Composite biomass hard carbon negative electrode material and preparation method thereof

Abstract

The invention relates to the technical field of sodium ion battery negative electrode materials, in particular to a composite biomass hard carbon negative electrode material and a preparation method thereof.The preparation method comprises the steps that a biomass-based hard carbon precursor is prepared, and a biomass raw material is subjected to crushing, hydrolysis, pre-carbonization, alkali activation and acid pickling to obtain the biomass-based precursor; taking the precursor as a carrier, and adding resin for compounding; the biomass resin composite hard carbon negative electrode material which is compact in structure, high in cycling stability and high in energy density is obtained after the composite material is subjected to surface modification in a deposition coating mode. The biomass-based raw material is subjected to structure regulation and control through hydrolysis, meanwhile, the pore structure of the precursor can be stably regulated and controlled through the synergistic effect of compounding with the resin, the low cost and natural structure of biomass and the chemical adjustability of the resin are combined, the advantages of being environmentally friendly and low in cost are achieved, and the industrial value is achieved.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion anode material technology, specifically to a composite biomass hard carbon anode material and its preparation method. Background Technology

[0002] With the rapid development of electrochemical energy storage technology, sodium-ion batteries, due to their abundant resources and low cost, are considered an important candidate system to replace lithium-ion batteries in the field of large-scale energy storage. The performance of the anode material is one of the keys to the commercial success of sodium-ion batteries. Among many candidate materials, biomass hard carbon has become the most promising sodium-ion battery anode material due to its widely available, renewable, and low-cost precursors, as well as its naturally formed disordered structure and abundant pores, which are conducive to the storage and transport of sodium ions.

[0003] Currently, the mainstream technical route for preparing hard carbon anodes using biomass as a precursor typically includes direct high-temperature carbonization. However, this route has several inherent drawbacks that limit further improvement in material performance and industrial application. First, the chemical composition and microstructure of biomass raw materials fluctuate significantly due to differences in species, origin, and location. For example, the ratio of lignin, cellulose, and hemicellulose makes it difficult to precisely control the microstructure of the carbonization products, such as the number of closed pores, size distribution, and defect concentration. This results in poor batch-to-batch stability of the electrochemical performance of the final hard carbon material, especially the first-cycle coulombic efficiency and reversible capacity. Second, conventional single carbonization processes have limited ability to regulate the precursor structure. It is difficult to optimize the formation of ideal pores and surface chemical environment conducive to rapid sodium ion insertion / extraction while ensuring high tap density. This often results in a trade-off between rate performance and cycle stability. Furthermore, the abundant oxygen-containing functional groups and defect sites on the surface of biomass hard carbon easily trigger violent initial irreversible side reactions, causing continuous depletion of the active sodium source. This is the core reason for the generally low first-cycle coulombic efficiency and constitutes a major bottleneck for improving the energy density of the entire battery.

[0004] To address the shortcomings of the existing technologies, our team proposes a method for effective structural design and precise conversion control of biomass-based precursors, in order to prepare hard carbon anode materials with high reproducibility, high first-efficiency, high capacity and excellent cycle stability. Summary of the Invention

[0005] To address the aforementioned deficiencies in the existing technology, the purpose of this invention is to provide a composite biomass hard carbon anode material and its preparation method.

[0006] One objective of this invention is to provide a method for preparing composite biomass hard carbon anode materials, comprising the following steps: Preparation of S1 biomass-based precursor: S11 The biomass raw material is crushed to Dv50 of (7±1)μm, passed through a 200-mesh sieve, washed with deionized water, and dried in an oven at 110℃ for 2 hours to obtain the dried body; S12 hydrolyzes the dried material, places it in a sulfuric acid solution, heats it in a water bath to 80°C, and stirs it continuously at 400-500 r / min for 3-6 hours. After hydrolysis, it is washed with deionized water until neutral, and then dried in an oven at 110°C for 2 hours. Subsequently, it is pre-carbonized at low temperature to obtain pre-carbonized material. Sulfuric acid hydrolysis reduces the hemicellulose content in biomass raw materials and increases the relative purity of cellulose.

[0007] S13 involves alkaline activation of the pre-carbonized material, mixing the pre-carbonized material with an alkaline chemical reagent, adding anhydrous ethanol and grinding evenly, then heating the mixture, cooling it, washing it with deionized water until neutral, and then drying it in an oven at 110°C for 2 hours to obtain the activated material. S14 The activated material is subjected to acid washing and purification treatment. The activated material is placed in an acid solution system for acid washing and purification treatment to reduce the ash content of the material and obtain a purified product. After washing with deionized water until neutral, it is dried in an oven at 110°C for 2 hours to obtain a biomass-based precursor. S2 Biomass-based precursor and resin precursor composite: The biomass-based precursor is placed in a tubular furnace reactor, and gaseous formaldehyde is introduced for adsorption. Then, the resin precursor is dissolved in an ethanol solution. The biomass-based precursor is then poured into the resin ethanol solution, where the resin accounts for 20-40%. The mixture is uniformly mixed and reacted with the biomass-based precursor. The mixture is then placed in an atmosphere furnace for stepwise carbonization to obtain a primary composite hard carbon precursor. Deposition and coating of S3 composite material: The primary composite hard carbon precursor obtained from S2 is deposited and coated to obtain composite biomass hard carbon anode material.

[0008] Furthermore, the biomass raw materials mentioned in S1 include at least one of coconut shells, bamboo, straw, walnut shells, etc., the concentration of the sulfuric acid solution is 1-3 mol / L, and the ratio of the dry mass to the volume of the sulfuric acid solution is 1 g: 5 ml.

[0009] Furthermore, the low-temperature pre-carbonization described in S12 involves heating at a rate of 2-5℃ / min to 200-450℃ and holding for 1-2 hours, then heating at a rate of 5-8℃ / min to 600-750℃ and holding for 1-2 hours, followed by cooling in the furnace to room temperature to obtain pre-carbonized material. The low-temperature pre-carbonization process is carried out under a nitrogen protective atmosphere.

