Rapid charging negative electrode active material and method for producing the same, negative electrode sheet, secondary battery, and power consumption device

Abstract

The present application provides a rapid charging negative electrode active material and a method for preparing the same, a negative electrode sheet, a secondary battery, and a power consumption device. The rapid charging negative electrode active material includes carbon-based material particles, a coating layer located on at least a part of the surface of the carbon-based material particles, and a ferroelectric material dispersed in the coating layer, the coating layer including a conductive carbon material, and at least a part of the ferroelectric material protruding from the surface of the coating layer. The rapid charging negative electrode active material according to the present application has good dynamic performance, can withstand high charging rates, and improves the rapid charging ability of the secondary battery without impairing the high energy density of the secondary battery.

Description

[Technical Field]

[0001] The present application relates to the technical field of batteries, and more particularly to a fast-charging negative electrode active material and a method for preparing the same, a negative electrode sheet, a secondary battery, and a power consuming device. [Background technology]

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydroelectric, thermal, wind, and solar power plants, as well as in many fields, including power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. As secondary batteries become more widely used and widespread, the demand for fast charging capabilities of secondary batteries is increasing. As a key component of secondary batteries, anode active materials have a significant impact on the charging capabilities of secondary batteries. Currently, graphite is one of the most commonly used anode active materials for secondary batteries; however, the fast charging capabilities of conventional graphite have already reached a bottleneck, making it unable to meet the demand for higher fast charging capabilities of secondary batteries. Summary of the Invention

[0003] The purpose of the present application is to provide a fast-charging negative electrode active material, a method for preparing the same, a negative electrode sheet, a secondary battery, and a power consumption device, which can significantly improve the fast charging capability of a secondary battery while providing a high energy density.

[0004] A first aspect of the present application provides a fast-charging negative electrode active material comprising: carbon-based material particles; a coating layer located on at least a portion of the surfaces of the carbon-based material particles; and a ferroelectric material dispersed in the coating layer, wherein the coating layer comprises a conductive carbon material, and at least a portion of the ferroelectric material protrudes from the surface of the coating layer.

[0005] On the premise that the negative electrode active material of the present application contains few inactive components, it can reduce the kinetic energy barrier in the desolvation process, increase the speed at which lithium ions reach the surface of the carbon-based material particles, and reduce the insertion resistance of lithium ions into the negative electrode. The negative electrode active material of the present application can also increase the speed at which the lithium insertion product diffuses from the particle surface to the inside in the solid phase. Therefore, the negative electrode active material of the present application has good kinetic performance without impairing the high energy density of the secondary battery, can withstand high-rate charging, and can improve the rapid charging ability of the secondary battery.

[0006] In any embodiment of the present application, the average thickness of the coating layer is H nm, the volume average particle diameter Dv50 of the ferroelectric material is d1 nm, and the rapid charging type negative electrode active material satisfies 0.25 ≦ H / d1 ≦ 1.1, preferably 0.25 ≦ H / d1 ≦ 0.5. Thereby, it is advantageous for the secondary battery to simultaneously have high rapid charging ability, high energy density and good cycle performance.

[0007] In any embodiment of the present application, the volume average particle diameter Dv50 of the ferroelectric material is d1 nm, 0 < d1 ≦ 200, preferably 0 < d1 ≦ 100. Thereby, the ferroelectric material adopted when the specific surface area is the same can be reduced, and the energy density loss of the secondary battery can be reduced.

[0008] In any embodiment of the present application, the average thickness of the coating layer is H nm, 20 ≦ H ≦ 100, preferably 20 ≦ H ≦ 50. Thereby, the secondary battery can simultaneously have high rapid charging ability, high energy density and high cycle capacity retention rate.

[0009] 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 to 10):100, preferably (1 to 3):100. Thereby, it is advantageous for the secondary battery to simultaneously have high rapid charging ability and high energy density.

[0010] 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, preferably (2-5):100. This is advantageous in that the negative electrode active material has a high fast charging capability, as well as a high capacity per gram, a high initial coulombic efficiency, and a high compaction density.

[0011] In any embodiment of the present application, the mass ratio of the ferroelectric material to the carbon-based material particles is α1, the mass ratio of the coating layer to the carbon-based material particles is α2, and α1:α2 is 1:6 to 4:1, preferably 1:4 to 2:1, thereby enabling the secondary battery to simultaneously have a high rapid charging capability, a high energy density, and a high cycle capacity retention rate.

[0012] In any embodiment of the present application, the graphitization degree of the coating layer is 45 to 80%.

[0013] In any embodiment of the present application, the conductive carbon material in the coating layer includes amorphous carbon, and preferably hard carbon, which can further improve the rapid charging capability of the secondary battery.

[0014] In any embodiment of the present application, the graphitization degree of the carbon-based material particles is 88% to 96%.

[0015] In any embodiment of the present application, the volume average particle size Dv50 of the carbon-based material particles is d2 μm, and 5≦d2≦20, preferably 8≦d2≦15, which allows the secondary battery to have a higher rapid charging capability.

[0016] In any embodiment of the present application, the carbon-based material particles are in the form of primary particles, secondary particles, or a combination thereof, and preferably, in the carbon-based material particles in the form of secondary particles, the ratio of the volume average particle diameter Dv50 of the primary particles to the volume average particle diameter Dv50 of the secondary particles formed therefrom is 0.2 to 0.5, which is advantageous in that the carbon-based material particles have good ion transport and electron transport properties as well as high structural stability.

[0017] In any embodiment of the present application, the carbon-based material particles include one or a combination of one or more selected from graphite, mesocarbon microbeads, hard carbon, and soft carbon, and are preferably selected from graphite, thereby providing the secondary battery with high energy density and high cycle stability.

[0018] In any embodiment of the present application, the dielectric constant of the ferroelectric material is 100 or more, preferably 100 to 100,000, which can better reduce the kinetic energy barrier in the desolvation process and improve the fast charging capability of the secondary battery.

[0019] In any embodiment of the present application, the ferroelectric material has a Curie temperature of 80° C. or higher, which can better reduce the kinetic energy barrier in the desolvation process and improve the fast charging capability of the secondary battery.

[0020] In any embodiment of the present application, the ferroelectric material includes one or a combination of a plurality of materials selected from a perovskite structure oxide, a tungsten bronze type compound, a bismuth oxide type layer structure compound, lithium niobate, and lithium tantalate.

[0021] In any embodiment of the present application, the volume average particle size Dv50 of the fast charging negative electrode active material is 5 μm to 20 μm, preferably 8 μm to 15 μm, which is advantageous for the negative electrode active material to have better ion transport and electron transport performance and fast charging performance.

[0022] In any embodiment of the present application, the specific surface area of ​​the fast charging negative electrode active material is 0.8 m 2 / g~1.3m 2 / g, preferably 0.9m 2 / g~1.2m 2 / g. This allows the secondary battery to have a higher rapid charging capability.

[0023] In any embodiment of the present application, the powder compression density of the fast charging negative electrode active material at an applied force of 20000 N is 1.5 g / cm 3 ~1.9g / cm 3 and preferably 1.5 g / cm 3 ~1.7g / cm 3 This allows the secondary battery to have a high energy density and improved cycle performance.

[0024] A second aspect of the present application provides a method for preparing a fast-charging negative electrode active material, including: step S10 of supplying carbon-based material particles, a carbon source, and a ferroelectric material, where the carbon source preferably comprises one or a combination of two or more types selected from the group consisting of asphalt, resin, and biomass material; and step S20 of uniformly mixing the carbon-based material particles, the carbon source, and the ferroelectric material, and forming a coating layer containing a conductive carbon material on at least a portion of the surface of the carbon-based material particles by a carbonization-sintering treatment, whereby 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.

[0025] In any embodiment of the present application, the carbonization sintering temperature in S20 is 700°C to 1800°C, and preferably 1000°C to 1300°C.

[0026] In any embodiment of the present application, the carbonization sintering time in S20 is 1 hour to 15 hours, and preferably 6 hours to 14 hours.

[0027] In any embodiment of the present application, the carbon-based material particles are produced by a method including: S101 supplying coke powder and placing the coke powder in a reaction vessel; and S102 graphitizing the coke powder to obtain carbon-based material particles.

[0028] A third aspect of the present application provides a negative electrode sheet including a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, the negative electrode film layer including the fast-charge negative electrode active material of the first aspect of the present application or the fast-charge negative electrode active material produced by the method of the second aspect of the present application.

[0029] A fourth aspect of the present application provides a secondary battery including the negative electrode sheet of the third aspect of the present application.

[0030] A fifth aspect of the present application provides a power consuming device including the secondary battery of the fourth aspect of the present application.

[0031] The fast-charging negative electrode active material of the present application has good dynamic performance, can withstand high charging rates, and can improve the fast-charging capability of secondary batteries without compromising the high energy density of the secondary batteries. The power consumption device of the present application includes the secondary battery of the present application, and therefore has at least the same advantages as the secondary battery. [Brief explanation of the drawings]

[0032] In order to more clearly explain the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can also obtain other drawings based on the drawings without any creative efforts. [Figure 1] FIG. 1 is a schematic diagram of one embodiment of the fast-charging negative electrode active material of the present application. [Figure 2] 1 is a schematic diagram of one embodiment of a secondary battery of the present application. [Figure 3] 3 is an exploded schematic view of the embodiment of the secondary battery of FIG. 2. FIG. [Figure 4]1 is a schematic diagram of one embodiment of a battery module of the present application. [Figure 5] 1 is a schematic diagram of one embodiment of a battery pack of the present application. [Figure 6] FIG. 6 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 5. [Figure 7] 1 is a schematic diagram of one embodiment of a power consuming device that includes a secondary battery of the present application as a power source.

