Preparation method and application of high-rate-performance bamboo-based hard carbon negative electrode material

Abstract

This invention discloses a method for preparing a high-rate performance bamboo-based hard carbon anode material, comprising the following steps: A1, immersing bamboo powder in an inorganic sodium salt solution and drying it to obtain a mixed powder; A2, calcining the mixed powder in a protective atmosphere to obtain a hard carbon precursor; A3, cleaning and drying the hard carbon precursor to obtain the bamboo-based hard carbon anode material. This invention has the advantages of simple preparation method and being environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode material technology, and in particular to a method for preparing a high-rate performance bamboo-based hard carbon anode material and its application. Background Technology

[0002] With the rapid development of electric vehicles and electronic devices, the demand for battery performance is increasing. Lithium-ion batteries, limited by the theoretical lithium storage capacity of graphite (372 mAh / g) and the Earth's lithium reserves, cannot meet future needs. Sodium ions, belonging to the same group of elements, have attracted widespread attention. Sodium is abundant and distributed globally, making the price of sodium-ion batteries, the main material, much lower than that of lithium-ion batteries. However, due to the large radius of sodium ions and the small interlayer spacing of graphite, repeated insertion and extraction of sodium ions in the graphite electrode can lead to structural collapse and a sharp decline in cycle performance. Therefore, graphite is not suitable as a negative electrode material for sodium-ion batteries. Hard carbon materials have a disordered internal crystal arrangement and more pores. Furthermore, sodium can be stored in the interlayer spaces, closed micropores, surfaces, and defect sites of graphite sheets, resulting in a high capacity and making it an ideal negative electrode material for sodium-ion batteries.

[0003] Using biomass to prepare hard carbon materials offers advantages such as abundant precursor varieties, sustainable use, and low cost. In particular, my country possesses abundant bamboo resources, is easily renewable, and has a relatively complete bamboo industry chain, making it an ideal raw material for hard carbon anode materials in sodium-ion batteries. However, existing methods for preparing bamboo-based hard carbon anode materials result in poor rate performance. This is mainly due to the low conductivity caused by the short-range ordered structure of bamboo-based hard carbon, leading to significant voltage lag during high-rate charge / discharge. This can cause the voltage at which some plateau capacities occur in the full cell to be lower than the voltage at which sodium metal is deposited. This means that higher current densities increase the likelihood of metal deposition and pose safety hazards. Poor rate performance is one of the main factors affecting the commercialization of hard carbon anodes.

[0004] Increasing the porosity of hard carbon is an effective way to improve its performance. Numerous studies have shown that macropores (>50 nm) are beneficial for increasing the contact between hard carbon and the electrolyte, thus increasing the effective reaction area; mesopores (2–50 nm) can improve the Na+... + The diffusion rate of Na significantly improves rate performance; micropores (<2 nm) can increase the specific surface area of ​​hard carbon, which is comparable to that of Na. + The storage provides more reactive sites, thereby optimizing electrochemical performance. Currently, the porosity of hard carbon materials is mainly controlled by pore-forming agents and templates. However, the use of conventional pore-forming agents and templates will increase the cost of large-scale production applications and cause environmental pollution to some extent, and may also introduce new impurities and increase the need for impurity removal processes.

[0005] Therefore, there is an urgent need for a simple, economical, green and environmentally friendly carbonization preparation method to improve the porosity of bamboo materials, enhance the electrochemical performance of bamboo-based biomass hard carbon anode materials, and obtain high-rate performance sodium-ion battery anode materials. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a simple, green and environmentally friendly method for preparing high-rate performance bamboo-based hard carbon anode materials and their application.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A method for preparing a high-rate-performance bamboo-based hard carbon anode material includes the following steps:

[0009] A1. Bamboo powder is impregnated in an inorganic sodium salt solution and dried to obtain a mixed powder;

[0010] A2, the mixed powder is calcined in a protective atmosphere to obtain a hard carbon precursor;

[0011] A3. After cleaning and drying the hard carbon precursor, bamboo-based hard carbon anode material is obtained.

[0012] As a further improvement to the above technical solution:

[0013] In step A1, the inorganic sodium salt in the inorganic sodium salt solution is one or more of sodium chloride, sodium carbonate, sodium bicarbonate, sodium sulfate, and sodium nitrate.

