A high-conductivity composite graphite anode material and its preparation method

Abstract

This invention discloses a high-conductivity composite graphite anode material and its preparation method, relating to the field of graphite anode materials. The high-conductivity composite graphite anode material is prepared by first depositing silicon onto the graphite surface via chemical vapor deposition; then, porous carbon is tightly coated onto the surface of the silicon-coated graphite product through a reaction of amino groups and acyl chlorides, resulting in a porous carbon / silicon-coated graphite product; next, MXene nanosheets, prepared by chemical etching, are coated onto the surface of the porous carbon / silicon-coated graphite product; subsequently, fluorine is introduced onto the MXene through treatment with a fluorinated silane coupling agent; and finally, the product is obtained by calcination. The high-conductivity composite graphite anode material exhibits excellent conductivity, capacity, and cycle stability, making it worthy of widespread application.

Description

Technical Field

[0001] This invention relates to the field of graphite anode materials, specifically to a high-conductivity composite graphite anode material and its preparation method. Background Technology

[0002] Currently, carbon-based and silicon-based materials are highly favored by experts as lithium-ion battery anode materials. Carbon-based anode materials, such as graphite, are widely used in lithium-ion batteries due to their high conductivity and ease of lithium-ion intercalation. Graphite anode materials typically include natural graphite and artificial graphite (asphalt, stone tar, etc.). However, graphite has a very small theoretical capacity, and the formation of dendritic lithium metal is unavoidable during high-rate charging of graphite anodes, causing capacity decay. Furthermore, during lithium-ion extraction and intercalation, graphite anode materials and porous carbon materials also undergo volume expansion, leading to particle pulverization and negatively impacting battery cycle performance.

[0003] Silicon-based materials, as anode materials for lithium-ion batteries, have advantages such as large capacity, moderate operating potential, environmental friendliness, and high abundance, and have been widely used in lithium-ion batteries. However, during lithium insertion and extraction, silicon-based anode materials suffer from significant volume changes, poor capacity retention, and low inherent conductivity, making it impossible for simple silicon electrodes to meet the current requirements of lithium-ion batteries.

[0004] In two-dimensional (2D) materials, MXene is a novel family of two-dimensional (2D) transition metal carbides / nitrides, which consists of M n+ 1AX n This is derived from etching away the "A" layer in a (n = 1, 2, 3) phase, where M represents a pre-transition metal element, A represents a main group element, X represents carbon and / or nitrogen, and Tx represents a functional group connected to the M layer. Ti3C2T x It is a typical representative of MXene, possessing a graphene-like structure, but Ti3C2T x It has higher electrical conductivity and Li + Diffusion rate. In addition, Ti3C2T x It also features low operating voltage, good hydrophilicity, abundant surface functional groups, large specific surface area and interlayer spacing, and excellent mechanical properties. Benefiting from these advantages, Ti3C2T... x When applied to the anode of lithium-ion batteries, it not only exhibits excellent physical and cycle stability but also demonstrates a significant contribution to pseudocapacitance. However, due to the Ti3C2T... x The theoretical capacity is relatively low, and self-stacking easily occurs during repeated charge and discharge processes. Furthermore, the edges of MXene materials are susceptible to adsorption of oxygen and water molecules, which may cause Ti3C2T to collapse. xPartial oxidation into non-conductive TiO2 limits the use of MXene materials in anode materials.

[0005] Therefore, a suitable modification method is needed to combine graphite anode materials and silicon-based anode materials to obtain composite graphite anode materials, achieving complementary advantages in conductivity and capacity. Furthermore, MXenes with improved oxidation resistance can be applied to the composite graphite anode materials to compensate for the excessive volume changes in carbon-based materials such as graphite anode materials and silicon-based anode materials during lithium-ion extraction and insertion, thereby obtaining composite graphite anode materials with superior comprehensive performance such as conductivity. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a high-conductivity composite graphite anode material and its preparation method.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A high-conductivity composite graphite anode material is prepared by the following steps:

[0009] Step S1: Place graphite in a protective gas atmosphere, heat to 700-800℃, then introduce silane gas at a flow rate of 1-2L / min, and calcine at a constant temperature for 25-35min to obtain silicon-coated graphite product; add the silicon-coated graphite product to anhydrous ethanol, ultrasonically disperse for 40-50min, then add an amino-containing silane coupling agent, and stir and react at 60-70℃ for 9-10h to obtain NH2-silicon-coated graphite product;

