High initial coulomb efficiency hard carbon material for sodium ion battery negative electrode and preparation method thereof

Abstract

The application relates to the technical field of battery materials and preparation methods, and is a high-initial Coulomb efficiency hard carbon material for a sodium ion battery negative electrode and a preparation method thereof.The high-initial Coulomb efficiency hard carbon material for the sodium ion battery negative electrode comprises the following steps: extruding a carbon precursor into a carbon column; removing volatile components in the carbon column after shaping through low-temperature carbonization; directly electrically heating the carbon column after the low-temperature carbonization and maintaining for a specific time length; and crushing the carbon column after cooling to a particle size of less than 32 um to obtain the high-initial Coulomb efficiency hard carbon material for the sodium ion battery negative electrode.The high-pressure compression of the porous biomass precursor greatly reduces the open pore volume of the biomass carbon, and the specific surface area of the material is reduced; in the subsequent pyrolysis and low-temperature carbonization processes, the tightly extruded biomass particles inhibit the volatilization of volatile components, more volatile components are decomposed into carbon, the carbon yield is improved, the closed pores are promoted to be generated, and then the high-initial-efficiency hard carbon product is prepared.

Description

High initial coulombic efficiency hard carbon material for sodium-ion battery anode and its preparation method Technical Field

[0001] This invention relates to the technical field of battery materials and preparation methods, and is a high initial coulombic efficiency hard carbon material for sodium-ion battery anodes and its preparation method, and also includes an anode prepared from the high initial coulombic efficiency hard carbon material for sodium-ion battery anodes. Background Technology

[0002] The limited production capacity of hard carbon has hindered large-scale production. Therefore, there is an urgent need to improve hard carbon carbonization methods to meet growing market demand. Battery technology plays a central role in achieving carbon neutrality, particularly in portable electronics, electric vehicles, and large-scale energy storage such as grid storage. Currently, lithium-ion batteries dominate the battery market due to their high energy density, long lifespan, stability, and compact design. However, the finite and uneven distribution of lithium and other rare metal resources means that the long-term growth of the lithium-ion battery market will face challenges, leading to a significant increase in costs. This has also driven the market to seek alternatives to lithium-ion batteries.

[0003] Due to the similarity of sodium's physical and chemical properties to lithium, coupled with its cost-effectiveness and abundant resources, sodium-ion batteries are gradually becoming a strong alternative to lithium-ion batteries. The structure of sodium-ion batteries is similar to that of lithium-ion batteries, including a positive electrode, negative electrode, separator, and electrolyte. Therefore, electrode design can draw upon lithium-ion battery technology. Currently, the main positive electrode materials for sodium-ion batteries, such as layered and tunnel-type transition metal oxides, transition metal sulfides and fluorides, oxygen-containing anionic compounds, Prussian blue analogs, and polymers, all originate from similar lithium-ion battery technologies. However, the chemical differences between lithium and sodium mean that their interactions with electrode materials differ, especially in the negative electrode. For example, the theoretical lithium-ion storage capacity is 372 mAhg. -1 Graphite is the most commonly used negative electrode in lithium-ion batteries. However, in sodium-ion batteries, graphite can only provide about 35 mAh / g. -1 The sodium storage specific capacity is attributed to the fact that the radius of Na+ (0.102 nm) is larger than that of Li+ (0.076 nm), which prevents Na+ from intercalating into the interlayer spacing of graphite (0.334 nm). Therefore, further development of novel sodium-ion battery anode materials is needed to meet the development requirements of sodium-ion batteries.

[0004] The main requirements for anode materials in sodium-ion batteries include high sodium-ion storage capacity, a potential similar to pure sodium metal, stability to the electrolyte, high electronic and ionic conductivity, low cost, and environmental impact. Currently, the main anode material technologies for sodium-ion batteries fall into three categories: metal oxides, alloy compounds, and carbon-based materials. While metal oxides and alloy compounds possess high theoretical capacities, their sodium storage methods, based on alloying and conversion reactions, lead to significant volume expansion during sodium storage, resulting in electrode deactivation and affecting long-term stability. In contrast, carbon-based materials, particularly hard carbon which stores sodium through intercalation, filling, and adsorption, exhibit better structural stability and safety during sodium formation and desodiumation. Hard carbon is a carbonaceous material that does not transform into graphite even at temperatures as high as 3000°C. It consists of randomly arranged, bent, and defective graphene nanosheets. This random, disordered structure generates surface defects, nanopores, and graphite-like domain structures, corresponding to the three different sodium storage methods of adsorption, filling, and intercalation, respectively, thus providing more active sites for sodium-ion storage. These properties make hard carbon not only have a high theoretical specific capacity and good safety, but also have significant advantages in commercial applications, making it an ideal choice for the anode of commercial sodium batteries.

[0005] Fossil fuels, polymers, and biomass are the main precursors for commercial hard carbon materials. However, fossil fuel-based hard carbon requires acid washing, chemical modification, and other pretreatment steps in its preparation, which increase the complexity of synthesis and may lead to additional environmental burdens during manufacturing. Polymer synthesis often involves energy-intensive processes, making the resulting hard carbon expensive. In contrast, biomass shows significant potential as a precursor for hard carbon. Biomass materials are not only widely available and inexpensive but also possess good sustainability. Biomass-based hard carbon can be prepared by pyrolyzing natural organic matter such as wood, agricultural waste, and food processing byproducts. Furthermore, the pyrolyzed hard carbon retains the original porous structure of biomass, which facilitates sodium ion diffusion, resulting in generally high specific capacities. These factors make biomass-based hard carbon a high-performance, environmentally friendly, and cost-effective option.

[0006] However, biomass-based hard carbon faces several key challenges in practical applications. First, while biomass sources are widespread, their diverse varieties and seasonality make it difficult to guarantee consistent and stable raw material supply. Different biomass varieties require different processing techniques, increasing the complexity of process selection and equipment configuration. Second, in the traditional carbonization process of biomass-based hard carbon, the yield primarily depends on the fixed carbon content of the precursor material, resulting in low yields, typically only 14% to 30%, lower than other precursor materials. This low yield not only affects the economics of hard carbon production but also increases the environmental burden. Furthermore, the inherent initial coulombic efficiency of biomass-based hard carbon is typically below 80%, posing a significant challenge in sodium-ion battery applications. The low initial coulombic efficiency of the negative electrode leads to irreversible consumption of sodium ions from the positive electrode in the full-cell system, thereby reducing the overall energy density of the battery. This phenomenon can be attributed to the retention of the inherent structure of biomass after carbonization, characterized by extensive surface defects, porosity, and high specific surface area, all of which contribute to the formation of an irreversible solid electrolyte interface layer.

