Preparation method and application of negative electrode material

Abstract

The invention relates to a preparation method and application of a negative electrode material, and the preparation method comprises the following steps: (1) under a protective atmosphere, carrying out a heating reaction on silicon carbide nanoparticles and an amino-containing silane coupling agent in the presence of a solvent to obtain aminated silicon carbide nanoparticles; the preparation method comprises the following steps: heating and melting asphalt, adding an anhydride monomer and an initiator, and carrying out a first stirring reaction to obtain an anhydridized asphalt melt; (2) adding the aminated silicon carbide nanoparticles into the anhydridized asphalt melt, carrying out a second stirring reaction, cooling after the reaction, and crushing to obtain aminated nano silicon carbide modified asphalt powder; and (3) uniformly mixing graphite with the aminated nano silicon carbide modified asphalt powder, and carrying out carbonization treatment to obtain the negative electrode material. The silicon carbide nanoparticles are uniformly doped in the carbon coating layer of the negative electrode material prepared by the method, so that the full charge expansion of a negative electrode plate can be effectively reduced, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a method for preparing and applying a negative electrode material. Background Technology

[0002] Lithium-ion batteries, due to their high energy density and long cycle life, have been widely used in consumer electronics, electric vehicles, and large-scale energy storage. Graphite, with its abundant sources, stable electrochemical performance, and low cost, is currently the most important anode material for commercially available lithium-ion batteries. As the requirements for anode energy density gradually increase, the requirements for graphite specific capacity are also becoming higher. While artificial graphite, such as needle coke or calcined petroleum coke, has a relatively high specific capacity, even reaching over 360 mA∙h / g, it also results in significant anode expansion, typically exceeding 25%. This increased expansion worsens the material's cycle life.

[0003] Currently, carbon coating is the most common and effective method for improving the fast charging and expansion of artificial graphite, and it has been widely used. This typically involves blending artificial graphite with pitch and then carbonizing it to form an amorphous carbon layer on the graphite surface. This coating layer can prevent the co-intercalation of organic solvents, reduce the specific surface area, and compensate for defects, thus improving the fast charging capability of artificial graphite. Furthermore, the carbon coating layer can also provide some buffering for expansion. However, during high-rate charging or long-term cycling, repeated volume changes can have a cumulative effect. This single carbon coating layer cannot provide sufficient and durable rigid support, and its buffering capacity will gradually saturate or even fail.

[0004] Therefore, there is an urgent need for a negative electrode material that can solve the problem of electrode expansion in high-capacity-density batteries under high-rate and long-cycle conditions, so as to improve the cycle life of the batteries. Summary of the Invention

[0005] To address the problem of insufficient structural rigidity in traditional carbon-coated graphite anode materials, which fails to effectively suppress irreversible expansion under high-rate, long-term cycling and thus leads to a decrease in the cycle life of lithium-ion batteries, this invention provides a method for preparing and applying an anode material. By introducing silicon carbide nanoparticles into the carbon coating layer, and by amylating and modifying the silicon carbide nanoparticles with anhydride, the silicon carbide nanoparticles can be uniformly dispersed in the carbon coating layer. This significantly improves the compressive strength of the prepared anode material, effectively suppresses the full-charge expansion problem, and significantly improves the capacity retention and cycle stability of lithium-ion batteries under high-rate conditions.

[0006] Specifically, the following technical solutions are provided: The first aspect of this invention provides a method for preparing a negative electrode material, comprising the following steps: (1) Under a protective atmosphere, silicon carbide nanoparticles and an amino-containing silane coupling agent are heated in the presence of a solvent to obtain amino-modified silicon carbide nanoparticles. After heating and melting the asphalt, acid anhydride monomers and initiators are added for the first stirring reaction to obtain anhydride-treated asphalt melt. (2) The aminated silicon carbide nanoparticles are added to the anhydride asphalt melt for a second stirring reaction. After the reaction, the mixture is cooled and pulverized to obtain aminated silicon carbide nanoparticle modified asphalt powder. (3) The graphite and the aminated nano-silicon carbide modified pitch powder are mixed evenly and then carbonized to obtain the negative electrode material.

[0007] Further, in step (1), the nano-carbide particles are obtained by mixing and ball milling silicon powder and graphite powder under a protective atmosphere; the molar ratio of silicon powder and graphite powder is preferably 1:(1-2), the ball milling medium is steel balls with a diameter of 5-15 mm, the ball-to-material ratio is preferably (15-30):1, the ball milling speed is 600-1000 r / min, and the ball milling time is 20-200 h.