[0010] Further, the protective gas is argon, and the flow rate of the protective gas is 1.5-2.0 L / min; the ratio of silicon-coated graphite product, anhydrous ethanol, and amino-containing silane coupling agent is 5-6 g: 100-120 mL: 10-11 g, and the amino-containing silane coupling agent is selected from one of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane;

[0011] In step S1, silicon is deposited on the graphite surface by chemical vapor deposition to obtain silicon-coated graphite product; silanol groups obtained by hydrolysis of amino-containing silane coupling agent react with active hydroxyl groups on the surface of silicon-coated graphite product to obtain NH2-silicon-coated graphite product.

[0012] Step S2: Wash and dry the rice husks, then place them in an acidic solution and heat in a water bath at 80-85℃ for 2-2.5 hours. After cooling, wash with water until neutral, then dry at 80-90℃, and finally calcine at 600-650℃ for 3-3.5 hours in a protective gas atmosphere to obtain a carbon-containing complex. Add the carbon-containing complex and potassium carbonate to a mortar and grind for 1-1.5 hours, then calcine at 900-950℃ for 1-1.5 hours. After cooling, wash with water until neutral, filter, and dry to obtain porous carbon. Add the porous carbon to a nitric acid solution, heat at 90-100℃ for 10-12 hours, cool to room temperature, wash until neutral, and vacuum dry at 80-90℃ for 3-4 hours to obtain carboxylated porous carbon.

[0013] Furthermore, the ratio of rice husk to acid solution is 1-2g:50-60mL, and the acid solution is a 2mol / L hydrochloric acid solution; the ratio of carbon-containing complex to potassium carbonate is 1-2g:3-6g; the ratio of porous carbon to nitric acid solution is 1g:40-50mL, and the mass fraction of nitric acid solution is 68-70%.

[0014] In step S2, alkali metal ions in rice husks are removed by acid treatment; then, porous carbon is obtained by activation and pore-forming effect of potassium carbonate at high temperature; after acidification treatment with nitric acid solution, carboxylated porous carbon is obtained.

[0015] Step S3: Add carboxylated porous carbon to DMF, add sulfoxide under stirring, and reflux and stir at 50-60℃ for 4-5 hours to obtain acyl chloride product; mix NH2-silicon coated graphite product, potassium carbonate and sulfoxide to obtain mixture 1, then add acyl chloride product to sulfoxide and stir to obtain mixture 2. Add mixture 2 dropwise to mixture 1 under ice-water bath. After the addition is complete, heat to 45-50℃ and stir at a constant temperature for 12-14 hours. Distill under reduced pressure to obtain porous carbon / silicon coated graphite product.

[0016] Furthermore, the ratio of carboxylated porous carbon, DMF, and sulfoxide is 6-7 g: 50-60 mL: 4-5 g; the ratio of NH2-silicon coated graphite product, potassium carbonate, and sulfoxide in mixture 1 is 7-8 g: 1-1.5 g: 55-65 mL; the ratio of acyl chloride product and sulfoxide in mixture 2 is 7-7.5 g: 40-50 mL; and the ratio of mixture 1 to mixture 2 is 70-80 mL: 50-60 mL.

[0017] In step S3, carboxylated porous carbon reacts with thionyl chloride to obtain an acyl chloride product; the acyl chloride product reacts with NH2-silicon-coated graphite product to coat the porous carbon onto the surface of the silicon-coated graphite product, thus obtaining a porous carbon / silicon-coated graphite product.

[0018] Step S4: Add Ti3AlC2 powder to the mixed solution and stir at 35-40℃ for 24-26h to obtain a suspension. Wash with water until neutral, filter, and add the precipitate to ethanol. Sonicate and disperse in an ice-water bath for 1-1.5h. After centrifugation, add the precipitate S to deionized water and sonicate again for 30-40min. Then centrifuge for 1-1.5h and collect the supernatant to obtain MXene nanosheet suspension.

[0019] Furthermore, the Ti3AlC2 powder is 200-325 mesh, and the mixed solution is obtained by mixing LiF and hydrochloric acid solution at a ratio of 2-2.5g:40-50mL. The volume ratio of Ti3AlC2 powder to mixed solution is 2-2.5g:45-55mL; the volume ratio of precipitate to ethanol is 2.8-3.0g:200-210mL, and the volume fraction of ethanol is 95%; the volume ratio of precipitate S to deionized water is 1.3-1.5g:150-160mL.

