Lithium-ion battery and electric device

Abstract

Disclosed in the present application are a lithium-ion battery and an electric device. A negative electrode film layer of a negative electrode sheet of the lithium-ion battery comprises a first negative electrode film layer and a second negative electrode film layer, wherein the specific capacity of a negative electrode active material of the first negative electrode film layer is less than or equal to the specific capacity of a negative electrode active material of the second negative electrode film layer; the first negative electrode active material comprises first graphite and a first carbon coating layer, and the second negative electrode active material comprises second graphite and a second carbon coating layer; and the weight proportion of the first carbon coating layer in the first negative electrode film layer is greater than or equal to the weight proportion of the second carbon coating layer in the second negative electrode film layer. In the embodiments of the present application, by means of the layered arrangement of the negative electrode film layers, differentiated regulation and control of the specific capacity of the negative electrode active material of each layer and the weight proportions of the carbon coating layers are achieved, and the charging performance of the lithium-ion battery is improved while the energy density and cycle life of the lithium-ion battery are also taken into consideration.

Description

Lithium-ion batteries and electrical equipment

[0001] This disclosure claims priority to Chinese patent application No. 2024115236275, filed on October 29, 2024, entitled “Lithium-ion Battery and Electrical Device”, which is incorporated herein by reference in its entirety. Technical Field

[0002] This invention relates to the field of new energy technology, and in particular to a lithium-ion battery and electrical equipment. Background Technology

[0003] This section provides only background information relevant to this application and is not necessarily prior art.

[0004] Lithium-ion batteries are widely used in wireless communication, transportation, aerospace, and many other fields. With continuous technological advancements, lithium-ion batteries will continue to play a vital role and drive innovation in energy storage technology. For lithium-ion batteries, cycle life and charging performance are crucial factors for their long-term development.

[0005] Therefore, this invention is proposed. Summary of the Invention

[0006] In view of the technical problems existing in the background art, this application provides a lithium-ion battery and electrical device, which aims to enable the lithium-ion battery to take into account both long cycle life and charging performance.

[0007] To achieve the above objectives, a first aspect of this application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector; the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer; the second negative electrode film layer is disposed between the negative current collector and the first negative electrode film layer;

[0008] The first negative electrode film layer includes a first negative electrode active material, and the second negative electrode film layer includes a second negative electrode active material; the specific capacity of the first negative electrode active material is less than or equal to the specific capacity of the second negative electrode active material.

[0009] The first negative electrode active material includes a first graphite and a first carbon coating layer covering at least a portion of the surface of the first graphite; the second negative electrode active material includes a second graphite and a second carbon coating layer covering at least a portion of the surface of the second graphite; the weight percentage of the first carbon coating layer in the first negative electrode film is greater than or equal to the weight percentage of the second carbon coating layer in the second negative electrode film.

[0010] The embodiments of this application improve the charging performance of lithium-ion batteries while maintaining energy density and cycle life by differentially controlling the specific capacity of the negative electrode active material and the weight ratio of the carbon coating layer in each layer through a layered negative electrode film. Specifically, the embodiments of this application improve the charging performance of lithium-ion batteries while maintaining energy density by gradient designing the specific capacity of the negative electrode active material in the first and second negative electrode film layers. Specifically, in the first and second negative electrode active materials, the specific capacity of the second negative electrode active material is controlled to be higher, resulting in a better energy density for the negative electrode film layer, while the specific capacity of the first negative electrode film layer is controlled to be lower, allowing for the design of more ion transport channels and improving the diffusion rate of lithium ions in the particles of the first negative electrode active material, thereby improving the charging performance of the lithium-ion battery. The embodiments of this application also improve the charging performance of lithium-ion batteries while maintaining cycle life by gradient designing the weight ratio of the carbon coating layer in the first and second negative electrode film layers. Specifically, in the first and second negative electrode films, the first carbon coating layer accounts for a larger weight proportion of the first negative electrode film, which is beneficial to increasing the number of sites for intercalation and deintercalation of active ions in the first negative electrode active material and improving the diffusion rate of active ions in the negative electrode active material particles, thereby improving the charging performance of the lithium-ion battery. The second carbon coating layer accounts for a smaller weight proportion of the second negative electrode film, resulting in fewer surface defects in the second negative electrode active material and better structural stability, which is beneficial to improving the cycle life of the lithium-ion battery.

[0011] In some embodiments, the specific capacity of the first negative electrode active material is less than or equal to 350 mAh / g, and the specific capacity of the second negative electrode active material is greater than or equal to 350 mAh / g.

[0012] The embodiments of this application improve the charging performance of lithium-ion batteries while taking into account their energy density by employing the first and second negative electrode active materials within the aforementioned specific capacity range.

[0013] In some embodiments, the specific capacity of the first negative electrode active material is greater than or equal to 325 mAh / g and less than or equal to 350 mAh / g.

[0014] The embodiments of this application, by employing the first negative electrode active material within the aforementioned specific capacity range, facilitate the improvement of the charging performance of lithium-ion batteries while maintaining the energy density of lithium-ion batteries.

[0015] In some embodiments, the specific capacity of the second negative electrode active material is greater than or equal to 355 mAh / g and less than or equal to 370 mAh / g.

[0016] The embodiments of this application employ a second negative electrode active material within the aforementioned specific capacity range, which is beneficial for improving the energy density of lithium-ion batteries and enabling them to have good cycle life.

[0017] In some embodiments, the first carbon coating layer accounts for 5% to 8% of the weight of the first negative electrode film layer; the second carbon coating layer accounts for 2% to 5% of the weight of the second negative electrode film layer.

[0018] The embodiments of this application improve the charging performance of lithium-ion batteries while taking into account their cycle life by using a first negative electrode film layer and a second negative electrode film layer within the weight percentage range of the above-mentioned carbon coating layer.

[0019] In some embodiments, the weight ratio of the first negative electrode film layer and the second negative electrode film layer is 4:6 to 5:5.

[0020] The embodiments of this application improve the charging performance of lithium-ion batteries by setting the first negative electrode film layer and the second negative electrode film layer within the above weight ratio range, while taking into account the energy density and cycle life of lithium-ion batteries.

[0021] In some embodiments, the compaction density of the negative electrode film is greater than or equal to 1.25 g / cc.

[0022] The negative electrode film layer of the embodiments of this application adopts the above-mentioned compaction density, which is beneficial to improving the energy density of lithium-ion batteries.

[0023] In some embodiments, the compaction density of the negative electrode film is greater than or equal to 1.25 g / cc and less than or equal to 2.0 g / cc.

[0024] The negative electrode film layer of the embodiments of this application adopts the above-mentioned compaction density, which is beneficial to improve the energy density of lithium-ion batteries while taking into account the structural stability of the negative electrode film layer.

[0025] In some embodiments, the electrolyte includes a solvent; the solvent includes a first solvent, which includes one or both of carboxylic acid ester solvents and ether solvents; based on the total weight of the solvents, the weight percentage of the first solvent is greater than or equal to 0 and less than or equal to 30%.

[0026] The embodiments of this application reduce the occurrence of film-forming side reactions and gas generation between the electrolyte and the negative electrode during battery cycling by adjusting the weight ratio of the first solvent in the electrolyte, thereby improving the film-forming stability of the electrolyte on the negative electrode sheet and enhancing the cycle life of the lithium-ion battery.

[0027] In some embodiments, the carboxylic acid ester solvent includes one or more of the following compounds in which the aforementioned carboxylic acid ester solvents are partially or completely substituted: γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, methyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, isobutyl propionate, pentyl propionate, isopentyl propionate, ethyl isobutyl propionate, methyl butyrate, ethyl butyrate, ethyl isobutyl butyrate, butyl butyrate, butyl isobutyl butyrate, pentyl butyrate, isopentyl butyrate, ethyl isopentyl valerate, ethyl isopentyl valerate, propyl isopentyl valerate, propyl isopentyl valerate, and compounds in which the aforementioned carboxylic acid ester solvents are partially or completely substituted.

[0028] The embodiments of this application use carboxylic acid ester solvents within the above-mentioned range. The high conductivity, low surface tension, and low viscosity of carboxylic acid ester solvents enhance the migration speed of lithium ions, facilitate sufficient and effective contact between the active material and the electrolyte, and improve the charging performance of lithium-ion batteries.

