Negative electrode active material and method for producing the same

Abstract

The present application provides a kind of negative electrode active material and its preparation method, the negative electrode active material is by graphite A and graphite B constitute self-embedded graphite, wherein, the surface of the graphite A has tenon structure, the surface of the graphite B has mortise structure, the tenon structure of the graphite A and the mortise structure of the graphite B are mutually embedded each other and the tenon structure of the graphite A and the mortise structure of the graphite B form hydrogen bond between each other. By the negative electrode active material of the present application, high adhesive force can be obtained with a small amount of binder during the preparation of electrode, so that a secondary battery with excellent battery kinetic performance, storage performance and cycle performance can be obtained.

Description

Technical Field

[0001] This application relates to the field of batteries, and in particular to a negative electrode active material and its preparation method. Background Technology

[0002] Due to their advantages such as high energy density, long cycle life, and safety and reliability, rechargeable batteries have been widely used in various digital products, portable devices, electric vehicles, and energy storage power supplies. In recent years, with the significant increase in the demand for rechargeable batteries as an energy source, higher requirements have been placed on their performance, such as kinetic performance and storage performance. Summary of the Invention

[0003] In view of the above problems, the purpose of this application is to provide a negative electrode active material that can achieve high adhesion with a small amount of binder during electrode preparation, thereby enabling a secondary battery with excellent kinetic performance, storage performance and cycle performance.

[0004] The first aspect of this application provides a negative electrode active material, wherein the negative electrode active material is a self-interlocking graphite composed of graphite A and graphite B, wherein the surface of graphite A has a tenon structure and the surface of graphite B has a mortise structure, the tenon structure of graphite A and the mortise structure of graphite B interlock with each other and hydrogen bonds are formed between the tenon structure of graphite A and the mortise structure of graphite B.

[0005] Thus, the particles of the negative electrode active material of this application are interlocked with each other through a physical tenon-and-mortise structure and chemical hydrogen bonds, thereby reducing the amount of binder used and improving the battery's kinetic and storage performance.

[0006] In any embodiment, the tenon structure of graphite A is formed by an oxygen-containing metal salt, and the contact angle between graphite A and the blank electrolyte is ≤20°. Preferably, the oxygen-containing metal salt is an oxygen-containing lithium metal salt or an oxygen-containing sodium metal salt, more preferably at least one selected from lithium aluminate, lithium zincate, sodium aluminate, and sodium zincate. The surface of the tenon structure of graphite B has hydroxyl groups, and the contact angle between graphite B and the blank electrolyte is ≤15°. The blank electrolyte is formed by dissolving lithium hexafluorophosphate at a concentration of 1 mol / L in a solvent formed by mixing ethylene carbonate and dimethyl carbonate in a mass ratio of 1:1.

[0007] The surface of graphite A has protrusions formed by the oxygen-containing metal salt (as a mortise structure), and the surface of the mortise structure of graphite B has hydroxyl groups, thereby enabling them to be combined through physical intercalation and chemical hydrogen bonding, thereby improving the kinetic performance of the battery.

[0008] In any embodiment, the contact angle between the self-intercalated graphite and the blank electrolyte is ≤15°, and the blank electrolyte is formed by dissolving lithium hexafluorophosphate at a concentration of 1 mol / L in a solvent formed by mixing ethylene carbonate and dimethyl carbonate in a mass ratio of 1:1.

[0009] By keeping the contact angle within the specified range, the surface wettability of self-intercalated graphite can be improved, which helps with slurry dispersion and electrolyte wetting and retention.

[0010] A second aspect of this application provides a method for preparing a negative electrode active material, comprising the following steps:

[0011] (1) The first graphite matrix is ​​added to a polar solvent, and then the raw material for preparing the oxygen-containing metal salt is added in such a way that the amount of oxygen-containing metal salt coated on the surface of the first graphite matrix is ​​1 to 5% by weight of the first graphite matrix. Then the mixture is stirred, evaporated and dried, and then calcined at 500 to 1200°C for 8 to 24 hours under a nitrogen atmosphere to obtain graphite A with a tenon structure.

[0012] (2) The second graphite matrix is ​​added to an alkaline solution with pH≥13 and stirred at a constant temperature of 60~100℃ for 8~36 hours. After filtration, the obtained product is washed and dried to obtain graphite B with mortise structure.

[0013] (3) Mix the graphite A and the graphite B to obtain the negative electrode active material.

[0014] The negative electrode active material of the first aspect of this application can be prepared by the above method.

[0015] In any embodiment, preferably, the first graphite matrix and the second graphite matrix are the same as or different from each other. Preferably, the first graphite matrix and the second graphite matrix are the same as or different synthetic graphite.

[0016] In any embodiment, preferably, the raw materials used to prepare the oxygen-containing metal salt include:

[0017] (1) Any one of lithium nitrate, sodium nitrate, and potassium nitrate; and

[0018] (2) At least one of aluminum nitrate, zinc nitrate and ferric nitrate.

[0019] In any embodiment, preferably, the Dv50 of the first graphite substrate and the second graphite substrate each satisfy the following condition: 3.0 μm ≤ Dv50 ≤ 15.0 μm, or optionally 5.0 μm ≤ Dv50 ≤ 13.5 μm. By making the Dv50 of the graphite substrate within the above-mentioned specific range, the lithium-ion solid-phase diffusion distance can be shortened, thereby improving the kinetic performance of the battery while appropriately taking into account the battery's storage performance.

[0020] In any embodiment, preferably, the Dv50, Dv90, and Dv10 of the first graphite matrix and the second graphite matrix each satisfy the following condition: 1.0 ≤ (Dv90 - Dv10) / Dv50 ≤ 2.0, or optionally 1.0 ≤ (Dv90 - Dv10) / Dv50 ≤ 1.7. By making (Dv90 - Dv10) / Dv50 of the graphite matrix within the above-mentioned specific range, the particle size of the graphite matrix can be relatively concentrated and similar, which is beneficial to improving the battery dynamic performance.

