Hard carbon negative electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of sodium ion batteries, and particularly relates to a hard carbon negative electrode material and a preparation method and application thereof. The preparation method of the hard carbon negative electrode material comprises the following steps: S1, carrying out pretreatment on wood to prepare a precursor; s2, adding a deep eutectic solvent into the prepared precursor, carrying out a reaction, and after the reaction is finished, carrying out cleaning and drying; s3, performing composite filling and curing on a product obtained in the step S2 by using a resin solution; s4, carbonizing the product obtained in the step S3; and S5, cleaning, drying and sieving the carbonized product obtained in the step S4 to obtain the hard carbon negative electrode material. When the prepared hard carbon negative electrode material is used as a negative electrode of a sodium ion battery, the negative electrode material has high first efficiency, high reversible capacity, excellent rate capability and long cycle life, and the problems of low first efficiency of single biomass carbon and poor rate capability of single resin carbon are solved.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a hard carbon anode material, its preparation method, and its application. Background Technology

[0002] Driven by the strategic goal of "peak carbon emissions and carbon neutrality," the construction of new power systems represented by wind and solar energy urgently requires large-scale, low-cost, and highly safe electrochemical energy storage technologies. Lithium-ion batteries have achieved tremendous success over the past few decades; however, the increasing scarcity and volatile prices of lithium resources have become a barrier to their large-scale application in the energy storage field. Sodium, as an alkali metal element in the same group as lithium, not only has a similar electrochemical mechanism but also boasts extremely abundant reserves in the Earth's crust and a significant cost advantage, making sodium-ion batteries an ideal candidate to support the multi-billion dollar energy storage market. However, the large ionic radius of sodium ions (1.02 Å vs. lithium ions 0.76 Å) poses a severe challenge to anode materials. The interlayer spacing of commercial graphite anodes (approximately 0.335 nm) is too narrow, resulting in slow sodium ion insertion / extraction kinetics, extremely low reversible capacity, and severe volume effects, failing to meet practical requirements.

[0003] Among numerous candidate materials, hard carbon is widely recognized by industry and academia as the sodium-ion battery anode material with the greatest near-term commercialization potential due to its comprehensive balance of cost, performance, and process. Unlike the regular layered structure of graphite, hard carbon is composed of disordered and interwoven graphite microcrystals. Its unique "card room" model structure contains the following key features: (1) widened interlayer spacing: providing more relaxed channels for sodium ion insertion and reducing the diffusion barrier; (2) abundant nanopores / defects: these regions provide a large number of adsorption sites, contributing considerable pseudocapacitive capacity; (3) closed micropores: believed to enable the cluster filling of sodium metal, thereby providing a plateau capacity. The overall performance of hard carbon (capacity, first efficiency, rate capability, cycle life) strongly depends on its microstructure, which is directly determined by the chemical composition and physical structure of the precursor and the carbonization process.

[0004] Currently, research on hard carbon precursors mainly revolves around biomass and synthetic polymer routes, both of which have insurmountable limitations. Biomass precursors, especially wood, have attracted widespread attention due to their natural three-dimensional interconnected porous channel structure, renewability, and low cost. These natural channels facilitate electrolyte wetting and rapid ion transport. However, hard carbon prepared solely from wood precursors has significant drawbacks: First, wood releases a large amount of volatile components during pyrolysis, resulting in a low yield of the final carbon material, affecting the yield and economic viability. Second, the natural porous structure of wood is prone to shrinkage or collapse at high temperatures, weakening its structural advantages. Third, the resulting hard carbon has low graphitization, poor conductivity, and insufficient mechanical strength of the carbon skeleton; structural degradation during cycling may lead to continuous capacity decay. On the other hand, synthetic polymer resins, as precursors, have advantages such as high carbon yield, high product purity, and tunable structure. However, they also have limitations: resin-based hard carbon is usually a dense bulk, lacking macroscopic ion transport channels like wood, limiting its rate performance. Meanwhile, compared to inexpensive biomass, resin raw materials are relatively expensive. Therefore, there is an urgent need to develop a hard carbon material that can effectively overcome the shortcomings of existing hard carbon materials prepared using wood as a precursor, while also possessing excellent electrochemical properties. Summary of the Invention

[0005] The present invention aims to provide a hard carbon anode material, its preparation method and application. The hard carbon anode material prepared by the present invention through a specific preparation method can effectively overcome the defects of existing hard carbon materials prepared with wood as a precursor, while significantly improving its sodium storage performance, increasing the first-cycle coulombic efficiency and ensuring excellent cycle stability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a hard carbon anode material, comprising the following steps: S1. Pre-treat the wood to obtain the precursor; S2. Add a eutectic solvent to the obtained precursor and react to remove some of the lignin and hemicellulose from the wood chips. After the reaction is complete, wash off the surface solvent and dry. S3. The product obtained in step S2 is composite-filled and cured with resin solution; S4. Carbonize the product obtained in step S3; S5. The carbonized product obtained in step S4 is cleaned, dried, and sieved to obtain the hard carbon anode material.

