A low-cost, high-performance biomass-based sodium ion hard carbon anode material

Abstract

The present application relates to the field of sodium-ion battery materials, and more specifically, to a low-cost, high-performance biomass-based sodium-ion hard carbon negative electrode material. A low-cost, high-performance biomass-based sodium-ion hard carbon negative electrode material, the preparation method of which comprises: biomass pretreatment: washing, drying, crushing, and screening the biomass material to obtain a precursor powder; precursor pretreatment: pretreating the obtained precursor powder, wherein the pretreatment includes one or more combined treatments of low-temperature pyrolysis, low-temperature pre-oxidation, and hydrothermal pre-oxidation to obtain a hard carbon precursor; cleaning and purification: washing and drying the pretreated sample; high-temperature calcination: mixing the treated sample and graphite phase g-C3N4 at a mass ratio of 1:(1-3), introducing protective gas, heating at a rate of 0.5-10°C / min to the final temperature, reacting at a constant temperature for 0.5-8h, and cooling to room temperature at a rate of 0.1-10°C / min; acid washing and drying: acid washing the sample and drying it to obtain the hard carbon negative electrode material. The present application discloses a low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material with good sodium storage performance, higher reversible specific capacity and first coulombic efficiency, showing excellent reversible sodium storage capacity. While reducing costs, it does not lead to a decrease in the performance of the graphite negative electrode material, and can still maintain the excellent performance of the hard carbon negative electrode material.

Description

Technical Field

[0001] The present application relates to the field of sodium ion battery materials, and more specifically, to a low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material. Background Art

[0002] Electrochemical energy storage systems, represented by lithium-ion batteries, are widely used in the energy storage field due to their advantages such as high energy density and high efficiency. With the continuous advancement of technology, lithium-ion batteries are widely used in electronic digital consumer batteries and electric vehicle power batteries. However, the limited reserves and uneven distribution of lithium have led to high costs in the energy storage field, which cannot meet the needs of future large-scale applications. The next generation of energy storage battery systems needs to be resource-rich, low-cost, environmentally friendly, and have electrochemical properties similar to those of lithium. Sodium and lithium belong to the same element family and have similar physical and chemical properties to lithium. Sodium is abundant and environmentally friendly, while also being low-cost. In addition, sodium ions have more stable electrochemical properties and safety performance.

[0003] Graphite, the negative electrode material for lithium-ion batteries, has a layered structure that allows lithium ions to intercalate into the graphite layers. However, the ionic radius of sodium ions (r = 0.113 nm) is at least 35% larger than that of lithium ions (r = 0.076 nm), making sodium ions relatively stable in the rigid lattice. Regular graphite structures and high-temperature graphitized carbon mesophase microspheres have almost no sodium intercalation capacity. The emergence of hard carbon materials has solved this key problem. Hard carbon materials have the advantages of abundant sources and simple preparation. However, problems such as low initial coulombic efficiency and insufficient capacity of hard carbon materials lead to low energy density of sodium-ion batteries, limiting the development of hard carbon anodes. At the same time, because the sodium storage mechanism of hard carbon is still unclear and the structural control methods of hard carbon are not targeted, improving the performance of hard carbon is particularly difficult. In addition, although the source of hard carbon is abundant, its cost increases significantly after multiple processing. Summary of the Invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the present application provides a low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material and a preparation method thereof.

[0005] In the first aspect, the present application provides a low-cost, high-performance biomass-based sodium ion hard carbon anode material, which adopts the following technical solutions:

[0006] A low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material, wherein the preparation method of the hard carbon negative electrode material comprises:

[0007] (1) Biomass pretreatment: The biomass material is cleaned, dried, crushed, and sieved to obtain a precursor powder;

[0008] (2) Precursor pretreatment: Pretreating the precursor powder obtained in (1), wherein the pretreatment includes one or more combined treatments selected from low-temperature pyrolysis, low-temperature pre-oxidation, and hydrothermal pre-oxidation to obtain a hard carbon precursor;

[0009] (3) Cleaning and purification: cleaning and drying the pretreated samples;

[0010] (4) High-temperature calcination: The sample treated in (3) and the graphite phase g-C3N4 were mixed uniformly at a mass ratio of 1:(1-3), and then a protective gas was introduced. The temperature was raised to the final temperature at a rate of 0.5-10°C / min, and the reaction was kept at a constant temperature for 0.5-8h, and then the temperature was lowered to room temperature at a rate of 0.1-10°C / min;

[0011] (5) Pickling and drying: The above sample is pickled and dried to obtain a hard carbon negative electrode material.

[0012] By adopting the above technical solution, hard carbon materials are prepared using biomass as a precursor. By pretreating the cheap and easily available biomass materials, impurities can be effectively removed and the particle size range of the precursor powder can be controlled to improve the consistency of the performance of biomass-derived hard carbon materials. Then, by limiting the combined steps of the precursor pretreatment, the organic matter in the biomass material reacts to produce a large amount of coal tar and other impurities. The pre-oxidation treatment can introduce oxygen-containing functional groups and other components into the biomass material, so that the pore structure and chemical environment are changed, and the basis for forming a material with rich pseudo-graphite layer microcrystalline domains and amorphous non-crystalline domains is improved to form a hard carbon precursor. Then, by washing, the residual impurities are removed to improve the purity. Subsequently, the graphite phase g-C3N4 is added in proportion. The stable network structure can be used as a template to guide the graphitization of hard carbon under high-temperature calcination, forming a pseudo-graphite layer and expanding the interlayer spacing, while forming rich pores. It also reduces defects and impurity functional groups, improves the degree of graphitization, and further improves the sodium storage capacity of hard carbon. The stable structure is conducive to the free movement of sodium ions between layers, and is more conducive to the embedding / de-embedding of sodium ions, making the energy density of the hard carbon material higher and enhancing the rate performance; adjusting the heating rate can effectively regulate the ratio of open and closed pores, thereby significantly improving the electrochemical performance of the sodium ion hard carbon negative electrode material. The electrochemical performance of the material within the mass ratio range of the treated sample and the graphite phase g-C3N4 of the present application is optimal. This may be because too little graphite phase g-C3N4 cannot fully guide calcination and provide a stable network structure, which is not conducive to the embedding / de-embedding of sodium ions. Too much graphite phase g-C3N4 leads to excessive hardness of the material, poor modifiable processability, and a relatively concentrated pore size distribution range, which is not conducive to the migration and diffusion of sodium ions, affecting the reversible embedding / de-embedding of sodium ions.