[0020] In step S4, a suspension containing MXene nanosheets is prepared by chemical etching.

[0021] Step S5: Add the porous carbon / silicon coated graphite product to ethanol and ultrasonically disperse for 30-40 min. Then add MXene nanosheet suspension and stir for 3-3.5 h. After vacuum filtration, vacuum dry at 60-70℃ to obtain MXene / porous carbon / silicon coated graphite product. Then add the MXene / porous carbon / silicon coated graphite product to ethanol and ultrasonically disperse for 1-1.5 h. Then add fluorinated silane coupling agent and stir the reaction at 55-65℃ for 18-20 h. Then calcine at 500-600℃ for 2-2.5 h to obtain high conductivity composite graphite anode material.

[0022] Furthermore, the ratio of porous carbon / silicon coated graphite product, ethanol, and MXene nanosheet suspension is 0.1-0.2g: 20-30mL: 20-30mL; the ratio of MXene / porous carbon / silicon coated graphite product, ethanol, and fluorinated silane coupling agent is 0.5-1.0g: 100-110mL: 13-15g, and the fluorinated silane coupling agent is selected from one of tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane, and heptadecafluorodecyltriisopropoxysilane; the volume fraction of ethanol is 95%.

[0023] In step S5, the porous carbon / silicon coated graphite product and the functional groups such as hydroxyl groups on the surface of MXene nanosheets are bonded by hydrogen bonds, thus coating the MXene nanosheets onto the surface of the porous carbon / silicon coated graphite product, resulting in an MXene / porous carbon / silicon coated graphite product. The MXene / porous carbon / silicon coated graphite product then reacts with the silanol groups obtained by hydrolysis of a fluorinated silane coupling agent, grafting the fluorinated silane coupling agent onto the MXene. After calcination, a high-conductivity composite graphite anode material is obtained.

[0024] The beneficial effects of this invention are as follows: This invention discloses a high-conductivity composite graphite anode material and its preparation method. The high-conductivity composite graphite anode material is prepared by first depositing silicon on the graphite surface via chemical vapor deposition, followed by treatment with an amino-containing silane coupling agent to obtain an NH2-silicon-coated graphite product; then, porous carbon is synthesized through potassium carbonate pore-forming, and the porous carbon is surface carboxylated to obtain carboxylated porous carbon; then, the carboxylated porous carbon is acylated and reacted with the NH2-silicon-coated graphite product to tightly coat the porous carbon onto the surface of the silicon-coated graphite product, resulting in a porous carbon / silicon-coated graphite product; then, MXene nanosheets prepared by chemical etching are coated onto the surface of the porous carbon / silicon-coated graphite product, followed by treatment with a fluorinated silane coupling agent to introduce fluorine onto the MXene, and finally, calcination is performed to obtain the final product.

[0025] In this invention, graphite anode material and silicon-based anode material are used in combination to obtain composite graphite anode material, achieving complementary advantages in conductivity and capacity. After carbonization, the amino-containing silane coupling agent forms N-doped porous carbon coating the silicon surface, which not only provides more electron and ion transport channels and pore space, but also avoids direct contact between silicon and electrolyte, further improving conductivity. Since MXene oxidation usually starts from the edge, the contact between MXene edge atoms and water molecules is cut off after treatment with fluorinated silane coupling agent, thereby reducing oxidation tendency and improving MXene's oxidation resistance. The high conductivity, excellent flexibility, and improved oxidation resistance of MXene can further promote electron and ion transport, buffer the excessive volume changes of graphite anode material, porous carbon, and silicon anode material during lithium insertion and extraction, thus making the obtained high-conductivity composite graphite anode material exhibit excellent conductivity, capacity, and cycle stability. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1

[0028] A high-conductivity composite graphite anode material is prepared by the following steps:

