Negative active material particle and preparation method thereof, negative pole piece and battery

Abstract

The invention discloses a negative electrode active material particle and a preparation method thereof, a negative electrode plate and a battery. The negative electrode active material particle includes: an inner core including a carbon material; the transition layer comprises graphitized carbon, and the transition layer is located on the surface of the inner core; the amorphous carbon layer is positioned on the surface of the transition layer; wherein the coating rate of the amorphous carbon layer on the surfaces of the negative electrode active material particles is 80%-100%. The negative electrode active material particle has good electrochemical performance and cycling stability, is applied to a battery, and is beneficial to improving the energy density and the cycling performance of the battery.

Description

Technical Field

[0001] This application belongs to the field of electrochemistry, specifically relating to a negative electrode active material particle and its preparation method, a negative electrode sheet, and a battery. Background Technology

[0002] With the development of secondary batteries represented by lithium-ion batteries, carbon materials, especially graphite-based carbon anode materials, have been widely used worldwide as battery anode materials due to their unique layered structure and easy lithium-ion intercalation characteristics.

[0003] Carbon materials offer advantages such as low cost, high capacity, and stable charge-discharge performance. However, they exhibit poor compatibility with certain organic solvents and slow reaction kinetics. Furthermore, carbon materials are sensitive to certain electrolytes; for example, when graphite comes into contact with propylene carbonate, the carbonate decomposes on the graphite surface, causing graphite flaking. This not only leads to capacity loss in carbon materials but also reduces their stability, resulting in decreased battery energy density and cycle performance. Summary of the Invention

[0004] To address the aforementioned issues, this application provides a negative electrode active material particle, its preparation method, a negative electrode sheet, and a battery. This negative electrode active material particle exhibits excellent electrochemical performance and cycle stability, and its application in batteries is beneficial for improving battery energy density and cycle performance.

[0005] The first aspect of this application provides a negative electrode active material particle, comprising:

[0006] The core, which includes carbon materials;

[0007] The transition layer, which includes graphitized carbon, is located on the surface of the core.

[0008] An amorphous carbon layer is located on the surface of the transition layer.

[0009] Among them, the amorphous carbon layer has a coating rate of 80% to 100% on the surface of the negative electrode active material particles.

[0010] The negative electrode active material particles of this application include a core, a transition layer on the surface of the core, and an amorphous carbon layer on the surface of the transition layer. The core comprises carbon material, and the transition layer comprises graphitized carbon. In these negative electrode active material particles, the amorphous carbon layer covers 80%–100% of the particle surface, allowing it to be uniformly and completely coated onto the core surface through the transition layer. On one hand, the coating of the amorphous carbon layer enhances the electronic conductivity of the carbon material, resulting in better kinetic performance of the negative electrode active material. On the other hand, the coating reduces the contact between the carbon material and the electrolyte, thereby reducing side reactions and improving the stability of the negative electrode active material particles in the electrolyte. Furthermore, in the negative electrode active material particles of this application, the transition layer containing graphitized carbon has a high bonding force with both the core and the amorphous carbon layer, allowing the amorphous carbon layer to tightly coat the core surface through the transition layer. Thus, the negative electrode active material particles of this application possess high structural stability, further enhancing their stability in the electrolyte. The negative electrode active material particles of this application exhibit good kinetic properties, maintain high stability in the electrolyte, and possess low irreversible capacity, good cycle stability, and electrochemical performance. Therefore, when applied to secondary batteries, the negative electrode active material particles of this application can improve the initial reversible capacity, energy density, and cycle performance of the secondary battery.

[0011] In any embodiment of this application, the carbon material includes graphite.

[0012] Preferably, the graphite includes one or more of the following: composite particle artificial graphite, single particle artificial graphite, spherical natural graphite, and mesophase carbon microspheres.

[0013] In any embodiment of this application, the thickness of the amorphous carbon layer is 3nm to 15nm, preferably 5nm to 10nm.

[0014] In any embodiment of this application, the amorphous carbon layer has a coating rate of 85% to 100% on the surface of the negative electrode active material particles.