[0013] In a specific embodiment, the hard carbon negative electrode material is an active negative electrode material having a large number of pseudo-graphite microcrystalline domains and amorphous non-crystalline domains.

[0014] The active negative electrode material forms a pseudo-graphite layer, which contains not only crystalline domains but also amorphous domains, and is accompanied by abundant edges, defects, and pores, and contains a large number of saturated carbon-carbon bonds, aromatic rings, or combinations thereof. Therefore, the microcrystalline domains with high arrangement and molecular order can be surrounded by less arranged and looser amorphous non-crystalline domains, making the pseudo-graphite layer of the sodium ion battery negative electrode material present short-range order and long-range disorder, and the presence of a large number of micropores. Further optimization of the internal pore size and improvement of the pore modifiability can regulate and improve the composition and structure of the derived hard carbon, increase the sodium storage capacity of the hard carbon, increase the disorder of the hard carbon, and improve the reversible sodium storage capacity, which can reduce the irreversible adsorption of sodium ions, making the sodium ions enter and exit faster, and significantly improving the electrochemical performance.

[0015] In a specific embodiment, the biomass material in (1) is sunflower seed hulls.

[0016] By adopting the above technical solution, the hard carbon negative electrode material for sodium ion batteries is prepared using cheap and easily available sunflower seed shell biomass as raw material. Compared with other biomass materials, the impurity content is lower and no complicated impurity removal process is required. Secondly, compared with other biomass materials, the sunflower seed shell can obtain a suitable specific surface area and more pores through pretreatment and high-temperature calcination process. The pore size distribution is larger, and the mesopores are conducive to the migration and diffusion of sodium ions. The micropores provide sodium storage sites for reversible insertion / extraction of sodium ions.

[0017] In a specific embodiment, the hydrothermal pre-oxidation in (2) is to add 0.5-5 wt% hydrogen peroxide solution, disperse (5-8) g of precursor powder per 100 ml of hydrogen peroxide solution, and conduct a constant temperature hydrothermal reaction at a temperature of 100-200° C. for 12-24 hours.

[0018] By adopting the above technical solution, hydrothermal pre-oxidation can increase the overall porosity and specific surface area of the material, providing more sites for sodium ion storage and reducing the ion diffusion barrier, allowing for faster sodium ion infiltration and extraction, thereby enhancing the reversible specific capacity and rate performance. The hydrothermal oxidation temperature can control the degree of pre-oxidation of the biomass precursor. Excessive temperatures increase the material's porosity and specific surface area, affecting the sodium ion infiltration and extraction rate, while too low temperatures hinder the embedding of sodium ions.

[0019] In a specific embodiment, the low-temperature cracking in (2) is carried out under a protective atmosphere at a heating rate of 0.5-10°C / min to 500-800°C, reacting at a constant temperature for 0.5-8h, and then cooling to room temperature at a cooling rate of 0.1-10°C / min.

[0020] In a specific embodiment, the protective atmosphere is at least one of argon and nitrogen, and the gas flow rate is 10-100 mL / min.

[0021] Preferably, the pretreatment is hydrothermal pre-oxidation followed by low-temperature cracking to obtain a hard carbon precursor;

[0022] In view of the large amount of cellulose and lignin in sunflower seed shells, hydrothermal pre-oxidation is first used to break the intramolecular hydrogen bonds, thereby forming short carbon rings, which are the basis for the material to have advantages such as high specific surface area and pore structure, and enhance sodium ion energy storage. During this process, hydrogen peroxide solution is added to oxidize the cellulose and other substances in the sunflower seed shells, making the hydrothermal oxidation reaction more thorough, with a higher oxygen content, forming more sodium storage sites, and enhancing sodium storage performance. In addition, oxygen-containing functional groups can make the graphite phase g-C3N4 produce more electron holes, optimize the structure of the precursor, and increase the sodium storage capacity of hard carbon. Subsequent low-temperature pyrolysis removes impurities such as coal tar, improving the thermal efficiency of carbonization and product quality. The applicant found that the hydrothermal pre-oxidation followed by low-temperature pyrolysis treatment has better material performance than either hydrothermal pre-oxidation or low-temperature pyrolysis alone. This may be because the two-step pre-treatment further regulates the particle size of the precursor powder within an appropriate range, improves the consistency of the performance of the biomass-derived hard carbon material, and forms a material with richer pseudo-graphite layer microcrystalline domains and amorphous non-crystalline domains. The cracking temperature environment can regulate the structural morphology, crystal structure, amorphous structure, and carbon layer spacing of the obtained hard carbon material. If the temperature is too high, the hard carbon material will be over-carbonized, the pore size distribution of the hard carbon material will be too large, and the layer spacing will expand, which is not conducive to the embedding of sodium ions, thereby affecting the sodium storage performance. If the temperature is too low, the carbonization effect is poor, which affects the high-temperature calcination process, reduces the hard carbon sodium storage capacity of the hard carbon negative electrode material, and thus affects its electrochemical performance.