[0029] Step S1: Place graphite (supplier: Shanghai Youmo Composite Materials Co., Ltd., product name: flake graphite) in an argon atmosphere with a gas flow rate of 1.5 L / min, heat to 700℃, then introduce silane gas at a flow rate of 1 L / min, and calcine at a constant temperature for 25 min to obtain silicon-coated graphite product; add the silicon-coated graphite product to anhydrous ethanol, ultrasonically disperse for 40 min, then add 3-aminopropyltrimethoxysilane, and stir and react at 60℃ for 9 h to obtain NH2-silicon-coated graphite product; the ratio of silicon-coated graphite product, anhydrous ethanol, and 3-aminopropyltrimethoxysilane is 5 g: 100 mL: 10 g;

[0030] Step S2: After washing and drying the rice husks, place them in a 2 mol / L hydrochloric acid solution and heat in a water bath at 80°C for 2 hours. After cooling, wash with water until neutral, then dry at 80°C again, and calcine at 600°C for 3 hours under a nitrogen atmosphere to obtain a carbon-containing complex. Grind the carbon-containing complex and potassium carbonate in a mortar for 1 hour, then calcine at 900°C for 1 hour. After cooling, wash with water until neutral, filter, and dry to obtain porous carbon. Add the porous carbon to a 68% nitric acid solution, heat at 90°C for 10 hours, cool to room temperature, wash until neutral, and vacuum dry at 80°C for 3 hours to obtain carboxylated porous carbon. The ratio of rice husks to 2 mol / L hydrochloric acid solution is 1 g: 50 mL; the ratio of carbon-containing complex to potassium carbonate is 1 g: 3 g; and the ratio of porous carbon to 68% nitric acid solution is 1 g: 40 mL.

[0031] Step S3: Add carboxylated porous carbon to DMF, add sulfoxide under stirring, and reflux at 50°C for 4 hours to obtain the acyl chloride product; mix NH2-silicon coated graphite product, potassium carbonate, and sulfoxide to obtain mixture 1, then add the acyl chloride product to sulfoxide and mix to obtain mixture 2. Add mixture 2 dropwise to mixture 1 under an ice-water bath. After the addition is complete, raise the temperature to 45°C and stir to maintain the temperature for reaction 1. After 2 hours of vacuum distillation, porous carbon / silicon-coated graphite products were obtained; the ratio of carboxylated porous carbon, DMF, and sulfoxide was 6 g: 50 mL: 4 g; the ratio of NH2-silicon-coated graphite products, potassium carbonate, and sulfoxide in mixture 1 was 7 g: 1 g: 55 mL; the ratio of acyl chloride products and sulfoxide in mixture 2 was 7 g: 40 mL; and the ratio of mixture 1 to mixture 2 was 70 mL: 50 mL.

[0032] Step S4: Add Ti3AlC2 powder to the mixed solution, stir at 35℃ for 24h to obtain a suspension, wash with water until neutral, filter, add the precipitate to ethanol, ultrasonically disperse in an ice-water bath for 1h, centrifuge to obtain precipitate s, add to deionized water, ultrasonically disperse for 30min, then centrifuge for 1h, collect the supernatant to obtain MXene nanosheet suspension; Ti3AlC2 powder is 200 mesh (supplier: Forsmann Technology (Beijing) Co., Ltd., No.: 2203015), the mixed solution is obtained by mixing LiF and hydrochloric acid solution at a ratio of 2g:40mL, the volume ratio of Ti3AlC2 powder to mixed solution is 2g:45mL; the volume ratio of precipitate to ethanol is 2.8g:200mL, the volume fraction of ethanol is 95%; the volume ratio of precipitate s to deionized water is 1.3g:150mL;

[0033] Step S5: The porous carbon / silicon coated graphite product was added to ethanol and ultrasonically dispersed for 30 min. Then, MXene nanosheet suspension was added, stirred for 3 h, vacuum filtered, and vacuum dried at 60 °C to obtain the MXene / porous carbon / silicon coated graphite product. The MXene / porous carbon / silicon coated graphite product was then added to ethanol and ultrasonically dispersed for 1 h. Then, tridecafluorooctyltrimethoxysilane was added, and the mixture was stirred at 55 °C for 18 h. Finally, it was calcined at 500 °C for 2 h to obtain a high-conductivity composite graphite anode material. The ratio of porous carbon / silicon coated graphite product, ethanol, and MXene nanosheet suspension was 0.1 g: 20 mL: 20 mL; the ratio of MXene / porous carbon / silicon coated graphite product, ethanol, and tridecafluorooctyltrimethoxysilane was 0.5 g: 100 mL: 13 g; and the volume fraction of ethanol was 95%.

