A long-cycle sodium-ion battery hard carbon material, a preparation method thereof, and a sodium-ion battery

Abstract

The application relates to the field of sodium ion batteries, in particular to a long-cycle sodium ion battery hard carbon material and a preparation method thereof and a sodium ion battery; the application adopts the composite use of dodecyl dimethyl betaine and a high-temperature pore forming agent to modify the structure of the hard carbon material. The dodecyl dimethyl betaine can make the precursor suspension have better dispersion effect, and is favorable to improving the uniformity of the pore structure of the hard carbon material. As a soft template, the micellar structure formed by the self-assembly of long-chain alkyl can form a mesoporous structure after heating and decomposition, promotes the ion transmission capacity of sodium ions in the electrolyte in the charging and discharging process, and meanwhile, the nitrogen element after decomposition can be in-situ doped to provide the hard carbon material with conductivity and active sites. The high-temperature pore forming agent forms a large number of micropores on the surface of the hard carbon through chemical etching at a high temperature, can make the hard carbon material have rich pore structures, and meanwhile, can provide a high specific surface area, and can effectively improve the specific surface area.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion batteries, and more particularly to a long-cycle sodium-ion battery hard carbon material, its preparation method, and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries have become the most influential rechargeable batteries after lithium-ion batteries. Because their working principle and manufacturing process are similar to those of lithium-ion batteries, sodium-ion batteries are currently in a phase of rapid development.

[0003] Hard carbon materials, due to their unique porous structure and excellent kinetic properties, have become the fastest-growing commercially available anode active material for sodium-ion batteries and are widely used in them. However, with rapid economic development and increasing energy demand, traditional hard carbon materials can no longer meet the performance requirements of sodium-ion batteries. Therefore, developing high-performance hard carbon materials has become an urgent problem to be solved.

[0004] Currently, existing technologies often use pore-forming agents to modify the structure of hard carbon materials. However, conventional methods use high-temperature pore-forming agents, which can easily create too many openings in the carbon material. This leads to a large amount of irreversible sodium ion consumption during the first charge and discharge of the battery, affecting the battery's initial efficiency. At the same time, the pore structure is also difficult to control. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a long-cycle sodium-ion battery hard carbon material, its preparation method, and a sodium-ion battery.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of this invention is to provide a method for preparing a hard carbon material for long-cycle sodium-ion batteries, comprising the steps of:

[0008] S1. The precursor material and the high-temperature pore-forming agent are dispersed in an aqueous solution of dodecyl dimethyl betaine to obtain a suspension, which is then dried to obtain the precursor powder.

[0009] S2. The precursor powder is subjected to solvent evaporation treatment, pre-carbonization treatment, etching treatment, washing treatment and drying treatment in sequence to obtain the long-cycle sodium-ion battery hard carbon material.

[0010] Preferably, in step S1, the precursor material is a biomass precursor; the biomass precursor includes at least one of coconut shell, bamboo, and pomelo peel.

[0011] Preferably, in step S1, the amount of dodecyl dimethyl betaine is 0.5-10% of the precursor material mass; the high-temperature pore-forming agent includes at least one of potassium hydroxide, sodium hydroxide, zinc chloride, phosphoric acid, potassium carbonate, and sodium bicarbonate; the amount of the high-temperature pore-forming agent is 10-50% of the precursor material mass.

[0012] Preferably, in step S2, the solvent evaporation treatment includes: heating to 150-200°C at a rate of 5°C / min under inert gas protection, and holding at that temperature for 2-4 hours.

[0013] Preferably, in step S2, the pre-carbonization treatment includes: heating to 300-500°C at a rate of 2°C / min and holding at that temperature for 2-4 hours.

[0014] Preferably, in step S2, the etching process includes: heating to 700-1300°C at a rate of 2°C / min and holding at that temperature for 2-4 hours.

[0015] Preferably, in step S2, the washing process includes: after the etched material is cooled to room temperature, it is rinsed and filtered multiple times with dilute acid and deionized water until the pH value of the filtrate approaches neutral.

[0016] Preferably, in step S2, the drying process includes drying at 100-150℃ for 12-16 hours.

[0017] A second aspect of the present invention is to provide a long-cycle sodium-ion battery hard carbon material, which is prepared by the above-described preparation method.