[0023] In a specific embodiment, the cleaning in (3) includes one or more of acid cleaning, 60-80° C. alkaline solution immersion cleaning and water cleaning.

[0024] Preferably, the sample is first washed with 2 wt % hydrochloric acid, then immersed in 5 mol / L potassium hydroxide solution heated to 70° C. for washing, with the solid-liquid ratio of the sample to the alkali solution being 1:15 g / mL, and finally washed with water 2-3 times.

[0025] Preferably, the drying in (3) comprises freeze drying at a temperature of -50-45°C for 9-11 hours.

[0026] By adopting the above technical solution, soluble ionic impurities such as natural organic matter in sunflower seed shells are removed by acid washing, and insoluble impurities such as oil impurities are removed by alkaline soaking to prevent pore blockage. The residual water molecules after washing are then quickly freeze-dried at low temperature to remove the water molecules, and there is still a certain pore-forming effect at the original position, further improving the electrochemical performance.

[0027] In a specific embodiment, the low-temperature pre-oxidation in (2) is to heat the temperature to 200-300°C at a rate of 0.5-10°C / min, react at a constant temperature for 0.5-8h, and then cool the temperature to room temperature at a rate of 0.1-10°C / min.

[0028] By adopting the above technical solution, oxygen-containing functional groups can be introduced through pre-oxidation treatment, thereby increasing the disorder of hard carbon and improving the reversible sodium storage capacity.

[0029] In a specific embodiment, the final temperature in (4) is 1100-1600°C.

[0030] By adopting the above technical solution, the temperature range can ensure that the degree of graphitization of the hard carbon anode material is within a certain range, forming an appropriate pseudo-graphite interlayer spacing, which is conducive to hard carbon graphitization, reducing the pseudo-graphite interlayer spacing, and improving the hard carbon low-voltage platform capacity and first coulombic efficiency. However, if the temperature is too high, the interlayer spacing will be too small, which is not conducive to sodium ion intercalation and embedding, and the hard carbon sodium storage capacity will decrease. If the temperature is too low, the degree of graphitization is low, which is not conducive to the stable embedding of sodium ions, affecting the capacity and first coulombic efficiency of the hard carbon anode material.

[0031] In a specific embodiment, the protective gas is at least one of argon and nitrogen, and the gas flow rate is 30-100 mL / min.

[0032] In summary, this application has the following beneficial effects:

[0033] 1. Prepare hard carbon materials using biomass as a precursor. By pretreating cheap and readily available biomass materials, impurities can be effectively removed and the particle size range of the precursor powder can be controlled to improve the consistency of the performance of biomass-derived hard carbon materials. Then, by limiting the combined steps of the precursor pretreatment, the organic matter in the biomass material reacts to produce a large amount of coal tar and other impurities. The pre-oxidation treatment can introduce oxygen-containing functional groups and other components into the biomass material, thereby changing the pore structure and chemical environment, and improving the basis for forming a material with rich pseudo-graphite layer microcrystalline domains and amorphous non-crystalline domains, forming a hard carbon precursor. Then, by washing, the remaining impurities are removed to improve the purity. Subsequently, the graphite phase g-C3N4 is added in proportion to stabilize the network. The g-C3N4-like structure can serve as a template to guide the graphitization of hard carbon under high-temperature calcination, forming pseudo-graphite layers and expanding the interlayer spacing, while forming rich pores and reducing defects and impurity functional groups, thereby improving the degree of graphitization and further improving the sodium storage capacity of hard carbon. The stable structure is conducive to the free movement of sodium ions between layers and is more conducive to the embedding / ejection of sodium ions, making the hard carbon material have a higher energy density and enhanced rate performance; adjusting the heating rate can effectively control the ratio of open and closed pores, thereby significantly improving the electrochemical performance of sodium ion hard carbon negative electrode materials. Excessive graphite phase g-C3N4 will lead to excessive hardness of the material, poor modifiable processability, and a relatively concentrated pore size distribution range, which is not conducive to the migration and diffusion of sodium ions and affects the reversible embedding / ejection of sodium ions.

[0034] 2. Pseudo-graphite layers are formed by high-temperature calcination. In addition to crystalline domains, they also contain amorphous domains, accompanied by abundant edges, defects, and pores, and contain a large number of saturated carbon-carbon bonds, aromatic rings, or combinations thereof. Therefore, microcrystalline domains with high arrangement and molecular order can be surrounded by less arranged and looser amorphous non-crystalline domains, making the pseudo-graphite layers of the sodium-ion battery negative electrode material present short-range order and long-range disorder, and the presence of a large number of micropores. Further optimization of the internal pore size and improvement of the pore modifiability can regulate and improve the composition and structure of the derived hard carbon, increase the sodium storage capacity of the hard carbon, increase the disorder of the hard carbon, and improve the reversible sodium storage capacity, which can reduce the irreversible adsorption of sodium ions, making the sodium ions enter and exit faster, and significantly improving the electrochemical performance.