[0008] Further, in step (1), the particle size D50 of the silicon carbide nanoparticles is preferably 2-10 nm; the amino-containing silane coupling agent includes one or more of aminosilanes KH550, KH792, and KH602; the acid anhydride monomer includes one or more of maleic anhydride, phthalic anhydride, and maleic anhydride; the initiator includes one or more of azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), and dicumyl peroxide (DCP).

[0009] Further, in step (1), the asphalt is selected from one or more of low temperature (softening point of 100-130 ℃), medium temperature asphalt (softening point of 130-180 ℃), and high temperature asphalt (softening point of 180-250 ℃) powders.

[0010] Further, in step (1), the mass ratio of the silicon carbide nanoparticles to the amino-containing silane coupling agent is preferably (10-30):(0.1-1), more preferably 1:(0.03-0.1); the mass ratio of the asphalt to the acid anhydride monomer is preferably (1-2):(0.05-0.1), more preferably 1:(0.04-0.08).

[0011] Furthermore, in step (1), the temperature of the heating reaction is preferably 80-90 °C.

[0012] Further, in step (1), the temperature of the first stirring reaction is greater than the softening temperature of the asphalt, and the time is 0.5-3 h; preferably, the temperature of the first stirring reaction is 100-300 ℃.

[0013] Further, in step (2), the preferred mass ratio of the aminated silicon carbide nanoparticles to the anhydride-modified asphalt melt is (0.01-0.02):1.

[0014] Further, in step (2), the temperature of the second stirring reaction is greater than the softening temperature of the asphalt, and the time is 1-2 h; preferably, the temperature of the first stirring reaction is 100-300 ℃.

[0015] Furthermore, in step (3), the preferred particle size D50 of the graphite is 8-20 μm.

[0016] Further, in step (3), the mass ratio of the graphite to the aminated nano-silicon carbide modified pitch powder is preferably 1:(0.01-0.06), more preferably 1:(0.025-0.04).

[0017] Further, in step (3), the carbonization process involves first heating to 200-400 ℃ and holding for 2-4 h, then heating to 600-1000 ℃ and holding for 1-3 h.

[0018] The second aspect of the present invention provides a negative electrode material prepared by the preparation method described in the first aspect; the negative electrode material has a core-shell structure and is composed of graphite particles and a soft carbon coating layer covering the graphite particles, wherein the soft carbon coating layer is doped with silicon carbide nanoparticles.

[0019] Furthermore, the particle size D50 of the graphite particles is preferably 8-20 μm, the thickness of the soft carbon coating layer is preferably 5-20 nm, and the particle size D50 of the silicon carbide nanoparticles is preferably 2-10 nm.

[0020] A third aspect of the present invention provides a negative electrode sheet comprising the negative electrode material described in the second aspect.

[0021] A fourth aspect of the present invention provides a secondary battery comprising the negative electrode sheet described in the third aspect.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a method for preparing a negative electrode material. By introducing silicon carbide nanoparticles into a carbon coating layer, and by amylating and modifying the silicon carbide nanoparticles with anhydride, the silicon carbide nanoparticles can be uniformly dispersed in the carbon coating layer, thus preparing a soft carbon-coated graphite negative electrode material doped with silicon carbide nanoparticles. Specifically, by amylating the silicon carbide nanoparticles, the hydrophilicity of the silicon carbide is reduced, improving the compatibility between the silicon carbide nanoparticles and the hydrophobic asphalt. Furthermore, by modifying the asphalt with anhydride, the amino groups on the surface of the silicon carbide nanoparticles can undergo a cross-linking reaction with the maleic anhydride grafted onto the asphalt, effectively preventing the aggregation and sedimentation of the silicon carbide nanoparticles. This effectively improves the dispersion of the silicon carbide nanoparticles in the asphalt, allowing them to be uniformly dispersed in the prepared negative electrode material coating layer. This effectively enhances the compressive strength of the negative electrode material and reduces its expansion during charging. It also suppresses the particle pulverization problem caused by the expansion of silicon nanoparticles during long-term battery cycling, significantly improving the cycle life of the material.

[0023] The negative electrode material prepared by the above preparation method has high specific capacity, and the lithium-ion battery prepared from it has small expansion when fully charged, and has high capacity retention and excellent cycle stability at 2C rate. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The terms “comprising” or “including” used in this invention may also be replaced with the closed form “is” or “consisting of”.