[0007] Depending on the specific needs and pain points of different application areas, the future of hard carbon anodes may see a diverse range of developments. For cost-sensitive markets (electric two-wheelers, low-speed vehicles, etc.), low-end hard carbon materials with a specific capacity of 280 mAh / g to 290 mAh / g and an initial coulombic efficiency of around 90% can meet the requirements, with a greater emphasis on low cost. However, for high-end market applications, the required specific capacity is generally above 350 mAh / g, and the initial coulombic efficiency must be greater than or equal to 92%. High initial coulombic efficiency remains a prerequisite for the commercial application of hard carbon anodes. Therefore, before commercial application, specific methods are usually needed to enhance the initial coulombic efficiency of biomass-based hard carbon.

[0008] More importantly, hard carbon production primarily involves the high-temperature carbonization of biomass raw materials, a process requiring an inert atmosphere exceeding 1100°C, making it a highly energy-intensive process. Currently, traditional carbonization processes are mainly based on indirect heating, supplying heat to the material from the outside through mechanisms such as conduction, convection, and radiation, as seen in industrial vacuum electric furnaces and continuous high-temperature kilns. This carbonization method has significant limitations. First, the furnace must operate at temperatures far exceeding the target to ensure the necessary inward heat flow, leading to heat loss and increased energy consumption. This inefficient heating process necessitates extended heating times, especially in large-scale production, to ensure thorough hard carbonization. Second, indirect heating struggles to achieve a uniform temperature distribution throughout the material, potentially resulting in inconsistent hard carbon product quality. Furthermore, the heat transfer limitations of traditional high-temperature furnaces generally result in small production scales, restricting hard carbon production capacity and hindering large-scale production. Therefore, there is an urgent need to improve hard carbonization methods to meet the growing market demand.

[0009] The following are some patent application documents related to biomass-based hard carbon:

[0010] In the prior art, for example, Chinese patent document CN106299365A discloses a method for preparing a biomass hard carbon anode. This biomass hard carbon anode material is prepared by the following method: 1) pulverizing biomass raw materials to obtain precursor particles; 2) under a protective atmosphere, pre-calcining the precursor particles at 400℃ to 600℃ for 1.5h to 2.5h, then cooling them to room temperature in the furnace, and then calcining them at 800℃ to 1600℃ for 2h to 5h, followed by cooling to obtain an intermediate product; 3) soaking the intermediate product in an alkaline solution, then soaking it in an acidic solution, washing it with water until neutral, and drying it to obtain a purified product; 4) subjecting the purified product to microwave vacuum activation at 1000W to 2000W power for 3s to 15s. The obtained biomass hard carbon anode material exhibits an initial charge-discharge efficiency of over 90%, good cycle stability, a reversible specific capacity of over 300mAh / g, and excellent electrochemical performance. This method still cannot produce biomass hard carbon products with coulombic efficiency comparable to graphite, and it cannot solve the problem of large-scale production of hard carbon.

[0011] Chinese patent document CN113224264A discloses a method for manufacturing biomass hard carbon for sodium-ion battery anodes, comprising: mixing a carbon source and nanopowder to obtain a precursor; placing the precursor in an oxygen-isolated environment; heating to carbonize the precursor to form a hard carbon mixture; acid washing the hard carbon mixture with an acidic solution to adjust the pH value to less than 0.5; washing the hard carbon mixture with pure water to adjust the pH value to greater than 6; and drying the hard carbon mixture to form biomass hard carbon. This method utilizes the high oxygen content of biomass thermochemical oils, which have the function of polymerizing and activating carbon materials at high temperatures. The pore size distribution of the hard carbon can be adjusted by changing the proportion of nano-calcium carbonate. Furthermore, the cost of biomass thermochemical oils is lower than that of general carbon material precursors. Moreover, when applied to sodium-ion or lithium-ion batteries, biomass hard carbon can improve the reversible specific capacity and conductivity of the battery.

[0012] Chinese patent document CN116730319A discloses a preparation device, preparation method, and application of a biomass-based hard carbon anode material. The preparation method includes the following steps: S1: Pre-pyrolyzing the biomass raw material, then crushing and sieving it to obtain a pre-treated raw material; S2: Sending the pre-treated raw material into the airflow crushing chamber (6) of the surface distortion system for further airflow crushing, thereby enhancing the surface lattice distortion of the further crushed raw material to obtain a first modified material; S3: [The text abruptly ends here, so the translation stops as well.] The gas delivery pipe (7) is sent into the high-energy modification chamber (10) of the high-energy surface modification system, and a modifier is added to the high-energy modification chamber (10). Then the plasma emission component is activated to ionize the modifier in the high-energy modification chamber (10) to obtain anions to modify the first modified material, thereby increasing the crystal disorder of the first modified material to obtain the second modified material; S4: The second modified material is sent into the high-temperature carbonization system, and the second modified material is heated in an inert atmosphere to carbonize and decompose the second modified material to obtain a biomass-based hard carbon anode material. The apparatus and method for preparing the biomass-based hard carbon anode material are based on the principle of biomass heteroatomic doping modification-high-temperature pyrolysis carbonization. Based on the crystal structure characteristics of hard carbon materials, and combining material surface distortion-high-energy surface modification-high-temperature carbonization, the process utilizes the ultra-high energy of high-speed collisions, friction, and shearing driven by high-speed airflow during precise crushing and pretreatment of raw materials to increase the degree of grain distortion in the pre-pyrolysis particles of biomass, thereby enhancing the reactivity of the pre-pyrolysis particles and making it easier to react with heteroatoms to complete doping. High-energy surface modification utilizes high-energy plasma to obtain high-energy charged heteroelement ions, which can complete the heteroatomic doping of the first modified material in a short time, increasing the disorder of the surface-distorted biomass particles and obtaining a second modified material with uniform size. Through the above apparatus and method, production efficiency can be improved and production costs reduced while achieving efficient preparation of biomass-based amorphous hard carbon anode materials. This hard carbon anode achieves a first-charge specific capacity of 348.22 mAh·g at a 0.1C rate. -1 The initial efficacy rate can reach 89.88%.