[0018] A third aspect of the present invention is to provide a sodium-ion battery, comprising: a negative electrode, a positive electrode, and a separator;

[0019] The negative electrode includes: a long-cycle sodium-ion battery hard carbon material prepared by the above preparation method;

[0020] The positive electrode includes at least one of the following: sodium iron pyrophosphate, sodium nickel manganese phosphate, Prussian blue, sodium iron sulfate, and sodium vanadium phosphate.

[0021] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0022] (1) This invention uses a combination of dodecyl dimethyl betaine and a high-temperature pore-forming agent to modify the structure of hard carbon materials. Dodecyl dimethyl betaine can improve the dispersion effect of the precursor suspension, prevent the aggregation of the pore-forming agent, and improve the uniformity of the pore structure of the hard carbon material. As a soft template, the micelle structure formed by the self-assembly of its long-chain alkyl groups can form a mesoporous structure after heating and decomposition, which can promote the ion transport capacity of sodium ions in the electrolyte during charging and discharging. At the same time, the nitrogen element after its decomposition can provide conductivity and active sites for the hard carbon material through in-situ doping. The high-temperature pore-forming agent forms a large number of micropores on the surface of hard carbon through chemical etching at a high temperature, which can make the hard carbon material have a rich pore structure and provide a high specific surface area, effectively improving the specific surface area of ​​the material.

[0023] (2) This invention employs the synergistic effect of two pore-forming agents to provide mesopores and micropores for hard carbon materials. This enables hard carbon materials to possess a porous structure, elemental doping modification, high ion transport capacity, and high specific surface area. Simultaneously, the pore structure exhibits good stability, resulting in high specific capacity and high rate performance. Using this method, the electrochemical and kinetic performance of sodium-ion batteries can be effectively improved, increasing the rate charge / discharge capability. Furthermore, during battery charging and discharging, the structural stability of the material can be effectively guaranteed, avoiding the impact of volume changes caused by sodium ion insertion and extraction on the battery's cycle stability, thereby effectively improving the cycle performance of sodium-ion batteries. Attached Figure Description

[0024] Figure 1 This is a diagram showing the results of the cell cycle test in the testing embodiment of the present invention. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0026] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0027] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0028] Example 1

[0029] This embodiment provides a method for preparing hard carbon materials for long-cycle sodium-ion batteries, the steps of which include:

[0030] S1. Coconut shell and potassium hydroxide (30% of the coconut shell mass) are dispersed in a dodecyl dimethyl betaine aqueous solution (2% of the coconut shell mass) to obtain a suspension, which is then dried to obtain a precursor powder.

[0031] S2. The precursor powder is placed in a tube furnace and protected with inert gas. The temperature is increased to 150°C at a rate of 5°C / min and held for 2 hours. After the solvent evaporates, the temperature is increased to 300°C at a rate of 2°C / min and held for 4 hours for pre-carbonization and decomposition of dodecyl dimethyl betaine. The temperature is then increased to 1000°C at a rate of 2°C / min and held for 4 hours for etching with potassium hydroxide. After cooling to room temperature, the product is rinsed and filtered multiple times with dilute acid and deionized water until the pH of the filtrate approaches neutral. Finally, the product is placed in a vacuum chamber and dried at 120°C for 12 hours to obtain the long-cycle sodium-ion battery hard carbon material.

[0032] Example 2

[0033] This embodiment provides another method for preparing hard carbon materials for long-cycle sodium-ion batteries, the steps of which include:

[0034] S1. Bamboo and sodium hydroxide (50% of the bamboo mass) are dispersed in a dodecyl dimethyl betaine aqueous solution (3% of the bamboo mass) to obtain a suspension, which is then dried to obtain a precursor powder.

[0035] S2. The precursor powder is placed in a tube furnace and protected with inert gas. The temperature is increased to 200°C at a rate of 5°C / min and held for 4 hours. After the solvent evaporates, the temperature is increased to 500°C at a rate of 2°C / min and held for 2 hours for pre-carbonization and decomposition of dodecyl dimethyl betaine. The temperature is then increased to 1200°C at a rate of 2°C / min and held for 3 hours for etching with sodium hydroxide. After cooling to room temperature, the product is rinsed and filtered multiple times with dilute acid and deionized water until the pH of the filtrate approaches neutral. Finally, the product is placed in a vacuum chamber and dried at 100°C for 16 hours to obtain the long-cycle sodium-ion battery hard carbon material.