[0010] Further, the alkaline chemical reagent mentioned in S13 is potassium hydroxide, with an addition amount of 20-50%. Anhydrous ethanol is added and ground evenly. The mixture is dried at 90°C for 6 hours to form a mixture. The mixture is placed in an atmosphere furnace and heated to 150-300°C at 2-5°C / min under a nitrogen inert gas atmosphere, and held at that temperature for half an hour. Then, the temperature is increased to 300-600°C at 6-8°C / min and held at that temperature for half an hour. Finally, the temperature is increased to 600-750°C at 6-8°C / min and held at that temperature for 1-3 hours to activate the material. After cooling, the material is washed with deionized water until neutral and then dried in an oven at 110°C for 2 hours to obtain the activated material.

[0011] Further, the acid system described in S14 is a mixture of hydrochloric acid, hydrofluoric acid, and nitric acid, with a volume ratio of 10-30:0.2-5:0.1-2. The ratio of the mass of the activated material to the volume of the acid system is 1g:5mL. The reaction is carried out in a water bath at 80℃ with a stirring rate of 400-500r / min for 4-8h for acid washing and purification treatment to reduce the ash content of the material and obtain the purified product. After washing with deionized water until neutral, the product is dried in an oven at 110℃ for 2h to obtain the biomass-based precursor.

[0012] Furthermore, the resin precursor mentioned in S2 includes at least one of phenolic resin, furan resin, epoxy resin, and lignin-based phenolic resin.

[0013] Furthermore, the composite of the S2 biomass-based precursor and the resin precursor specifically involves placing the biomass-based precursor in a tubular furnace reactor at a temperature of 40-60℃, introducing gaseous formaldehyde (1%-5% by volume in the mixed gas, with a gas flow rate controlled between 0.1-0.5 L / min) for 1-3 hours to allow it to adsorb onto the inner surface of the pores of the biomass-based precursor); mixing the resin precursor and ethanol solution in a 1:2 ratio and stirring until homogeneous; then pouring the biomass-based precursor into the resin-ethanol solution (resin content 20-40%) and gently heating at 60℃ for 2-6 hours.

[0014] Furthermore, the stepwise carbonization in the atmosphere furnace described in S2 includes: In the low-temperature pre-carbonization stage, the temperature is increased to 300-400℃ at a rate of 2-5℃ / min, and pre-carbonization is carried out in an inert atmosphere; the temperature is increased slowly so that the resin and biomass undergo cross-linking and pyrolysis simultaneously, thus locking in the composite structure.

[0015] During the intermediate-temperature pore-forming and polycondensation stage, the temperature is increased to 400-800℃ at a rate of 5-8℃ / min, and then switched. or The atmosphere is used to etch the carbon layer, controlling the closed-pore size and the degree of graphitization of the pore walls; the atmosphere is a nitrogen inert atmosphere as the carrier gas. or The gas volume fraction is 1%, and the gas flow rate is 0.5 L / min; this stage is crucial for pore formation, and extremely low concentrations of weak oxidizing gases are introduced, such as... It can gently etch carbon layers.

[0016] During the high-temperature stabilization stage, the temperature is increased to 800-1300℃ at a rate of 5-10℃ / min, and carbonization is carried out in an inert atmosphere to finally solidify the precursor, resulting in a primary composite hard carbon precursor. This forms a highly disordered but locally ordered hard carbon structure.

[0017] Furthermore, in S3, the deposition coating process involves placing the obtained primary composite hard carbon precursor in a CVD vapor deposition apparatus and performing deposition coating under nitrogen protection. The temperature is increased to 450-650℃ at a heating rate of 5℃-10℃ / min and held for 1 hour. Then, carbon source gas is introduced at a flow rate of 1L / min-2L / min for 0.5-5 hours. The flow rate of carbon source gas is then increased to 2L / min-5L / min for 1-5 hours. Finally, the carbon source gas is stopped, and the material is cooled to room temperature under nitrogen protection to obtain the composite hard carbon anode material. The carbon source gas is methane.

[0018] Another object of the present invention is to provide a composite biomass hard carbon anode material prepared by the aforementioned preparation method.

[0019] The beneficial effects of this invention are: 1. The method of this invention involves crushing, hydrolyzing, pre-carbonizing, alkali-activating, and acid-washing biomass raw materials to obtain a biomass-based precursor. Using biomass as a raw material, the resource is renewable, the raw material source is wide, and the cost is low. Using the biomass precursor as a carrier, a resin precursor is added for composite. The resin, as a chemical substance, has tunability. Direct composite utilization can reduce material costs while accurately utilizing its structural stability. After surface modification of the composite material by deposition coating, the structure becomes more compact, which can improve cycle stability and high energy density, with a capacity retention rate of up to 98.6%.

[0020] 2. The core pore type of the composite biomass hard carbon anode material prepared by this invention is dominated by mesopores / macropores, with mesopores and macropores accounting for 84.45%. This makes the SEI film more stable, and the buffering effect of mesopores can also alleviate volume changes and reduce cycle decay rate. The electrical performance of the prepared composite hard carbon anode material was tested, and the first charge specific capacity was 342.0 mAh / g and the first coulombic efficiency was 94.5%. Attached Figure Description

