Method for preparing sodium-ion battery hard carbon negative electrode material from low-temperature activated corncob

Abstract

The present application relates to the technical field of sodium ion battery, especially to a method for preparing a hard carbon negative electrode material of a sodium ion battery from corncob at low temperature activation, wherein the method uses waste corncob as a raw material, and through methods such as zinc acetate solution soaking, pre-carbonization and ball milling, the corncob is decontaminated and modified in composition, and a large number of defects and closed pores are generated in the high and low temperature annealing process, so that the capacity is significantly improved, the first coulomb efficiency is improved, and a high-performance sodium ion battery negative electrode material is obtained. Compared with the blank sample, the specific capacity of the negative electrode material prepared based on the method is 356.7 mAh / g, and the first coulomb efficiency can be increased to 98.1%. By using waste corncob as a raw material, the utilization range of agricultural and sideline products is increased, which has great environmental and economic benefits in reducing pollution, saving biomass resources and developing new energy. At the same time, the preparation method is simple, low in cost and excellent in performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically a method for preparing hard carbon anode materials for sodium-ion batteries by low-temperature activation of corn cobs. Background Technology

[0002] In recent years, lithium-ion batteries (LIBs) have dominated the electrochemical energy storage market due to their high energy density, high power, and long lifespan. However, my country's lithium resources are relatively scarce and of low quality, leading to a large-scale import of lithium. As energy demand continues to grow, lithium-ion batteries cannot fully meet the needs of large-scale energy storage. Under these circumstances, sodium-ion batteries have rapidly developed as a supplement to lithium-ion batteries. Sodium resources are widely distributed, abundant, and inexpensive, and sodium-ion batteries offer relatively good safety performance and high low-temperature resistance. To date, extensive research has been conducted on a large number of sodium-ion battery anode materials, such as carbon-based materials, titanium-based materials, alloy materials, and organic compound materials. However, many materials are unsuitable for practical applications due to their inherent electrochemical defects and complex preparation processes. Carbon-based materials offer the best overall electrochemical performance, low cost, and simple preparation. Hard carbon materials, in particular, are considered the best candidate materials for sodium-ion battery anodes and have broad industrial application prospects.

[0003] Among resin-based, polymer-based, biomass-based, and carbohydrate-based carbon precursors, biomass-based precursors are abundant, cheaper, and possess a naturally porous structure, which is crucial for the performance of hard carbon anode materials. Corn cobs are a high-volume but difficult-to-manage agricultural byproduct, currently primarily used as fuel. However, burning corn cobs causes smoke pollution, polluting the environment and causing respiratory diseases. Statistics show that my country's annual corn cob production is around 55 million tons; therefore, recycling and reusing corn cobs as carbon material precursors has significant economic and environmental benefits. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing hard carbon anode material for sodium-ion batteries by low-temperature activation of corn cobs, comprising the following steps: (1) Crush the corn cob, wash and dry it with deionized water, and pass it through a 10-20 mesh sieve to obtain corn cob fragments; (2) Soak the corn cob fragments in a zinc acetate solution with a concentration of 0.25-1 mol / L at room temperature for 8 hours. After pouring out the solution, put the solid into an oven to dry. (3) The corn cob fragments are pre-carbonized at low temperature, and Ar / N2 protective gas is introduced during the pre-carbonization process; (4) The pre-carbonized product is ball-milled to obtain a powder material with a relatively uniform particle size; (5) The powder is carbonized at high temperature, and Ar / N2 protective gas is introduced during the carbonization process to obtain hard carbon powder material; (6) Hard carbon powder is mixed with conductive carbon black, PVDF and NMP to prepare a negative electrode slurry. The negative electrode slurry is coated on the surface of aluminum foil and dried in a vacuum drying oven. Then, a tablet press is used to make a tablet to obtain a hard carbon negative electrode sheet for sodium-ion batteries.

[0006] Preferably, in step (1), the cleaning of the crushed corn cobs includes: first soaking in deionized water for 2 hours with stirring; after stopping stirring, letting it stand or using a centrifuge to separate the layers, pouring out the upper liquid, and then adding deionized water; repeating this operation 3-5 times, and finally putting the sieved corn cob pieces into a forced-air drying oven and drying them thoroughly at 60°C.