[0007] Preferably, the pretreatment of wood in step S1 includes the following steps: slicing the wood, washing it with deionized water, drying it, and obtaining a precursor; the thickness of the slices is 2-5 mm; the drying temperature is 60-100℃, and the drying time is 10-14 h.

[0008] Preferably, the wood used in step S1 can be conventional wood materials in the art, such as pine or balsa wood.

[0009] Preferably, the molar ratio of hydrogen bond acceptor to hydrogen bond donor in the eutectic solvent in step S2 is 1:(1~5).

[0010] This invention effectively ensures the removal of some lignin and hemicellulose from wood by selecting appropriate ratios of hydrogen bond acceptors and hydrogen bond donors. If the proportion of hydrogen bond donors is too low, the solvent's acidity is too weak, resulting in insufficient ability to remove lignin and hemicellulose. This leads to insufficient pore development in the wood template, making it difficult for subsequent resin to fully penetrate and fill. Conversely, if the proportion of hydrogen bond donors is too high, the solvent's acidity is too strong, causing excessive corrosion of the wood skeleton and even destroying the crystalline structure of cellulose. This results in an overly fragile wood template that is more prone to collapse during carbonization.

[0011] Preferably, the hydrogen bond acceptor includes at least one of choline chloride and quaternary ammonium salt; the hydrogen bond donor includes at least one of urea, acetic acid, and lactic acid.

[0012] More preferably, the hydrogen bond acceptor is choline chloride.

[0013] Preferably, the ratio of the eutectic solvent to the obtained precursor in step S2 is (180~220) ml: 10 g.

[0014] Preferably, the reaction temperature in step S2 is 60~90℃ and the reaction time is 6~72h.

[0015] Preferably, the drying temperature in step S2 is 50~100℃ and the drying time is 8~72h.

[0016] Preferably, the resin solution in step S3 includes at least one of epoxy resin and phenolic resin.

[0017] Preferably, the ratio of the resin solution to the precursor obtained in step S2 is 40~60mL:10g.

[0018] Preferably, the composite filling in step S3 is performed by filling the resin solution with the product obtained in step S2 using a vacuum method; the curing is performed by natural curing.

[0019] Preferably, the vacuuming pressure is -0.05 MPa, the time is 3 to 8 minutes, and the process is repeated three times.

[0020] This invention employs a three-stage vacuum process. The first vacuuming primarily removes large pores and surface-adsorbed gases from the wood; the second is used to treat microbubbles deep within the capillaries; and the third vacuuming addresses newly formed micropores created by curing shrinkage. Each depressurization utilizes atmospheric pressure differences to drive resin penetration into smaller pores, controlling resin penetration into the wood and ensuring deep filling before entering the main curing stage. Maintaining a continuous vacuum state would not achieve the same effect.

[0021] In this invention, resin filling is used to immerse the resin into the natural pore structure of the wood. During the subsequent carbonization process, hydrocarbon fragments and intermediate phases generated by the decomposition of the resin at high temperature can be effectively utilized to deposit and fill the shrinking and pore-forming carbon skeleton of the wood. This reduces the specific surface area while increasing the closed-pore structure in the material, thereby increasing the sodium storage capacity and coulombic efficiency of the final material.

[0022] Preferably, the carbonization in step S4 includes the following steps: transferring the product obtained in step S3 to a high-temperature tube furnace, carbonizing it in an inert atmosphere at a temperature of 900–1700°C for 1–8 hours, with a heating rate of 1–10°C / min and an inert gas flow rate of 20–120 mL / min.

[0023] In the preparation method of the present invention, if the carbonization temperature selected during carbonization is not suitable, the hard carbon anode material finally obtained will not be able to obtain a good multi-level porous structure, and its structure is prone to problems such as shrinkage or collapse.

[0024] Preferably, the inert atmosphere can be a conventional inert gas in the art, such as nitrogen.

[0025] Preferably, the cleaning in step S5 is as follows: add 1-3 mol / L hydrochloric acid solution to the carbonized product, stir for 6-24 h, and then wash with water until the filtrate is neutral.

[0026] Preferably, the drying temperature in step S5 is 50~100℃ and the drying time is 8~72h.

[0027] Preferably, the sieving in step S5 is done through a 200-500 mesh sieve.

