A sodium-ion hard carbon negative electrode material based on a composite raw material and a preparation method thereof

Abstract

This application relates to the field of sodium-ion battery materials. More specifically, it relates to a sodium-ion hard carbon anode material based on composite raw materials and a preparation method thereof. A sodium-ion hard carbon anode material based on composite raw materials, wherein the composite raw materials of the hard carbon anode material include a biomass precursor and a modifier; the biomass precursor is a carbonizable algal biomass material; the modifier is one or two of sodium citrate and sodium carboxymethylcellulose. The sodium-ion hard carbon anode material based on composite raw materials of this application has a large pore size distribution range, a relatively large graphite layer spacing, a low degree of graphitization, good sodium storage performance, high reversible specific capacity and first Coulomb efficiency. These performance indicators can be key factors in promoting the commercialization of sodium-ion batteries and are conducive to commercial promotion and application.

Description

Technical Field

[0001] This application relates to the field of sodium-ion battery materials, and more specifically, to a sodium-ion hard carbon anode material based on composite raw materials and a preparation method thereof. Background Art

[0002] Sodium and lithium are in the same main group, so sodium has physical and chemical properties similar to those of lithium. Different from lithium, the source of sodium is very extensive. With the continuous in-depth research on sodium batteries by people, it is fully hoped that excellent commercial sodium-ion batteries can be obtained in the future.

[0003] The development of advanced sodium-ion batteries depends on the construction of high-performance electrode materials. Research and development of low-cost and high-performance anode materials is a key link among them. Hard carbon (HC) materials, due to advantages such as rich reserves, low cost, stable structure, and a relatively low sodium intercalation voltage platform, make hard carbon the most commercially promising anode material. However, hard carbon anodes are still restricted by bottlenecks such as low first-cycle Coulomb efficiency, low specific capacity, and unsatisfactory cycling performance, and these performance indicators are key factors for promoting the commercialization of sodium-ion batteries. Although a large number of optimization process means have been used to modify the structure, components, surface functionalization, etc. of hard carbon materials, these methods often can only improve a single property of hard carbon anodes. For example, although the specific capacity is increased by introducing doping defects, the first-cycle Coulomb efficiency is significantly reduced; reducing defects and porosity, although improving the first-cycle Coulomb efficiency and cycling stability, the performance such as specific capacity cannot be guaranteed; expanding the layer spacing increases the specific capacity of hard carbon materials due to the insertion and extraction of sodium ions, but the microstructure of hard carbon is easily damaged during this process and its cycling stability is poor.

[0004] Therefore, it is urgent to develop more effective optimization strategies to multi-dimensionally improve the sodium storage performance of hard carbon anodes to promote the commercial application of sodium-ion batteries based on hard carbon anodes. Summary of the Invention

[0005] In order to overcome the above-mentioned disadvantages of the prior art, this application provides a sodium-ion hard carbon anode material based on composite raw materials and a preparation method thereof.

[0006] In the first aspect, this application provides a sodium-ion hard carbon anode material based on composite raw materials, and the following technical scheme is adopted:

[0007] A sodium-ion hard carbon anode material based on composite raw materials, wherein the composite raw materials of the hard carbon anode material include a biomass precursor and a modifier; the biomass precursor is a carbonizable algal biomass material; the modifier is one or both of sodium citrate and sodium carboxymethylcellulose.

[0008] By adopting the above technical solution, an algal biomass and a modifier are used in combination to prepare a hard carbon material with low graphitization degree, abundant edge defects and abundant closed pores, which makes the hard carbon material have a high degree of disorder and abundant defects, being beneficial to sodium storage; the biomass precursor is selected as a carbonizable algal material, and algae, microorganisms, etc. contain a large amount of nitrogen-containing organic substances, and after carbonization and reconstruction, they have a large number of nitrogen-containing conjugated heterocyclic structures. Combining with the modifier can form graphite-like nanosheet layers with a random orientation, bending, edge defects and a large interlayer distance, ensuring the smooth insertion / extraction of sodium ions and enhancing the electrochemical properties such as cycle stability and specific capacity; the applicant found that sodium citrate and sodium carboxymethyl cellulose in nature can be transformed into long layers similar to graphite, surrounding and shrinking the active sites to form a closed pore structure. The presence of amorphous components (cellulose, carboxylic acid, etc.) not only facilitates the formation of nanopores, but also has good cross-linking ability, which can prevent the excessive graphitization of the carbon layer during the high-temperature carbonization process. As the carbonization temperature increases, the length of the graphite-like carbon layer increases, which is beneficial to the formation of a closed pore structure. The biomass precursor and the modifier are used in combination to regulate the microstructure of the hard carbon, construct abundant closed pores, and the abundant closed pores can increase the amount of sodium stored in the "pore filling", increase the specific capacity of the hard carbon material, and the enlarged interlayer distance enables the sodium ions not to damage the microstructure of the hard carbon during the insertion and extraction process, enhancing its cycle stability, and reducing the specific surface area of the hard carbon, thereby reducing the consumption of the electrolyte and improving the first Coulombic efficiency.

[0009] The carbonizable algal biomass material includes chlorella and brown algae, and the mass ratio of chlorella to brown algae is (2-5):1; the mass ratio of the biomass precursor to the modifier is (0.5-5):1.