[0035] 3. For the cellulose and lignin in sunflower seed shells, hydrothermal pre-oxidation is first used to break the hydrogen bonds in the molecules, thereby forming short carbon rings, which are the basis for the material to have advantages such as high specific surface area and pore structure, and enhance the sodium ion energy storage. In this process, hydrogen peroxide solution is added to oxidize the cellulose in the sunflower seed shells, making the hydrothermal oxidation reaction more thorough, the oxygen content higher, and the formation of more sodium storage sites, thereby enhancing the sodium storage performance. In addition, the oxygen-containing functional groups can make the graphite phase g-C3N4 produce more electron holes, optimizing the adjustment of the precursor. structure, improving the sodium storage capacity of hard carbon; and then removing impurities such as coal tar through subsequent low-temperature cracking to improve the thermal efficiency of carbonization and product quality. The cracking temperature environment can regulate the structural morphology, crystal, amorphous structure, and carbon layer spacing of the obtained hard carbon material. If the temperature is too high, the hard carbon material will be over-carbonized, resulting in an excessively large pore size distribution and an enlarged interlayer spacing, which is not conducive to the embedding of sodium ions, thereby affecting the sodium storage performance. If the temperature is too low, the carbonization effect is poor, which affects the high-temperature calcination process, resulting in a smaller hard carbon sodium storage capacity of the hard carbon negative electrode material and thus affecting its electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a scanning electron microscope (SEM) image of the hard carbon negative electrode material in Example 1 of the present invention;

[0037] Figure 2 This is a transmission electron microscope (TEM) image of the hard carbon negative electrode material in Example 1 of the present invention;

[0038] Figure 3 is the nitrogen adsorption-desorption curve in Example 1 of the present invention;

[0039] Figure 4 is the pore size distribution curve of the hard carbon negative electrode material in Example 1 of the present invention;

[0040] Figure 5 This is the first cycle charge and discharge curve of the hard carbon negative electrode material in Example 1 of the present invention. DETAILED DESCRIPTION

[0041] The present application is further described in detail below with reference to the embodiments.

[0042] The raw materials used in the examples and comparative examples that are not otherwise specified are all conventional products that can be purchased from the market.

[0043] Example Example

[0044] A low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: the biomass material is cleaned, dried, crushed, and sieved to obtain a precursor powder; the precursor powder is placed in a tubular furnace for low-temperature cracking pretreatment, a protective gas argon gas with a flow rate of 60 mL / min is introduced, the temperature is increased at a heating rate of 5°C / min to a final temperature of 650°C for low-temperature cracking, after isothermal reaction for 2 hours, the temperature is cooled to room temperature at a cooling rate of 5°C / min to obtain a hard carbon precursor. The hard carbon precursor was first washed with 2wt% hydrochloric acid, and then soaked and washed with a 5mol / L potassium hydroxide solution heated to 70°C. The solid-liquid ratio of the sample to the alkali solution was 1:15g / mL. Finally, it was washed with water three times and freeze-dried at -45°C for 9h. The dried sample and the graphite phase g-C3N4 were mixed evenly with a mass ratio of 1:3, and then placed in a high-temperature tubular furnace for high-temperature calcination. The protective gas argon was introduced at a flow rate of 60mL / min, and the temperature was increased to a final temperature of 1400°C at a heating rate of 5°C / min. After constant temperature reaction for 2h, the temperature was cooled to room temperature at a cooling rate of 5°C / min, washed with 2wt% hydrochloric acid, and dried at 60°C to obtain a hard carbon negative electrode material for sodium ion batteries.

[0045] Example 2

[0046] A low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: the biomass material is cleaned, dried, crushed, and sieved to obtain a precursor powder; the precursor powder is placed in a tubular furnace for low-temperature cracking pretreatment, a protective gas argon gas with a flow rate of 60 mL / min is introduced, the temperature is increased at a heating rate of 5°C / min to a final temperature of 650°C for low-temperature cracking, after isothermal reaction for 2 hours, the temperature is cooled to room temperature at a cooling rate of 5°C / min to obtain a hard carbon precursor. The hard carbon precursor was first washed with 2wt% hydrochloric acid, and then soaked and washed with a 5mol / L potassium hydroxide solution heated to 70°C. The solid-liquid ratio of the sample to the alkali solution was 1:15g / mL. Finally, it was washed with water three times and freeze-dried at -45°C for 9h. The dried sample was mixed with the graphite phase g-C3N4 in a mass ratio of 1:1, and then placed in a high-temperature tubular furnace for high-temperature calcination. The protective gas argon was introduced at a flow rate of 60mL / min, and the temperature was increased to a final temperature of 1600°C at a heating rate of 5°C / min. After constant temperature reaction for 2h, the temperature was cooled to room temperature at a cooling rate of 5°C / min, washed with 2wt% hydrochloric acid, and dried at 60°C to obtain a hard carbon negative electrode material for sodium ion batteries.

[0047] Example 3

[0048] A low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: the biomass material is cleaned, dried, crushed, and sieved to obtain a precursor powder; the precursor powder is placed in a tubular furnace for low-temperature cracking pretreatment, a protective gas argon gas with a flow rate of 60 mL / min is introduced, the temperature is increased at a heating rate of 5°C / min to a final temperature of 650°C for low-temperature cracking, after isothermal reaction for 2 hours, the temperature is cooled to room temperature at a cooling rate of 5°C / min to obtain a hard carbon precursor. The hard carbon precursor was first washed with 2wt% hydrochloric acid, and then soaked and washed with a 5mol / L potassium hydroxide solution heated to 70°C. The solid-liquid ratio of the sample to the alkali solution was 1:15g / mL. Finally, it was washed with water three times and freeze-dried at -45°C for 9h. The dried sample and the graphite phase g-C3N4 were mixed evenly with a mass ratio of 1:3, and then placed in a high-temperature tubular furnace for high-temperature calcination. The protective gas argon was introduced at a flow rate of 60mL / min, and the temperature was increased to a final temperature of 1000°C at a heating rate of 5°C / min. After constant temperature reaction for 2h, the temperature was cooled to room temperature at a cooling rate of 5°C / min, washed with 2wt% hydrochloric acid, and dried at 60°C to obtain a hard carbon negative electrode material for sodium ion batteries.