[0034] Example 2

[0035] A high-conductivity composite graphite anode material is prepared by the following steps:

[0036] Step S1: Place graphite (supplier: Shanghai Youmo Composite Materials Co., Ltd., product name: flake graphite) in an argon atmosphere, heat to 700℃, then introduce silane gas at a flow rate of 1.5L / min, and calcine at a constant temperature for 30min to obtain silicon-coated graphite product; add the silicon-coated graphite product to anhydrous ethanol, ultrasonically disperse for 45min, then add 3-aminopropyltriethoxysilane, and stir and react at 65℃ for 9.5h to obtain NH2-silicon-coated graphite product; the protective gas is argon, and the protective gas flow rate is 1.5L / min; the ratio of silicon-coated graphite product, anhydrous ethanol, and 3-aminopropyltriethoxysilane is 5.5g:110mL:10.5g;

[0037] Step S2: Wash and dry the rice husks, then place them in a container for 2 months. In a 1 / L hydrochloric acid solution, the mixture was heated in a water bath at 82°C for 2.2 hours. After cooling, it was washed with water until neutral, dried at 85°C, and then calcined at 620°C for 3.2 hours under a nitrogen atmosphere to obtain a carbon-containing complex. The carbon-containing complex and potassium carbonate were then added to a mortar and ground for 1.3 hours, followed by calcination at 920°C for 1.2 hours. After cooling, it was washed with water until neutral, filtered, and dried to obtain porous carbon. The porous carbon was then added to a 69% nitric acid solution and heated at 95°C for 11 hours. After cooling to room temperature, it was washed until neutral and then vacuum dried at 85°C for 3.5 hours to obtain carboxylated porous carbon. The ratio of rice husk to 2 mol / L hydrochloric acid solution was 1.5 g: 55 mL; the ratio of carbon-containing complex to potassium carbonate was 1.5 g: 4.5 g; and the ratio of porous carbon to 69% nitric acid solution was 1 g: 45 mL.

[0038] Step S3: Add carboxylated porous carbon to DMF, add sulfoxide under stirring, and reflux at 55°C for 4.5 h to obtain the acyl chloride product; mix NH2-silicon coated graphite product, potassium carbonate, and sulfoxide to obtain mixture 1, then add the acyl chloride product to sulfoxide and mix to obtain mixture 2. Add mixture 2 dropwise to mixture 1 under an ice-water bath. After the addition is complete, raise the temperature to 47°C and stir for 13 h. Pressure distillation yields porous carbon / silicon-coated graphite products; the ratio of carboxylated porous carbon, DMF, and sulfoxide is 6.5 g: 55 mL: 4.5 g; the ratio of NH2-silicon-coated graphite products, potassium carbonate, and sulfoxide in mixture 1 is 7.5 g: 1.2 g: 60 mL; the ratio of acyl chloride products and sulfoxide in mixture 2 is 7.2 g: 45 mL; the ratio of mixture 1 to mixture 2 is 75 mL: 55 mL.

[0039] Step S4: Add Ti3AlC2 powder to the mixed solution, stir at 37℃ for 25h to obtain a suspension, wash with water until neutral, filter, add the precipitate to ethanol, ultrasonically disperse in an ice-water bath for 1.2h, centrifuge to obtain precipitate s, add to deionized water, ultrasonically disperse for 35min, then centrifuge for 1.2h, collect the supernatant to obtain MXene nanosheet suspension; Ti3AlC2 powder is 200 mesh (supplier: Forsmann Technology (Beijing) Co., Ltd., No.: 2203009), the mixed solution is obtained by mixing LiF and hydrochloric acid solution at a ratio of 2.2g:45mL, the volume ratio of Ti3AlC2 powder to mixed solution is 2.2g:50mL; the volume ratio of precipitate to ethanol is 2.9g:205mL, the volume fraction of ethanol is 95%; the volume ratio of precipitate s to deionized water is 1.4g:155mL;

[0040] Step S5: The porous carbon / silicon coated graphite product was added to ethanol and ultrasonically dispersed for 35 min. Then, MXene nanosheet suspension was added, and the mixture was stirred for 3.2 h. After vacuum filtration, the product was vacuum dried at 65 °C to obtain the MXene / porous carbon / silicon coated graphite product. The MXene / porous carbon / silicon coated graphite product was then added to ethanol and ultrasonically dispersed for 1.2 h. Then, tridecafluorooctyltriethoxysilane was added, and the mixture was stirred at 60 °C for 19 h. Finally, it was calcined at 550 °C for 2.3 h to obtain a high-conductivity composite graphite anode material. The ratio of porous carbon / silicon coated graphite product, ethanol, and MXene nanosheet suspension was 0.15 g: 25 mL: 25 mL. The ratio of MXene / porous carbon / silicon coated graphite product, ethanol, and tridecafluorooctyltriethoxysilane was 0.7 g: 105 mL: 14 g. The volume fraction of ethanol was 95%.