[0021] In any embodiment, preferably, the aspect ratio (D) of the first graphite matrix and the second graphite matrix is... L / D W Each satisfies the following condition: 1.0 ≤ D L / D W ≤2.5, can be replaced by 1.4≤D L / D W ≤2.4. By making the aspect ratio of the graphite matrix within the above-mentioned specific range, the particles of the graphite matrix can be made closer to spherical, which is beneficial for self-intercalation behavior.

[0022] In any embodiment, preferably, the oxygen-containing metal salt is an oxygen-containing lithium metal salt or an oxygen-containing sodium metal salt, more preferably, it is at least one selected from lithium aluminate, lithium zincate, sodium aluminate and sodium zincate.

[0023] In any embodiment, preferably, in step (1), the contact angle between the obtained graphite A and the blank electrolyte is ≤20°, and in step (2), the contact angle between the obtained graphite B and the blank electrolyte is ≤15°. The blank electrolyte is formed by dissolving lithium hexafluorophosphate at a concentration of 1 mol / L in a solvent formed by mixing ethylene carbonate and dimethyl carbonate at a mass ratio of 1:1.

[0024] The negative electrode active material obtained by the preparation method of the second aspect of this application is a self-intercalating graphite composed of graphite A and graphite B, wherein the tenon structure of graphite A and the mortise structure of graphite B are interlocked with each other and hydrogen bonds are formed between the tenon structure of graphite A and the mortise structure of graphite B.

[0025] Preferably, the contact angle between the self-intercalated graphite obtained by the above preparation method and the blank electrolyte is ≤15°. The blank electrolyte is formed by dissolving lithium hexafluorophosphate at a concentration of 1 mol / L in a solvent formed by mixing ethylene carbonate and dimethyl carbonate at a mass ratio of 1:1.

[0026] A third aspect of this application provides a negative electrode sheet, wherein the negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer including the aforementioned negative electrode active material or a negative electrode active material obtained by the aforementioned preparation method.

[0027] In any embodiment, preferably, the negative electrode active material layer further includes a binder, and the content of the binder is 1.3% by weight or more and less than 2.0% by weight relative to the weight of the negative electrode active material layer.

[0028] A fourth aspect of this application provides a secondary battery, wherein the secondary battery includes the negative electrode sheet of the present application described above.

[0029] The fifth aspect of this application provides an electrical device, wherein the electrical device includes the secondary battery described above.

[0030] Invention Effects

[0031] The novel negative electrode active material of this application can achieve at least the following technical effects:

[0032] (1) To achieve self-intercalation of graphite particles and make them in close contact, high adhesion can still be obtained even with a small amount of binder, thereby improving the dynamic performance, storage performance and cycle performance of the battery.

[0033] (2) The surface wettability of self-intercalated graphite can be improved by metal coating and alkaline etching (e.g. by increasing the abundance of hydroxyl groups (hydrophilic polar groups) on the graphite surface), which helps the slurry dispersion and electrolyte wetting and retention.

[0034] (3) By making the self-intercalated graphite particles present a specific spherical shape, it is convenient for the uniform nucleation of the coating layer and the simultaneous alkaline etching, so as to obtain a secondary battery with better kinetic performance, storage performance and cycle performance.

[0035] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application, it can be implemented according to the contents of the specification. In order to make the above and other objects, features and advantages of this application more obvious and understandable, the specific implementation methods of this application are listed below. Attached Figure Description

[0036] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. In the drawings:

[0037] Figure 1 This is a scanning electron microscope (SEM) image of graphite A in Embodiment 2 of this application;

[0038] Figure 2 This is an SEM image of graphite B in Embodiment 2 of this application;

[0039] Figure 3 This is an SEM image of the self-intercalating graphite in Embodiment 2 of this application. Detailed Implementation

[0040] The following will describe in detail the negative electrode active material of the present invention, its preparation method, the negative electrode sheet containing the negative electrode active material, the secondary battery containing the negative electrode sheet, and the electrical device containing the secondary battery.

[0041] For simplicity, this document only discloses some numerical ranges by example. However, any lower limit can be combined with any other upper limit to form an unstated range; and any lower limit can be combined with other lower limits to form an unstated range, just as any upper limit can be combined with any other upper limit to form an unstated range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit, combined with any other point or individual value, or combined with other lower or upper limits to form an unstated range. It should be understood that the listing of numerical values ​​is merely illustrative and should not be construed as exhaustive.

[0042] In the description of this article, it should be noted that, unless otherwise stated, "above", "below", "≤", and "≥" all include the number itself, "at least one" means including one or more, and "multiple" in "one or more" means two or more.

[0043] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0044] In the manufacturing process of the negative electrode sheet of existing secondary batteries, binders are usually required. However, as the amount of binder increases, the resistance of the negative electrode sheet increases, which degrades the battery's dynamic performance and storage performance.

[0045] As a method to reduce the amount of binder used, a core-shell structured anode material has been reported in the literature. Specifically, a roughened amorphous carbon layer (shell) is coated on the surface of a graphite (core). This roughened amorphous carbon layer has a roughened surface obtained through machining. Because this anode active material has a roughened surface, the adhesion strength can be improved by using a small amount of binder through an anchoring effect. Here, the anchoring effect refers to the anchoring of the bent surfaces of the active material particles in contact with each other.

[0046] However, the inventors discovered in their research that the battery's storage performance was poor when using the aforementioned negative electrode active material. This is because the uniformity of the traditional carbon coating is poor during the formation of the amorphous carbon layer, and the secondary cutting and roughening process during machining damages the graphite, leading to material consumption. Furthermore, the battery's cycle performance is poor because the surface roughening process during the preparation of this negative electrode active material requires machining, which damages the coating layer, reducing its strength and integrity. During cycling, graphite undergoes volume changes, and the stress generated by these changes makes the incomplete coating layer and the attached SEI film more prone to breakage, causing the graphite substrate to react directly with the electrolyte, resulting in deteriorated cycle performance. In addition, there is room for further improvement in the kinetic performance of the battery using the aforementioned negative electrode active material.