[0010] By adopting the above technical solution, a large number of organic components such as proteins, sugars, cellulose, and alkaloids contained in the algal biomass material form a heterocyclic structure containing nitrogen-conjugated after carbonization and reconstruction, increasing the electrochemical redox sites of the hard carbon material and improving the sodium storage performance. The applicant's research shows that the rich vitamins and minerals contained in Chlorella, during the carbonization process, mineral ions frequently enter and exit the pseudo-graphite layer structure, carbonization intermediates, and the heterocyclic structure after carbonization and reconstruction, further expanding the layer spacing of the pseudo-graphite layer and further increasing the pore distribution range, improving the graphitization degree, which is beneficial to the free insertion / extraction of sodium ions between the layers. In addition, fucoxanthin contained in brown algae has a long conjugated double bond and a special structure containing allene and epoxy alkane. When co-carbonized with Chlorella, rearrangement is more likely to occur during the carbonization process, increasing the random orientation and edge properties, improving the pseudo-graphitization degree, enhancing the cycle stability of the battery, and having the characteristics of low-temperature performance and high energy density, improving the first Coulomb efficiency, realizing the charge and discharge cycle of the battery, further increasing the specific capacity of sodium ions, and improving the sodium storage performance. In addition, if the mass of brown algae is too much, the pseudo-graphite layer spacing will be smaller, which is instead not conducive to the free movement of sodium ions between the layers.

[0011] Preferably, the mass ratio of the biomass precursor to the modifier is (0.5 - 2):1.

[0012] By adopting the above technical solution, the biomass and the modifier are mixed in a certain proportion. The modifier has good cross-linking ability, significantly enhancing the cross-linking effect of the biomass precursor and the structural stability during the heat treatment process, avoiding the direct pyrolysis of the precursor into small molecules, and thus making a hard carbon material with a relatively low graphitization degree, rich edge defects, and rich closed pores. By adjusting the microstructure of the hard carbon and increasing the sodium storage active sites, the sodium storage performance of the sodium-ion battery is further improved. If there is too much modifier, the number of closed pores is too many and the pore size range is small, which will affect the extraction of sodium. Although the cycle stability is enhanced, the first Coulomb efficiency and specific capacity are affected; if there is too little modifier, the number of closed pores decreases, the sodium storage capacity decreases, the specific capacity of the hard carbon material decreases, and in addition, the cycle stability of the sodium-ion negative electrode material is insufficient, and it is easy to damage the microstructure of the hard carbon.

[0013] In a second aspect, the present application provides a preparation method of a sodium-ion hard carbon negative electrode material based on a composite raw material, adopting the following technical solution:

[0014] A preparation method of a sodium-ion hard carbon negative electrode material based on a composite raw material includes the following steps:

[0015] (1) Cleaning, drying, pulverizing, and sieving the biomass precursor material;

[0016] (2) Mixing the obtained biomass precursor and the modifier in proportion;

[0017] (3) Dry the material obtained in (2).

[0018] (4) Carry out low-temperature pyrolysis on the above-obtained material, introduce a protective gas, raise the temperature to the final temperature at a heating rate of 0.1 - 10 °C / min, after the isothermal reaction, lower the temperature to room temperature at a cooling rate of 0.1 - 10 °C / min.

[0019] (5) Wash the sample after the above treatment with a cleaning solution and then dry it.

[0020] (6) Carry out high-temperature calcination on the sample treated in (5), introduce a protective gas, raise the temperature to the final temperature at a heating rate of 0.1 - 10 °C / min, after the isothermal reaction, lower the temperature to room temperature at a cooling rate of 0.1 - 10 °C / min, and carbonize to obtain a hard carbon negative electrode material.

[0021] By adopting the above technical solution, by compounding the biomass precursor and the modifier, through a simple two-step calcination process, namely low-temperature pyrolysis and high-temperature calcination, regulating composite conditions, carbonization temperature, heating rate, holding time, etc., a hard carbon negative electrode material for sodium-ion batteries with stable cycling, high initial Coulomb efficiency, and high specific capacity is obtained, improving the performance of sodium-ion batteries. That is, a suitable specific surface area and more closed pores are obtained, which is beneficial to the migration and diffusion of sodium ions, provides sodium storage sites for reversible insertion / extraction of sodium ions, and a smaller specific surface area means fewer defects, reducing the impact of irreversible sodium ion adsorption on the capacity; in addition, by adjusting the heating and cooling rates within an appropriate range, the microstructure of hard carbon can be regulated, enabling the construction of rich closed pores while also making the pore size distribution range more uniform, facilitating the insertion and extraction of sodium ions.

[0022] In a specific feasible implementation, the drying method in (3) includes one of freeze-drying and drying.

[0023] Preferably, the temperature for drying is 50 - 300 °C.

[0024] By adopting the above technical solution, after the biomass precursor and the modifier are fully mixed and dried, it helps to remove the residual moisture in the material, preventing the gasification of moisture during the pyrolysis and carbonization processes, which affects the graphitization degree and edge defects of hard carbon, and thus affects the electrochemical performance.

[0025] In a specific feasible implementation, the final temperature of the low-temperature pyrolysis is 300 - 900 °C, and the isothermal reaction is carried out for 0.5 - 10 h.

[0026] By adopting the above technical solution, the volatile components in the biomass material are removed through low-temperature pyrolysis, and oxygen-containing functional groups are introduced, which changes the pore structure and chemical environment. The resulting hard carbon material mainly contains C and O elements, forms abundant closed pores, increases the sodium storage sites in the internal structure of the material, and makes the hard carbon material have a high degree of disorder and rich defects, which is beneficial to the basis of sodium storage. In this process, if the final temperature is too high, the degree of graphitization is too high, the number of closed pores decreases, and the sodium storage performance is affected. If the final temperature is too low, the layer spacing of the hard carbon material makes it easy to damage the microstructure of the hard carbon during the process of sodium ion insertion and extraction, affecting its cycle stability.