[0013] Chinese patent document CN110719891A discloses a biomass-based hard carbon anode material for sodium-ion batteries, its preparation method, and its application. The method includes the following steps: washing and drying biomass materials, heating them in an oxygen-deficient atmosphere at 100-800°C for 1-24 hours in the absence of air to obtain a carbon precursor; pulverizing the obtained carbon precursor and impregnating it in a permanganate solution to oxidize the carbon material and generate more sodium storage sites; drying and sieving the treated carbon precursor, followed by secondary sintering at 800-2500°C for 0.5-48 hours in an inert atmosphere; washing the product with acid, rinsing with water until pH=7, and drying to obtain the final product. Using this hard carbon anode material as the positive electrode, coin cells are assembled in a glove box filled with argon gas and with strictly controlled water and oxygen levels. At a voltage of 0-2V and a current density of 20mA / g, the initial charge specific capacity reaches 288mAh g. -1 Up to 324mAh g -1 The initial coulomb efficiency can reach 76.60% to 81.05%. Summary of the Invention

[0014] This invention provides a high initial coulombic efficiency hard carbon material for sodium-ion battery anodes and its preparation method, overcoming the shortcomings of the prior art. It can effectively solve the problems of low initial efficiency and low carbonization process efficiency of sodium-ion battery hard carbon electrodes in the prior art. The high initial coulombic efficiency hard carbon material for sodium-ion battery anodes of this invention has an initial charge-discharge coulombic efficiency of over 95%, and has higher specific capacity and longer cycle life performance.

[0015] One of the technical solutions of the present invention is achieved through the following measures: a method for preparing a high initial coulombic efficiency hard carbon material for sodium-ion battery anodes, comprising directly extruding a carbon precursor into a carbon column, the formed carbon column being subjected to low-temperature carbonization to completely remove volatiles, the low-temperature carbonized carbon column being directly electrically heated and maintained for a specific time, and after cooling, being pulverized to a particle size of less than 32 μm to obtain a high initial coulombic efficiency hard carbon material for sodium-ion battery anodes.

[0016] The second technical solution of the present invention is achieved through the following measures: a method for preparing a high initial coulombic efficiency hard carbon material for sodium-ion battery anodes, comprising mixing a carbon precursor with an organic binder, heating the mixture to soften the organic binder, then extruding it into a carbon column, the formed carbon column first undergoing low-temperature carbonization to completely remove the volatiles therein, the low-temperature carbonized carbon column being directly electrically heated and maintained for a specific time, and after cooling, being pulverized to a particle size of less than 32 μm to obtain a high initial coulombic efficiency hard carbon material for sodium-ion battery anodes.

[0017] The third technical solution of the present invention is achieved through the following measures: a method for preparing a high initial coulombic efficiency hard carbon material for sodium-ion battery anodes, comprising the following steps:

[0018] Step 1: Purify the carbon precursor;

[0019] Step 2: When the fixed carbon content in the purified carbon precursor is less than 40%, the purified carbon precursor is pressed into shape to obtain a carbon column. The carbon column is heated in an inert atmosphere for a certain period of time to obtain a low-temperature carbonized carbon column.

[0020] Step 3: The low-temperature carbonized carbon column is directly electrically heated in an inert atmosphere, and after cooling, it is crushed to a particle size of less than 32 μm to obtain a high initial coulombic efficiency hard carbon material for sodium-ion battery anodes.

[0021] The fourth technical solution of the present invention is achieved through the following measures: a method for preparing a high initial coulombic efficiency hard carbon material for sodium-ion battery anodes, comprising the following steps:

[0022] Step 1: Purify the carbon precursor;

[0023] Step 2: When the fixed carbon content in the purified carbon precursor is greater than or equal to 40%, the carbon precursor is mixed with an organic binder and heated to soften the organic binder. Then, the carbon precursor and organic binder are pressed into shape to obtain a carbon column. The carbon column is heated in an inert atmosphere for a certain period of time to obtain a low-temperature carbonized carbon column.

[0024] Step 3: The low-temperature carbonized carbon column is directly electrically heated in an inert atmosphere, and after cooling, it is crushed to a particle size of less than 32 μm to obtain a high initial coulombic efficiency hard carbon material for sodium-ion battery anodes.

[0025] The fifth technical solution of the present invention is achieved through the following measures: a method for preparing a high initial coulombic efficiency hard carbon material for sodium-ion battery anodes, comprising the following steps:

[0026] Step 1: Prepare biochar from carbon precursors and purify the biochar.

[0027] Step 2: When the fixed carbon content in the purified biochar is less than 40%, the purified biochar is pressed into shape to obtain a carbon column. The carbon column is then heated in an inert atmosphere for a certain period of time to obtain a low-temperature carbonized carbon column.

[0028] Step 3: The low-temperature carbonized carbon column is directly electrically heated in an inert atmosphere, and after cooling, it is crushed to a particle size of less than 32 μm to obtain a high initial coulombic efficiency hard carbon material for sodium-ion battery anodes.

[0029] The sixth technical solution of the present invention is achieved through the following measures: a method for preparing a high initial coulombic efficiency hard carbon material for sodium-ion battery anodes, comprising the following steps:

[0030] Step 1: Prepare biochar from carbon precursors and purify the biochar.

[0031] Step 2: When the fixed carbon content in the purified biochar is greater than or equal to 40%, the biochar is mixed with an organic binder and heated to soften the organic binder. Then, the biochar and organic binder are pressed into shape to obtain a carbon column. The carbon column is heated in an inert atmosphere for a certain period of time to obtain a low-temperature carbonized carbon column.

[0032] Step 3: The low-temperature carbonized carbon column is directly electrically heated in an inert atmosphere, and after cooling, it is crushed to a particle size of less than 32 μm to obtain a high initial coulombic efficiency hard carbon material for sodium-ion battery anodes.

[0033] The seventh technical solution of the present invention is achieved by the following measures: a high initial coulombic efficiency hard carbon material for sodium-ion battery anode prepared by the preparation method of the high initial coulombic efficiency hard carbon material for sodium-ion battery anode described in any of the above technical solutions.

[0034] The following are further optimizations and / or improvements to the above-mentioned technical solution:

[0035] Further, the purification method described in step one is as follows: the carbon precursor is sequentially acid-washed, water-washed until the pH value is neutral, and then sequentially alkali-washed and water-washed until the pH value is neutral to obtain the purified carbon precursor.

[0036] Furthermore, direct electric heating can be achieved through induction heating or Joule heating.

[0037] Furthermore, in step two, the carbon column is heated to 600°C to 800°C under an inert atmosphere and held at that temperature for 2 to 3 hours to obtain a low-temperature carbonized carbon column.

