Fast-charging negative electrode active material, preparation method thereof, negative electrode sheet, secondary battery, and electric device

Abstract

The application provides a fast-charging negative electrode active material, a preparation method thereof, a negative electrode sheet, a secondary battery and an electric device. The fast-charging negative electrode active material comprises carbon-based material particles, a coating layer on at least part of the surfaces of the carbon-based material particles, and ferroelectric material dispersed in the coating layer, wherein the coating layer comprises conductive carbon material, and at least part of the ferroelectric material protrudes from the surface of the coating layer. The fast-charging negative electrode active material provided by the application has good kinetic performance, can withstand large-rate charging, and improves the fast-charging capability of the secondary battery, while not sacrificing the high energy density of the secondary battery.

Description

[0001] This application is a divisional application of the invention patent application with application number 202280005863.0, application date June 24, 2022, entitled "Fast-charging negative electrode active material and its preparation method, negative electrode sheet, secondary battery and power device". Technical Field

[0002] This application belongs to the field of battery technology, specifically relating to a fast-charging negative electrode active material and its preparation method, a negative electrode sheet, a secondary battery, and an electrical device. Background Technology

[0003] In recent years, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. With the application and promotion of rechargeable batteries, the demand for their fast charging capabilities is increasing. As a crucial component of rechargeable batteries, the negative electrode active material significantly impacts their charging capacity. Currently, graphite is one of the most commonly used negative electrode active materials in rechargeable batteries; however, the fast charging capability of conventional graphite has reached its limit and cannot meet the higher demands for fast charging performance. Summary of the Invention

[0004] The purpose of this application is to provide a fast-charging negative electrode active material and its preparation method, a negative electrode sheet, a secondary battery and an electrical device, which enables the secondary battery to have a high energy density and a significantly improved fast charging capability.

[0005] The first aspect of this application provides a fast-charging negative electrode active material, wherein the fast-charging negative electrode active material includes carbon-based material particles, a coating layer located on at least a portion of the surface of the carbon-based material particles, and a ferroelectric material dispersed in the coating layer, the coating layer including conductive carbon material, and at least a portion of the ferroelectric material protruding from the surface of the coating layer.

[0006] The negative electrode active material of this application can reduce the kinetic energy barrier of the desolvation process, accelerate the rate at which lithium ions reach the surface of carbon-based material particles, and reduce the resistance to lithium ion intercalation into the negative electrode, while containing fewer inactive components. Furthermore, the negative electrode active material of this application can increase the rate of solid-phase diffusion of lithium intercalation products from the particle surface to the interior. Therefore, the negative electrode active material of this application has excellent kinetic performance, can withstand high-rate charging, and improves the fast-charging capability of the secondary battery without sacrificing the high energy density of the secondary battery.

[0007] In any embodiment of the present application, the average thickness of the coating layer is H nm, the volume average particle size Dv50 of the ferroelectric material is d1 nm, and the fast-charging anode active material satisfies: 0.25 ≤ H / d1 ≤ 1.1. Optionally, 0.25 ≤ H / d1 ≤ 0.5. This is beneficial for the secondary battery to simultaneously have high fast-charging ability, high energy density, and good cycling performance.

[0008] In any embodiment of the present application, the volume average particle size Dv50 of the ferroelectric material is d1 nm, where 0 < d1 ≤ 200. Optionally, 0 < d1 ≤ 100. Thus, less ferroelectric material can be used at the same specific surface area, thereby reducing the energy density loss of the secondary battery.

[0009] In any embodiment of the present application, the average thickness of the coating layer is H nm, where 20 ≤ H ≤ 100. Optionally, 20 ≤ H ≤ 50. Thus, the secondary battery can simultaneously have high fast-charging ability, high energy density, and high cycling capacity retention rate.

[0010] In any embodiment of the present application, the mass ratio of the ferroelectric material to the carbon-based material particles is α1, and α1 is (0.5 - 10):100. Optionally, it is (1 - 3):100. This is beneficial for the secondary battery to simultaneously have high fast-charging ability and high energy density.

[0011] In any embodiment of the present application, the mass ratio of the coating layer to the carbon-based material particles is α2, and α2 is (2 - 10):100. Optionally, it is (2 - 5):100. This is beneficial for the anode active material to have high fast-charging ability while also having high specific capacity, high initial Coulomb efficiency, and high tap density.

[0012] In any embodiment of the present application, the mass ratio of the ferroelectric material to the carbon-based material particles is α1, and the mass ratio of the coating layer to the carbon-based material particles is α2. The ratio of α1:α2 is 1:6 to 4:1. Optionally, it is 1:4 to 2:1. This is beneficial for the secondary battery to simultaneously have high fast-charging ability, high energy density, and high cycling capacity retention rate.

[0013] In any embodiment of the present application, the graphitization degree of the coating layer is 45% to 80%.

[0014] In any embodiment of the present application, the conductive carbon material in the coating layer includes amorphous carbon. Optionally, it includes hard carbon. This can further improve the fast-charging ability of the secondary battery.

[0015] In any embodiment of the present application, the graphitization degree of the carbon-based material particles is 88% to 96%.

[0016] In any embodiment of this application, the volume average particle size Dv50 of the carbon-based material particles is d2μm, where 5≤d2≤20, and optionally, 8≤d2≤15. This enables the secondary battery to have a higher fast charging capability.

[0017] In any embodiment of this application, the morphology of the carbon-based material particles is primary particles, secondary particles, or a combination thereof. Optionally, in the carbon-based material particles with a secondary particle morphology, the ratio of the volume average particle size Dv50 of the primary particles to the volume average particle size Dv50 of the secondary particles they comprise is 0.2 to 0.5. This is beneficial for the carbon-based material particles to possess both good ion transport and electron transport properties and high structural stability.

[0018] In any embodiment of this application, the carbon-based material particles comprise one or more combinations selected from graphite, mesophase carbon microspheres, hard carbon, and soft carbon, and optionally selected from graphite. This enables the secondary battery to have high energy density and high cycle stability.

[0019] In any embodiment of this application, the dielectric constant of the ferroelectric material is 100 or higher, optionally from 100 to 100,000. This allows for a better reduction of the kinetic energy barrier during the desolvation process, thereby improving the fast-charging capability of the secondary battery.

[0020] In any embodiment of this application, the Curie temperature of the ferroelectric material is above 80°C. This allows for a better reduction of the kinetic energy barrier during the desolvation process, thereby improving the fast-charging capability of the secondary battery.

[0021] In any embodiment of this application, the ferroelectric material comprises one or more combinations selected from perovskite structure oxides, tungsten bronze type compounds, bismuth oxide type layered structure compounds, lithium niobate, and lithium tantalate.

[0022] In any embodiment of this application, the volume average particle size Dv50 of the fast-charging negative electrode active material is 5 μm to 20 μm, optionally 8 μm to 15 μm. This is beneficial for the negative electrode active material to have better ion transport and electron transport performance, as well as fast charging performance.

[0023] In any embodiment of this application, the specific surface area of ​​the fast-charging negative electrode active material is 0.8 m². 2 / g to 1.3m 2 / g, optionally 0.9m 2 / g to 1.2m 2 / g. This enables secondary batteries to have a higher fast charging capability.

[0024] In any embodiment of this application, the powder compaction density of the fast-charging negative electrode active material under a force of 20000N is 1.5g / cm³. 3 Up to 1.9 g / cm 3 Optionally, it can be 1.5 g / cm³. 3 Up to 1.7 g / cm 3 This enables secondary batteries to have higher energy density and improved cycle performance.

[0025] The second aspect of this application provides a method for preparing a fast-charging negative electrode active material, comprising the steps of: S10, providing carbon-based material particles, a carbon source, and a ferroelectric material, wherein optionally, the carbon source includes one or more combinations selected from asphalt, resin, and biomass materials; S20, uniformly mixing the carbon-based material particles, the carbon source, and the ferroelectric material, and performing a carbonization sintering treatment to form a coating layer including conductive carbon material on at least a portion of the surface of the carbon-based material particles, wherein the ferroelectric material is dispersed in the coating layer and at least a portion of the ferroelectric material protrudes from the surface of the coating layer.

[0026] In any embodiment of this application, the carbonization sintering temperature in S20 is 700°C to 1800°C, and optionally 1000°C to 1300°C.

[0027] In any embodiment of this application, the carbonization sintering time in S20 is 1 hour to 15 hours, and optionally 6 hours to 14 hours.

[0028] In any embodiment of this application, the carbon-based material particles are prepared by the following method: S101, providing coke powder and placing the coke powder into a reaction vessel; S102, graphitizing the coke powder to obtain carbon-based material particles.

[0029] A third aspect of this application provides a negative electrode sheet, including a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, wherein the negative electrode film layer includes a fast-charging negative electrode active material of the first aspect of this application or a fast-charging negative electrode active material prepared by the method of the second aspect of this application.

[0030] The fourth aspect of this application provides a secondary battery, including the negative electrode sheet of the third aspect of this application.

[0031] The fifth aspect of this application provides an electrical device, including the secondary battery of the fourth aspect of this application.

[0032] The fast-charging negative electrode active material provided in this application has excellent kinetic performance, can withstand high-rate charging, and improves the fast-charging capability of the secondary battery without sacrificing its high energy density. The power device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the aforementioned secondary battery. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of one embodiment of the fast-charging negative electrode active material of this application.