[0007] Preferably, in step (2), deionized water is first heated to 50°C, and zinc acetate of different masses is dissolved in deionized water to prepare zinc acetate solutions of different concentrations. Corn cobs are soaked in the prepared zinc acetate solutions for 8 hours with stirring. After stirring is stopped, the layers are allowed to separate, the upper layer of solution is poured out, and the soaked corn cob fragments are placed in an oven to dry at 80°C.

[0008] Preferably, in step (3), the low-temperature pre-carbonization is carried out by heating to 350-500°C in a tube furnace, holding for 2 hours, with a heating rate of 2-10°C / min, and during this period, Ar / N2 protective gas is introduced.

[0009] Preferably, in step (4), a planetary ball mill is used to ball mill the pre-carbonized corn cobs, with a material ratio of 20:1. The ball milling process is set to alternate between forward rotation for 30 minutes and reverse rotation for 30 minutes, with an interval of 10 minutes and a cycle of 3-5 times.

[0010] Preferably, in step (5), carbonization is performed by heating to 1100-1500℃ in a tube furnace, holding for 2-6 hours, with a heating rate of 2-5℃ / min, during which Ar / N2 protective gas is introduced.

[0011] Preferably, in step (6), hard carbon powder, conductive carbon black, and PVDF are mixed evenly in a mass ratio of 8:1:1, and NMP is added dropwise to prepare a negative electrode slurry. The negative electrode slurry is then applied to the surface of aluminum foil using a 75µm wire rod applicator and dried in a vacuum drying oven at 80-100℃ for 10-12 hours. Afterward, it is cut into electrode sheets with a diameter of 10-12 mm, and the active material loading on the substrate is controlled at 0.5-1 mg / cm³. 2 The electrode is transferred to a glove box, with the sodium sheet used as the counter electrode. The electrolyte is a NaPF6 or NaClO4 electrolyte containing additives. The battery assembly process is carried out in a glove box under argon atmosphere protection. Finally, the battery performance is tested.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: In the high-temperature carbonization process of this invention, the transformation during heat treatment is divided into two stages: (1) Low temperature stage (<500℃): First, acetate ions are pyrolyzed to produce zinc oxide, carbon dioxide and ether products. As the temperature rises, zinc oxide is reduced by carbon materials to produce elemental zinc and carbon monoxide or carbon dioxide gas, introducing structural defect sites. These defects, as active centers, can adsorb more sodium ions and contribute additional double layer capacitance. (2) High-temperature stage (>900℃): Hard carbon materials prepared from corn cobs without zinc acetate modification contain a large number of closed or semi-closed micropores. During the initial sodium intercalation process, Na... + After entering these pores, some sodium is irreversibly trapped by defects or functional groups on the pore walls (forming "dead sodium"), leading to a decrease in ICE (internal ion exchange rate). However, in materials with added zinc acetate, after low-temperature treatment, the Zn vaporizes and escapes at high temperatures, leaving a large number of micro / mesopores in situ, which are then used to contain sodium. + These pores provide a smoother transport channel, shortening the ion diffusion path and reducing Na+ diffusion. + Irreversible traps in a dense carbon matrix, along with the fact that these pores can serve as sodium storage sites in subsequent cycles (closed-pore filling), improve the first coulombic efficiency and increase capacity. The synergistic effect of zinc acetate increasing active sites through pore formation and introducing additional capacity through defect engineering makes the electrochemical performance (first coulombic efficiency, reversible capacity) of corn cob-based carbon materials significantly better than that of untreated control samples. Attached Figure Description