[0047] Therefore, there is a need to develop a new type of negative electrode active material that can achieve excellent adhesion without using too much binder, thereby improving the battery's kinetic performance, storage performance, and cycle performance.

[0048] Negative electrode active materials

[0049] To address the aforementioned problems, in a first aspect of this application, a negative electrode active material is provided, wherein the negative electrode active material is a self-interlocking graphite composed of graphite A and graphite B, wherein the surface of graphite A has a tenon structure, the surface of graphite B has a mortise structure, the tenon structure of graphite A and the mortise structure of graphite B interlock with each other, and hydrogen bonds are formed between the tenon structure of graphite A and the mortise structure of graphite B.

[0050] After graphite A and graphite B are mixed, they achieve precise anchoring and self-interlocking through surface tenon and mortise structures and hydrogen bonding, thus forming a stable self-interlocking structure. Therefore, the negative electrode active material of this application does not require secondary cutting of the graphite surface, and can achieve precise anchoring between graphite particles through tenon and mortise structures and hydrogen bonding without degrading storage performance. This allows for excellent adhesion without excessive binders, while improving battery performance.

[0051] In one embodiment of this application, a graphite matrix is ​​coated with an oxygen-containing metal salt to form graphite A. The coating layer formed is not a uniformly thick layer, but rather forms protrusions, equivalent to a tenon structure on the surface of graphite A. The oxygen-containing metal salt is an oxygen-containing lithium metal salt or an oxygen-containing sodium metal salt, preferably at least one selected from lithium aluminate, lithium zincate, sodium aluminate, and sodium zincate. Furthermore, the contact angle between graphite A and the blank electrolyte is preferably ≤20°, more preferably ≤17°.

[0052] The surface of the morphological structure of the above-mentioned graphite B has hydroxyl groups, and the contact angle between the above-mentioned graphite B and the blank electrolyte is ≤15°. The above-mentioned graphite B can be obtained by treating the graphite matrix by alkaline etching or other methods.

[0053] In this specification, blank electrolyte refers to an electrolyte formed by dissolving lithium hexafluorophosphate at a concentration of 1 mol / L in a solvent formed by mixing ethylene carbonate and dimethyl carbonate in a mass ratio of 1:1.

[0054] Specifically, the coating layer of graphite A has a weakly acidic structure containing hydroxyl groups. For example, the actual structure of lithium aluminate (LiAlO2) in water is LiAl(OH)4. Graphite B can have hydroxyl functional groups attached to its surface through alkaline etching. When graphite A and graphite B are mixed and thoroughly stirred and dispersed during slurry production, hydrogen bonds easily form between the oxygen-containing metal salt-coated graphite A (which is more electronegative due to the presence of metal ions) and the alkaline-etched graphite B (which is more electronegative due to the presence of oxygen).

[0055] In addition, the contact angle is an important measure of the wettability of a substance with a liquid. This application controls the contact angles of graphite A and graphite B with the blank electrolyte within the above-mentioned specific range to ensure a high hydroxyl abundance (i.e., the contact angle can reflect the level of hydroxyl abundance of graphite), making it easier to achieve electrolyte wetting and also easier to form intermolecular hydrogen bonds.

[0056] The graphite matrices constituting graphite A and graphite B (hereinafter, the graphite matrix constituting graphite A is sometimes simply referred to as the first graphite matrix, and the graphite matrix constituting graphite B is sometimes simply referred to as the second graphite matrix) can be the same or different artificial graphite. For both the first and second graphite matrices, preferably, Dv50 satisfies the following condition: 3.0 μm ≤ Dv50 ≤ 15.0 μm, more preferably 5.0 μm ≤ Dv50 ≤ 13.5 μm. Furthermore, preferably, Dv50, Dv90, and Dv10 satisfy the following condition: 1.0 ≤ (Dv90 - Dv10) / Dv50 ≤ 2.0, more preferably 1.0 ≤ (Dv90 - Dv10) / Dv50 ≤ 1.7. Additionally, preferably, the aspect ratio (D...) is... L / D W The following condition must be met: 1.0 ≤ D L / D W ≤2.5, more preferably 1.4≤D L / D W ≤2.4.

[0057] Where Dv50 refers to the particle size corresponding to a cumulative volumetric distribution percentage of 50% in the graphite matrix. Dv90 is the particle size corresponding to a cumulative volumetric distribution percentage of 90% in the graphite matrix, Dv10 is the particle size corresponding to a cumulative volumetric distribution percentage of 10% in the graphite matrix, and (Dv90-Dv10) / Dv50 represents the particle size distribution width of the graphite matrix. L D represents the length of the longest diameter inside a graphite matrix particle. W D represents the length of the longest diameter within a graphite matrix particle in the direction perpendicular to the aforementioned longest diameter. L / D W This indicates the aspect ratio of the graphite matrix particles.

[0058] The negative electrode active material of this application utilizes the hydrogen bonding between the oxygen-containing functional groups of the metal coating layer of graphite A and the hydroxyl groups in the tenon structure of graphite B, as well as the tenon-and-mortise structure, to achieve self-intercalation of graphite, thereby reducing the amount of binder used. This application avoids using amorphous carbon as a coating layer (although using amorphous carbon as a coating layer enhances kinetic performance, it degrades the battery's storage performance), and also eliminates the need for secondary surface cutting. Instead, it improves the battery's kinetic performance through the tenon and mortise structures formed by the metal salt coating layer.

[0059] Furthermore, by coating the aforementioned oxygen-containing lithium metal salt or oxygen-containing sodium metal salt and forming depressions (mortise structures) on the surface, fast ion channels that facilitate rapid lithium ion insertion and extraction can be provided, effectively improving kinetics. Additionally, the tenon structure of graphite A is preferably formed from an oxygen-containing lithium metal salt. Thus, this application avoids the use of amorphous carbon while replenishing the lithium ion consumption during film formation due to the presence of lithium ions in the tenon structure, reducing side reactions and thereby contributing to improved first coulombic efficiency and storage performance.

