Preparation method of hard carbon anode material for sodium-ion batteries

Abstract

This invention discloses a method for preparing hard carbon anode material for sodium-ion batteries, comprising the following steps: preliminary carbonization, modification, gas etching, secondary carbonization, oxidation, pre-sodiumization, and tertiary carbonization. First, biomass materials are subjected to preliminary carbonization, and appropriate amounts of citric acid and a pore-forming agent are added to react with the preliminary carbonization raw materials to form esterification and pores, respectively. In the second carbonization step, the esterification increases the interlayer spacing of the hard carbon, and carbon dioxide is introduced at high temperature to chemically etch the product surface, effectively increasing the surface micropores, which is beneficial for sodium ion storage and improves the initial efficiency. Then, a strongly acidic solution is used for oxidation to introduce hydroxyl groups to the surface of the hard carbon. The hydroxyl groups undergo a hydrothermal reaction with sodium benzenesulfonate. Subsequently, a tertiary carbonization is performed, where sodium benzenesulfonate dehydrates and condenses with the hydroxyl groups on the hard carbon surface, forming a coating layer that reduces the surface area while simultaneously completing pre-sodiumization, effectively reducing SEI film loss and improving the cycle performance of the anode material.

Description

Technical Field

[0001] This invention relates to the field of anode materials, and in particular to a method for preparing a hard carbon anode material for sodium-ion batteries. Background Technology

[0002] Sodium-ion batteries are rechargeable batteries that primarily function by the movement of sodium ions between the positive and negative electrodes, similar in principle to lithium-ion batteries. They were named one of the top ten emerging technologies in the field of chemistry in 2022. As a novel electrochemical energy storage system, sodium-ion batteries benefit from abundant and inexpensive sodium resources, showing broad application prospects in large-scale energy storage.

[0003] Hard carbon offers significant advantages as a material for sodium-ion batteries, with a theoretical capacity of 350-530 mAh / g and a practical capacity of 200-350 mAh / g, far exceeding that of graphite anodes. Furthermore, hard carbon, with its low cost, low redox potential, and high sodium storage capacity, has become a core anode material driving the industrialization of sodium-ion batteries (SIBs) and is currently the most commercially promising anode material for sodium batteries. However, current biomass hard carbon anodes still face challenges such as low initial coulombic efficiency and poor cycle performance. Therefore, it is necessary to propose a new approach to improve biomass hard carbon anodes to address these issues. Summary of the Invention

[0004] In view of this, the present invention addresses the deficiencies of the prior art, and its main objective is to provide a method for preparing a hard carbon anode material for sodium-ion batteries, which produces a biomass hard carbon anode material with high initial efficiency and excellent cycle performance.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a hard carbon anode material for sodium-ion batteries, characterized by comprising the following steps:

[0007] (1) Place the biomass material into a muffle furnace and heat it to 200-300℃ under a protective atmosphere for preliminary carbonization. The preliminary carbonization time is 1-15h to obtain the preliminary carbonized raw material.

[0008] (2) Citric acid, pore-forming agent and preliminary carbonization raw material obtained in step (1) are put into a ball mill in a mass ratio of (1-10):(2-10):100 for ball milling. The ball milling speed is 500 r / min and the ball milling time is 1-8 h to obtain preliminary modified carbon material.

[0009] (3) The preliminary modified carbon material obtained in step (2) is placed in a muffle furnace and heated under a protective atmosphere at a heating rate of 5-10℃ / min. When the temperature reaches 800℃, carbon dioxide gas is introduced for etching and the temperature is held for 2 hours. Then, a protective gas is introduced and the temperature is continued to rise to 1000-1400℃ for a second carbonization at a heating rate of 5-10℃ / min. The second carbonization time is 1-10 hours to obtain the secondary carbonization product.

[0010] (4) The secondary carbonization product obtained in step (3) is immersed in a strong acid solution, wherein the solute of the strong acid solution is sulfuric acid and nitric acid, and the molar ratio of sulfuric acid and nitric acid is (2-5):1. The temperature is raised to 100-200℃, and the oxidation reaction is carried out for 3-24 hours. Then, the product is filtered, washed with water until neutral, and dried at 50-80℃ for 10-24 hours to obtain the oxidation product.