[0027] In a specific feasible embodiment, the final temperature of the high-temperature calcination is 1000 - 1800 °C, and the constant-temperature reaction is 0.1 - 10 h.

[0028] By adopting the above technical solution, high-temperature calcination enables the hard carbon material to be fully carbonized. A certain temperature range can ensure an appropriate degree of graphitization of the hard carbon anode material, form an appropriate graphite layer spacing, improve the low-voltage platform capacity and the first Coulombic efficiency of the hard carbon. If the calcination temperature is too high, the layer spacing is too small, affecting the specific capacity of the hard carbon material; if the temperature is too low, the degree of graphitization is small, the number of closed pores decreases, affecting the capacity and the first Coulombic efficiency of the hard carbon anode material.

[0029] In a specific feasible embodiment, the protective atmosphere is at least one of argon, nitrogen, and helium, and the gas flow rate is 5 - 100 mL / min.

[0030] In a specific feasible embodiment, the cleaning solution in (5) includes at least one of an acid solution, an alkali solution, or an aqueous solution.

[0031] By adopting the above technical solution, using an acid solution, an alkali solution, or an aqueous solution as the cleaning solution to wash and remove the metal salt ions obtained after low-temperature pyrolysis, avoiding the excessive evaporation of metal salt ions during the subsequent high-temperature calcination, which may lead to too large a specific surface area of the hard carbon, excessive consumption of the electrolyte, and reduction of its Coulombic efficiency.

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

[0033] 1. The combined use of algal biomass and a modifier results in a hard carbon material with low graphitization degree, abundant edge defects, and numerous closed pores. This makes the hard carbon material highly disordered and defect-rich, which is beneficial for sodium storage. The biomass precursor is selected as a carbonizable algal material that forms a large number of nitrogen-containing conjugated heterocyclic structures during carbonization and reconstruction. Combining with the modifier, it can form graphite-like nanosheet layers with random orientation, bending, edge defects, and a relatively large interlayer distance, ensuring the smooth insertion / extraction of sodium ions and enhancing electrochemical properties such as cycle stability and specific capacity. The applicant found that sodium citrate and sodium carboxymethylcellulose in nature can be transformed into graphite-like long layers, surrounding and shrinking the active sites to form a closed pore structure. The presence of amorphous components (such as cellulose and carboxylic acids) not only facilitates the formation of nanopores but also has good cross-linking ability, preventing excessive graphitization of the carbon layer during high-temperature carbonization. As the carbonization temperature increases, the length of the graphite-like carbon layer increases, which is beneficial for the formation of a closed pore structure. By combining the biomass precursor and the modifier, the microstructure of the hard carbon can be regulated to construct numerous closed pores. The numerous closed pores can increase the sodium storage capacity by "filling the pores", increase the specific capacity of the hard carbon material, and the enlarged interlayer distance enables sodium ions to insert and extract without damaging the microstructure of the hard carbon, enhancing its cycle stability and reducing the specific surface area of the hard carbon, thereby reducing the consumption of the electrolyte and improving the initial Coulombic efficiency.

[0034] 2. The biomass and the modifier are mixed in a certain proportion. The modifier has good cross-linking ability, significantly enhancing the cross-linking effect of the biomass precursor and the structural stability during the heat treatment process, and preventing the precursor from directly pyrolyzing into small molecules, thus resulting in a hard carbon material with relatively low graphitization degree, abundant edge defects, and numerous closed pores. By adjusting the microstructure of the hard carbon and increasing the sodium storage active sites, the sodium storage performance of the sodium-ion battery can be further improved. If there is too much modifier, the number of closed pores is excessive and the pore size range is small, which will affect the extraction of sodium. Although it enhances its cycle stability, it affects the initial Coulombic efficiency and specific capacity. If there is too little modifier, the number of closed pores decreases, the sodium storage capacity decreases, the specific capacity of the hard carbon material decreases, and in addition, the cycle stability of the sodium-ion negative electrode material is insufficient, easily damaging the microstructure of the hard carbon.

[0035] 3. Using an acid solution, an alkali solution, or an aqueous solution as a cleaning liquid to remove the metal salt ions obtained after low-temperature pyrolysis, preventing the metal salt ions from evaporating during the subsequent high-temperature calcination, which may lead to too large a specific surface area of the hard carbon, excessive consumption of the electrolyte, and reduction of its Coulombic efficiency. Description of the Drawings

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

[0037] Figure 2XRD pattern of the hard carbon negative electrode material in Example 1 of the present invention;

[0038] Figure 3 Raman scattering (Raman) pattern of the hard carbon negative electrode material in Example 1 of the present invention;

[0039] Figure 4 X-ray photoelectron spectroscopy (XPS) pattern of the hard carbon negative electrode material in Example 1 of the present invention;

[0040] Figure 5 Initial charge-discharge curve of the hard carbon negative electrode material in Example 1 of the present invention. Detailed implementation manners

[0041] The following further elaborates on the present application in conjunction with examples.

[0042] Some raw materials used in the preparation examples and examples: The native organism is Chlorella vulgaris, purchased from Jiangsu Huace Biotechnology Co., Ltd.; the plant is Dalbergia melanoxylon, purchased from Zhangjiagang Jinang Qianxiang Wood Business Department; sodium citrate is purchased from Henan Mingzhixin Chemical Products Co., Ltd.; the carboxymethyl cellulose sodium has the product number: cmc-Na.