[0036] Comparative Example 1

[0037] This comparative example provides a method for preparing a hard carbon material without adding dodecyl dimethyl betaine or a high-temperature pore-forming agent; all other aspects are the same as in Example 1.

[0038] Comparative Example 2

[0039] This comparative example provides another method for preparing hard carbon material, without the addition of dodecyl dimethyl betaine, and all other aspects are the same as in Example 1.

[0040] Comparative Example 3

[0041] This comparative example provides another method for preparing hard carbon material, without adding a high-temperature pore-forming agent, and all other aspects are the same as in Example 1.

[0042] Detection Examples

[0043] Sodium-ion batteries were prepared using the hard carbon materials of Examples 1-2 and Comparative Examples 1-3 as negative electrodes, and cell cycle tests were performed on the batteries. The results are shown in Table 1 and... Figure 1 As shown;

[0044] Table 1

[0045]

[0046] According to the test data, the sodium-ion batteries prepared using the hard carbon materials of Examples 1-2 exhibit better cycle performance. Compared to conventional methods, the present invention employs two pore-forming agents in a synergistic effect, which effectively improves the structural stability of the hard carbon and enhances the kinetic performance of the sodium-ion batteries. Compared to Comparative Example 1, the hard carbon material in the examples exhibits a rich and uniform pore structure after the addition of pore-forming agents, effectively buffering structural changes in the electrodes during charge and discharge, thus contributing to improved battery cycle stability. Compared to Comparative Example 2, the dodecyl dimethyl betaine pore-forming agent in the examples effectively improves the uniformity of the precursor suspension, ensuring the formation of a uniform pore structure, which improves the battery's kinetic performance. Compared to Comparative Example 3, the high-temperature pore-forming agent in the examples provides micropores and a high specific surface area, mitigating solvent-induced side reactions at the interface and thus improving cycle stability.

[0047] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for preparing a hard carbon material for long-cycle sodium-ion batteries, characterized in that the steps include... include: S1. The precursor material and the high-temperature pore-forming agent are dispersed in an aqueous solution of dodecyl dimethyl betaine to obtain a suspension, which is then dried to obtain the precursor powder. S2. The precursor powder is subjected to solvent evaporation treatment, pre-carbonization treatment, etching treatment, washing treatment and drying treatment in sequence to obtain the long-cycle sodium-ion battery hard carbon material.

2. The preparation method according to claim 1, characterized in that, In step S1, the precursor material is a biomass precursor; Biomass precursors include at least one of the following: coconut shell, bamboo, and grapefruit peel.

3. The preparation method according to claim 1, characterized in that, In step S1, the amount of dodecyl dimethyl betaine used is 0.5-10% of the mass of the precursor material; The high-temperature pore-forming agent includes at least one of potassium hydroxide, sodium hydroxide, zinc chloride, phosphoric acid, potassium carbonate, and sodium bicarbonate; the amount of high-temperature pore-forming agent used is 10-50% of the mass of the precursor material.

4. The preparation method according to claim 1, characterized in that, In step S2, the solvent evaporation treatment includes: heating to 150-200℃ at a rate of 5℃ / min under inert gas protection, and holding at that temperature for 2-4 hours.

5. The preparation method according to claim 1, characterized in that, In step S2, the pre-carbonization treatment includes: heating to 300-500℃ at a rate of 2℃ / min and holding at that temperature for 2-4 hours.

6. The preparation method according to claim 1, characterized in that, In step S2, the etching process includes: heating to 700-1300℃ at a rate of 2℃ / min and holding at that temperature for 2-4 hours.

7. The preparation method according to claim 1, characterized in that, In step S2, the washing process includes: after the etched material is cooled to room temperature, it is rinsed and filtered multiple times with dilute acid and deionized water until the pH value of the filtrate approaches neutral.

8. The preparation method according to claim 1, characterized in that, In step S2, the drying process includes drying at 100-150℃ for 12-16 hours.

9. A hard carbon material for long-cycle sodium-ion batteries, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. A sodium-ion battery, characterized in that, include: Negative electrode, positive electrode, and separator; The negative electrode includes: a long-cycle sodium-ion battery hard carbon material prepared by the preparation method according to any one of claims 1-8; The positive electrode includes at least one of the following: sodium iron pyrophosphate, sodium nickel manganese phosphate, Prussian blue, sodium iron sulfate, and sodium vanadium phosphate.

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