[0014] Preferably, the inorganic sodium salt in the inorganic sodium salt solution is one or more of sodium chloride, sodium carbonate, and sodium sulfate.

[0015] In step A1, the solvent in the inorganic sodium salt solution is water or ethanol.

[0016] In step A1, the inorganic sodium salt solution is a saturated inorganic sodium salt solution. Compared to an unsaturated inorganic sodium salt solution, under the same soaking time and volume, a saturated inorganic sodium salt solution allows more inorganic sodium salt to enter the internal pores of the bamboo before it shrinks during carbonization. This better prevents the bamboo from shrinking during the subsequent calcination and carbonization process, resulting in a more porous structure.

[0017] In step A1, the mass ratio of the bamboo powder to the inorganic sodium salt in the inorganic sodium salt solution is 10:1 to 1:15.

[0018] Preferably, the mass ratio of the bamboo powder to the inorganic sodium salt in the inorganic sodium salt solution is 1:4 to 1:12.

[0019] In step A2, the protective atmosphere is an inert gas and / or nitrogen, and the calcination includes the following steps: first, calcining at a temperature of 300-500°C for 1-4 hours, and then calcining at a temperature of 700-1500°C for 1-4 hours.

[0020] Preferably, in step A2, the calcination includes the following steps: first, calcining at a temperature of 300-500°C for 1-4 hours, and then calcining at a temperature of 700-900°C for 1-4 hours.

[0021] Preferably, the heating rate during calcination is 2–10 °C / min.

[0022] In step A3, the cleaning temperature is 20℃~80℃, and the cleaning time is 2~24h.

[0023] Preferably, in step A3, the temperature during cleaning is 60℃~80℃, and the cleaning time is 6h~10h.

[0024] After step A3, the method further includes the following step: A4, salt crystallization recovery: collect and heat the cleaning solution from step A3, and evaporate and crystallize to obtain recovered inorganic sodium salt.

[0025] In step A4, the heating temperature is 60℃~100℃, preferably 70℃~90℃.

[0026] Preferably, the bamboo powder is bamboo powder that has been pulverized and sieved, with a mesh size of 40 to 1000 mesh.

[0027] As a general inventive concept, this invention also discloses the application of bamboo-based hard carbon anode material prepared according to the aforementioned preparation method in the anode of sodium-ion batteries.

[0028] The application includes the following steps: bamboo-based hard carbon anode material, CMC and conductive carbon black are mixed evenly in a mass ratio of 8:1:1, the resulting mixture is dispersed in an aqueous solution to form a uniform slurry, the slurry is then coated on aluminum foil and dried to obtain a sodium-ion battery anode.

[0029] The application of the bamboo-based hard carbon anode material or sodium-ion battery anode in sodium-ion batteries includes electric vehicles, mobile phones, laptops, smart grids, electronic products, and the manufacturing of mobile energy storage devices.

[0030] Compared with the prior art, the advantages of the present invention are as follows:

[0031] (1) The present invention provides a method for preparing a high-rate bamboo-based hard carbon anode material, which uses bamboo as a precursor and employs a wet-mixing bamboo powder and inorganic sodium salt-assisted bamboo carbonization technology. The preparation process is simple, requires no impurity removal, is green and environmentally friendly, and bamboo is inexpensive and readily available. my country has abundant resources, is easy to regenerate, and has a relatively complete bamboo industry chain, which can greatly reduce the cost of sodium-ion batteries. It also has the following advantages:

[0032] A. Inorganic sodium salts, used as a calcination medium, have a low melting point and provide a liquid-phase sintering environment during the carbonization process of bamboo. They penetrate into the interior of the bamboo, making the carbonization process more thorough and uniform, especially for bamboo, a denser biomass material with smaller fiber diameters.

[0033] B. In the wet-mixing process, bamboo is soaked in a saturated inorganic sodium salt solution and then dried and crystallized. This allows the inorganic sodium salt to fully penetrate the bamboo tissue before carbonization. After drying, the salt crystals precipitate and form a support structure within the bamboo's pores, effectively preventing bamboo shrinkage during carbonization, maintaining the hollow structure of the bamboo, increasing the effective reaction area and porosity of the bamboo charcoal, increasing the contact between the hard carbon and the electrolyte, and improving the Na+ content. + The diffusion rate is improved, thus enhancing rate performance.