[0011] (5) The oxidation product obtained in step (4) and sodium benzenesulfonate are placed in a reaction vessel at a mass ratio of (7-10):(0.5-1.5). Ethanol is used as the solvent, and a surfactant is added to carry out a hydrothermal reaction. The rotation speed of the reaction vessel is 500-1400 r / min, the reaction time is 8-12 h, and the reaction temperature is 170-190℃. Then, the mixture is filtered, washed with water until neutral, and dried at 60-80℃ for 12-24 h to obtain the pre-sodiumized product.

[0012] (6) The pre-sodium product obtained in step (5) is placed in a muffle furnace and heated to 800-1000℃ under a protective atmosphere. The heating rate is 1-5℃ / min and the holding time is 4-6h to obtain hard carbon anode material.

[0013] As a preferred option, the biomass material in step (1) is coconut shell.

[0014] As a preferred embodiment, the protective atmosphere in steps (1) and (3) is an argon atmosphere.

[0015] As a preferred embodiment, the pore-forming agent in step (2) is zinc carbonate.

[0016] As a preferred option, the protective gas in step (3) is argon.

[0017] As a preferred option, the surfactant in step (5) is poloxamer F127.

[0018] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, as can be seen from the above technical solution:

[0019] By initially carbonizing biomass materials and adding appropriate amounts of citric acid and pore-forming agents to form esterification reactions and create pores with the initial carbonization raw materials, and then in the second carbonization step, the esterification increases the interlayer spacing of hard carbon, and carbon dioxide is introduced at high temperature to chemically etch the product surface, effectively increasing the surface micropores, which is beneficial for sodium ion storage and improving the first-stage efficiency. In addition, strong acid solution is used for oxidation to introduce hydroxyl groups to the surface of hard carbon. The hydroxyl groups react with sodium benzenesulfonate in a hydrothermal reaction, followed by a third carbonization. Sodium benzenesulfonate dehydrates and condenses with the hydroxyl groups on the surface of hard carbon to form a coating layer, reducing the surface area and completing pre-sodiumization, which effectively reduces the loss of SEI film and improves the cycle performance of negative electrode material.

[0020] To more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail below with reference to specific embodiments. Detailed Implementation

[0021] This invention discloses a method for preparing a hard carbon anode material for sodium-ion batteries, characterized by comprising the following steps:

[0022] (1) The biomass material is placed in a muffle furnace and heated to 200-300°C under a protective atmosphere for preliminary carbonization. The preliminary carbonization time is 1-15 hours to obtain the preliminary carbonized raw material. The biomass material is coconut shell and the protective atmosphere is argon atmosphere.

[0023] (2) Citric acid, pore-forming agent and preliminary carbonization raw material obtained in step (1) are put into a ball mill in a mass ratio of (1-10):(2-10):100 for ball milling. The ball milling speed is 500 r / min and the ball milling time is 1-8 h to obtain preliminary modified carbon material. The pore-forming agent is zinc carbonate.

[0024] (3) The preliminary modified carbon material obtained in step (2) is placed in a muffle furnace and heated under a protective atmosphere at a heating rate of 5-10℃ / min. When the temperature reaches 800℃, carbon dioxide gas is introduced for etching and the temperature is held for 2 hours. Then, a protective gas is introduced and the temperature is continued to rise to 1000-1400℃ for a second carbonization at a heating rate of 5-10℃ / min. The second carbonization time is 1-10 hours to obtain a secondary carbonization product. The protective atmosphere is an argon atmosphere and the protective gas is argon.

[0025] (4) The secondary carbonization product obtained in step (3) is immersed in a strong acid solution, wherein the solutes of the strong acid solution are sulfuric acid and nitric acid, and the molar ratio of sulfuric acid and nitric acid is (2-5):1. The temperature is raised to 100-200℃, and the oxidation reaction is carried out for 3-24 hours. Then, the product is filtered, washed with water until neutral, and dried at 50-80℃ for 10-24 hours to obtain the oxidation product.

[0026] (5) The oxidation product obtained in step (4) and sodium benzenesulfonate are placed in a reaction vessel at a mass ratio of (7-10):(0.5-1.5). Ethanol is used as the solvent, and a surfactant is added to carry out a hydrothermal reaction. The rotation speed of the reaction vessel is 500-1400 r / min, the reaction time is 8-12 h, and the reaction temperature is 170-190 °C. Then, the mixture is filtered, washed with water until neutral, and dried at 60-80 °C for 12-24 h to obtain the pre-sodiumized product. The surfactant is poloxamer F127.