[0029] In some embodiments, the ether solvent includes one or both of cyclic ether solvents and chain ether solvents; wherein the cyclic ether solvent includes one or both of tetrahydrofuran and 2-methyl-tetrahydrofuran; and the chain ether solvent includes one or both of dimethylmethane and 1,2-dimethylethane.

[0030] The embodiments of this application use ether solvents within the above-mentioned range to improve the charging performance of lithium-ion batteries.

[0031] In some embodiments, the weight percentage of the first solvent is between 10% and 30% based on the total weight of the solvent.

[0032] The embodiments of this application use the first solvent with the above-mentioned weight ratio to improve the charging performance of lithium-ion batteries.

[0033] In some embodiments, the electrolyte further includes a second solvent, which includes a carbonate solvent, and the weight percentage of the second solvent is between 70% and 90% based on the total weight of the solvent.

[0034] The embodiments of this application improve the cycle life of lithium-ion batteries by reducing the side reactions and gas generation that occur with the negative electrode during battery cycling using a second solvent.

[0035] In some embodiments, carbonate solvents include one or more of ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, butylene carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and compounds in which the foregoing compounds are partially or completely substituted.

[0036] The embodiments of this application use carbonate solvents within the above-mentioned range to reduce film-forming side reactions and gas generation with the negative electrode during battery cycling, thereby improving the cycle performance of lithium-ion batteries.

[0037] In some embodiments, the conductivity of the electrolyte is between 7.2 mS / cm and 13.3 mS / cm.

[0038] The embodiments of this application improve the transport capability of lithium ions in the electrolyte and enhance the charging performance of lithium-ion batteries by using electrolytes within the above-mentioned conductivity range.

[0039] In some embodiments, the electrolyte injection coefficient is greater than or equal to 2.8 g / Ah.

[0040] The embodiments of this application improve the uniformity of electrolyte distribution inside the lithium-ion battery by using electrolytes within the above-mentioned electrolyte injection coefficient range, improve the film formation stability of electrolytes on the negative electrode sheet, and enhance the cycle life of the lithium-ion battery.

[0041] In some embodiments, the electrolyte injection coefficient is greater than or equal to 2.8 g / Ah and less than or equal to 3.8 g / Ah.

[0042] The embodiments of this application improve the uniformity of electrolyte distribution inside the lithium-ion battery by using electrolytes within the above-mentioned electrolyte injection coefficient range, improve the film formation stability of electrolytes on the negative electrode sheet, and enhance the cycle life of the lithium-ion battery.

[0043] In some embodiments, the density of the electrolyte is 0.8 g / cm³. 3 ~1.5g / cm 3 .

[0044] The embodiments of this application use electrolytes within the aforementioned density range, which is beneficial for the electrolytes to have suitable conductivity and viscosity, so that lithium ions have good transport capabilities in the electrolyte and improve the charging performance of lithium-ion batteries.

[0045] In some embodiments, the electrolyte includes a lithium salt; the concentration of the lithium salt in the electrolyte is between 0.7 mol / L and 1 mol / L.

[0046] The embodiments of this application, by employing lithium salts of the above concentration, are beneficial to improving the film-forming stability of the electrolyte at the negative electrode, regulating the conductivity of the electrolyte, enhancing the migration rate of lithium ions, and improving the cycle life of lithium-ion batteries.

[0047] In some embodiments, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; the positive electrode film layer includes a positive electrode active material; the positive electrode active material includes one or two of lithium nickel cobalt manganese oxide and lithium phosphate with an olivine structure.

[0048] The embodiments of this application employ positive electrode sheets comprising the above-mentioned positive electrode active materials, which is beneficial for improving the cycle life and / or energy density of lithium-ion batteries.

[0049] Secondly, embodiments of this application provide an electrical device including the lithium-ion battery provided in the first aspect.

[0050] The electrical devices provided by the embodiments of this application have at least the same advantages as lithium-ion batteries, which can improve the battery life of the electrical devices. Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. Other drawings can be obtained based on these drawings without creative effort.

[0052] Figure 1 is a schematic diagram of the vehicle structure provided in an embodiment of this application;

[0053] Figure 2 is an exploded structural diagram of a lithium-ion battery provided in an embodiment of this application;

[0054] Figure 3 is an exploded structural diagram of a battery cell provided in an embodiment of this application.

[0055] Explanation of reference numerals: 1000-vehicle, 100-lithium-ion battery, 200-controller, 300-motor, 10-box, 20-cell battery, 11-first part, 12-second part, 21-end cap, 22-housing, 23-electrode assembly, 21a-electrode terminal. Detailed Implementation

[0056] The present application will be further described below with reference to specific embodiments. It should be understood that these specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0057] For the sake of brevity, this article only discloses some specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value, or with other lower or upper limits, to form an unspecified range.

[0058] In this description, unless otherwise stated, the term "or" is inclusive. That is, the phrase "A or (or) B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0059] In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" include the number itself, and "several" in "one or more" means two or more.

[0060] Unless otherwise stated, the terms used in this application have their common meanings in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0061] New energy vehicles powered by lithium-ion batteries are pursuing longer driving ranges and faster and more convenient recharging methods, which puts higher demands on the research and development of lithium-ion batteries. However, conventional methods of improving charging often deteriorate cycle life.

[0062] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use lithium-ion batteries, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0063] For ease of explanation, the following embodiments will be described using a vehicle 1000 as an example of an electrical device according to an embodiment of this application.

[0064] Please refer to Figure 1, which is a structural schematic diagram of a vehicle provided in an embodiment of this application.

[0065] Referring to Figure 1, vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A lithium-ion battery 100 is installed inside vehicle 1000, which can be located at the bottom, front, or rear of vehicle 1000. The lithium-ion battery 100 can be used to power vehicle 1000; for example, it can serve as the operating power source for vehicle 1000. Vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 controls the lithium-ion battery 100 to supply power to the motor 300, for example, to meet the power needs of vehicle 1000 during startup, navigation, and driving.

[0066] In some embodiments of this application, the lithium-ion battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0067] Please refer to Figure 2, which is a schematic diagram of the exploded structure of a lithium-ion battery provided in an embodiment of this application.

[0068] Referring to Figure 2, the lithium-ion battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 provides a space for the battery cell 20 and can have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, collectively defining a space for accommodating the battery cell 20. The second portion 12 can be a hollow structure with one open end, and the first portion 11 can be a plate-like structure, covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 together define the space. Alternatively, both the first portion 11 and the second portion 12 can be hollow structures with one open side, with the open side of the first portion 11 covering the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can have various shapes, such as a cylinder, a cuboid, etc.

[0069] In the lithium-ion battery 100, there can be multiple battery cells 20, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 20 is housed within the casing 10. Alternatively, the lithium-ion battery 100 can also consist of multiple battery cells 20 first connected in series, parallel, or in a mixed manner to form a battery module, and then these battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the casing 10. The lithium-ion battery 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 20.

[0070] Among them, the battery cell 20 can be in the form of a cylinder, a flat shape, a cuboid, or other shapes.

[0071] Please refer to Figure 3, which is an exploded structural diagram of a battery cell provided in an embodiment of this application.

[0072] Referring to Figure 3, the battery cell 20 refers to the smallest unit that makes up the lithium-ion battery 100. The battery cell 20 includes an end cap 21, a housing 22, an electrode assembly 23, and other functional components.

[0073] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. The shape of end cap 21 can be adapted to the shape of housing 22 to fit it. Optionally, end cap 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 21 is not easily deformed under pressure and impact, giving battery cell 20 higher structural strength and improved safety performance. Functional components such as electrode terminals 21a can be provided on end cap 21. Electrode terminals 21a can be used for electrical connection with electrode assembly 23 for outputting or inputting electrical energy to battery cell 20. In some embodiments, end cap 21 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of battery cell 20 reaches a threshold. The material of end cap 21 can also be various, including but not limited to copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. In some embodiments, an insulating element may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0074] The housing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can accommodate the electrode assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 closes the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and the housing 22 can be integrated. Specifically, the end cap 21 and the housing 22 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 22, the end cap 21 closes the housing 22. The housing 22 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the electrode assembly 23. The housing 22 can be made of various materials, including but not limited to copper, iron, aluminum, stainless steel, aluminum alloy, and plastic.