[0049] Example 4

[0050] A low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: the biomass material is cleaned, dried, crushed, and sieved to obtain a precursor powder; the precursor powder is placed in a tubular furnace for low-temperature cracking pretreatment, a protective gas argon gas with a flow rate of 60 mL / min is introduced, the temperature is increased at a heating rate of 5°C / min to a final temperature of 650°C for low-temperature cracking, after isothermal reaction for 2 hours, the temperature is cooled to room temperature at a cooling rate of 5°C / min to obtain a hard carbon precursor. The hard carbon precursor was first washed with 2wt% hydrochloric acid, and then soaked and washed with a 5mol / L potassium hydroxide solution heated to 70°C. The solid-liquid ratio of the sample to the alkali solution was 1:15g / mL. Finally, it was washed with water three times and freeze-dried at -45°C for 9h. The dried sample and the graphite phase g-C3N4 were mixed evenly in a mass ratio of 1:3, and then placed in a high-temperature tubular furnace for high-temperature calcination. The protective gas argon was introduced at a flow rate of 60mL / min, and the temperature was increased to a final temperature of 1800°C at a heating rate of 5°C / min. After constant temperature reaction for 2h, the temperature was cooled to room temperature at a cooling rate of 5°C / min, washed with 2wt% hydrochloric acid, and dried at 60°C to obtain a hard carbon negative electrode material for sodium ion batteries.

[0051] Example 5

[0052] A low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: the biomass material is cleaned, dried, crushed, and sieved to obtain a precursor powder; the precursor powder is placed in a tubular furnace for low-temperature cracking pretreatment, a protective gas argon gas with a flow rate of 60 mL / min is introduced, the temperature is increased at a heating rate of 5°C / min to a final temperature of 650°C for low-temperature cracking, after isothermal reaction for 2 hours, the temperature is cooled to room temperature at a cooling rate of 5°C / min to obtain a hard carbon precursor. The hard carbon precursor was first washed with 2wt% hydrochloric acid, and then soaked and washed with a 5mol / L potassium hydroxide solution heated to 70°C. The solid-liquid ratio of the sample to the alkali solution was 1:15g / mL. Finally, it was washed with water three times and freeze-dried at -45°C for 9h. The dried sample and the graphite phase g-C3N4 were mixed evenly with a mass ratio of 1:3, and then placed in a high-temperature tubular furnace for high-temperature calcination. The protective gas argon was introduced at a flow rate of 60mL / min, and the temperature was increased to a final temperature of 1100°C at a heating rate of 5°C / min. After constant temperature reaction for 2h, the temperature was cooled to room temperature at a cooling rate of 5°C / min, washed with 2wt% hydrochloric acid, and dried at 60°C to obtain a hard carbon negative electrode material for sodium ion batteries.

[0053] Example 6

[0054] A low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: the biomass material is cleaned, dried, crushed, and sieved to obtain a precursor powder; the precursor powder is placed in a muffle furnace for low-temperature pre-oxidation treatment, and the temperature is raised to the final temperature at a heating rate of 5°C / min under the condition of a final temperature of 300°C, and after constant temperature reaction for 2 hours, the temperature is cooled to room temperature at a cooling rate of 5°C / min to obtain a hard carbon precursor; the hard carbon precursor is first washed with 2wt% hydrochloric acid, and then heated to 7 with a potassium hydroxide solution with a concentration of 5mol / L The sample was soaked and cleaned at 0℃, the solid-liquid ratio of the sample to the alkali solution was 1:15g / mL, and finally washed with water 3 times. After freeze-drying at -45℃ for 9h, the dried sample and the graphite phase g-C3N4 were mixed evenly with a mass ratio of 1:3, and then placed in a high-temperature tubular furnace for high-temperature calcination. The protective gas argon was introduced at a flow rate of 60mL / min, and the temperature was increased to a final temperature of 1400℃ at a heating rate of 5℃ / min. After constant temperature reaction for 2h, the temperature was cooled to room temperature at a cooling rate of 5℃ / min, washed with 2wt% hydrochloric acid, and dried at 60℃ to obtain a hard carbon negative electrode material for sodium ion batteries.

[0055] Example 7

[0056] A low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: the biomass material is washed, dried, crushed, and sieved to obtain a precursor powder; then a 2wt% hydrogen peroxide solution is added, and 5g of the precursor powder is dispersed per 100ml of hydrogen peroxide solution, and the precursor powder is placed in a hydrothermal reactor in a constant temperature box for hydrothermal pre-oxidation treatment. The temperature is 100°C and the constant temperature hydrothermal reaction is carried out for 24h. The hard carbon precursor is first washed with 2wt% hydrochloric acid and then heated to 70 with a 5mol / L potassium hydroxide solution. ℃ soaking and cleaning, the solid-liquid ratio of the sample to the alkali solution is 1:15g / mL, and finally washed with water 3 times. After freeze-drying at -45℃ for 9h, the dried sample and graphite phase g-C3N4 are mixed evenly with a mass ratio of 1:3, and then placed in a high-temperature tubular furnace for high-temperature calcination. The protective gas argon is introduced at a flow rate of 60mL / min, and the temperature is increased to a final temperature of 1400℃ at a heating rate of 5℃ / min. After constant temperature reaction for 2h, the temperature is cooled to room temperature at a cooling rate of 5℃ / min, washed with 2wt% hydrochloric acid, and dried at 60℃ to obtain a hard carbon negative electrode material for sodium ion batteries.