[0015] A second aspect of this application provides a method for preparing negative electrode active material particles, comprising:

[0016] Provide core material particles, including carbon materials;

[0017] The preparation of the intermediate includes placing core material particles in a carbon source gas stream at a first temperature under stirring conditions, so that the carbon source undergoes a thermal decomposition reaction on the surface of the core material particles, thereby forming a transition layer on the surface of the core material particles, and obtaining the intermediate, wherein the transition layer includes graphitized carbon.

[0018] The preparation of negative electrode active material particles includes placing an intermediate in a carbon source gas stream at a second temperature under stirring conditions, so that the carbon source undergoes a thermal decomposition reaction on the surface of the intermediate, thereby forming an amorphous carbon layer on the surface of the transition layer, and obtaining negative electrode active material particles, wherein the coating rate of the amorphous carbon layer on the surface of the negative electrode active material particles is 80% to 100%.

[0019] In any embodiment of this application, the first temperature is 700°C to 1200°C, preferably 900°C to 1200°C.

[0020] In any embodiment of this application, the preparation of the intermediate includes:

[0021] Under stirring conditions, the core material particles are placed in a carbon source gas stream at a first temperature for 0.5h to 1h.

[0022] In any embodiment of this application, the second temperature is 500°C to 800°C, preferably 600°C to 700°C.

[0023] In any embodiment of this application, the preparation of negative electrode active material particles includes:

[0024] Under stirring conditions, the intermediate is placed in a carbon source gas stream at a second temperature for 0.5 h to 5 h, preferably 0.5 h to 3 h.

[0025] In any embodiment of this application, the carbon source gas flow includes a carbon source gas flow and a carrier gas flow.

[0026] The carbon source gas stream includes one or more of methane, toluene, and acetylene, preferably methane; and / or

[0027] The carrier gas flow includes at least one of nitrogen or argon.

[0028] Preferably, the flow rate of the carbon source gas is 2 mL / min to 20 mL / min, and the flow rate of the carrier gas is 0.5 L / min to 1 L / min.

[0029] In any embodiment of this application, before preparing the negative electrode active material particles, the method further includes:

[0030] The intermediate is placed in an inert gas flow, and the temperature is reduced from a first temperature to a second temperature at a rate of 1℃ / min to 10℃ / min.

[0031] A third aspect of this application provides a negative electrode sheet, including a negative current collector and a negative active material layer located on at least one side of the negative current collector, wherein the negative active material layer includes negative active material particles of the first aspect, or negative active material particles are prepared according to the method of the second aspect.

[0032] The fourth aspect of this application provides a battery, including the negative electrode sheet of the third aspect. Attached Figure Description

[0033] Figure 1 This is a transmission electron microscope image of the negative electrode active material particles prepared in Example 1 of this application. Detailed Implementation

[0034] To make the purpose, technical solution, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the embodiments described in this specification are merely for explaining this application and are not intended to limit it.

[0035] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0036] In the description of this application, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more.

[0037] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0038] As described in the background section, carbon materials exhibit poor compatibility with certain organic solvents and slow reaction kinetics. Furthermore, carbon materials are sensitive to certain electrolytes; for example, when graphite comes into contact with propylene carbonate, the propylene carbonate decomposes on the graphite surface, causing graphite flaking. This not only leads to capacity loss in carbon materials but also reduces their stability, resulting in decreased battery energy density and cycle performance.

[0039] The relevant technologies involve coating carbon materials. However, these technologies typically involve coating carbon materials using solid-phase or liquid-phase methods, resulting in poor contact between the coating layer and the carbon material, and often leading to uneven coating layers, which makes it difficult to meet the performance requirements of lithium-ion battery anodes.

[0040] In view of this, the inventors, through in-depth research and extensive experiments, have provided a negative electrode active material particle and its preparation method, a negative electrode sheet, and a battery.

[0041] This application provides a negative electrode active material particle, comprising a core, a transition layer located on the surface of the core, and an amorphous carbon layer located on the surface of the transition layer. The core comprises a carbon material, and the transition layer comprises graphitized carbon. The amorphous carbon layer has a coating rate of 80% to 100% on the surface of the negative electrode active material particle. For example, the coating rate can be 80%, 85%, 90%, 95%, 100%, or within any two of the above values.