[0033] In the drawings, the drawings are not necessarily drawn to scale.

[0034] The symbols are explained as follows: 1 battery pack 2 Upper housing 3 Lower housing 4 Battery Module 5 Secondary battery 51 cases 52 Electrode Assembly 53 Cover plate 10 Fast charging negative electrode active material 101 Carbon-based material particles 102 Covering layer 103 Ferroelectric Materials DETAILED DESCRIPTION OF THE INVENTION

[0035] Hereinafter, embodiments specifically disclosing the present application's fast-charging negative electrode active material and its manufacturing method, negative electrode sheet, secondary battery, and power consumption device will be described in detail with appropriate reference to the drawings. However, unnecessary detailed description may be omitted. For example, detailed description of already well-known matters or redundant description of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0036] The "ranges" disclosed herein are defined in the form of lower and upper limits, where a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits specifically define the boundaries of the range. Ranges defined in this manner may or may not include the endpoints and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a single range. For example, reciting ranges of 60 to 120 and 80 to 110 for a particular parameter is understood to also contemplate ranges of 60 to 110 and 80 to 120. Furthermore, reciting minimum range values ​​of 1 and 2 and maximum range values ​​of 3, 4, and 5 contemplates ranges of 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. Unless otherwise specified, the numerical range "a to b" herein refers to a contraction of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" indicates that all real numbers between "0 and 5" are listed herein, and "0 to 5" is a contraction of combinations of these numerical values. Furthermore, when a parameter is expressed as an integer ≧2, this is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] Unless otherwise stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present application.

[0038] Unless otherwise stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present application.

[0039] Unless otherwise specified, all steps herein can be performed in sequence or randomly, preferably in sequence. For example, when a method includes steps (a) and (b), it means that the method can include steps (a) and (b) performed in sequence, or can include steps (b) and (a) performed in sequence. For example, when a method can further include step (c), it means that step (c) can be added to the method in any order, and for example, the method can include steps (a), (b), and (c), or can include steps (a), (c), and (b), or can further include steps (c), (a), and (b), etc.

[0040] Unless otherwise specified, the terms "comprise" and "include" referred to in this application may be open or closed. For example, the terms "comprise" and "include" indicate that the term may comprise or include other components not further listed, or may comprise or include only the listed components.

[0041] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions satisfy the condition "A or B": 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 A and B are both true (or exist).

[0042] As used herein, the terms "plurality" and "multiple types" refer to two or more types.

[0043] In this application, the use of "about" a certain value indicates a range, indicating that the value is within a range of ±10%.

[0044] The key to improving the fast charging capability of secondary batteries is to improve the performance of the negative electrode active material and negative electrode sheet. During the charging process of secondary batteries, using graphite as an example, the electrode dynamics process typically 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 graphite particle surface; (2) Surface conversion step: During the first charge, solvated lithium ions adsorb and react on the graphite particle surface to form a solid electrolyte interphase (SEI) film. During subsequent charge processes, solvated lithium ions adsorb on the SEI film surface and undergo a desolvation process, allowing the lithium ions to reach the graphite particle surface; (3) Charge exchange step: Lithium ions gain electrons from the graphite particle surface to form lithium intercalation products; and (4) Solid-phase mass transfer step of lithium intercalation products: Lithium intercalation products diffuse from the graphite particle surface to the interior, completing the charging process.

[0045] Previous studies have shown that the solid-state diffusion rate of the lithium intercalation product is relatively slow, and therefore step (4) is a step for controlling the dynamic process of the negative electrode. Furthermore, previous studies have focused primarily on increasing the solid-state diffusion rate of the lithium intercalation product and shortening the solid-state diffusion distance. For example, to improve the fast charging capacity of graphite, prior art techniques have primarily used methods including (1) etching voids on the graphite surface to increase surface active sites and lithium ion intercalation channels, thereby shortening the lithium ion diffusion distance, and (2) coating graphite with amorphous carbon to increase the interlayer spacing of the graphite surface and increase the lithium ion diffusion rate. However, these methods have limited effectiveness in improving the fast charging capacity of secondary batteries.

[0046] The present inventors conducted a detailed study of the electrode dynamics during charging of secondary batteries and discovered that one of the key factors affecting the improvement of the fast charging capability of graphite is the effect of electrolyte solvation. An electrolyte is typically obtained by uniformly mixing a lithium salt with solvent molecules, and therefore typically contains three components: solvent molecules, anions, and solvated lithium ions. During charging, before lithium ions reach the surface of graphite particles and are inserted into them, the solvated lithium ions must undergo a desolvation process to release the solvent molecules. This process requires a high kinetic energy barrier, e.g., approximately 50 kJ / mol to 70 kJ / mol.

[0047] The formation of "lithium dendrites" and "dead lithium" is another important factor affecting the rapid charging capability of secondary batteries. During the charging process of a secondary battery, if abnormalities occur, such as insufficient lithium intercalation space at the negative electrode, excessive resistance to lithium ion intercalation into the negative electrode, or lithium ions rapidly escaping from the positive electrode without being able to intercalate equally into the negative electrode, the lithium ions that are not intercalated into the negative electrode can only obtain electrons on the surface of the negative electrode, resulting in the formation of silvery-white metallic lithium atoms, or "lithium dendrites." The formation of lithium dendrites not only reduces the performance of secondary batteries, such as shortening their cycle life, but in severe cases can also form sharp edges that pierce the separator, causing short circuits within the secondary battery and potentially resulting in fires, explosions, and other catastrophic consequences. At the same time, the constantly accumulating metallic lithium atoms fall off the surface of the negative electrode, forming "dead lithium" that can no longer participate in reactions, thereby reducing the energy density of the secondary battery.

[0048] The inventors of the present application have studied the electrode dynamics process during charging of a secondary battery and have further discovered that the presence of a high kinetic energy barrier in the desolvation process limits the speed at which lithium ions reach the surface of graphite particles, increases the resistance to insertion of lithium ions into the negative electrode, and is particularly likely to induce "lithium dendrites" and "dead lithium" when the secondary battery is rapidly charged at a large rate.

[0049] Through extensive research, the inventors of the present application have proposed a new type of fast-charging negative electrode active material that can significantly improve the fast-charging capability of secondary batteries on the premise that they have high energy density. negative electrode active material

[0050] Specifically, a first aspect of an embodiment of the present application provides a fast-rechargeable negative electrode active material.

[0051] 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, wherein the coating layer includes a conductive carbon material, and at least a portion of the ferroelectric material protrudes from the surface of the coating layer.

[0052] The negative electrode active material of the present invention has good dynamic performance without compromising the high energy density of the secondary battery, and can improve the fast charging capability of the secondary battery. Although the mechanism is not clear, the following points are considered as possible causes.

[0053] First, the negative electrode active material of the present application has a surface made of a ferroelectric material with a spontaneous polarization strength, and the spontaneous polarization strength reverses when the external electric field is reversed, thereby lowering the kinetic energy barrier during 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. As a result, the negative electrode active material of the present application has good kinetic performance, can withstand high charging rates, and can improve the fast charging capability of secondary batteries.

[0054] Second, in the negative electrode active material of the present application, at least a portion of the ferroelectric material protrudes from the surface of the coating layer, allowing the portion of the ferroelectric material to directly contact the electrolyte and the carbon-based material particles. The surface of the ferroelectric material in contact with the electrolyte is negatively induced, and the surface in contact with the carbon-based material particles is positively induced, thereby better reducing the kinetic energy barrier in the desolvation process, accelerating the speed at which lithium ions reach the surface of the carbon-based material particles, and reducing the resistance to lithium ion insertion into the negative electrode. As a result, the negative electrode active material of the present application has good kinetic performance and can withstand high-power charging, improving the rapid charging capability of secondary batteries.

[0055] Third, as the charging process progresses, the amount of lithium inserted into the negative electrode gradually increases, and the activation energy that must be overcome when the lithium insertion product diffuses from the particle surface to the interior increases, making solid-state diffusion more difficult. In the negative electrode active material of the present application, the coating layer includes a conductive carbon material with good conductivity, which increases the rate of solid-state diffusion of the lithium insertion product from the particle surface to the interior, thereby providing the negative electrode active material with good kinetic performance.

[0056] Fourth, in the negative electrode active material of the present application, the conductive carbon material and carbon-based material particles in the coating layer are both active components and contribute to capacity, while the ferroelectric material is an inactive component and does not contribute to capacity, but it lowers the kinetic energy barrier in the desolvation process, increases 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. In the negative electrode active material of the present application, by dispersing the ferroelectric material in the coating layer and having at least a portion of the ferroelectric material protrude from the surface of the coating layer, the exposed surface area of ​​the ferroelectric material is increased, increasing the contact area with the electrolyte and reducing the kinetic energy barrier in the desolvation process even when the amount used is small. Therefore, secondary batteries using the negative electrode active material of the present application have high rapid charging capabilities without compromising high energy density.

[0057] The present negative electrode active material, provided that it contains a small amount of inactive components, can lower the kinetic energy barrier of the desolvation process, increase the rate at which lithium ions reach the surface of carbon-based material particles, and reduce the resistance to lithium ion insertion into the negative electrode. The present negative electrode active material can also increase the rate at which lithium insertion products diffuse from the particle surface to the interior of the particles. Therefore, the present negative electrode active material has good kinetic performance, can withstand high charging rates, and can improve the rapid charging capability of secondary batteries without compromising the high energy density of the secondary battery.