[0075] Electrode assembly 23 is the component in the battery cell 20 where electrochemical reactions occur. The casing 22 may contain one or more electrode assemblies 23. The electrode assembly 23 is mainly formed by winding or stacking positive and negative electrode sheets, and typically a separator is provided between the positive and negative electrode sheets. The portions of the positive and negative electrode sheets containing active material constitute the main body of the cell assembly, while the portions of the positive and negative electrode sheets without active material each constitute a tab. The positive and negative tabs may be located together at one end of the main body or separately at both ends of the main body. During the charging and discharging process of the battery cell 20, the positive and negative active materials react with the electrolyte, and the tabs connect to the electrode terminals to form a current loop.

[0076] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode active material, which may include, but is not limited to, one or more of the following materials: lithium phosphates with an olivine structure, lithium nickel cobalt manganese oxides, and their respective modified compounds. These positive electrode active materials may be used alone or in combination. Examples of lithium nickel cobalt manganese oxides include, but are not limited to, LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2( It can also be abbreviated as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 One or more of O2 (also referred to as NCM811). Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0077] In one embodiment, the positive electrode film layer further includes a positive electrode conductive agent and a positive electrode binder.

[0078] A positive electrode conductive agent imparts conductivity to the positive electrode. The positive electrode conductive agent can include any conductive material, as long as it does not cause a chemical change. Positive electrode conductive agents include, but are not limited to: carbon-based materials (e.g., natural graphite, conductive graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0079] Positive electrode binders improve the adhesion stability of the positive electrode film and reduce the probability of powder shedding. Positive electrode binders may include one or more of the following: styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), lithium-ionized polyacrylic acid (PAALi), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0080] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

[0081] In some embodiments, the negative electrode film layer includes a negative electrode active material. The negative electrode active material may be any negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include, but is not limited to, at least one of the following materials: artificial graphite, natural graphite, etc. These negative electrode active materials may be used alone or in combination of two or more.

[0082] In some embodiments, the negative electrode film layer may further include a negative electrode binder, a negative electrode conductive agent, and other optional additives. For example, the negative electrode conductive agent may be one or more of superconducting carbon, carbon black (examples may include acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. For example, the negative electrode binder may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), lithium-ionized polyacrylic acid (PAALi), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB). For example, other optional additives may be thickeners and dispersants (e.g., sodium carboxymethyl cellulose CMC-Na) and PTC thermistor materials.

[0083] In some embodiments, the material of the separator can be selected from one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer can be the same or different.

[0084] To achieve the above objectives, a first aspect of this application provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector; the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer; the second negative electrode film layer is disposed between the negative current collector and the first negative electrode film layer; the first negative electrode film layer includes a first negative electrode active material; the second negative electrode film layer includes a second negative electrode active material; the specific capacity of the first negative electrode active material is less than or equal to the specific capacity of the second negative electrode active material; wherein the first negative electrode active material includes a first graphite and a first carbon coating layer covering at least a portion of the surface of the first graphite, and the second negative electrode active material includes a second graphite and a second carbon coating layer covering at least a portion of the surface of the second graphite; the weight percentage of the first carbon coating layer in the first negative electrode film layer is greater than or equal to the weight percentage of the second carbon coating layer in the second negative electrode film layer.

[0085] The specific capacity of the negative electrode active material refers to the ratio of the electrical capacity that the negative electrode active material inside the lithium-ion battery can release to the mass of the negative electrode active material. It is an important indicator for measuring the energy storage capacity of the negative electrode material of lithium-ion batteries, and is usually expressed in milliampere-hours per gram (mAh / g).

[0086] The specific capacity of the negative electrode active material can be tested using any known method. As an example, a method for testing the specific capacity of the negative electrode active material may include: assembling a CR2430 coin cell using the negative electrode sheet of this invention as the positive electrode, a lithium metal sheet as the negative electrode, a separator, and an electrolyte in an argon-protected glove box. The resulting coin cell is left to stand for 12 hours, then discharged at a constant current of 0.05C to 0.005V, left to stand for 10 minutes, then discharged at a constant current of 50μA to 0.005V, left to stand for 10 minutes, and then discharged at a constant current of 10μA to 0.005V. Finally, it is charged at a constant current of 0.1C to 2V, and the charging capacity is recorded. The ratio of the charging capacity to the mass of the negative electrode active material is the specific capacity of the negative electrode active material.

[0087] Compared to graphite, carbon coatings have a greater number of surface defects, which helps to increase the number of sites for the insertion and extraction of active ions in the negative electrode active material. This allows active ions to diffuse more quickly within the particles of the negative electrode active material, thereby improving the charging performance of lithium-ion batteries.

[0088] The embodiments of this application improve the charging performance of lithium-ion batteries while maintaining energy density and cycle life by differentially controlling the specific capacity of the negative electrode active material and the weight ratio of the carbon coating layer in each layer through a layered negative electrode film. Specifically, the embodiments of this application improve the charging performance of lithium-ion batteries while maintaining energy density by gradient designing the specific capacity of the negative electrode active material in the first and second negative electrode film layers. Specifically, in the first and second negative electrode active materials, the specific capacity of the second negative electrode active material is controlled to be higher, resulting in a better energy density for the negative electrode film layer, while the specific capacity of the first negative electrode film layer is controlled to be lower, allowing for the design of more ion transport channels and improving the diffusion rate of lithium ions in the particles of the first negative electrode active material, thereby improving the charging performance of the lithium-ion battery. The embodiments of this application also improve the charging performance of lithium-ion batteries while maintaining cycle life by gradient designing the weight ratio of the carbon coating layer in the first and second negative electrode film layers. Specifically, in the first and second negative electrode films, the first carbon coating layer accounts for a larger weight proportion of the first negative electrode film, which is beneficial to increasing the number of sites for intercalation and deintercalation of active ions in the first negative electrode active material and improving the diffusion rate of active ions in the negative electrode active material particles, thereby improving the charging performance of the lithium-ion battery. The second carbon coating layer accounts for a smaller weight proportion of the second negative electrode film, resulting in fewer surface defects in the second negative electrode active material and better structural stability, which is beneficial to improving the cycle life of the lithium-ion battery.

[0089] In some embodiments, the specific capacity of the first negative electrode active material is less than or equal to 350 mAh / g. The specific capacity of the first negative electrode active material can be 295 mAh / g, 300 mAh / g, 305 mAh / g, 310 mAh / g, 315 mAh / g, 320 mAh / g, 325 mAh / g, 330 mAh / g, 335 mAh / g, 340 mAh / g, 345 mAh / g, 345.5 mAh / g, 346 mAh / g, 346.5 mAh / g, 347 mAh / g, 347.5 mAh / g, 348 mAh / g, 348.5 mAh / g, 349 mAh / g, 349.5 mAh / g, 350 mAh / g, etc., or a range of any two of the above values, for example, 295 mAh / g to 320 mAh / g, 300 mAh / g to 330 mAh / g, 320 mAh / g to 350 mAh / g, etc.

[0090] In some embodiments, the specific capacity of the second negative electrode active material is greater than or equal to 350 mAh / g. The specific capacity of the second negative electrode active material can be 350 mAh / g, 360 mAh / g, 370 mAh / g, 380 mAh / g, 390 mAh / g, 400 mAh / g, 410 mAh / g, 420 mAh / g, 430 mAh / g, 440 mAh / g, 450 mAh / g, 460 mAh / g, 470 mAh / g, 480 mAh / g, 490 mAh / g, etc., or a range of any two of the above values, for example, 350 mAh / g to 380 mAh / g, 360 mAh / g to 390 mAh / g, 370 mAh / g to 400 mAh / g, 380 mAh / g to 410 mAh / g, 390 mAh / g to 420 mAh / g, 400 mAh / g to 450 mAh / g, 420 mAh / g to 490 mAh / g, etc.

[0091] The embodiments of this application improve the charging performance of lithium-ion batteries while taking into account their energy density by employing the first and second negative electrode active materials within the aforementioned specific capacity range.