[0042] In this application, carbon materials may include carbon materials known in the art that can be used as negative electrode materials for secondary batteries. For example, carbon materials may include, but are not limited to, one or more of graphite, hard carbon, and soft carbon.

[0043] In this application, the coating percentage of the amorphous carbon layer on the surface of the negative electrode active material particles has a meaning known in the art, which can represent the percentage of the area covered by the amorphous carbon layer on the surface of the negative electrode active material particles to the total surface area of ​​the negative electrode active material particles. The coating percentage of the amorphous carbon layer on the surface of the negative electrode active material particles can be determined by equipment and methods known in the art. For example, it can be determined by transmission electron microscopy (TEM).

[0044] The negative electrode active material particles of this application include a core, a transition layer on the surface of the core, and an amorphous carbon layer on the surface of the transition layer. The core comprises carbon material, and the transition layer comprises graphitized carbon. In these negative electrode active material particles, the amorphous carbon layer covers 80%–100% of the particle surface, allowing it to be uniformly and completely coated onto the core surface through the transition layer. On one hand, the coating of the amorphous carbon layer enhances the electronic conductivity of the carbon material, resulting in better kinetic performance of the negative electrode active material. On the other hand, the coating reduces the contact between the carbon material and the electrolyte, thereby reducing side reactions and improving the stability of the negative electrode active material particles in the electrolyte. Furthermore, in the negative electrode active material particles of this application, the transition layer containing graphitized carbon has a high bonding force with both the core and the amorphous carbon layer, allowing the amorphous carbon layer to tightly coat the core surface through the transition layer. Thus, the negative electrode active material particles of this application possess high structural stability, further enhancing their stability in the electrolyte. The negative electrode active material particles of this application exhibit good kinetic properties, maintain high stability in the electrolyte, and possess low irreversible capacity, good cycle stability, and electrochemical performance. Therefore, when applied to secondary batteries, the negative electrode active material particles of this application can improve the initial reversible capacity, energy density, and cycle performance of the secondary battery.

[0045] In some embodiments, the carbon material may include graphite.

[0046] Preferably, the graphite includes one or more of the following: composite particle artificial graphite, single particle artificial graphite, spherical natural graphite, and mesophase carbon microspheres.

[0047] In some embodiments, the thickness of the amorphous carbon layer can be 3 nm to 15 nm. For example, the thickness of the amorphous carbon layer can be 3 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, or within any two of the above values.

[0048] In some embodiments, the thickness of the amorphous carbon layer can be 5 nm to 10 nm. For example, the thickness of the amorphous carbon layer can be 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or within any two of the above values.

[0049] In the embodiments of this application, the thickness of the amorphous carbon layer has a meaning known in the art and can be measured by devices and methods known in the art. For example, the thickness of the amorphous carbon layer can be measured by TEM.

[0050] When the thickness of the amorphous carbon layer is within the aforementioned suitable range, on the one hand, it allows the negative electrode active material particles to have a smaller specific surface area, thereby reducing irreversible lithium-ion loss and thus improving the initial coulombic efficiency and specific capacity of the battery; on the other hand, it allows the amorphous carbon layer to have lower ion transport resistance, thereby delaying battery capacity decay. Therefore, the amorphous carbon layer of this application, when applied to a secondary battery, can improve the initial coulombic efficiency, energy density, and cycle performance of the secondary battery.

[0051] In some embodiments, the coating rate of the amorphous carbon layer on the surface of the negative electrode active material particles can be 85% to 100%. For example, the coating rate can be 85%, 88%, 90%, 95%, 98%, 100%, or within any two of the above values.

[0052] The second aspect of this application provides a method for preparing negative electrode active material particles. This method can be used to prepare negative electrode active material particles according to any embodiment of the first aspect of this application. The method includes the following steps S10 to S30.

[0053] S10 provides core material particles, which include carbon materials.

[0054] S20, preparing an intermediate, includes placing core material particles in a carbon source gas stream at a first temperature under stirring conditions, so that the carbon source undergoes a thermal decomposition reaction on the surface of the core material particles, thereby forming a transition layer on the surface of the core material particles, and obtaining an intermediate, wherein the transition layer includes graphitized carbon.