[0013] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a SEM image of the hard carbon powder prepared from corn cob biomass in Example 1 of the present invention; Figure 2 The image shows the XRD pattern of hard carbon powder prepared from corn cob biomass in Example 1 of this invention. Figure 3 Raman spectroscopy diagrams of hard carbon powder prepared from corn cob biomass in Comparative Example 1 and Example 1 of this invention; Figure 4 The above are charge-discharge curves of sodium-ion batteries assembled from hard carbon negative electrode sheets prepared in Comparative Example 1 and Example 1 of this invention. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1 (1) Crush the corn cob, soak it in deionized water for 2 hours while stirring; after stopping the stirring, let it stand to separate into layers, pour out the upper liquid, and then add deionized water; repeat this operation 3-5 times, and finally put the sieved corn cob pieces into a forced-air drying oven and dry them thoroughly at 60°C. (2) Soak the corn cob fragments in a 0.5 mol / L zinc acetate solution at room temperature for 8 hours. After pouring out the solution, put the solid into an oven to dry. (3) The corn cob fragments were pre-carbonized at low temperature and placed in a tube furnace and heated to 500°C. The temperature was maintained for 2 hours with a heating rate of 5°C / min. Argon gas was introduced during the process. (4) Use a planetary ball mill to ball mill the pre-carbonized corn cobs. The material ratio is 20:1. The ball milling process is set to alternate between forward rotation for 30 minutes and reverse rotation for 30 minutes, with an interval of 10 minutes and a cycle of 3 times. (5) After ball milling, the sample was placed in a tube furnace and heated to 1300℃, held for 2 hours, with a heating rate of 5℃ / min, during which argon gas was introduced; (6) Hard carbon powder, conductive carbon black, and PVDF were mixed evenly in a mass ratio of 8:1:1. NMP was added dropwise to prepare a negative electrode slurry. The negative electrode slurry was coated onto the surface of aluminum foil using a 75µm wire rod applicator. The foil was dried at 100℃ for 12 hours in a vacuum drying oven. After drying, the foil was cut into electrodes with a diameter of 12mm. The active material loading on the substrate was controlled at 0.5-1mg / cm³. 2 .

[0017] Example 2 (1) Crush the corn cob, soak it in deionized water for 2 hours while stirring; after stopping the stirring, let it stand to separate into layers, pour out the upper liquid, and then add deionized water; repeat this operation 3-5 times, and finally put the sieved corn cob pieces into a forced-air drying oven and dry them thoroughly at 60°C. (2) Soak the corn cob fragments in a 0.25 mol / L zinc acetate solution at room temperature for 8 hours. After pouring out the solution, put the solid into an oven to dry. (3) The corn cob fragments were pre-carbonized at low temperature and placed in a tube furnace and heated to 500°C. The temperature was maintained for 2 hours with a heating rate of 5°C / min. Argon gas was introduced during the process. (4) Use a planetary ball mill to ball mill the pre-carbonized corn cobs. The material ratio is 20:1. The ball milling process is set to alternate between forward rotation for 30 minutes and reverse rotation for 30 minutes, with an interval of 10 minutes and a cycle of 3 times. (5) After ball milling, the sample was placed in a tube furnace and heated to 1300℃, held for 2 hours, with a heating rate of 5℃ / min, during which argon gas was introduced; (6) Hard carbon powder, conductive carbon black, and PVDF were mixed evenly in a mass ratio of 8:1:1. NMP was added dropwise to prepare a negative electrode slurry. The negative electrode slurry was coated onto the surface of aluminum foil using a 75µm wire rod applicator. The foil was dried at 100℃ for 12 hours in a vacuum drying oven. After drying, the foil was cut into electrodes with a diameter of 12mm. The active material loading on the substrate was controlled at 0.5-1mg / cm³. 2 .