[0035] Figure 2 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0036] Figure 3 yes Figure 2 An exploded view of the implementation method of the secondary battery.

[0037] Figure 4 This is a schematic diagram of one embodiment of the battery module of this application.

[0038] Figure 5 This is a schematic diagram of one embodiment of the battery pack of this application.

[0039] Figure 6 yes Figure 5 An exploded view of an embodiment of the battery pack shown.

[0040] Figure 7 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0041] In the accompanying drawings, the figures may not be drawn to scale. The reference numerals are explained as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Secondary battery, 51 Casing, 52 Electrode assembly, 53 Cover plate, 10 Fast-charging negative electrode active material, 101 Carbon-based material particles, 102 Coating layer, 103 Ferroelectric material. Detailed Implementation

[0042] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the fast-charging negative electrode active material, its preparation method, negative electrode sheet, secondary battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0043] The "range" disclosed in this application is defined by 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 a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; 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 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 "ab" 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 "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0044] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0045] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0046] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. 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.

[0047] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0048] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A 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).

[0049] In this application, the terms "multiple" or "various" refer to two or more kinds of things.

[0050] In this application, "about" a certain value represents a range, specifically a range of ±10% of that value.

[0051] The key to improving the fast charging capability of secondary batteries lies in improving the performance of the negative electrode active material and the negative electrode sheet. In the charging process of secondary batteries, taking graphite as an example, the electrode dynamics process usually includes the following steps: (1) Liquid phase mass transfer step in the electrolyte phase: solvated lithium ions in the electrolyte diffuse and transfer to the surface of graphite particles; (2) Surface conversion step: during the first charge, solvated lithium ions are adsorbed on the surface of graphite particles and react to form a solid electrolyte interphase (SEI) film. During subsequent charging, solvated lithium ions are adsorbed on the surface of the SEI film. After the desolvation process, lithium ions reach the surface of graphite particles; (3) Charge exchange step: lithium ions gain electrons from the surface of graphite particles and form lithium intercalation products; (4) Solid phase mass transfer step of lithium intercalation products: lithium intercalation products diffuse from the solid phase of the graphite particle surface to the interior, completing the charging process.

[0052] Existing research generally considers the solid-phase diffusion rate of lithium intercalation products to be slow, therefore step (4) is considered the controlling step of the negative electrode kinetic process. Consequently, current research mainly focuses on how to increase the solid-phase diffusion rate of lithium intercalation products and shorten the solid-phase diffusion distance. For example, to improve the fast-charging capability of graphite, existing technologies mainly employ the following methods: (1) etching pores on the graphite surface to increase surface active sites and lithium-ion intercalation channels, thereby shortening the lithium-ion diffusion distance; (2) coating graphite with amorphous carbon to increase the interlayer spacing of the graphite surface and increase the lithium-ion diffusion rate. However, the above methods have limited effect on improving the fast-charging capability of secondary batteries.

[0053] The inventors of this application conducted a detailed study of the electrode kinetics during secondary battery charging and discovered that a crucial factor affecting the improvement of graphite's fast-charging capability is the influence of electrolyte solvation. Electrolytes are typically obtained by uniformly mixing lithium salts and solvent molecules, thus usually comprising three components: solvent molecules, anions, and solvated lithium ions. Before lithium ions reach the surface of graphite particles and embed themselves during charging, solvated lithium ions need to undergo a desolvation process to remove solvent molecules. However, this process involves a high kinetic energy barrier, for example, approximately 50 kJ / mol to 70 kJ / mol.

[0054] Furthermore, the formation of lithium dendrites and dead lithium is another important factor affecting the fast-charging capability of secondary batteries. During the charging process of a secondary battery, when abnormalities occur such as insufficient lithium intercalation space at the negative electrode, excessive resistance to lithium ion intercalation at the negative electrode, or lithium ions rapidly detaching from the positive electrode but failing to intercalate into the negative electrode in equal quantities, the lithium ions that cannot intercalate into the negative electrode can only gain electrons on the surface of the negative electrode, thus forming silvery-white metallic lithium, i.e., "lithium dendrites." The formation of lithium dendrites not only degrades the performance of secondary batteries, such as shortening cycle life, but in severe cases, it can also form sharp morphologies that pierce the separator, causing a short circuit within the battery, potentially leading to catastrophic consequences such as combustion and explosion. At the same time, the continuously deposited metallic lithium can also detach from the surface of the negative electrode, forming "dead lithium" that cannot continue to participate in the reaction, resulting in a decrease in the energy density of the secondary battery.

[0055] The inventors of this application also discovered during their research on electrode dynamics during secondary battery charging that the high kinetic energy barrier in the desolvation process limits the speed at which lithium ions reach the surface of graphite particles and increases the resistance to lithium ion insertion into the negative electrode. In particular, when the secondary battery is charged at a high rate, it is easier to induce "lithium dendrites" and "dead lithium".

[0056] The inventors of this application, through extensive research, have proposed a novel fast-charging negative electrode active material that enables secondary batteries to have both high energy density and significantly improved fast-charging capability.

[0057] Negative electrode active materials

[0058] Specifically, the first aspect of the embodiments of this application provides a fast-charging negative electrode active material.

[0059] The fast-charging negative electrode active material includes carbon-based material particles, a coating layer located on at least a portion of the surface of the carbon-based material particles, and ferroelectric material dispersed in the coating layer. The coating layer includes conductive carbon material, and at least a portion of the ferroelectric material protrudes from the surface of the coating layer.

[0060] The negative electrode active material of this application exhibits excellent kinetic properties, which can improve the fast charging capability of the secondary battery without sacrificing its high energy density. Although the mechanism is not yet clear, the inventors speculate that the possible reasons include the following.

[0061] First, the surface of the negative electrode active material of this application has ferroelectric material, which has spontaneous polarization intensity. This spontaneous polarization intensity can reverse when the external electric field reverses, thereby reducing the kinetic energy barrier of the desolvation process of solvated lithium ions, accelerating the speed at which lithium ions reach the surface of carbon-based material particles, and reducing the resistance to lithium ion insertion into the negative electrode. Therefore, the negative electrode active material of this application has good kinetic performance and can withstand high-rate charging, thus improving the fast-charging capability of the secondary battery.

[0062] Secondly, in the negative electrode active material of this application, at least a portion of the ferroelectric material protrudes from the surface of the coating layer. This allows the ferroelectric material to directly contact both the electrolyte and the carbon-based material particles. The surface in contact with the electrolyte exhibits a negative charge, while the surface in contact with the carbon-based material particles exhibits a positive charge. This effectively reduces the kinetic energy barrier during the desolvation process, accelerates the rate at which lithium ions reach the surface of the carbon-based material particles, and reduces the resistance to lithium ion insertion into the negative electrode. Consequently, the negative electrode active material of this application possesses excellent kinetic performance, can withstand high-rate charging, and thus enhances the fast-charging capability of the secondary battery.

[0063] Third, as the charging process proceeds, the amount of lithium intercalated in the negative electrode gradually increases, and the activation energy that needs to be overcome for the lithium intercalation products to diffuse from the particle surface to the interior increases, making solid-phase diffusion more difficult. In the negative electrode active material of this application, the coating layer includes a conductive carbon material with good conductivity, which can increase the rate of lithium intercalation products to diffuse from the particle surface to the interior, giving the negative electrode active material good kinetic performance.

[0064] Fourth, in the negative electrode active material of this application, the conductive carbon material and carbon-based material particles in the coating layer are both active components that contribute to capacity, while the ferroelectric material is an inactive component that does not contribute to capacity. However, it can reduce the kinetic energy barrier of the desolvation process, accelerate the rate at which lithium ions reach the surface of the carbon-based material particles, and reduce the resistance to lithium ion insertion into the negative electrode. The negative electrode active material of this application disperses the ferroelectric material in the coating layer, and at least some of the ferroelectric material protrudes from the surface of the coating layer. This results in a larger exposed surface area of ​​the ferroelectric material and a larger contact area with the electrolyte, thereby reducing the kinetic energy barrier of the desolvation process with a smaller amount. Therefore, the secondary battery using the negative electrode active material of this application has high fast charging capability without sacrificing high energy density.

[0065] The negative electrode active material of this application can reduce the kinetic energy barrier of the desolvation process, accelerate the rate at which lithium ions reach the surface of carbon-based material particles, and reduce the resistance to lithium ion intercalation into the negative electrode, while containing fewer inactive components. Furthermore, the negative electrode active material of this application can increase the rate of solid-phase diffusion of lithium intercalation products from the particle surface to the interior. Therefore, the negative electrode active material of this application has excellent kinetic performance, can withstand high-rate charging, and improves the fast-charging capability of the secondary battery without sacrificing the high energy density of the secondary battery.

[0066] In some embodiments, optionally, all ferroelectric materials protrude from the surface of the coating layer. This results in a larger exposed surface area of ​​the ferroelectric materials, increasing the contact area with the electrolyte and enabling the reduction of the kinetic energy barrier in the desolvation process with a smaller dosage.