[0055] In step S20, the core material particles are continuously stirred, which can fully expose the surface of the core material particles to the carbon source gas flow, which is conducive to the formation of a uniform and complete transition layer.

[0056] S30, preparing negative electrode active material particles, includes placing an intermediate in a carbon source gas stream at a second temperature under stirring conditions, so that the carbon source undergoes a thermal decomposition reaction on the surface of the intermediate, thereby forming an amorphous carbon layer on the surface of the transition layer, and obtaining negative electrode active material particles, wherein the coating rate of the amorphous carbon layer on the surface of the negative electrode active material particles is 80% to 100%.

[0057] In step S30, the intermediate is continuously stirred, which can fully expose the surface of the intermediate to the carbon source gas flow, which is conducive to the formation of a uniform and complete amorphous carbon layer.

[0058] In this application, a carbon source can refer to a substance capable of providing carbon atoms in a thermal decomposition reaction. Those skilled in the art can select appropriate types of carbon sources according to actual needs, and no limitation is made here. The carbon sources in steps S20 and S30 above can be the same carbon source or different carbon sources.

[0059] This application does not limit the first temperature, as long as it ensures that the carbon source, after undergoing a thermal decomposition reaction on the surface of the core material particles at the first temperature, can form a graphitized carbon transition layer on the surface of the core material particles. This application does not limit the second temperature, as long as it ensures that the carbon source, after undergoing a thermal decomposition reaction on the surface of the intermediate at the second temperature, can form an amorphous carbon layer on the surface of the transition layer. Those skilled in the art can select appropriate first and second temperatures based on factors such as the type of carbon source. Generally, for the same carbon source, the temperature required to form a graphitized carbon transition layer is higher, and the temperature required to form an amorphous carbon layer is lower. Therefore, when the carbon source is the same in steps S20 and S30, the first temperature is higher than the second temperature.

[0060] This application employs a segmented chemical vapor deposition (CVD) method. First, a graphitized carbon layer is formed at high temperature as a transition layer between the core material particles and the amorphous carbon layer. Then, the amorphous carbon layer is deposited at a moderate temperature. This transition layer not only enhances the bonding strength between the amorphous carbon layer and the core material particles but also facilitates the formation of a uniform and continuous amorphous carbon layer, improving its integrity. The negative electrode active material particles prepared according to this method exhibit good morphology and uniform coating, with the amorphous carbon layer covering 80%–100% of the particle surface. Furthermore, the coating thickness of the negative electrode active material particles prepared according to this method is controllable, and the interfaces between different parts of the particles are stable, resulting in high structural stability. The negative electrode active material particles prepared according to this method, when applied to secondary batteries, can improve the initial reversible capacity and cycle performance. Additionally, the negative electrode active material particles prepared according to this method have high consistency, simple processing operation, and are conducive to mass production and large-scale use.

[0061] In some embodiments, the first temperature can be 700°C to 1200°C, for example, it can be 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, or a range consisting of any two of the above values.

[0062] In some embodiments, the first temperature can be 900°C to 1200°C, for example, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, or a range consisting of any two of the above values.

[0063] Carbon sources can release carbon atoms during thermal decomposition. Within the aforementioned suitable temperature range, the carbon atoms accumulated on the surface of the core material particles are conducive to the gradual transformation of graphitized carbon at high temperatures. This facilitates the formation of a uniform, continuous, and highly pure graphitized carbon transition layer on the carbon material surface, thereby promoting the subsequent growth of amorphous carbon layers.

[0064] In some embodiments, the preparation of the intermediate may specifically include:

[0065] Under stirring conditions, the core material particles are placed in a carbon source gas stream at a first temperature for 0.5h to 1h.

[0066] In some embodiments, the second temperature can be 500°C to 800°C, for example, it can be 500°C, 600°C, 700°C, 800°C, or a range consisting of any two of the above values.

[0067] In some embodiments, the second temperature can be 600°C to 700°C, for example, 600°C, 620°C, 650°C, 680°C, 700°C, or a range consisting of any two of the above values.