[0092] In some embodiments, the specific capacity of the first negative electrode active material is greater than or equal to 325 mAh / g and less than or equal to 350 mAh / g. The specific capacity of the first negative electrode active material can be 325 mAh / g, 325.5 mAh / g, 326 mAh / g, 326.5 mAh / g, 327 mAh / g, 327.5 mAh / g, 328 mAh / g, 328.5 mAh / g, 329 mAh / g, 329.5 mAh / g, 330 mAh / g, 330.5 mAh / g, 331 mAh / g, 331.5 mAh / g, 332 mAh / g, 332.5 mAh / g, 333 mAh / g, 333.5 mAh / g, 334 mAh / g, 334.5 mAh / g, 335 mAh / g, 33... 6mAh / g, 336.5mAh / g, 337mAh / g, 337.5mAh / g, 338mAh / g, 338.5mAh / g, 339mAh / g, 339.5mAh / g, 340mAh / g, 340.5mAh / g, 341mAh / g, 341.5mAh / g, 342mAh / g, 342.5mAh / g, 343mAh / g, 343.5mAh / g, 344mAh / g, 344.5mAh / g, 345mAh / g, 345.1mAh / g, 345.2mAh / g, 345.3mAh / g, 345.4mAh / g, 345.5m Ah / g, 345.6mAh / g, 345.7mAh / g, 345.8mAh / g, 345.9mAh / g, 346mAh / g, 346.1mAh / g, 346.2mAh / g, 346.3mAh / g, 346.4mAh / g, 346.5mAh / g, 346.6 mAh / g, 346.7mAh / g, 346.8mAh / g, 346.9mAh / g, 347mAh / g, 347.1mAh / g, 347.2mAh / g, 347.3mAh / g, 347.4mAh / g, 347.5mAh / g, 347.6mAh / g, 347.7 mAh / g, 347.8mAh / g, 347.9mAh / g, 348mAh / g, 348.1mAh / g, 348.2mAh / g, 348.3mAh / g, 348.4mAh / g, 348.5mAh / g, 348.6mAh / g, 348.7mAh / g, 348. 8mAh / g, 348.9mAh / g, 349mAh / g, 349.1mAh / g, 349.2mAh / g, 349.3mAh / g, 349.4mAh / g, 349.5mAh / g, 349.6mAh / g, 349.7mAh / g, 349.8mAh / g, 349.9mAh / g, 350mAh / g, etc., or a range consisting of any two of the above values, for example, 325mAh / g~330mAh / g, 328mAh / g~335mAh / g, 330mAh / g~340mAh / g, 335mAh / g~345mAh / g, 345mAh / g~347mAh / g, 346mAh / g~348mAh / g, 347mAh / g~349mAh / g, 348mAh / g~350mAh / g, etc.

[0093] The embodiments of this application, by employing the first negative electrode active material within the aforementioned specific capacity range, facilitate the improvement of the charging performance of lithium-ion batteries while maintaining the energy density of lithium-ion batteries.

[0094] In some embodiments, the specific capacity of the second negative electrode active material is greater than or equal to 355 mAh / g and less than or equal to 370 mAh / g.

[0095] The specific capacity of the second negative electrode active material can be 355mAh / g, 356mAh / g, 357mAh / g, 358mAh / g, 359mAh / g, 360mAh / g, 361mAh / g, 362mAh / g, 363mAh / g, 364mAh / g, 365mAh / g, 366mAh / g, 367mAh / g, 368mAh / g, 369mAh / g, 370mAh / g, etc., or a range of any two of the above values, for example, 355mAh / g~358mAh / g, 356mAh / g~359mAh / g, 357mAh / g~360mAh / g, 360mAh / g~370mAh / g, etc.

[0096] The embodiments of this application, by employing a second negative electrode active material within the aforementioned specific capacity range, facilitate the improvement of the energy density of lithium-ion batteries while enabling them to have good cycle life.

[0097] In some embodiments, the first carbon coating layer accounts for 5% to 8% of the weight of the first negative electrode film. The weight percentage of the first carbon coating layer in the first negative electrode film can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, or any range of two of the above values, for example, 5% to 6%, 5.5% to 7.5%, 6% to 8%, etc.

[0098] In some embodiments, the second carbon coating layer accounts for 2% to 5% of the weight of the second negative electrode film. The weight percentage of the second carbon coating layer in the second negative electrode film can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range of two of the above values, for example, 2% to 3%, 2.5% to 4.5%, 3% to 5%, etc.

[0099] The embodiments of this application improve the charging performance of lithium-ion batteries while taking into account their cycle life by using a first negative electrode film layer and a second negative electrode film layer within the weight percentage range of the above-mentioned carbon coating layer.

[0100] In some embodiments, the weight ratio of the first negative electrode film layer and the second negative electrode film layer is between 4:6 and 5:5. The weight ratio of the first negative electrode film layer and the second negative electrode film layer can be 4:6, 4.1:5.9, 4.2:5.8, 4.3:5.7, 4.4:5.6, 4.5:5.5, 4.6:5.4, 4.7:5.3, 4.8:5.2, 4.9:5.1, 5:5, etc., or a range consisting of any two of the above values, for example, 4.1:5.9 to 4.5:5.5, 4.4:5.6 to 4.9:5.1, etc.

[0101] The embodiments of this application improve the charging performance of lithium-ion batteries by setting the first negative electrode film layer and the second negative electrode film layer within the above weight ratio range, while taking into account the energy density and cycle life of lithium-ion batteries.

[0102] In some embodiments, the compaction density of the negative electrode film layer is greater than or equal to 1.25 g / cc. The compaction density of the negative electrode film layer can be 1.25 g / cc, 1.3 g / cc, 1.35 g / cc, 1.4 g / cc, 1.45 g / cc, 1.5 g / cc, 1.55 g / cc, 1.6 g / cc, 1.65 g / cc, 1.7 g / cc, 1.75 g / cc, 1.8 g / cc, 1.85 g / cc, 1.9 g / cc, 2.0 g / cc, 2.1 g / cc, 2.2 g / cc, 2.3 g / cc, 2.4 g / cc, 2.5 g / cc, 2.6 g / cc, 2.7 g / cc, 2.8 g / cc, 2.9 g / cc, or a range of any two of the above values. For example, it can be 1.25 g / cc to 1.35 g / cc, 1.3 g / cc, etc. / cc~1.4g / cc, 1.4g / cc~1.5g / cc, 1.5g / cc~1.6g / cc, 1.6g / cc~1.7g / cc, 1.7g / cc~1.8g / cc, 1.75g / cc~1.85g / cc, 1.8g / cc~1.9g / cc, 1.9g / cc~2.0g / cc, 2.0g / cc~2.2g / cc, 2.1g / cc~2.3g / cc, 2.2g / cc~2.4g / cc, 2.3g / cc~2.5g / cc, 2.4g / cc~2.6g / cc, 2.5g / cc~2.7g / cc, 2.6g / cc~2.8g / cc, 2.7g / cc~2.9g / cc, etc.

[0103] The compaction density of the negative electrode film refers to the weight per unit volume of the material forming the negative electrode film on the current collector after compaction treatment. It is usually expressed in g / cc (grams per cubic centimeter). The compaction density of the negative electrode film reflects the degree of compaction of the material forming the negative electrode film.

[0104] The negative electrode film layer of the embodiments of this application adopts the above-mentioned compaction density, which is beneficial to improving the energy density of lithium-ion batteries.

[0105] In some embodiments, the compaction density of the negative electrode film is greater than or equal to 1.25 g / cc and less than or equal to 2.0 g / cc. The compaction density of the negative electrode film can be 1.25 g / cc, 1.3 g / cc, 1.35 g / cc, 1.4 g / cc, 1.45 g / cc, 1.5 g / cc, 1.55 g / cc, 1.6 g / cc, 1.65 g / cc, 1.7 g / cc, 1.75 g / cc, 1.8 g / cc, 1.85 g / cc, 1.9 g / cc, 2.0 g / cc, or a range consisting of any two of the above values. For example, the dosage can be 1.25g / cc~1.35g / cc, 1.3g / cc~1.4g / cc, 1.4g / cc~1.5g / cc, 1.5g / cc~1.6g / cc, 1.6g / cc~1.7g / cc, 1.7g / cc~1.8g / cc, 1.75g / cc~1.85g / cc, 1.8g / cc~1.9g / cc, 1.9g / cc~2.0g / cc, etc.