[0028] The preparation method of this invention, through the effective filling and structural synergy of the resin in the hierarchical pores of wood during pyrolysis, precisely controls the final microstructure of the material, successfully achieving a combination of low specific surface area and large carbon interlayer spacing, thereby significantly improving its sodium storage performance. This structural advantage directly translates into superior electrochemical performance: First, the significantly reduced specific surface area greatly reduces side reactions and promotes the formation of a stable SEI film, not only improving the first-cycle coulombic efficiency but also ensuring excellent cycle stability. Second, the increased interlayer spacing provides a wider diffusion channel for sodium ion insertion / extraction, effectively improving the material's reversible capacity and rate performance. The preparation method of this invention not only provides a high-performance, low-cost sodium-ion battery anode material but also demonstrates broad application prospects in large-scale energy storage and other fields through the composite strategy of biomass and polymer resins.

[0029] The present invention also claims protection for a hard carbon anode material prepared by the preparation method of the aforementioned hard carbon anode material.

[0030] Preferably, the specific surface area of ​​the hard carbon anode material is <20 m². 2 / g, interlayer spacing >0.38 nm.

[0031] The present invention also claims protection for the use of the aforementioned hard carbon anode material in the preparation of sodium-ion batteries.

[0032] Compared with the prior art, the present invention has the following beneficial effects: This invention selects specific precursor combinations with synergistic effects and, through a specific composite process design, enables in-situ carbonization of the resin solution within the pores of wood. This synergistically regulates the pore structure and carbon layer spacing of the hard carbon material, successfully achieving a low specific surface area (<20 m²). 2 The optimized combination of ( / g) and large interlayer spacing (>0.38 nm) results in a hard carbon anode material prepared by this invention. When used as an anode in sodium-ion batteries, the hard carbon anode material exhibits high initial efficiency, high reversible capacity, excellent rate performance, and long cycle life, solving the problems of low initial efficiency of single biomass carbon and poor rate performance of single resin carbon. Attached Figure Description

[0033] Figure 1 This is a BET curve of nitrogen adsorption-desorption test of the hard carbon anode material prepared in Example 1 of the present invention.

[0034] Figure 2 The image shows the XRD pattern of the hard carbon anode material prepared in Example 1 of this invention.

[0035] Figure 3 This is a charge-discharge curve of a button battery assembled from the hard carbon negative electrode material prepared in Example 1 of the present invention.

[0036] Figure 4This is a graph showing the charge / discharge rate performance of a button battery assembled from the hard carbon anode material prepared in Example 1 of this invention.

[0037] Figure 5 This is a graph showing the long-cycle performance of a button cell assembled from the hard carbon anode material prepared in Example 1 of this invention. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] Unless otherwise specified, the experimental methods used in the examples and comparative examples are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0040] Example 1 A method for preparing a hard carbon anode material includes the following steps: S1. Pine wood is cut into 3 mm thick slices and cleaned with deionized water, and then dried at 80°C for 12 hours to obtain the precursor. S2. Prepare 200 ml of eutectic solvent in a beaker, with a molar ratio of choline chloride to lactic acid of 1:2; add 10 g of the treated pine wood chips to the beaker, and remove some of the lignin and hemicellulose from the wood chips in an oil bath at 90°C for 48 h; then wash off the solvent on the surface of the pine wood chips with deionized water and dry them at 80°C. S3. Prepare 50ml of epoxy resin solution, immerse the product obtained in step S2 into the resin solution, transfer it to a vacuum oven, and perform three vacuum treatments to allow the resin to be composite filled and cured; the vacuum pressure is -0.05Mpa and the time is 5 minutes. S4. The product obtained in step S3 is transferred to a high-temperature tube furnace and carbonized at 1400°C at a rate of 2°C / min under N2 atmosphere. The heating rate is 2°C / min, the carbonization time is 2h, and the gas flow rate is 80 mL / min. S5. The carbonized product obtained in step S4 is acid-washed with 2 M HCl solution for 12 hours and repeatedly washed with deionized water until the filtrate is neutral. Then the carbonized product is dried at 80°C for 12 hours and sieved through a 300-mesh sieve to obtain the hard carbon anode material.

[0041] Nitrogen adsorption on porous carbon materials was tested using a Micromeritics 3Flex adsorption analyzer. The BET specific surface area of ​​the porous carbon material was found to be 16 m². 2 g -1 Based on the adsorption capacity at relative pressure P / P0, the total pore volume was calculated to be 0.019 cm³. 3 g -1 The specific surface area and pore volume are greatly reduced, such as Figure 1 As shown in the image, this demonstrates that resin filling of pine wood can effectively regulate the natural pore structure of the pine wood.

[0042] like Figure 2 As shown, the XRD pattern reveals two distinct characteristic peaks of the hard carbon material, the (002) and (100) crystal planes. The (002) crystal plane is located at 23.48°, and the interplanar spacing is calculated to be 0.38 nm using the Bragg lattice equation, which is beneficial for the insertion and extraction of sodium ions.