[0068] During thermal decomposition, the carbon source releases carbon atoms. At lower temperatures, these carbon atoms can gradually accumulate and crystallize on the surface of the intermediate, forming an amorphous carbon layer. A second temperature within the aforementioned suitable range facilitates the uniform crystallization of the accumulated carbon atoms on the intermediate surface, resulting in a uniform coating of the amorphous carbon layer. This not only improves the integrity of the amorphous carbon layer but also enhances the bonding strength between the amorphous carbon layer and other parts of the negative electrode active material particles.

[0069] In some embodiments, the preparation of negative electrode active material particles may specifically include:

[0070] Under stirring conditions, the intermediate was placed in a carbon source gas stream at a second temperature for 0.5 h to 5 h.

[0071] In some embodiments, the preparation of negative electrode active material particles may specifically include:

[0072] Under stirring conditions, the intermediate was placed in a carbon source gas stream at a second temperature for 0.5 h to 3 h.

[0073] Controlling the time for the formation of the amorphous carbon layer within the aforementioned appropriate range is beneficial for regulating the thickness of the amorphous carbon layer, ensuring that the thickness of the amorphous carbon layer remains within a suitable range.

[0074] In some embodiments, the carbon source gas flow may include a carbon source gas flow and a carrier gas flow. The carrier gas flow may include an inert gas flow. This inert gas flow may consist of an inert gas. The inert gas includes gases that do not participate in any chemical reactions during the preparation of the negative electrode active material particles.

[0075] In some embodiments, the carbon source gas stream may include one or more of methane, toluene, and acetylene.

[0076] In some embodiments, the carbon source gas stream may include methane.

[0077] In some embodiments, the carrier gas flow may include at least one of nitrogen or argon.

[0078] In some embodiments, the flow rate of the carbon source gas stream can be 2 mL / min to 20 mL / min, and the flow rate of the carrier gas stream can be 0.5 L / min to 1 L / min.

[0079] In some embodiments, before preparing the negative electrode active material particles, the method may further include:

[0080] Under stirring conditions, the intermediate is placed in an inert gas flow, and the temperature is reduced from a first temperature to a second temperature at a rate of 1℃ / min to 10℃ / min.

[0081] In some embodiments, the preparation of intermediates may specifically include:

[0082] The core material particles are placed in an inert gas flow, and the temperature is raised to the first temperature at a temperature variation rate of 2℃ / min to 5℃ / min.

[0083] A carbon source gas flow is introduced, placing the core material particles in the carbon source gas flow, and the core material particles are stirred to cause the carbon source to undergo a thermal decomposition reaction on the surface of the core material particles, thereby forming a transition layer on the surface of the core material particles to obtain an intermediate, wherein the transition layer includes graphitized carbon.

[0084] In some embodiments, steps S20 and S30 can both be performed in a pyrolysis device.

[0085] The pyrolysis equipment can be any pyrolysis equipment known in the art, and those skilled in the art can select it as needed, without limitation. For example, the pyrolysis equipment may include, but is not limited to, a horizontal furnace, a rotary furnace, or a box furnace.

[0086] In some embodiments, the method may further include a post-processing step after S30.

[0087] The post-processing step may include: allowing the negative electrode active material particles to cool naturally, then washing and drying them to obtain the finished negative electrode active material particles.

[0088] For example, drying methods may include, but are not limited to, spray drying, freeze drying, vacuum drying, or rotary evaporation drying.

[0089] A third aspect of this application provides a negative electrode sheet, including a negative current collector and a negative active material layer located on at least one side of the negative current collector, wherein the negative active material layer includes negative active material particles of the first aspect, or negative active material particles are prepared according to the method of the second aspect.

[0090] The negative electrode sheet of this application can be used in secondary batteries to improve the initial reversible capacity, energy density and cycle performance of secondary batteries.

[0091] The fourth aspect of this application provides a battery, including the negative electrode sheet of the third aspect.

[0092] The battery described in this application may include, but is not limited to, secondary batteries such as lithium-ion batteries and sodium-ion batteries. The battery described in this application includes a negative electrode sheet, which can have high initial reversible capacity, high energy density, and good cycle performance.

[0093] Example

[0094] The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are commercially available or synthesized by conventional methods and can be used directly without further processing. The instruments used in the examples are also commercially available.