[0106] The negative electrode film layer of the embodiments of this application adopts the above-mentioned compaction density, which is beneficial to improve the energy density of lithium-ion batteries while taking into account the structural stability of the negative electrode film layer.

[0107] In some embodiments, the electrolyte includes a solvent; the solvent includes a first solvent, which includes one or both of carboxylic acid ester solvents and ether solvents; based on the total weight of the solvents, the weight percentage of the first solvent is greater than or equal to 0 and less than or equal to 30%.

[0108] The first solvent has the advantages of low viscosity and low freezing point, which helps to improve the migration speed of lithium ions and facilitates sufficient and effective contact between the active material and the electrolyte. Adding it to the electrolyte is beneficial to improving the charging performance of lithium-ion batteries. However, the first solvent is prone to film-forming side reactions with the negative electrode and gas generation during battery cycling, which affects the cycle performance of lithium-ion batteries.

[0109] Carboxylic acid ester solvents are organic solvents containing carboxylic acid ester functional groups. They typically have high conductivity, low surface tension, and low viscosity, which helps to improve the migration speed of lithium ions and facilitates sufficient and effective contact between the active material and the electrolyte.

[0110] Ether solvents typically have low viscosity, good flowability, and high conductivity, which are beneficial for promoting the rapid transport of lithium ions and improving the charge and discharge performance of batteries.

[0111] The components and their contents of the electrolyte can be determined according to methods known in the art. For example, they can be determined by gas chromatography, gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), inductively coupled plasma optical emission spectrometry (ICP-OES), etc.

[0112] Based on the total weight of the solvent, the weight percentage of the first solvent can be 0%, 0.1%, 0.2%, 0.5%, 1%, 1.1%, 1.2%, 1.5%, 2%, 2.1%, 2.2%, 2.5%, 3%, 3.1%, 3.2%, 3.5%, 4%, 4.1%, 4.2%, 4.5%, 5%, 5.1%, 5.2%, 5.5%, 6%, 6.1%, 6.2%, 6.5%, 7%, 7.1%, 7.2%, 7.5%, 8%, 8.1%, 8.2%, 8.5%. %, 9%, 9.1%, 9.2%, 9.5%, 10%, 10.1%, 10.2%, 10.5%, 11%, 11.1%, 11.2%, 11.5%, 12%, 12.1%, 12.2%, 12.5%, 13%, 13.1%, 13.2%, 13.5%, 14%, 14.1%, 14.2%, 14.5%, 15%, 15.1%, 15.2%, 15.5%, 16%, 16.1%, 16.2%, 16.5%, 17%, 17%. 1%, 17.2%, 17.5%, 18%, 18.1%, 18.2%, 18.5%, 19%, 19.1%, 19.2%, 19.5%, 20%, 20.1%, 20.2%, 20.5%, 21%, 21.1%, 21.2%, 21.5%, 22%, 22.1%, 22.2%, 22.5%, 23%, 23.1%, 23.2%, 23.5%, 24%, 24.1%, 24.2%, 24.5%, 25%, 25.1%, 25 0.2%, 25.5%, 26%, 26.1%, 26.2%, 26.5%, 27%, 27.1%, 27.2%, 27.5%, 28%, 28.1%, 28.2%, 28.5%, 29%, 29.1%, 29.2%, 29.5%, 30%, etc., or any range of two of the above values, for example, 0% to 2%, 1% to 5%, 3% to 8%, 5% to 10%, 8% to 15%, 10% to 20%, 15% to 25%, 20% to 30%, etc.

[0113] The embodiments of this application reduce the occurrence of film-forming side reactions and gas generation between the electrolyte and the negative electrode during battery cycling by adjusting the weight ratio of the first solvent in the electrolyte, thereby improving the film-forming stability of the electrolyte on the negative electrode sheet and enhancing the cycle life of the lithium-ion battery.

[0114] In some embodiments, the first solvent comprises a carboxylic acid ester solvent. For example, the carboxylic acid ester solvent may include one or more of the following: methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, isobutyl propionate, pentyl propionate, isoamyl propionate, ethyl isopropionate, methyl butyrate, ethyl butyrate, ethyl isobutyrate, butyl butyrate, butyl isobutyrate, pentyl butyrate, isoamyl butyrate, ethyl valerate, ethyl isovalerate, propyl valerate, propyl isovalerate, and compounds in which the foregoing carboxylic acid ester solvents are partially or completely substituted.

[0115] The embodiments of this application use carboxylic acid ester solvents within the above-mentioned range. The high conductivity, low surface tension, and low viscosity of carboxylic acid ester solvents enhance the migration speed of lithium ions, facilitate sufficient and effective contact between the active material and the electrolyte, and improve the charging performance of lithium-ion batteries.

[0116] In some embodiments, the ether solvent includes one or both of cyclic ether solvents and chain ether solvents; wherein the cyclic ether solvent includes one or both of tetrahydrofuran and 2-methyl-tetrahydrofuran; and the chain ether solvent includes one or both of dimethylmethane and 1,2-dimethylethane.

[0117] The embodiments of this application use ether solvents within the above-mentioned range to improve the charging performance of lithium-ion batteries.

[0118] In some embodiments, the weight percentage of the first solvent is between 10% and 30% based on the total weight of the solvent.

[0119] Based on the total weight of the solvent, the weight percentage of the first solvent can be 10%, 10.1%, 10.2%, 10.5%, 11%, 11.1%, 11.2%, 11.5%, 12%, 12.1%, 12.2%, 12.5%, 13%, 13.1%, 13.2%, 13.5%, 14%, 14.1%, 14.2%, and 14%. 5%, 15%, 15.1%, 15.2%, 15.5%, 16%, 16.1%, 16.2%, 16.5%, 17%, 17.1%, 17.2%, 17.5%, 18%, 18.1%, 18.2%, 18.5%, 19%, 19.1%, 19.2%, 19.5%, 20%, 20.1%, 20.2% 20.5%, 21%, 21.1%, 21.2%, 21.5%, 22%, 22.1%, 22.2%, 22.5%, 23%, 23.1%, 23.2%, 23.5%, 24%, 24.1%, 24.2%, 24.5%, 25%, 25.1%, 25.2%, 25.5%, 26%, 26.1%, 2 6.2%, 26.5%, 27%, 27.1%, 27.2%, 27.5%, 28%, 28.1%, 28.2%, 28.5%, 29%, 29.1%, 29.2%, 29.5%, 30%, etc., or a range consisting of any two of the above values, for example, 10% to 20%, 15% to 25%, 20% to 30%, etc.

[0120] The embodiments of this application use the first solvent with the above-mentioned weight ratio to improve the charging performance of lithium-ion batteries.

[0121] In some embodiments, the electrolyte further includes a second solvent, which is a carbonate solvent, and the weight percentage of the second solvent is between 70% and 90% based on the total weight of the solvent. The weight percentage of the second solvent can be 70%, 70.1%, 70.2%, 70.5%, 71%, 71.1%, 71.2%, 71.5%, 72%, 72.1%, 72.2%, 72.5%, 73%, 73.1%, 73.2%, 73.5%, 74%, 74.1%, 74.2%, or 74%. 5%, 75%, 75.1%, 75.2%, 75.5%, 76%, 76.1%, 76.2%, 76.5%, 77%, 77.1%, 77.2%, 77.5%, 78%, 78.1%, 78.2%, 78.5%, 79%, 79.1%, 79.2%, 79.5%, 80%, 80.1%, 80.2% 80.5%, 81%, 81.1%, 81.2%, 81.5%, 82%, 82.1%, 82.2%, 82.5%, 83%, 83.1%, 83.2%, 83.5%, 84%, 84.1%, 84.2%, 84.5%, 85%, 85.1%, 85.2%, 85.5%, 86%, 86.1%, 8 6.2%, 86.5%, 87%, 87.1%, 87.2%, 87.5%, 88%, 88.1%, 88.2%, 88.5%, 89%, 89.1%, 89.2%, 89.5%, 90%, etc., or a range consisting of any two of the above values, such as 70%–80%, 75%–85%, 80%–90%, etc.