[0027] (6) The pre-sodium product obtained in step (5) is placed in a muffle furnace and heated to 800-1000℃ under a protective atmosphere. The heating rate is 1-5℃ / min and the holding time is 4-6h to obtain hard carbon anode material.

[0028] The following detailed description is based on several specific embodiments.

[0029] Example 1

[0030] (1) Place the coconut shell in a muffle furnace and heat it to 200°C under an argon atmosphere for preliminary carbonization. The preliminary carbonization time is 3 hours to obtain the preliminary carbonized raw material.

[0031] (2) Citric acid, zinc carbonate and the preliminary carbonization raw material obtained in step (1) are put into a ball mill in a mass ratio of 2:2:100 for ball milling. The ball milling speed is 500 r / min and the ball milling time is 6 h to obtain the preliminary modified carbon material.

[0032] (3) The preliminary modified carbon material obtained in step (2) is placed in a muffle furnace and heated in an argon atmosphere at a heating rate of 5℃ / min. When the temperature reaches 800℃, carbon dioxide gas is introduced for etching. The temperature is held for 2 hours, and then argon gas is introduced and the heating continues. The temperature is raised to 1100℃ for a second carbonization at a heating rate of 10℃ / min. The second carbonization time is 6 hours, and a secondary carbonization product is obtained.

[0033] (4) The secondary carbonization product obtained in step (3) is immersed in a strong acid solution, wherein the solutes of the strong acid solution are sulfuric acid and nitric acid, and the molar ratio of sulfuric acid and nitric acid is 3:1. The temperature is raised to 120°C and the oxidation reaction is carried out for 8 hours. Then, the product is filtered, washed with water until neutral, and dried at 50°C for 14 hours to obtain the oxidation product.

[0034] (5) The oxidation product obtained in step (4) and sodium benzenesulfonate were placed in a reaction vessel at a mass ratio of 8:1. Poloxamer F127 was added with ethanol as solvent and hydrothermal reaction was carried out. The rotation speed of the reaction vessel was 600 r / min, the reaction time was 10 h, and the reaction temperature was 180 °C. Then, the product was filtered, washed with water until neutral, and dried at 70 °C for 20 h to obtain the pre-sodiumized product.

[0035] (6) The pre-sodium product obtained in step (5) is placed in a muffle furnace and heated to 800°C under a protective atmosphere. The heating rate is 5°C / min and the holding time is 5h to obtain hard carbon anode material.

[0036] Example 2

[0037] (1) Place the coconut shell in a muffle furnace and heat it to 300°C under an argon atmosphere for preliminary carbonization. The preliminary carbonization time is 15 hours to obtain the preliminary carbonized raw material.

[0038] (2) Citric acid, zinc carbonate and the preliminary carbonization raw material obtained in step (1) are put into a ball mill in a mass ratio of 1:3:100 for ball milling. The ball milling speed is 500 r / min and the ball milling time is 1 h to obtain the preliminary modified carbon material.

[0039] (3) The preliminary modified carbon material obtained in step (2) is placed in a muffle furnace and heated in an argon atmosphere at a heating rate of 10℃ / min. When the temperature reaches 800℃, carbon dioxide gas is introduced for etching. The temperature is held for 2 hours, and then argon gas is introduced and the heating continues. The temperature is raised to 1300℃ for a second carbonization at a heating rate of 5℃ / min. The second carbonization time is 1 hour, and a second carbonization product is obtained.

[0040] (4) The secondary carbonization product obtained in step (3) is immersed in a strong acid solution, wherein the solutes of the strong acid solution are sulfuric acid and nitric acid, and the molar ratio of sulfuric acid and nitric acid is 2:1. The temperature is raised to 100°C and the oxidation reaction is carried out for 13 hours. Then, the product is filtered, washed with water until neutral, and dried at 60°C for 12 hours to obtain the oxidation product.

[0041] (5) The oxidation product obtained in step (4) and sodium benzenesulfonate were placed in a reaction vessel at a mass ratio of 10:0.5. Poloxamer F127 was added with ethanol as solvent and hydrothermal reaction was carried out. The rotation speed of the reaction vessel was 500 r / min, the reaction time was 9 h, and the reaction temperature was 185 °C. Then, the product was filtered, washed with water until neutral, and dried at 70 °C for 18 h to obtain the pre-sodiumized product.

[0042] (6) The pre-sodium product obtained in step (5) is placed in a muffle furnace and heated to 890°C under a protective atmosphere. The heating rate is 5°C / min and the holding time is 6h to obtain hard carbon anode material.