[0034] C. During the high-temperature carbonization process, the inorganic sodium salt is in a molten state, which is the process of diffusion and transport of inorganic ions in bamboo charcoal. This is beneficial for simulating the migration and diffusion path of sodium ions in the battery, and provides an effective and fast transport channel for sodium ions in the prepared hard carbon anode material.

[0035] D. Inorganic sodium salts act as "molecular templates" during carbonization, reacting with bamboo and entering its structure. After carbonization, they are removed by water washing, creating abundant pores, especially macropores and mesopores. This increases the contact area between the hard carbon and the electrolyte, improving the effective reaction area; it also increases the sodium content of the bamboo. + The diffusion rate is improved, thus enhancing rate performance.

[0036] E. The inorganic sodium used can be removed simply by washing with water without adding other impurities. At the same time, the used crystalline inorganic sodium salt can be recycled and reused after a simple crystallization process.

[0037] (2) The present invention provides a method for preparing a high-rate performance bamboo-based hard carbon anode material. When the prepared bamboo-based hard carbon anode material is used as a sodium-ion battery anode material, it has a higher rate performance than bamboo-based hard carbon prepared by direct carbonization. Attached Figure Description

[0038] Figure 1 This is a rate-of-capacity diagram of the bamboo-based hard carbon anode material of Example 1 of the present invention.

[0039] Figure 2 This is a rate-of-capacity diagram of the bamboo-based hard carbon anode material of Example 2 of the present invention.

[0040] Figure 3 This is a rate-capacity diagram of the bamboo-based hard carbon anode material of Example 3 of the present invention.

[0041] Figure 4 This is a rate-up diagram of the bamboo-based hard carbon anode material of Comparative Example 1 of the present invention.

[0042] Figure 5 This is a rate-up diagram of the bamboo-based hard carbon anode material of Comparative Example 2 of the present invention.

[0043] Figure 6 This is a process flow diagram of Embodiment 1 of the present invention. Detailed Implementation

[0044] The present invention will be further described in detail below. Unless otherwise specified, the instruments or materials used in the present invention are commercially available.

[0045] Example 1:

[0046] like Figure 6 As shown, the preparation method of a high-rate performance bamboo-based hard carbon anode material in this embodiment includes the following steps:

[0047] S1. Crushing process: The dried fresh bamboo is crushed and sieved to 80 mesh using a crusher to obtain bamboo powder.

[0048] S2. Bamboo powder and salt mixture: Add 40 mL of deionized water, 30 g of NaCl and 30 g of Na2CO3 to a beaker to form a salt saturated solution. Place 5 g of pulverized bamboo powder in the beaker, mix well and soak thoroughly. Then place it in a 60℃ oven to dry and obtain mixed powder.

[0049] S3. Calcination: The mixed powder (without any cleaning process) is placed directly in a tube furnace filled with argon and calcined at 500℃ for 2 hours, and then calcined at 800℃ for 2 hours in the tube furnace. The heating rate is 10℃ / min for both times to obtain bamboo-based hard carbon precursor.

[0050] S4. Water washing: The bamboo-based hard carbon precursor is immersed in 60℃ water multiple times for 6 hours, filtered, and the filter residue is dried to obtain the hard carbon anode material.

[0051] In some embodiments, the method further includes: S5, salt crystallization recovery: collecting the washing filtrate from the previous step, evaporating and crystallizing it at 80°C to obtain recovered salt.

[0052] An application of the bamboo-based hard carbon anode material for sodium-ion batteries prepared in this embodiment includes the following steps:

[0053] 1) The bamboo-based sodium-ion battery hard carbon negative electrode material, CMC and conductive carbon black prepared in this embodiment are mixed evenly in a mass ratio of 8:1:1 and dispersed in an aqueous solution to form a uniform slurry. The slurry is then coated on aluminum foil and vacuum dried at 80°C to obtain a hard carbon electrode sheet.

[0054] 2) The hard carbon electrode sheet was paired with the metallic sodium negative electrode, and a CR2016 coin cell was assembled in an inert atmosphere in a glove box. The electrochemical performance of the hard carbon electrode was then tested. The coin cell structure includes a positive electrode shell (stainless steel), a negative electrode shell (stainless steel), a gasket (stainless steel), a hard carbon electrode, a sodium sheet, an electrolyte, and a separator (PP).