[0043] Performance testing was conducted using a Xinwei electrochemical testing instrument. The charge / discharge test voltage range was 0.01~2.5 V, and the current density was 30 mA / g. The test results showed that the hard carbon anode had a working voltage plateau of 0.1 V, an initial charge specific capacity of 264 mAh / g, and an initial coulombic efficiency of 89.9%. Figure 3 As shown. It still retains a specific capacity of 158 mAh / g at a current density of 1 A / g, as... Figure 4 As shown. Furthermore, it exhibits excellent cycling performance, such as... Figure 5 As shown, the capacity did not decrease significantly after 1600 cycles at a current density of 1 A / g.

[0044] Example 2 A method for preparing a hard carbon anode material includes the following steps: S1. The balsa wood is cut into 5 mm thick slices and cleaned with deionized water, and then dried at 60°C for 8 hours to obtain the precursor. S2. Prepare 180 ml of eutectic solvent in a beaker, with a molar ratio of choline chloride to urea of ​​1:5; add 10 g of the treated balsa wood chips to the beaker, and remove some of the lignin and hemicellulose from the wood chips in an oil bath at 60°C for 72 h; then wash off the solvent on the surface of the pine wood chips with deionized water and dry them at 60°C. S3. Prepare 40ml of phenolic resin solution, immerse the product obtained in step S2 into the resin solution, transfer it to a vacuum oven, and perform three vacuum treatments to allow the resin to be composite-filled and cured; the vacuum pressure is -0.05Mpa and the time is 8 minutes. S4. The product obtained in step S3 is transferred to a high-temperature tube furnace and carbonized at 1000°C at a rate of 5°C / min under N2 atmosphere. The heating rate is 5°C / min, the carbonization time is 6h, and the gas flow rate is 20 mL / min. S5. The carbonized product obtained in step S4 is acid-washed with 1 M HCl solution for 24 hours and repeatedly washed with deionized water until the filtrate is neutral. Then the carbonized product is dried at 50°C for 72 hours and sieved through a 200-mesh sieve to obtain the hard carbon anode material.

[0045] Example 3 A method for preparing a hard carbon anode material includes the following steps: S1. Pine wood is cut into 2 mm thick slices and cleaned with deionized water, and then dried at 100°C for 8 hours to obtain the precursor. S2. Prepare 220ml of eutectic solvent in a beaker, with a molar ratio of choline chloride to acetic acid of 1:2; add 10g of the treated pine wood chips to the beaker, and remove some of the lignin and hemicellulose from the wood chips in an oil bath at 90℃ for 6 hours; then wash off the solvent on the surface of the pine wood chips with deionized water and dry them at 100℃. S3. Prepare 60ml of epoxy resin solution, immerse the product obtained in step S2 into the resin solution, transfer it to a vacuum oven, and perform three vacuum treatments to allow the resin to be composite filled and cured; the vacuum pressure is -0.05Mpa and the time is 3 minutes. S4. The product obtained in step S3 is transferred to a high-temperature tube furnace and carbonized at 1700°C at a rate of 10°C / min under a N2 atmosphere. The heating rate is 10°C / min, the carbonization time is 2h, and the gas flow rate is 120 mL / min. S5. The carbonized product obtained in step S4 is acid-washed with 3 M HCl solution for 6 hours and repeatedly washed with deionized water until the filtrate is neutral. Then the carbonized product is dried at 100°C for 8 hours and sieved through a 500-mesh sieve to obtain the hard carbon anode material.

[0046] Example 4 A method for preparing a hard carbon anode material includes the following steps: S1. Pine wood is cut into 3 mm thick slices and cleaned with deionized water, and then dried at 80°C for 12 hours to obtain the precursor. S2. Prepare 200 ml of eutectic solvent in a beaker, with a molar ratio of choline chloride to lactic acid of 1:6; add 10 g of the treated pine wood chips to the beaker, and remove some of the lignin and hemicellulose from the wood chips in an oil bath at 90°C for 48 h; then wash off the solvent on the surface of the pine wood chips with deionized water and dry them at 80°C. S3. Prepare 50ml of epoxy resin solution, immerse the product obtained in step S2 into the resin solution, transfer it to a vacuum oven, and perform three vacuum treatments to allow the resin to be composite filled and cured; the vacuum pressure is -0.05Mpa and the time is 5 minutes. S4. The product obtained in step S3 is transferred to a high-temperature tube furnace and carbonized at 1400°C at a rate of 2°C / min under N2 atmosphere. The heating rate is 2°C / min, the carbonization time is 2h, and the gas flow rate is 80 mL / min. S5. The carbonized product obtained in step S4 is acid-washed with 2 M HCl solution for 12 hours and repeatedly washed with deionized water until the filtrate is neutral. Then the carbonized product is dried at 80°C for 12 hours and sieved through a 300-mesh sieve to obtain the hard carbon anode material.