[0041] Example 3

[0042] A high-conductivity composite graphite anode material is prepared by the following steps:

[0043] Step S1: Place graphite (supplier: Shanghai Youmo Composite Materials Co., Ltd., product name: flake graphite) in an argon atmosphere, heat to 800℃, then introduce silane gas at a flow rate of 2L / min, and calcine at a constant temperature for 35min to obtain silicon-coated graphite product; add the silicon-coated graphite product to anhydrous ethanol, ultrasonically disperse for 50min, then add N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and stir and react at 70℃ for 10h to obtain NH2-silicon-coated graphite product; the protective gas is argon, and the protective gas flow rate is 2.0L / min; the ratio of silicon-coated graphite product, anhydrous ethanol, and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane is 6g:120mL:11g;

[0044] Step S2: Wash and dry the rice husks, then place them in a 2 mol / L hydrochloric acid solution and heat in a water bath at 85°C for 2.5 hours. After cooling, wash with water until neutral, then dry at 90°C, and finally calcine at 650°C for 3.5 hours under a nitrogen atmosphere to obtain a carbon-containing complex. Grind the carbon-containing complex and potassium carbonate in a mortar for 1.5 hours, then calcine at 950°C for 1.5 hours. After cooling, wash with water until neutral, filter, and dry to obtain porous carbon. Add the porous carbon to a 70% nitric acid solution, heat at 100°C for 12 hours, cool to room temperature, wash until neutral, and vacuum dry at 90°C for 4 hours to obtain carboxylated porous carbon. Rice husks, 2 mol / L hydrochloric acid solution... The volume ratio of l / L hydrochloric acid solution is 2g:60mL; the volume ratio of carbon-containing complex and potassium carbonate is 2g:6g; the volume ratio of porous carbon and 70% nitric acid solution is 1g:50mL.

[0045] Step S3: Add carboxylated porous carbon to DMF, add sulfoxide under stirring, and reflux at 60°C for 5 hours to obtain the acyl chloride product. Mix NH2-silicon-coated graphite product, potassium carbonate, and sulfoxide to obtain mixture 1. Then add the acyl chloride product to sulfoxide and mix to obtain mixture 2. Add mixture 2 dropwise to mixture 1 under an ice-water bath. After the addition is complete, raise the temperature to 50°C and stir for 14 hours. Vacuum distillation yielded porous carbon / silicon-coated graphite products; the ratio of carboxylated porous carbon, DMF, and sulfoxide was 7 g: 60 mL: 5 g; the ratio of NH2-silicon-coated graphite products, potassium carbonate, and sulfoxide in mixture 1 was 8 g: 1.5 g: 65 mL; the ratio of acyl chloride products and sulfoxide in mixture 2 was 7.5 g: 50 mL; and the ratio of mixture 1 to mixture 2 was 80 mL: 60 mL.

[0046] Step S4: Add Ti3AlC2 powder to the mixed solution, stir at 40℃ for 26h to obtain a suspension, wash with water until neutral, filter, add the precipitate to ethanol, ultrasonically disperse for 1.5h in an ice-water bath, centrifuge to obtain precipitate s, add to deionized water, ultrasonically disperse for 40min, then centrifuge for 1.5h, collect the supernatant to obtain MXene nanosheet suspension; Ti3AlC2 powder is 325 mesh (supplier: Forsmann Technology (Beijing) Co., Ltd., No.: 2203026), the mixed solution is obtained by mixing LiF and hydrochloric acid solution at a ratio of 2.5g:50mL, the volume ratio of Ti3AlC2 powder to mixed solution is 2.5g:55mL; the volume ratio of precipitate to ethanol is 3.0g:210mL, the volume fraction of ethanol is 95%; the volume ratio of precipitate s to deionized water is 1.5g:160mL;