[0055] Example 2:

[0056] The preparation method of the high-rate performance bamboo-based hard carbon anode material in this embodiment includes the following steps:

[0057] S1. Crushing process: The dried fresh bamboo is crushed and sieved to 80 mesh using a crusher to obtain bamboo powder.

[0058] S2. Bamboo powder and salt mixture: Add 40 mL of deionized water, 10 g of NaCl and 10 g of Na2CO3 to a beaker to form a salt saturated solution. Place 5 g of pulverized bamboo powder in the beaker, mix well and soak thoroughly. Then place it in a 60℃ oven to dry and obtain mixed powder.

[0059] S3. Calcination: The mixed powder (without any cleaning process) is placed directly in a tube furnace filled with argon and calcined at 500℃ for 2 hours, and then calcined at 800℃ for 2 hours in the tube furnace. The heating rate is 10℃ / min for both times to obtain bamboo-based hard carbon precursor.

[0060] S4. Water washing: The bamboo-based hard carbon precursor is immersed in 60℃ water multiple times for 6 hours, filtered, and the filter residue is dried to obtain the bamboo-based hard carbon anode material.

[0061] S5. Salt crystallization recovery: Collect the washing filtrate from the previous step, and evaporate and crystallize it at 80°C to obtain recovered salt. The recovered salt can be reused in step S2.

[0062] Example 3:

[0063] This embodiment describes a method for preparing a high-rate-performance bamboo-based hard carbon anode material, comprising the following steps:

[0064] S1. Crushing process: The dried fresh bamboo is crushed and sieved to 80 mesh using a crusher to obtain bamboo powder.

[0065] S2. Bamboo powder and salt mixture: Add 40 mL of ethanol, 30 g of NaCl and 30 g of Na2CO3 to a beaker to form a salt saturated solution. Place 5 g of pulverized bamboo powder in the beaker, mix well and soak thoroughly. Then place it in a 60℃ oven to dry to obtain mixed powder.

[0066] S3. Calcination: The mixed powder (without any cleaning process) is placed directly in a tube furnace filled with argon and calcined at 500℃ for 2 hours, and then calcined at 800℃ for 2 hours in the tube furnace. The heating rate is 10℃ / min for both times to obtain the hard carbon precursor.

[0067] S4. Water washing: The hard carbon precursor powder is immersed in 60℃ water multiple times for 6 hours, filtered, and the filter residue is dried to obtain bamboo-based hard carbon anode material.

[0068] S5. Salt crystallization recovery: Collect the washing filtrate from the previous step, and evaporate and crystallize it at 80°C to obtain recovered salt.

[0069] Comparative Example 1:

[0070] This comparative example describes a method for preparing a bamboo-based hard carbon anode material (dry mixing of bamboo powder and inorganic sodium salt), which includes the following steps:

[0071] S1. Crushing process: The dried fresh bamboo is crushed and sieved to 80 mesh using a crusher to obtain bamboo powder.

[0072] S2. Bamboo powder and salt mixture: Place 5 g of pulverized bamboo powder in a beaker, add 30 g of NaCl and 30 g of Na2CO3 respectively, and stir dry to mix evenly to obtain a mixed powder.

[0073] S3. Calcination: The mixed powder (without any cleaning process) is placed directly in a tube furnace filled with argon and calcined at 500℃ for 2 hours, and then calcined at 800℃ for 2 hours in the tube furnace. The heating rate is 10℃ / min for both times to obtain the hard carbon precursor.

[0074] S4. Water washing: The hard carbon precursor powder is washed multiple times with 60℃ water for 6 hours, filtered, and the filter residue is dried to obtain the hard carbon anode material.

[0075] S5. Salt crystallization recovery: Collect the washing filtrate from the previous step, and evaporate and crystallize it at 80°C to obtain recovered salt.

[0076] Comparative Example 2:

[0077] A method for preparing a hard carbon anode material for bamboo-based sodium-ion batteries (without adding inorganic sodium salts) includes the following steps:

[0078] S1. Crushing process: The dried fresh bamboo is crushed and sieved to 80 mesh using a crusher to obtain bamboo powder.