[0038] Furthermore, in step three, the low-temperature carbonized carbon column is heated to 1000°C to 1600°C under an inert atmosphere for induction heating or Joule heating, and then held at that temperature for 1 to 3 hours before cooling.

[0039] Furthermore, the organic binder may be one or more of biomass tar, bitumen, and resin. Other existing, well-known, and commonly used organic binders may also be used.

[0040] Furthermore, the carbon precursor is one of biomass, coal, and resin.

[0041] Anthracite can be used as the coal.

[0042] Furthermore, when plant biomass is used as biomass, both biochar and biotar are products derived from the pyrolysis of plant biomass at 350°C to 550°C.

[0043] Furthermore, the mass ratio of biochar to biotar is 6 to 8: 2 to 4.

[0044] The negative electrode prepared using a high initial coulombic efficiency hard carbon material for sodium-ion batteries, as described above, has a loading of 1 mg / cm³. 2 Up to -7mg / cm 2 .

[0045] The method for preparing high initial coulombic efficiency hard carbon material for sodium-ion battery anodes described in this invention is a novel method for preparing hard carbon by direct electrothermal carbonization, which solves the problem of low energy efficiency in existing technologies. Compared with traditional processes, it requires less heating time, has higher efficiency, and consumes less energy.

[0046] This invention provides a method for preparing hard carbon by mixing and pressing biochar and biochar tar, converting biochar tar, which cannot be applied in traditional processes, into biochar hard carbon. It solves the problem of low yield in existing technologies, increasing the yield of hard carbon production from biomass by more than 40% compared to traditional processes, while reducing the environmental burden by 30%.

[0047] The high initial coulombic efficiency hard carbon material for sodium-ion battery anodes of this invention greatly reduces the open pore volume of biomass char through high-pressure compression of porous biomass precursors, thereby reducing the specific surface area of ​​the material. During subsequent pyrolysis and low-temperature carbonization, the tightly compressed biomass particles suppress the volatilization of volatiles, and more volatiles decompose into carbon, which improves carbon yield and promotes the formation of closed pores, thus preparing high initial efficiency hard carbon products. Attached Figure Description

[0048] Figure 1 is a comparison of the heating efficiency and energy efficiency of the induction heating of the present invention and the traditional indirect heating.

[0049] Figure 2 is a comparison of the temperature distribution of the induction heating of the present invention and the traditional indirect heating.

[0050] Figure 3 is a SEM image of the hard carbon anode material obtained in Example 1.

[0051] Figure 4 is a TEM image of the hard carbon anode material obtained in Example 1.

[0052] Figure 5 is a SEM image of the hard carbon anode material obtained in Example 1.

[0053] Figure 6 is a SEM image of the negative electrode prepared in Example 1.

[0054] Figure 7 is a SEM image of the hard carbon anode material obtained in Example 2.

[0055] Figure 8 is a TEM image of the hard carbon anode material obtained in Example 2.

[0056] Figure 9 is a process flow diagram of the present invention (e.g., Example 3, Example 11).

[0057] Figure 10 is a SEM image of the hard carbon anode material obtained in Example 3.

[0058] Figure 11 is a SEM image of the hard carbon anode material obtained in Example 5.

[0059] Figure 12 is a TEM image of the hard carbon anode material obtained in Example 6.

[0060] Figure 13 is a SEM image of the hard carbon anode material obtained in Example 6.

[0061] Figure 14 is a SEM image of the carbon column obtained after induction heating in Example 7.

[0062] Figure 15 is a SEM image of the hard carbon anode material obtained in Example 7.

[0063] Figure 16 shows the carbon column obtained after induction heating in Example 7.

[0064] Figure 17 is a SEM image of the biochar obtained in step 1) of Example 8.

[0065] Figure 18 is a SEM image of the low-temperature carbonized carbon column obtained in step 2) of Example 8.

[0066] Figure 19 shows the carbon column obtained after induction heating in Example 8.

[0067] Figure 20 shows the laminate used in Example 9 (left) and the carbon column obtained after induction heating (right).

[0068] Figure 21 illustrates the manufacturing process of this invention.

[0069] Figure 22 is a SEM image of the hard carbon powder obtained by carbonization in Comparative Example 1.

[0070] Figure 23 is a SEM image of the hard carbon powder obtained by carbonization in Comparative Example 2.

[0071] Figure 24 is a SEM image of the hard carbon obtained by carbonization in Comparative Example 5.

[0072] Figure 25 shows the initial charge-discharge curves of the sodium-ion battery. Detailed Implementation

[0073] This invention is not limited to the following embodiments; specific implementation methods can be determined according to the technical solution of this invention and actual conditions. Unless otherwise specified, all chemical reagents and chemical products mentioned in this invention are well-known and commonly used chemical reagents and chemical products in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent.

[0074] The sodium-ion battery anode material of the present invention uses a high initial coulombic efficiency hard carbon material. The surface of the carbon precursor with open pores is filled with tar or binder, and then further filled with open pores by subsequent high pressure pressing, which reduces the specific surface area of ​​biomass carbon. After direct electric heating high temperature treatment, the closure of open pores and the growth of closed pores are promoted, thereby reducing the specific surface area of ​​the sample, increasing the closed pore volume of the sample, and thus improving the specific capacity and initial coulombic efficiency of the sample.

[0075] The carbonization technology described in this invention uses direct electric heating, where heat is generated directly inside the sample through electromagnetic induction. Compared to traditional processes (indirect heating), the heat flow through the sample in the same amount of time is four times that of traditional processes, and the energy consumption required is only one-fifth of that of traditional processes (see Figures 1 and 2).

[0076] The present invention will be further described below with reference to embodiments:

[0077] Example 1

[0078] The high initial coulombic efficiency hard carbon material (hereinafter referred to as hard carbon anode material) used in the sodium-ion battery anode of this embodiment is prepared by the following method:

[0079] 1) Preparation of biochar and biotar:

[0080] Take 50g of biomass (mixed sawdust from fir and pine trees) and heat it to 550℃ at 20℃ / min under an inert atmosphere, holding it at that temperature for 1 hour. Collect the condensable gas through a condenser flask, and after standing, take the lower layer of viscous liquid, which is the biomass tar used in the production of negative electrode materials. The solid remaining after pyrolysis is the biochar.

[0081] Carbon column preparation:

[0082] Take 20g of biochar (fixed carbon content 94.9%) and 5g of biochar tar from step 1), heat the mixture to 100℃ and stir thoroughly. After cooling, fill the mixture into the corresponding mold and maintain a pressure of 10 bar for 10 minutes to obtain a carbon column with dimensions of d40*20mm. Heat the carbon column to 800℃ at a rate of 5℃ / min under an inert atmosphere and hold for 3 hours. After cooling, obtain a low-temperature carbonized carbon column.