[0043] Example 3

[0044] (1) Place the coconut shell in a muffle furnace and heat it to 250°C under an argon atmosphere for preliminary carbonization. The preliminary carbonization time is 1 hour to obtain the preliminary carbonized raw material.

[0045] (2) Citric acid, zinc carbonate and the preliminary carbonization raw material obtained in step (1) are put into a ball mill in a mass ratio of 6:3:100 for ball milling. The ball milling speed is 500 r / min and the ball milling time is 1 h to obtain the preliminary modified carbon material.

[0046] (3) The preliminary modified carbon material obtained in step (2) is placed in a muffle furnace and heated in an argon atmosphere at a heating rate of 8°C / min. When the temperature reaches 800°C, carbon dioxide gas is introduced for etching. The temperature is held for 2 hours, and then argon gas is introduced and the heating continues. The temperature is raised to 1000°C for a second carbonization at a heating rate of 5°C / min. The second carbonization time is 6 hours, and a secondary carbonization product is obtained.

[0047] (4) The secondary carbonization product obtained in step (3) is soaked in a strong acid solution, wherein the solutes of the strong acid solution are sulfuric acid and nitric acid, and the molar ratio of sulfuric acid and nitric acid is 5:1. The temperature is raised to 140°C and the oxidation reaction is carried out for 24 hours. Then, the product is filtered, washed with water until neutral, and dried at 70°C for 18 hours to obtain the oxidation product.

[0048] (5) The oxidation product obtained in step (4) and sodium benzenesulfonate were placed in a reaction vessel at a mass ratio of 8:0.8. Poloxamer F127 was added with ethanol as solvent and hydrothermal reaction was carried out. The rotation speed of the reaction vessel was 1400 r / min, the reaction time was 8 h, and the reaction temperature was 190 °C. Then, the product was filtered, washed with water until neutral, and dried at 70 °C for 16 h to obtain the pre-sodiumized product.

[0049] (6) The pre-sodium product obtained in step (5) is placed in a muffle furnace and heated to 1000℃ under a protective atmosphere. The heating rate is 2℃ / min and the holding time is 4.5h to obtain hard carbon anode material.

[0050] Example 4

[0051] (1) Place the coconut shell in a muffle furnace and heat it to 300°C under an argon atmosphere for preliminary carbonization. The preliminary carbonization time is 1 hour to obtain the preliminary carbonized raw material.

[0052] (2) Citric acid, zinc carbonate and the preliminary carbonization raw material obtained in step (1) are put into a ball mill in a mass ratio of 10:8:100 for ball milling. The ball milling speed is 500 r / min and the ball milling time is 6 h to obtain the preliminary modified carbon material.

[0053] (3) The preliminary modified carbon material obtained in step (2) is placed in a muffle furnace and heated in an argon atmosphere at a heating rate of 8°C / min. When the temperature reaches 800°C, carbon dioxide gas is introduced for etching. The temperature is held for 2 hours, and then argon gas is introduced and the heating continues. The temperature is raised to 1400°C for a second carbonization at a heating rate of 6°C / min. The second carbonization time is 6 hours, and a second carbonization product is obtained.

[0054] (4) The secondary carbonization product obtained in step (3) is immersed in a strong acid solution, wherein the solutes of the strong acid solution are sulfuric acid and nitric acid, and the molar ratio of sulfuric acid and nitric acid is 4:1. The temperature is raised to 200°C and the oxidation reaction is carried out for 3 hours. Then, the product is filtered, washed with water until neutral, and dried at 55°C for 20 hours to obtain the oxidation product.

[0055] (5) The oxidation product obtained in step (4) and sodium benzenesulfonate were placed in a reaction vessel at a mass ratio of 8.5:0.5. Poloxamer F127 was added with ethanol as solvent and hydrothermal reaction was carried out. The rotation speed of the reaction vessel was 800 r / min, the reaction time was 10 h, and the reaction temperature was 175 °C. Then, the product was filtered, washed with water until neutral, and dried at 68 °C for 13 h to obtain the pre-sodiumized product.

[0056] (6) The pre-sodium product obtained in step (5) is placed in a muffle furnace and heated to 950°C under a protective atmosphere. The heating rate is 3°C / min and the holding time is 5h to obtain hard carbon anode material.

[0057] Example 5

[0058] (1) Place the coconut shell in a muffle furnace and heat it to 260°C under an argon atmosphere for preliminary carbonization. The preliminary carbonization time is 10 hours to obtain the preliminary carbonized raw material.

