ion batteries can be selected based on its usage requirements.

[0150] 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.

[0151] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can be powered by a battery.

[0152] 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.

[0153] 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.

[0154] Example 1

[0155] (1) Positive electrode plate

[0156] LiNi, the positive electrode active material 0.9 Co 0.09 Mn 0.01 O2, polyvinylidene fluoride (PVDF) binder, and conductive carbon black were mixed in a weight ratio of 98:1.2:0.8, and N-methylpyrrolidone (NMP) solvent was added. The mixture was stirred to prepare a positive electrode slurry. This slurry was then coated onto a 13 μm thick aluminum foil, dried, and subsequently cold-pressed, slit, and cut to form the positive electrode sheet. The positive electrode active material contained 1800 ppm of impurity lithium and consisted of polycrystalline and single-crystal particles in a mass ratio of 8:2. The polycrystalline particles had a Dv50 of 9.5 μm and a specific surface area of ​​0.3 m². 2 / g. The Dv50 of the single crystal particles is 2.3μm, and the specific surface area of ​​the single crystal particles is 1.2m². 2 / g. The Dv50 of the positive electrode active material is 8μm. The specific surface area of ​​the positive electrode active material is 0.4m². 2 / g. The specific surface area of ​​the positive electrode is 0.9m².2 / g. 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%.

[0157] (2) Negative electrode plate

[0158] 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 as a current collector, dried, and subsequently cold-pressed, slit, and cut into sheets to form the negative electrode sheet. The Dv50 of the negative electrode active material was 12.5 μm. The specific surface area of ​​the negative electrode active material was 1 m². 2 / g. The specific surface area of ​​the negative electrode is 1.3m². 2 / g. The compaction density of the negative electrode active layer is 1.65 g / cm³. 3 .

[0159] (3) Separating membrane

[0160] Polyethylene (PE) film is used as the separator.

[0161] (4) Electrolyte

[0162] In an argon-atmospheric glove box with a water content <1 ppm and an oxygen content <1 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 20:80 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, and finally lithium salts LiFSI and LiPF6 were added. 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 47 ppm.

[0163] (5) Lithium-ion batteries

[0164] 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.

[0165] Examples 2 to 11, Comparative Examples 1 to 3

[0166] The differences between Examples 2 to 11 and Comparative Examples 1 to 3 compared to Example 1 are shown in Table 1.

[0167] Test case

[0168] (1) The lithium-ion battery was subjected to a hot box test. The test method was as follows:

[0169] At 25℃, the lithium-ion battery was discharged to 2.8V at a rate of 0.33C, allowed to stand for 30 minutes, and then charged at a constant current rate of 0.33C to 4.25V. It was then charged at a constant voltage until the current was less than or equal to 0.05C, and allowed to stand for 1 hour. The lithium-ion battery was then placed in a temperature chamber, and the temperature was increased to 100℃ at a rate of 5℃ / min and held for 1 hour. The temperature was then increased again at a rate of 5℃ / min, held for 30 minutes each time, until the battery failed (the battery temperature and positive and negative electrode voltage changes were recorded in real time; any sudden change in temperature or voltage was considered a thermal runaway failure). Finally, the temperature chamber heating program was turned off, and the chamber was held for 1 hour. The temperature and time of battery failure in the temperature chamber were recorded. The test results are shown in Table 2. A higher temperature at which the temperature chamber fails indicates better performance. At the same failure temperature, a longer failure time indicates better performance.

[0170] (2) The cycle capacity retention rate of lithium-ion batteries was tested using the following method:

[0171] At 45°C, the lithium-ion battery was charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage of 4.25V until the current was less than 0.05C. Finally, the lithium-ion battery was discharged at a constant current of 0.33C to 2.8V. This constitutes one charge-discharge cycle. This charging and discharging process was repeated, and the capacity retention rate of the lithium-ion battery after 1000 cycles was calculated.

[0172] The capacity retention rate (%) of a lithium-ion battery after 1000 cycles at 45℃ is calculated as follows: (Discharge capacity of the 1000th cycle / Discharge capacity of the first cycle) × 100%. The test results are shown in Table 2.

[0173] Table 1

[0174] Table 2

[0175] In Table 1, the unit for Dv50 of the positive electrode active material is μm. The unit for the specific surface area (BET) of the positive electrode active material is m². 2 / g. In the "Active Material Crystal Form" column, "polycrystalline" indicates polycrystalline particles, "monocrystalline" indicates monocrystalline particles, and "polycrystalline:monocrystalline" indicates the mass ratio of polycrystalline particles to monocrystalline particles. "Conductive carbon material" indicates the mass percentage of conductive carbon material in the positive electrode active layer, in %. The unit for the BET of the positive electrode sheet is m.2 / g. Aluminum foil thickness is measured in μm. Anode active material Dv50 is measured in μm. Anode active material BET is measured in m. 2 / g. The unit for the negative electrode BET is m. 2 / g. In the electrolyte, the columns for LiFSI, LiPF6, LiFSO3, FEC, and PS represent the mass percentages of LiFSI, LiPF6, LiFSO3, FEC, and PS in the electrolyte, respectively. The column for EC represents the mass percentage of EC in the electrolyte relative to the solvent. The results of the hot box test indicate the temperature and time at which the battery failed. The cycle capacity retention rate represents the capacity retention rate of the battery after 1000 cycles. In Table 1, " / " indicates that the corresponding component was not added.