[0060] In one embodiment of this application, the contact angle between the self-intercalated graphite, which serves as the negative electrode active material, and the blank electrolyte is ≤15°. By controlling the contact angle between the self-intercalated graphite and the blank electrolyte within the aforementioned specific range, the wettability of the graphite surface can be improved, which helps in slurry dispersion and electrolyte wetting and retention.

[0061] Preparation method of negative electrode active material

[0062] A second aspect of this application provides a method for preparing a negative electrode active material, which includes the following steps.

[0063] Step (1): The first graphite matrix is ​​added to a polar solvent, and then the raw material for preparing the oxygen-containing metal salt is added in such a way that the amount of oxygen-containing metal salt coated on the surface of the first graphite matrix is ​​1 to 5% by weight of the first graphite matrix. Then, the mixture is stirred, evaporated and dried, and then calcined in a nitrogen atmosphere at 500 to 1200°C, preferably at 600 to 1000°C, more preferably at 700 to 900°C for 8 to 24 hours (preferably 10 to 20 hours, more preferably 12 hours) to obtain graphite A with a tenon structure.

[0064] In this step, artificial graphite can be used as the first graphite matrix. There are no particular limitations on the polar solvent used; examples include deionized water, methanol, ethanol, isopropanol, and water, which are commonly used polar solvents in the art.

[0065] The raw materials used to prepare the above-mentioned oxygen-containing metal salts include:

[0066] (1) Any one of lithium nitrate, sodium nitrate, and potassium nitrate; and

[0067] (2) At least one of aluminum nitrate, zinc nitrate and ferric nitrate.

[0068] In this step, the amount of raw material used to prepare the oxygen-containing metal salt is preferably 2 to 12% by weight of the first graphite matrix, more preferably 4 to 8% by weight.

[0069] The oxygen-containing metal salt can be an oxygen-containing lithium metal salt or an oxygen-containing sodium metal salt, preferably at least one selected from lithium aluminate, lithium zincate, sodium aluminate and sodium zincate.

[0070] In the preparation process, preferably, a small amount of the above-mentioned oxygen-containing metal salt raw material is added first, so that the small amount of oxygen-containing metal salt can first nucleate on the graphite substrate to form a dot-like coating layer. Then, the remaining raw material is gradually added. Thus, the subsequently added raw material will preferentially attach and grow on the nucleated coating points, thereby forming a more uniform convex structure.

[0071] Preferably, in step (1) above, the contact angle between the obtained graphite A and the blank electrolyte is ≤20°.

[0072] Step (2): The second graphite matrix is ​​added to an alkaline solution with pH ≥ 13 and stirred at 60-100°C, preferably 70-90°C, more preferably 80°C for 8-36 hours (preferably 12-24 hours). After filtration, the obtained product is washed and dried to obtain graphite B with a mortise structure.

[0073] In this step, artificial graphite can be used as the second graphite matrix. There are no special restrictions on the alkaline solution used in this step, as long as its pH is ≥13; for example, sodium hydroxide solution or potassium hydroxide solution can be used.

[0074] Preferably, in step (2) above, the contact angle between the obtained graphite B and the blank electrolyte is ≤15°.

[0075] Step (3): Mix the above graphite A and the above graphite B to obtain the negative electrode active material.

[0076] In this step, there are no particular limitations on the mixing method; any method commonly used in the art can be employed, such as using a stirrer.

[0077] In one embodiment of this application, preferably, the first graphite matrix and the second graphite matrix are the same or different artificial graphite.

[0078] When artificial graphite is used in the first graphite matrix and the second graphite matrix described above in this application, the artificial graphite can be commercially available or can be prepared in the following manner:

[0079] (a) Raw material crushing

[0080] The coking raw material includes one or more of petroleum-based non-needle coke and petroleum-based needle coke. Optionally, the coking raw material includes petroleum green coke. The raw material is crushed using a mechanical mill or roller mill. The feeding frequency can be 10Hz to 40Hz, preferably 25Hz to 35Hz, and the crushing frequency can be 20Hz to 50Hz, preferably 35Hz to 45Hz. After the above treatment, crushed aggregate is obtained.

[0081] (b) Reshaping and removing fine powder

[0082] The material obtained from (a) is placed in a shaping machine for shaping and fine powder removal. The grading frequency can be 30Hz to 60Hz, preferably 40Hz to 50Hz, and the induced draft frequency can be 30Hz to 55Hz, preferably 35Hz to 45Hz. After the above treatment, the shaped aggregate is obtained.

[0083] (c) Heat treatment

[0084] The material obtained from (b) is placed in a horizontal or vertical reactor and heated to 300–700°C, preferably 400–550°C, and held at that temperature for a period of time, wherein a stepped heating method is used. Multiple (e.g., 2–4) programmed heating platforms are set during the heating process to facilitate obtaining the desired particle size distribution of the product.

[0085] (d) Graphitization

[0086] High-temperature graphitization can be performed using equipment known in the art, such as graphitization furnaces or Atchison graphitization furnaces. The graphitization temperature is 2500℃~3500℃.

[0087] In the above preparation process, Dv50 is controlled by setting the pulverizing frequency to 20Hz–50Hz, (Dv90-Dv10) / Dv50 is controlled by setting the grading frequency to 30Hz–60Hz, and Dv90 / Dv50 is controlled by setting the feeding frequency to 10Hz–40Hz and the induced draft frequency to 30Hz–55Hz. L / D W Control.

[0088] The artificial graphite used as the graphite matrix preferably satisfies the following condition: Dv50 satisfies the condition that 3.0 μm ≤ Dv50 ≤ 15.0 μm, more preferably 5.0 μm ≤ Dv50 ≤ 13.5 μm. Furthermore, preferably, Dv50, Dv90, and Dv10 satisfy the condition that 1.0 ≤ (Dv90 - Dv10) / Dv50 ≤ 2.0, more preferably 1.0 ≤ (Dv90 - Dv10) / Dv50 ≤ 1.7. Additionally, preferably, D... L and D W The following condition must be met: 1.0 ≤ D L / DW ≤2.5, more preferably 1.4≤D L / D W ≤2.4.