[0067] In some embodiments, the average thickness of the coating layer is H nm, the volume average particle size Dv50 of the ferroelectric material is d1 nm, and the fast-charging type negative electrode active material satisfies: 0.25 ≤ H / d1 ≤ 1.1. When H / d1 is less than 1.1, at least part of the ferroelectric material can protrude from the surface of the coating layer, thereby increasing the contact area with the electrolyte, so that the kinetic energy barrier of the desolvation process can be reduced when the amount used is small. When H / d1 is less than 0.25, the contact area between the ferroelectric material and the electrolyte is large, and the kinetic energy barrier of the desolvation process can be better reduced. However, at this time, the overall negative electrode active material is not easy to be compacted, resulting in possible deterioration of the ionic conductivity and electronic conductivity of the negative electrode sheet, which may in turn affect the fast charging ability, energy density and cycle performance of the secondary battery. Therefore, when H / d1 is within a suitable range, it is beneficial for the secondary battery to have high fast charging ability, high energy density and good cycle performance. Optionally, 0.25 ≤ H / d1 ≤ 1.0, 0.25 ≤ H / d1 ≤ 0.9, 0.25 ≤ H / d1 ≤ 0.8, 0.25 ≤ H / d1 ≤ 0.7, 0.25 ≤ H / d1 ≤ 0.6, 0.25 ≤ H / d1 ≤ 0.5, 0.25 ≤ H / d1 ≤ 0.4, 0.30 ≤ H / d1 ≤ 0.9, 0.30 ≤ H / d1 ≤ 0.8, 0.30 ≤ H / d1 ≤ 0.7, 0.30 ≤ H / d1 ≤ 0.6, 0.30 ≤ H / d1 ≤ 0.5, 0.30 ≤ H / d1 ≤ 0.4, 0.35 ≤ H / d1 ≤ 0.9, 0.35 ≤ H / d1 ≤ 0.8, 0.35 ≤ H / d1 ≤ 0.7, 0.35 ≤ H / d1 ≤ 0.6 or 0.35 ≤ H / d1 ≤ 0.5.

[0068] In some embodiments, the volume average particle size Dv50 of the ferroelectric material is d1 nm, and 0 < d1 ≤ 200. Optionally, 0 < d1 ≤ 180, 0 < d1 ≤ 160, 0 < d1 ≤ 140, 0 < d1 ≤ 120, 0 < d1 ≤ 100, 0 < d1 ≤ 80, 0 < d1 ≤ 60, 0 < d1 ≤ 40, 20 ≤ d1 ≤ 180, 20 ≤ d1 ≤ 160, 20 ≤ d1 ≤ 140, 20 ≤ d1 ≤ 120, 20 ≤ d1 ≤ 100, 20 ≤ d1 ≤ 80, 20 ≤ d1 ≤ 60, 20 ≤ d1 ≤ 40, 30 ≤ d1 ≤ 180, 30 ≤ d1 ≤ 160, 30 ≤ d1 ≤ 140, 30 ≤ d1 ≤ 120, 30 ≤ d1 ≤ 100, 30 ≤ d1 ≤ 80 or 30 ≤ d1 ≤ 60. The smaller the volume average particle size Dv50 of the ferroelectric material, the larger its specific surface area. Therefore, less ferroelectric material can be used at the same specific surface area, thereby reducing the energy density loss of the secondary battery.

[0069] In some embodiments, the average thickness of the coating layer is H nm, where 20 ≤ H ≤ 100. The coating layer comprises a conductive carbon material with good conductivity, thereby increasing the rate of diffusion of lithium intercalation products from the solid phase of the particle surface to the interior, resulting in good kinetic performance of the negative electrode active material. Therefore, a thicker coating layer can improve the fast charging capability of the secondary battery. However, the conductive carbon material in the coating layer has more pores, more surface defects, and a larger specific surface area. Consequently, a thicker coating layer leads to more interfacial side reactions between the negative electrode active material and the electrolyte, which can easily result in a lower initial coulombic efficiency and faster capacity decay of the negative electrode active material. Therefore, when the average thickness of the coating layer is within a suitable range, it is beneficial for the negative electrode active material to have both high fast charging capability and high specific capacity and high initial coulombic efficiency, thus enabling the secondary battery to simultaneously possess high fast charging capability, high energy density, and high cycle capacity retention. Alternatively, 20≤H≤95, 20≤H≤90, 20≤H≤85, 20≤H≤80, 20≤H≤75, 20≤H≤70, 20≤H≤65, 20≤H≤60, 20≤H≤55, 20≤H≤50, 20≤H≤45 or 20≤H≤40.

[0070] In some embodiments, optionally, the dielectric constant of the ferroelectric material is 100 or higher. When a ferroelectric material has a high dielectric constant, its surface can provide a new pathway for the desolvation process of solvated lithium ions. Furthermore, the higher the dielectric constant of the ferroelectric material, the better its effect in lowering the kinetic energy barrier of the desolvation process. However, this effect does not continuously increase. Simultaneously, a higher dielectric constant places increasingly higher demands on the fabrication process of the ferroelectric material, thereby increasing production costs. In some embodiments, optionally, the dielectric constant of the ferroelectric material can be from 100 to 100,000, for example, 100 to 50,000, 100 to 25,000, 100 to 10,000, 100 to 5,000, 100 to 4,000, 100 to 3,000, 100 to 2,000, 100 to 1,000, 100 to 500, 150 to 50,000, 150 to 250,000. 000, 150 to 10000, 150 to 5000, 150 to 4000, 150 to 3000, 150 to 2000, 150 to 1000, 150 to 500, 200 to 50000, 200 to 25000, 200 to 10000, 200 to 5000, 200 to 4000, 200 to 3000, 200 to 2000 or 200 to 1000.

[0071] In this application, the dielectric constant of ferroelectric materials refers to the dielectric constant at room temperature (25±5℃), which has a meaning known in the art and can be tested using instruments and methods known in the art. For example, after preparing the ferroelectric material into a circular sample, the capacitance C can be measured using an LCR meter and calculated according to the formula: dielectric constant ε=(C×d) / (ε0×A). C represents the capacitance, in farads (F); d represents the sample thickness, in cm; and A represents the sample area, in cm². 2 ε0 represents the vacuum permittivity, ε0 ​​= 8.854 × 10⁻⁶. -14 F / cm. In this application, the test conditions can be 1kHz, 1.0V, 25±5℃. The test standard can be based on GB / T 11297.11-2015. For sample preparation, please refer to Chinese patent application CN114217139A.

[0072] In some embodiments, the dielectric constant of the ferroelectric material is optionally higher than that of the electrolyte, thereby better reducing the kinetic energy barrier of the desolvation process and improving the fast charging capability of the secondary battery.

[0073] In some embodiments, the ferroelectric material is insoluble in water and has a high Curie temperature, typically above 80°C. This allows the ferroelectric material to better exert its effects during the use of secondary batteries.

[0074] In some embodiments, the ferroelectric material may optionally comprise one or more combinations selected from perovskite-structured oxides, tungsten bronze-type compounds, bismuth oxide-type layered compounds, lithium niobate (LiNbO3), and lithium tantalate (LiTaO3). More preferably, the ferroelectric material is selected from perovskite-structured oxides.

[0075] Optionally, the perovskite oxide has the molecular formula Ba. 1-x A x Ti 1-y B y O3. A includes one or more combinations selected from Pb, Sr, Ca, K, Na, and Cd, and B includes one or more combinations selected from Sn, Hf, Zr, Ce, Nb, and Th, where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1. For example, the perovskite structure oxide may include BaTiO3, Ba... 1-x1 Sr x1 TiO3(0≤x1≤1), SrTiO3, PbTiO3, PbZr y1 Ti 1-y1 O3(0≤y1≤1), BaZr y2 Ti 1-y2One or a combination of more of O3 (0 < y2 < 1), KNbO3, and NaNbO3.

[0076] Optionally, the tungsten bronze type compound may have the molecular formula M z WO3. M includes a combination of one or more selected from Na, K, Rb, and Cs, and 0 < z < 1. For example, the tungsten bronze type compound may include one or a combination of more selected from Na z1 WO3 (0 < z1 < 1), K z2 WO3 (0 < z2 < 1).

[0077] Optionally, the bismuth oxide type layered structure compound has the molecular formula (Bi2O2)(C n-1 D n O 3n+1 ). C includes a combination of one or more selected from Na, K, Ba, Sr, Pb, Ca, Ln, and Bi, D includes a combination of one or more selected from Zr, Cr, Nb, Ta, Mo, W, Fe, Ti, and V, and 2 ≤ n ≤ 5. For example, the bismuth oxide type layered structure compound may be one or a combination of more of SrBi2Nb2O9, SrBi2Ta2O9, SrBi2Nb2O9, Bi4Ti3O 12 .

[0078] In some embodiments, the mass ratio of the ferroelectric material to the carbon-based material particles is α1, and α1 is (0.5 - 10):100. Optionally, α1 is (0.5 - 9):100, (0.5 - 8):100, (0.5 - 7):100, (0.5 - 6):100, (0.5 - 5):100, (0.5 - 4):100, (0.5 - 3):100, (1 - 9):100, (1 - 8):100, (1 - 7):100, (1 - 6):100, (1 - 5):100, (1 - 4):100, or (1 - 3):100.

[0079] When α1 is within a suitable range, it is beneficial for the secondary battery to have both high fast charging ability and high energy density. And it can also effectively avoid the following situations: when α1 is larger, the content of non-active components in the negative electrode active material particles increases, and the content of active components decreases, which may cause the secondary battery to lose more energy density; when α1 is larger, the ferroelectric material may also cover more surfaces of the negative electrode active material, thereby reducing the active sites on the surface of the negative electrode active material, which may also lead to a deterioration of the fast charging ability and cycle performance of the secondary battery; when α1 is smaller, the content of the ferroelectric material is less, and its effect of reducing the kinetic energy barrier of the desolvation process may not be obvious, which may be disadvantageous for improving the fast charging ability of the secondary battery.