[0095] Example 1

[0096] Composite granular artificial graphite was placed in a rotary kiln and heated to 1000℃ under a nitrogen atmosphere at a heating rate of 5℃ / min and a nitrogen gas flow rate of 1L / min. Methane gas was then introduced at a flow rate of 5mL / min for 0.5h. During the reaction, the graphite was continuously stirred to ensure that the surface of the graphite particles was fully exposed to the methane-containing mixed atmosphere. The methane gas was then turned off, and the temperature was lowered to 600℃ under a nitrogen atmosphere at a cooling rate of 5℃ / min. Methane gas was then introduced at a flow rate of 5mL / min for 2h, followed by natural cooling. After cooling to room temperature, the material was discharged and sieved to obtain negative electrode active material particles.

[0097] Example 2

[0098] Composite granular artificial graphite was placed in a horizontal furnace and heated to 1200℃ at a rate of 2℃ / min under a nitrogen atmosphere, with a nitrogen gas flow rate of 0.8 L / min. Toluene gas was then introduced at a flow rate of 10 mL / min for 1 h. During the reaction, the graphite was continuously stirred to ensure that the surface of the graphite particles was fully exposed to the toluene-containing mixed atmosphere. The toluene gas was then turned off, and the temperature was lowered to 800℃ at a rate of 5℃ / min under a nitrogen atmosphere. Toluene gas was then introduced at a flow rate of 5 mL / min for 2 h, followed by natural cooling. After cooling to room temperature, the material was discharged and sieved to obtain negative electrode active material particles.

[0099] Example 3

[0100] Spherical natural graphite was placed in a rotary furnace and heated to 900°C at a heating rate of 2°C / min under an argon atmosphere, with an argon gas flow rate of 1 L / min. Acetylene gas was then introduced at a flow rate of 10 mL / min for 1 h. During the reaction, the graphite was continuously stirred to ensure the graphite particle surface was fully exposed to the methane-containing mixed atmosphere. The acetylene gas was then turned off, and the temperature was lowered to 600°C at a cooling rate of 2°C / min under an argon atmosphere. Acetylene gas was then introduced at a flow rate of 10 mL / min for 2 h, followed by natural cooling. After cooling to room temperature, the material was discharged and sieved to obtain negative electrode active material particles.

[0101] Example 4

[0102] Mesophase carbon microspheres were placed in a rotary kiln and heated to 1200℃ at a rate of 7℃ / min under a nitrogen atmosphere, with a nitrogen gas flow rate of 0.9 L / min. Methane gas was then introduced at a flow rate of 2 mL / min for 3 h. During the reaction, the graphite was continuously stirred to ensure that the surface of the graphite particles was fully exposed to the methane-containing mixed atmosphere. The methane gas was then turned off, and the temperature was lowered to 600℃ at a rate of 5℃ / min under a nitrogen atmosphere. Methane gas was then introduced at a flow rate of 5 mL / min for 5 h, followed by natural cooling. After cooling to room temperature, the material was discharged and sieved to obtain negative electrode active material particles.

[0103] Example 5

[0104] Spherical natural graphite was placed in a rotary furnace and heated to 800°C at a rate of 3°C / min under an argon atmosphere, with an argon gas flow rate of 0.8 L / min. Toluene gas was then introduced at a flow rate of 20 mL / min for 1 h. During the reaction, the graphite was continuously stirred to ensure that the surface of the graphite particles was fully exposed to the toluene-containing mixed atmosphere. The toluene gas was then turned off, and the temperature was lowered to 500°C at a rate of 10°C / min under an argon atmosphere. Toluene gas was then introduced at a flow rate of 2 mL / min for 5 h, followed by natural cooling. After cooling to room temperature, the material was discharged and sieved to obtain negative electrode active material particles.

[0105] Comparative Example 1

[0106] Untreated spherical natural graphite particles were used as the negative electrode active material.

[0107] Comparative Example 2

[0108] Spherical natural graphite was placed in a horizontal furnace and heated to 500°C at a rate of 3°C / min under an argon atmosphere, with an argon gas flow rate of 1 L / min. Toluene gas was then introduced at a flow rate of 20 mL / min for 1 h. During the reaction, the graphite was continuously stirred to ensure that the surface of the graphite particles was fully exposed to the vapor. The mixture was then allowed to cool naturally. After cooling to room temperature, the material was discharged and sieved to obtain negative electrode active material particles.