[0043] For the relevant raw materials not specified in the examples and comparative examples, they are all conventional products that can be obtained through market purchase. Example 1

[0044] A sodium-ion hard carbon negative electrode material based on a composite raw material, where the composite raw material of the hard carbon negative electrode material is a biomass precursor and a modifier; among them, the biomass precursor is Chlorella vulgaris, and the modifier is carboxymethyl cellulose sodium; the sodium-ion hard carbon negative electrode material based on the composite raw material is prepared according to the following steps: Wash and dry Chlorella vulgaris with water, crush and sieve it. After the obtained Chlorella vulgaris and carboxymethyl cellulose sodium are mixed evenly at a mass ratio of 0.5:1, take 10 g of the composite raw material and place it in an oven at 60 °C for 6 h of drying, then put it into a high-temperature tube furnace for low-temperature pyrolysis. After heating to the final temperature of 700 °C at a heating rate of 5 °C / min, introduce the protective gas argon, with a gas flow rate of 60 mL / min, keep the temperature constant for 120 min, and cool down to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination, heat it to the final temperature of 1300 °C at a heating rate of 5 °C / min, introduce the protective gas argon, with a gas flow rate of 60 mL / min, continuously react for 180 min, and cool down to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon negative electrode material based on the composite raw material. Example 2

[0045] The composite raw material of the hard carbon anode material is a biomass precursor and a modifier; among them, the biomass precursor is Chlorella, and the modifier is sodium citrate; the sodium-ion hard carbon anode material based on the composite raw material is prepared according to the following steps: Wash the Chlorella with water, dry it, crush and screen it. After the obtained Chlorella and sodium citrate are mixed evenly at a mass ratio of 0.5:1, take 10 g of the composite raw material and place it in an oven at 60 °C for drying for 6 h, then put it into a high-temperature tube furnace for low-temperature pyrolysis. After rising to the final temperature of 700 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, keep the temperature constant for reaction for 120 min, and cool down to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination. After rising to the final temperature of 1300 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, continue the reaction for 180 min, and cool down to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon anode material based on the composite raw material. Example 3

[0046] The composite raw material of the hard carbon anode material is a biomass precursor and a modifier; among them, the biomass precursor is Chlorella, and the modifier is sodium carboxymethylcellulose; the sodium-ion hard carbon anode material based on the composite raw material is prepared according to the following steps: Wash the Chlorella with water, dry it, crush and screen it. After the obtained Chlorella and sodium carboxymethylcellulose are mixed evenly at a mass ratio of 2:1, take 10 g of the composite raw material and place it in an oven at 60 °C for drying for 6 h, then put it into a high-temperature tube furnace for low-temperature pyrolysis. After rising to the final temperature of 700 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, keep the temperature constant for reaction for 120 min, and cool down to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination. After rising to the final temperature of 1300 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, continue the reaction for 180 min, and cool down to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon anode material based on the composite raw material. Example 4

[0047] The composite raw material of the hard carbon negative electrode material is a biomass precursor and a modifier; among them, the biomass precursor is Chlorella, and the modifier is sodium carboxymethyl cellulose; the sodium-ion hard carbon negative electrode material based on the composite raw material is prepared according to the following steps: Wash the Chlorella with water, dry it, crush and screen it. After the obtained Chlorella and sodium carboxymethyl cellulose are mixed evenly at a mass ratio of 5:1, take 10 g of the composite raw material and place it in an oven at 60 °C for 6 h of drying. Then put it into a high-temperature tube furnace for low-temperature cracking. After heating to the final temperature of 700 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, and keep the temperature constant for reaction for 120 min. Then cool it to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination. Heat it to the final temperature of 1300 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, continuously react for 180 min, and cool it to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon negative electrode material based on the composite raw material. Example 5

[0048] The composite raw material of the hard carbon negative electrode material is a biomass precursor and a modifier; among them, the biomass precursor is Chlorella, and the modifier is sodium carboxymethyl cellulose; the sodium-ion hard carbon negative electrode material based on the composite raw material is prepared according to the following steps: Wash the Chlorella with water, dry it, crush and screen it. After the obtained Chlorella and sodium carboxymethyl cellulose are mixed evenly at a mass ratio of 5:3, take 10 g of the composite raw material and place it in an oven at 60 °C for 6 h of drying. Then put it into a high-temperature tube furnace for low-temperature cracking. After heating to the final temperature of 700 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, and keep the temperature constant for reaction for 120 min. Then cool it to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination. Heat it to the final temperature of 1300 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, continuously react for 180 min, and cool it to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon negative electrode material based on the composite raw material. Example 6

[0049] The composite raw material of the hard carbon negative electrode material is a biomass precursor and a modifier; among them, the biomass precursor is Chlorella, and the modifier is sodium carboxymethyl cellulose; the sodium-ion hard carbon negative electrode material based on the composite raw material is prepared according to the following steps: Wash the Chlorella with water, dry it, crush and screen it. After the obtained Chlorella and sodium carboxymethyl cellulose are mixed evenly at a mass ratio of 5:0.5, take 10 g of the composite raw material and dry it in an oven at 60 °C for 6 h, then put it into a high-temperature tube furnace for low-temperature cracking. After heating to the final temperature of 700 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, keep the temperature constant for reaction for 120 min, and cool down to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination, heat it to the final temperature of 1300 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, continuously react for 180 min, and cool down to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon negative electrode material based on the composite raw material. Example 7