[0047] Example 5 A method for preparing a hard carbon anode material includes the following steps: S1. Pine wood is cut into 3 mm thick slices and cleaned with deionized water, and then dried at 80°C for 12 hours to obtain the precursor. S2. Prepare 250 ml of eutectic solvent in a beaker, with a molar ratio of choline chloride to lactic acid of 1:2; add 10 g of the treated pine wood chips to the beaker, and remove some of the lignin and hemicellulose from the wood chips in an oil bath at 90°C for 48 h; then wash off the solvent on the surface of the pine wood chips with deionized water and dry them at 80°C. S3. Prepare 50ml of epoxy resin solution, immerse the product obtained in step S2 into the resin solution, transfer it to a vacuum oven, and perform three vacuum treatments to allow the resin to be composite filled and cured; the vacuum pressure is -0.05Mpa and the time is 5 minutes. S4. The product obtained in step S3 is transferred to a high-temperature tube furnace and carbonized at 1400°C at a rate of 2°C / min under N2 atmosphere. The heating rate is 2°C / min, the carbonization time is 2h, and the gas flow rate is 80 mL / min. S5. The carbonized product obtained in step S4 is acid-washed with 2 M HCl solution for 12 hours and repeatedly washed with deionized water until the filtrate is neutral. Then the carbonized product is dried at 80°C for 12 hours and sieved through a 300-mesh sieve to obtain the hard carbon anode material.

[0048] Example 6 A method for preparing a hard carbon anode material includes the following steps: S1. Pine wood is cut into 3 mm thick slices and cleaned with deionized water, and then dried at 80°C for 12 hours to obtain the precursor. S2. Prepare 200 ml of eutectic solvent in a beaker, with a molar ratio of choline chloride to lactic acid of 1:2; add 10 g of the treated pine wood chips to the beaker, and remove some of the lignin and hemicellulose from the wood chips in an oil bath at 90°C for 48 h; then wash off the solvent on the surface of the pine wood chips with deionized water and dry them at 80°C. S3. Prepare 80ml of epoxy resin solution, immerse the product obtained in step S2 into the resin solution, transfer it to a vacuum oven, and perform three vacuum treatments to allow the resin to be composite filled and cured; the vacuum pressure is -0.05Mpa and the time is 5 minutes. S4. The product obtained in step S3 is transferred to a high-temperature tube furnace and carbonized at 1400°C at a rate of 2°C / min under N2 atmosphere. The heating rate is 2°C / min, the carbonization time is 2h, and the gas flow rate is 80 mL / min. S5. The carbonized product obtained in step S4 is acid-washed with 2 M HCl solution for 12 hours and repeatedly washed with deionized water until the filtrate is neutral. Then the carbonized product is dried at 80°C for 12 hours and sieved through a 300-mesh sieve to obtain the hard carbon anode material.

[0049] Example 7 A method for preparing a hard carbon anode material includes the following steps: S1. Pine wood is cut into 3 mm thick slices and cleaned with deionized water, and then dried at 80°C for 12 hours to obtain the precursor. S2. Prepare 200 ml of eutectic solvent in a beaker, with a molar ratio of choline chloride to lactic acid of 1:2; add 10 g of the treated pine wood chips to the beaker, and remove some of the lignin and hemicellulose from the wood chips in an oil bath at 100°C for 48 h; then wash off the solvent on the surface of the pine wood chips with deionized water and dry them at 80°C. S3. Prepare 50ml of epoxy resin solution, immerse the product obtained in step S2 into the resin solution, transfer it to a vacuum oven, and perform three vacuum treatments to allow the resin to be composite filled and cured; the vacuum pressure is -0.05Mpa and the time is 5 minutes. S4. The product obtained in step S3 is transferred to a high-temperature tube furnace and carbonized at 1400°C at a rate of 2°C / min under N2 atmosphere. The heating rate is 2°C / min, the carbonization time is 2h, and the gas flow rate is 80 mL / min. S5. The carbonized product obtained in step S4 is acid-washed with 2 M HCl solution for 12 hours and repeatedly washed with deionized water until the filtrate is neutral. Then the carbonized product is dried at 80°C for 12 hours and sieved through a 300-mesh sieve to obtain the hard carbon anode material.

[0050] Example 8 A method for preparing a hard carbon anode material includes the following steps: S1. Pine wood is crushed into powder, washed with deionized water, and then dried at 80°C for 12 hours to obtain the precursor. S2. Prepare 200 ml of eutectic solvent of choline chloride / lactic acid in a beaker, with a molar ratio of choline chloride to lactic acid of 1:2; add 10 g of the treated pine wood chips to the beaker and remove some of the lignin and hemicellulose from the wood chips in an oil bath at 90°C for 48 h; then wash off the solvent on the surface of the pine wood chips with deionized water and dry them at 80°C. S3. Prepare 50ml of epoxy resin solution, immerse the product obtained in step S2 into the resin solution, transfer it to a vacuum oven, and perform three vacuum treatments to allow the resin to be composite filled and cured; the vacuum pressure is -0.05Mpa and the time is 5 minutes. S4. The product obtained in step S3 is transferred to a high-temperature tube furnace and carbonized at 1400°C at a rate of 2°C / min under N2 atmosphere. The heating rate is 2°C / min, the carbonization time is 2h, and the gas flow rate is 80 mL / min. S5. The carbonized product obtained in step S4 is acid-washed with 2 M HCl solution for 12 hours and repeatedly washed with deionized water until the filtrate is neutral. Then the carbonized product is dried at 80°C for 12 hours and sieved through a 300-mesh sieve to obtain the hard carbon anode material.