[0080] In some embodiments, the mass ratio of the coating layer to the carbon-based material particles is α2, where α2 is (2–10):100. Optionally, α2 is (2–9):100, (2–8):100, (2–7):100, (2–6):100, (2–5):100, (3–9):100, (3–8):100, (3–7):100, (3–6):100, or (3–5):100.

[0081] When α2 is within a suitable range, it is beneficial for the negative electrode active material to possess high fast charging capability while also exhibiting high specific capacity, high initial coulombic efficiency, and high compaction density. Consequently, the secondary battery can simultaneously possess high fast charging capability, high energy density, and high cycle capacity retention. Furthermore, it can effectively avoid the following situations: When α2 is large, the coating layer is thicker, and the content of conductive carbon material is higher. Due to the numerous pores and large specific surface area of ​​the conductive carbon material, there are more interfacial side reactions between the negative electrode active material and the electrolyte. Simultaneously, when α2 is large, the surface morphology of the conductive carbon material is rough and has more surface defects, making it difficult to compact the negative electrode active material. In addition, due to the unstable surface defect structure of the conductive carbon material, it is also prone to lower initial coulombic efficiency and faster capacity decay, which may further degrade the capacity utilization and cycle performance of the secondary battery. When α2 is small, it is not conducive to the rapid insertion and extraction of lithium ions, which may hinder the improvement of the fast charging capability of the secondary battery.

[0082] In some embodiments, the mass ratio of the ferroelectric material to the carbon-based material particles is α1, and the mass ratio of the coating layer to the carbon-based material particles is α2, wherein α1:α2 is 1:6 to 4:1, optionally 1:4 to 2:1.

[0083] When α1:α2 is within a suitable range, it is beneficial for the negative electrode active material to possess high fast charging capability while also exhibiting high specific capacity, high initial coulombic efficiency, and high compaction density. Consequently, the secondary battery can simultaneously possess high fast charging capability, high energy density, and high cycle capacity retention. Furthermore, it effectively avoids the following situations: When α1:α2 is large, the content of inactive components in the negative electrode active material particles increases, while the content of active components decreases, which may lead to a significant loss of energy density in the secondary battery and also hinder the rapid insertion and extraction of lithium ions; when α1:α2 is small, the content of ferroelectric materials is low, and their effect on lowering the kinetic energy barrier of the desolvation process may be insignificant, which may result in a poorer fast charging capability of the secondary battery and also easily lead to a lower initial coulombic efficiency and faster capacity decay of the negative electrode active material.

[0084] The coating layer comprises a conductive carbon material. Optionally, the conductive carbon material comprises amorphous carbon. Amorphous carbon refers to a transitional carbon material with a low degree of graphitization and crystallization, exhibiting an approximately amorphous morphology (or lacking a fixed shape and periodic structural regularity). It can be obtained through carbonization and sintering treatment with a carbon source (e.g., pitch, resin, biomass materials, etc.). Amorphous carbon has a larger interlayer spacing and does not cause volume shrinkage or expansion effects during lithium-ion extraction and insertion, resulting in a more stable crystal structure. This enables the negative electrode active material to possess good kinetic performance and withstand high-rate charging, thereby improving the fast-charging capability of the secondary battery. The amorphous carbon includes soft carbon, hard carbon, or a combination thereof. Optionally, in some embodiments, the conductive carbon material includes hard carbon, thereby further improving the fast-charging capability of the secondary battery.

[0085] In some embodiments, the carbon-based material particles comprise one or more combinations selected from graphite (e.g., artificial graphite, natural graphite, graphite oxide, etc.), mesophase carbon microspheres, hard carbon, and soft carbon, optionally selected from graphite. Graphite has the advantages of stable cycle performance and high specific capacity, thereby enabling secondary batteries to have high energy density and high cycle stability.

[0086] In some embodiments, the graphitization degree of the coating layer is 45% to 80%.

[0087] In some embodiments, the degree of graphitization of the carbon-based material particles is 88% to 96%.

[0088] The inventors discovered that when the coating layer and carbon-based material particles are within the above-mentioned graphitization range, it helps to achieve a reasonable match between the crystal structure of the coating layer and the carbon-based material particles, thereby effectively improving the solid-phase diffusion rate of lithium ions and thus improving the fast charging capability and cycle performance of secondary batteries.

[0089] In some embodiments, the morphology of the carbon-based material particles is primary particles, secondary particles, or a combination thereof. Secondary particles are typically obtained by agglomeration of primary particles. Optionally, in the carbon-based material particles with a secondary particle morphology, the ratio of the volume average particle size Dv50 of the primary particles to the volume average particle size Dv50 of the secondary particles they comprise is 0.2 to 0.5. When the carbon-based material particles have a secondary particle morphology and the ratio of the volume average particle size Dv50 of the primary particles to the volume average particle size Dv50 of the secondary particles they comprise is adjusted to a suitable range, it is beneficial for the carbon-based material particles to have a better degree of secondary particle formation, thereby achieving both good ion transport and electron transport performance and high structural stability.

[0090] In some embodiments, the volume average particle size Dv50 of the carbon-based material particles is d2μm, where 5≤d2≤20, and optionally, 8≤d2≤15. When the volume average particle size Dv50 of the carbon-based material particles is within a suitable range, it is beneficial for the negative electrode active material of this application to have higher electrochemical activity, thereby enabling the secondary battery to have a higher fast charging capability. Furthermore, it can effectively avoid the following situations: When the volume average particle size (Dv50) of carbon-based material particles is small, the specific capacity and compaction density of the negative electrode active material are low, which is not conducive to the design of high-energy-density batteries; at the same time, when the volume average particle size (Dv50) of carbon-based material particles is small, their specific surface area is large and their reactivity is high, which may lead to an increase in interfacial side reactions between the negative electrode active material and the electrolyte, resulting in an increase in the irreversible consumption of active lithium ions, and the capacity utilization and energy density of the secondary battery may deteriorate; when the volume average particle size (Dv50) of carbon-based material particles is large, the number of active sites on the particle surface is reduced, and the path for lithium intercalation products to diffuse from the solid phase on the particle surface to the interior is longer, which may be detrimental to improving the fast charging capability of the secondary battery.

[0091] In some embodiments, the volume average particle size Dv50 of the fast-charging negative electrode active material is 5 μm to 20 μm, optionally 8 μm to 15 μm. By adjusting the volume average particle size Dv50 of the negative electrode active material to a suitable range, it is beneficial for the negative electrode active material to have better ion transport and electron transport performance and fast charging performance, while also having a higher powder compaction density.

[0092] In some embodiments, the specific surface area of ​​the fast-charging negative electrode active material is 0.8 m². 2 / g to 1.3m 2 / g, optionally 0.9m 2 / g to 1.2m 2 / g. By adjusting the specific surface area of ​​the negative electrode active material within a suitable range, interfacial side reactions between the negative electrode sheet using it and the electrolyte can be reduced. At the same time, the negative electrode sheet using it can also have suitable electrochemical reactivity, thereby enabling the secondary battery to have a higher fast charging capability.

[0093] In some embodiments, the compaction density of the fast-charging negative electrode active material under a force of 20000N is 1.5 g / cm³. 3 Up to 1.9 g / cm 3 Optionally, it can be 1.5 g / cm³. 3 Up to 1.7 g / cm 3By adjusting the compaction density of the negative electrode active material powder within a suitable range, a higher compaction density of the negative electrode film can be achieved, resulting in a higher energy density for the secondary battery. Furthermore, adjusting the compaction density of the negative electrode active material powder within a suitable range also enhances the ability of the negative electrode film to maintain its pore structure during cycling, leading to better electrolyte wettability and improved cycle performance of the secondary battery.

[0094] In this application, the average thickness of the coating layer has a meaning known in the art and can be tested using instruments and methods known in the art. For example, a TEM (Transmission Electron Microscope) image can be obtained using a transmission electron microscope, and then the thickness at multiple (e.g., more than 30) different locations can be measured on the TEM image, and the average value can be taken as the average thickness of the coating layer.

[0095] In this application, the volume average particle size Dv50 of the material has a well-known meaning in the art, representing the particle size corresponding to a cumulative volume distribution percentage of 50%, which can be tested using instruments and methods known in the art. For example, it can be conveniently tested using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0096] In this application, the degree of graphitization of the material has a meaning known in the art and can be tested using instruments and methods known in the art. For example, it can be tested using an X-ray diffractometer (such as a Bruker D8 Discover), and the testing can be performed in accordance with JIS K 0131-1996 and JB / T 4220-2011 to obtain d. 002 Then, according to the formula g = (0.344 - d) 002 The degree of graphitization of the material is calculated as d / (0.344-0.3354)×100%. In the above formula, d 002 It is the interlayer spacing of the (002) crystal plane in the crystal structure of a material, expressed in nanometers (nm).

[0097] In this application, the specific surface area of ​​a material has a meaning known in the art and can be tested using instruments and 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 the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc., USA.

[0098] In this application, the powder compaction density of the material has a meaning known in the art and can be tested using instruments and methods known in the art. For example, it can be tested using an electronic pressure testing machine (e.g., UTM7305 type) according to standard GB / T24533-2009. An exemplary test method is as follows: Weigh 1g of material and add it to a container with a base area of ​​1.327cm². 2 In the mold, the pressure is increased to 2000 kg (equivalent to 20000 N), held for 30 s, then depressurized and held for 10 s. The compaction density of the powder under a force of 20000 N is then recorded and calculated.