[0059] (2) Citric acid, zinc carbonate and the preliminary carbonization raw material obtained in step (1) are put into a ball mill in a mass ratio of 4:5:100 for ball milling. The ball milling speed is 500 r / min and the ball milling time is 6.5 h to obtain the preliminary modified carbon material.

[0060] (3) The preliminary modified carbon material obtained in step (2) is placed in a muffle furnace and heated in an argon atmosphere at a heating rate of 8.5℃ / min. When the temperature reaches 800℃, carbon dioxide gas is introduced for etching and the temperature is held for 2 hours. Then argon gas is introduced and the temperature is continued to rise to 1400℃ for a second carbonization at a heating rate of 6.5℃ / min. The second carbonization time is 8 hours to obtain the secondary carbonization product.

[0061] (4) The secondary carbonization product obtained in step (3) is soaked in a strong acid solution, wherein the solutes of the strong acid solution are sulfuric acid and nitric acid, and the molar ratio of sulfuric acid and nitric acid is 4:1. The temperature is raised to 200°C and the oxidation reaction is carried out for 15 hours. Then, the product is filtered, washed with water until neutral, and dried at 80°C for 11 hours to obtain the oxidation product.

[0062] (5) The oxidation product obtained in step (4) and sodium benzenesulfonate were placed in a reaction vessel at a mass ratio of 8:1.1. Poloxamer F127 was added with ethanol as solvent and a hydrothermal reaction was carried out. The rotation speed of the reaction vessel was 1400 r / min, the reaction time was 10 h, and the reaction temperature was 180 °C. Then, the product was filtered, washed with water until neutral, and dried at 60 °C for 24 h to obtain the pre-sodiumized product.

[0063] (6) The pre-sodium product obtained in step (5) is placed in a muffle furnace and heated to 900°C under a protective atmosphere. The heating rate is 2°C / min and the holding time is 6h to obtain hard carbon anode material.

[0064] Example 6

[0065] (1) Place the coconut shell in a muffle furnace and heat it to 280°C under an argon atmosphere for preliminary carbonization. The preliminary carbonization time is 12 hours to obtain the preliminary carbonized raw material.

[0066] (2) Citric acid, zinc carbonate and the preliminary carbonization raw material obtained in step (1) are put into a ball mill in a mass ratio of 10:7:100 for ball milling. The ball milling speed is 500 r / min and the ball milling time is 6 h to obtain the preliminary modified carbon material.

[0067] (3) The preliminary modified carbon material obtained in step (2) is placed in a muffle furnace and heated in an argon atmosphere at a heating rate of 7°C / min. When the temperature reaches 800°C, carbon dioxide gas is introduced for etching. The temperature is held for 2 hours, and then argon gas is introduced and the heating continues. The temperature is raised to 1400°C for a second carbonization at a heating rate of 8°C / min. The second carbonization time is 10 hours, and a second carbonization product is obtained.

[0068] (4) The secondary carbonization product obtained in step (3) is immersed in a strong acid solution, wherein the solutes of the strong acid solution are sulfuric acid and nitric acid, and the molar ratio of sulfuric acid and nitric acid is 2.5:1. The temperature is raised to 160°C and the oxidation reaction is carried out for 23 hours. Then, the product is filtered, washed with water until neutral, and dried at 68°C for 10 hours to obtain the oxidation product.

[0069] (5) The oxidation product obtained in step (4) and sodium benzenesulfonate were placed in a reaction vessel at a mass ratio of 7:1.5. Poloxamer F127 was added with ethanol as solvent and hydrothermal reaction was carried out. The rotation speed of the reaction vessel was 800 r / min, the reaction time was 10 h, and the reaction temperature was 175 °C. Then, the product was filtered, washed with water until neutral, and dried at 65 °C for 12 h to obtain the pre-sodiumized product.

[0070] (6) The pre-sodium product obtained in step (5) is placed in a muffle furnace and heated to 900°C under a protective atmosphere. The heating rate is 3°C / min and the holding time is 4h to obtain hard carbon anode material.

[0071] Example 7

[0072] (1) Place the coconut shell in a muffle furnace and heat it to 230°C under an argon atmosphere for preliminary carbonization. The preliminary carbonization time is 10 hours to obtain the preliminary carbonized raw material.