[0176] As can be seen from Tables 1 and 2, the hot-box test performance and cycle capacity retention of Examples 1 to 11 are higher than those of Comparative Examples 1 to 3, indicating that in the ion battery of this application, through high-nickel lithium-containing transition metal oxides and a positive electrode with a specific surface area of ​​0.6 m², the battery achieves high performance. 2 / g~3m 2 With the addition of LiFSI within the / g range, the battery can achieve both good thermal safety performance and good cycle performance.

[0177] As can be seen from Examples 1 and 5, the thermal safety performance of the battery can be further improved when the aluminum foil thickness is within a suitable range.

[0178] As can be seen from Examples 1 and 6, the specific surface area of ​​the negative electrode sheet within a suitable range can further improve the thermal safety performance and cycle performance of the battery.

[0179] As can be seen from Examples 1 and 7, including LiPF6 in the electrolyte can further improve the thermal safety performance of the battery.

[0180] As can be seen from Examples 1 and 8, including fluorosulfonates in the electrolyte can further improve the cycle performance of the battery.

[0181] As can be seen from Examples 1 and 9, a smaller mass percentage of EC in the electrolyte is beneficial to improving the thermal safety and cycle performance of lithium-ion batteries.

[0182] As can be seen from Examples 1 and 10, the positive electrode active material includes polycrystalline particles and monocrystalline particles, which is beneficial to improving the thermal safety performance and cycle performance of the battery.

[0183] 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.

[0184] 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 comprising 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 specific surface area of ​​the positive electrode is 0.6 m². 2 / g~3m 2 / g; the electrolyte comprises an electrolyte salt, which includes lithium difluorosulfonylimide.

2. The lithium-ion battery according to claim 1, wherein, The positive electrode active layer satisfies one or more of the following characteristics: (1) The porosity of the positive electrode active layer is 20% to 35%; (2) The compaction density of the positive electrode active layer is 3.4 g / cm³. 3 ~3.75g / cm 3 ; (3) The Dv50 of the positive electrode active material is 5μm to 11μm; (4) The specific surface area of ​​the positive electrode active material is 0.2 m². 2 / g~1m 2 / g.

3. The lithium-ion battery according to any one of claims 1 to 2, wherein, The positive electrode active material includes polycrystalline particles and single-crystal particles.

4. The lithium-ion battery according to claim 3, wherein, The positive electrode active material satisfies one or more of the following characteristics: (1) The mass ratio of the polycrystalline particles to the single crystal particles is 7:3 to 9:1; (2) The Dv50 of the single crystal particles is 1.5μm to 3μm; (3) The specific surface area of ​​the single crystal particles is 0.85 m². 2 / g~1.5m 2 / g; (4) The Dv50 of the polycrystalline particles is 7.5μm to 11μm; (5) The specific surface area of ​​the polycrystalline particles is 0.1 m². 2 / g~0.7m 2 / g.

5. The lithium-ion battery according to any one of claims 1 to 4, wherein, The positive electrode active layer comprises a conductive carbon material; optionally, the conductive carbon material accounts for 0.3% to 2% of the mass percentage of the positive electrode active layer.

6. The lithium-ion battery according to any one of claims 1 to 5, wherein, The thickness of the positive electrode current collector is 8μm to 16μm.

7. The lithium-ion battery according to any one of claims 1 to 6, wherein, The lithium difluorosulfonylimide accounts for 9% to 17% of the mass of the electrolyte.

8. The lithium-ion battery according to any one of claims 1 to 7, wherein, The electrolyte salt also includes lithium hexafluorophosphate.

9. The lithium-ion battery according to claim 8, wherein, The mass percentage of lithium difluorosulfonylimide in the electrolyte is greater than the mass percentage of lithium hexafluorophosphate in the electrolyte.

10. The lithium-ion battery according to any one of claims 8 to 9, wherein, The lithium hexafluorophosphate accounts for 1% to 8% of the mass of the electrolyte.

11. The lithium-ion battery according to any one of claims 8 to 10, wherein, The sum of the mass percentages of the lithium difluorosulfonyl imide and the lithium hexafluorophosphate in the electrolyte is 11.5% to 22%.

12. The lithium-ion battery according to any one of claims 1 to 11, wherein, The electrolyte also includes fluorosulfonate.

13. The lithium-ion battery according to claim 12, wherein, The fluorosulfonate accounts for 0.01% to 0.5% of the mass of the electrolyte.

14. The lithium-ion battery according to any one of claims 12 to 13, 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.

15. The lithium-ion battery according to any one of claims 1 to 14, wherein, The electrolyte includes a solvent; the mass percentage of ethylene carbonate in the solvent is less than or equal to 35%.

16. The lithium-ion battery according to any one of claims 1 to 15, wherein, The specific surface area of ​​the negative electrode sheet is 0.5 m². 2 / g~3m 2 / g.

17. An electrical device comprising a lithium-ion battery as claimed in any one of claims 1 to 16.

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