[0099] It should be noted that the various parameter tests for the negative electrode active material mentioned above can be performed by sampling before coating or by sampling from the cold-pressed negative electrode film. As an example, when the negative electrode active material test sample is taken from the cold-pressed negative electrode film, the sampling can be performed as follows: Randomly select a cold-pressed negative electrode film and sample the negative electrode active material (e.g., by scraping powder with a blade); place the collected negative electrode active material powder in deionized water, then filter and dry it; finally, sinter the dried negative electrode active material at a certain temperature and time (e.g., 400℃, 2h) to remove the binder and conductive agent, thus obtaining the negative electrode active material test sample.

[0100] The fast-charging negative electrode active material of this application is described below with reference to the accompanying drawings. Figure 1 This is a schematic diagram of one embodiment of the fast-charging negative electrode active material 10 of this application. Figure 1 As shown, the fast-charging negative electrode active material 10 includes carbon-based material particles 101, a coating layer 102 located on at least a portion of the surface of the carbon-based material particles 101, and ferroelectric material 103 dispersed in the coating layer 102. The coating layer 102 includes conductive carbon material, and at least a portion of the ferroelectric material 103 protrudes from the surface of the coating layer 102.

[0101] Preparation method

[0102] The second aspect of this application provides a method for preparing a fast-charging negative electrode active material according to the first aspect of this application, comprising the steps of: S10, providing carbon-based material particles, a carbon source, and a ferroelectric material; S20, uniformly mixing the carbon-based material particles, the carbon source, and the ferroelectric material, and forming a coating layer including conductive carbon material on at least a portion of the surface of the carbon-based material particles by carbonization sintering treatment, wherein the ferroelectric material is dispersed in the coating layer and at least a portion of the ferroelectric material protrudes from the surface of the coating layer.

[0103] In this application, "carbon source" refers to a compound capable of forming a conductive carbon material. The carbon source includes one or more combinations selected from organic carbon sources and inorganic carbon sources. Optionally, the carbon source is an organic carbon source.

[0104] In some embodiments, the carbon source may optionally include one or more combinations selected from asphalt, resin, and biomass materials. For example, the asphalt may include one or more combinations selected from coal tar pitch and petroleum asphalt, optionally being petroleum asphalt. For example, the resin may include one or more combinations selected from phenolic resin and epoxy resin. For example, the biomass material refers to materials derived from living organisms such as animals, plants, and microorganisms, mainly composed of organic polymers, and chemically composed primarily of carbon, hydrogen, and oxygen; for example, it may be a polysaccharide (such as starch, sucrose polymers, glucose polymers, cellulose, etc.).

[0105] In some embodiments, the carbonization sintering temperature in S20 is optionally from 700°C to 1800°C, and more preferably from 1000°C to 1300°C.

[0106] In some embodiments, the carbonization sintering time in S20 is optionally 1 h to 15 h, or optionally 6 h to 14 h.

[0107] In S20, by controlling the carbonization sintering temperature and carbonization sintering time within the above range, the carbon source can be carbonized, and a coating layer containing conductive carbon material can be formed on at least a portion of the surface of the carbon-based material particles. At the same time, the coating layer can also have a suitable thickness and graphitization degree.

[0108] In some embodiments, the carbon-based material particles may be commercially available products, or optionally, they may be prepared by the following method: S101, providing coke powder and placing the coke powder into a reaction vessel; S102, graphitizing the coke powder to obtain carbon-based material particles.

[0109] In some embodiments, the coke powder may be a commercially available product, or optionally, it may be prepared by the following method: S1011, coking the coke raw material to obtain coke; S1012, crushing, shaping and grading the obtained coke to obtain coke powder.

[0110] In this application, "coke raw material" refers to a component that can be processed to obtain "coke", that is, a raw material used to prepare coke; "coke" refers to the product obtained by coking coke raw material; "coke powder" is completely identical to "coke" in composition, the difference being that "coke powder" refers to "coke" existing in the form of powder with a certain particle size, that is, "coke" is obtained by crushing and other processing to obtain "coke powder".

[0111] Optionally, the coking feedstock may include one or more combinations selected from petroleum-based feedstocks and coal-based feedstocks. As an example, the petroleum-based feedstock includes one or more combinations selected from heavy oil, residual oil, and vacuum residue, while the coal-based feedstock mainly includes coal tar pitch. Heavy oil, residual oil, and vacuum residue are typically produced in petroleum refining processes, while coal tar pitch is typically produced in coal dry distillation processes.

[0112] Optionally, the coke obtained in S1011 includes one or more combinations selected from petroleum-based non-needle coke, petroleum-based needle coke, coal-based non-needle coke, and coal-based needle coke. More preferably, the coke obtained in S1011 includes one or more combinations selected from petroleum-based non-needle coke (e.g., petroleum calcined coke, petroleum-based green coke) and petroleum-based needle coke. In particular, the coke obtained in S1011 is petroleum-based green coke. Using suitable coke can enable the prepared carbon-based material particles to have a suitable number of end faces and defects, thereby exhibiting better ion transport and electron transport properties and higher structural stability, which can improve the fast charging capability and cycle performance of the secondary battery.

[0113] Optionally, the coking treatment of the coking raw material in S1011 is carried out in a delayed coking unit. The delayed coking unit includes a heating furnace and a coking tower. The delayed coking process refers to the process of rapidly heating the coking raw material to the required coking temperature in the heating furnace, and then feeding it into the coking tower, where it undergoes preheating, cooling and other processes to produce coke.

[0114] Optionally, in S1012, the obtained coke may be crushed using equipment and methods known in the art, such as air jet mills, mechanical mills, roller mills or other crushing equipment.

[0115] The morphology of the coke powder obtained after crushing can include one or more combinations of lumpy, spherical, and near-spherical shapes. After crushing, the coke powder is further shaped to smooth out its sharp edges. The greater the degree of shaping, the closer the powder particles are to spherical shapes, which increases the active sites on the surface of the carbon-based material particles. Shaping also benefits the subsequent granulation process, giving the secondary particle portion of the resulting carbon-based material particles higher structural stability. Shaping can be performed using equipment and methods known in the art, such as shaping machines or other shaping equipment.

[0116] Crushing and shaping processes often produce a large number of excessively small particles, and sometimes excessively large particles as well. Therefore, grading can be performed as needed to remove these excessively small and large particles from the powder. Grading results in coke powder with a better particle size distribution, which is beneficial for subsequent granulation processes. Grading can be carried out using equipment and methods known in the art, such as grading sieves, gravity classifiers, and centrifugal classifiers.

[0117] In some embodiments, step S101 may optionally include: adding a binder to the reaction vessel, uniformly mixing the binder with the coke powder, and then granulating. Adding a binder can give the resulting carbon-based material particles a better secondary particle size, which is beneficial for improving the ion and electron transport performance of the negative electrode active material while also giving it higher structural stability.

[0118] Optionally, the binder comprises 3% to 12% by mass, more preferably 5% to 8%, based on the total mass of the coke powder. A suitable binder content avoids excessive particle agglomeration.

[0119] Optionally, the binder comprises one or more combinations selected from coal tar pitch, petroleum pitch, mesophase pitch, phenolic resin, epoxy resin, and petroleum resin.

[0120] Granulation can be performed using equipment and methods known in the art, such as granulators. Granulators typically include a stirred reactor and a module for temperature control of the reactor. By adjusting the stirring speed, heating rate, granulation temperature, and cooling rate during the granulation process, the degree of granulation and the structural strength of the particles can be controlled, ensuring that the volume average particle size Dv50 of the final carbon-based material particles is within the desired range.

[0121] In some embodiments, the graphitization temperature in S102 may optionally be 2400°C to 3200°C, more preferably 2800°C to 3200°C or 2900°C to 3100°C.

[0122] In some embodiments, the graphitization process in S102 may optionally be 20h to 48h.

[0123] Graphitization treatment can give carbon-based material particles a suitable degree of graphitization, thereby improving the specific capacity of the negative electrode active material; graphitization treatment can also give carbon-based material particles a smaller lattice expansion rate, thereby improving structural stability; graphitization treatment can also effectively eliminate bulk structural defects in carbon-based material particles, thereby improving the cycle stability of secondary batteries.

[0124] Graphitization can be carried out using equipment and methods known in the art, such as graphitization furnaces, particularly the Atchison graphitization furnace. After graphitization, a small number of excessively large particles formed during the graphitization process can be removed by sieving. This prevents excessively large particles from affecting the processing performance of the obtained negative electrode active material, such as the stability and coating performance of the negative electrode slurry.

[0125] In some embodiments, the preparation method of the fast-charging negative electrode active material includes the following steps: uniformly mixing coke powder and binder in a reaction vessel and then granulating; graphitizing the obtained granulation product to obtain carbon-based material particles; uniformly mixing the obtained carbon-based material particles with a carbon source and ferroelectric material, and forming a coating layer including conductive carbon material on at least a portion of the surface of the carbon-based material particles by carbonization sintering treatment, wherein the ferroelectric material is dispersed in the coating layer and at least a portion of the ferroelectric material protrudes from the surface of the coating layer.