[0089] The negative electrode active material obtained by the above preparation method is a self-intercalating graphite composed of graphite A and graphite B, wherein the tenon structure of graphite A and the mortise structure of graphite B are interlocked, and hydrogen bonds are formed between the tenon structure of graphite A and the mortise structure of graphite B. Preferably, the contact angle between the self-intercalating graphite obtained by the above preparation method and the blank electrolyte is ≤15°.

[0090] Negative electrode sheet

[0091] A third aspect of this application provides a negative electrode sheet, which includes a negative electrode active material layer, wherein the negative electrode active material layer includes the negative electrode active material of the first aspect of this application or the negative electrode active material obtained by the preparation method of the second aspect of this application.

[0092] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer including a negative active material.

[0093] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0094] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder is not particularly limited and may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). There is no particular limitation on the binder content. However, this application allows for a significant reduction in the amount of binder used; the binder content relative to the weight of the negative electrode active material layer can be reduced to less than 2.0% by weight, and excellent adhesion can still be obtained even when the binder content is as low as 1.3% by weight.

[0095] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0096] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0097] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0098] Secondary batteries

[0099] A fourth aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode is the negative electrode of this application as described above.

[0100] In the secondary battery of this application, there are no specific limitations on the positive electrode sheet, which can be appropriately selected according to actual needs, and may include conductive agents, binders, positive electrode active materials, etc. There are no specific limitations on the types of conductive agents, binders, and positive electrode active materials, which can be appropriately selected.

[0101] For example, positive electrode active materials may include at least one of the following: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM)211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0102] In the secondary battery of this application, the electrolyte plays the role of conducting ions between the positive and negative electrodes. This application does not have specific restrictions on the type of electrolyte and it can be selected according to needs. For example, the electrolyte can be liquid, gel, or all-solid.

[0103] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution comprises an electrolyte salt and a solvent. The electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate. Additionally, the electrolyte solution may include additives as needed.

[0104] In the secondary battery of this application, the aforementioned separator is disposed between the positive and negative electrodes, serving as a separator. This application does not specifically limit the type of separator; it can be any separator material used in secondary batteries. For example, it can be at least one of polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation.

[0105] Electrical appliances

[0106] The electrical device of the fifth aspect of the present invention includes the secondary battery of the fourth aspect of the present invention.

[0107] In the electrical device of the present invention, the secondary battery of the present invention can be used as a power source for the aforementioned electrical device, or as an energy storage unit for the aforementioned electrical device. The aforementioned electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, and energy storage systems.

[0108] Example

[0109] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0110] Dv50 and (Dv90-Dv10) / Dv50 of graphite matrix

[0111] The particle size distribution shall be determined using a laser particle size analyzer (e.g., Malven Master Size 3000) in accordance with standard GB / T19077.1-2016.

[0112] The aspect ratio (D) of the graphite matrix L / D W )

[0113] The particle morphology was tested using a scanning electron microscope (ZEISS Sigma 300). The tests were conducted based on JY / T010-1996. To ensure the accuracy of the test results, multiple (e.g., 5) different regions were randomly selected from the sample for scanning, and the aspect ratio of each region was calculated at a magnification of 3000x. To further ensure the accuracy of the test results, the above tests were repeated on multiple test samples (e.g., 10), and the average value of each test sample was taken as the final test result.

[0114] Contact angle with blank electrolyte :

[0115] Test sample: 45mg of graphite was pressed into a 1cm diameter tablet using a pressure of 20MPa, held for 30 seconds, and left to stand for 5 minutes. The contact angle of the tablet was then tested.

[0116] Test solvent: blank electrolyte (its composition is as follows: 1 mol / L of lithium hexafluorophosphate dissolved in a solvent formed by mixing ethylene carbonate and dimethyl carbonate in a mass ratio of 1:1).

[0117] Test procedure: Drop 20 μL of the above blank electrolyte onto the test sample using a 100 μL Top Pette pipette. Using the shape image analysis method, with Data Physics OcA40, measure the angle between the tangent of the outer surface of the blank electrolyte droplet and the plane of the test sample, and use it as the contact angle.

[0118] Example 1

[0119] (1) Preparation of graphite matrix

[0120] Petroleum coke was crushed using a mechanical mill at a feeding frequency of 40 Hz and a grinding frequency of 40 Hz. The crushed material was then placed in a shaping machine for shaping and fine powder removal at a grading frequency of 50 Hz and an induced draft frequency of 45 Hz to obtain shaped aggregate. This aggregate was then placed in a horizontal reactor and heated to 500℃ and held at that temperature for 8 hours, using a stepped heating method with two programmed heating platforms. Finally, high-temperature graphitization was performed in a graphitization furnace at a graphitization temperature of 3000℃.

[0121] The Dv50, (Dv90-Dv10) / Dv50, and aspect ratio (D) of the obtained graphite matrix were determined using the above method. L / D W The results are shown in Table 1.

[0122] (2) Preparation of self-intercalated graphite

[0123] The graphite matrix obtained in (1) is used as the first graphite matrix and the second graphite matrix.

[0124] First, 300g of the first graphite matrix was added to 1000ml of deionized water in batches. Then, 7.7g of sodium nitrate and 34.10g of aluminum nitrate nonahydrate were added so that the amount of sodium aluminate coated on the surface of the graphite matrix was 2% of the weight of the graphite matrix. The mixture was stirred at room temperature for 2 hours, then stirred and evaporated. The resulting product was dried in a vacuum at 120℃ for 8 hours, and then calcined at 800℃ for 12 hours in a nitrogen atmosphere at a heating rate of 10℃ / min to obtain a dry powder, which was used as graphite A.

[0125] In addition, 1000 ml of a 20% potassium hydroxide solution with a pH of 14.78 was prepared as an etchant, and 300 g of the second graphite matrix was added sequentially. The solution was kept at a constant temperature and magnetically stirred in an 80°C water bath for 24 hours. After the solution was allowed to stand for 2 hours, the supernatant was removed by vacuum filtration. The resulting product was washed three times with deionized water and dried at 120°C under vacuum for 8 hours to obtain a dry powder, which was used as graphite B.