[0026] As described in the background section, artificial graphite has high capacity, but suffers from significant anode expansion. While carbon coating can mitigate this expansion to some extent, a single carbon coating layer cannot provide sufficient and durable rigid support, and its buffering capacity gradually saturates or even fails. Therefore, it is urgent to address the problem that traditional carbon-coated graphite anode materials, due to insufficient structural rigidity, cannot effectively suppress irreversible expansion under high-rate, long-term cycling, thus leading to a decrease in the cycle life of lithium-ion batteries.

[0027] To address the above problems, this invention provides a method for preparing a negative electrode material, comprising the following steps: (1) Under a protective atmosphere, silicon carbide nanoparticles and an amino-containing silane coupling agent are heated in the presence of a solvent to obtain amino-modified silicon carbide nanoparticles. After heating and melting the asphalt, acid anhydride monomers and initiators are added for the first stirring reaction to obtain anhydride-treated asphalt melt. (2) The aminated silicon carbide nanoparticles are added to the anhydride asphalt melt for a second stirring reaction. After the reaction, the mixture is cooled and pulverized to obtain aminated silicon carbide nanoparticle modified asphalt powder. (3) The graphite and the aminated nano-silicon carbide modified pitch powder are mixed evenly and then carbonized to obtain the negative electrode material.

[0028] Due to insufficient structural rigidity of existing carbon-coated graphite materials, they cannot effectively suppress the irreversible expansion of the negative electrode caused by lithium-ion insertion / extraction under high-rate, long-term cycling, leading to a decrease in the cycle life of lithium-ion batteries. To address this issue, in the early stages of research, the inventors planned to introduce silicon carbide nanoparticles into the carbon coating layer to improve its compressive strength. However, during actual research, it was found that silicon carbide nanoparticles easily agglomerate in the asphalt used to prepare the carbon coating layer. The resulting carbon-coated graphite material failed to effectively improve the full-charge expansion problem and cycle performance, and instead reduced the rate performance of the lithium-ion battery. To address the dispersion problem of nano-silicon carbide in asphalt, the inventors performed an amination treatment on the nano-silicon carbide to improve its compatibility with hydrophobic asphalt. Simultaneously, they further modified the asphalt with anhydride, allowing the silicon carbide nanoparticles to undergo cross-linking reactions with the maleic anhydride grafted onto the asphalt via surface amino groups (e.g., amidation reaction between the carbonyl and amino groups in the anhydride to form amide bonds). This effectively prevents the aggregation and sedimentation of the silicon carbide nanoparticles, thereby significantly improving their dispersion in the asphalt and ensuring uniform dispersion of the nano-silicon carbide in the prepared negative electrode material coating layer. The negative electrode material prepared through the above modification and cross-linking process exhibits high compressive strength, which helps reduce expansion during charging and suppresses particle pulverization caused by silicon nanoparticle expansion during long-term battery cycling, greatly improving the material's cycle life.

[0029] In step (1) of this invention, the nano-carbide particles are obtained by ball milling silicon powder and graphite powder under a protective atmosphere, namely nitrogen, to prevent the silicon powder from oxidizing and forming silicon dioxide. The preferred molar ratio of silicon powder to graphite powder is 1:(1-2), for example, 1:1, 1:1.5, 1:2, etc. The ball milling media are steel balls with a diameter of 5-15 mm, and the preferred ball-to-material ratio is (15-30):1, for example, 15:1, 20:1, 25:1, 30:1, etc. The ball milling speed is 600-1000 r / min, and the ball milling time is 20-200 h, for example, 20 h, 50 h, 100 h, 150 h, 200 h, etc., to obtain silicon carbide nanoparticles of different particle sizes.

[0030] In step (1) of this invention, the particle size D50 of the silicon carbide nanoparticles is preferably 2-10 nm, such as 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, etc., including but not limited to the particle size values ​​listed above. Nanoscale silicon carbide particles exhibit better kinetic performance. If the size is too large, the kinetic performance of the anode material will rapidly deteriorate. Furthermore, the thickness of the carbon coating layer is generally within 100 nm; excessively large silicon carbide particles cannot effectively coat the material.

[0031] In step (1) of this invention, silicon carbide nanoparticles are first mixed with an amino-containing silane coupling agent and a solvent and then ultrasonically dispersed before being heated to react.

[0032] In step (1) of this invention, the amino-containing silane coupling agent includes, but is not limited to, one or more of aminosilanes KH550, KH792, and KH602; the acid anhydride monomers include, but are not limited to, one or more of maleic anhydride, phthalic anhydride, and maleic anhydride; and the initiator includes, but is not limited to, one or more of azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), and dicumyl peroxide (DCP).