[0083] Preparation of hard carbon anode materials:

[0084] Take the low-temperature carbonized carbon column from step 2), place it in a high-frequency induction heating furnace, rapidly heat it to 1300℃ under an inert atmosphere, and hold it at that temperature for 1 hour. After cooling, grind and sieve the carbon column to obtain hard carbon anode material.

[0085] The SEM image of the hard carbon anode material obtained in Example 1 is shown in Figure 3, and the TEM image is shown in Figure 4. Figure 3 shows that the hard carbon anode material is granular, with a size between 5 μm and 20 μm; the surface is smooth, and it still retains some of the biomass precursor morphology. Figure 4 shows that the biochar forms closed pores, with fewer open pores. Figure 5 shows that even after pulverization, the biochar and biomass oil are tightly bonded and not easily separated, facilitating the subsequent storage of the hard carbon anode material.

[0086] The hard carbon anode material prepared in Example 1 was mixed with a 95:5 doped binder CMC to prepare the anode of a sodium-ion battery. The electrolyte was 1M NaPF6 / diethylene glycol dimethyl ether, and the cathode was sodium metal, which was then assembled into a soft-pack battery (sodium-ion battery).

[0087] As can be seen from Figure 6, the negative electrode is granular, with small particle size and tightly packed particles.

[0088] Example 2

[0089] The hard carbon anode material in this embodiment is prepared by the following method:

[0090] 1) Preparation of biochar and biotar:

[0091] Take 50g of biomass (mixed sawdust from fir and pine trees) and heat it to 500℃ at 20℃ / min under an inert atmosphere, holding it at that temperature for 1 hour. Collect the condensable gas through a condenser flask, and take the lower layer of viscous liquid after standing. This is the biomass tar used in the production of anode materials. The solid remaining after pyrolysis is the biochar used in the production of anode materials.

[0092] Carbon column preparation:

[0093] Take 20g of biochar (fixed carbon content 94.9%) and 5g of biomass oil from step 1), heat the mixture to 100℃ and stir thoroughly. After cooling, fill the corresponding mold and maintain a pressure of 10 bar for 10 minutes to obtain a carbon column with dimensions d40*20mm. Heat the carbon column to 700℃ at a rate of 5℃ / min under an inert atmosphere and hold for 3 hours. After cooling, obtain a low-temperature carbonized carbon column.

[0094] Preparation of hard carbon anode materials:

[0095] Take the low-temperature carbonized carbon column from step 2), place it in a high-frequency induction heating furnace, rapidly heat it to 1000℃ under an inert atmosphere, and hold it at that temperature for 3 hours. After cooling, grind and sieve the carbon column to obtain hard carbon anode material.

[0096] The SEM image of the hard carbon anode material obtained in Example 2 is shown in Figure 7, and the TEM image is shown in Figure 8. As can be seen from Figure 7, the hard carbon anode material is granular with a size between 5 μm and 20 μm. The surface is smooth and still retains some of the morphology of the biomass precursor.

[0097] The hard carbon anode material prepared in Example 2 was mixed with a 95:5 doped binder CMC to prepare the anode of a sodium-ion battery. The electrolyte was 1M NaPF6 / diethylene glycol dimethyl ether, and the cathode was sodium metal assembled into a pouch battery.

[0098] Example 3

[0099] The hard carbon anode material in this embodiment is prepared by the following method (see Figure 9):

[0100] 1) Preparation of biochar and biotar:

[0101] Take 50g of biomass (mixed sawdust from fir and pine trees) and heat it to 550℃ at 20℃ / min under an inert atmosphere, holding it at that temperature for 1 hour. Collect the condensable gas through a condenser flask, and after standing, take the lower layer of viscous liquid, which is the biomass tar used in the production of anode materials. The solid remaining after pyrolysis is the biochar used in the production of anode materials.

[0102] Purification of biochar:

[0103] Take 20g of the biochar from step 1) (fixed carbon content 94.9%), add 300ml of 4mol / L acetic acid solution, and stir and acid wash at 60℃ for 24h. Rinse the obtained biochar with deionized water until the pH value is 7, then add 300ml of 20% KOH solution and stir at 60℃ for 2h. Rinse with deionized water until the pH value is 7 to obtain high-purity biochar.

[0104] Carbon column preparation:

[0105] Take 20g of high-purity biochar (fixed carbon content 96.2%) from step 2) and 5g of biochar tar from step 1), heat the mixture to 100℃ and stir thoroughly. After cooling, fill the corresponding mold and maintain a pressure of 10 bar for 10 minutes to obtain a carbon column with dimensions of d40*20mm. Heat the carbon column to 800℃ at a rate of 5℃ / min under an inert atmosphere and hold for 3 hours. After cooling, obtain a low-temperature carbonized carbon column.

[0106] Preparation of hard carbon anode materials:

[0107] Take the low-temperature carbonized carbon column from step 3), place it in a high-frequency induction heating furnace, rapidly heat it to 1300℃ under an inert atmosphere, and hold it at that temperature for 1 hour. After cooling, grind and sieve the carbon column to obtain hard carbon anode material.

[0108] Figure 10 shows the SEM image of the hard carbon anode material prepared in Example 3. As can be seen from Figure 10, the hard carbon anode material is granular with a size between 5 μm and 20 μm. The surface is smooth and still retains some of the morphology of the biomass precursor.

[0109] The hard carbon anode material prepared in Example 3 was mixed with a 95:5 doped binder CMC to prepare the anode of a sodium-ion battery. The electrolyte was 1M NaPF6 / diethylene glycol dimethyl ether, and the cathode was sodium metal assembled into a pouch battery.

[0110] Example 4

[0111] The hard carbon anode material in this embodiment is prepared by the following method:

[0112] 1) Preparation of biochar and biotar:

[0113] Take 50g of biomass (mixed sawdust from fir and pine trees) and heat it to 350℃ at 20℃ / min under an inert atmosphere, holding it at that temperature for 1 hour. Collect the condensable gas through a condenser flask, and take the lower layer of viscous liquid after standing. This is the biomass tar used in the production of anode materials. The solid remaining after pyrolysis is the biochar used in the production of anode materials.