[0058] In some embodiments, preferably, all of the ferroelectric material protrudes from the surface of the coating layer, which increases the exposed surface area of ​​the ferroelectric material, increases the contact area with the electrolyte, and reduces the kinetic energy barrier of the desolvation process when the amount used is smaller.

[0059] In some embodiments, the coating layer has an average thickness of H nm, the ferroelectric material has a volume average particle diameter Dv50 of d1 nm, and the fast charge negative electrode active material satisfies 0.25≦H / d1≦1.1. When H / d1 is less than 1.1, at least a portion of the ferroelectric material can protrude from the surface of the coating layer, thereby increasing the contact area with the electrolyte and lowering the kinetic energy barrier during the desolvation process when used in small amounts. When H / d1 is less than 0.25, the contact area between the ferroelectric material and the electrolyte is large, which can better lower the kinetic energy barrier during the desolvation process. However, this can make it difficult for the negative electrode active material to be compacted as a whole, resulting in poor ionic and electronic conductivity of the negative electrode sheet, which may affect the fast charge capacity, energy density, and cycle performance of the secondary battery. Therefore, having H / d1 within an appropriate range is advantageous for secondary batteries to simultaneously exhibit high fast charge capacity, high energy density, and good cycle performance. Preferably, 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.

[0060] In some embodiments, the volume average particle diameter Dv50 of the ferroelectric material is d1 nm, where 0 < d1 ≤ 200. Preferably, 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. As the volume average particle diameter Dv50 of the ferroelectric material becomes smaller, the specific surface area becomes larger. Therefore, the amount of ferroelectric material employed at the same specific surface area can be reduced, and the energy density loss of the secondary battery can be reduced.

[0061] In some embodiments, the average thickness of the coating layer is H nm, where 20 ≤ H ≤ 100. By including a conductive carbon material with good conductivity in the coating layer, the rate of solid-phase diffusion of lithium insertion products from the particle surface to the interior can be increased, and the negative electrode active material can be given good kinetic performance. Therefore, when the thickness of the coating layer is thick, the rapid charging ability of the secondary battery can be improved. However, since there are many voids, many surface defects, and a large specific surface area in the conductive carbon material in the coating layer, when the thickness of the coating layer is thick, there are many interfacial side reactions between the negative electrode active material and the electrolyte, the initial Coulomb efficiency of the negative electrode active material is low, and the capacity decay is fast. Therefore, when the average thickness of the coating layer is within an appropriate range, it is advantageous for the negative electrode active material to have a high rapid charging ability, a high capacity per gram, and a high initial Coulomb efficiency. Furthermore, the secondary battery can simultaneously have a high rapid charging ability, a high energy density, and a high cycle capacity retention rate. Preferably, 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.

[0062] In some embodiments, the dielectric constant of the ferroelectric material is preferably 100 or more. When a ferroelectric material has a high dielectric constant, its surface can provide a new path for the desolvation process of solvated lithium ions. The higher the dielectric constant of the ferroelectric material, the better the effect of reducing the kinetic energy barrier in the desolvation process. However, this effect does not always increase. At the same time, the higher the dielectric constant, the higher the requirements for the fabrication process of the ferroelectric material, which increases the production cost. In some embodiments, the dielectric constant of the ferroelectric material is preferably 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 25 000, 150 to 10,000, 150 to 5,000, 150 to 4,000, 150 to 3,000, 150 to 2,000, 150 to 1,000, 150 to 500, 200 to 50,000, 200 to 25,000, 200 to 10,000, 200 to 5,000, 200 to 4,000, 200 to 3,000, 200 to 2,000, or 200 to 1,000.

[0063] In this application, the dielectric constant of a ferroelectric material refers to the dielectric constant at room temperature (25±5°C), has the meaning known in the art, and can be tested using equipment and methods known in the art. For example, after preparing a circular sample of the ferroelectric material, the capacitance C can be tested using an LCR meter, and the dielectric constant ε can be calculated using the formula ε=(C×d) / (ε0×A). C represents the capacitance in farads (F), d represents the thickness of the sample in cm, and A represents the area of ​​the sample in cm. 2 where ε0 is the vacuum dielectric constant, ε0=8.854×10 -14 The coefficient of thermal expansion (F / cm) is shown. In this application, the test conditions may be 1KHz, 1.0V, and 25±5°C. The test standard may conform to GB / T11297.11-2015. When preparing samples, reference may be made to Chinese patent application CN114217139A.

[0064] In some embodiments, preferably, the dielectric constant of the ferroelectric material is higher than that of the electrolyte, so that the kinetic energy barrier of the desolvation process can be better reduced, and the rapid charging ability of the secondary battery can be improved.

[0065] In some embodiments, the ferroelectric material is insoluble in water and has a high Curie temperature, for example, usually 80 °C or higher. Thereby, in the process of using the secondary battery, the action effect of the ferroelectric material can be better exerted.

[0066] In some embodiments, preferably, the ferroelectric material includes one or a combination of more than one selected from perovskite structure oxides, tungsten bronzes, bismuth oxide type layered structure compounds, lithium niobate (LiNbO3), and lithium tantalate (LiTaO3). More preferably, the ferroelectric material is selected from perovskite structure oxides.

[0067] Preferably, the perovskite structure oxide has the molecular formula Ba 1-x A x Ti 1-y B y O3. A includes one or a combination of more than one selected from Pb, Sr, Ca, K, Na, and Cd, B includes one or a combination of more than one selected from Sn, Hf, Zr, Ce, Nb, and Th, and 0 ≦ x ≦ 1, 0 ≦ y ≦ 1. For example, the perovskite structure oxide may include one or a combination of more than one selected from 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-y2 O3 (0 < y2 < 1), KNbO3, and NaNbO3.

[0068] In addition, the tungsten bronze type compound may have a molecular formula M z WO3. M includes one or a combination of multiple types 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 multiple types selected from Na z1 WO3 (0 < z1 < 1), K z2 WO3 (0 < z2 < 1).

[0069] Preferably, the bismuth oxide type layered structure compound has a molecular formula (Bi2O2)(C n-1 D n O 3n+1 ). C includes one or a combination of multiple types selected from Na, K, Ba, Sr, Pb, Ca, Ln, and Bi, D includes one or a combination of multiple types 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 multiple types including SrBi2Nb2O9, SrBi2Ta2O9, SrBi2Nb2O9, Bi4Ti3O 12 .

[0070] In some embodiments, the mass ratio of the ferroelectric material to the carbon-based material particles is α1, and α1 is (0.5 to 10):100. Preferably, α1 is (0.5 to 9):100, (0.5 to 8):100, (0.5 to 7):100, (0.5 to 6):100, (0.5 to 5):100, (0.5 to 4):100, (0.5 to 3):100, (1 to 9):100, (1 to 8):100, (1 to 7):100, (1 to 6):100, (1 to 5):100, (1 to 4):100, or (1 to 3):100.

[0071] When α1 is within an appropriate range, it is advantageous for the secondary battery to have both high fast charging capacity and high energy density. Furthermore, the following situation can be effectively avoided: When α1 is large, the content of inactive components in the negative electrode active material particles increases, and the content of active components decreases, which can impair the high energy density of the secondary battery. When α1 is large, the ferroelectric material covers a large portion of the surface of the negative electrode active material, thereby reducing the surface active sites of the negative electrode active material and potentially deteriorating the fast charging capacity and cycle performance of the secondary battery. When α1 is small, the content of the ferroelectric material is low, and the effect of lowering the kinetic energy barrier of the desolvation process is unclear, which is detrimental to improving the fast charging capacity of the secondary battery.

[0072] In some embodiments, the mass ratio of the coating layer to the carbon-based material particles is α2, and α2 is (2-10): 100. Preferably, 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.

[0073] When α2 is within an appropriate range, the negative electrode active material has a high fast charge capacity, a high capacity per gram, a high initial coulombic efficiency, and a high compaction density, and the secondary battery simultaneously has a high fast charge capacity, a high energy density, and a high cycle capacity retention rate. Furthermore, the following situation can be effectively avoided: When α2 is large, the coating layer is thick, the conductive carbon material content is high, the conductive carbon material has many voids, and the specific surface area is large, resulting in many interfacial side reactions between the negative electrode active material and the electrolyte. At the same time, when α2 is large, the conductive carbon material has a rough surface morphology and many surface defects, making it difficult to compact the negative electrode active material. In addition, the surface defect structure of the conductive carbon material is unstable, resulting in low initial coulombic efficiency of the negative electrode active material, rapid capacity fade, and poor capacity performance and cycle performance of the secondary battery. When α2 is small, rapid insertion and extraction of lithium ions is unfavorable, which is unfavorable for improving the fast charge capacity of the secondary battery.

[0074] In some embodiments, the mass ratio of the ferroelectric material to the carbon-based material particles is α1, the mass ratio of the coating layer to the carbon-based material particles is α2, and α1:α2 is between 1:6 and 4:1, preferably between 1:4 and 2:1.

[0075] When the α1:α2 ratio is within an appropriate range, the negative electrode active material has high fast charging capability, high capacity per gram, high initial coulombic efficiency, and high compaction density, and the secondary battery can simultaneously have high fast charging capability, high energy density, and high cycle capacity retention. Furthermore, the following situation can be effectively avoided: When the α1:α2 ratio is large, the content of inactive components in the negative electrode active material particles increases and the content of active components decreases, significantly reducing the energy density of the secondary battery and being unfavorable for rapid lithium ion insertion and extraction. When the α1:α2 ratio is small, the content of ferroelectric material is low, and the effect of reducing the kinetic energy barrier of the desolvation process is not significant, thereby deteriorating the fast charging capability of the secondary battery. At the same time, the initial coulombic efficiency of the negative electrode active material is low, making it prone to rapid capacity fade.