[0126] The graphite A and graphite B obtained above were thoroughly mixed, and self-intercalation was achieved through hydrogen bonding forces on the graphite surfaces and the surface roughness of the mixture, resulting in self-intercalated graphite. The contact angles of the obtained self-intercalated graphite with the blank electrolyte are shown in Table 1.

[0127] In addition, to demonstrate that the processing method of this application has no substantial impact on the volumetric energy density of the material, the inventors tested the specific capacity and initial coulombic efficiency of the first graphite matrix, the second graphite matrix, and the prepared self-intercalated graphite pair. Details are as follows.

[0128] A slurry was prepared by uniformly mixing a first graphite matrix, conductive agent Super P, and binder (PVDF) with solvent NMP (N-methylpyrrolidone) at a mass ratio of 91.6:1.8:6.6. The prepared slurry was then coated onto a copper foil current collector, dried in an oven, and cold-pressed for later use. The compaction range was 1.4–1.6 g / cm³. 3 A lithium metal sheet was used as the counter electrode; a polyethylene (PE) film was used as the separator; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and LiPF6 was uniformly dissolved in the above solution to obtain the electrolyte, wherein the concentration of LiPF6 was 1 mol / L; the above components were assembled into a CR2430 coin cell in an argon-protected glove box. After the obtained coin cell was left to stand for 12 hours, it was discharged at a constant current of 0.05C to 0.005V, left to stand for 10 minutes, and then discharged at a constant current of 50μA to 0.005V again, left to stand for 10 minutes, and then discharged at a constant current of 10μA to 0.005V again. The sum of the three discharge capacities was the discharge capacity; then it was charged at a constant current of 0.1C to 2.000V, and the charging capacity was recorded. The ratio of charging capacity to the mass of the first graphite matrix is ​​the specific capacity of the first graphite matrix, and the ratio of charging capacity to discharging capacity is the initial coulombic efficiency.

[0129] The second graphite matrix, conductive agent Super P, and binder (PVDF) were mixed with solvent NMP (N-methylpyrrolidone) at a mass ratio of 91.6:1.8:6.6. The specific capacity and initial coulombic efficiency of the second graphite matrix were determined using the same method as described above.

[0130] Self-intercalated graphite, conductive agent Super P, and binder (PVDF) were mixed with solvent NMP (N-methylpyrrolidone) at a mass ratio of 91.6:1.8:6.6. The specific capacity and initial coulombic efficiency of the self-intercalated graphite were determined using the same method as described above.

[0131] The specific values ​​of the specific volume and the initial coulombic efficiency measured as described above are shown in Table 1 below.

[0132] Example 2

[0133] Except for the addition of 6.27g of lithium nitrate and 34.10g of aluminum nitrate nonahydrate to make the amount of lithium aluminate coated on the surface of the graphite matrix 2% of the weight of the graphite matrix, the preparation was carried out in the same manner as in Example 1.

[0134] The SEM images of graphite A, graphite B, and self-intercalating graphite obtained in Example 2 are shown below. Figure 1 , 2 3. For example Figure 1 As shown, granular protrusions with a tenon structure are formed on the surface of graphite A. Figure 2 As shown, depressions are formed on the surface of graphite B, that is, the surface of the obtained graphite B has a mortise structure. Figure 3 As shown, graphite A and graphite B self-interlock.

[0135] Example 3

[0136] Except for the addition of 15.66g of lithium nitrate and 85.25g of aluminum nitrate nonahydrate to make the amount of lithium aluminate coated on the surface of the graphite matrix 5% of the weight of the graphite matrix, the preparation was carried out in the same manner as in Example 1.

[0137] Example 4

[0138] The preparation was carried out in the same manner as in Example 2, except that a sodium hydroxide solution with a pH of 14.96 (30% by mass) was used as an etchant and the mixture was magnetically stirred at a constant temperature in a water bath at 90°C for 8 hours.

[0139] Examples 5-16

[0140] (1) Preparation of graphite matrix

[0141] A graphite matrix was prepared by appropriately adjusting the feeding frequency, crushing frequency, classification frequency, and induced draft frequency. The resulting graphite matrix was analyzed for its Dv50, (Dv90-Dv10) / Dv50, and aspect ratio (D...). L / D W As shown in Table 1.

[0142] (2) Preparation of self-intercalated graphite

[0143] The preparation was carried out in the same manner as in Example 2, except that the graphite matrix shown in Table 1 was used accordingly.

[0144] The contact angles of graphite A and graphite B with the blank electrolyte, the contact angle of self-intercalated graphite with the blank electrolyte, the specific capacity, and the initial coulombic efficiency obtained through Examples 1 to 16 are shown in Table 1.

[0145] Comparative Example 1

[0146] Except for the addition of 18.81g of lithium nitrate and 102.3g of aluminum nitrate nonahydrate to make the amount of lithium aluminate coated on the surface of the graphite matrix 6% by weight of the graphite matrix, the preparation was carried out in the same manner as in Example 1. Due to the excessive amount of coated lithium aluminate, the protrusions formed on the surface of graphite A did not match the depressions on graphite B, thus failing to form the self-intercalating graphite of the present invention.

[0147] Comparative Example 2

[0148] The preparation was carried out in the same manner as in Example 1, except that a sodium hydroxide solution with a pH of 12 was used as an etchant and the mixture was magnetically stirred at room temperature for 12 hours. Since sufficient depressions were not formed on the surface of graphite B, the self-intercalating graphite of the present invention could not be formed.

[0149] Comparative Example 3

[0150] 1000g of the graphite matrix (core) from Example 1 and 100g of coal tar pitch as an amorphous carbon layer precursor were mixed in a drum mixer for 2 hours, followed by heat treatment at 1150°C for 600 minutes to obtain graphite coated with an amorphous carbon layer (shell). The graphite coated with the amorphous carbon layer thus prepared was introduced into a spheroidizing apparatus (equipment name: AMD3) and spheroidized using a spheroidizing cutter at a speed of 1,000 rpm for 2 hours.