[0033] In step (1) of the present invention, the asphalt can be selected from one or more of the following: low temperature (softening point is 100-130 ℃), medium temperature asphalt (softening point is 130-180 ℃), and high temperature asphalt (softening point is 180-250 ℃) powders.

[0034] In step (1) of this invention, the preferred mass ratio of silicon carbide nanoparticles to amino-containing silane coupling agent is (10-30):(0.1-1), more preferably 1:(0.03-0.1), for example 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:1, etc., including but not limited to the mass ratios listed above. Excessive or insufficient addition of the amino-containing silane coupling agent will affect the subsequent dispersibility of silicon carbide nanoparticles in asphalt. Excessive addition will lead to excessively high viscosity of the reaction solution, uneven coupling, and affect the uniformity of subsequent dispersion in asphalt. Insufficient addition will result in insufficient amino groups on the surface of the silicon carbide nanoparticles, making uniform dispersion in asphalt impossible.

[0035] In step (1) of this invention, the preferred mass ratio of asphalt to anhydride monomers is (1-2):(0.05-0.1), more preferably 1:(0.04-0.08), such as 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1, etc., including but not limited to the mass ratios listed above. If the content of anhydride monomers used to modify asphalt is too low, the number of anhydride grafts will be insufficient, and the dispersion of silicon carbide nanoparticles will be poor. If the content of anhydride monomers is too low, the asphalt itself will undergo a self-crosslinking reaction after grafting, leading to asphalt solidification. Preferably, controlling the mass ratio of asphalt to anhydride monomers within the range of 1:(0.04-0.08) can effectively improve the dispersibility of silicon carbide nanoparticles.

[0036] In step (1) of the present invention, the preferred temperature for the heating reaction is 80-90 °C.

[0037] In step (1) of the present invention, the temperature of the first stirring reaction is greater than the softening temperature of the asphalt, and the time is 0.5-3 h; preferably, the temperature of the first stirring reaction is 100-300 ℃.

[0038] In step (2) of this invention, the preferred mass ratio of aminated silicon carbide nanoparticles to anhydride-modified pitch melt is (0.01-0.02):1, such as 0.01:1, 0.015:1, 0.02:1, etc., including but not limited to the mass ratios listed above. Insufficient addition of aminated silicon carbide nanoparticles cannot effectively suppress expansion, while excessive addition increases the risk of agglomeration, thus worsening the expansion suppression effect. Furthermore, since silicon carbide has poorer kinetic properties than graphite, the addition of excessive silicon carbide nanoparticles will degrade the overall kinetic properties of the material. Preferably, controlling the mass ratio of aminated silicon carbide nanoparticles to anhydride-modified pitch melt within the range of (0.01-0.02):1 can effectively suppress the expansion of the negative electrode material and optimize its cycle performance.

[0039] In step (2) of the present invention, the temperature of the second stirring reaction is greater than the softening temperature of the asphalt, and the time is 1-2 hours; preferably, the temperature of the first stirring reaction is 100-300 ℃.

[0040] In step (3) of the present invention, the preferred particle size D50 of graphite is 8-20 μm, such as 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, etc., including but not limited to the particle size values ​​listed above.

[0041] In step (3) of this invention, the preferred mass ratio of graphite to aminated nano-silicon carbide modified pitch powder is 1:(0.01-0.06), more preferably 1:(0.025-0.04), such as 1:0.025, 1:0.03, 1:0.035, 1:0.04, etc., including but not limited to the mass ratios listed above. If too much aminated nano-silicon carbide modified pitch powder is added, the resulting coating layer of the negative electrode material will be too thick, leading to high-temperature capacity deterioration. If the amount added is too low, the coating layer will be too thin, failing to effectively suppress expansion and improve fast charging.

[0042] In step (3) of this invention, the carbonization process involves first heating to 200-400 ℃ and holding for 2-4 h, then heating to 600-1000 ℃ and holding for 1-3 h.

[0043] The present invention also provides an anode material prepared by the above-described preparation method. This anode material has a core-shell structure, consisting of graphite particles and a soft carbon coating layer covering the graphite particles, wherein silicon carbide nanoparticles are doped into the soft carbon coating layer.

[0044] In this invention, the particle size D50 of the ink particles is preferably 8-20 μm, such as 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, etc., including but not limited to the particle size values ​​listed above; the thickness of the soft carbon coating layer is preferably 5-20 nm, such as 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm, 20 nm, etc., including but not limited to the layer thicknesses listed above; the particle size D50 of the silicon carbide nanoparticles is preferably 2-10 nm, such as 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, etc., including but not limited to the particle size values ​​listed above.