[0021] Figure 1 SEM image of the composite biomass hard carbon anode material prepared in Example 1; Figure 2 SEM image of the uncomposite biomass hard carbon anode material prepared in Comparative Example 2; Figure 3 The charge-discharge curve of the composite biomass hard carbon anode material prepared in Example 1 is shown. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0023] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0024] Example 1 Preparation of S1 biomass precursors: S11 The raw material of moso bamboo biomass, namely bamboo biomass raw material, is crushed to Dv50 of (7±1)μm and passed through a 200-mesh sieve. It is then washed with deionized water and dried in an oven at 110℃ for 2 hours to obtain a dried body. S12 involves sulfuric acid hydrolysis of the dried material. The hydrolysis conditions are: water bath heating to 80°C, continuous stirring at 400 rpm for 3 hours, sulfuric acid concentration of 1 mol / L, and a material mass to acid volume ratio of 1 g: 5 ml. Pre-carbonization is then performed. The pre-carbonization process involves heating at a rate of 2°C / min to 200°C and holding for 1 hour, then heating at a rate of 5°C / min to 600°C and holding for 1 hour, followed by furnace cooling to room temperature to obtain the pre-carbonized material. The entire pre-carbonization process is carried out under a nitrogen protective atmosphere. After pre-carbonization of S13, the material was activated with alkali using potassium hydroxide as the activating agent (20% potassium hydroxide was added). Anhydrous ethanol was added and the mixture was ground evenly. The mixture was dried at 90°C for 6 hours to form a mixture. The mixture was placed in an atmosphere furnace and heated to 150°C at 2°C / min under a nitrogen inert gas atmosphere. The temperature was held for half an hour, then increased to 300°C at 6°C / min and held for half an hour. Finally, the temperature was increased to 600°C at 6°C / min and held for 1 hour. After cooling, the material was washed with deionized water until neutral and then dried in an oven at 110°C for 2 hours to obtain the activated material. S14 involves acid washing and purification of the activated material. The activated material is placed in an acid system for acid washing and purification. The acid system is a mixture of hydrochloric acid, hydrofluoric acid, and nitric acid, with a volume ratio of 10:0.2:0.1 for each acid. The mass ratio of the material to the volume of the acid is 1g:5mL. The acid washing conditions are: water bath heating at 80℃ and stirring at 400r / min for 4h. After acid washing, the material is washed with water until neutral and then dried in an oven at 110℃ for 2h to obtain the biomass-based precursor.

[0025] The S2 biomass precursor and resin precursor composite: The phenolic resin precursor and ethanol solution were mixed and stirred evenly in a 1:2 ratio to dissolve the precursor. The biomass-based precursor was placed in a tubular furnace reactor with the temperature stabilized at 40℃. Gaseous formaldehyde was first introduced, in which the volume fraction of formaldehyde in the mixture of formaldehyde and inert nitrogen was 1%, and the gas flow rate was controlled at 0.1 L / min. The gas was introduced for 1 hour to allow it to be adsorbed onto the internal surface of the biomass pores. Then, the biomass-based precursor was poured into the phenolic resin ethanol solution, with the resin accounting for 20%, and the mixture was gently heated at 60℃ for 2 hours.

[0026] Then it is placed in an atmosphere furnace for stepwise carbonization: Low-temperature pre-carbonization stage, heating rate 2℃ / min, 300℃, inert atmosphere, slow heating; During the intermediate-temperature pore-forming and polycondensation stages, the heating rate is 5℃ / min, reaching 400℃, and then switching to micro-volume... A gentle atmosphere is used to etch the carbon layer, controlling the closed-pore size and the degree of graphitization of the pore walls; the atmosphere is a nitrogen inert atmosphere as the carrier gas. The gas volume fraction is 1%, and the gas flow rate is 0.5 L / min; During the high-temperature stabilization stage, at 8℃ / min, 1100℃, under an inert atmosphere, the structure is finally stabilized, forming a highly disordered but locally ordered hard carbon structure.

[0027] Deposition and Coating of S3 Composite Material: Deposition and coating of the composite material can modify surface defects and further densify the structure. The composite material is placed in a vapor deposition apparatus and deposited and coated under nitrogen protection. The temperature is increased to 450°C at a heating rate of 5°C / min and held for 1 hour; then carbon source gas is introduced at a flow rate of 1 L / min for 0.5 hours; then the flow rate of carbon source gas is increased to 2 L / min for 1 hour; the carbon source gas is stopped, and the material is cooled to room temperature in the furnace under nitrogen protection to obtain the composite hard carbon anode material.

[0028] Example 2 Preparation of S1 biomass precursors: S11 The coconut shell biomass raw material is crushed to Dv50 of (7±1)μm, passed through a 200-mesh sieve, washed with deionized water, and dried in an oven at 110℃ for 2 hours. S12 is then subjected to sulfuric acid hydrolysis, with the hydrolysis conditions being water bath heating to 80℃, continuous stirring at 450 r / min for 5 h, sulfuric acid concentration of 1 mol / L, and a material mass to acid volume ratio of 1 g: 5 ml. Pre-carbonization is then performed, with the temperature increased at a rate of 2℃ / min to 300℃ and held for 1 h, then increased at a rate of 5℃ / min to 600℃ and held for 1 h, followed by furnace cooling to room temperature to obtain pre-carbonized material. The entire pre-carbonization process is carried out under a nitrogen protective atmosphere. After S13 carbonization, the material was activated with alkali using potassium hydroxide as the activating agent (30% potassium hydroxide added). Anhydrous ethanol was added and the mixture was ground evenly. The mixture was dried at 90°C for 6 hours to form a mixture. The mixture was placed in an atmosphere furnace and heated to 250°C at a rate of 2°C / min under a nitrogen inert gas atmosphere. The temperature was held for half an hour, then increased to 400°C at a rate of 6°C / min and held for half an hour. Finally, the temperature was increased to 650°C at a rate of 8°C / min and held for 2 hours to activate the material. After cooling, the material was washed with deionized water until neutral and then dried in an oven at 110°C for 2 hours to obtain the activated material. S14 is used to acid wash the activated material. The acid solution is a mixture of hydrochloric acid, hydrofluoric acid and nitric acid, with a volume ratio of 15:0.5:0.2 for each acid. The mass ratio of the material to the volume of the acid solution is 1g:5mL. The acid washing conditions are water bath heating at 80℃ and stirring at 450r / min for 5h. After acid washing, the material is washed with water until neutral and then dried in an oven at 110℃ for 2h to obtain the biomass-based precursor.

[0029] S2 Biomass Precursor and Resin Combination: Phenolic resin precursor and ethanol solution were mixed and stirred evenly in a 1:2 ratio to dissolve the precursor. The biomass-based precursor was placed in a tubular furnace reactor with a stable temperature of 50℃. Gaseous formaldehyde was first introduced, with a formaldehyde volume fraction of 2.5% in the formaldehyde and inert nitrogen mixture. The gas flow rate was controlled at 0.3 L / min, and the gas was introduced for 1.5 h to allow it to adsorb onto the internal surface of the biomass pores. Then, the biomass-based precursor was poured into the phenolic resin ethanol solution, with the resin accounting for 25%, and the mixture was gently heated at 60℃ for 3 h.