[0076] The coating layer includes a conductive carbon material. Preferably, the conductive carbon material includes amorphous carbon. Amorphous carbon is a transition-state carbon material with low graphitization crystallinity and close to an amorphous form (or amorphous and periodic structural order), obtained by carbonization and sintering with a carbon source (e.g., asphalt, resin, biomass material, etc.). Amorphous carbon has a large interlayer spacing, which prevents volume shrinkage and expansion during the lithium ion deintercalation and intercalation process. This stabilizes its crystalline structure, providing the anode active material with good dynamic performance, enduring high charging rates, and improving the rapid charging capability of the secondary battery. The amorphous carbon includes soft carbon, hard carbon, or a combination thereof. Preferably, in some embodiments, the conductive carbon material includes hard carbon, which further improves the rapid charging capability of the secondary battery.

[0077] In some embodiments, the carbon-based material particles include one or a combination of graphite (e.g., artificial graphite, natural graphite, graphite oxide, etc.), mesocarbon microbeads, hard carbon, and soft carbon, preferably graphite. Graphite has the advantages of stable cycle performance and high capacity per gram, which can provide secondary batteries with high energy density and high cycle stability.

[0078] In some embodiments, the coating layer has a graphitization degree of 45 to 80%.

[0079] In some embodiments, the carbon-based material particles have a graphitization degree of 88% to 96%.

[0080] Through research, the inventors have found that if the coating layer and the carbon-based material particles further satisfy the graphitization degree within the above range, this contributes to a reasonable matching of the crystalline structures of the coating layer and the carbon-based material particles, thereby effectively improving the solid-state diffusion rate of lithium ions and improving the fast charging ability and cycle performance of the secondary battery.

[0081] In some embodiments, the carbon-based material particles are in the form of primary particles, secondary particles, or a combination thereof. Secondary particles are typically obtained by agglomeration of primary particles. Preferably, in the carbon-based material particles in the form of secondary particles, the ratio of the volume average particle diameter Dv50 of the primary particles to the volume average particle diameter Dv50 of the secondary particles formed therefrom is 0.2 to 0.5. When the carbon-based material particles are in the form of secondary particles and the ratio of the volume average particle diameter Dv50 of the primary particles to the volume average particle diameter Dv50 of the secondary particles formed therefrom is adjusted within an appropriate range, it is advantageous for the carbon-based material particles to have good secondary particle size, and can have good ion transport and electron transport properties while maintaining high structural stability.

[0082] In some embodiments, the carbon-based material particles have a volume average particle diameter Dv50 of d2 μm, and 5≦d2≦20, preferably 8≦d2≦15. When the volume average particle diameter Dv50 of the carbon-based material particles is within an appropriate range, the negative electrode active material of the present invention has high electrochemical activity, thereby providing a secondary battery with higher rapid charging capabilities. Furthermore, the following situations can be effectively avoided: When the volume average particle diameter Dv50 of the carbon-based material particles is small, the negative electrode active material has a low capacity per gram and a low compressed density, which is disadvantageous for designing a battery with a high energy density. Furthermore, when the volume average particle diameter Dv50 of the carbon-based material particles is small, the large specific surface area and high reactivity of the carbon-based material particles can increase interfacial side reactions between the negative electrode active material and the electrolyte, which can further increase the irreversible consumption of active lithium ions, potentially resulting in poor capacity and energy density of the secondary battery. If the volume average particle diameter Dv50 of the carbon-based material particles is large, the number of surface active sites on the particle surface decreases, and the path for the lithium insertion product to diffuse into the solid phase from the particle surface to the interior becomes longer, which is disadvantageous in improving the rapid charging capability of the secondary battery.

[0083] In some embodiments, the volume average particle diameter Dv50 of the fast charging negative electrode active material is 5 μm to 20 μm, preferably 8 μm to 15 μm. By adjusting the volume average particle diameter Dv50 of the negative electrode active material within an appropriate range, the negative electrode active material can have better ion transport and electron transport performance, fast charging performance, and high powder compaction density.

[0084] In some embodiments, the specific surface area of ​​the fast-charging negative electrode active material is 0.8 m 2 / g~1.3m 2 / g, preferably 0.9m 2 / g~1.2m 2By adjusting the specific surface area of ​​the negative electrode active material within an appropriate range, it is possible to reduce the interfacial side reaction between the negative electrode sheet using the material and the electrolyte, and to impart appropriate electrochemical reaction activity to the negative electrode sheet using the material, thereby enabling the secondary battery to have a higher rapid charging capability.

[0085] In some embodiments, the powder of the fast charging negative electrode active material has a compressed density of 1.5 g / cm under a force of 20,000 N. 3 ~1.9g / cm 3 and preferably 1.5 g / cm 3 ~1.7g / cm 3 By adjusting the compressed density of the negative electrode active material powder within an appropriate range, the negative electrode film layer can have a high compressed density, and the secondary battery can have a high energy density. In addition, by adjusting the compressed density of the negative electrode active material powder within an appropriate range, the negative electrode film layer can maintain a strong channel structure during cycling, which improves the wettability of the negative electrode sheet with the electrolyte and improves the cycle performance of the secondary battery.

[0086] In the present application, the average thickness of the coating layer has a meaning known in the art, and can be tested using equipment and methods known in the art. For example, a TEM (Transmission Electron Microscope) picture can be obtained using a transmission electron microscope, and then the thickness can be measured at multiple (e.g., 30 or more) different positions in the TEM picture, and the average value can be taken as the average thickness of the coating layer.

[0087] In this application, the volume average particle size Dv50 of a material has the meaning known in the art, and refers to the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%, and can be tested using equipment and methods known in the art, for example, GB / T19077-2016 Particle Size Distribution Laser Diffraction Method, and can be easily tested using a laser particle size analyzer, for example, the Mastersizer 2000E laser particle size analyzer manufactured by Malvern Instruments, UK.

[0088] In this application, the graphitization degree of a material has a meaning known in the art and can be tested using equipment and methods known in the art. For example, the graphitization degree can be tested using an X-ray diffractometer (e.g., Bruker D8 Discover) in accordance with JIS K0131-1996 and JB / T4220-2011. 002 After obtaining the formula g=(0.344-d 002 The graphitization degree of the material was calculated from the formula: ) / (0.344-0.3354)×100%. 002 is the layer spacing of the (002) crystal plane in the crystal structure of the material, expressed in nanometers (nm).

[0089] In this application, the specific surface area of ​​a material has the meaning known in the art and can be tested using instruments and methods known in the art. For example, the specific surface area can be tested using the nitrogen adsorption specific surface area analysis test method described in GB / T19587-2017 and calculated using the Brunauer Emmett Teller (BET) method. The nitrogen adsorption specific surface area analysis test can be performed using a Tri-Star 3020 specific surface area pore size analyzer manufactured by Micromeritics, Inc., USA.

[0090] In this application, the powder compaction density of a material has a meaning known in the art and can be tested using equipment and methods known in the art. For example, it can be tested by an electronic pressure test machine (e.g., UTM7305 type) with reference to standard GB / T24533-2009. One exemplary test method is to weigh 1 g of material and measure the density of the material with a base area of ​​1.327 cm. 2 The method includes the steps of placing the powder in a mold, pressurizing it to 2000 kg (equivalent to 20,000 N), holding the pressure for 30 seconds, releasing the pressure, holding it for 10 seconds, and then recording and calculating the compressed density of the powder at an applied force of 20,000 N of the material.

[0091] The above-mentioned tests for various parameters of the negative electrode active material can be performed by sampling before application or by sampling from the negative electrode film layer after cold pressing. When the test sample of the negative electrode active material is sampled from the negative electrode film layer after cold pressing, the sampling can be performed, for example, by the following steps: Randomly select a negative electrode film layer after cold pressing and sample the negative electrode active material (for example, by scraping off the powder with a blade). The collected negative electrode active material powder is placed in deionized water, then suction filtered and dried. The dried negative electrode active material is sintered at a certain temperature and time (for example, 400°C, 2 hours) to remove the adhesive and conductive agent, and a test sample of the negative electrode active material is obtained.

[0092] The fast charging negative electrode active material of the present application will be described below with reference to the drawings. FIG. 1 is a schematic diagram of one embodiment of the fast charging negative electrode active material 10 of the present application. As shown in FIG. 1, 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 a ferroelectric material 103 dispersed in the coating layer 102, wherein the coating layer 102 includes a conductive carbon material, and at least a portion of the ferroelectric material 103 protrudes from the surface of the coating layer 102. Production method

[0093] A second aspect of the present embodiment provides a method for preparing a fast-charging negative electrode active material of the first aspect of the present application, the method including: a step S10 of supplying carbon-based material particles, a carbon source, and a ferroelectric material; and a step S20 of uniformly mixing the carbon-based material particles, the carbon source, and the ferroelectric material, and forming a coating layer containing a conductive carbon material on at least a portion of the surface of the carbon-based material particles by a carbonization-sintering process, 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.

[0094] In the present application, the term "carbon source" refers to a compound capable of forming a conductive carbon material. The carbon source may be one or a combination of organic and inorganic carbon sources. Preferably, the carbon source is an organic carbon source.

[0095] In some embodiments, the carbon source preferably includes one or more combinations selected from asphalt, resin, and biomass material. For example, the asphalt includes one or more combinations selected from coal asphalt and petroleum asphalt, preferably petroleum asphalt. For example, the resin includes one or more combinations selected from phenolic resin and epoxy resin. For example, the biomass material refers to a material derived from living organisms such as animals, plants, and microorganisms, and is primarily composed of organic polymeric substances, primarily consisting of the three elements carbon, hydrogen, and oxygen in its chemical composition, and may be, for example, a polysaccharide (e.g., starch, sucrose polymer, glucose polymer, cellulose, etc.).