[0018] Example 3 (1) Crush the corn cob, soak it in deionized water for 2 hours while stirring; after stopping the stirring, let it stand to separate into layers, pour out the upper liquid, and then add deionized water; repeat this operation 3-5 times, and finally put the sieved corn cob pieces into a forced-air drying oven and dry them thoroughly at 60°C. (2) Soak the corn cob fragments in a 0.75 mol / L zinc acetate solution at room temperature for 8 hours. After pouring out the solution, put the solid into an oven to dry. (3) The corn cob fragments were pre-carbonized at low temperature and placed in a tube furnace and heated to 500°C. The temperature was maintained for 2 hours with a heating rate of 5°C / min. Argon gas was introduced during the process. (4) Use a planetary ball mill to ball mill the pre-carbonized corn cobs. The material ratio is 20:1. The ball milling process is set to alternate between forward rotation for 30 minutes and reverse rotation for 30 minutes, with an interval of 10 minutes and a cycle of 3 times. (5) After ball milling, the sample was placed in a tube furnace and heated to 1300℃, held for 2 hours, with a heating rate of 5℃ / min, during which argon gas was introduced; (6) Hard carbon powder, conductive carbon black, and PVDF were mixed evenly in a mass ratio of 8:1:1. NMP was added dropwise to prepare a negative electrode slurry. The negative electrode slurry was coated onto the surface of aluminum foil using a 75µm wire rod applicator. The foil was dried at 100℃ for 12 hours in a vacuum drying oven. After drying, the foil was cut into electrodes with a diameter of 12mm. The active material loading on the substrate was controlled at 0.5-1mg / cm³. 2 .

[0019] Example 4 (1) Crush the corn cob, soak it in deionized water for 2 hours while stirring; after stopping the stirring, let it stand to separate into layers, pour out the upper liquid, and then add deionized water; repeat this operation 3-5 times, and finally put the sieved corn cob pieces into a forced-air drying oven and dry them thoroughly at 60°C. (2) Soak the corn cob fragments in a 1 mol / L zinc acetate solution at room temperature for 8 hours. After pouring out the solution, put the solid into an oven to dry. (3) The corn cob fragments were pre-carbonized at low temperature and placed in a tube furnace and heated to 500°C. The temperature was maintained for 2 hours with a heating rate of 5°C / min. Argon gas was introduced during the process. (4) Use a planetary ball mill to ball mill the pre-carbonized corn cobs. The material ratio is 20:1. The ball milling process is set to alternate between forward rotation for 30 minutes and reverse rotation for 30 minutes, with an interval of 10 minutes and a cycle of 3 times. (5) After ball milling, the sample was placed in a tube furnace and heated to 1300℃, held for 2 hours, with a heating rate of 5℃ / min, during which argon gas was introduced; (6) Hard carbon powder, conductive carbon black, and PVDF were mixed evenly in a mass ratio of 8:1:1. NMP was added dropwise to prepare a negative electrode slurry. The negative electrode slurry was coated onto the surface of aluminum foil using a 75µm wire rod applicator. The foil was dried at 100℃ for 12 hours in a vacuum drying oven. After drying, the foil was cut into electrodes with a diameter of 12mm. The active material loading on the substrate was controlled at 0.5-1mg / cm³. 2 .

[0020] Comparative Example 1 (1) Crush the corn cob, soak it in deionized water for 2 hours while stirring; after stopping the stirring, let it stand to separate into layers, pour out the upper liquid, and then add deionized water; repeat this operation 3-5 times, and finally put the sieved corn cob pieces into a forced-air drying oven and dry them thoroughly at 60°C. (2) The corn cob fragments were pre-carbonized at low temperature and placed in a tube furnace and heated to 500°C for 2 hours. The heating rate was 5°C / min, and argon gas was introduced during the process. (3) Use a planetary ball mill to ball mill the pre-carbonized corn cobs. The material ratio is 20:1. The ball milling process is set to alternate between forward rotation for 30 minutes and reverse rotation for 30 minutes, with an interval of 10 minutes and a cycle of 3 times. (4) After ball milling, the sample was placed in a tube furnace and heated to 1300℃, held for 2 hours, with a heating rate of 5℃ / min, during which argon gas was introduced; (5) Hard carbon powder, conductive carbon black, and PVDF were mixed evenly in a mass ratio of 8:1:1. NMP was added dropwise to prepare a negative electrode slurry. The negative electrode slurry was coated onto the surface of aluminum foil using a 75µm wire rod applicator. The foil was dried at 100℃ for 12 hours in a vacuum drying oven. After drying, the foil was cut into electrodes with a diameter of 12mm. The active material loading on the substrate was controlled at 0.5-1mg / cm³. 2 .