[0114] Carbon column preparation:

[0115] Take 21g of biochar (fixed carbon content 83.5%) and 7g of biochar tar from step 1), heat the mixture to 100℃ and stir thoroughly. After cooling, fill the corresponding mold and maintain a pressure of 10 bar for 5 minutes to obtain a carbon column with dimensions of d40*20mm. Heat the carbon column to 600℃ at a rate of 5℃ / min under an inert atmosphere and hold for 3 hours. After cooling, obtain a low-temperature carbonized carbon column.

[0116] Preparation of hard carbon anode materials:

[0117] Take the low-temperature carbonized carbon column from step 2), place it in a high-frequency induction heating furnace, rapidly heat it to 1400℃ under an inert atmosphere, and hold it at that temperature for 3 hours. After cooling, grind and sieve the carbon column to obtain hard carbon anode material.

[0118] The hard carbon anode material prepared in Example 4 is granular with a size between 5 μm and 20 μm. It has a smooth surface and retains some of the morphology of a biomass precursor.

[0119] The hard carbon anode material prepared in this embodiment is mixed with a 95:5 doped binder CMC to prepare the anode of a sodium-ion battery. The electrolyte is 1M NaPF6 / diethylene glycol dimethyl ether, and the cathode is sodium metal assembled into a pouch battery.

[0120] Example 5

[0121] The hard carbon anode material in this embodiment is prepared by the following method:

[0122] 1) Preparation of biochar and biotar:

[0123] Take 50g of biomass (mixed sawdust from fir and pine trees) and heat it to 550℃ at 20℃ / min under an inert atmosphere, holding it at that temperature for 1 hour. Collect the condensable gas through a condenser flask, and after standing, take the lower layer of viscous liquid, which is the biomass tar used in the production of anode materials. The solid remaining after pyrolysis is the biochar used in the production of anode materials.

[0124] Carbon column preparation:

[0125] Take 24g of biochar (fixed carbon content 83.5%) and 16g of biochar tar from step 1), heat the mixture to 100℃ and stir thoroughly. After cooling, fill the corresponding mold and maintain a pressure of 10 bar for 8 minutes to obtain a carbon column with dimensions of d40*20mm. Heat the carbon column to 650℃ at a rate of 5℃ / min under an inert atmosphere and hold for 2 hours. After cooling, obtain a low-temperature carbonized carbon column.

[0126] Preparation of hard carbon anode materials:

[0127] Take the low-temperature carbonized carbon column from step 2), place it in a high-frequency induction heating furnace, rapidly heat it to 1100℃ under an inert atmosphere, and hold it at that temperature for 3 hours. After cooling, grind and sieve the carbon column to obtain hard carbon anode material.

[0128] The SEM image of the hard carbon anode material prepared in Example 5 is shown in Figure 11. As can be seen from Figure 11, the hard carbon anode material is granular with a size between 5 μm and 20 μm. The surface is smooth and still retains some of the morphology of the biomass precursor.

[0129] The hard carbon anode material prepared in this embodiment is mixed with a 95:5 doped binder CMC to prepare the anode of a sodium-ion battery. The electrolyte is 1M NaPF6 / diethylene glycol dimethyl ether, and the cathode is sodium metal assembled into a pouch battery.

[0130] Example 6

[0131] The hard carbon anode material in this embodiment is prepared by the following method:

[0132] 1) Preparation of biochar and biotar:

[0133] Take 50g of biomass (mixed sawdust from fir and pine trees) and heat it to 450℃ at 20℃ / min under an inert atmosphere, holding it at that temperature for 1 hour. Collect the condensable gas through a condenser flask, and after standing, take the lower layer of viscous liquid, which is the biomass tar used in the production of anode materials. The solid remaining after pyrolysis is the biochar used in the production of anode materials.

[0134] Carbon column preparation:

[0135] Take 21g of biochar (fixed carbon content 83.5%) and 9g of biochar tar from step 1), heat the mixture to 100℃ and stir thoroughly. After cooling, fill the corresponding mold and maintain a pressure of 10 bar for 7 minutes to obtain a carbon column with dimensions of d40*20mm. Heat the carbon column to 800℃ at a rate of 5℃ / min under an inert atmosphere and hold for 3 hours. After cooling, obtain a low-temperature carbonized carbon column.

[0136] Preparation of hard carbon anode materials:

[0137] Take the low-temperature carbonized carbon column from step 2), place it in a high-frequency induction heating furnace, rapidly heat it to 1600℃ under an inert atmosphere, and hold it at that temperature for 2 hours. After cooling, grind and sieve the carbon column to obtain hard carbon anode material.

[0138] The SEM image of the hard carbon anode material prepared in Example 6 is shown in Figure 12, and the TEM image is shown in Figure 13. As can be seen from Figure 12, the hard carbon anode material is granular with a size between 5 μm and 20 μm. The surface is smooth and still retains some of the morphology of the biomass precursor.

[0139] The hard carbon anode material prepared in Example 6 was mixed with a 95:5 doped binder CMC to prepare the anode of a sodium-ion battery. The electrolyte was 1M NaPF6 / diethylene glycol dimethyl ether, and the cathode was sodium metal, which was then assembled into a pouch battery.

[0140] Example 7:

[0141] 1) Preparation of biochar:

[0142] Take 50g of biomass (mixed sawdust from fir and pine trees) and heat it to 550℃ at 20℃ / min under an inert atmosphere, holding it at that temperature for 1 hour. The solid remaining after pyrolysis is the biochar used in the production of negative electrode materials.

[0143] Carbon column preparation:

[0144] Take 21g of biochar (fixed carbon content 83.5%) from step 1) and 7g of commercial bitumen, heat the mixture to 100℃ and stir thoroughly. After cooling, fill the corresponding mold and maintain a pressure of 10 bar for 8 minutes to obtain a carbon column with dimensions of d40*20mm. Heat the carbon column to 800℃ at a rate of 5℃ / min under an inert atmosphere and hold for 2 hours. After cooling, obtain a low-temperature carbonized carbon column.

[0145] Preparation of hard carbon anode materials:

[0146] Take the low-temperature carbonized carbon column from step 2), place it in a high-frequency induction heating furnace, rapidly heat it to 1500℃ under an inert atmosphere, and hold it at that temperature for 2 hours. After cooling, grind and sieve the carbon column to obtain hard carbon anode material.

[0147] In Example 7, the SEM image of the carbon column obtained after induction heating is shown in Figure 14. The SEM image of the hard carbon anode material obtained in Example 7 is shown in Figure 15. As can be seen from Figure 15, the hard carbon anode material is granular with a size between 5 μm and 20 μm. The surface is smooth and still retains some of the morphology of the biomass precursor.