[0126] The method for preparing the fast-charging negative electrode active material of this application is simple, inexpensive, and compatible with current carbon-based material particle preparation processes, particularly for artificial graphite, thus eliminating the need for additional production equipment and process steps. When preparing the fast-charging negative electrode active material using this method, ferroelectric materials are less prone to aggregation, allowing the desolvation effect of solvated lithium ions to act throughout the entire negative electrode active material. This results in a higher fast-charging capability and a longer lifespan for the negative electrode active material.

[0127] The raw materials and their contents used in the preparation method of the fast-charging negative electrode active material of this application can be referred to the fast-charging negative electrode active material of the first aspect of the embodiments of this application, and will not be repeated here.

[0128] Negative electrode sheet

[0129] A third aspect of this application provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a fast-charging negative electrode active material of the first aspect of this application or a fast-charging negative electrode active material prepared by the method of the second aspect of this application. For example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0130] In some embodiments, the negative electrode film may further comprise other negative electrode active materials known in the art for use in secondary batteries. As an example, the other negative electrode active materials include one or more combinations selected from natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials may include one or more combinations selected from elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials may include one or more combinations selected from elemental tin, tin oxide, and tin alloys.

[0131] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more combinations selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent is less than 5% based on the total mass of the negative electrode film layer.

[0132] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include one or more combinations selected from styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder is less than 5% based on the total mass of the negative electrode film layer.

[0133] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass percentage of the other additives is less than 2% based on the total mass of the negative electrode film.

[0134] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include copper foil or copper alloy foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. Examples of the metal material include one or more combinations selected from copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer base layer may include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0135] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0136] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0137] Secondary batteries

[0138] The fourth aspect of this application provides a secondary battery that includes the negative electrode sheet of the third aspect of this application.

[0139] A secondary battery, also known as a rechargeable battery or accumulator, is a battery that can be recharged after discharge to reactivate its active materials and continue to be used. A secondary battery includes an electrode assembly and an electrolyte. The electrode assembly typically includes a positive electrode, a negative electrode, and a separator. The separator is positioned between the positive and negative electrodes, primarily preventing short circuits between them while allowing lithium ions to pass through. The electrolyte, located between the positive and negative electrodes, conducts lithium ions. The secondary battery of this application can be a lithium-containing secondary battery, particularly a lithium-ion secondary battery.

[0140] [Negative electrode plate]

[0141] The negative electrode used in the secondary battery of this application is the negative electrode of any embodiment of the third aspect of this application.

[0142] [Positive electrode plate]

[0143] In some embodiments, 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. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0144] The positive electrode film layer includes a positive electrode active material, which may be a positive electrode active material known in the art for use in secondary batteries. For example, the positive electrode active material may include one or more combinations selected from lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include one or more combinations selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of lithium-containing phosphates with an olivine structure may include one or more combinations selected from lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, lithium iron manganese phosphate and carbon composites, and their respective modified compounds.

[0145] In some embodiments, to further improve the energy density of the secondary battery, the positive electrode active material may include one or more combinations of lithium transition metal oxides and their modified compounds as shown in Formula 1.

[0146] Li a Ni b Co c M d O e A f Formula 1

[0147] In Equation 1, 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes one or more combinations selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes one or more combinations selected from N, F, S and Cl.

[0148] In this application, the modified compounds of the above-mentioned positive electrode active materials may be those that have undergone doping modification and / or surface coating modification of the positive electrode active materials.

[0149] In some embodiments, the positive electrode film may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes one or more combinations selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent is less than 5% based on the total mass of the positive electrode film.

[0150] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include one or more combinations selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. In some embodiments, the mass percentage of the positive electrode binder is less than 5% based on the total mass of the positive electrode film layer.

[0151] In some embodiments, the positive current collector may be a metal foil or a composite current collector. Examples of metal foils include aluminum foil or aluminum alloy foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. Examples of the metal material include one or more combinations selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer substrate may include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0152] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this.

[0153] Electrolyte

[0154] The electrolyte used in this application may be a known electrolyte for secondary batteries. The electrolyte includes lithium salt and organic solvent.

[0155] As an example, the lithium salt may include one or more combinations selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0156] As an example, the organic solvent may include one or more combinations selected from ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ester carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0157] [Isolation membrane]

[0158] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0159] In some embodiments, the material of the separator may include one or more combinations selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different.

[0160] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process or a stacking process.

[0161] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0162] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as one or more combinations of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0163] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 2 This is an example of a square-structured secondary battery 5.

[0164] In some embodiments, such as Figure 3As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0165] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer packaging, dried, and injected with an electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0166] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0167] Figure 4 This is a schematic diagram of battery module 4 as an example. Figure 4 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0168] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0169] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0170] Figure 5 and Figure 6 This is a schematic diagram of battery pack 1 as an example. Figure 5 and Figure 6 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0171] Electrical appliances

[0172] A fifth aspect of this application provides an electrical device, which includes at least one of the secondary battery, battery module, and battery pack described in this application. The secondary battery, battery module, and battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0173] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0174] Figure 7 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0175] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0176] Example

[0177] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0178] Example 1

[0179] Step (1): Preparation of negative electrode active material

[0180] S10 involves delayed coking of petroleum residue oil at 490℃~510℃ to obtain petroleum non-needle coke raw coke. The raw coke is then crushed, shaped, and graded to obtain coke powder. This coke powder is mixed with coal tar pitch as a binder and then granulated. The granulated product is placed in a graphite crucible, which is then placed in an Atchison graphitization furnace. Resistance material is filled around the graphite crucible, and current is passed through the resistance material to generate heat. Graphitization is carried out at approximately 3000℃ for about 30 hours to obtain artificial graphite particles. The volume average particle size (Dv50) of the artificial graphite particles is approximately 9.8 μm, and the degree of graphitization is approximately 92%.

[0181] S20: The obtained artificial graphite particles are uniformly mixed with carbon source petroleum asphalt (added by weight based on residual carbon value) and ferroelectric material BaTiO3 (volume average particle size Dv50 of 200 nm and dielectric constant of 2000) at a mass ratio of 100:3:3. The mixture is then subjected to carbonization sintering in a track kiln at a maximum temperature of approximately 1150°C for approximately 12 hours. This process forms an amorphous carbon coating layer on at least a portion of the surface of the artificial graphite particles, resulting in the negative electrode active material. In the obtained negative electrode active material, BaTiO3 is dispersed within the coating layer, and at least a portion of the BaTiO3 protrudes from the surface of the coating layer.

[0182] Step (2): Preparation of negative electrode sheet

[0183] The prepared negative electrode active material, styrene-butadiene rubber (SBR) binder, sodium carboxymethyl cellulose (CMC-Na) thickener, and carbon black conductive agent were thoroughly mixed in an appropriate amount of deionized water at a mass ratio of 96.8:1.2:1.2:0.8 to form a uniform negative electrode slurry. The negative electrode slurry was then uniformly coated onto the surface of a copper foil current collector. After drying and cold pressing, the negative electrode sheet was obtained. The coating amount was 0.162 kg / m². 2 The compacted density is 1.65 g / cm³. 3 .

[0184] Step (3): Preparation of the positive electrode sheet

[0185] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2 (NCM523), conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an appropriate amount of NMP solvent at a mass ratio of 96.2:1.8:2 to form a uniform positive electrode slurry. The positive electrode slurry was then uniformly coated onto the surface of the positive electrode current collector aluminum foil. After drying and cold pressing, the positive electrode sheet was obtained. The coating amount was 0.256 kg / m². 2 The compacted density is 3.4 g / cm³. 3 .

[0186] Step (4): Preparation of electrolyte

[0187] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0188] Step (5): Preparation of the separating membrane

[0189] Porous polyethylene film is used as the separator.

[0190] Step (6): Preparation of secondary battery

[0191] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0192] Examples 2 to 16

[0193] The secondary batteries in Examples 2 to 16 were prepared in a similar manner to those in Example 1, except that the relevant parameters in the "Preparation of Negative Electrode Active Material" were adjusted. The specific parameters are detailed in Table 2.

[0194] Comparative Example 1

[0195] The secondary battery of Comparative Example 1 was prepared in a similar manner to that of Example 1, except that conventional uncoated artificial graphite was used as the negative electrode active material. Specifically, the artificial graphite was prepared according to the following method.

[0196] Petroleum residue oil was subjected to delayed coking at 490℃~510℃ to obtain petroleum non-needle coke raw coke. The raw coke was then crushed, shaped, and graded to obtain coke powder. The obtained coke powder was mixed with coal tar pitch as a binder and then granulated. The granulated product was placed in a graphite crucible, which was then placed in an Atchison graphitization furnace. Resistance material was filled around the graphite crucible, and current was passed through the resistance material to generate heat. Graphitization was carried out at approximately 3000℃ for about 30 hours to obtain artificial graphite particles. The volume average particle size (Dv50) of the artificial graphite particles was approximately 9.8 μm, and the degree of graphitization was approximately 92%.

[0197] Comparative Example 2

[0198] The secondary battery of Comparative Example 2 was prepared in a similar manner to that of Example 1, except that the negative electrode active material was prepared in accordance with the following method.