[0047] Step S5: The porous carbon / silicon coated graphite product was added to ethanol and ultrasonically dispersed for 40 min. Then, MXene nanosheet suspension was added, and the mixture was stirred for 3.5 h. After vacuum filtration, the product was vacuum dried at 70 °C to obtain the MXene / porous carbon / silicon coated graphite product. The MXene / porous carbon / silicon coated graphite product was then added to ethanol and ultrasonically dispersed for 1.5 h. Then, heptadecafluorodecyltriisopropoxysilane was added, and the mixture was stirred at 65 °C for 20 h. Finally, it was calcined at 600 °C for 2.5 h to obtain a high-conductivity composite graphite anode material. The ratio of porous carbon / silicon coated graphite product, ethanol, and MXene nanosheet suspension was 0.2 g: 30 mL: 30 mL. The ratio of MXene / porous carbon / silicon coated graphite product, ethanol, and heptadecafluorodecyltriisopropoxysilane was 1.0 g: 110 mL: 15 g. The volume fraction of ethanol was 95%.

[0048] Comparative Example 1

[0049] Compared with Example 3, the high conductivity composite graphite anode material was replaced with Compound 1, which was obtained by calcining the porous carbon / silicon coated graphite product in step S3 at 600°C for 2.5 hours. That is, MXene was not introduced and no fluorinated silane coupling agent was used. Everything else was exactly the same as in Example 3.

[0050] Comparative Example 2

[0051] Compared with Example 3, the high conductivity composite graphite anode material was replaced with Compound 2. Compound 2 was obtained by calcining the MXene / porous carbon / silicon coated graphite product in step S5 at 600°C for 2.5 hours. That is, no fluorine-containing silane coupling agent was used for treatment, and no fluorine was introduced onto MXene. Everything else was exactly the same as in Example 3.

[0052] The high conductivity composite graphite anode material prepared by this invention was further tested below, and the test results are as follows.

[0053] The high-conductivity composite graphite anode materials obtained in Examples 1-3 and Comparative Examples 1-2 were used as anode materials for lithium-ion batteries. Lithium iron phosphate was used as the cathode material, LiPF6 / EC+DEC (EC to DEC volume ratio of 1:1) was used as the electrolyte, and a glass fiber membrane was used as the separator to prepare 5AH soft-pack batteries. The performance of the prepared batteries was tested according to the methods in GB / T24533-2009 "Graphite Anode Materials for Lithium-ion Batteries". Simultaneously, the composite graphite anode material was immersed in deionized water and allowed to stand for 6 hours; the conductivity after oxidation was tested according to the above method. The results are recorded in Table 1.

[0054] Table 1: Test Results

[0055]

[0056] According to the data in Table 1, the high-conductivity composite graphite anode material of the present invention exhibits excellent conductivity, capacity, and cycle stability. Comparing Example 3 with Comparative Example 1, it can be seen that without the introduction of MXene and without treatment with a fluorinated silane coupling agent, the transport of electrons and ions cannot be further promoted, and the excessive volume changes of the graphite anode material, porous carbon, and silicon anode materials during lithium insertion and extraction cannot be buffered. Consequently, the conductivity, capacity, and cycle stability of the composite graphite anode material all decrease. Comparing Example 3 with Comparative Example 2, it can be seen that without treatment with a fluorinated silane coupling agent (i.e., without introducing fluorine onto MXene), the oxidation resistance of MXene is not improved, the conductivity of the composite graphite anode material decreases after oxidation, the capacity retention after 600 cycles also decreases, and the cycle stability decreases.