[0045] The present invention also provides a negative electrode sheet comprising the above-mentioned negative electrode material.

[0046] The present invention also provides a lithium-ion secondary battery comprising the aforementioned negative electrode sheet.

[0047] In the following examples and comparative examples, a Malvern laser particle size analyzer was used to test silicon carbide nanoparticles. Example 1

[0048] This embodiment relates to the preparation of a negative electrode material, as detailed below: (1) Preparation of silicon carbide nanoparticles: Silicon powder and graphite powder were mixed in a molar ratio of 1:1 and put into a ball mill jar together with steel balls with a diameter of 15 mm. The mass ratio of ball to material was 15:1. Nitrogen gas was introduced into the ball mill jar as a protective gas to prevent silicon powder from oxidizing and forming silicon dioxide. The ball mill jar was rotated at 800 r / min and milled for 80 h to obtain silicon carbide nanoparticles with a particle size D50 of 6 nm.

[0049] (2) Preparation of aminated silicon carbide nanoparticles: 10 g of nano silicon carbide, 500 mL of toluene and 0.4 g of silane coupling agent KH-550 were mixed and ultrasonically dispersed for 60 min. The mixture was heated to 90 °C under nitrogen atmosphere, refluxed and condensed, stirred for 5 h, filtered and washed, and vacuum dried at 100 °C for 12 h to obtain aminated silicon carbide nanoparticles.

[0050] (3) Preparation of anhydride-modified asphalt: 1 kg of asphalt powder was heated and melted at 200 °C, and 60 g of maleic anhydride and 0.5 g of initiator were added. The same temperature was maintained and the mixture was stirred at 1000 rpm for 0.5 h to obtain anhydride-modified asphalt melt.

[0051] (4) Preparation of aminated nano-silicon carbide modified asphalt powder: Weigh 15 g of aminated silicon carbide nanoparticles prepared by the method in step (2) and slowly add them to the asphalt melt in step (3). Stir at 200 ℃ and 1000 rpm for 2 h. After cooling, pulverize to obtain aminated nano-silicon carbide modified asphalt powder.

[0052] (5) Preparation of negative electrode material: Weigh 0.67 kg of graphite powder, add 0.02 kg of aminated nano-silicon carbide modified pitch powder prepared in step (4), mix with a mixer, heat the mixed material to 300 ℃ at 2 ℃ / min in a carbonization furnace, keep the temperature for 4 h, then heat to 1000 ℃ at 5 ℃ / min, keep the temperature for 2 h, and then cool to obtain negative electrode material. Example 2

[0053] This embodiment relates to the preparation of a negative electrode material. The only difference from Example 1 is that 10g of aminated silicon carbide nanoparticles are added in step (4), and the rest of the operations are the same, and the corresponding negative electrode material is prepared. Example 3

[0054] This embodiment relates to the preparation of a negative electrode material. The only difference from Example 1 is that 20g of aminated silicon carbide nanoparticles are added in step (4), and the rest of the operations are the same, and the corresponding negative electrode material is prepared. Example 4

[0055] This embodiment relates to the preparation of a negative electrode material. The only difference from Example 1 is that 30g of aminated silicon carbide nanoparticles are added in step (4). All other operations are the same, and the corresponding negative electrode material is prepared. Example 5

[0056] This embodiment relates to the preparation of a negative electrode material. The only difference from Example 1 is that 0.3g of silane coupling agent KH-550 is added in step (1), and the rest of the operations are the same, and the corresponding negative electrode material is prepared. Example 6

[0057] This embodiment relates to the preparation of a negative electrode material. The only difference from Example 1 is that 1 g of silane coupling agent KH-550 is added in step (1), and the rest of the operations are the same, and the corresponding negative electrode material is prepared. Example 7

[0058] This embodiment relates to the preparation of a negative electrode material. The only difference from Example 1 is that 40g of maleic anhydride is added in step (3), and the rest of the operations are the same, and the corresponding negative electrode material is prepared. Example 8

[0059] This embodiment relates to the preparation of a negative electrode material. The only difference from Example 1 is that 80g of maleic anhydride is added in step (3), and the rest of the operations are the same, and the corresponding negative electrode material is prepared. Example 9

[0060] This embodiment relates to the preparation of a negative electrode material. The only difference from Example 1 is that 1.5g of silane coupling agent KH-550 is added in step (1), and 90g of maleic anhydride is added in step (3). All other operations are the same, and the corresponding negative electrode material is prepared. Example 10