[0148] Figure 16 shows the actual image of the carbon column obtained after induction heating in Example 7.

[0149] The hard carbon anode material prepared in Example 7 was mixed with a 95:5 doped binder CMC to prepare the anode of a sodium-ion battery. The electrolyte was 1M NaPF6 / diethylene glycol dimethyl ether, and the cathode was sodium metal assembled into a pouch battery.

[0150] Example 8:

[0151] 1) Preparation of biochar and biotar:

[0152] Take 50g of biomass (mixed sawdust from fir and pine trees) and heat it to 550℃ at 20℃ / min under an inert atmosphere and keep it at that temperature for 1h. Collect the condensable gas through a condenser flask, and take the lower layer of thick liquid after standing. This is the biomass tar used in the production of anode materials. The solid remaining after pyrolysis is the biochar used in the production of anode materials (SEM image shown in Figure 17).

[0153] Carbon column preparation:

[0154] Take 20g of biochar (fixed carbon content 83.5%) from step 1), 5g of biochar tar, and 5g of commercial bitumen. Heat the mixture to 100℃ and stir thoroughly. After cooling, fill the corresponding mold and maintain a pressure of 10 bar for 8 minutes to obtain a carbon column with dimensions of d40*20mm. Heat the carbon column to 700℃ at a rate of 5℃ / min under an inert atmosphere and hold for 2 hours. After cooling, a low-temperature carbonized carbon column is obtained (SEM image shown in Figure 18).

[0155] Preparation of hard carbon anode materials:

[0156] Take the low-temperature carbonized carbon column from step 2), place it in a high-frequency induction heating furnace, and rapidly heat it to 1350℃ under an inert atmosphere and hold it at that temperature for 2 hours. After cooling, the carbon column (see Figure 6) is ground, pulverized, and sieved to obtain hard carbon anode material.

[0157] The hard carbon anode material prepared in Example 8 is granular with a size between 5 μm and 20 μm. It has a smooth surface and retains some of the biomass precursor morphology.

[0158] Figure 19 shows the actual image of the carbon column obtained after induction heating in Example 8.

[0159] The hard carbon anode material prepared in Example 8 was mixed with a 95:5 doped binder CMC to prepare the anode of a sodium-ion battery. The electrolyte was 1M NaPF6 / diethylene glycol dimethyl ether, and the cathode was sodium metal assembled into a pouch battery.

[0160] Example 9:

[0161] 1) Biomass block preparation:

[0162] Take the high-pressure compressed biomass (laminated boards, biomass pellets, etc., with a fixed carbon content of 16.6%) and cut it into pieces approximately 1.5 times the size of the heating furnace.

[0163] Carbon column preparation:

[0164] Take the biomass block from step 1), heat it to 800℃ at a rate of 5℃ / min under an inert atmosphere and keep it at that temperature for 2 hours. After cooling, a low-temperature carbonized carbon column is obtained.

[0165] Preparation of hard carbon anode materials:

[0166] Take the low-temperature carbonized carbon column from step 2), place it in a high-frequency induction heating furnace, rapidly heat it to 1300℃ under an inert atmosphere, and hold it at that temperature for 2 hours. After cooling, the carbon column (see Figure 7) is ground, pulverized, and sieved to obtain hard carbon anode material.

[0167] The hard carbon anode material prepared in Example 9 is granular with a size between 5 μm and 20 μm. It has a smooth surface and retains some of the morphology of a biomass precursor.

[0168] Figure 20 shows the actual image of the carbon column obtained after induction heating in Example 9.

[0169] The hard carbon anode material prepared in Example 9 was mixed with a 95:5 doped binder CMC to prepare the anode of a sodium-ion battery. The electrolyte was 1M NaPF6 / diethylene glycol dimethyl ether, and the cathode was sodium metal, which was then assembled into a pouch battery.

[0170] Example 10

[0171] The high initial coulombic efficiency hard carbon material for the sodium-ion battery anode in this embodiment is prepared by the following method:

[0172] 1) Preparation of biochar and biotar:

[0173] Take 50g of biomass (mixed sawdust from fir and pine trees) and heat it to 550℃ at 20℃ / min under an inert atmosphere, holding it at that temperature for 1 hour. Collect the condensable gas through a condenser flask, and after standing, take the lower layer of viscous liquid, which is the biomass tar used in the production of negative electrode materials. The solid remaining after pyrolysis is the biochar.

[0174] Carbon column preparation:

[0175] Take 21g of biochar and 7g of biochar tar from step 1), heat the mixture to 100℃ and stir thoroughly. After cooling, fill the corresponding mold and maintain a pressure of 10 bar for 10 minutes to obtain a carbon column with dimensions of d40*20mm. Heat the carbon column to 600℃ at a rate of 5℃ / min under an inert atmosphere and hold for 3 hours. After cooling, obtain a low-temperature carbonized carbon column.

[0176] Preparation of hard carbon anode materials:

[0177] Take the low-temperature carbonized carbon column from step 2) and place it in a Joule furnace, connecting both ends of the carbon column to the positive and negative electrodes of the device. Rapidly heat to 1300℃ under an inert atmosphere and hold for 1 hour. After cooling, grind and sieve the carbon column to obtain hard carbon anode material.

[0178] The hard carbon anode material obtained in Example 10 is granular with a size between 5 μm and 20 μm; the surface is smooth and still retains some of the biomass precursor morphology.

[0179] The hard carbon anode material prepared in Example 10 was mixed with a 95:5 doped binder CMC to prepare the anode of a sodium-ion battery. The electrolyte was 1M NaPF6 / diethylene glycol dimethyl ether, and the cathode was sodium metal, which was then assembled into a soft-pack battery (sodium-ion battery).

[0180] Large-scale Example 11 (fixed carbon content same as Example 3)

[0181] The hard carbon anode material in this embodiment is prepared by the following method:

[0182] 1) Preparation of biochar and biotar:

[0183] The biomass (a mixture of fir and pine sawdust) is fed at a rate of 1 kg / h and heated at 550°C for 1 hour in an inert atmosphere via a fluidized bed. The condensable gas is collected by a condenser, and the lower layer of viscous liquid is collected after settling, which is the biomass tar used in the production of anode materials. The solid remaining after pyrolysis is the biochar used in the production of anode materials.

[0184] Purification of biochar:

[0185] The biochar (fixed carbon content 94.9%) from step 1) was repeatedly acid-washed with 4 mol acetic acid in a large-scale purification device, then repeatedly alkaline-washed with 20% KOH, and finally washed with water to obtain purified biochar.