[0057] Example 8

[0058] A low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: the biomass material is washed, dried, crushed, and sieved to obtain a precursor powder; then a 2wt% hydrogen peroxide solution is added, and 5g of the precursor powder is dispersed per 100ml of hydrogen peroxide solution and placed in a hydrothermal reactor in a constant temperature box for hydrothermal pre-oxidation treatment. After a constant temperature hydrothermal reaction of 100°C for 24h, the precursor is placed in a tubular furnace for low-temperature cracking treatment, and a protective gas argon gas with a flow rate of 60mL / min is introduced. The temperature is increased at a heating rate of 5°C / min to a final temperature of 650°C for low-temperature cracking. After a constant temperature reaction of 2h, the precursor is cooled to room temperature at a cooling rate of 5°C / min. temperature to obtain a hard carbon precursor; the hard carbon precursor was first washed with 2wt% hydrochloric acid, and then soaked and washed with a 5mol / L potassium hydroxide solution heated to 70°C, the solid-liquid ratio of the sample to the alkali solution was 1:15g / mL, and finally washed with water 3 times, and freeze-dried at -45°C for 9h, and the dried sample and the graphite phase g-C3N4 were mixed uniformly with a mass ratio of 1:3, and then placed in a high-temperature tube furnace for high-temperature calcination, and a protective gas argon gas was introduced with a flow rate of 60mL / min. The temperature was increased to a final temperature of 1400°C at a heating rate of 5°C / min, and after isothermal reaction for 2h, the temperature was cooled to room temperature at a cooling rate of 5°C / min, washed with 2wt% hydrochloric acid, and dried at 60°C to obtain a hard carbon negative electrode material for sodium ion batteries.

[0059] Example 9

[0060] A low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: the biomass material is cleaned, dried, crushed, and sieved to obtain a precursor powder; the precursor powder is placed in a hydrothermal reactor in a constant temperature box for hydrothermal pre-oxidation treatment at a temperature of 100°C for 24 hours, and cooled to room temperature at a cooling rate of 5°C / min to obtain a hard carbon precursor; the hard carbon precursor is first washed with 2wt% hydrochloric acid, and then immersed in a 5mol / L potassium hydroxide solution heated to 70°C for washing. The solid-liquid ratio of the sample to the alkali solution is 1:15 g / mL. Finally, it is washed with water three times and freeze-dried at -45°C for 9 hours. The dried sample and the graphite phase g-C3N4 are mixed evenly in a mass ratio of 1:3, and then placed in a high-temperature tubular furnace for high-temperature calcination. The protective gas argon is introduced at a flow rate of 60 mL / min, and the temperature is increased to a final temperature of 1400°C at a heating rate of 5°C / min. After constant temperature reaction for 2 hours, it is cooled to room temperature at a cooling rate of 5°C / min, washed with 2wt% hydrochloric acid, and dried at 60°C to obtain a hard carbon negative electrode material for sodium ion batteries.

[0061] Example 10

[0062] A low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: the biomass material is cleaned, dried, crushed, and sieved to obtain a precursor powder; the precursor powder is placed in a tubular furnace for low-temperature cracking pretreatment, a protective gas argon gas with a flow rate of 60 mL / min is introduced, the temperature is increased at a heating rate of 5°C / min to a final temperature of 650°C for low-temperature cracking, after isothermal reaction for 2 hours, the temperature is cooled to room temperature at a cooling rate of 5°C / min to obtain a hard carbon precursor. The hard carbon precursor was washed with deionized water several times and dried in a vacuum oven for 12 hours. The dried sample and graphite phase g-C3N4 were mixed evenly in a mass ratio of 1:3, and then placed in a high-temperature tubular furnace for high-temperature calcination. The protective gas argon was introduced at a flow rate of 60 mL / min, and the temperature was increased to a final temperature of 1400°C at a heating rate of 5°C / min. After constant temperature reaction for 2 hours, the temperature was cooled to room temperature at a cooling rate of 5°C / min, washed with 2wt% hydrochloric acid, and dried at 60°C to obtain a hard carbon negative electrode material for sodium ion batteries.

[0063] Comparative Example

[0064] Comparative Example 1

[0065] A low-cost, high-performance biomass-based sodium ion hard carbon anode material is prepared according to the following steps: washing, drying, crushing, and sieving the biomass material to obtain a precursor powder; mixing the precursor powder and graphite phase g-C3N4 at a mass ratio of 1:3, placing the mixture in a high-temperature tube furnace for high-temperature calcination, introducing protective gas argon at a flow rate of 60 mL / min, heating the mixture at a heating rate of 5°C / min to a final temperature of 1400°C, reacting at a constant temperature for 2 hours, cooling the mixture to room temperature at a cooling rate of 5°C / min, washing the mixture with 2wt% hydrochloric acid, and drying the mixture at 60°C to obtain a sodium ion battery hard carbon anode material.

[0066] Comparative Example 2

[0067] A low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: the biomass material is cleaned, dried, crushed, and sieved to obtain a precursor powder; the precursor powder is placed in a tubular furnace for low-temperature cracking pretreatment, a protective gas argon gas with a flow rate of 60 mL / min is introduced, the temperature is increased at a heating rate of 5°C / min to a final temperature of 650°C for low-temperature cracking, after isothermal reaction for 2 hours, the temperature is cooled to room temperature at a cooling rate of 5°C / min to obtain a hard carbon precursor. The hard carbon precursor was first washed with 2wt% hydrochloric acid, and then soaked and washed with a 5mol / L potassium hydroxide solution heated to 70°C. The solid-liquid ratio of the sample to the alkali solution was 1:15g / mL. Finally, it was washed with water three times and freeze-dried at -45°C for 9h. The dried sample and the graphite phase g-C3N4 were mixed evenly with a mass ratio of 1:4, and then placed in a high-temperature tubular furnace for high-temperature calcination. The protective gas argon was introduced at a flow rate of 60mL / min, and the temperature was increased to a final temperature of 1400°C at a heating rate of 5°C / min. After constant temperature reaction for 2h, the temperature was cooled to room temperature at a cooling rate of 5°C / min, washed with 2wt% hydrochloric acid, and dried at 60°C to obtain a hard carbon negative electrode material for sodium ion batteries.