[0051] Example 9 A method for preparing a hard carbon anode material includes the following steps: S1. Pine wood is cut into 3 mm thick slices and cleaned with deionized water, and then dried at 80°C for 12 hours to obtain the precursor. S2. Prepare 200 ml of eutectic solvent in a beaker, with a molar ratio of choline chloride, lactic acid, and urea of ​​1:1:1; add 10 g of the treated pine wood chips to the beaker and remove some of the lignin and hemicellulose from the wood chips in an oil bath at 90°C for 48 h; then wash off the solvent on the surface of the pine wood chips with deionized water and dry them at 80°C. S3. Prepare 50ml of epoxy resin solution, immerse the product obtained in step S2 into the resin solution, transfer it to a vacuum oven, and perform three vacuum treatments to allow the resin to be composite filled and cured; the vacuum pressure is -0.05Mpa and the time is 5 minutes. S4. The product obtained in step S3 is transferred to a high-temperature tube furnace and carbonized at 1400°C at a rate of 2°C / min under N2 atmosphere. The heating rate is 2°C / min, the carbonization time is 2h, and the gas flow rate is 80 mL / min. S5. The carbonized product obtained in step S4 is acid-washed with 2 M HCl solution for 12 hours and repeatedly washed with deionized water until the filtrate is neutral. Then the carbonized product is dried at 80°C for 12 hours and sieved through a 300-mesh sieve to obtain the hard carbon anode material.

[0052] Comparative Example 1 A method for preparing a hard carbon anode material includes the following steps: S1. Pine wood is cut into 3 mm thick slices and cleaned with deionized water, and then dried at 80°C for 12 hours to obtain the precursor. S2. Prepare 200 ml of eutectic solvent in a beaker, with a molar ratio of choline chloride to lactic acid of 1:2; add 10 g of the treated pine wood chips to the beaker, and remove some of the lignin and hemicellulose from the wood chips in an oil bath at 90°C for 48 h; then wash off the solvent on the surface of the pine wood chips with deionized water and dry them at 80°C. S3. Prepare 50 ml of epoxy resin solution and mix the product obtained in step S2 with the resin solution. S4. The product obtained in step S3 is transferred to a high-temperature tube furnace and carbonized at 1400°C at a rate of 2°C / min under N2 atmosphere. The heating rate is 2°C / min, the carbonization time is 2h, and the gas flow rate is 80 mL / min. S5. The carbonized product obtained in step S4 is acid-washed with 2 M HCl solution for 12 hours and repeatedly washed with deionized water until the filtrate is neutral. Then the carbonized product is dried at 80°C for 12 hours and sieved through a 300-mesh sieve to obtain the hard carbon anode material.

[0053] Compared with Example 1, the only difference in this comparative example is that in step S3, the epoxy resin solution is directly mixed with the product obtained in step S2, without performing a vacuum filling process.

[0054] Comparative Example 2 A method for preparing a hard carbon anode material includes the following steps: S1. Pine wood is cut into 3 mm thick slices and cleaned with deionized water, and then dried at 80°C for 12 hours to obtain the precursor. S2. Measure 200 ml of sulfuric acid solution into a beaker, add 10 g of the treated pine wood chips into the beaker, and remove some of the lignin and hemicellulose from the wood chips in an oil bath at 90°C for 48 hours; then wash off the solvent on the surface of the pine wood chips with deionized water and dry them at 80°C. S3. Prepare 50ml of epoxy resin solution, immerse the product obtained in step S2 into the resin solution, transfer it to a vacuum oven, and perform three vacuum treatments to allow the resin to be composite filled and cured; the vacuum pressure is -0.05Mpa and the time is 5 minutes. S4. The product obtained in step S3 is transferred to a high-temperature tube furnace and carbonized at 1400°C at a rate of 2°C / min under N2 atmosphere. The heating rate is 2°C / min, the carbonization time is 2h, and the gas flow rate is 80 mL / min. S5. The carbonized product obtained in step S4 is acid-washed with 2 M HCl solution for 12 hours and repeatedly washed with deionized water until the filtrate is neutral. Then the carbonized product is dried at 80°C for 12 hours and sieved through a 300-mesh sieve to obtain the hard carbon anode material.