[0030] Then it is placed in an atmosphere furnace for stepwise carbonization: Low-temperature pre-carbonization stage, heating rate 3℃ / min, 350°C, inert atmosphere, slow heating; During the intermediate-temperature pore-forming and polycondensation stages, the heating rate is 8℃ / min, reaching 800℃, and then switching to micro-volume... A gentle atmosphere is used to etch the carbon layer, controlling the closed-pore size and the degree of graphitization of the pore walls; the atmosphere is a nitrogen inert atmosphere as the carrier gas. The gas volume fraction is 1%, and the gas flow rate is 0.5 L / min; During the high-temperature stabilization stage, at 5°C / min, 1100°C, under an inert atmosphere, the structure is finally stabilized, forming a highly disordered but locally ordered hard carbon structure.

[0031] Deposition and Coating of S3 Composite Material: Deposition and coating of the composite material can modify surface defects and further densify the structure. The composite material is placed in a vapor deposition apparatus and deposited and coated under nitrogen protection. The temperature is increased to 600℃ at a heating rate of 7℃ / min and held for 1 hour; then carbon source gas is introduced at a flow rate of 1L / min for 1 hour; then the flow rate of carbon source gas is increased to 2L / min for 1 hour; the carbon source gas is stopped, and the material is cooled to room temperature in the furnace under nitrogen protection to obtain the composite hard carbon anode material.

[0032] Example 3 Preparation of S1 biomass precursors: S11 crushes the straw biomass raw material to a Dv50 of (7±1)μm, passes it through a 200-mesh sieve, washes it with deionized water, and then dries it in an oven at 110℃ for 2 hours. S12 is then subjected to sulfuric acid hydrolysis, with the hydrolysis conditions being water bath heating to 80℃, continuous stirring at 500 r / min for 5 h, sulfuric acid concentration of 2 mol / L, and a material mass to acid volume ratio of 1 g: 5 ml. Pre-carbonization is then performed, with the temperature increased at a rate of 2℃ / min to 400℃ and held for 1 h, then increased at a rate of 5℃ / min to 650℃ and held for 2 h, followed by furnace cooling to room temperature to obtain pre-carbonized material. The entire pre-carbonization process is carried out under a nitrogen protective atmosphere. After S13 carbonization, the material was activated with alkali using potassium hydroxide as the activating agent (30% potassium hydroxide added). Anhydrous ethanol was added and the mixture was ground evenly. The mixture was dried at 90°C for 6 hours to form a mixture. The mixture was placed in an atmosphere furnace and heated to 250°C at a rate of 2°C / min under a nitrogen inert gas atmosphere. The temperature was held for half an hour, then increased to 500°C at a rate of 6°C / min and held for half an hour. Finally, the temperature was increased to 750°C at a rate of 8°C / min and held for 2 hours. After cooling, the material was washed with deionized water until neutral and dried to obtain the activated material. S14 is used to acid wash the activated material. The acid solution is a mixture of hydrochloric acid, hydrofluoric acid and nitric acid. The volume ratio of each acid in the acid solution is 30:3:1. The mass ratio of the material to the volume of the acid solution is 1g:5mL. The acid washing conditions are water bath heating at 80℃ and stirring at 450r / min for 5h. After acid washing, the material is washed with water until neutral and dried to obtain the biomass-based precursor.

[0033] S2 Biomass Precursor and Resin Combination: Phenolic resin precursor and ethanol solution were mixed and stirred evenly to dissolve the precursor. The biomass-based precursor was placed in a tubular furnace reactor with a stable temperature of 60℃. Gaseous formaldehyde was first introduced, with a formaldehyde volume fraction of 3% in the mixture of formaldehyde and inert nitrogen. The gas flow rate was controlled at 0.3 L / min, and the gas was introduced for 2 hours to allow it to be adsorbed onto the internal surface of the biomass pores. Then, the biomass-based precursor was poured into the phenolic resin ethanol solution, with the resin accounting for 25%, and the mixture was gently heated at 60℃ for 3 hours.

[0034] Then it is placed in an atmosphere furnace for stepwise carbonization: Low-temperature pre-carbonization stage, heating rate 3℃ / min, 350℃, inert atmosphere, slow heating; During the intermediate-temperature pore-forming and polycondensation stages, the heating rate is 5℃ / min, reaching 450℃, and then switching to micro-volume... A gentle atmosphere is used to etch the carbon layer, controlling the closed-pore size and the degree of graphitization of the pore walls; the atmosphere is a nitrogen inert atmosphere as the carrier gas. The gas volume fraction is 1%, and the gas flow rate is 0.5 L / min; During the high-temperature stabilization stage, at 6℃ / min, 1300℃, under an inert atmosphere, the structure is finally stabilized, forming a highly disordered but locally ordered hard carbon structure.

[0035] Deposition coating of S3 composite material: Deposition coating of composite materials can modify surface defects and further densify the structure. The composite material is placed in a vapor deposition apparatus and deposited under nitrogen protection. The temperature is raised to 600℃ at a rate of 7℃ / min and held for 1 hour; then, carbon source gas is introduced at a flow rate of 2L / min for 1 hour; the flow rate is then increased to 2L / min for 1.5 hours; finally, the carbon source gas is stopped, and the material is cooled to room temperature under nitrogen protection before being discharged to obtain the composite hard carbon anode material.