[0199] S10 involves delayed coking of petroleum residue oil at 490℃~510℃ to obtain petroleum non-needle coke raw coke. The raw coke is then crushed, shaped, and graded to obtain coke powder. This coke powder is mixed with coal tar pitch as a binder and then granulated. The granulated product is placed in a graphite crucible, which is then placed in an Atchison graphitization furnace. Resistance material is filled around the graphite crucible, and current is passed through the resistance material to generate heat. Graphitization is carried out at approximately 3000℃ for about 30 hours to obtain artificial graphite particles. The volume average particle size (Dv50) of the artificial graphite particles is approximately 9.8 μm, and the degree of graphitization is approximately 92%.

[0200] S20 involves mixing the obtained artificial graphite particles with carbon source petroleum asphalt and then performing carbonization and sintering treatment in a track kiln. The highest temperature zone is approximately 1150°C, and the running time in the highest temperature zone is approximately 12 hours, in order to form an amorphous carbon coating layer on at least a portion of the surface of the artificial graphite particles, thereby obtaining the negative electrode active material.

[0201] Comparative Example 3

[0202] The secondary battery of Comparative Example 3 was prepared in a similar manner to that of Example 1, except that the negative electrode active material and the negative electrode sheet were prepared in accordance with the following method.

[0203] Step (1): Preparation of negative electrode active material

[0204] S10 involves delayed coking of petroleum residue oil at 490℃~510℃ to obtain petroleum non-needle coke raw coke. The raw coke is then crushed, shaped, and graded to obtain coke powder. This coke powder is mixed with coal tar pitch as a binder and then granulated. The granulated product is placed in a graphite crucible, which is then placed in an Atchison graphitization furnace. Resistance material is filled around the graphite crucible, and current is passed through the resistance material to generate heat. Graphitization is carried out at approximately 3000℃ for about 30 hours to obtain artificial graphite particles. The volume average particle size (Dv50) of the artificial graphite particles is approximately 9.8 μm, and the degree of graphitization is approximately 92%.

[0205] S20 involves mixing the obtained artificial graphite particles with carbon source petroleum asphalt and then performing carbonization and sintering treatment in a track kiln. The highest temperature zone is approximately 1150°C, and the running time in the highest temperature zone is approximately 12 hours, in order to form an amorphous carbon coating layer on at least a portion of the surface of the artificial graphite particles, thereby obtaining the negative electrode active material.

[0206] Step (2): Preparation of negative electrode sheet

[0207] The above-prepared anode active material, ferroelectric material BaTiO3 (volume average particle size Dv50 of 85nm), binder styrene-butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC-Na), and conductive agent carbon black were mixed thoroughly in an appropriate amount of deionized water at a mass ratio of 93.8:3:1.2:1.2:0.8 to form a uniform anode slurry. The anode slurry was then uniformly coated onto the surface of the copper foil of the anode current collector. After drying and cold pressing, the anode sheet was obtained.

[0208] Comparative Example 4

[0209] The secondary battery of Comparative Example 4 was prepared in a similar manner to that of Example 1, except that the negative electrode active material was prepared in accordance with the following method.

[0210] S10 involves delayed coking of petroleum residue oil at 490℃~510℃ to obtain petroleum non-needle coke raw coke. The raw coke is then crushed, shaped, and graded to obtain coke powder. This coke powder is mixed with coal tar pitch as a binder and then granulated. The granulated product is placed in a graphite crucible, which is then placed in an Atchison graphitization furnace. Resistance material is filled around the graphite crucible, and current is passed through the resistance material to generate heat. Graphitization is carried out at approximately 3000℃ for about 30 hours to obtain artificial graphite particles. The volume average particle size (Dv50) of the artificial graphite particles is approximately 9.8 μm, and the degree of graphitization is approximately 92%.

[0211] S20 involves mixing the obtained artificial graphite particles with carbon source petroleum asphalt and then performing carbonization and sintering treatment in a track kiln. The highest temperature zone is approximately 1150°C, and the running time in the highest temperature zone is approximately 12 hours, in order to form an amorphous carbon coating layer on at least a portion of the surface of the artificial graphite particles.

[0212] S30: The obtained artificial graphite particles with amorphous carbon coating are ball-milled with ferroelectric material BaTiO3 (volume average particle size Dv50 of 85nm) at a mass ratio of 97:3. The mixture is then placed in a planetary ball mill and ball-milled for 2 hours at an ambient temperature of 25℃ and a rotation speed of 300 rpm to obtain the negative electrode active material.

[0213] Test section

[0214] (1) Volume average particle size Dv50 test

[0215] A certain amount of the prepared negative electrode active material sample was taken and the volume average particle size Dv50 was measured using a Mastersizer 2000E laser particle size analyzer. The testing standard was based on GB / T 19077-2016.

[0216] (2) Specific surface area test

[0217] A certain amount of the prepared negative electrode active material sample was taken, and the specific surface area was measured using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA. The specific surface area was calculated using the BET (Brunauer-Emmett-Teller) method. The testing standard was based on GB / T 19587-2017.

[0218] (3) Powder compaction density test

[0219] A certain amount of the negative electrode active material sample prepared above was added to a UTM7305 electronic pressure testing machine with a bottom area of ​​1.327 cm². 2 In the mold, pressure was applied to 2000 kg (equivalent to 20000 N), held for 30 seconds, then depressurized and held for 10 seconds. The compacted density of the negative electrode active material under a force of 20000 N was then recorded and calculated. The test standard was based on GB / T24533-2009.

[0220] (4) Graphitization degree test

[0221] A certain amount of the negative electrode active material sample prepared above was taken and tested using a Bruker D8 Discover X-ray diffractometer to obtain the interlayer spacing d of the (002) crystal plane of the coating layer and the carbon-based material particles, respectively. 002 Then, according to the formula g = (0.344 - d) 002 The graphitization degree of the coating layer, g1, and the graphitization degree of the carbon-based material particles, g2, are calculated by multiplying g1 by (0.344-0.3354) by 100%. The testing standards are based on JIS K 0131-1996 and JB / T 4220-2011.

[0222] (5) Average thickness test of the coating layer

[0223] Take a certain amount of the negative electrode active material sample prepared above, cut a thin slice of about 100 nm from the middle of a single particle, and then perform transmission electron microscopy analysis on the thin slice to obtain TEM image. Then measure the thickness at multiple (e.g., more than 5) different positions on the TEM image, and test at least 6 negative electrode active material samples. Take the average value of the test results as the average thickness of the coating layer.

[0224] (6) Initial capacity test

[0225] The negative electrode active material, conductive carbon black, and binder polyvinylidene fluoride (PVDF) prepared above were mixed evenly with solvent N-methylpyrrolidone (NMP) at a mass ratio of 91.6:1.8:6.6 to form a slurry. The prepared slurry was coated onto copper foil and dried in an oven for later use. Then, a lithium metal sheet was used as the counter electrode, a polyethylene (PE) film was used as the separator, a few drops of the same electrolyte as the above secondary battery were added, and the CR2430 coin cell was assembled in an argon-protected glove box.

[0226] After the obtained coin cells were allowed to stand for 12 hours, they were discharged at 25°C with a constant current of 0.05C to 0.005V, allowed to stand for 10 minutes, and then discharged again with a constant current of 50μA to 0.005V. After standing for 10 minutes, they were discharged again with a constant current of 10μA to 0.005V. Then, they were charged at a constant current of 0.1C to 2V, and the charging capacity was recorded. The ratio of the charging capacity to the mass of the negative electrode active material is the initial specific capacity of the negative electrode active material.

[0227] (7) Secondary battery fast charging performance test

[0228] At 25°C, the prepared secondary battery was charged at a constant current of 0.33C to the charging cutoff voltage of 4.4V, 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 2.8V. Its actual capacity was recorded as C0.

[0229] Then, the secondary battery was sequentially charged at a constant current of 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, 3.5C0, 4C0, and 4.5C0 until the full battery charging cutoff voltage of 4.4V or the negative terminal cutoff potential of 0V (whichever comes first). After each charging, it was discharged at 1C0 until the full battery discharge cutoff voltage of 2.8V. The state of charge (SOC) was recorded at different charging rates until 10%, 20%, 30%...80%. By plotting the negative electrode potential corresponding to the state of charge (SOC), rate-negative electrode potential curves are generated for different SOC states. Linear fitting yields the charging rate corresponding to a negative electrode potential of 0V at each SOC state. This charging rate is the charging window for that SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC. The charging time T from 10% SOC to 80% SOC is calculated using the formula (60 / C20%SOC + 60 / C30%SOC + 60 / C40%SOC + 60 / C50%SOC + 60 / C60%SOC + 60 / C70%SOC + 60 / C80%SOC) × 10%. A shorter charging time T indicates better fast-charging performance of the secondary battery.

[0230] (8) Cyclic performance test

[0231] At 25°C, the prepared secondary battery was charged at a constant current of 0.33C to the charging cutoff voltage of 4.4V, then charged at 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 2.8V. Its initial capacity was recorded as C0. Then, charging was performed according to the strategy shown in Table 1, followed by discharging at 0.33C. The discharge capacity Cn for each cycle was recorded until the cycle capacity retention (i.e., Cn / C0 × 100%) reached 80%, and the number of cycles was recorded. A higher number of cycles indicates better cycle performance of the secondary battery.

[0232] Table 1

[0233] State of charge (SOC) of a secondary battery Charging rate (C) 0～10％ 0.33 10％～20％ 5.2 20％～30％ 4.5 30％～40％ 4.2 40％～50％ 3.3 50％～60％ 2.6 60％～70％ 2.0 70％～80％ 1.5 80％～100％ 0.33

[0234] Table 2 shows the preparation parameters of the negative electrode active materials in Examples 1 to 16.