[0186] Carbon column preparation:

[0187] Take the high-purity biochar from step 2) and the biochar tar from step 1), heat and stir them in a 7:3 ratio to mix thoroughly. Fill the mixture into an extrusion molding machine to obtain a carbon column with dimensions d1*2m. Heat the carbon column to 800℃ at a rate of 5℃ / min under an inert atmosphere and hold for 3 hours. After cooling, obtain a low-temperature carbonized carbon column.

[0188] Preparation of hard carbon anode materials:

[0189] Take the low-temperature carbonized carbon column from step 3), place it in a continuous high-frequency induction heating furnace, rapidly heat it to 1300℃ under an inert atmosphere, and hold it at that temperature for 1 hour. After cooling, grind and sieve the carbon column to obtain hard carbon anode material.

[0190] The hard carbon anode material prepared in Example 11 is granular with a size between 5 μm and 20 μm. The surface is smooth and still retains some of the biomass precursor morphology.

[0191] The manufacturing process of this invention is shown in Figure 21.

[0192] The capacity and initial coulombic efficiency of the sodium-ion batteries prepared in Examples 1 to 3 were tested.

[0193] The battery was charged and discharged at 0.2C to 2.5V, and discharged at 0.2C with a cutoff voltage of 0.001V. The test results are shown in Table 1 and Figure 25.

[0194] In the comparative examples used in the test, the negative electrode materials of Comparative Example 1 and Comparative Example 2 were hard carbon powders obtained by carbonization in an electric resistance furnace at 1300℃ and 1600℃ for 3 hours, respectively. The SEM image of the hard carbon powder obtained by carbonization in Comparative Example 1 is shown in Figure 22, and the SEM image of the hard carbon powder obtained by carbonization in Comparative Example 2 is shown in Figure 23.

[0195] The negative electrode materials of Comparative Examples 3 to 5 were hard carbon obtained by carbonizing hard carbon pillars, which were formed using the same molding process as in Example 1, in an electric resistance furnace at 800°C, 1000°C, and 1300°C for 3 hours. A TEM image of the hard carbon powder obtained by carbonization in Comparative Example 5 is shown in Figure 24.

[0196] As can be seen from Table 1 and Figure 25, the initial charging capacity and initial coulombic efficiency of the sodium-ion batteries prepared in Examples 1 to 3 are significantly better than those in Comparative Example 1. This is because the negative electrode material (hard carbon negative electrode material) of this invention has an extremely low specific surface area and few surface defect sites, reducing the irreversible reaction between the electrolyte and the surface of the hard carbon material, thus improving the initial coulombic efficiency. Simultaneously, induction heating promotes the formation of closed pores within the hard carbon, providing more sites for sodium ion storage, thereby effectively improving the charging capacity.

[0197] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

[0198] Table 1. Comparison of the electrochemical performance of the first charge-discharge cycle between the examples and the comparative examples.

[0199] Object, Positive Electrode, Negative Electrode Treatment Method, Initial Discharge Capacity, Initial Charge Capacity, Initial Coulombic Efficiency. Example 1: Na Hard Carbon-1300 Molding, Induction Heating, 278.72%, 72%, 97.6%. Example 2: Na Hard Carbon-1000 Molding, Induction Heating, 251.12%, 40.1%, 95.6%. Example 3: Na Purified Hard Carbon-1300 Molding, Induction Heating, 304.62%, 90.3%, 95.3%. Comparative Example 1: Na Traditional Hard Carbon Powder-1300 Powder, Traditional Heating, 301.42%, 50.2%, 83%. Comparative Example 2: Na Traditional Hard Carbon Powder-1600 Powder, Traditional Heating, 257.32%, 11.82%. Comparative Example 3: Na Traditional Hard Carbon-800 Molding, Traditional Heating, 277.32%, 04.1%, 73.6%. Comparative Example 4: Na Traditional Hard Carbon-1000 Molding, Traditional Heating, 257.31%, 96.4%, 77.3%. Comparative Example 5: Na Traditional Hard Carbon-1300 Molding, Traditional Heating, 257.32%, 68%, 89.9%. surface

Claims

1. A method for preparing a high initial coulombic efficiency hard carbon material for sodium-ion battery anodes, characterized in that... Includes the following steps: Step 1: Purify the carbon precursor. Step 2: When the fixed carbon content in the purified carbon precursor is less than 40%, press the purified carbon precursor into a carbon column. Heat the carbon column in an inert atmosphere for a certain period of time to obtain a low-temperature carbonized carbon column. Step 3: Directly electrically heat the low-temperature carbonized carbon column in an inert atmosphere. After cooling, pulverize it to a particle size of less than 32 μm to obtain a high initial coulombic efficiency hard carbon material for sodium-ion battery anodes. The carbon precursor is biomass. The direct electrical heating method is induction heating. In Step 2, the carbon column is heated to 600℃ to 800℃ in an inert atmosphere and held for 2 to 3 hours to obtain a low-temperature carbonized carbon column. In Step 3, the low-temperature carbonized carbon column is heated to 1000℃ to 1600℃ in an inert atmosphere for induction heating and held for 1 to 3 hours before cooling. Before purification, the carbon precursor is first made into biochar, and then the biochar is purified.

2. The method for preparing a high initial coulombic efficiency hard carbon material for a sodium-ion battery anode according to claim 1, characterized in that... The purification method described in step one is as follows: the carbon precursor is sequentially acid-washed and water-washed until the pH value is neutral, and then sequentially alkali-washed and water-washed until the pH value is neutral to obtain the purified carbon precursor; or / and, in step two, when the fixed carbon content in the purified carbon precursor is greater than or equal to 40%, the carbon precursor is mixed with an organic binder, heated to soften the organic binder, and then the carbon precursor and organic binder are pressed into shape to obtain a carbon column.

3. The method for preparing a high initial coulombic efficiency hard carbon material for a sodium-ion battery anode according to claim 1 or 2, characterized in that... When plant biomass is used as biomass, both biochar and biotar are products of the pyrolysis of plant biomass at 350℃ to 550℃, and the organic binder is biotar.

4. The method for preparing a high initial coulombic efficiency hard carbon material for a sodium-ion battery anode according to claim 3, characterized in that... The mass ratio of biochar to biotar is 6 to 8: 2 to 4.

5. A high initial coulombic efficiency hard carbon material for sodium-ion battery anode prepared by the method for preparing a high initial coulombic efficiency hard carbon material for sodium-ion battery anode according to any one of claims 1 to 4.

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