[0050] The composite raw material of the hard carbon negative electrode material is a biomass precursor and a modifier; among them, the biomass precursor is Chlorella, and the modifier is sodium carboxymethyl cellulose; the sodium-ion hard carbon negative electrode material based on the composite raw material is prepared according to the following steps: Wash the Chlorella with water, dry it, crush and screen it. After the obtained Chlorella and sodium carboxymethyl cellulose are mixed evenly at a mass ratio of 0.5:1, take 10 g of the composite raw material and dry it in an oven at 60 °C for 6 h, then put it into a high-temperature tube furnace for low-temperature cracking. After heating to the final temperature of 200 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, keep the temperature constant for reaction for 120 min, and cool down to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination, heat it to the final temperature of 1300 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, continuously react for 180 min, and cool down to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon negative electrode material based on the composite raw material. Example 8

[0051] The composite raw material of the hard carbon negative electrode material is a biomass precursor and a modifier; among them, the biomass precursor is Chlorella, and the modifier is sodium carboxymethyl cellulose; the sodium-ion hard carbon negative electrode material based on the composite raw material is prepared according to the following steps: Wash the Chlorella with water, dry it, crush and screen it. After the obtained Chlorella and sodium carboxymethyl cellulose are mixed evenly according to a mass ratio of 0.5:1, take 10 g of the composite raw material and place it in an oven at 60 °C for drying for 6 h, then put it into a high-temperature tube furnace for low-temperature cracking. After heating to a final temperature of 1000 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, keep the temperature constant for reaction for 120 min, and cool down to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination, heat it to a final temperature of 1300 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, continuously react for 180 min, and cool down to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon negative electrode material based on the composite raw material. Example 9

[0052] The composite raw material of the hard carbon negative electrode material is a biomass precursor and a modifier; among them, the biomass precursor is Chlorella, and the modifier is sodium carboxymethyl cellulose; the sodium-ion hard carbon negative electrode material based on the composite raw material is prepared according to the following steps: Wash the Chlorella with water, dry it, crush and screen it. After the obtained Chlorella and sodium carboxymethyl cellulose are mixed evenly according to a mass ratio of 0.5:1, take 10 g of the composite raw material and place it in an oven at 60 °C for drying for 6 h, then put it into a high-temperature tube furnace for low-temperature cracking. After heating to a final temperature of 700 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, keep the temperature constant for reaction for 120 min, and cool down to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination, heat it to a final temperature of 900 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, continuously react for 180 min, and cool down to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon negative electrode material based on the composite raw material. Example 10

[0053] The composite raw material of the hard carbon anode material is a biomass precursor and a modifier; among them, the biomass precursor is Chlorella vulgaris, and the modifier is sodium carboxymethylcellulose; the sodium-ion hard carbon anode material based on the composite raw material is prepared according to the following steps: Wash the Chlorella vulgaris with water, dry it, crush and screen it. After the obtained Chlorella vulgaris and sodium carboxymethylcellulose are mixed evenly at a mass ratio of 0.5:1, take 10 g of the composite raw material and place it in an oven at 60 °C for 6 h of drying, then put it into a high-temperature tube furnace for low-temperature pyrolysis. After rising to the final temperature of 700 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, keep the temperature constant for reaction for 120 min, and cool down to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination, rise to the final temperature of 2000 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, continuously react for 180 min, and cool down to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon anode material based on the composite raw material. Example 11

[0054] A sodium-ion hard carbon anode material based on a composite raw material. The composite raw material of the hard carbon anode material is a biomass precursor and a modifier; among them, the biomass precursor is Sargassum, and the modifier is sodium carboxymethylcellulose; the sodium-ion hard carbon anode material based on the composite raw material is prepared according to the following steps: Wash the Sargassum with water, dry it, crush and screen it. After the obtained Sargassum and sodium carboxymethylcellulose are mixed evenly at a mass ratio of 0.5:1, take 10 g of the composite raw material and place it in an oven at 60 °C for 6 h of drying, then put it into a high-temperature tube furnace for low-temperature pyrolysis. After rising to the final temperature of 700 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, keep the temperature constant for reaction for 120 min, and cool down to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination, rise to the final temperature of 1300 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, continuously react for 180 min, and cool down to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon anode material based on the composite raw material. Example 12

[0055] The composite raw material of the hard carbon negative electrode material is a biomass precursor and a modifier; among them, the biomass precursor is Chlorella and brown algae with a mass ratio of 2:1, and the modifier is sodium carboxymethyl cellulose; the sodium-ion hard carbon negative electrode material based on the composite raw material is prepared according to the following steps: Wash the biomass precursor with water, dry it, crush and screen it. After the obtained biomass precursor and sodium carboxymethyl cellulose are mixed evenly at a mass ratio of 0.5:1, take 10 g of the composite raw material and place it in an oven at 60 °C for drying for 6 h, then put it into a high-temperature tube furnace for low-temperature cracking. After heating to the final temperature of 700 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, keep the temperature constant for reaction for 120 min, and cool down to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination, heat it to the final temperature of 2000 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, continuously react for 180 min, and cool down to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon negative electrode material based on the composite raw material. Example 13

[0056] The composite raw material of the hard carbon negative electrode material is a biomass precursor and a modifier; among them, the biomass precursor is Chlorella and brown algae with a mass ratio of 5:1, and the modifier is sodium carboxymethyl cellulose; the sodium-ion hard carbon negative electrode material based on the composite raw material is prepared according to the following steps: Wash the biomass precursor with water, dry it, crush and screen it. After the obtained biomass precursor and sodium carboxymethyl cellulose are mixed evenly at a mass ratio of 0.5:1, take 10 g of the composite raw material and place it in an oven at 60 °C for drying for 6 h, then put it into a high-temperature tube furnace for low-temperature cracking. After heating to the final temperature of 700 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, keep the temperature constant for reaction for 120 min, and cool down to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination, heat it to the final temperature of 2000 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, continuously react for 180 min, and cool down to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon negative electrode material based on the composite raw material. Example 14