[0036] Example 4 Preparation of S1 biomass precursors: S11 The raw material of moso bamboo biomass, namely bamboo biomass raw material, is crushed to Dv50 of (7±1)μm and passed through a 200-mesh sieve. It is then washed with deionized water and dried in an oven at 110℃ for 2 hours to obtain a dried body. S12 involves sulfuric acid hydrolysis of the dried material. The hydrolysis conditions are: water bath heating to 80°C, continuous stirring at 400 rpm for 3 hours, sulfuric acid concentration of 1 mol / L, and a material mass to acid volume ratio of 1 g: 5 ml. Pre-carbonization is then performed. The pre-carbonization process involves heating at a rate of 2°C / min to 200°C and holding for 1 hour, then heating at a rate of 5°C / min to 600°C and holding for 1 hour, followed by furnace cooling to room temperature to obtain the pre-carbonized material. The entire pre-carbonization process is carried out under a nitrogen protective atmosphere. After pre-carbonization of S13, the material was activated with alkali using potassium hydroxide as the activating agent (20% potassium hydroxide was added). Anhydrous ethanol was added and the mixture was ground evenly. The mixture was dried at 90°C for 6 hours to form a mixture. The mixture was placed in an atmosphere furnace and heated to 150°C at 2°C / min under a nitrogen inert gas atmosphere. The temperature was held for half an hour, then increased to 300°C at 6°C / min and held for half an hour. Finally, the temperature was increased to 600°C at 6°C / min and held for 1 hour. After cooling, the material was washed with deionized water until neutral and then dried in an oven at 110°C for 2 hours to obtain the activated material. S14 involves acid washing and purification of the activated material. The activated material is placed in an acid system for acid washing and purification. The acid system is a mixture of hydrochloric acid, hydrofluoric acid, and nitric acid, with a volume ratio of 10:0.2:0.1 for each acid. The mass ratio of the material to the volume of the acid is 1g:5mL. The acid washing conditions are: water bath heating at 80℃ and stirring at 400r / min for 4h. After acid washing, the material is washed with water until neutral and then dried in an oven at 110℃ for 2h to obtain the biomass-based precursor.

[0037] The S2 biomass precursor and resin precursor composite: The phenolic resin precursor and ethanol solution were mixed and stirred evenly in a 1:2 ratio to dissolve the precursor. The biomass-based precursor was placed in a tubular furnace reactor with the temperature stabilized at 40℃. Gaseous formaldehyde was first introduced, in which the volume fraction of formaldehyde in the mixture of formaldehyde and inert nitrogen was 1%, and the gas flow rate was controlled at 0.1 L / min. The gas was introduced for 1 hour to allow it to be adsorbed onto the internal surface of the biomass pores. Then, the biomass-based precursor was poured into the phenolic resin ethanol solution, with the resin accounting for 30%, and the mixture was gently heated at 60℃ for 2 hours.

[0038] Then it is placed in an atmosphere furnace for stepwise carbonization: Low-temperature pre-carbonization stage, heating rate 2℃ / min, 300℃, inert atmosphere, slow heating; During the intermediate-temperature pore-forming and polycondensation stages, the heating rate is 5℃ / min, reaching 400℃, and then switching to micro-volume... A gentle atmosphere is used to etch the carbon layer, controlling the closed-pore size and the degree of graphitization of the pore walls; the atmosphere is a nitrogen inert atmosphere as the carrier gas. The gas volume fraction is 1%, and the gas flow rate is 0.5 L / min; During the high-temperature stabilization stage, at 5℃ / min, 800℃, under an inert atmosphere, the structure is finally stabilized, forming a highly disordered but locally ordered hard carbon structure.

[0039] Deposition and Coating of S3 Composite Material: Deposition and coating of the composite material can modify surface defects and further densify the structure. The composite material is placed in a vapor deposition apparatus and deposited and coated under nitrogen protection. The temperature is increased to 450°C at a heating rate of 5°C / min and held for 1 hour; then carbon source gas is introduced at a flow rate of 1 L / min for 0.5 hours; then the flow rate of carbon source gas is increased to 2 L / min for 1 hour; the carbon source gas is stopped, and the material is cooled to room temperature in the furnace under nitrogen protection to obtain the composite hard carbon anode material.

[0040] Example 5 Preparation of S1 biomass precursors: S11 The walnut shell biomass raw material was crushed to Dv50 of (7±1)μm and passed through a 200-mesh sieve. It was then washed with deionized water and dried in an oven at 110℃ for 2 hours to obtain a dried body. S12 involves sulfuric acid hydrolysis of the dried material. The hydrolysis conditions are: water bath heating to 80℃, continuous stirring at 460 r / min for 6 hours, sulfuric acid concentration of 3 mol / L, and a material mass to acid volume ratio of 1 g: 5 ml. Pre-carbonization is then performed. The pre-carbonization process involves heating at a rate of 5℃ / min to 450℃ and holding for 2 hours, then heating at a rate of 8℃ / min to 750℃ and holding for 1.5 hours, followed by furnace cooling to room temperature to obtain the pre-carbonized material. The entire pre-carbonization process is carried out under a nitrogen protective atmosphere. After pre-carbonization of S13, the material is activated with alkali using potassium hydroxide as the activating agent (50% of the material is added). Anhydrous ethanol is added and the mixture is ground evenly. The mixture is then dried at 90°C for 6 hours to form a mixture. The mixture is placed in an atmosphere furnace and heated to 300°C at 5°C / min under a nitrogen inert gas atmosphere. The temperature is held for half an hour, then increased to 600°C at 8°C / min and held for half an hour. Finally, the temperature is increased to 680°C at 8°C / min and held for 3 hours to activate the material. After cooling, the material is washed with deionized water until neutral and then dried in an oven at 110°C for 2 hours to obtain the activated material. S14 involves acid washing and purification of the activated material. The activated material is placed in an acid solution system for acid washing and purification. The acid solution system is a mixture of hydrochloric acid, hydrofluoric acid, and nitric acid, with a volume ratio of 20:5:2 for each acid. The mass ratio of the material to the volume of the acid solution is 1g:5mL. The acid washing conditions are: water bath heating at 80℃ and stirring at 500r / min for 8h. After acid washing, the material is washed with water until neutral and then dried in an oven at 110℃ for 2h to obtain the biomass-based precursor.

[0041] The S2 biomass precursor and resin precursor composite: The furan resin precursor and ethanol solution were mixed and stirred evenly in a 1:2 ratio to dissolve the precursor. The biomass-based precursor was placed in a tubular furnace reactor with the temperature stabilized at 40℃. Gaseous formaldehyde was first introduced, in which the volume fraction of formaldehyde in the mixture of formaldehyde and inert nitrogen was 5%, and the gas flow rate was controlled at 0.5 L / min. The gas was ventilated for 3 hours to allow it to be adsorbed onto the internal surface of the biomass pores. Then, the biomass-based precursor was poured into the furan resin ethanol solution, with the resin accounting for 40%, and the reaction was carried out under gentle heating at 60℃ for 6 hours.