[0151] Graphite coated with a spheroidized amorphous carbon layer is introduced into a spheroidizing apparatus. A needle-shaped roughening cutter with a diameter of 10 μm is used instead of the spheroidizing cutter, and the process is carried out at 500 rpm to form a first roughened surface with a surface roughness of 7 μm. Then, a roughening cutter with a diameter of 2 μm is used instead of the needle-shaped roughening cutter, and the first roughened surface is processed at 200 rpm to form a second roughened surface with a surface roughness of 3 μm. This process prepares a core-shell structured anode active material containing an amorphous carbon layer with a roughened surface.

[0152]

[0153] Next, the negative electrode active materials obtained in the above examples and comparative examples were used to prepare secondary batteries as shown below, and performance tests were conducted. The test results are shown in Table 2 below.

[0154] (1) Preparation of positive electrode sheet

[0155] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 A positive electrode slurry is prepared in N-methylpyrrolidone (NMP) using O2, conductive agent Super P, and binder polyvinylidene fluoride (PVDF). The solid content of the positive electrode slurry is 50 wt%, and the solid component is LiNi.0.8 Co 0.1 Mn 0.1 The mass ratio of O2, Super P, and PVDF is 8:1:1. The positive electrode slurry is coated onto the current collector aluminum foil and dried at 85°C. After cold pressing, the foil is trimmed, cut, and slit. Then, it is dried under vacuum at 85°C for 4 hours to produce the positive electrode sheet.

[0156] (2) Preparation of negative electrode sheet

[0157] The negative electrode active material, styrene-butadiene rubber (SBR) binder, sodium carboxymethyl cellulose (CMC-Na) thickener, and carbon black (Super P) conductive agent of the above embodiments or comparative examples are added to achieve a weight ratio of 96.3:1.3:1.2:1.2, and then mixed evenly in deionized water to prepare a negative electrode slurry. The negative electrode slurry is coated onto a current collector copper foil and dried at 85°C. After cold pressing, edge trimming, cutting, and slitting, it is dried under vacuum at 120°C for 12 hours to prepare the negative electrode sheet.

[0158] The adhesion strength of the prepared negative electrode sheet was measured using a high-speed rail tensile testing machine according to the usual 180-degree peel test. The results are shown in Table 2.

[0159] (3) Preparation of secondary batteries

[0160] A 16μm polyethylene film (PE) was used as the separator. The positive electrode, separator, and negative electrode were stacked in sequence, with the separator positioned between the positive and negative electrodes to isolate them. The resulting bare cell was wound up, tabs were welded on, and the bare cell was placed in an outer package. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1. Then, fully dried lithium salt LiPF6 was uniformly dissolved in the above solution to obtain the electrolyte. The electrolyte was then injected into the dried cell, and the cell was packaged, allowed to stand, formed, shaped, and its capacity was tested to prepare a secondary battery.

[0161] The prepared secondary battery underwent the following performance tests, and the specific test results are shown in Table 2.

[0162] (a) Battery fast charging performance (0-80% SOC)

[0163] At 25°C, the secondary batteries prepared in the examples and comparative examples were charged at a constant current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour) to 4.25V, then charged at a constant voltage to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 1C to 2.8V. The actual capacity was recorded as C0. The batteries were then sequentially charged at constant currents of 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, 3.5C0, 4C0, and 4.5C0 to 4.25V or 0V negative electrode cutoff potential (whichever comes first). After each charge, the batteries were discharged at 1C0 to 2.8V. The SOC (State of Charge) was recorded at different charging rates until 10%, 20%, 30%...80%. By plotting the negative electrode potential corresponding to the state of charge (SOC), rate-negative electrode potential curves are generated for different SOC states. Linear fitting yields the charging rate corresponding to a negative electrode potential of 0V for each SOC state. This charging rate is the charging window for that SOC state, denoted as C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC. The charging time T (in minutes) from 10% SOC to 80% SOC is calculated using the formula (60 / C20%SOC + 60 / C30%SOC + 60 / C40%SOC + 60 / C50%SOC + 60 / C60%SOC + 60 / C70%SOC + 60 / C80%SOC) × 10%. A shorter time indicates better fast-charging performance.

[0164] (b) Battery storage performance test

[0165] At 25°C, the secondary batteries prepared in the examples and comparative examples were charged at a constant current of 0.33C to the charging cutoff voltage of 4.25V, then charged at a constant voltage to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.33C to the discharge cutoff voltage of 2.8V. The initial capacity was recorded as C0. The batteries were then stored at a constant temperature of 60°C until the cycle capacity retention (Cn / C0×100%) reached 80%, and the number of storage days was recorded. A longer storage period indicates a better battery lifespan.

[0166] (c) Battery cycle performance (degradation to 80% of initial reversible capacity)

[0167] At 25°C, the secondary batteries prepared in the examples and comparative examples were charged at a constant current of 0.33C to the charging cutoff voltage of 4.25V, then charged at a constant voltage to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.33C to the discharge cutoff voltage of 2.8V. The initial capacity was recorded as C0. Then, the batteries were charged at 2C and discharged at 1C, and the discharge capacity Cn was recorded for each cycle until the cycle capacity retention rate (Cn / C0×100%) reached 80%. The number of cycles was recorded. A higher number of cycles indicates a better cycle life.

[0168] Table 2

[0169]

[0170] As shown in Table 1, in Examples 1-16, processing the graphite matrix to form self-intercalated graphite had no significant impact on the specific capacity and initial coulombic efficiency of the material. Furthermore, by processing the graphite matrix, the contact angles between graphite A and graphite B and the blank electrolyte decreased, making it easier for hydrogen bonds to form between graphite A and graphite B.

[0171] As can be seen from the data in Table 2, very high bonding strength was obtained in Examples 1 to 16 of this application with very little adhesive (1.3% by weight), and the resulting secondary batteries have excellent battery kinetic performance, storage performance and cycle performance.