[0057] The above description is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined in the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-conductivity composite graphite anode material, characterized in that: Includes the following steps: Step S1: Place graphite in a protective gas atmosphere, heat it, introduce silane gas, and calcine at a constant temperature to obtain a silicon-coated graphite product; add the silicon-coated graphite product to anhydrous ethanol, and treat it with an amino-containing silane coupling agent to obtain an NH2-silicon-coated graphite product; the ratio of the amino-containing silane coupling agent is 5-6g:100-120mL:10-11g, and the amino-containing silane coupling agent is selected from 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane; Step S2: Wash and dry the rice husks, then heat and dry them in an acid solution, and then calcine them in a protective gas atmosphere to obtain a carbon-containing complex; grind and calcine the carbon-containing complex and potassium carbonate to obtain porous carbon; add the porous carbon to a nitric acid solution and heat to react to obtain carboxylated porous carbon; Step S3: Add carboxylated porous carbon to DMF and react with thionyl chloride to obtain acyl chloride product; stir and mix NH2-silicon coated graphite product, potassium carbonate and dimethyl sulfoxide to obtain mixture 1; then add acyl chloride product to dimethyl sulfoxide and stir to obtain mixture 2; under ice-water bath, add mixture 2 dropwise to mixture 1 and stir to obtain porous carbon / silicon coated graphite product; Step S4: Add Ti3AlC2 powder to the mixed solution and stir to obtain a suspension. Wash with water until neutral, filter, add the precipitate to ethanol, disperse by ultrasonication and centrifuge, add the precipitate to deionized water, disperse by ultrasonication again and centrifuge, and collect the supernatant to obtain MXene nanosheet suspension. Step S5: Add the porous carbon / silicon coated graphite product to ethanol and stir with the MXene nanosheet suspension to obtain the MXene / porous carbon / silicon coated graphite product; then add the MXene / porous carbon / silicon coated graphite product to ethanol and ultrasonically disperse it, treat it with a fluorinated silane coupling agent and calcine it to obtain a high conductivity composite graphite anode material. The fluorinated silane coupling agent is selected from one of tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane and heptadecafluorodecyltriisopropoxysilane.

2. The method for preparing a high-conductivity composite graphite anode material according to claim 1, characterized in that: In step S1, the protective gas is argon, the flow rate of the protective gas is 1.5-2.0 L / min, and the flow rate of the silane gas is 1-2 L / min; Silicon-coated graphite products, anhydrous ethanol.

3. The method for preparing a high-conductivity composite graphite anode material according to claim 1, characterized in that: In step S2, the ratio of rice husk to acid solution is 1-2g: 50-60mL, and the acid solution is a 2mol / L hydrochloric acid solution; the ratio of carbon-containing complex to potassium carbonate is 1-2g: 3-6g; the ratio of porous carbon to nitric acid solution is 1g: 40-50mL, and the mass fraction of nitric acid solution is 68-70%.

4. The method for preparing a high-conductivity composite graphite anode material according to claim 1, characterized in that: In step S3, the ratio of carboxylated porous carbon, DMF, and thionyl chloride is 6-7g: 50-60mL: 4-5g; the ratio of NH2-silicon coated graphite product, potassium carbonate, and dimethyl sulfoxide in mixture 1 is 7-8g: 1-1.5g: 55-65mL.

5. The method for preparing a high-conductivity composite graphite anode material according to claim 1, characterized in that: In step S3, the ratio of acyl chloride product to dimethyl sulfoxide in mixture 2 is 7-7.5g:40-50mL; the ratio of mixture 1 to mixture 2 is 70-80mL:50-60mL.

6. The method for preparing a high-conductivity composite graphite anode material according to claim 1, characterized in that: In step S4, the Ti3AlC2 powder is 200-325 mesh, and the mixed solution is obtained by mixing LiF and hydrochloric acid solution at a ratio of 2-2.5g:40-50mL. The ratio of Ti3AlC2 powder to mixed solution is 2-2.5g:45-55mL.

7. The method for preparing a high-conductivity composite graphite anode material according to claim 1, characterized in that: In step S4, the ratio of precipitate to ethanol is 2.8-3.0g: 200-210mL, and the volume fraction of ethanol is 95%; the ratio of precipitate to deionized water is 1.3-1.5g: 150-160mL.

8. The method for preparing a high-conductivity composite graphite anode material according to claim 1, characterized in that: In step S5, the ratio of porous carbon / silicon coated graphite product, ethanol, and MXene nanosheet suspension is 0.1-0.2g: 20-30mL: 20-30mL.

9. The method for preparing a high-conductivity composite graphite anode material according to claim 1, characterized in that: In step S5, the ratio of MXene / porous carbon / silicon coated graphite product, ethanol, and fluorinated silane coupling agent is 0.5-1.0g: 100-110mL: 13-15g; the volume fraction of ethanol is 95%.

10. A high-conductivity composite graphite anode material is prepared by the preparation method of a high-conductivity composite graphite anode material according to any one of claims 1-9.

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