[0061] This embodiment relates to the preparation of a negative electrode material. The only difference from Example 1 is that 16.75 g of aminated nano-silicon carbide modified pitch powder is added in step (5). All other operations are the same, and the corresponding negative electrode material is prepared. Example 11

[0062] This embodiment relates to the preparation of a negative electrode material. The only difference from Example 1 is that 26.8 g of aminated nano-silicon carbide modified pitch powder is added in step (5). All other operations are the same, and the corresponding negative electrode material is prepared. Example 12

[0063] This embodiment relates to the preparation of a negative electrode material. The only difference from Example 1 is that 33.5 g of aminated nano-silicon carbide modified pitch powder is added in step (5). All other operations are the same, and the corresponding negative electrode material is prepared. Comparative Example 1

[0064] This comparative example relates to the preparation of a negative electrode material, which differs from Example 1 only in that: aminated silicon carbide nanoparticles were not added, as detailed below: Weigh 0.67 kg of graphite powder and add 0.02 kg of asphalt powder. Mix the mixture using a mixer. Heat the mixture in a carbonization furnace to 300 °C at 2 °C / min and hold for 4 h. Then heat it to 1000 °C at 5 °C / min and hold for 2 h. After cooling, the negative electrode material is obtained. Comparative Example 2

[0065] This comparative example relates to the preparation of a negative electrode material. The only difference from Example 1 is that the silicon carbide nanoparticles were not aminated, and the asphalt was not anhydride-treated. Instead, the silicon carbide nanoparticles were directly added to the asphalt melt to prepare a nano-silicon carbide-asphalt composite powder, which was then mixed with graphite powder and carbonized to prepare the negative electrode material, as detailed below: 15 g of silicon carbide nanoparticles were weighed and slowly added to the asphalt melt. The mixture was stirred at 1000 rpm for 2 h, cooled, and then pulverized to obtain nano-silicon carbide-asphalt composite powder.

[0066] Weigh 0.67 kg of graphite powder and add 0.02 kg of nano-silicon carbide-asphalt composite powder. Mix the powder using a mixer. Heat the mixed material in a carbonization furnace to 300 °C at 2 °C / min and hold for 4 h. Then heat it to 1000 °C at 5 °C / min and hold for 2 h. After cooling, the negative electrode material is obtained.

[0067] The mass relationships between the different raw materials used in the preparation of the anode materials in the above embodiments and comparative examples are shown in the table below:

[0068] In the table, A1 represents the amount of aminated nano-silicon carbide (Examples 1-12 and Comparative Example 1) or silicon carbide nanoparticles (Comparative Example 2) added, and A2 represents the amount of asphalt added. B1 represents the amount of aminated nano-silicon carbide modified pitch powder (Examples 1-12), pitch powder (Comparative Example 1), or nano-silicon carbide-pitch composite powder (Comparative Example 2) added to the negative electrode materials prepared in the above embodiments and comparative examples, and B2 represents the amount of graphite powder added to the negative electrode materials. Application and performance testing

[0069] The specific capacity of coin cells was tested using the negative electrode materials prepared in the above embodiments and comparative examples as negative electrode active materials. Additionally, lithium-ion batteries were prepared and their full-charge expansion, rate performance, and cycle performance were tested, as detailed below: Preparation of button cell: The negative electrode material, conductive agent SP, dispersant CMC, and binder (PAA) were mixed and stirred evenly in a mass ratio of 95.5:1:1.5:2, and then coated on one side of a copper foil with a coating density of 190 g / m². 2 After drying and roller compaction, the density is 1.65 g / cm³. 3 A standard negative electrode sheet is obtained; it is then assembled with a lithium sheet to form a coin cell.

[0070] Specific capacity test: At room temperature, discharge to 1 mV with a constant current of 0.5 C; let stand for 10 min; charge to 1.5 V with a constant current of 0.1 C, and record the capacity at this time. Specific capacity = capacity / mass of negative electrode active material.