[0172] Compared to Comparative Examples 1-3, in Examples 1-16, graphite A and graphite B form self-intercalating graphite through a tenon-and-mortise structure and hydrogen bonding, which significantly improves the adhesion of the negative electrode, resulting in excellent fast-charging performance, greatly enhancing the battery's kinetic performance, and also improving its storage and cycle performance. Comparative Examples 1-3 did not form the self-intercalating structure described in this application and therefore failed to achieve the technical effects of this application.

[0173] Furthermore, compared to Example 16, Examples 5-8, Examples 9-12, and Examples 13-15 improved upon the previous methods by adjusting the Dv50, (Dv90-Dv10) / Dv50, and D of the graphite matrix. L / D W The values, within a specific range of this application, can further improve adhesion, further enhance fast charging performance, and achieve excellent battery storage performance and cycle performance.

[0174] Furthermore, compared to Examples 5-16, Examples 1-4 improved the graphite matrix by adjusting the Dv50, (Dv90-Dv10) / Dv50, and D... L / D W The values ​​are all within the specific range of this application, which can achieve better technical effects.

[0175] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A negative electrode active material, wherein, The negative electrode active material is a self-intercalating graphite composed of graphite A and graphite B. The surface of graphite A has a tenon structure, and the surface of graphite B has a mortise structure. The tenon structure of graphite A and the mortise structure of graphite B are interlocked, and hydrogen bonds are formed between the tenon structure of graphite A and the mortise structure of graphite B.

2. The negative electrode active material according to claim 1, wherein, The tenon structure of the graphite A is formed by an oxygen-containing metal salt, and the contact angle between the graphite A and the blank electrolyte is ≤20°. The oxygen-containing metal salt is an oxygen-containing lithium metal salt or an oxygen-containing sodium metal salt. The blank electrolyte is formed by dissolving lithium hexafluorophosphate at a concentration of 1 mol / L in a solvent formed by mixing ethylene carbonate and dimethyl carbonate in a mass ratio of 1:

1.

3. The negative electrode active material according to claim 2, wherein, The surface of the morphological structure of the graphite B has hydroxyl groups, and the contact angle between the graphite B and the blank electrolyte is ≤15°.

4. The negative electrode active material according to claim 2 or 3, wherein, The oxygen-containing metal salt is selected from at least one of lithium aluminate, lithium zincate, sodium aluminate, and sodium zincate.

5. The negative electrode active material according to claim 1, wherein, The contact angle between the self-intercalating graphite and the blank electrolyte is ≤15°. The blank electrolyte is formed by dissolving lithium hexafluorophosphate at a concentration of 1 mol / L in a solvent formed by mixing ethylene carbonate and dimethyl carbonate in a mass ratio of 1:

1.

6. A method for preparing the negative electrode active material according to any one of claims 1 to 5, comprising the following steps: (1) The first graphite matrix is ​​added to a polar solvent, and then the raw material for preparing the oxygen-containing metal salt is added in such a way that the amount of oxygen-containing metal salt coated on the surface of the first graphite matrix is ​​1 to 5% by weight of the first graphite matrix. Then the mixture is stirred, evaporated and dried, and then calcined at 500 to 1200°C for 8 to 24 hours under a nitrogen atmosphere to obtain graphite A with a tenon structure; the oxygen-containing metal salt is an oxygen-containing lithium metal salt or an oxygen-containing sodium metal salt. (2) The second graphite matrix was added to an alkaline solution with pH≥13 and stirred at a constant temperature of 60~100℃ for 8~36 hours. After filtration, the resulting product was washed and dried to obtain graphite B with a mortise structure. (3) Mix the graphite A and the graphite B to obtain the negative electrode active material.

7. The preparation method according to claim 6, wherein, The first graphite matrix and the second graphite matrix may be the same as or different from each other.

8. The preparation method according to claim 6 or 7, wherein, The first graphite matrix and the second graphite matrix are the same or different artificial graphite.

9. The preparation method according to claim 6, wherein, The raw materials used to prepare the oxygen-containing metal salt include: (1) Either lithium nitrate or sodium nitrate; and (2) At least one of aluminum nitrate and zinc nitrate.

10. The preparation method according to claim 6, wherein, The Dv50 of the first graphite matrix and the second graphite matrix each satisfy the following conditions: 3.0μm≤Dv50≤15.0μm.

11. The preparation method according to claim 6, wherein, The Dv50 of the first graphite matrix and the second graphite matrix each satisfy the following conditions: 5.0μm≤Dv50≤13.5μm.

12. The preparation method according to claim 10 or 11, wherein, The Dv50, Dv90, and Dv10 of the first graphite matrix and the second graphite matrix each satisfy the following conditions: 1.0≤(Dv90-Dv10) / Dv50≤2.

0.

13. The preparation method according to claim 10 or 11, wherein, The Dv50, Dv90, and Dv10 of the first graphite matrix and the second graphite matrix each satisfy the following conditions: 1.0≤(Dv90-Dv10) / Dv50≤1.

7.

14. The preparation method according to claim 6, wherein, The aspect ratio D of the first graphite matrix and the second graphite matrix L / D W Each of them meets the following conditions: 1.0≤D L / D W ≤2.5。 15. The preparation method according to claim 6, wherein, The aspect ratio D of the first graphite matrix and the second graphite matrix L / D W Each of them meets the following conditions: 1.4≤D L / D W ≤2.4。 16. A negative electrode plate, wherein, The negative electrode sheet includes a negative electrode active material layer, which includes the negative electrode active material according to any one of claims 1 to 5 or the negative electrode active material obtained by the preparation method according to any one of claims 6 to 15.

17. The negative electrode sheet according to claim 16, wherein, The negative electrode active material layer further includes a binder, and the content of the binder is more than 1.3% by weight and less than 2.0% by weight relative to the weight of the negative electrode active material layer.

18. A secondary battery, wherein, The secondary battery includes the negative electrode sheet as described in claim 16 or 17.

19. An electrical appliance, wherein, The electrical device includes the secondary battery as described in claim 18.

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