[0109] Comparative Example 3

[0110] Spherical natural graphite was placed in a tube furnace and heated to 1000℃ at a heating rate of 5℃ / min under an argon atmosphere, with an argon gas flow rate of 1L / min. Toluene gas was then introduced at a flow rate of 5mL / min for 0.5h. The toluene gas was then turned off, and the temperature was lowered to 600℃ at a cooling rate of 5℃ / min under an argon atmosphere. Toluene gas was then introduced at a flow rate of 5mL / min for 2h, followed by natural cooling. After cooling to room temperature, the material was discharged and sieved to obtain negative electrode active material particles.

[0111] Comparative Example 4

[0112] Composite granular artificial graphite was placed in a rotary kiln and heated to 1000℃ at a rate of 5℃ / min under a methane atmosphere, with a gas flow rate of 5 mL / min for 0.5 h. Argon was used as the carrier gas at a flow rate of 1 L / min. During the reaction, the graphite was continuously stirred to ensure the surface of the graphite particles was fully exposed to the vapor. The temperature was then lowered to 500℃ at a rate of 5℃ / min for 2 h, followed by natural cooling. After cooling to room temperature, the material was discharged and sieved to obtain negative electrode active material particles.

[0113] Test section

[0114] (1) The negative electrode active material particles prepared in Examples 1-5 and Comparative Example 3 were characterized by TEM. The thickness d1 of the amorphous carbon layer and the coating rate of the amorphous carbon layer in the negative electrode active material particles were measured, and the results are shown in Table 1. Among them, the TEM image of the negative electrode active material particles of Example 1 is shown in Table 1. Figure 1 As shown. By Figure 1 As can be seen, in the negative electrode active material particles prepared according to the method of this application, the core surface is coated with a transition layer, and the surface of the transition layer is coated with a uniform and continuous amorphous carbon layer.

[0115] (2) The negative electrode active material particles from the above examples and comparative examples were mixed with carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) at a mass ratio of 9:0.5:0.5 to form a slurry, which was then coated onto copper foil using a doctor blade method. The prepared electrode sheets were vacuum dried at 90°C for 12 hours, and after drying, they were rolled and die-cut. They were assembled into button half-cells using conventional methods. Under room temperature (25°C) conditions, the button half-cells were subjected to constant current charge-discharge at 0.1C, with a voltage range of 0.001V to 1.5V. The initial discharge capacity and initial coulombic efficiency were tested and recorded. The test results of each example and comparative example are shown in Table 1.

[0116] Table 1

[0117] Serial Number <![CDATA[d1(nm)]]> Coverage rate (%) Initial discharge capacity (mAh / g) First-time coulomb efficiency (%) Example 1 3～5 85～93 353.8 95.8 Example 2 4～7 88～96 362.2 96.3 Example 3 3～5 95～99 366.8 98.7 Example 4 5～9 94～98 365.4 96.3 Example 5 4～6 92～96 363.6 97.4 Comparative Example 1 / / 333.7 89.2 Comparative Example 2 / / 356.2 88.1 Comparative Example 3 3～5 60～80 345.3 91.2 Comparative Example 4 / / 351.6 90.4

[0118] As can be seen from Table 1, the negative electrode active material particles prepared according to the method of this application have good morphology, uniform coating and controllable coating thickness. When applied to batteries, they can improve the first discharge capacity and first coulombic efficiency of the battery.