[0042] Then it is placed in an atmosphere furnace for stepwise carbonization: Low-temperature pre-carbonization stage, heating rate 5℃ / min, 400℃, inert atmosphere, slow heating; During the intermediate-temperature pore-forming and polycondensation stages, the heating rate is 8℃ / min, reaching 500℃, and then switching to micro-volume... A gentle atmosphere is used to etch the carbon layer, controlling the closed-pore size and the degree of graphitization of the pore walls; the atmosphere is a nitrogen inert atmosphere as the carrier gas. The gas volume fraction is 1%, and the gas flow rate is 0.5 L / min; During the high-temperature stabilization stage, at 10℃ / min, 800℃, under an inert atmosphere, the structure is finally stabilized, forming a highly disordered but locally ordered hard carbon structure.

[0043] Deposition and Coating of S3 Composite Material: Deposition and coating of the composite material can modify surface defects and further densify the structure. The composite material is placed in a vapor deposition apparatus and deposited and coated under nitrogen protection. The temperature is raised to 650℃ at a heating rate of 10℃ / min and held for 1 hour; then carbon source gas is introduced at a flow rate of 1.5L / min for 5 hours; the flow rate of carbon source gas is then increased to 5L / min for 5 hours; the carbon source gas is then stopped, and the material is cooled to room temperature in the furnace under nitrogen protection to obtain the composite hard carbon anode material.

[0044] Example 6 Preparation of S1 biomass precursors: S11 The walnut shell biomass raw material was crushed to Dv50 of (7±1)μm and passed through a 200-mesh sieve. It was then washed with deionized water and dried in an oven at 110℃ for 2 hours to obtain a dried body. S12 involves sulfuric acid hydrolysis of the dried material. The hydrolysis conditions are: water bath heating to 80℃, continuous stirring at 460 r / min for 6 hours, sulfuric acid concentration of 3 mol / L, and a material mass to acid volume ratio of 1 g: 5 ml. Pre-carbonization is then performed. The pre-carbonization process involves heating at a rate of 3℃ / min to 450℃ and holding for 1.5 hours, then heating at a rate of 6℃ / min to 750℃ and holding for 1.5 hours, followed by furnace cooling to room temperature to obtain the pre-carbonized material. The entire pre-carbonization process is carried out under a nitrogen protective atmosphere. After pre-carbonization of S13, the material is activated with alkali using potassium hydroxide as the activating agent (40% potassium hydroxide added). Anhydrous ethanol is added and the mixture is ground evenly. The mixture is dried at 90°C for 6 hours to form a mixture. The mixture is placed in an atmosphere furnace and heated to 300°C at 3°C / min under a nitrogen inert gas atmosphere. The temperature is held for half an hour, then increased to 600°C at 7°C / min and held for half an hour. Finally, the temperature is increased to 680°C at 7°C / min and held for 3 hours to activate the material. After cooling, the material is washed with deionized water until neutral and then dried in an oven at 110°C for 2 hours to obtain the activated material. S14 involves acid washing and purification of the activated material. The activated material is placed in an acid solution system for acid washing and purification. The acid solution system is a mixture of hydrochloric acid, hydrofluoric acid, and nitric acid, with a volume ratio of 20:5:2 for each acid. The mass ratio of the material to the volume of the acid solution is 1g:5mL. The acid washing conditions are: water bath heating at 80℃ and stirring at 500r / min for 8h. After acid washing, the material is washed with water until neutral and then dried in an oven at 110℃ for 2h to obtain the biomass-based precursor.

[0045] The S2 biomass precursor and resin precursor composite: Epoxy resin and lignin-based phenolic resin precursors are mixed with ethanol solution in a 1:2 ratio and stirred until dissolved. The biomass-based precursor is placed in a tubular furnace reactor with a stable temperature of 40℃. Gaseous formaldehyde is first introduced, wherein the volume fraction of formaldehyde in the mixture of formaldehyde and inert nitrogen is 5%, and the gas flow rate is controlled at 0.5L / min. The gas is ventilated for 3 hours to allow it to be adsorbed onto the internal surface of the biomass pores. Then, the biomass-based precursor is poured into the epoxy resin-lignin-based phenolic resin ethanol solution, with the resin accounting for 35%, and the reaction is carried out under gentle heating at 60℃ for 6 hours.

[0046] Then it is placed in an atmosphere furnace for stepwise carbonization: Low-temperature pre-carbonization stage, heating rate 5℃ / min, 400℃, inert atmosphere, slow heating; During the intermediate-temperature pore-forming and polycondensation stages, the heating rate is 8℃ / min, reaching 500℃, and then switching to micro-volume... A gentle atmosphere is used to etch the carbon layer, controlling the closed-pore size and the degree of graphitization of the pore walls; the atmosphere is a nitrogen inert atmosphere as the carrier gas. The gas volume fraction is 1%, and the gas flow rate is 0.5 L / min; During the high-temperature stabilization stage, at 10℃ / min, 800℃, under an inert atmosphere, the structure is finally stabilized, forming a highly disordered but locally ordered hard carbon structure.

[0047] Deposition and Coating of S3 Composite Material: Deposition and coating of the composite material can modify surface defects and further densify the structure. The composite material is placed in a vapor deposition apparatus and deposited and coated under nitrogen protection. The temperature is increased to 650℃ at a heating rate of 10℃ / min and held for 1 hour; then carbon source gas is introduced at a flow rate of 1.5L / min for 3 hours; then the flow rate of carbon source gas is increased to 5L / min for 5 hours; the carbon source gas is stopped, and the material is cooled to room temperature in the furnace under nitrogen protection to obtain the composite hard carbon anode material.

[0048] Comparative Example 1 Unlike Example 1, the biomass-based raw materials in step S1 do not undergo a hydrolysis process.

[0049] Comparative Example 2 Unlike Example 1, instead of using resin for compounding, the biomass precursor obtained in step S1 is directly coated in step S3.

[0050] Comparative Example 3 Unlike Example 1, the surface coating modification treatment in step (3) is not performed.

[0051] To further verify the effectiveness of the present invention, the inventors conducted a series of verification experiments, some of which are excerpted below.