[0073] (2) Citric acid, zinc carbonate and the preliminary carbonization raw material obtained in step (1) are put into a ball mill in a mass ratio of 6:10:100 for ball milling. The ball milling speed is 500 r / min and the ball milling time is 8 h to obtain the preliminary modified carbon material.

[0074] (3) The preliminary modified carbon material obtained in step (2) is placed in a muffle furnace and heated in an argon atmosphere at a heating rate of 9°C / min. When the temperature reaches 800°C, carbon dioxide gas is introduced for etching and the temperature is held for 2 hours. Then argon gas is introduced and the temperature is continued to rise to 1400°C for a second carbonization at a heating rate of 6°C / min. The second carbonization time is 6 hours, and a second carbonization product is obtained.

[0075] (4) The secondary carbonization product obtained in step (3) is immersed in a strong acid solution, wherein the solutes of the strong acid solution are sulfuric acid and nitric acid, and the molar ratio of sulfuric acid and nitric acid is 3.5:1. The temperature is raised to 120°C and the oxidation reaction is carried out for 17 hours. Then, the product is filtered, washed with water until neutral, and dried at 55°C for 10-24 hours to obtain the oxidation product.

[0076] (5) The oxidation product obtained in step (4) and sodium benzenesulfonate were placed in a reaction vessel at a mass ratio of 7:1. Poloxamer F127 was added with ethanol as solvent and hydrothermal reaction was carried out. The rotation speed of the reaction vessel was 900 r / min, the reaction time was 9 h, and the reaction temperature was 180 °C. Then, the product was filtered, washed with water until neutral, and dried at 60 °C for 24 h to obtain the pre-sodiumized product.

[0077] (6) The pre-sodium product obtained in step (5) is placed in a muffle furnace and heated to 900°C under a protective atmosphere. The heating rate is 2°C / min and the holding time is 5h to obtain hard carbon anode material.

[0078] Example 8

[0079] (1) Place the coconut shell in a muffle furnace and heat it to 245°C under an argon atmosphere for preliminary carbonization. The preliminary carbonization time is 13 hours to obtain the preliminary carbonized raw material.

[0080] (2) Citric acid, zinc carbonate and the preliminary carbonization raw material obtained in step (1) are put into a ball mill in a mass ratio of 6:10:100 for ball milling. The ball milling speed is 500 r / min and the ball milling time is 5 h to obtain the preliminary modified carbon material.

[0081] (3) The preliminary modified carbon material obtained in step (2) is placed in a muffle furnace and heated in an argon atmosphere at a heating rate of 6℃ / min. When the temperature reaches 800℃, carbon dioxide gas is introduced for etching. The temperature is held for 2 hours, and then argon gas is introduced and the heating continues. The temperature is raised to 1000℃ for a second carbonization at a heating rate of 6℃ / min. The second carbonization time is 5 hours, and a secondary carbonization product is obtained.

[0082] (4) The secondary carbonization product obtained in step (3) is immersed in a strong acid solution, wherein the solutes of the strong acid solution are sulfuric acid and nitric acid, and the molar ratio of sulfuric acid and nitric acid is 5:1. The temperature is raised to 110°C and the oxidation reaction is carried out for 18 hours. Then, the product is filtered, washed with water until neutral, and dried at 60°C for 14 hours to obtain the oxidation product.

[0083] (5) The oxidation product obtained in step (4) and sodium benzenesulfonate were placed in a reaction vessel at a mass ratio of 7:1.2. Poloxamer F127 was added with ethanol as solvent and hydrothermal reaction was carried out. The rotation speed of the reaction vessel was 600 r / min, the reaction time was 12 h, and the reaction temperature was 170 °C. Then, the mixture was filtered, washed with water until neutral, and dried at 60-80 °C for 12-24 h to obtain the pre-sodiumized product.

[0084] (6) The pre-sodium product obtained in step (5) is placed in a muffle furnace and heated to 880°C under a protective atmosphere. The heating rate is 4°C / min and the holding time is 4h to obtain hard carbon anode material.

[0085] Example 9

[0086] (1) Place the coconut shell in a muffle furnace and heat it to 260°C under an argon atmosphere for preliminary carbonization. The preliminary carbonization time is 11 hours to obtain the preliminary carbonized raw material.

[0087] (2) Citric acid, zinc carbonate and the preliminary carbonization raw material obtained in step (1) are put into a ball mill in a mass ratio of 10:4:100 for ball milling. The ball milling speed is 500 r / min and the ball milling time is 6 h to obtain the preliminary modified carbon material.