[0119] In contrast to Example 5, Comparative Example 1 did not coat the spherical natural graphite, and Comparative Example 2 only coated the surface of the spherical natural graphite with an amorphous carbon layer. Consequently, when the negative electrode active material particles of Comparative Examples 1 and 2 were applied to batteries, their initial discharge capacity and initial coulombic efficiency were significantly lower than those of Example 5. In Comparative Example 3, the graphite was not stirred during the preparation of the negative electrode active material. As a result, the graphite could not fully contact the carbon source, leading to the inability to form a relatively uniform and complete coating layer on the graphite surface. Therefore, when the negative electrode active material particles of Comparative Example 3 were applied to batteries, their initial discharge capacity and initial coulombic efficiency were significantly lower than those of Examples 1-5. In Comparative Example 4, during the preparation of the negative electrode active material, the composite particle artificial graphite was heated in a methane atmosphere to undergo a thermal decomposition reaction. In this thermal decomposition reaction, as the temperature increased, the carbon source first formed an amorphous carbon layer on the graphite surface, and then formed a graphitized carbon layer. Therefore, the amorphous carbon layer cannot uniformly and completely coat the graphite surface through the transition effect of the graphitized carbon layer, and the bonding force between the amorphous carbon layer and graphite is also low. As a result, when the negative electrode active material particles of Comparative Example 4 are applied to a battery, their initial discharge capacity and initial coulombic efficiency are much lower than those of Examples 1-5.

[0120] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A negative electrode active material particle, comprising: The core comprises carbon material; A transition layer comprising graphitized carbon, the transition layer being located on the surface of the core; An amorphous carbon layer is located on the surface of the transition layer; The amorphous carbon layer has a coating rate of 80% to 100% on the surface of the negative electrode active material particles.

2. The negative electrode active material particles according to claim 1, wherein, The carbon material includes graphite; Preferably, the graphite includes one or more of the following: composite particle artificial graphite, single particle artificial graphite, spherical natural graphite, and mesophase carbon microspheres.

3. The negative electrode active material particles according to claim 1, wherein, The thickness of the amorphous carbon layer is 3nm to 15nm, preferably 5nm to 10nm.

4. The negative electrode active material particles according to any one of claims 1-3, wherein, The amorphous carbon layer has a coating rate of 85% to 100% on the surface of the negative electrode active material particles.

5. A method for preparing negative electrode active material particles, comprising: Provide core material particles, said core material particles comprising carbon materials; The preparation of the intermediate includes placing the core material particles in a carbon source gas stream at a first temperature under stirring conditions, so that the carbon source undergoes a thermal decomposition reaction on the surface of the core material particles, thereby forming a transition layer on the surface of the core material particles, and obtaining the intermediate, wherein the transition layer comprises graphitized carbon; The preparation of negative electrode active material particles includes placing the intermediate in a carbon source gas stream at a second temperature under stirring conditions, so that the carbon source undergoes a thermal decomposition reaction on the surface of the intermediate, thereby forming an amorphous carbon layer on the surface of the transition layer, and obtaining negative electrode active material particles, wherein the amorphous carbon layer has a coating rate of 80% to 100% on the surface of the negative electrode active material particles.

6. The method according to claim 5, wherein, The first temperature is 700℃~1200℃, preferably 900℃~1200℃.

7. The method according to claim 5, wherein, The preparation intermediate includes: Under stirring conditions, the core material particles are placed in a carbon-containing gas stream at a first temperature for 0.5h to 1h.

8. The method according to claim 5, wherein, The second temperature is 500℃~800℃, preferably 600℃~700℃.

9. The method according to claim 5, wherein, The preparation of the negative electrode active material particles includes: Under stirring conditions, the intermediate is placed in a carbon source gas stream at a second temperature for 0.5h to 5h, preferably 0.5h to 3h.

10. The method according to any one of claims 5-9, wherein, The carbon source gas flow includes a carbon source gas flow and a carrier gas flow; The carbon source gas stream includes one or more of methane, toluene, and acetylene, preferably methane; and / or The carrier gas flow includes at least one of nitrogen or argon; Preferably, the flow rate of the carbon source gas stream is 2 mL / min to 20 mL / min, and the flow rate of the carrier gas stream is 0.5 L / min to 1 L / min.

11. The method according to claim 5, wherein, Before preparing the negative electrode active material particles, the method further includes: The intermediate is placed in an inert gas flow, and the temperature is reduced from the first temperature to the second temperature at a rate of 1℃ / min to 10℃ / min.

12. A negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector, wherein, The negative electrode active material layer comprises negative electrode active material particles as described in any one of claims 1-4, or negative electrode active material particles prepared by any one of claims 5-11.

13. A battery comprising the negative electrode as described in claim 12.

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