[0052] 1 SEM test The composite biomass hard carbon anode materials prepared in Example 1 and Comparative Example 2 were subjected to SEM testing, and the results are as follows: Figure 1 , Figure 2 As shown. From Figure 1 It can be seen that the composite biomass hard carbon anode materials prepared in Example 1 all exhibit a uniform granular structure with a uniform size distribution and no obvious pores.

[0053] 2. Pore size distribution test The pore size distribution of Examples 1-2 and Comparative Examples 1-2 was tested using the nitrogen adsorption-desorption method. The nitrogen adsorption-desorption method determines the specific surface area and pore size distribution of hard carbon material samples by analyzing the curve of nitrogen adsorption as a function of pressure at liquid nitrogen temperature. The samples were pretreated by vacuum degassing, and nitrogen adsorption and desorption experiments were conducted at low temperature. The pore size distribution was calculated from the desorption curves using methods such as BJH. The pore size distribution data for Examples 1-2 and Comparative Examples 1-2 are shown in Table 1.

[0054] .

[0055] As can be seen from Table 1, Comparative Example 2 is mainly dominated by micropores, which makes the SEI film overgrowth prone to capacity decay in the later stage; Examples 1 and 2 are dominated by mesopores / macropores, which can make the SEI film more stable. At the same time, the buffering effect of mesopores can also alleviate volume changes and the cycle decay rate is lower. Among them, Example 1 can contribute the most to cycle stability.

[0056] 3. Charge-discharge cycle performance test The composite hard carbon anode materials obtained in Examples 1-4 and Comparative Examples 1-3 were subjected to electrical performance tests. The test method was as follows: hard carbon anode material, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in an 8:1:1 ratio and then uniformly mixed in N-methylpyrrolidone (NMP). The mixture was coated onto copper foil and dried in a vacuum drying oven at 110°C for 3 hours. The resulting material was then sliced ​​to obtain a sodium-ion battery anode sheet. Using a sodium sheet as the counter electrode, the anode sheet and sodium sheet were assembled into a CR2032 button cell in an argon-filled glove box. The battery was then tested using a Blue Battery Tester with a charge / discharge voltage range of 0.005V to 2.0V and a charge / discharge rate of 0.1C. The cycle performance of the button cell (0.1C, 100 cycles) was tested, with the initial efficiency calculated as (initial charge specific capacity / initial discharge specific capacity) * 100%.

[0057] The test data results are shown in Table 2.

[0058] .

[0059] The following conclusions can be drawn from the electrical performance test results in Table 2: (1) Example 1 is the most effective example in this invention, with a first charge specific capacity of 342.0 mAh / g and a first coulombic efficiency of 94.5%; (2) Comparative Example 1 did not hydrolyze the biomass-based raw materials, and its initial charge specific capacity was 312.6 mAh / g and initial coulombic efficiency was 87.6%; Comparative Example 2 did not use resin for composite reaction, and its initial charge specific capacity was 305.2 mAh / g and initial coulombic efficiency was 88.4%; Comparative Example 3 did not perform carbon coating deposition modification on the surface, and its initial charge specific capacity was 320.4 mAh / g and initial coulombic efficiency was 89.5%; Through performance test results, it was found that, compared with the examples, the three comparative examples showed that hydrolyzing the biomass-based precursor raw materials, using resin for composite reaction, and then modifying the surface of the composite material can effectively improve the performance of the material.

[0060] From the composite hard carbon anode materials prepared in Comparative Examples 1 and 2 and Examples 1-4, the initial charge specific capacity, initial efficiency, and cycle performance of the materials were significantly improved. This is mainly due to the synergistic effect of the composite resin-based reuse coating deposition process after hydrolysis of biomass raw materials. The effect mainly comes from: (1) Sulfuric acid hydrolysis of biomass raw materials can regulate the chemical composition of the raw materials, mainly by reducing the proportion of hemicellulose, thereby effectively controlling the number of closed pores in the microstructure of carbonization products. As shown in Table 1, this process is beneficial to increase the defect concentration of the material, increase the active sites for sodium storage, and thus improve the specific capacity of the material. (2) By introducing sulfide monomers through resin-based composites, as can be seen from the comparison of pore size data between the examples and comparative examples in Table 1, the pore size distribution can be positioned and controlled. Through the coordinated effect of the composite of biomass-based natural material structure and resin-based stable chemical structure, the dense coating layer or three-dimensional cross-linked network formed can strengthen the fragile skeleton of biomass carbon and effectively buffer stress changes during charging and discharging, thereby improving the cycle performance of the material. (3) Finally, a uniform coating layer is formed on the surface of the material. The coating layer can close some micropores, thereby reducing the specific surface area of ​​the material, reducing the side reactions between the material and the electrolyte, and forming a stable SEI film, improving the initial coulombic efficiency and long-term cycle stability of the material.

[0061] In summary, this invention pre-treats biomass raw materials, including crushing, hydrolysis, pre-carbonization, alkali activation, and acid washing, to obtain a biomass-based precursor. Using biomass as a raw material ensures resource sustainability, wide availability, and low cost. Secondly, the biomass precursor serves as a carrier, incorporating resin for composite processing. While resin, as a chemical substance, offers tunability, its high cost hinders large-scale use. Direct composite utilization reduces material costs while precisely utilizing its structural stability. Thirdly, surface modification of the composite material using deposition coating enhances its density, improving cycle stability and energy density. Simultaneously, the generated acid and alkali wastewater can be neutralized, reducing environmental harm from wastewater treatment. This invention possesses advantages of being green, environmentally friendly, and cost-effective, making it valuable for industrialization.