[0088] (3) The preliminary modified carbon material obtained in step (2) is placed in a muffle furnace and heated in an argon atmosphere at a heating rate of 5℃ / min. When the temperature reaches 800℃, carbon dioxide gas is introduced for etching. The temperature is held for 2 hours, and then argon gas is introduced and the temperature is continued to rise to 1300℃ for a second carbonization at a heating rate of 5℃ / min. The second carbonization time is 8 hours, and a secondary carbonization product is obtained.

[0089] (4) The secondary carbonization product obtained in step (3) is immersed in a strong acid solution, wherein the solutes of the strong acid solution are sulfuric acid and nitric acid, and the molar ratio of sulfuric acid and nitric acid is 2.2:1. The temperature is raised to 100°C and the oxidation reaction is carried out for 22 hours. Then, the product is filtered, washed with water until neutral, and dried at 50°C for 24 hours to obtain the oxidation product.

[0090] (5) The oxidation product obtained in step (4) and sodium benzenesulfonate were placed in a reaction vessel at a mass ratio of 8:1.3. Poloxamer F127 was added with ethanol as solvent and a hydrothermal reaction was carried out. The rotation speed of the reaction vessel was 800 r / min, the reaction time was 9 h, and the reaction temperature was 1890 °C. Then, the product was filtered, washed with water until neutral, and dried at 60 °C for 24 h to obtain the pre-sodiumized product.

[0091] (6) The pre-sodium product obtained in step (5) is placed in a muffle furnace and heated to 900°C under a protective atmosphere. The heating rate is 2.8°C / min and the holding time is 5.5h to obtain hard carbon anode material.

[0092] Example 10

[0093] (1) Place the coconut shell in a muffle furnace and heat it to 280°C under an argon atmosphere for preliminary carbonization. The preliminary carbonization time is 10 hours to obtain the preliminary carbonized raw material.

[0094] (2) Citric acid, zinc carbonate and the preliminary carbonization raw material obtained in step (1) are put into a ball mill in a mass ratio of 8:10:100 for ball milling. The ball milling speed is 500 r / min and the ball milling time is 8 h to obtain the preliminary modified carbon material.

[0095] (3) The preliminary modified carbon material obtained in step (2) is placed in a muffle furnace and heated in an argon atmosphere at a heating rate of 7°C / min. When the temperature reaches 800°C, carbon dioxide gas is introduced for etching. The temperature is held for 2 hours, and then argon gas is introduced and the heating continues. The temperature is raised to 1350°C for a second carbonization at a heating rate of 8°C / min. The second carbonization time is 6 hours, and a second carbonization product is obtained.

[0096] (4) The secondary carbonization product obtained in step (3) is immersed in a strong acid solution, wherein the solutes of the strong acid solution are sulfuric acid and nitric acid, and the molar ratio of sulfuric acid and nitric acid is 4.5:1. The temperature is raised to 180°C and the oxidation reaction is carried out for 16 hours. Then, the product is filtered, washed with water until neutral, and dried at 70°C for 24 hours to obtain the oxidation product.

[0097] (5) The oxidation product obtained in step (4) and sodium benzenesulfonate were placed in a reaction vessel at a mass ratio of 8:1.5. Poloxamer F127 was added with ethanol as solvent and hydrothermal reaction was carried out. The rotation speed of the reaction vessel was 700 r / min, the reaction time was 8 h, and the reaction temperature was 190 °C. Then, the product was filtered, washed with water until neutral, and dried at 70 °C for 14 h to obtain the pre-sodiumized product.

[0098] (6) The pre-sodium product obtained in step (5) is placed in a muffle furnace and heated to 900°C under a protective atmosphere. The heating rate is 1°C / min and the holding time is 5h to obtain hard carbon anode material.

[0099] Comparative Example 1

[0100] (1) Place the coconut shell in a muffle furnace and heat it to 245°C under an argon atmosphere for preliminary carbonization. The preliminary carbonization time is 13 hours to obtain the preliminary carbonized raw material.

[0101] (2) The preliminary carbonized raw material obtained in (1) is put into a ball mill for ball milling. The ball milling speed is 500 r / min and the ball milling time is 5 h to obtain the preliminary carbon material.

[0102] (3) The preliminary carbon material obtained in step (2) is placed in a muffle furnace and heated to 880°C under a protective atmosphere at a heating rate of 4°C / min for 4 hours to obtain a hard carbon anode material.