[0057] The composite raw material of the hard carbon negative electrode material is a biomass precursor and a modifier; among them, the biomass precursor is Chlorella and brown algae with a mass ratio of 2:4, and the modifier is sodium carboxymethylcellulose; the sodium-ion hard carbon negative electrode material based on the composite raw material is prepared according to the following steps: Wash the biomass precursor with water, dry it, crush and screen it. After the obtained biomass precursor and sodium carboxymethylcellulose are mixed evenly at a mass ratio of 0.5:1, take 10 g of the composite raw material and put it in an oven at 60 °C for drying for 6 h, then put it into a high-temperature tube furnace for low-temperature pyrolysis. After heating to the final temperature of 700 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, keep the temperature constant for reaction for 120 min, and cool down to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination, heat it to the final temperature of 2000 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, continuously react for 180 min, and cool down to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon negative electrode material based on the composite raw material. Example 15

[0058] The composite raw material of the hard carbon negative electrode material is a biomass precursor and a modifier; among them, the biomass precursor is Chlorella and brown algae with a mass ratio of 5:1, and the modifier is sodium carboxymethylcellulose; the sodium-ion hard carbon negative electrode material based on the composite raw material is prepared according to the following steps: Wash the biomass precursor with water, dry it, crush and screen it. After the obtained biomass precursor and sodium carboxymethylcellulose are mixed evenly at a mass ratio of 2:1, take 10 g of the composite raw material and put it in an oven at 60 °C for drying for 6 h, then put it into a high-temperature tube furnace for low-temperature pyrolysis. After heating to the final temperature of 700 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, keep the temperature constant for reaction for 120 min, and cool down to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination, heat it to the final temperature of 2000 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, continuously react for 180 min, and cool down to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon negative electrode material based on the composite raw material. Example 16

[0059] The composite raw material of the hard carbon anode material is a biomass precursor and a modifier; wherein, the biomass precursor is Chlorella, and the modifier is sodium carboxymethylcellulose; the sodium-ion hard carbon anode material based on the composite raw material is prepared according to the following steps: Wash the Chlorella with water, dry it, crush and screen it. After the obtained Chlorella and sodium carboxymethylcellulose are mixed evenly at a mass ratio of 0.5:1, take 10 g of the composite raw material and dry it in an oven at 60 °C for 6 h, then put it into a high-temperature tube furnace for low-temperature pyrolysis.

[0060] After rising to the final temperature of 700 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, and keep the temperature constant for reaction for 120 min. Then cool it to room temperature at a cooling rate of 3.3 °C / min; Subsequently, put the above material into a high-temperature tube furnace for high-temperature calcination. Rise to the final temperature of 1300 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, continue the reaction for 180 min, and cool it to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon anode material based on the composite raw material.

[0061] Comparative Example 1

[0062] The composite raw material of the hard carbon anode material is a biomass precursor; wherein, the biomass precursor is Chlorella; the sodium-ion hard carbon anode material based on the composite raw material is prepared according to the following steps: Wash the Chlorella with water, dry it, crush and screen it. Take 10 g of the above Chlorella and dry it in an oven at 60 °C for 6 h, then put it into a high-temperature tube furnace for low-temperature pyrolysis. After rising to the final temperature of 700 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, and keep the temperature constant for reaction for 120 min. Then cool it to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination. Rise to the final temperature of 1300 °C at a heating rate of 5 °C / min, introduce the protective gas argon with a gas flow rate of 60 mL / min, continue the reaction for 180 min, and cool it to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon anode material based on the composite raw material.

[0063] Comparative Example 2

[0064] The composite raw material of the hard carbon negative electrode material is a modifier; among them, the modifier is sodium carboxymethyl cellulose; the sodium-ion hard carbon negative electrode material based on the composite raw material is prepared according to the following steps: dry and screen the modifier, take 10 g of the modifier and put it into an oven at 60 °C for drying for 6 h, then put it into a high-temperature tube furnace for low-temperature pyrolysis, raise the temperature to the final temperature of 700 °C at a heating rate of 5 °C / min, then introduce the protective gas argon, the gas flow rate is 60 mL / min, keep the temperature constant for reaction for 120 min, cool down to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination, raise the temperature to the final temperature of 1300 °C at a heating rate of 5 °C / min, introduce the protective gas argon, the gas flow rate is 60 mL / min, continue the reaction for 180 min, and cool down to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon negative electrode material based on the composite raw material.

[0065] Comparative Example 3

[0066] The composite raw material of the hard carbon negative electrode material is a biomass precursor; among them, the biomass precursor is Dalbergia oliveri Gamble; the sodium-ion hard carbon negative electrode material based on the composite raw material is prepared according to the following steps: wash and dry Dalbergia oliveri Gamble with water, crush and screen it, take 10 g of the above Dalbergia oliveri Gamble and put it into an oven at 60 °C for drying for 6 h, then put it into a high-temperature tube furnace for low-temperature pyrolysis, raise the temperature to the final temperature of 700 °C at a heating rate of 5 °C / min, then introduce the protective gas argon, the gas flow rate is 60 mL / min, keep the temperature constant for reaction for 120 min, cool down to room temperature at a cooling rate of 3.3 °C / min. Subsequently, wash it three times with deionized water and dry it at 60 °C for 6 h. Finally, put the above material into a high-temperature tube furnace for high-temperature calcination, raise the temperature to the final temperature of 1300 °C at a heating rate of 5 °C / min, introduce the protective gas argon, the gas flow rate is 60 mL / min, continue the reaction for 180 min, and cool down to room temperature at a cooling rate of 3.3 °C / min to obtain the sodium-ion hard carbon negative electrode material based on the composite raw material.