[0062] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a composite biomass hard carbon anode material, characterized in that, Includes the following steps: Preparation of S1 biomass-based precursor: S11 The biomass raw material is crushed to Dv50 of 7±1μm, passed through a 200-mesh sieve, washed with deionized water, and dried in an oven at 110℃ for 2 hours to obtain the dried body; S12 hydrolyzes the dried body, places the dried body in sulfuric acid solution, heats it in a water bath to 80℃, stirs it continuously at 400-500r / min for 3-6h, after hydrolysis, washes it with deionized water until neutral, and dries it in an oven at 110℃ for 2h, and then pre-carbonizes it at low temperature to obtain pre-carbonized material. S13 involves alkaline activation of the pre-carbonized material, mixing the pre-carbonized material with an alkaline chemical reagent, adding anhydrous ethanol and grinding evenly, then heating the mixture, cooling it, washing it with deionized water until neutral, and then drying it in an oven at 110°C for 2 hours to obtain the activated material. S14 The activated material is subjected to acid washing and purification treatment. The activated material is placed in an acid solution system for acid washing and purification treatment to reduce the ash content of the material and obtain a purified product. After washing with deionized water until neutral, it is dried in an oven at 110°C for 2 hours to obtain a biomass-based precursor. S2 Biomass-based precursor and resin precursor composite: The biomass-based precursor is placed in a tubular furnace reactor, and gaseous formaldehyde is introduced for adsorption. Then, the resin precursor is dissolved in an ethanol solution. The biomass-based precursor is then poured into the resin ethanol solution, where the resin accounts for 20-40%. The mixture is uniformly mixed and reacted with the biomass-based precursor. The mixture is then placed in an atmosphere furnace for stepwise carbonization to obtain a primary composite hard carbon precursor. Deposition and coating of S3 composite material: The primary composite hard carbon precursor obtained from S2 is deposited and coated to obtain composite biomass hard carbon anode material.

2. The preparation method of the composite biomass hard carbon anode material according to claim 1, characterized in that, The biomass raw materials mentioned in S1 include at least one of coconut shells, bamboo, straw, walnut shells, etc., and the concentration of the sulfuric acid solution is 1-3 mol / L, with the ratio of dry mass to sulfuric acid solution volume being 1 g: 5 ml.

3. The preparation method of the composite biomass hard carbon anode material according to claim 1, characterized in that, The low-temperature pre-carbonization described in S12 involves heating at a rate of 2-5℃ / min to 200-450℃ and holding for 1-2 hours, then heating at a rate of 5-8℃ / min to 600-750℃ and holding for 1-2 hours, followed by cooling in the furnace to room temperature to obtain the pre-carbonized material. The low-temperature pre-carbonization process is carried out under a nitrogen protective atmosphere.

4. The preparation method of the composite biomass hard carbon anode material according to claim 1, characterized in that, The alkaline chemical reagent mentioned in S13 is potassium hydroxide, with an addition amount of 20-50%. Anhydrous ethanol is added and the mixture is ground evenly. The mixture is dried at 90°C for 6 hours to form a mixture. The mixture is placed in an atmosphere furnace and heated to 150-300°C at a rate of 2-5°C / min under a nitrogen inert gas atmosphere. The temperature is held for half an hour, then increased to 300-600°C at a rate of 6-8°C / min and held for half an hour. Finally, the temperature is increased to 600-750°C at a rate of 6-8°C / min and held for 1-3 hours to activate the material. After cooling, the material is washed with deionized water until neutral and then dried in an oven at 110°C for 2 hours to obtain the activated material.

5. The preparation method of the composite biomass hard carbon anode material according to claim 1, characterized in that, The acid system described in S14 is a mixture of hydrochloric acid, hydrofluoric acid, and nitric acid, with a volume ratio of 10-30. The ratio of activated material mass to acid solution volume is 1g:5mL. The reaction is carried out at 80℃ in a water bath with a stirring rate of 400-500r / min for 4-8h. Acid washing and purification are performed to reduce the ash content of the material and obtain the purified product. After washing with deionized water until neutral, the product is dried in an oven at 110℃ for 2h to obtain the biomass-based precursor.

6. The method for preparing the composite biomass hard carbon anode material according to claim 1, characterized in that, The resin precursor mentioned in S2 includes at least one of phenolic resin, furan resin, epoxy resin, and lignin-based phenolic resin.

7. The preparation method of the composite biomass hard carbon anode material according to claim 1, characterized in that, The composite of the S2 biomass-based precursor and the resin precursor is specifically carried out by placing the biomass-based precursor in a tubular furnace reactor at a temperature of 40-60℃, introducing gaseous formaldehyde, wherein the volume fraction of formaldehyde in the mixed gas is 1%-5%, the gas flow rate is controlled between 0.1-0.5L / min, and aeration is carried out for 1-3 hours to allow it to be adsorbed onto the internal surface of the pores of the biomass-based precursor; the resin precursor and ethanol solution are mixed and stirred evenly in a 1:2 ratio, and then the biomass-based precursor is poured into the resin ethanol solution and gently heated at 60℃ for 2-6 hours.

8. The method for preparing the composite biomass hard carbon anode material according to claim 1, characterized in that, The stepwise carbonization in the atmosphere furnace described in S2 includes: In the low-temperature pre-carbonization stage, the temperature is increased to 300-400℃ at a heating rate of 2-5℃ / min, and pre-carbonization is carried out in a nitrogen inert atmosphere. During the intermediate-temperature pore-forming and polycondensation stage, the temperature is increased to 400-800℃ at a rate of 5-8℃ / min, and then switched. or The atmosphere is used to etch the carbon layer, controlling the closed-pore size and the degree of graphitization of the pore walls; the atmosphere is a nitrogen inert atmosphere as the carrier gas. or The gas volume fraction is 1%, and the gas flow rate is 0.5 L / min; In the high-temperature stabilization stage, the temperature is increased to 800-1300℃ at a heating rate of 5-10℃ / min, and carbonized in a nitrogen inert atmosphere to finally solidify and obtain the primary composite hard carbon precursor.

9. The method for preparing the composite biomass hard carbon anode material according to claim 1, characterized in that, The deposition coating process described in S3 involves placing the obtained primary composite hard carbon precursor in a CVD vapor deposition apparatus and performing deposition coating under nitrogen protection. The temperature is increased to 450-650℃ at a heating rate of 5℃-10℃ / min and held for 1 hour. Then, carbon source gas is introduced at a flow rate of 1L / min-2L / min for 0.5-5 hours. The flow rate of carbon source gas is then increased to 2L / min-5L / min for 1-5 hours. Finally, the carbon source gas is stopped, and the material is cooled to room temperature under nitrogen protection to obtain the composite hard carbon anode material. The carbon source gas is methane.

10. A composite biomass hard carbon anode material, characterized in that, The negative electrode material is prepared by the method described in any one of claims 1-9.

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