[0071] Preparation of lithium-ion batteries: Anode material, carbon black conductive agent, sodium carboxymethyl cellulose and binder are mixed in a mass ratio of 96.6:1:0.9:1.5, deionized water is added and stirred, and the viscosity is adjusted to obtain anode slurry. This slurry is coated on at least one side of the negative electrode copper foil current collector, dried and pressed to obtain a 120 μm thick anode sheet. Lithium iron phosphate cathode material (LiFePO4), dispersant (CMC) and PVDF binder are mixed in a mass ratio of 98.2:0.1:1.7, NMP solvent is added, stirred and the viscosity is adjusted to obtain cathode slurry. This slurry is coated on at least one side of the positive electrode aluminum foil current collector, dried and pressed to obtain cathode sheet. Anode sheet, separator and cathode sheet are wound to obtain battery cell. Battery cell is assembled into battery case, dried, electrolyte injected, packaged, formed and capacity tested to obtain lithium-ion battery.

[0072] Full charge expansion test: Using the Blue Battery testing system, the battery was left to stand at 25±2 ℃ for 5 minutes, discharged at 1 C to 2.5 V, left to stand for 15 minutes, charged at 1 C constant current to 3.65 V, charged at constant voltage to ≤0.05 C, and left to stand for 5 minutes. The negative electrode sheet was then disassembled to test its full charge expansion percentage. Full charge expansion percentage = (thickness of the negative electrode sheet after full charge / thickness of the electrode sheet after coating and rolling) × 100%.

[0073] Rate performance test: The initial battery capacity is C0. After standing at 25℃ for 5 minutes, it is charged at 1C constant current to 3.65V, then charged at constant current and constant voltage until the current is ≤0.05C. After standing for 30 minutes, it is discharged at 2C to 2.5V. The test is completed, and the discharge capacity at this time is recorded as C1. The capacity retention rate at 2C is calculated as C1 / C0 × 100%.

[0074] Cyclic performance test: Using the Blue Battery test system, the battery was charged at 25 ℃ with a constant current of 1 C to 3.65 V, and then discharged at a constant current of 1 C to 3.65 V. The above charge and discharge operation was repeated until the capacity dropped to 80% of the initial value. The number of cycles was recorded.

[0075] The test results are shown in Table 1 below: Table 1

[0076] As shown in Table 1, compared to the negative electrode material prepared without silicon carbide nanoparticle modification (Comparative Example 1), the negative electrode materials prepared in Examples 1-12 exhibited less full-charge expansion and significantly improved cycle life in lithium-ion batteries. Furthermore, compared to the negative electrode material prepared in Example 1 using aminated silicon carbide nanoparticles, anhydride-modified asphalt, and cross-linked asphalt powder as the coating material, the negative electrode material prepared in Comparative Example 2 using a nano-silicon carbide-asphalt composite powder directly mixed with asphalt melt as the coating material not only failed to effectively suppress expansion and improve cycle life, but also showed a significant decrease in rate performance. This is because the dispersion of silicon carbide nanoparticles in asphalt is very poor, resulting in uneven dispersion during the coating process, leading to a significant deterioration in battery full-charge expansion, rate performance, and cycle life.

[0077] Furthermore, as shown in Examples 1-4, with the continuous increase of the nano-silicon carbide content in asphalt, the full-charge expansion gradually decreases, and the battery's room-temperature cycle life is significantly improved. In Example 4, the excessive addition of nano-silicon carbide (3%) resulted in uneven dispersion in the asphalt, thus worsening the full-charge expansion and causing a greater relative decrease in its rate performance.

[0078] As can be seen from Examples 1, 5, and 6, compared to Example 1, the content of silane coupling agent in Example 5 is reduced, resulting in a decrease in the number of amino grafts on the surface of nano-silicon carbide. This leads to poorer dispersibility in asphalt and more severe aggregation, thus resulting in poorer full-charge expansion and cycling performance. Compared to Example 1, the content of silane coupling agent in Example 6 is greatly increased, but it is excessive. Therefore, the number of amino grafts on the surface of nano-silicon carbide will not be significantly improved. Thus, the dispersibility in asphalt is not significantly changed, and it may even slightly degrade the rate and cycle performance of the battery.

[0079] As shown in Examples 1 and 7-9, compared to Example 1, the reduced maleic anhydride addition in Example 7 leads to decreased dispersion uniformity of nano-silicon carbide in asphalt, resulting in deterioration of overall cycle performance and full-charge expansion. Conversely, the increased maleic anhydride addition in Example 8 results in better dispersion uniformity and improved overall performance. In Example 9, compared to Example 1, the silane coupling dosage reached 15%, which ironically increased the overall solution viscosity, caused uneven grafting on the surface of nano-silicon carbide, and worsened dispersion in asphalt. Excessive maleic anhydride addition to asphalt causes self-crosslinking and solidification within the asphalt, increasing its viscosity. Both of these factors severely deteriorate the dispersion of nano-silicon carbide in asphalt, leading to a significant decrease in overall cycle performance and full-charge expansion.