[0103] The hard carbon anode materials prepared in the above embodiments and comparative examples were used to prepare anode sheets, and then the electrical performance of the anode sheets was tested. The preparation method is as follows, and the test results are shown in Table 1.

[0104] Preparation method of negative electrode sheet: The hard carbon negative electrode material obtained above is mixed and stirred with conductive agent SP, binder CMC, binder SBR and deionized water. The mass ratio of carbon negative electrode material, conductive agent SP, binder CMC and binder SBR is 95:1.5:1.5:2 to obtain negative electrode slurry. The solid content of the negative electrode slurry is 30%. The negative electrode slurry is uniformly coated on copper foil and dried in a vacuum environment at 100℃ to remove water. The dried electrode sheet is punched to obtain the negative electrode sheet. Sodium is selected as positive electrode. 1 mol NaFP6 is dissolved in a solvent composed of EC, DEC and DMC, and the volume ratio of EC, DEC and DMC is 1:1:1 to prepare electrolyte. The separator is Celgard 2400.

[0105]

[0106]

[0107] Table 1

[0108] Analysis of the above data clearly shows that, compared with the comparative examples, the hard carbon anode material prepared by the method of the present invention has a higher first-pass efficiency and excellent cycle performance. The improvement in first-pass efficiency is mainly due to the increased interlayer spacing after esterification, the pore-forming effect of the pore-forming agent, and the microporous structure formed by chemical etching. The synergistic effect of these three factors significantly improves the first-pass efficiency. The improvement in cycle performance is mainly due to the dehydration condensation of sodium benzenesulfonate with the hydroxyl groups on the surface of hard carbon during the pre-sodiumization process to form a coating layer. The formation of the coating layer is carried out simultaneously with the pre-sodiumization, which greatly reduces the loss of the SEI film during film formation and effectively improves the cycle performance.

[0109] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a hard carbon anode material for sodium-ion batteries, characterized in that: It includes the following steps: (1) Place the biomass material into a muffle furnace and heat it to 200-300℃ under a protective atmosphere for preliminary carbonization. The preliminary carbonization time is 1-15h to obtain the preliminary carbonized raw material. (2) Citric acid, pore-forming agent and preliminary carbonization raw material obtained in step (1) are put into a ball mill in a mass ratio of (1-10):(2-10):100 for ball milling. The ball milling speed is 500 r / min and the ball milling time is 1-8 h to obtain preliminary modified carbon material. (3) The preliminary modified carbon material obtained in step (2) is placed in a muffle furnace and heated under a protective atmosphere at a heating rate of 5-10℃ / min. When the temperature reaches 800℃, carbon dioxide gas is introduced for etching and the temperature is held for 2 hours. Then, a protective gas is introduced and the temperature is continued to rise to 1000-1400℃ for a second carbonization at a heating rate of 5-10℃ / min. The second carbonization time is 1-10 hours to obtain the secondary carbonization product. (4) The secondary carbonization product obtained in step (3) is immersed in a strong acid solution, wherein the solute of the strong acid solution is sulfuric acid and nitric acid, and the molar ratio of sulfuric acid and nitric acid is (2-5):

1. The temperature is raised to 100-200℃, and the oxidation reaction is carried out for 3-24 hours. Then, the product is filtered, washed with water until neutral, and dried at 50-80℃ for 10-24 hours to obtain the oxidation product. (5) The oxidation product obtained in step (4) and sodium benzenesulfonate are placed in a reaction vessel at a mass ratio of (7-10):(0.5-1.5). Ethanol is used as a solvent and a surfactant is added to carry out a hydrothermal reaction. The rotation speed of the reaction vessel is 500-1400 r / min, the reaction time is 8-12 h, and the reaction temperature is 170-190℃. Then, the mixture is filtered, washed with water until neutral, and dried at 60-80℃ for 12-24 h to obtain the pre-sodiumized product. (6) The pre-sodium product obtained in step (5) is placed in a muffle furnace and heated to 800-1000℃ under a protective atmosphere. The heating rate is 1-5℃ / min and the holding time is 4-6h to obtain hard carbon anode material.

2. The method for preparing hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: The biomass material in step (1) is coconut shell.

3. The method for preparing hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: The protective atmosphere in steps (1) and (3) is an argon atmosphere.

4. The method for preparing hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: The pore-forming agent in step (2) is zinc carbonate.

5. The method for preparing hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: The protective gas in step (3) is argon.

6. The method for preparing hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that: The surfactant used in step (5) is poloxamer F127.

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