[0096] In some embodiments, the carbonization sintering temperature in S20 is preferably 700°C to 1800°C, more preferably 1000°C to 1300°C.

[0097] In some embodiments, the carbonization sintering time in S20 is preferably 1 hour to 15 hours, and more preferably 6 hours to 14 hours.

[0098] In S20, by controlling the carbonization-sintering temperature and the carbonization-sintering time within the above ranges, the carbon source is carbonized, and a coating layer containing a conductive carbon material is formed on at least a part of the surface of the carbon-based material particles, and the coating layer can have an appropriate thickness and graphitization degree.

[0099] In some embodiments, the carbon-based material particles may be commercially available products, or preferably, are prepared by the following method: S101: providing coke powder and placing the coke powder in a reaction vessel; S102: graphitizing the coke powder to obtain carbon-based material particles.

[0100] In some embodiments, the coke powder may be a commercially available product, or preferably, is prepared by the following method: In S1011, a coke raw material is subjected to a coking process to obtain coke, and in S1012, the obtained coke is crushed, shaped, and classified to obtain coke powder.

[0101] In this application, "coke raw material" refers to a component from which "coke" can be obtained by processing, i.e., a raw material for producing coke, and "coke" is a product of a coking process performed on a coke raw material. "Coke powder" and "coke" have exactly the same composition, but differ in that "coke powder" is "coke" that exists as a powder of a certain particle size, i.e., "coke powder" is obtained after "coke" has been subjected to processing such as crushing.

[0102] Preferably, the coke feedstock can include one or a combination of petroleum-based and coal-based feedstocks. For example, the petroleum-based feedstock can include one or a combination of heavy oil, residual oil, and vacuum residue, and the coal-based feedstock mainly includes coal asphalt. Heavy oil, residual oil, and vacuum residue are typically generated in petroleum refining processes, and coal asphalt is typically generated in coal carbonization processes.

[0103] Preferably, the coke obtained in S1011 includes one or a combination of 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 a combination of 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. By using an appropriate coke, the produced carbonaceous material particles have an appropriate number of end faces and defects, and further have good ion transport and electron transport properties and high structural stability, thereby improving the rapid charging capability and cycle performance of secondary batteries.

[0104] Preferably, the coking treatment of the coke feedstock in S1011 is carried out in a delayed coking apparatus, which includes a heating furnace and a coke tower. The delayed coking process means that the coke feedstock is first rapidly heated to a desired coking temperature in the heating furnace, and then enters the coke tower, where it undergoes processes such as preheating and cold coking to produce coke.

[0105] Preferably, in S1012, the resulting coke can be crushed using equipment and methods known in the art, for example, jet mills, mechanical mills, roll presses, or other crushing equipment can be employed.

[0106] The morphology of the coke powder obtained after crushing can include one or a combination of agglomerated, spherical, and near-spherical shapes. After crushing is complete, the corners of the coke powder are removed by shaping. The greater the degree of shaping, the more spherical the powder particles become, thereby increasing the number of active sites on the surface of the carbonaceous material particles. The shaping process also contributes to the subsequent granulation process and provides high structural stability to the secondary particle portion of the obtained carbonaceous material particles. The shaping process can be performed using equipment and methods known in the art, such as a shaping machine or other shaping equipment.

[0107] During the crushing and shaping process, many undersized particles are often generated, and oversized particles may also be present. Therefore, classification can be performed as needed to remove the undersized and oversized particles from the powder. After classification, coke powder with a good particle size distribution suitable for the subsequent granulation process can be obtained. Classification can be performed using equipment and methods known in the art, such as a classifying sieve, a gravity classifier, or a centrifugal classifier.

[0108] In some embodiments, step S101 preferably further includes adding an adhesive to a reaction vessel, uniformly mixing the adhesive and the coke powder, and then granulating the mixture. The addition of the adhesive can provide the resulting carbon-based material particles with excellent secondary particle size, which is advantageous for improving the ion transport and electron transport performance of the negative electrode active material and for providing high structural stability.

[0109] Preferably, the mass percentage content of the adhesive is 3% to 12%, more preferably 5% to 8%, calculated based on the total mass of the coke powder. When the content of the adhesive is within an appropriate range, excessive aggregation of particles can be avoided.

[0110] Preferably, the adhesive comprises one or a combination of two or more selected from coal asphalt, petroleum asphalt, mesophase asphalt, phenolic resin, epoxy resin, and petroleum resin.

[0111] The granulation process can be carried out using equipment and methods known in the art, such as a granulator. The granulator typically includes a stirring reactor and a module for controlling the temperature of the reactor. By adjusting the stirring rotation speed, heating rate, granulation temperature, and temperature decrease rate during the granulation process, the degree of granulation and the structural strength of the particles can be controlled, and the volume average particle size Dv50 of the finally produced carbon-based material particles can be set within a desired range.

[0112] In some embodiments, the graphitization temperature in S102 may be preferably 2400°C to 3200°C, and more preferably 2800°C to 3200°C or 2900°C to 3100°C.

[0113] In some embodiments, the graphitization treatment time in S102 may be preferably 20 hours to 48 hours.

[0114] The graphitization treatment can provide the carbon-based material particles with an appropriate degree of graphitization, thereby increasing the capacity per gram of the negative electrode active material; the graphitization treatment can reduce the lattice expansion coefficient of the carbon-based material particles, thereby improving the structural stability; and the graphitization treatment can effectively remove phase structural defects in the carbon-based material particles, thereby improving the cycle stability of the secondary battery.

[0115] The graphitization treatment can be carried out using equipment and methods known in the art, such as a graphitization furnace, particularly an Acheson graphitization furnace. After the graphitization treatment is completed, a small amount of excessively large particles formed by agglomeration during the graphitization treatment can be removed by sieving, thereby preventing the excessively large particles from affecting the processing performance of the resulting negative electrode active material, such as the stability and coating performance of the negative electrode slurry.

[0116] In some embodiments, the method for preparing the fast charging negative electrode active material includes: a step of uniformly mixing coke powder and an adhesive in a reaction vessel, followed by granulation; a step of graphitizing the obtained granulation product to obtain carbon-based material particles; a step of uniformly mixing the obtained carbon-based material particles with a carbon source and a ferroelectric material, and forming a coating layer containing a conductive carbon material on at least a portion of the surface of the carbon-based material particles by a carbonization sintering process, 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.

[0117] The method for preparing a fast-charging negative electrode active material of the present application is simple, has low production costs, and is compatible with current processes for preparing carbon-based material particles, especially artificial graphite, without the need for additional production equipment or process steps. When preparing a fast-charging negative electrode active material using the method of the present application, the ferroelectric material is less likely to agglomerate, which allows the desolvation effect of solvated lithium ions to be applied to the entire negative electrode active material, which is advantageous for the negative electrode active material to have higher fast-charging capability and longer service life.

[0118] Some of the raw materials used in the method for preparing the fast charging negative electrode active material of the present application and their contents, etc., can be referred to in the fast charging negative electrode active material of the first aspect of the embodiment of the present application, and further description thereof will be omitted here. Negative electrode sheet

[0119] A third aspect of the present invention provides a negative electrode sheet including a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, the negative electrode film layer including the fast-charging negative electrode active material according to the first aspect of the present invention or the fast-charging negative electrode active material produced by the method according to the second aspect of the present invention. For example, the negative electrode current collector has opposite surfaces in its thickness direction, and the negative electrode film layer is provided on one or both of the two opposite surfaces of the negative electrode current collector.

[0120] In some embodiments, the negative electrode film layer may further include other negative electrode active materials used in secondary batteries known in the art. For example, the other negative electrode active materials may 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 oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloy materials. The tin-based materials may include one or more combinations selected from elemental tin, tin oxides, and tin alloy materials.

[0121] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent, if necessary. The type of the negative electrode conductive agent is not particularly limited herein. For example, the negative electrode conductive agent may include one or a combination of two or more selected from the group consisting of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage content of the negative electrode conductive agent is 5% or less of the total mass of the negative electrode film layer.

[0122] In some embodiments, the negative electrode film layer may further include a negative electrode adhesive, if necessary. The type of the negative electrode adhesive is not particularly limited in the present application. For example, the negative electrode adhesive may include one or a combination of materials selected from the group consisting of styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-soluble acrylic resin (e.g., polyacrylic acid (PAA), polymethacrylic acid (PMAA), and sodium polyacrylate (PAAS)), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage content of the negative electrode adhesive is 5% or less of the total mass of the negative electrode film layer.

[0123] In some embodiments, the negative electrode membrane layer may further contain other additives as needed. For example, the other additives may include thickeners such as sodium carboxymethyl cellulose (CMC-Na) or PTC thermistor materials. In some embodiments, the mass percentage content of the other additives is 2% or less relative to the total mass of the negative electrode membrane layer.