[0068] Comparative Example 3

[0069] A low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: the biomass material is cleaned, dried, crushed, and sieved to obtain a precursor powder; the precursor powder is placed in a tubular furnace for low-temperature cracking pretreatment, a protective gas argon gas with a flow rate of 60 mL / min is introduced, the temperature is increased at a heating rate of 5°C / min to a final temperature of 650°C for low-temperature cracking, after isothermal reaction for 2 hours, the temperature is cooled to room temperature at a cooling rate of 5°C / min to obtain a hard carbon precursor. The hard carbon precursor was first washed with 2wt% hydrochloric acid, and then soaked and washed with a 5mol / L potassium hydroxide solution heated to 70°C. The solid-liquid ratio of the sample to the alkali solution was 1:15g / mL. Finally, it was washed with water three times and freeze-dried at -45°C for 9h. The dried sample was placed in a high-temperature tubular furnace for high-temperature calcination. Argon gas was introduced at a flow rate of 60mL / min and the temperature was increased to a final temperature of 1400°C at a heating rate of 5°C / min. After constant temperature reaction for 2h, the temperature was cooled to room temperature at a cooling rate of 5°C / min, washed with 2wt% hydrochloric acid, and dried at 60°C to obtain a hard carbon negative electrode material for sodium ion batteries.

[0070] Comparative Example 4

[0071] A low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: the biomass material is cleaned, dried, crushed, and sieved to obtain a precursor powder; the precursor powder is placed in a tubular furnace for low-temperature cracking pretreatment, a protective gas argon gas with a flow rate of 60 mL / min is introduced, the temperature is increased at a heating rate of 5°C / min to a final temperature of 650°C for low-temperature cracking, after isothermal reaction for 2 hours, the temperature is cooled to room temperature at a cooling rate of 5°C / min to obtain a hard carbon precursor. The hard carbon precursor and the graphite phase g-C3N4 were mixed evenly in a mass ratio of 1:3, placed in a high-temperature tubular furnace for high-temperature calcination, and a protective gas argon gas was introduced at a flow rate of 60 mL / min. The temperature was increased to a final temperature of 1400°C at a heating rate of 5°C / min. After constant temperature reaction for 2 hours, the temperature was cooled to room temperature at a cooling rate of 5°C / min, washed with 2wt% hydrochloric acid, and dried at 60°C to obtain a hard carbon negative electrode material for sodium ion batteries.

[0072] Comparative Example 5

[0073] A low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: the biomass material is cleaned, dried, crushed, and sieved to obtain a precursor powder; the precursor powder is placed in a tubular furnace for low-temperature cracking pretreatment, a protective gas argon gas with a flow rate of 60 mL / min is introduced, the temperature is increased at a heating rate of 5°C / min to a final temperature of 650°C for low-temperature cracking, after isothermal reaction for 2 hours, the temperature is cooled to room temperature at a cooling rate of 5°C / min to obtain a hard carbon precursor. The hard carbon precursor was first washed with 2wt% hydrochloric acid, and then soaked and washed with a 5mol / L potassium hydroxide solution heated to 70°C. The solid-liquid ratio of the sample to the alkali solution was 1:15g / mL. Finally, it was washed with water three times and freeze-dried at -45°C for 9h. The dried sample and the graphite phase g-C3N4 were mixed evenly with a mass ratio of 2:1, and then placed in a high-temperature tubular furnace for high-temperature calcination. The protective gas argon was introduced at a flow rate of 60mL / min, and the temperature was increased to a final temperature of 1400°C at a heating rate of 5°C / min. After constant temperature reaction for 2h, the temperature was cooled to room temperature at a cooling rate of 5°C / min, washed with 2wt% hydrochloric acid, and dried at 60°C to obtain a hard carbon negative electrode material for sodium ion batteries.

[0074] Performance testing

[0075] The physical and chemical performance test technical indicators of a low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material prepared in the examples and comparative examples were measured using the following methods:

[0076] a. Specific Surface Area and Pore Size Analysis: N2 isothermal adsorption and desorption curves were measured using a BEL-SorpMax II specific surface area and vapor adsorption analyzer manufactured by Microtrac BEL, Japan. Before the adsorption test, the sample was activated as required. The specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method in the relative pressure range of 0.05 to 0.20. The pore volume was calculated based on the adsorption capacity at a relative pressure of approximately 0.99.

[0077] b. Electrical performance test: The test was conducted using a half-cell test method. Specifically, the hard carbon negative electrode materials of the above examples and comparative examples: sodium alginate: Super-p = 90:5:5 (weight ratio) were added with water to adjust the slurry, coated on aluminum foil, and dried in a vacuum drying oven for 12 hours to form a negative electrode sheet. 1 mol of NaPF6 was dissolved in 1L of a 1:1 volume ratio of ethylene carbonate and diethyl carbonate solution as the electrolyte, a polypropylene microporous membrane was used as the separator, and a sodium sheet was used as the counter electrode to assemble the battery. Constant current charge and discharge experiments were conducted on the LAND battery test system, with the charge and discharge voltage limited to 0.01-2.0V. The results are shown in Table 1 below:

[0078] Table 1 Performance test results

[0079]

[0080] As can be seen from Table 1, the low-cost and high-performance biomass-based sodium ion hard carbon negative electrode material obtained in the above embodiment has a large pore size distribution range and porosity, its particle size is 1-10 μm and shows a typical granular morphology, and has a relatively large specific surface area (110 m 2 / g or more), has good sodium storage performance, higher reversible specific capacity and first coulombic efficiency, showing excellent reversible sodium storage capacity. While reducing costs, it does not lead to a decrease in the performance of graphite negative electrode materials, and can still maintain the excellent performance of hard carbon negative electrode materials, which is conducive to promotion and application.