[0067] The following method is adopted for the physical and chemical property test technical indexes of a sodium-ion hard carbon negative electrode material based on the composite raw material prepared in the examples and comparative examples:

[0068] a. Electrical property test: respectively modulate the hard carbon materials A, D, E, and F with conductive carbon black and sodium alginate into a slurry according to a mass ratio of 80:10:10 with deionized water, then coat it on the copper foil with a film applicator, dry it at 70 °C for 6 h and then dry it in vacuum at 120 °C for 12 h. After the copper foil coated with the sample is roll-pressed, it is punched into an electrode sheet with a diameter of 12 mm for use, and the mass of the active substance is about 1.3 mg / cm 2. Then, it was assembled into a 2032-type button battery in a glove box, and the electrolyte had a composition of 1.0 mol / L NaClO4 / EC+DMC (volume ratio 1:1). A glass fiber membrane was used as the separator, and a sodium metal sheet was used as the counter electrode. The button battery was subjected to cycling and rate tests on a CT-3008 Neware battery tester (room temperature, voltage range 0.01–2.0V vs. Na / Na+). The results are shown in Table 1 below and Figures 1-5 :

[0069] In the above preparation method, the XRD pattern of the purified product obtained in Example 1 is as shown in Figure 2 . It can be seen from Figure 2 that the position of the 2θ peak, combined with the Bragg equation d = λ / 2sinθ, was calculated to obtain d = 0.38 nm. After high-temperature carbonization of the sodium-ion hard carbon negative electrode material based on the composite raw materials, the interlayer spacing of the hard carbon was 0.38 nm. This interlayer spacing of the hard carbon is much larger than the graphite interlayer spacing (0.335 nm), which is suitable for the insertion and extraction of sodium ions and can improve the reversible specific capacity.

[0070] The Raman scattering (Raman) pattern of the obtained sodium-ion hard carbon negative electrode material based on the composite raw materials is as shown in Figure 3 . It can be seen from Figure 3 that the sodium-ion hard carbon negative electrode material based on the composite raw materials has typical characteristic peaks, the D peak and the G peak, after high-temperature carbonization, indicating a high degree of disorder and rich defects, which is beneficial to sodium storage.

[0071] Table 1 Performance test results

[0072]

[0073] As can be seen from Table 1, a sodium-ion hard carbon negative electrode material based on the composite raw materials obtained in the above examples has a large pore size distribution range, a relatively large graphite interlayer spacing, a low degree of graphitization, good sodium storage performance, a higher reversible specific capacity, and a high initial Coulomb efficiency, showing excellent cycle stability. These performance indicators are the key factors for promoting the commercialization of sodium-ion batteries and are conducive to commercial promotion and application.

[0074] Comparing Comparative Example 1, Examples 3-6 and Comparative Examples 1-3, it can be seen that the graphite layer spacing, reversible specific capacity, and initial Coulombic efficiency of the sodium-ion hard carbon anode material based on the composite raw material prepared in Comparative Examples 1-3 are lower than those in Example 1 and Examples 3-6. Through comparative analysis, it can be obtained that when algae biomass and a modifier are used in combination, the biomass precursor is selected as a carbonizable algae material, which is carbonized and reconstructed to form a large number of nitrogen-containing conjugated heterocyclic structures. Combining with the modifier can form a graphite-like nanosheet layer with a random orientation, bending, edge defects, and a large interlayer distance, thereby regulating the microstructure of hard carbon, constructing abundant closed pores. The abundant closed pores can increase the sodium storage capacity in the "pore filling", increase the specific capacity of the hard carbon material, and the enlarged interlayer distance enables sodium ions not to damage the microstructure of hard carbon during the process of insertion and extraction, enhancing its cycle stability, and reducing the specific surface area of hard carbon, thereby reducing the consumption of the electrolyte and improving the initial Coulombic efficiency.

[0075] The proportion range of the biomass and the modifier disclosed in this application enables the modifier to have good cross-linking ability, significantly enhancing the cross-linking effect of the biomass precursor and the structural stability during the heat treatment process. By regulating the microstructure of hard carbon and increasing the sodium storage active sites, the sodium storage performance of the sodium-ion battery is further improved. If there is too much modifier, there will be too many closed pores and a small pore size range, which will affect the extraction of sodium. Although the cycle stability is enhanced, the initial Coulombic efficiency and specific capacity are affected; if there is too little modifier, the number of closed pores will decrease, the sodium storage capacity will decrease, and the specific capacity of the hard carbon material will decrease. In addition, the cycle stability of the sodium-ion anode material is insufficient, and it is easy to damage the microstructure of hard carbon.

[0076] Comparing Example 1 and Examples 11-16, it can be seen that the graphite layer spacing, reversible specific capacity, and initial Coulombic efficiency of the sodium-ion hard carbon anode material based on the composite raw material prepared in Examples 12-16 are better than those in Example 1 and Example 11. The applicant's research believes that during the carbonization process, the mineral ions contained in Chlorella frequently enter and exit the pseudo-graphite layer structure, the carbonization intermediate, and the heterocyclic structure after carbonization and reconstruction, further expanding the interlayer distance of the pseudo-graphite layer and further increasing the pore distribution range, improving the graphitization degree, which is beneficial to the free insertion / extraction of sodium ions between the layers. In addition, fucoxanthin contained in brown algae has a long conjugated double bond and a special structure containing allene and epoxy alkane. Reacting with Chlorella during carbonization increases the random orientation and edge properties, and rearrangement is more likely to occur during the carbonization process, improving the pseudo-graphitization degree, enhancing the cycle stability of the battery, increasing the specific capacity of sodium ions, and improving the sodium storage performance. In addition, if the mass of brown algae is too large, the interlayer distance of the pseudo-graphite layer will be smaller, which is instead not conducive to the free movement of sodium ions between the layers.