[0124] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. Examples of the metal foil include copper foil and copper alloy foil. The composite current collector may include a polymeric base layer and a metal layer formed on at least one surface of the polymeric base layer. For example, the metal layer may include one or more combinations selected from copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. The polymeric base layer may include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0125] The negative electrode film layer is typically formed by applying a negative electrode slurry to a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, an optional conductive agent, an optional adhesive, and other optional auxiliary agents in a solvent and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0126] The negative electrode sheet does not exclude additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode sheet described herein further includes a conductive primer 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 provided on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet described herein further includes a protective layer covering the surface of the negative electrode film layer. secondary battery

[0127] A secondary battery, also known as a rechargeable battery or storage battery, is a battery that can continue to be used after discharge by recharging to activate the active material. A secondary battery includes an electrode assembly and an electrolyte. The electrode assembly typically includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is disposed between the positive electrode sheet and the negative electrode sheet and primarily serves to prevent short-circuiting between the positive and negative electrodes while allowing metal ions to pass through. The electrolyte serves to conduct metal ions between the positive electrode sheet and the negative electrode sheet. The secondary battery of the present application may be a lithium-containing secondary battery, and in particular may be a lithium-ion secondary battery. [Negative electrode sheet]

[0128] The negative electrode sheet used in the secondary battery of the present application is the negative electrode sheet of any of the embodiments of the third aspect of the present application. [Positive electrode sheet]

[0129] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, for example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode film layer is disposed on one or both of the two facing surfaces of the positive electrode current collector.

[0130] The positive electrode film layer contains a positive electrode active material, and the positive electrode active material may employ a positive electrode active material for secondary batteries known in the art. For example, the positive electrode active material may include one or a combination of multiple types selected from lithium transition metal oxides, lithium-containing phosphates having an olivine structure, and their respective modified compounds. Examples of the lithium transition metal oxide may include one or a combination of multiple types 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 the lithium-containing phosphate having an olivine structure may include one or a combination of multiple types selected from lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their modified compounds.

[0131] In some embodiments, in order to further increase the energy density of the secondary battery, the positive electrode active material may include one or a combination of multiple types of the lithium transition metal oxide represented by Formula 1 and its modified compounds.

[0132] Li a Ni b Co c M d O e A f Formula 1

[0133] In Formula 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 a combination of multiple types selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A includes one or a combination of multiple types selected from N, F, S, and Cl.

[0134] In the present application, the modified compound of each positive electrode active material may perform doping modification and / or surface coating modification on the positive electrode active material.

[0135] In some embodiments, the positive electrode film layer may optionally contain a positive electrode conductive agent. The type of the positive electrode conductive agent is not particularly limited in the present application. For example, the positive electrode conductive agent may include one or a combination of materials selected from the group consisting of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage content of the positive electrode conductive agent is 5% or less of the total mass of the positive electrode film layer.

[0136] In some embodiments, the positive electrode film layer may optionally include a positive electrode adhesive. The type of the positive electrode adhesive is not particularly limited in the present application. For example, the positive electrode adhesive may include one or a combination of two or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. In some embodiments, the mass percentage content of the positive electrode adhesive is 5% or less of the total mass of the positive electrode film layer.

[0137] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. Examples of the metal foil include aluminum foil or aluminum alloy foil. The composite current collector may include a polymeric substrate and a metal layer formed on at least one surface of the polymeric substrate. For example, the metal layer may include one or more metals selected from aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. The polymeric substrate may include one or more metals selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0138] The positive electrode film layer is typically formed by applying a positive electrode slurry to a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing a positive electrode active material, an optional conductive agent, an optional adhesive, and any other components in a solvent and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0139] [Electrolyte]

[0140] The electrolyte solution of the present application may be any electrolyte solution for secondary batteries known in the art, and includes a lithium salt and an organic solvent.

[0141] As an example, the lithium salt may include one or a combination of two or more selected from lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPOF), lithium difluorobisoxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP).

[0142] By way of example, the organic solvent may include at least one or a combination of more than one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene 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). [Separator]

[0143] In the present application, the type of the separator is not particularly limited, and any known porous structure separator having good chemical stability and mechanical stability can be selected.

[0144] In some embodiments, the separator may be made of one or a combination of materials selected from the group consisting of 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 the layers may be the same or different.

[0145] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be wound or stacked to form an electrode assembly.

[0146] In some embodiments, the secondary battery may include an exterior case that can be used to seal the electrode assembly and the electrolyte.

[0147] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a soft package, such as a bag-type soft package. The material of the soft package may be, for example, plastic, such as one or a combination of plastics including polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0148] In the present application, the shape of the secondary battery is not particularly limited, and may be cylindrical, rectangular, or any other shape. For example, Fig. 2 shows a secondary battery 5 having a rectangular structure as an example.

[0149] In some embodiments, as shown in FIG. 3 , the exterior may include a case 51 and a cover plate 53. The case 51 includes a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a storage chamber. The case 51 has an opening communicating with the storage chamber, and the cover plate 53 covers the opening to close the storage chamber. The positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is sealed in the storage chamber. The electrode assembly 52 is impregnated with an electrolyte. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more and may be adjusted according to needs.

[0150] Methods for fabricating the secondary battery of the present application are well known. In some embodiments, a secondary battery can be formed by assembling a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. For example, the positive electrode sheet, the separator, and the negative electrode sheet can be wound or stacked to form an electrode assembly, which can then be placed in a housing and dried. The electrode assembly can then be infused with an electrolyte, and the secondary battery can be obtained through processes such as vacuum sealing, standing, chemical formation, and shaping.

[0151] In some embodiments of the present application, the secondary battery according to the present application may be assembled into a battery module, and the number of secondary batteries included in the battery module may be multiple, and the specific number may be adjusted according to the application and capacity of the battery module.

[0152] Fig. 4 is a schematic diagram of an example battery module 4. As shown in Fig. 4, in the battery module 4, the plurality of secondary batteries 5 may be arranged in order along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed with fasteners.

[0153] Preferably, the battery module 4 further includes a housing having an accommodation space, and the plurality of secondary batteries 5 are accommodated in the accommodation space.

[0154] In some embodiments, the battery modules may be assembled into a battery pack, and the number of battery modules included in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0155] 5 and 6 are schematic diagrams of an example battery pack 1. As shown in FIGS. 5 and 6, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box. The battery box includes an upper housing 2 and a lower housing 3, and the upper housing 2 is covered by the lower housing 3, forming an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner. power consumption equipment

[0156] A fifth embodiment of the present application provides a power consuming device including at least one of the secondary battery, battery module, and battery pack of the present application. The secondary battery, battery module, and battery pack may be used as a power source for the power consuming device, or as an energy storage unit for the power consuming device. The power consuming device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0157] The power consumption device can select a secondary battery, a battery module, or a battery pack according to its usage needs.

[0158] 7 is a schematic diagram of an example power consuming device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, which may employ a battery pack or battery module to meet the high power and high energy density needs of the power consuming device.

[0159] Other examples of power consuming devices include mobile phones, tablet computers, notebook computers, etc. Such power consuming devices are usually required to be thin and can employ secondary batteries as their power source. Example

[0160] The following examples will more specifically illustrate the contents of the present disclosure, and these examples are merely used for illustrative purposes, and it will be apparent to those skilled in the art that various modifications and variations can be made within the scope of the contents of the present disclosure. Unless otherwise specified, all parts, percentages, and ratios described in the following examples are calculated by mass, and all reagents used in the examples can be purchased or synthesized according to conventional methods and can be used directly without further treatment, and all devices used in the examples can be purchased. Example 1

[0161] Step (1): Preparation of negative electrode active material

[0162] In S10, petroleum residual oil is subjected to delayed coking at 490°C to 510°C to obtain petroleum non-needle coke. The raw coke is crushed, shaped, and classified to obtain coke powder. The obtained coke powder is mixed with coal asphalt as an adhesive and then granulated. The obtained granulated product is placed in a graphite crucible, which is then placed in an Acheson graphitization furnace. An electrical resistance material is placed around the graphite crucible, and electricity is applied to pass an electric current through the electrical resistance material to generate thermal energy. Graphitization is carried out at approximately 3000°C for approximately 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%.

[0163] In S20, the resulting artificial graphite particles are uniformly mixed with petroleum asphalt (carbon source, mass calculated based on residual carbon), and ferroelectric material BaTiO3 (volume average particle size Dv50 of 200 nm, dielectric constant of 2000) in a mass ratio of 100:3:3. The mixture is then carbonized and sintered in a roller hearth kiln at a maximum temperature of approximately 1150°C for approximately 12 hours. This produces an amorphous carbon coating on at least a portion of the surface of the artificial graphite particles, resulting in an anode active material. In the resulting anode active material, BaTiO3 is dispersed within the coating, with at least a portion of the BaTiO3 protruding from the surface of the coating.

[0164] Step (2): Preparation of negative electrode sheet

[0165] The negative electrode active material prepared above, styrene butadiene rubber (SBR) as an adhesive, sodium carboxymethyl cellulose (CMC-Na) as a thickener, and carbon black as a conductive agent were thoroughly mixed and stirred in an appropriate amount of deionized water in 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 applied to the surface of copper foil as a negative electrode current collector, dried, and cold-pressed to obtain a negative electrode sheet. The coating weight was 0.162 kg / m. 2 , compressed density is 1.65g / cm 3 is.

[0166] Step (3): Preparation of the positive electrode sheet

[0167] Positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), carbon black (conductive agent), and polyvinylidene fluoride (PVDF) (adhesive) are mixed in a mass ratio of 96.2:1.8:2 in an appropriate amount of NMP solvent and thoroughly stirred to form a uniform cathode slurry. The cathode slurry is then uniformly applied to the surface of aluminum foil (positive electrode current collector), dried, and cold-pressed to obtain a cathode sheet. The coating weight is 0.256 kg / m. 2 , compressed density is 3.4g / cm 3 is.

[0168] Step (4): Preparation of the electrolyte

[0169] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then thoroughly dried LiPF6 is dissolved in the organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L.