[0122] The second solvent has a high dielectric constant and good electrochemical stability, which helps to reduce the side reactions and gas generation with the negative electrode during battery cycling, thereby improving the cycle life of lithium-ion batteries.

[0123] Carbonate solvents are organic solvents containing carbonate functional groups, and they typically have high dielectric constants and good electrochemical stability.

[0124] The embodiments of this application improve the cycle life of lithium-ion batteries by reducing the side reactions and gas generation that occur with the negative electrode during battery cycling using a second solvent.

[0125] In some embodiments, carbonate solvents include one or more of ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, butylene carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and compounds in which the foregoing compounds are partially or completely substituted.

[0126] The embodiments of this application use carbonate solvents within the above-mentioned range to reduce film-forming side reactions and gas generation with the negative electrode during battery cycling, thereby improving the cycle performance of lithium-ion batteries.

[0127] In some embodiments, the conductivity of the electrolyte is between 7.2 mS / cm and 13.3 mS / cm. The conductivity of the electrolyte can be 7.2 mS / cm, 7.3 mS / cm, 7.4 mS / cm, 7.5 mS / cm, 7.6 mS / cm, 7.7 mS / cm, 7.8 mS / cm, 7.9 mS / cm, 8 mS / cm, 8.1 mS / cm, 8.2 mS / cm, 8.3 mS / cm, 8.4 mS / cm, 8.5 mS / cm, 8.6 mS / cm, 8.7 mS / cm, 8.8 mS / cm, 8.9 mS / cm, 9.1 mS / cm, 9.2 mS / cm, 9... .3mS / cm, 9.4mS / cm, 9.5mS / cm, 9.6mS / cm, 9.7mS / cm, 9.8mS / cm, 9.9mS / cm, 10mS / cm, 10.1mS / cm, 10.2mS / cm, 10.3mS / c m, 10.4mS / cm, 10.5mS / cm, 10.6mS / cm, 10.7mS / cm, 10.8mS / cm, 10.9mS / cm, 11mS / cm, 11.1mS / cm, 11.2mS / cm, 11.3mS / cm , 11.4mS / cm, 11.5mS / cm, 11.6mS / cm, 11.7mS / cm, 11.8mS / cm, 11.9mS / cm, 12mS / cm, 12.1mS / cm, 12.2mS / cm, 12.3mS / cm , 12.4mS / cm, 12.5mS / cm, 12.6mS / cm, 12.7mS / cm, 12.8mS / cm, 12.9mS / cm, 13mS / cm, 13.1mS / cm, 13.2mS / cm, 13.3mS / cm The range can be any two of the above values, such as 7.2mS / cm~8.2mS / cm, 8.2mS / cm~9.2mS / cm, 8.7mS / cm~9.7mS / cm, 9.2mS / cm~10.2mS / cm, 9.7mS / cm~10.7mS / cm, 10.2mS / cm~11.2mS / cm, 10.7mS / cm~11.7mS / cm, 11.2mS / cm~12.3mS / cm, 12.2mS / cm~13.3mS / cm, etc.

[0128] Electrolyte conductivity refers to the ability of active ions to conduct within the electrolyte. Higher conductivity indicates greater conductivity, which is beneficial for improving the charging performance of lithium-ion batteries. The conductivity of an electrolyte at 25°C can be tested using any known method. For example, a possible testing method for electrolytes could be: heating the test sample and standard liquid to 25°C (±0.1°C); calibrating the testing instrument (Leici DDSJ-308F) using two standard liquids at an ambient temperature of 25°C (±0.5°C); after calibration and cleaning the electrodes, vertically immersing the test sample electrode in the test liquid to begin testing; and recording the test results after the data has stabilized for at least 10 seconds.

[0129] The embodiments of this application improve the transport capability of lithium ions in the electrolyte and enhance the charging performance of lithium-ion batteries by using electrolytes within the above-mentioned conductivity range.

[0130] In some embodiments, the electrolyte injection coefficient is greater than or equal to 2.8 g / Ah. The electrolyte injection coefficient can be 2.8 g / Ah, 2.85 g / Ah, 2.9 g / Ah, 2.95 g / Ah, 3.0 g / Ah, 3.05 g / Ah, 3.1 g / Ah, 3.15 g / Ah, 3.2 g / Ah, 3.25 g / Ah, 3.3 g / Ah, 3.35 g / Ah, 3.4 g / Ah, 3.45 g / Ah, or 3.5 g / Ah. The concentrations can be g / Ah, 3.55 g / Ah, 3.6 g / Ah, 3.65 g / Ah, 3.7 g / Ah, 3.75 g / Ah, 3.8 g / Ah, 3.85 g / Ah, 3.9 g / Ah, etc., or ranges consisting of any two of the above values. For example, it could be 2.8 g / Ah to 3.0 g / Ah, 2.9 g / Ah to 3.1 g / Ah, 3.0 g / Ah, etc. Ah~3.2g / Ah, 3.1g / Ah~3.3g / Ah, 3.15g / Ah~3.25g / Ah, 3.2g / Ah~3.3g / Ah, 3.25g / Ah~3.35g / Ah, 3.3g / Ah~3.4g / Ah, 3.35g / Ah~3.45g / Ah, 3.4g / Ah~3.5g / Ah, 3.45 g / Ah~3.55g / Ah, 3.5g / Ah~3.6g / Ah, 3.55g / Ah~3.65g / Ah, 3.6g / Ah~3.7g / Ah, 3.65g / Ah~3.75g / Ah, 3.7g / Ah~3.8g / Ah, 3.75g / Ah~3.85g / Ah, 3.8g / Ah~3.9g / Ah, etc.

[0131] The electrolyte injection coefficient is the ratio of the amount of electrolyte injected to the battery's rated capacity. The battery's rated capacity refers to the amount of electricity the battery can discharge to its cutoff voltage under specified charge and discharge conditions.

[0132] The embodiments of this application improve the uniformity of electrolyte distribution inside the lithium-ion battery by using electrolytes within the above-mentioned electrolyte injection coefficient range, improve the film formation stability of electrolytes on the negative electrode sheet, and enhance the cycle life of the lithium-ion battery.

[0133] In some embodiments, the electrolyte injection coefficient is greater than or equal to 2.8 g / Ah and less than or equal to 3.8 g / Ah. The electrolyte injection coefficient can be 2.8 g / Ah, 2.85 g / Ah, 2.9 g / Ah, 2.95 g / Ah, 3.0 g / Ah, 3.05 g / Ah, 3.1 g / Ah, 3.15 g / Ah, 3.2 g / Ah, 3.25 g / Ah, 3.3 g / Ah, 3.35 g / Ah, 3.4 g / Ah, 3.45 g / Ah, 3.5 g / Ah, 3.55 g / Ah, 3.6 g / Ah, 3.65 g / Ah, 3.7 g / Ah, 3.75 g / Ah, 3.8 g / Ah, etc., or a range of any two of the above values, for example, 2.8 g / Ah to 3.0 g / Ah, 2.9 g / Ah to 3.1 g / Ah. / Ah, 3.0g / Ah~3.2g / Ah, 3.1g / Ah~3.3g / Ah, 3.15g / Ah~3.25g / Ah, 3.2g / Ah~3.3g / Ah, 3.25g / Ah~3.35g / Ah, 3.3g / Ah~3.4g / Ah, 3.35g / Ah~3.45g / Ah, 3.4g / Ah~3.5g / Ah, 3.45g / Ah~3.55g / Ah, 3.5g / Ah~3.6g / Ah, 3.55g / Ah~3.65g / Ah, 3.6g / Ah~3.7g / Ah, 3.65g / Ah~3.75g / Ah, 3.7g / Ah~3.8g / Ah, etc.

[0134] The embodiments of this application improve the uniformity of electrolyte distribution inside the lithium-ion battery by using electrolytes within the above-mentioned electrolyte injection coefficient range, improve the film formation stability of electrolytes on the negative electrode sheet, and enhance the cycle life of the lithium-ion battery.

[0135] In some embodiments, the density of the electrolyte is 0.8 g / cm³. 3 ~1.5g / cm 3 The density of the electrolyte can be 0.8 g / cm³. 3 0.9g / cm 3 1.0g / cm 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3etc., or a range consisting of any two of the above values, for example, 0.8 g / cm³. 3 ~1.0g / cm 3 1.0g / cm 3 ~1.2g / cm 3 1.1g / cm 3 ~1.3g / cm 3 1.2g / cm 3 ~1.5g / cm 3 wait.