[0077] Comparing Example 3 with Example 16, under the condition of the optimal proportion of combined use of algal biomass and modifier and the optimal preparation conditions, Chlorella and brown algae are mixed in an appropriate proportion, so that the electrochemical properties such as the graphite layer spacing, reversible specific capacity, and first Coulomb efficiency of the sodium-ion hard carbon anode material based on the composite raw material are optimal.

[0078] Comparing Example 1 with Examples 7 - 8, it can be seen that the graphite layer spacing, reversible specific capacity, and first Coulomb efficiency of the sodium-ion hard carbon anode material based on the composite raw material prepared in Examples 7 - 8 are all lower than those in Example 1. Through analysis, it is considered that low-temperature pyrolysis removes the volatile components in the biomass material, introduces oxygen-containing functional groups, and forms abundant closed pores, increasing the sodium storage sites in the internal structure of the material, and making the hard carbon material have a high degree of disorder and abundant defects, which is beneficial to sodium storage. During this process, if the final temperature is too high, the degree of graphitization is too high, the number of closed pores decreases, affecting the sodium storage performance and reducing the specific capacity; if the final temperature is too low, the layer spacing of the hard carbon material makes it easy to damage the microstructure of the hard carbon during the process of sodium ion insertion and extraction, affecting its cycle stability, and the high first Coulomb efficiency also decreases accordingly.

[0079] Comparing Example 1 with Examples 9 - 10, it can be seen that the graphite layer spacing, reversible specific capacity, and first Coulomb efficiency of the sodium-ion hard carbon anode material based on the composite raw material prepared in Examples 9 - 10 are all lower than those in Example 1. Through comparative analysis, it can be obtained that the temperature range disclosed in this application can make the degree of graphitization of the hard carbon anode material, so as to form an appropriate pseudo-graphite layer spacing, which is beneficial to the graphitization of the hard carbon, improving the low-voltage platform capacity and first Coulomb efficiency of the hard carbon. If the calcination temperature is too high, the layer spacing is too small, affecting the specific capacity of the hard carbon material; if the temperature is too low, the degree of graphitization is small, the number of closed pores decreases, affecting the capacity and first Coulomb efficiency of the hard carbon anode material.

[0080] Comparing Example 1 with Example 16, it can be seen that after low-temperature pyrolysis, washing and drying can elute the metal salt ions obtained after pyrolysis, preventing the metal salt ions from evaporating during the subsequent high-temperature calcination, resulting in too large a specific surface area of the hard carbon, consuming too much electrolyte, and reducing its Coulomb efficiency.

[0081] The above are all preferred embodiments of this application. The protection scope of this application is not limited by this. Therefore, all equivalent changes made according to the structure, shape, and principle of this application should be covered within the protection scope of this application.

Claims

1. A preparation method of a sodium-ion hard carbon anode material based on a composite raw material, comprising the following steps: (1) Cleaning, drying, pulverizing, and sieving the biomass precursor material; (2) Mixing the obtained biomass precursor and the modifier in proportion; (3) Drying the material obtained in (2); (4) Subjecting the obtained material to low-temperature pyrolysis, introducing a protective gas, heating to the final temperature at a heating rate of 0.1 - 10 °C / min, after holding the temperature for reaction, cooling to room temperature at a cooling rate of 0.1 - 10 °C / min; (5) Cleaning the treated sample with a cleaning solution and then drying; (6) Subjecting the sample treated in (5) to high-temperature calcination, introducing a protective gas, heating to the final temperature at a heating rate of 0.1 - 10 °C / min, after holding the temperature for reaction, cooling to room temperature at a cooling rate of 0.1 - 10 °C / min, and carbonizing to obtain the hard carbon anode material; the biomass precursor is a carbonizable algal biomass material; the carbonizable algal biomass material includes chlorella and brown algae, and the mass ratio of chlorella to brown algae is (2 - 5):1; the modifier is one or two of sodium citrate and sodium carboxymethyl cellulose; the mass ratio of the biomass precursor to the modifier is (0.5 - 5):

1.

2. The preparation method of a sodium-ion hard carbon anode material based on a composite raw material according to claim 1, wherein: The drying method in (3) includes one of freeze-drying and drying.

3. The preparation method of a sodium-ion hard carbon negative electrode material based on a composite raw material according to claim 2, characterized in that: The drying temperature in (3) is 50 - 300 °C.

4. The preparation method of a sodium-ion hard carbon anode material based on a composite raw material according to claim 1, characterized in that: The final temperature of the low-temperature pyrolysis is 300 - 900 °C, and the holding time for reaction is 0.5 - 10 h.

5. The preparation method of a sodium-ion hard carbon negative electrode material based on a composite raw material according to claim 1, characterized in that: The final temperature of the high-temperature calcination is 1000 - 1800 °C, and the holding time for reaction is 0.1 - 10 h.

6. The preparation method of a sodium-ion hard carbon anode material based on a composite raw material according to claim 1, characterized in that: The protective gas in (6) is at least one of argon, nitrogen, and helium, and the gas flow rate is 5 - 100 mL / min.

7. The preparation method of a sodium-ion hard carbon anode material based on a composite raw material according to claim 1, characterized in that: The cleaning solution in (5) includes at least one of an acid solution, an alkali solution, or an aqueous solution.

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