[0021]

[0022] It should be noted that any content not described in detail in this specification belongs to the prior art known to those skilled in the art. The specific embodiments described herein are merely illustrative examples of the spirit of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for preparing hard carbon anode material for sodium-ion batteries by low-temperature activation of corn cobs, characterized in that: Includes the following steps: (1) Crush the corn cob, wash and dry it with deionized water, and pass it through a 10-20 mesh sieve to obtain corn cob fragments; (2) Soak the corn cob fragments in a zinc acetate solution with a concentration of 0.25-1 mol / L at room temperature for 8 hours. After pouring out the solution, put the solid into an oven to dry. (3) The corn cob fragments are pre-carbonized at low temperature, and Ar / N2 protective gas is introduced during the pre-carbonization process; (4) The pre-carbonized product is ball-milled to obtain a powder material with a relatively uniform particle size; (5) The powder is carbonized at high temperature, and Ar / N2 protective gas is introduced during the carbonization process to obtain hard carbon powder material; (6) Hard carbon powder is mixed with conductive carbon black, PVDF and NMP to prepare a negative electrode slurry. The negative electrode slurry is coated on the surface of aluminum foil and dried in a vacuum drying oven. Then, a tablet press is used to make a tablet to obtain a hard carbon negative electrode sheet for sodium-ion batteries.

2. The method for preparing hard carbon anode material for sodium-ion batteries by low-temperature activation of corn cobs according to claim 1, characterized in that: In step (1), the cleaning of the crushed corn cobs includes: first soaking them in deionized water for 2 hours with stirring; after stopping the stirring, letting them stand or using a centrifuge to separate them into layers, pouring out the upper liquid, and then adding deionized water; repeating this operation 3-5 times, and finally putting the sieved corn cob pieces into a forced-air drying oven and drying them thoroughly at 60°C.

3. The method for preparing hard carbon anode material for sodium-ion batteries by low-temperature activation of corn cobs according to claim 1, characterized in that: In step (2), deionized water is first heated to 50°C, and zinc acetate of different masses is dissolved in deionized water to prepare zinc acetate solutions of different concentrations. Corn cobs are soaked in the prepared zinc acetate solutions for 8 hours with stirring. After stirring is stopped, the layers are allowed to separate, and the upper layer of solution is poured out. The soaked corn cob fragments are placed in an oven and dried at 80°C.

4. The method for preparing hard carbon anode material for sodium-ion batteries by low-temperature activation of corn cobs according to claim 1, characterized in that: In step (3), the low-temperature pre-carbonization is carried out by heating to 350-500℃ in a tube furnace, holding for 2 hours, with a heating rate of 2-10℃ / min, and during this period, Ar / N2 protective gas is introduced.

5. The method for preparing hard carbon anode material for sodium-ion batteries by low-temperature activation of corn cobs according to claim 1, characterized in that: In step (4), a planetary ball mill is used to ball mill the pre-carbonized corn cobs. The material ratio is 20:

1. The ball milling process is set to alternate between forward rotation for 30 minutes and reverse rotation for 30 minutes, with an interval of 10 minutes and a cycle of 3-5 times.

6. The method for preparing hard carbon anode material for sodium-ion batteries by low-temperature activation of corn cobs according to claim 1, characterized in that: In step (5), carbonization is carried out in a tube furnace by heating to 1100-1500℃ and holding for 2-6 hours, with a heating rate of 2-5℃ / min, during which Ar / N2 protective gas is introduced.

7. The method for preparing hard carbon anode material for sodium-ion batteries by low-temperature activation of corn cobs according to claim 1, characterized in that: In step (6), hard carbon powder, conductive carbon black, and PVDF are mixed evenly in a mass ratio of 8:1:1, and NMP is added dropwise to prepare a negative electrode slurry. The negative electrode slurry is then coated onto the surface of aluminum foil using a 75µm wire rod applicator and dried in a vacuum drying oven at 80-100℃ for 10-12 hours. After drying, the slurry is cut into electrode sheets with a diameter of 10-12mm, and the active material loading on the substrate is controlled at 0.5-1mg / cm³. 2 The electrode is transferred to a glove box, with the sodium sheet used as the counter electrode. The electrolyte is a NaPF6 or NaClO4 electrolyte containing additives. The battery assembly process is carried out in a glove box under argon atmosphere protection. Finally, the battery performance is tested.

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