[0136] The density of the electrolyte refers to the mass of the electrolyte per unit volume, usually expressed in g / cm³. 3 The density of the electrolyte is expressed in grams per cubic centimeter. The density is affected by the type of solvent, the concentration of lithium salts, and other additives.

[0137] The embodiments of this application use electrolytes within the aforementioned density range, which is beneficial for the electrolytes to have suitable conductivity and viscosity, so that lithium ions have good transport capabilities in the electrolyte and improve the charging performance of lithium-ion batteries.

[0138] In some embodiments, the electrolyte includes a lithium salt; the concentration of the lithium salt in the electrolyte is between 0.7 mol / L and 1 mol / L. The concentration of the lithium salt in the electrolyte can be 0.7 mol / L, 0.71 mol / L, 0.72 mol / L, 0.73 mol / L, 0.74 mol / L, 0.75 mol / L, 0.76 mol / L, 0.77 mol / L, 0.78 mol / L, 0.79 mol / L, 0.8 mol / L, 0.81 mol / L, 0.82 mol / L, 0.83 mol / L, 0.84 mol / L, 0.85 mol / L, or 0.86 mol / L. The values ​​can be 0.87 mol / L, 0.88 mol / L, 0.9 mol / L, 0.91 mol / L, 0.92 mol / L, 0.93 mol / L, 0.94 mol / L, 0.95 mol / L, 0.96 mol / L, 0.97 mol / L, 0.98 mol / L, 1.0 mol / L, etc., or any range of two of the above values, such as 0.7 mol / L to 0.9 mol / L, 0.8 mol / L to 1.0 mol / L, etc.

[0139] Lithium salts are compounds containing lithium ions that act as carriers of these ions in the electrolyte, migrating between the positive and negative electrodes. Solvents are used to dissolve the lithium salts, serving as the medium that supports the migration of lithium ions.

[0140] In some embodiments, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bistrifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0141] The embodiments of this application, by employing lithium salts of the above concentration, are beneficial to improving the film-forming stability of the electrolyte at the negative electrode, regulating the conductivity of the electrolyte, enhancing the migration rate of lithium ions, and improving the cycle life of lithium-ion batteries.

[0142] In some embodiments, the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; the positive electrode film layer includes a positive electrode active material; the positive electrode active material includes one or two of lithium nickel cobalt manganese oxide and lithium phosphate with an olivine structure.

[0143] Lithium nickel cobalt manganese oxides possess high theoretical and practical capacities, which are beneficial for improving the energy density of lithium-ion batteries. Lithium-containing phosphates with an olivine structure have a stable layered structure, which is beneficial for improving the cycle life of lithium-ion batteries.

[0144] The embodiments of this application employ positive electrode sheets comprising the above-mentioned positive electrode active materials, which is beneficial for improving the cycle life and / or energy density of lithium-ion batteries.

[0145] Secondly, embodiments of this application provide an electrical device including the lithium-ion battery provided in the first aspect.

[0146] The electrical devices provided by the embodiments of this application have at least the same advantages as lithium-ion batteries, which can improve the battery life of the electrical devices.

[0147] The beneficial effects of this application are further illustrated below with reference to the embodiments.

[0148] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0149] Example 1

[0150] The preparation of a lithium-ion battery includes the following steps:

[0151] (1) Provide positive electrode plates:

[0152] The positive electrode active material (lithium iron phosphate), conductive agent (Super-P), binder (carboxymethyl cellulose), and softener (polyurethane resin) were mixed in a weight ratio of 97.3:0.7:1.8:0.2. Then, a solvent (N-methylpyrrolidone) was added, and after thorough mixing, the mixture was coated onto aluminum foil. Following drying and cold pressing, the positive electrode sheet was obtained. The coating weight of the positive electrode film was 320 mg / 1540.25 mm². 2 The compacted density is 2.6 g / cc.

[0153] (2) Providing a negative electrode sheet: The first negative electrode active material (artificial graphite with carbon coating), conductive agent (Super-P), binder (carboxymethyl cellulose), and plasticizer (polyacrylic acid) are mixed evenly in a solvent (deionized water) at a weight ratio of 97.7:0.7:1:0.6 to obtain the first negative electrode film layer.

[0154] The second negative electrode active material (artificial graphite with carbon coating), conductive agent (Super-P), binder (carboxymethyl cellulose), and plasticizer (polyacrylic acid) are mixed evenly in a solvent (deionized water) at a weight ratio of 96.4:0.7:2.5:0.4 to obtain the second negative electrode film layer.

[0155] The second negative electrode film is pre-coated on the copper foil, and the first negative electrode film is pre-coated on the surface of the first negative electrode film away from the copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0156] (3) Provide a separating membrane:

[0157] A 7-micrometer-thick polyethylene film was used as the separator.

[0158] (4) Provide electrolyte:

[0159] The electrolyte solvent includes a first solvent and a second solvent. The first solvent is ethyl acetate and methyl formate, and the second solvent is ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Ethyl acetate, methyl formate, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate are mixed in a weight ratio of 8%, 12%, 16%, 8%, and 56%, respectively. LiPF6 (lithium hexafluorophosphate) is dissolved in the above solvents to obtain an electrolyte with a lithium salt concentration of 1 mol / L.

[0160] (5) The electrodes are arranged in the order of "separator-negative electrode-separator-positive electrode". One end of the positive electrode, negative electrode and two separators is fixed to the discharge roller, and the other end is stacked together and fixed to the winding shaft. The winding shaft is rotated by a motor to wind the positive electrode, negative electrode and two separators to obtain a dry cell. The dry cell is then subjected to one liquid injection, high-temperature settling, formation, a second liquid injection and high-temperature settling, with a liquid injection coefficient of 3.3 g / Ah, to obtain a lithium-ion battery.

[0161] The steps for preparing lithium-ion batteries in Examples 2 and 3 are similar to those in Example 1. The difference is that the weight ratio of the first carbon coating layer to the first negative electrode film layer in step (2) of Examples 2 and 3 is different.

[0162] The steps for preparing lithium-ion batteries in Examples 4 and 5 are similar to those in Example 1. The difference is that the weight ratio of the second carbon coating layer to the second negative electrode film layer is different in step (2) of Examples 4 and 5.

[0163] The steps for preparing the lithium-ion battery in Example 6 are similar to those in Example 1. The difference is that the weight ratio of the first negative electrode film and the second negative electrode film is different in step (2) of Example 6.

[0164] The steps for preparing the lithium-ion battery in Example 7 are similar to those in Example 1, except that the compaction density of the negative electrode film is different in step (2) of Example 7.

[0165] The steps for preparing lithium-ion batteries in Examples 8 to 11 are similar to those in Example 1, except that the electrolyte formulation is different in step (4) of Examples 8 to 11.

[0166] The steps for preparing the lithium-ion battery in Example 12 are similar to those in Example 1, except that the electrolyte injection coefficient is different in step (4) of Example 12.

[0167] The steps for preparing the lithium-ion battery in Comparative Example 1 are similar to those in Example 1. The difference is that in step (2) of Comparative Example 1, the first negative electrode film layer is prepared according to the formula of the second negative electrode film layer.

[0168] The steps for preparing the lithium-ion battery in Comparative Example 2 are similar to those in Example 1. The difference is that in step (2) of Comparative Example 2, the second negative electrode film is prepared according to the formula of the first negative electrode film.

[0169] The lithium-ion batteries prepared in Examples 1 to 12 and Comparative Examples 1 to 2 were tested for cycle life, energy density, and charging performance. The test results are shown in Table 1.

[0170] (1) Cyclic performance test:

[0171] The prepared lithium-ion battery was charged at 25℃ with a constant current of 1C to the charging cutoff voltage of 3.8V, then charged with a constant voltage to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.33C to the discharge cutoff voltage of 2.0V. Its actual capacity was recorded as C0. Then, it was discharged at a rate of 1C followed by a discharge at 0.33C, and the discharge capacity C of each cycle was recorded. n Until the battery's capacity retention rate reaches 80%, capacity retention rate = C n / C0*100%, records the number of cycles at this point. The more cycles, the better the cycle performance of the secondary battery.