[0079] S2. Calcination: Bamboo powder is placed directly in a tube furnace filled with argon and calcined at 500℃ for 2 hours, and then calcined at 800℃ for 2 hours in the tube furnace. The heating rate is 10℃ / min for both times to obtain hard carbon precursor.

[0080] Performance testing

[0081] Taking the coin cells assembled in the examples and comparative examples as examples, the performance of the batteries assembled with bamboo-based hard carbon electrodes prepared in the examples and comparative examples was evaluated using a charge-discharge device (Blue Electric 3001). The results are as follows: Figures 1 to 5 As shown. Example 1 is a molten salt treatment of bamboo powder and inorganic sodium salt aqueous solution; Example 2 is a molten salt treatment of bamboo powder and inorganic sodium salt aqueous solution, with the proportion of inorganic sodium salt in Example 2 being reduced compared to Example 1; Example 3 is a molten salt treatment of bamboo powder and inorganic sodium salt alcohol solution; Comparative Example 1 is a molten salt treatment of bamboo powder and inorganic sodium salt dry blending; and Comparative Example 2 is a molten salt treatment without the addition of inorganic sodium salt.

[0082] The results showed that the bamboo-based hard carbon anode material obtained by wet mixing with water as a solvent (Example 1) exhibited the best specific capacity and rate performance, significantly improved compared to Comparative Example 2. This was mainly because the carbonization process assisted by sodium chloride and sodium carbonate significantly increased the pore structure of the bamboo charcoal, facilitating the rapid diffusion of sodium ions. However, reducing the amount of molten salt (Example 2) and using ethanol as a solvent (Example 3) resulted in lower capacity and rate performance compared to Example 1. This was primarily because reducing the amount of molten salt decreased the degree of carbonization, and the solubility of molten salt in ethanol is lower than in water, making it difficult for it to fully penetrate the pore structure of the bamboo and crystallize to form a better support, thus affecting its effective surface area.

[0083] The bamboo-based hard charcoal obtained by dry blending in Comparative Example 1 showed inferior specific capacity and rate performance compared to the wet blending process using water as a solvent, indicating that the wet process is more beneficial for improving the specific capacity and rate performance of bamboo charcoal.

[0084] The above results show that the preparation method of the present invention significantly improves the specific capacity and rate performance of bamboo-based hard carbon anode materials under high current density.

[0085] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the present invention, should fall within the protection scope of the present invention.

Claims

1. A method for preparing a high rate performance bamboo-based hard carbon anode material, characterized by: The method comprises the following steps: A1, impregnating bamboo powder in an inorganic sodium salt solution, drying and crystallizing to form a support of salt crystals in the pores of the bamboo, and obtaining a mixed powder; the inorganic sodium salt in the inorganic sodium salt solution is one or more of sodium chloride, sodium carbonate and sodium sulfate; A2, calcining the mixed powder in a protective atmosphere to obtain a hard carbon precursor; the calcining comprises the following steps: first, calcining at 300-500 DEG C for 1-4 h, and then calcining at 700-1500 DEG C for 1-4 h; A3, washing and drying the hard carbon precursor to obtain a bamboo-based hard carbon negative electrode material.

2. The method of claim 1, wherein: In the step A1, the solvent in the inorganic sodium salt solution is water or ethanol.

3. The method of claim 1, wherein: In the step A1, the inorganic sodium salt solution is a saturated inorganic sodium salt solution.

4. The method of claim 1, wherein: In the step A1, the mass ratio of the bamboo powder to the inorganic sodium salt in the inorganic sodium salt solution is 10:1-1:

15.

5. The production method according to any one of claims 1 to 4, characterized by: In the step A2, the protective atmosphere is inert gas and / or nitrogen.

6. The method of any one of claims 1 to 4, wherein: In the step A3, the temperature during washing is 20-80 DEG C, and the washing time is 2-24 h.

7. The method of any one of claims 1 to 4, wherein: After the step A3, the following step A4 is further included: A4, salt crystallization recovery: collecting and heating the washing liquid of step A3, evaporating and crystallizing to obtain recovered inorganic sodium salt.

8. The method of claim 7, wherein: In the step A4, the heating temperature is 60-100 DEG C.

9. A bamboo-based hard carbon negative electrode material prepared by the preparation method according to any one of claims 1-8, used in a sodium ion battery negative electrode.

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