[0055] Comparative Example 3 A method for preparing a hard carbon anode material includes the following steps: S1. Pine wood is cut into 3 mm thick slices and cleaned with deionized water, and then dried at 80°C for 12 hours to obtain the precursor. S2. Prepare 200 ml of eutectic solvent in a beaker, with a molar ratio of choline chloride to lactic acid of 1:2; add 10 g of the treated pine wood chips to the beaker, and remove some of the lignin and hemicellulose from the wood chips in an oil bath at 90°C for 48 h; then wash off the solvent on the surface of the pine wood chips with deionized water and dry them at 80°C. S3. Prepare 50ml of epoxy resin solution, immerse the product obtained in step S2 into the resin solution, transfer it to a vacuum oven, and perform three vacuum treatments to allow the resin to be composite filled and cured; the vacuum pressure is -0.05Mpa and the time is 5 minutes. S4. The product obtained in step S3 is transferred to a high-temperature tube furnace and carbonized at 1800°C at a rate of 2°C / min under N2 atmosphere. The heating rate is 2°C / min, the carbonization time is 2h, and the gas flow rate is 80 mL / min. S5. The carbonized product obtained in step S4 is acid-washed with 2 M HCl solution for 12 hours and repeatedly washed with deionized water until the filtrate is neutral. Then the carbonized product is dried at 80°C for 12 hours and sieved through a 300-mesh sieve to obtain the hard carbon anode material.

[0056] Comparative Example 4 A method for preparing a hard carbon anode material includes the following steps: S1. Pine wood is cut into 3 mm thick slices and cleaned with deionized water, and then dried at 80°C for 12 hours to obtain the precursor. S2. Prepare 200 ml of eutectic solvent in a beaker, with a molar ratio of choline chloride to lactic acid of 1:2; add 10 g of the treated pine wood chips to the beaker, and remove some of the lignin and hemicellulose from the wood chips in an oil bath at 90°C for 48 h; then wash off the solvent on the surface of the pine wood chips with deionized water and dry them at 80°C. S3. Prepare 50ml of epoxy resin solution, immerse the product obtained in step S2 into the resin solution, transfer it to a vacuum oven, and perform three vacuum treatments to allow the resin to be composite filled and cured; the vacuum pressure is -0.05Mpa and the time is 5 minutes. S4. The product obtained in step S3 is transferred to a high-temperature tube furnace and carbonized at 800°C at a rate of 2°C / min under N2 atmosphere. The heating rate is 2°C / min, the carbonization time is 2h, and the gas flow rate is 80 mL / min. S5. The carbonized product obtained in step S4 is acid-washed with 2 M HCl solution for 12 hours and repeatedly washed with deionized water until the filtrate is neutral. Then the carbonized product is dried at 80°C for 12 hours and sieved through a 300-mesh sieve to obtain the hard carbon anode material.

[0057] Comparative Example 5 A method for preparing a hard carbon anode material includes the following steps: S1. Pine wood is cut into 3 mm thick slices and cleaned with deionized water, and then dried at 80°C for 12 hours to obtain the precursor. S2. Prepare 200 ml of eutectic solvent in a beaker, with a molar ratio of choline chloride to lactic acid of 1:2; add 10 g of the treated pine wood chips to the beaker, and remove some of the lignin and hemicellulose from the wood chips in an oil bath at 90°C for 48 h; then wash off the solvent on the surface of the pine wood chips with deionized water and dry them at 80°C. S3. Transfer the product obtained in step S2 to a vacuum oven and perform three vacuuming processes; the vacuuming pressure is -0.05 MPa and the time is 5 minutes. S4. The product obtained in step S3 is transferred to a high-temperature tube furnace and carbonized at 1400°C at a rate of 2°C / min under N2 atmosphere. The heating rate is 2°C / min, the carbonization time is 2h, and the gas flow rate is 80 mL / min. S5. The carbonized product obtained in step S4 is acid-washed with 2 M HCl solution for 12 hours and repeatedly washed with deionized water until the filtrate is neutral. Then the carbonized product is dried at 80°C for 12 hours and sieved through a 300-mesh sieve to obtain the hard carbon anode material.

[0058] Experiment 1: Performance Testing The hard carbon anode materials prepared in the examples and comparative examples were mixed with Ketjen black and sodium carboxymethyl cellulose in a mass ratio of 90:5:5 to form a slurry. This slurry was then uniformly coated onto copper foil and vacuum dried at 80°C for 12 hours to obtain the anode sheet, wherein the areal density of the sheet was 1.5~2.5 mg / cm³. 2 The battery was assembled in an argon-protected glove box using a sodium metal sheet as the counter electrode, glass fiber as the separator, and 1.0M NaPF6 / DME solution as the electrolyte.