[0235] Table 3 shows the test results of Examples 1 to 16 and Comparative Examples 1 to 4 obtained according to the above performance test method.

[0236]

[0237]

[0238] As can be seen from the test results in Table 3, the negative electrode active material of this application has good kinetic performance, which can shorten the fast charging time of the secondary battery and extend the cycle life of the secondary battery, without sacrificing the high specific capacity of the negative electrode active material.

[0239] Compared with Comparative Example 1, Comparative Example 2 uses amorphous carbon-coated artificial graphite as the negative electrode active material, which can improve the fast charging performance and cycle performance of the secondary battery to a certain extent, but the improvement effect is limited and cannot meet people's requirements for higher fast charging capability and longer cycle life of secondary batteries.

[0240] Compared to Comparative Example 2, Comparative Example 3 also added ferroelectric materials to the negative electrode slurry, which further improved the fast-charging and cycle performance of the secondary battery. However, the improvement effect was limited and could not meet the requirements for higher fast-charging capabilities and longer cycle life of secondary batteries. The possible reasons are that, by physically mixing ferroelectric materials into the negative electrode slurry, on the one hand, the high density of ferroelectric materials makes them prone to settling in the slurry, making it difficult to form a stable negative electrode slurry, thus affecting production yield and the quality of the negative electrode sheet; on the other hand, the physical mixing method can lead to some ferroelectric materials and negative electrode active materials not forming physical contact in the negative electrode sheet, thus failing to exert the function of the ferroelectric materials, resulting in limited improvement in the fast-charging and cycle performance of the secondary battery.

[0241] Compared to Comparative Example 1, Comparative Example 4 uses barium titanate-coated artificial graphite as the negative electrode active material. However, the negative electrode active material is obtained through direct ball milling. Compared to Comparative Example 1, it improves the fast charging performance and cycle performance of the secondary battery to some extent, but the improvement is limited and cannot meet the requirements for higher fast charging capability and longer cycle life of secondary batteries. The possible reasons are as follows: Firstly, direct ball milling combines artificial graphite particles and ferroelectric material particles by impacting and grinding them to form the negative electrode active material. However, high-energy ball milling can damage the morphology of the already formed artificial graphite particles, potentially causing the amorphous carbon coating layer on the surface to detach, affecting the fast charging performance of the negative electrode active material. Secondly, damage to the surface of the negative electrode active material can lead to the embedding of electrolyte (especially solvent) into the negative electrode active material, increasing the irreversible consumption of active lithium ions, thereby reducing the cycle performance of the secondary battery.

[0242] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A fast-charging negative electrode active material, wherein, The fast-charging negative electrode active material includes carbon-based material particles, a coating layer located on at least a portion of the surface of the carbon-based material particles, and ferroelectric material dispersed in the coating layer. The coating layer includes conductive carbon material, and all of the ferroelectric material protrudes from the surface of the coating layer. Wherein, the volume average particle size Dv50 of the ferroelectric material is d1 nm, 0 < d1 ≤ 200, and / or, the average thickness of the coating layer is H nm, 20 ≤ H ≤ 95.

2. The fast-charging negative electrode active material according to claim 1, wherein, The average thickness of the coating layer is H nm, the volume average particle size Dv50 of the ferroelectric material is d1 nm, and the fast-charging negative electrode active material satisfies: 0.25 ≤ H / d1 ≤ 1.

1.

3. The fast-charging negative electrode active material according to claim 2, wherein, 0.25 ≤ H / d1 ≤ 0.

5.

4. The fast-charging negative electrode active material according to any one of claims 1-3, wherein 0 < d1 ≤ 100; and / or, 20 ≤ H ≤ 50.

5. The fast-charging negative electrode active material according to any one of claims 1-4, wherein, The mass ratio of the ferroelectric material to the carbon-based material particles is α1, where α1 is (0.5~10):100; and / or, The mass ratio of the coating layer to the carbon-based material particles is α2, where α2 is (2~10):

100.

6. The fast-charging negative electrode active material according to claim 5, wherein, α1 is (1~3):

100.

7. The fast-charging negative electrode active material according to claim 5, wherein, α2 is (2~5):

100.

8. The fast-charging negative electrode active material according to any one of claims 1-7, wherein, The mass ratio of the ferroelectric material to the carbon-based material particles is α1, and the mass ratio of the coating layer to the carbon-based material particles is α2, where α1:α2 is 1:6 to 4:

1.

9. The fast-charging negative electrode active material according to claim 8, wherein, The ratio of α1:α2 is 1:4 to 2:

1.

10. The fast-charging negative electrode active material according to any one of claims 1-9, wherein, The graphitization degree of the coating layer is 45% to 80%; and / or, The degree of graphitization of the carbon-based material particles is 88% to 96%.

11. The fast-charging negative electrode active material according to any one of claims 1-10, wherein, The volume average particle size Dv50 of the carbon-based material particles is d2 μm, where 5 ≤ d2 ≤ 20.

12. The fast-charging negative electrode active material according to claim 11, wherein, 8 ≤ d2≤ 15。 13. The fast-charging negative electrode active material according to any one of claims 1-12, wherein, The morphology of the carbon-based material particles is primary particles, secondary particles, or a combination thereof.

14. The fast-charging negative electrode active material according to claim 13, wherein, In the carbon-based material particles with the secondary particle morphology, the ratio of the volume average particle size Dv50 of the primary particles to the volume average particle size Dv50 of the secondary particles they form is 0.2 to 0.

5.

15. The fast-charging negative electrode active material according to any one of claims 1-14, wherein, The dielectric constant of the ferroelectric material is 100 or higher; and / or, The Curie temperature of the ferroelectric material is above 80°C.

16. The fast-charging negative electrode active material according to claim 15, wherein, The dielectric constant of the ferroelectric material is between 100 and 100,000.

17. The fast-charging negative electrode active material according to any one of claims 1-16, wherein, The carbon-based material particles include one or more combinations selected from graphite, mesophase carbon microspheres, hard carbon, and soft carbon; and / or, The conductive carbon material in the coating layer includes amorphous carbon; and / or, The ferroelectric material includes one or more combinations selected from perovskite structure oxides, tungsten bronze type compounds, bismuth oxide type layered structure compounds, lithium niobate, and lithium tantalate.

18. The fast-charging negative electrode active material according to claim 17, wherein, The carbon-based material particles are selected from graphite.

19. The fast-charging negative electrode active material according to claim 17, wherein, The conductive carbon material in the coating layer includes hard carbon.

20. The fast-charging negative electrode active material according to any one of claims 1-19, wherein, The fast-charging negative electrode active material satisfies at least one of the following conditions (1) to (3): (1) The volume average particle size Dv50 of the fast-charging negative electrode active material is 5 μm to 20 μm; (2) The specific surface area of ​​the fast-charging negative electrode active material is 0.8 m². 2 / g to 1.3 m 2 / g; (3) The compaction density of the fast-charging negative electrode active material under a force of 20000N is 1.5 g / cm³. 3 Up to 1.9 g / cm 3 .

21. The fast-charging negative electrode active material according to claim 20, wherein, The volume average particle size Dv50 of the fast-charging negative electrode active material is 8 μm to 15 μm.

22. The fast-charging negative electrode active material according to claim 20, wherein, The specific surface area of ​​the fast-charging negative electrode active material is 0.9 m². 2 / g to 1.2 m 2 / g.

23. The fast-charging negative electrode active material according to claim 20, wherein, The compacted density of the fast-charging negative electrode active material under a force of 20000N is 1.5 g / cm³. 3 Up to 1.7 g / cm 3 .

24. A method for preparing a fast-charging negative electrode active material, comprising the following steps: S10 provides carbon-based material particles, carbon sources, and ferroelectric materials; S20, the carbon-based material particles, the carbon source, and the ferroelectric material are uniformly mixed, and a coating layer including conductive carbon material is formed on at least a portion of the surface of the carbon-based material particles through carbonization sintering treatment, wherein... The ferroelectric material is dispersed in the coating layer and all of the ferroelectric material protrudes from the surface of the coating layer; Wherein, the volume average particle size Dv50 of the ferroelectric material is d1 nm, 0 < d1 ≤ 200, and / or, the average thickness of the coating layer is H nm, 20 ≤ H ≤ 95.

25. The method according to claim 24, wherein, The carbon source includes one or more combinations selected from bitumen, resin, and biomass materials.

26. The method according to claim 24 or 25, wherein, The carbonization and sintering temperature in S20 is from 700°C to 1800°C; and / or, The carbonization and sintering time in S20 is 1 hour to 15 hours.

27. The method according to claim 26, wherein, The carbonization and sintering temperature in S20 is 1000℃ to 1300℃.

28. The method according to claim 26, wherein, The carbonization and sintering time in S20 is 6 to 14 hours.

29. The method according to any one of claims 24-28, wherein, The carbon-based material particles are prepared by the following method: S101, provide coke powder and place the coke powder into a reaction vessel; S102, the coke powder is graphitized to obtain carbon-based material particles.

30. A negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein, The negative electrode film layer comprises the fast-charging negative electrode active material according to any one of claims 1-23 or the fast-charging negative electrode active material prepared by any one of claims 24-29.

31. A secondary battery comprising the negative electrode sheet as described in claim 30.

32. An electrical device comprising the secondary battery as described in claim 31.

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