[0172] (2) Charging performance test:

[0173] At 25°C, the prepared lithium-ion battery was charged at a constant current of 0.33C to the charging cutoff voltage of 3.8V, then charged at a constant voltage to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to the discharge cutoff voltage of 2.0V. Its actual capacity was recorded as C0.

[0174] Then, the lithium-ion battery was sequentially charged at constant currents of 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, 3.5C0, 4C0, and 4.5C0 until the full-cell charging cutoff voltage or the 0V negative electrode cutoff potential (whichever comes first). After each charge, it was discharged at 1C0 until the full-cell discharge cutoff voltage. The negative electrode potentials corresponding to 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% SOC (State of Charge) were recorded at different charging rates. The rate-negative electrode potential curves under different SOC states were plotted. After linear fitting, the charging rate corresponding to the negative electrode potential of 0V under different SOC states was obtained. This charging rate is the charging window under that SOC state, denoted as C. 10％SOC C 20％ SOC C 30％SOC C 40％SOC C 50％SOC C 60％SOC C 70％SOC C 80％SOC According to the formula (60 / C) 10％SOC +60 / C 20％SOC +60 / C 30％ SOC +60 / C 40％SOC +60 / C 50％SOC +60 / C 60％SOC +60 / C 70％SOC +60 / C 80％SOCThe charging time T for the secondary battery to charge from 10% SOC to 80% SOC is calculated by multiplying the charging time by 10%. The shorter the charging time, the better the charging performance.

[0175] (3) Energy density test:

[0176] The lithium-ion batteries prepared in each embodiment and comparative example were placed at 25°C and charged to 3.8V with a constant current of 0.33C, allowed to stand for 1 minute, and then charged to 0.05C with a constant voltage of 3.8V, allowed to stand for 30 minutes. They were then discharged to 2.0V with a constant current of 0.33C, and the discharge capacity A0 was recorded at this point, in Ah. The length, width, and height of the outer surface of the lithium-ion battery were measured using calipers, and the volume of a single cell V0 was calculated, in L. The volumetric energy density of the lithium-ion battery, VED, is calculated as (A0 × discharge plateau voltage of the lithium-ion battery) / V0, in Wh / L. It should be understood that the discharge plateau voltage of lithium-ion batteries with different positive and negative electrode systems varies, and can be obtained by testing their charge-discharge curves or referring to existing literature. It should be noted that the energy density values ​​of some embodiments and / or comparative examples are rounded to show the same value.

[0177] Table 1. Performance test results of lithium-ion batteries in the examples and comparative examples.

[0178] Table 1 (continued) Performance test results of lithium-ion batteries in the examples and comparative examples

[0179] As shown in Table 1, compared with Comparative Examples 1-2, the lithium-ion batteries of Examples 1-12 improve the charging performance of lithium-ion batteries by layering the negative electrode film and differentially controlling the specific capacity of the negative electrode active material and the weight ratio of the carbon coating layer in each layer, while taking into account the energy density and cycle life of lithium-ion batteries.

[0180] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, or indirect coupling or communication connection between apparatuses or units, and may be electrical, mechanical, or other forms.

[0181] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0182] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A lithium-ion battery, wherein, It includes a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector; the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer; the second negative electrode film layer is disposed between the negative current collector and the first negative electrode film layer; The first negative electrode film layer includes a first negative electrode active material, and the second negative electrode film layer includes a second negative electrode active material; the specific capacity of the first negative electrode active material is less than or equal to the specific capacity of the second negative electrode active material; The first negative electrode active material includes a first graphite and a first carbon coating layer covering at least a portion of the surface of the first graphite; the second negative electrode active material includes a second graphite and a second carbon coating layer covering at least a portion of the surface of the second graphite; the weight percentage of the first carbon coating layer in the first negative electrode film is greater than or equal to the weight percentage of the second carbon coating layer in the second negative electrode film.

2. The lithium-ion battery according to claim 1, wherein, The specific capacity of the first negative electrode active material is less than or equal to 350 mAh / g, and the specific capacity of the second negative electrode active material is greater than or equal to 350 mAh / g.

3. The lithium-ion battery according to claim 1 or 2, wherein, The specific capacity of the first negative electrode active material is greater than or equal to 325 mAh / g and less than or equal to 350 mAh / g.

4. The lithium-ion battery according to any one of claims 1 to 3, wherein, The specific capacity of the second negative electrode active material is greater than or equal to 355 mAh / g and less than or equal to 370 mAh / g.

5. The lithium-ion battery according to any one of claims 1 to 4, wherein, The first carbon coating layer accounts for 5% to 8% of the weight of the first negative electrode film layer; the second carbon coating layer accounts for 2% to 5% of the weight of the second negative electrode film layer.

6. The lithium-ion battery according to any one of claims 1 to 5, wherein, The weight ratio of the first negative electrode film layer to the second negative electrode film layer is 4:6 to 5:

5.

7. The lithium-ion battery according to any one of claims 1 to 6, wherein, The compaction density of the negative electrode film is greater than or equal to 1.25 g / cc.

8. The lithium-ion battery according to any one of claims 1 to 7, wherein, The compaction density of the negative electrode film is greater than or equal to 1.25 g / cc and less than or equal to 2.0 g / cc.

9. The lithium-ion battery according to any one of claims 1 to 8, wherein, The electrolyte includes a solvent; the solvent includes a first solvent, which includes one or both of carboxylic acid ester solvents and ether solvents; based on the total weight of the solvents, the weight percentage of the first solvent is greater than or equal to 0 and less than or equal to 30%.

10. The lithium-ion battery according to claim 9, wherein, The carboxylic acid ester solvents include one or more of the following: γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, isobutyl propionate, pentyl propionate, isoamyl propionate, ethyl isopropionate, methyl butyrate, ethyl butyrate, ethyl isobutyrate, butyl butyrate, butyl isobutyrate, pentyl butyrate, isoamyl butyrate, ethyl valerate, ethyl isovalerate, propyl valerate, propyl isovalerate, and compounds in which the aforementioned carboxylic acid ester solvents are partially or completely substituted.

11. The lithium-ion battery according to claim 9 or 10, wherein, The ether solvents include one or both of cyclic ether solvents and chain ether solvents; wherein the cyclic ether solvents include one or both of tetrahydrofuran and 2-methyl-tetrahydrofuran; and the chain ether solvents include one or both of dimethylmethane and 1,2-dimethylethane.

12. The lithium-ion battery according to any one of claims 9 to 11, wherein, Based on the total weight of the solvents, the weight percentage of the first solvent is between 10% and 30%.

13. The lithium-ion battery according to any one of claims 1 to 12, wherein, The electrolyte also includes a second solvent, which comprises a carbonate solvent, and the weight percentage of the second solvent is between 70% and 90% based on the total weight of the solvent.

14. The lithium-ion battery according to claim 13, wherein, The carbonate solvents include one or more of ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, butylene carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and compounds in which the foregoing compounds are partially or completely substituted.

15. The lithium-ion battery according to any one of claims 1 to 14, wherein, The conductivity of the electrolyte is between 7.2 mS / cm and 13.3 mS / cm.

16. The lithium-ion battery according to any one of claims 1 to 15, wherein, The electrolyte injection coefficient is greater than or equal to 2.8 g / Ah.

17. The lithium-ion battery according to any one of claims 1 to 16, wherein, The electrolyte injection coefficient is greater than or equal to 2.8 g / Ah and less than or equal to 3.8 g / Ah.

18. The lithium-ion battery according to any one of claims 1 to 17, wherein, The density of the electrolyte is 0.8 g / cm³. 3 ~1.5g / cm 3 .

19. The lithium-ion battery according to any one of claims 1 to 18, wherein, The electrolyte includes a lithium salt; the concentration of the lithium salt in the electrolyte is between 0.7 mol / L and 1 mol / L.

20. The lithium-ion battery according to any one of claims 1 to 19, wherein, The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector; the positive electrode film layer includes a positive electrode active material; the positive electrode active material includes one or two of lithium nickel cobalt manganese oxide and lithium phosphate with an olivine structure.

21. An electrical appliance, wherein, Including the lithium-ion battery as described in any one of claims 1 to 20.

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