[0059] Performance tests were conducted using a Xinwei electrochemical tester. The voltage range for charge-discharge tests was 0.01~2.5 V, and the current density was 30 mA / g. The test results are shown in Table 1.

[0060] Table 1 Performance test results for each group Group Initial charge specific capacity (mAh / g) at a working voltage plateau of 0.1 V Initial coulombic efficiency (%) Specific capacity (mAh / g) at a current density of 1 A / g Example 1 264 89.9 188 Example 2 243 83.7 151 Example 3 238 84.5 146 Example 4 237 83.6 147 Example 5 217 78.7 117 Example 6 233 83.4 105 Example 7 227 79.8 107 Example 8 225 77.5 114 Example 9 215 76.3 108 Comparative Example 1 205 68.4 87 Comparative Example 2 157 58.2 43 Comparative Example 3 184 63.5 68 Comparative Example 4 197 67.3 72 Comparative Example 5 182 66 57 The data in Table 1 show that the hard carbon anode material prepared in the embodiments of the present invention has good electrochemical performance.

[0061] In Comparative Example 1, the epoxy resin solution and the product treated with a eutectic solvent were only physically mixed, resulting in a deterioration in the electrochemical performance of the hard carbon anode material. In Comparative Example 2, sulfuric acid solution was used to treat the wood. Due to the excessive acidity of the sulfuric acid solution, the wood skeleton was excessively corroded and even the crystalline structure of cellulose was destroyed. As a result, the wood template formed was too fragile and more likely to collapse during the carbonization process, which led to a deterioration in the electrochemical performance of the hard carbon anode material finally obtained. In Comparative Examples 3 and 4, the electrochemical performance of the final anode material was significantly worse due to an unsuitable carbonization temperature during the material preparation process. Comparative Example 5 shows that the hard carbon material prepared using wood alone performs poorly in terms of sodium storage performance. This is because the natural structure of wood forms a large specific surface area under high-temperature carbonization. A large specific surface area means that the solid electrolyte membrane formed during the charging and discharging process of the battery consumes more sodium, resulting in a reduction in capacity and initial efficiency.

[0062] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a hard carbon anode material, characterized in that, Includes the following steps: S1. Pre-treat the wood to obtain the precursor; S2. Add a eutectic solvent to the obtained precursor and react. After the reaction is complete, clean and dry. S3. The product obtained in step S2 is composite-filled and cured with resin solution; S4. Carbonize the product obtained in step S3; S5. The carbonized product obtained in step S4 is cleaned, dried, and sieved to obtain the hard carbon anode material.

2. The method for preparing a hard carbon anode material as described in claim 1, characterized in that, The pretreatment of wood in step S1 includes the following steps: slicing the wood, washing it with deionized water, drying it, and obtaining the precursor.

3. The method for preparing a hard carbon anode material as described in claim 1, characterized in that, In step S2, the ratio of the eutectic solvent to the obtained precursor is (180~220) ml: 10 g; In step S2, the molar ratio of hydrogen bond acceptor to hydrogen bond donor in the eutectic solvent is 1:(1~5).

4. The method for preparing a hard carbon anode material as described in claim 3, characterized in that, The hydrogen bond acceptor includes at least one of choline chloride and quaternary ammonium salt; the hydrogen bond donor includes at least one of urea, acetic acid, and lactic acid.

5. The method for preparing a hard carbon anode material as described in claim 1, characterized in that, The reaction temperature in step S2 is 60~90℃, and the reaction time is 6~72h.

6. The method for preparing a hard carbon anode material as described in claim 1, characterized in that, The resin solution mentioned in step S3 includes at least one of epoxy resin and phenolic resin; The ratio of the resin solution to the precursor obtained in step S2 is 40~60mL:10g.

7. The method for preparing a hard carbon anode material as described in claim 1, characterized in that, The composite filling in step S3 is achieved by filling the resin solution with the product obtained in step S2 using a vacuum method; the curing is natural curing. The carbonization in step S4 includes the following steps: the product obtained in step S3 is transferred to a high-temperature tube furnace and carbonized in an inert atmosphere at a temperature of 900–1700°C for 1–8 hours, with a heating rate of 1–10°C / min and an inert gas flow rate of 20–120 mL / min.

8. The method for preparing a hard carbon anode material as described in claim 1, characterized in that, The cleaning process described in step S5 is as follows: add 1-3 mol / L hydrochloric acid solution to the carbonized product, stir for 6-24 hours, and then wash with water until the filtrate is neutral; The drying temperature in step S5 is 50~100℃, and the drying time is 8~72h; The sieving mentioned in step S5 refers to passing the material through a 200-500 mesh sieve.

9. A hard carbon anode material prepared by the preparation method of the hard carbon anode material as described in any one of claims 1 to 8.

10. The application of the hard carbon anode material as described in claim 9 in the preparation of sodium-ion batteries.

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