[0080] Furthermore, as shown in Examples 1 and 10-12, compared to Example 1, the amount of nano-silicon carbide modified asphalt powder added in Example 10 was reduced, resulting in a thinner carbon coating layer and a lower content of nano-silicon carbide in the negative electrode material. This led to ineffective suppression of expansion, deteriorated cycle performance, and a decline in fast-charging performance. Conversely, the amount of nano-silicon carbide modified asphalt powder added in Example 11 was increased, resulting in a thicker coating layer and a higher nano-silicon carbide content in the negative electrode material. This better suppressed expansion, further improving the cycle life and full-charge expansion of the battery, and also enhancing rate performance. However, the increased coating thickness led to a decrease in the specific capacity of the negative electrode material. Notably, in Example 12, the amount of nano-silicon carbide modified asphalt powder added increased to 5% compared to Example 1. The excessive asphalt resulted in an excessively thick coating layer. While this significantly improved the suppression of expansion, cycle performance, and rate performance, it also resulted in a severe loss of specific capacity.

[0081] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for producing a negative electrode material, characterized by, The method comprises the following steps: (1) heating and reacting silicon carbide nanoparticles and amino-containing silane coupling agent in the presence of a solvent under a protective atmosphere to obtain amino-modified silicon carbide nanoparticles; After the asphalt is heated and melted, an acid anhydride monomer and an initiator are added for a first stirring reaction to obtain an acid anhydride asphalt melt; (2) adding the amino-modified silicon carbide nanoparticles to the acid anhydride asphalt melt for a second stirring reaction, and then cooling and crushing to obtain an amino-modified silicon carbide nanoparticle modified asphalt powder; (3) uniformly mixing graphite and the amino-modified silicon carbide nanoparticle modified asphalt powder, and then performing carbonization treatment to obtain the negative electrode material.

2. The production method according to claim 1, characterized by, In step (1), at least one of the following features is included: (1) the particle size D50 of the silicon carbide nanoparticles is 2-10 nm; (2) the amino-containing silane coupling agent includes one or more of amino silane KH550, KH792, and KH602; (3) the acid anhydride monomer includes one or more of maleic anhydride, phthalic anhydride, and fumaric anhydride; (4) the initiator includes one or more of azobisisobutyronitrile, dibenzoyl peroxide, and dicumyl peroxide.

3. The production method according to claim 1 or 2, characterized by, In step (1), the mass ratio of the silicon carbide nanoparticles to the amino-containing silane coupling agent is (10-30):(0.1-1); The mass ratio of the asphalt to the acid anhydride monomer is (1-2):(0.05-0.1).

4. The method of claim 1, wherein, In step (1), the temperature of the heating reaction is 80-90 ℃; The temperature of the first stirring reaction is greater than the softening temperature of the asphalt, and the time is 0.5-3 h; preferably, the temperature of the first stirring reaction is 100-300 ℃.

5. The preparation method according to claim 1, characterized in that, In step (2), at least one of the following features is included: (1) the mass ratio of the amino-modified silicon carbide nanoparticles to the acid anhydride asphalt melt is (0.01-0.02):1; (2) the temperature of the second stirring reaction is greater than the softening temperature of the asphalt, and the time is 1-2 h; preferably, the temperature of the first stirring reaction is 100-300 ℃.

6. The preparation method according to claim 1, characterized in that, In step (3), at least one of the following features is included: (1) the particle size D50 of the graphite is 8-20 μm; (2) the mass ratio of the graphite to the amino-modified silicon carbide nanoparticle modified asphalt powder is 1:(0.01-0.06); (3) in the carbonization treatment step: first heated to 200-400 ℃, kept for 2-4 h, then heated to 600-1000 ℃, kept for 1-3 h.

7. A negative electrode material, characterized by, Prepared by the preparation method of any one of claims 1-6; the negative electrode material has a core-shell structure, which is composed of graphite particles and a soft carbon coating layer covering the graphite particles, and the soft carbon coating layer is doped with silicon carbide nanoparticles.

8. The negative electrode material according to claim 7, characterized in that, The particle size D50 of the graphite particles is 8-20 μm, the layer thickness of the soft carbon coating layer is 5-20 nm, and the particle size D50 of the silicon carbide nanoparticles is 2-10 nm.

9. A negative electrode sheet characterized by comprising: The negative electrode material of claim 7 or 8.

10. A secondary battery characterized by comprising: The negative electrode sheet of claim 9.

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