[0170] Step (5): Making the separator

[0171] The separator is a porous polyethylene film.

[0172] Step (6): Fabrication of secondary battery

[0173] A positive electrode sheet, a separator, and a negative electrode sheet are stacked in this order and wound up to obtain an electrode assembly. The electrode assembly is then placed in an outer casing and dried. After that, an electrolyte is injected, and the assembly goes through processes such as vacuum sealing, leaving it to stand, chemical formation, and shaping to obtain a secondary battery. (Examples 2 to 16)

[0174] The secondary batteries of Examples 2 to 16 were prepared in a similar manner to that of Example 1, except that the relevant parameters in "Preparation of negative electrode active material" were adjusted. The specific parameters are shown in Table 2. Comparative Example 1

[0175] The secondary battery of Comparative Example 1 was fabricated in a similar manner to Example 1, except that conventional artificial graphite without a coating layer was used as the negative electrode active material. Specifically, the artificial graphite was fabricated by the following method.

[0176] Petroleum residual oil is subjected to delayed coking at temperatures between 490°C and 510°C to produce petroleum non-needle coke. The raw coke is then crushed, shaped, and classified to produce coke powder. The resulting coke powder is mixed with coal asphalt as an adhesive and then granulated. The resulting granulated product is placed in a graphite crucible, which is then placed in an Acheson graphitization furnace. An electrical resistance material is placed around the graphite crucible, and electricity is passed through the electrical resistance material to generate thermal energy. Graphitization is carried out at approximately 3000°C for approximately 30 hours to produce 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%. Comparative Example 2

[0177] The secondary battery of Comparative Example 2 was fabricated in a similar manner to Example 1, except that the negative electrode active material was prepared in the following manner.

[0178] In S10, petroleum residual oil is subjected to delayed coking at 490°C to 510°C to obtain petroleum non-needle coke. The raw coke is then crushed, shaped, and classified to obtain coke powder. The resulting coke powder is mixed with coal asphalt as an adhesive and then granulated. The resulting granulated product is placed in a graphite crucible, which is then placed in an Acheson graphitization furnace. An electrical resistance material is placed around the graphite crucible, and electricity is applied to pass an electric current through the electrical resistance material to generate thermal energy. Graphitization is carried out at approximately 3000°C for approximately 30 hours to obtain artificial graphite particles. The artificial graphite particles have a volume average particle size Dv50 of approximately 9.8 μm and a degree of graphitization of approximately 92%.

[0179] In S20, the obtained artificial graphite particles are mixed with petroleum asphalt as a carbon source, and then subjected to a carbonization sintering process in a roller hearth kiln, with the temperature in the maximum temperature range being approximately 1150°C and the operating time at the maximum temperature range being approximately 12 hours, thereby forming an amorphous carbon coating layer on at least a portion of the surface of the artificial graphite particles and obtaining a negative electrode active material. Comparative Example 3

[0180] The secondary battery of Comparative Example 3 was fabricated in a similar manner to Example 1, except that the negative electrode active material and the negative electrode sheet were prepared in the following manner.

[0181] Step (1): Preparation of negative electrode active material

[0182] In S10, petroleum residual oil is subjected to delayed coking at 490°C to 510°C to obtain petroleum non-needle coke. The raw coke is then crushed, shaped, and classified to obtain coke powder. The resulting coke powder is mixed with coal asphalt as an adhesive and then granulated. The resulting granulated product is placed in a graphite crucible, which is then placed in an Acheson graphitization furnace. An electrical resistance material is placed around the graphite crucible, and electricity is applied to pass an electric current through the electrical resistance material to generate thermal energy. Graphitization is carried out at approximately 3000°C for approximately 30 hours to obtain artificial graphite particles. The artificial graphite particles have a volume average particle size Dv50 of approximately 9.8 μm and a degree of graphitization of approximately 92%.

[0183] In S20, the obtained artificial graphite particles are mixed with petroleum asphalt as a carbon source, and then subjected to a carbonization sintering process in a roller hearth kiln, with the temperature in the maximum temperature range being approximately 1150°C and the operating time at the maximum temperature range being approximately 12 hours, thereby forming an amorphous carbon coating layer on at least a portion of the surface of the artificial graphite particles and obtaining a negative electrode active material.

[0184] Step (2): Preparation of negative electrode sheet

[0185] The negative electrode active material prepared above, the ferroelectric material BaTiO3 (volume average particle size Dv50 is 85 nm), the adhesive styrene butadiene rubber (SBR), the thickener carboxymethyl cellulose sodium (CMC-Na), and the conductive agent carbon black are thoroughly mixed in an appropriate amount of solvent deionized water in a mass ratio of 93.8:3:1.2:1.2:0.8 to form a uniform negative electrode slurry. The negative electrode slurry is uniformly applied to the surface of the negative electrode current collector copper foil, dried, and cold-pressed to obtain a negative electrode sheet. Comparative Example 4

[0186] The secondary battery of Comparative Example 4 was fabricated in a similar manner to Example 1, except that the negative electrode active material was prepared in the following manner.

[0187] In S10, petroleum residual oil is subjected to delayed coking at 490°C to 510°C to obtain petroleum non-needle coke. The raw coke is then crushed, shaped, and classified to obtain coke powder. The resulting coke powder is mixed with coal asphalt as an adhesive and then granulated. The resulting granulated product is placed in a graphite crucible, which is then placed in an Acheson graphitization furnace. An electrical resistance material is placed around the graphite crucible, and electricity is applied to pass an electric current through the electrical resistance material to generate thermal energy. Graphitization is carried out at approximately 3000°C for approximately 30 hours to obtain artificial graphite particles. The artificial graphite particles have a volume average particle size Dv50 of approximately 9.8 μm and a degree of graphitization of approximately 92%.

[0188] In S20, the obtained artificial graphite particles are mixed with petroleum asphalt, which is a carbon source, and then subjected to a carbonization sintering process in a roller hearth kiln, with the temperature in the maximum temperature range being approximately 1150°C and the operating time at the maximum temperature range being approximately 12 hours, thereby forming an amorphous carbon coating layer on at least a portion of the surface of the artificial graphite particles.

[0189] In step S30, the obtained artificial graphite particles with an amorphous carbon coating layer and the ferroelectric material BaTiO3 (volume average particle size Dv50 is 85 nm) are ball-milled in a mass ratio of 97:3 to be uniformly mixed, and then placed in a planetary ball mill and ball-milled at an ambient temperature of 25°C and a rotation speed of 300 rpm for 2 hours, after which the mixture is removed to obtain the negative electrode active material. Test part

[0190] (1) Volume average particle size Dv50 test

[0191] A certain amount of the prepared negative electrode active material sample was taken and tested for volume average particle size Dv50 using a Mastersizer 2000E laser particle size analyzer, in accordance with GB / T 19077-2016.

[0192] (2) Specific surface area test

[0193] A certain amount of the prepared negative electrode active material sample was taken and the specific surface area was tested using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc., USA. The specific surface area was calculated using the Brunauer Emmett Teller (BET) method. The test standard was in accordance with GB / T19587-2017.

[0194] (3) Powder compression density test

[0195] A certain amount of the prepared negative electrode active material sample was taken and measured using a UTM7305 electronic pressure tester with a base area of ​​1.327 cm 2 The powder was placed in a mold, pressurized to 2000 kg (equivalent to 20,000 N), and held for 30 seconds. The pressure was then released and held for 10 seconds, and the data was recorded to calculate the powder compaction density of the negative electrode active material at a force of 20,000 N. The test standard was in accordance with GB / T24533-2009.

[0196] (4) Graphitization degree test

[0197] A certain amount of the prepared negative electrode active material sample was taken and tested using a Bruker D8Discover X-ray diffractometer to determine the interlayer distance d between the (002) crystal planes of the coating layer and the carbonaceous material particles. 002 After obtaining each, the formula g=(0.344-d 002 The graphitization degree g1 of the coating layer and the graphitization degree g2 of the carbon-based material particles were calculated based on the following formula: ) / (0.344-0.3354)×100%. The test standards conform to JIS K0131-1996 and JB / T4220-2011.

[0198] (5) (Test of average coating thickness)

[0199] A certain amount of the prepared negative electrode active material sample is taken, and a thin slice of about 100 nm is cut from the middle of a single particle. Then, a transmission electron microscope analysis test is performed on the thin slice to obtain a TEM picture, and the thickness is measured at multiple (e.g., five or more) different positions on the TEM picture. At least six negative electrode active material samples are tested, and the average value of the test results is taken as the average thickness of the coating layer.

[0200] (6) Initial capacity per gram test

[0201] The negative electrode active material, carbon black (conductive agent), and polyvinylidene fluoride (PVDF) (adhesive) were uniformly mixed in a mass ratio of 91.6:1.8:6.6 with N-methylpyrrolidone (NMP) (solvent) to form a slurry. The slurry was applied to copper foil and dried in an oven to form a backup. A piece of metallic lithium was then used as the counter electrode, a polyethylene (PE) film was used as the separator, and a few drops of the same electrolyte as the secondary battery were added. A CR2430 button battery was then assembled in an argon-gas-protected glove box.

[0202] The resulting button battery was allowed to stand for 12 hours, then discharged at a constant current of 0.05 C to 0.005 V at 25°C, allowed to stand for 10 minutes, discharged at a constant current of 50 μA to 0.005 V, allowed to stand for 10 minutes, discharged at a constant current of 10 μA to 0.005 V, and then charged at a constant current of 0.1 C to 2 V. The charge capacity was recorded. The ratio of charge capacity to the mass of the negative electrode active material is the initial capacity per gram of negative electrode active material.