[0081] By comparing Example 1 with Examples 6-8 and Comparative Example 1, it can be seen that the specific surface area, reversible specific capacity, low-potential platform specific capacity and first coulombic efficiency of the low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material prepared in Comparative Example 1 are all lower than those in Examples 6-8. Comparative analysis shows that, in view of the relatively large amount of cellulose and lignin in sunflower seed shells, a two-stage pretreatment and high-temperature calcination are adopted. First, hydrothermal pre-oxidation is performed to break the intramolecular hydrogen bonds, thereby forming a short carbon ring, which is the basis for the material to have the advantages of high specific surface area and pore structure, and enhance sodium ion energy storage. In this process, hydrogen peroxide solution is added, and the cellulose in the sunflower seed shells is oxidized, making the hydrothermal oxidation reaction more thorough, the oxygen content higher, and more sodium storage sites formed, thereby enhancing the sodium storage performance. Subsequently, low-temperature pyrolysis is performed to remove impurities such as coal tar, thereby improving the thermal efficiency and product quality of carbonization, optimizing the edges, defects and pores of pseudo-graphite microcrystalline domains and amorphous nanodomains, improving the hard carbon sodium storage capacity, regulating the pseudo-graphite interlayer spacing, and improving the electrochemical properties of the hard carbon negative electrode material such as the hard carbon sodium storage capacity.

[0082] By comparing Example 1 with Comparative Examples 2-3 and Comparative Example 5, it can be seen that: by adding graphite phase g-C3N4 in proportion, the stable network structure can be used as a template to guide the graphitization of hard carbon under high temperature calcination, forming a pseudo-graphite layer and expanding the interlayer spacing, while forming rich pores and reducing defects and impurity functional groups, thereby improving the degree of graphitization and further improving the sodium storage capacity of hard carbon. The stable structure is conducive to the free movement of sodium ions between layers, and is more conducive to the embedding / ejection of sodium ions, making the energy density of hard carbon materials higher and enhancing the rate performance; adjusting the heating rate can effectively control the opening of pores. and closed-pore ratio, thereby significantly improving the electrochemical properties of sodium ion hard carbon negative electrode materials. The electrochemical properties of the materials within the mass ratio range of the treated samples and graphite phase g-C3N4 of the present application are optimal. This may be because too little graphite phase g-C3N4 cannot fully guide calcination and provide a stable network structure, which is not conducive to the embedding / ejection of sodium ions. Too much graphite phase g-C3N4 leads to excessive hardness of the material, poor modifiable processability, and a relatively concentrated pore size distribution range, which is not conducive to the migration and diffusion of sodium ions, affecting the reversible embedding / ejection of sodium ions.

[0083] Comparison with Examples 1-5 shows that the specific surface area, reversible specific capacity, low-potential platform specific capacity, and first coulombic efficiency of the low-cost, high-performance biomass-based sodium ion hard carbon anode materials prepared in Examples 3-4 are all lower than those in Examples 1-2 and Example 5. Comparative analysis shows that the temperature range disclosed in this application can increase the degree of graphitization of the hard carbon anode material, allowing the formation of an appropriate pseudo-graphite interlayer spacing, which is beneficial to hard carbon graphitization, reducing the pseudo-graphite interlayer spacing, and improving the hard carbon low-voltage platform capacity and first coulombic efficiency. Excessively high temperatures will result in too small an interlayer spacing, which is not conducive to sodium ion intercalation and insertion, resulting in a decrease in the sodium storage capacity of the hard carbon. Excessively low temperatures will result in a low degree of graphitization, which is not conducive to the stable insertion of sodium ions, affecting the capacity and first coulombic efficiency of the hard carbon anode material.

[0084] The above are all preferred embodiments of the present application, and are not intended to limit the scope of protection of the present application. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A low-cost, high-performance biomass-based sodium ion hard carbon anode material, characterized by: The biomass-based sodium ion hard carbon negative electrode material is prepared according to the following steps: the biomass material is washed, dried, crushed and sieved to obtain a precursor powder; then 2 wt% hydrogen peroxide solution is added, 5 g of the precursor powder is dispersed per 100 ml of hydrogen peroxide solution, and the precursor powder is placed in a hydrothermal reactor in a constant temperature box for hydrothermal pre-oxidation treatment. After a constant temperature hydrothermal reaction of 24 hours at a temperature of 100 ° C, the precursor powder is placed in a tubular furnace for low-temperature cracking treatment, and a protective gas argon gas with a flow rate of 60 mL / min is introduced. The temperature is increased at a heating rate of 5 ° C / min to a final temperature of 650 ° C for low-temperature cracking. After a constant temperature reaction of 2 hours, the precursor powder is cooled to room temperature at a cooling rate of 5 ° C / min to obtain a hard carbon precursor; the hard carbon precursor is The body was first washed with 2wt% hydrochloric acid, and then immersed and washed with a 5mol / L potassium hydroxide solution heated to 70℃. The solid-liquid ratio of the sample to the potassium hydroxide solution was 1:15g / mL. Finally, it was washed with water three times and freeze-dried at -45℃ for 9h. The dried sample and the graphite phase g-C3N4 were mixed evenly with a mass ratio of 1:3, and then placed in a high-temperature tubular furnace for high-temperature calcination. The protective gas argon was introduced at a flow rate of 60mL / min, and the temperature was increased to a final temperature of 1400℃ at a heating rate of 5℃ / min. After isothermal reaction for 2h, the temperature was cooled to room temperature at a cooling rate of 5℃ / min, washed with 2wt% hydrochloric acid, and dried at 60℃ to obtain a hard carbon negative electrode material for sodium ion batteries.

2. The low-cost, high-performance biomass-based sodium ion hard carbon negative electrode material according to claim 1, characterized in that: The hard carbon negative electrode material is an active negative electrode material having pseudo-graphite microcrystalline domains and amorphous non-crystalline domains.

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