[0203] (7) Testing the rapid charging performance of secondary batteries

[0204] At 25°C, the secondary battery prepared above was charged at a constant current of 0.33 C up to a charge cutoff voltage of 4.4 V, then charged at a constant voltage of 0.05 C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.33 C down to a discharge cutoff voltage of 2.8 V, and the actual capacity was recorded as C0.

[0205] Then, the secondary battery was charged at a constant current of 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, 3.5C0, 4C0, and 4.5C0 in order to a total battery charge cutoff voltage of 4.4V or a negative electrode cutoff potential of 0V (whichever reached first). After each charge, the secondary battery was discharged at 1C0 to a total battery discharge cutoff voltage of 2.8V, and the SOC (State of Charge) was measured at different charge rates of 10%, 20%, 30%, 80%, and 10%. The negative electrode potential corresponding to charging up to a maximum SOC (charge, state of charge) was recorded, and the charge rate vs. negative electrode potential curves at different SOC states were plotted and linearly fitted to obtain the charge rate corresponding to the negative electrode potential of 0 V at different SOC states. The charge rate was the charge window for each SOC state, which was C10% SOC, C20% SOC, C30% SOC, C40% SOC, C50% SOC, C60% SOC, C70% SOC, and C80% SOC, and the charge time T for charging the secondary battery from 10% SOC to 80% SOC was calculated from the formula (60 / C20% SOC + 60 / C30% SOC + 60 / C40% SOC + 60 / C50% SOC + 60 / C60% SOC + 60 / C70% SOC + 60 / C80% SOC) × 10%. The shorter the charging time T, the better the rapid charging performance of the secondary battery.

[0206] (8) (Cycle performance test)

[0207] At 25°C, the secondary battery prepared above was charged at a constant current of 0.33 C to a charge cutoff voltage of 4.4 V, then charged at a constant voltage of 0.05 C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.33 C to a discharge cutoff voltage of 2.8 V, and the initial capacity was recorded as C0. The battery was then charged according to the policy shown in Table 1 and discharged at 0.33 C. The discharge capacity Cn per cycle was recorded until the cycle capacity retention rate (i.e., Cn / C0 × 100%) reached 80%, and the number of cycles was recorded. The higher the number of cycles, the better the cycle performance of the secondary battery. [Table 1]

[0208] Table 2 shows the preparation parameters of the negative electrode active materials of Examples 1-16.

[0209] Table 3 shows the test results obtained for Examples 1 to 16 and Comparative Examples 1 to 4 according to the above performance test method. [Table 2] [Table 3]

[0210] The test results in Table 3 show that the negative electrode active material of the present invention has good dynamic performance, shortens the fast charging time of the secondary battery, and extends the cycle life of the secondary battery without compromising the high capacity per gram of the negative electrode active material.

[0211] Compared to Comparative Example 1, Comparative Example 2 uses artificial graphite coated with amorphous carbon 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 the demands for higher fast charging capability and longer cycle life for the secondary battery.

[0212] In Comparative Example 3, the addition of a ferroelectric material to the negative electrode slurry further improved the fast charging performance and cycle performance of the secondary battery compared to Comparative Example 2, but the improvement effect was limited and the demand for higher fast charging capacity and longer cycle life for secondary batteries could not be met. Possible reasons for this include the fact that when the ferroelectric material is added to the negative electrode slurry by physical mixing, the high density of the ferroelectric material makes it prone to settling in the negative electrode slurry, making it difficult to form a stable negative electrode slurry, which affects productivity and the quality of the negative electrode sheet. Meanwhile, when the ferroelectric material is added by physical mixing, some of the ferroelectric material and the negative electrode active material do not form physical contact in the negative electrode sheet, preventing the ferroelectric material from exerting its function, thereby limiting the improvement effect on the fast charging performance and cycle performance of the secondary battery.

[0213] In Comparative Example 4, artificial graphite coated with barium titanate was used as the negative electrode active material, compared to Comparative Example 1. However, the negative electrode active material was obtained by direct ball milling. Although the fast charge performance and cycle performance of the secondary battery were somewhat improved compared to Comparative Example 1, the improvement effect was limited and the demand for higher fast charge capacity and longer cycle life for secondary batteries could not be met. One possible reason for this is that the direct ball milling method combines artificial graphite particles and ferroelectric material particles by colliding and grinding them to form the negative electrode active material. However, high-energy ball milling destroys the morphology of the pre-formed artificial graphite particles, causing the amorphous carbon coating layer on the surface to peel off, which may affect the fast charge performance of the negative electrode active material. Furthermore, after the surface of the negative electrode active material is destroyed, the electrolyte (especially the solvent) is intercalated into the negative electrode active material, increasing the irreversible consumption of active lithium ions and thereby reducing the cycle performance of the secondary battery.

[0214] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiment that has substantially the same configuration as the technical idea within the technical scope of the present application and that achieves similar effects is included within the technical scope of the present application. In addition, various modifications that a person skilled in the art can conceive of may be made to the embodiments, and other forms constructed by combining some of the components of the embodiments are also included within the scope of the present application, as long as they do not deviate from the spirit of the present application.

Claims

1. A fast charging negative electrode active material comprising: carbon-based material particles; a coating layer located on at least a portion of the carbon-based material particles; and a ferroelectric material dispersed in the coating layer, the covering layer includes a conductive carbon material, and at least a portion of the ferroelectric material protrudes from a surface of the covering layer; The average thickness of the coating layer is H nm, the volume average particle diameter Dv50 of the ferroelectric material is d 1 nm, and the fast charging negative electrode active material has a ratio of 0.25≦H / d 1 ≦1.0; the carbon-based material particles include one or a combination of two or more types selected from graphite, mesocarbon microbeads, hard carbon, and soft carbon; The ferroelectric material is a fast charging negative electrode active material, comprising one or a combination of a plurality of materials selected from the group consisting of perovskite structure oxides, tungsten bronze type compounds, bismuth oxide type layer structure compounds, lithium niobate, and lithium tantalate.

2. 0.25≦H / d １ 2. The fast-charging negative electrode active material of claim 1, wherein the active material satisfies ≦0.

5.

3. The volume average particle diameter Dv50 of the ferroelectric material is d １ nm, and 20<d １ ≦200, and / or 2. The fast charging negative electrode active material according to claim 1, wherein the coating layer has an average thickness of H nm, and 20≦H≦100.

4. The mass ratio of the ferroelectric material to the carbon-based material particles is α １ and α １ is (0.5-10):100, and / or The mass ratio of the coating layer to the carbon-based material particles is α ２ and α ２ 2. The fast-charging negative electrode active material of claim 1, wherein R is (2-10):

100.

5. The mass ratio of the ferroelectric material to the carbon-based material particles is α １ and the mass ratio of the coating layer to the carbon-based material particles is α ２ and α １ :α ２ 2. The fast charging negative electrode active material of claim 1, wherein the ratio of the ionic liquid to the ionic liquid is 1:6 to 4:

1.

6. The graphitization degree of the coating layer is between 45% and 80%, and / or 2. The fast charging negative electrode active material according to claim 1, wherein the graphitization degree of the carbon-based material particles is 88% to 96%.

7. The volume average particle diameter Dv50 of the carbon-based material particles is ２ μm, and 5≦d ２ 20. The fast charging negative electrode active material of claim 1, wherein

8. 2. The rapid charging negative electrode active material according to claim 1, wherein the carbon-based material particles are in the form of primary particles, secondary particles, or a combination thereof, and in the carbon-based material particles in the form of secondary particles, the ratio of the volume average particle diameter Dv50 of the primary particles to the volume average particle diameter Dv50 of the secondary particles is 0.2 to 0.

5.

9. the dielectric constant of the ferroelectric material is 100 or greater; and / or 2. The fast charging negative electrode active material of claim 1, wherein the ferroelectric material has a Curie temperature of 80°C or higher.

10. The carbon-based material particles are selected from graphite, and / or 2. The fast charging negative electrode active material of claim 1, wherein the conductive carbon material in the coating layer comprises amorphous carbon.

11. 2. The fast charging negative electrode active material according to claim 1, 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 rapid 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 m ２ / g to 1.3m ２ / g. (3) The powder compression density of the rapid charging negative electrode active material under a force of 20,000 N is 1.5 g / cm ３ ~1.9 g / cm ３ is.

12. Step S10: supplying carbonaceous material particles, a carbon source, and a ferroelectric material, wherein the carbon source includes one or a combination of two or more types selected from asphalt, resin, and biomass material; a step S20 of uniformly mixing the carbon-based material particles, the carbon source, and the ferroelectric material, and forming a coating layer containing a conductive carbon material on at least a part of the surface of the carbon-based material particles by a carbonization sintering process, so that the ferroelectric material is dispersed in the coating layer and at least a part of the ferroelectric material protrudes from the surface of the coating layer; A method for making a fast-charging negative electrode active material comprising:

13. The carbonization sintering temperature in S20 is 700°C to 1800°C, and / or The method according to claim 12, wherein the carbonization sintering time in S20 is 1 hour to 15 hours.

14. 14. The method according to claim 12, wherein the carbon-based material particles are produced by a method including: S101 supplying coke powder and placing the coke powder in a reaction vessel; and S102 graphitizing the coke powder to obtain the carbon-based material particles.

15. 12. A negative electrode sheet comprising: a negative electrode current collector; and a negative electrode film layer provided on at least one surface of the negative electrode current collector, the negative electrode film layer comprising the fast-charging negative electrode active material according to claim 1.

16. A secondary battery comprising the negative electrode sheet according to claim 15.

17. A power consuming device comprising the secondary battery of claim 16.

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