A method for preparing cellulose-derived hard carbon anode material based on ionic liquid treatment and its application in sodium-ion batteries

Abstract

This invention belongs to the technical field of sodium-ion battery anode materials, and discloses a method for preparing a cellulose-derived hard carbon anode material based on ionic liquid treatment and its application in sodium-ion batteries. The invention first utilizes an ionic liquid to pretreat cellulose, leveraging the unique solubility and reactivity of the ionic liquid to disrupt the crystalline structure of cellulose and enhance its reactivity. Subsequently, the pretreated cellulose is carbonized at high temperature under an inert atmosphere to prepare a hard carbon material with abundant nanopores and excellent electrochemical performance. This hard carbon material, as an anode in sodium-ion batteries, exhibits high specific capacity, excellent cycle stability, and good rate performance. The hard carbon anode material preparation process provided by this invention is simple and suitable for large-scale production, offering a new technical path for the development of high-performance anode materials for sodium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery anode materials, and relates to a method for preparing a cellulose-derived hard carbon anode material based on ionic liquid treatment and its application in sodium-ion batteries. Background Technology

[0002] With the rapid growth of global energy demand and the increasing depletion of fossil fuel resources, the development of efficient and sustainable energy storage technologies has become an urgent need for society today. Sodium-ion batteries (SIBs), due to their abundant sodium resources, low cost, and similar working principle to lithium-ion batteries, are considered one of the important candidate technologies for large-scale energy storage. However, the development of sodium-ion batteries is limited by the performance of anode materials. Traditional graphite anode materials are difficult to use due to the difficulty of sodium ion intercalation, making it difficult to meet the requirements of high capacity and long cycle life. Therefore, the development of novel anode materials suitable for sodium-ion storage has become a current research focus.

[0003] Hard carbon materials, due to their unique disordered structure and abundant nanopores, can effectively store sodium ions and exhibit excellent electrochemical performance, making them a research hotspot for anode materials in sodium-ion batteries. In particular, hard carbon materials prepared using biomass as a precursor are not only widely available and inexpensive, but also possess tunable microstructures and excellent electrochemical performance, demonstrating enormous application potential. Cellulose, as an abundant natural biomass resource, has the advantages of being renewable, environmentally friendly, and low-cost, making it an ideal precursor for preparing hard carbon materials. However, traditional cellulose carbonization processes suffer from problems such as high reaction temperatures, high energy consumption, and difficulty in controlling the product structure, limiting its application in sodium-ion batteries.

[0004] To address the aforementioned problems, this invention proposes a method for preparing cellulose-derived hard carbon materials based on ionic liquid pretreatment. Ionic liquids, as green solvents, possess advantages such as low volatility, high thermal stability, and designability, and have been widely applied in biomass pretreatment and materials synthesis. Pretreatment of cellulose with ionic liquids can effectively disrupt its crystalline structure and alter its microcrystalline arrangement, thereby enhancing its reactivity. This pretreatment method enables precise control over the microstructure of hard carbon materials during subsequent carbonization processes, such as optimizing pore distribution, increasing defect sites, and controlling the number of closed pores, thus significantly improving the electrochemical performance of hard carbon materials.

[0005] Research on the preparation of hard carbon anode materials from cellulose using ionic liquids is still in its early stages, and the mechanisms for process optimization and performance regulation remain unclear. Therefore, developing a cellulose-derived hard carbon anode material based on ionic liquid treatment and exploring its application in sodium-ion batteries is of significant scientific and practical value. This invention aims to prepare high-performance hard carbon anode materials by optimizing the ionic liquid treatment process and carbonization conditions, providing a new solution for the development of sodium-ion batteries. Summary of the Invention

[0006] The purpose of this invention is to provide a cellulose-derived sodium-ion battery hard carbon anode material based on ionic liquid processing.

[0007] The technical solution of this invention:

[0008] A method for preparing cellulose-derived hard carbon anode materials based on ionic liquid treatment is disclosed. First, cellulose is pretreated with an ionic liquid. The unique solubility and reactivity of the ionic liquid disrupt the crystalline structure of cellulose and enhance its reactivity. Subsequently, the pretreated cellulose is carbonized at high temperature under an inert atmosphere to prepare a hard carbon material with abundant nanopores and excellent electrochemical performance. The specific experimental procedure is as follows:

[0009] (1) Add cellulose to the ionic liquid and control the ratio of cellulose mass g to ionic liquid volume mL to be 6:24 to 100:24. Place the mixture in a water bath at 60 to 80°C and stir continuously on a magnetic stirrer for 8 hours until the cellulose is completely dispersed in the ionic liquid to obtain a cellulose-ionic liquid mixture.

[0010] (2) Transfer the above uniformly dispersed cellulose-ionic liquid mixture to a quartz boat, ensuring that the cellulose-ionic liquid mixture is evenly spread, and heat it to 1400°C at a heating rate of 5°C / min in an Ar gas environment, and keep it for 1 hour to obtain the carbonized hard carbon material.

[0011] (3) Take out the carbonized hard carbon material, wash it repeatedly with detergent to remove residual ionic liquid and other impurities, and dry the washed material in a vacuum drying oven at 80°C for 12 hours to obtain hard carbon anode material HC-ILs-1400.

[0012] The detergent comprises hydrochloric acid solution and deionized water, and the hydrochloric acid solution and deionized water are used alternately for washing. The molar concentration of the hydrochloric acid solution is 0.5-1.2M.

[0013] In step (1), the ionic liquid is 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium chloride or 1-butylpyridinium chloride.

[0014] The hard carbon anode material obtained by the above preparation method can be used as an anode material for sodium-ion batteries.

[0015] The beneficial effects of this invention are as follows: By treating cellulose with ionic liquid, the crystalline structure of cellulose is effectively destroyed, and its reactivity is improved. This results in the hard carbon material obtained after carbonization having more abundant nanopores and a higher specific surface area, thereby significantly improving the specific capacity and rate performance of sodium-ion batteries. Attached Figure Description

[0016] Figure 1 The charge-discharge curves of HC-ILs-1400 and HC-1400 materials prepared in Example 2 and Comparative Example 1 are shown.

[0017] Figure 2 Cyclic test curves of HC-ILs-1400 and HC-1400 materials prepared in Example 2 and Comparative Example 1.

[0018] Figure 3 The rate test curves are for HC-ILs-1400 and HC-1400 materials prepared in Example 2 and Comparative Example 1. Detailed Implementation

[0019] The specific implementation schemes of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0020] The following comparative examples and embodiments demonstrate performance testing using an assembled sodium-ion battery system: Active materials, conductive additives (Super P), and binders (PVDF) were mixed in an 8:1:1 ratio to form a slurry, which was then coated onto copper foil. The copper foil was dried in a vacuum oven at 60°C for 12 hours and then cut into electrode sheets with a diameter of 10 mm. In an argon-filled glove box (H2O and O2 < 0.1 ppm), the electrode sheets, separator (glass fiber filter GF / D), and metallic sodium were assembled into a CR2032 button cell. 1 mol L -1 NaPF6 was dissolved in ethylene glycol dimethyl ether as the electrolyte. First, HC-ILs-1400 was pre-sodiumized by simple contact with a sodium sheet. Charge-discharge curves (GCD) and cycle performance were obtained using a LAND-CT2001A battery tester (Wuhan, China). Electrochemical impedance spectroscopy and cyclic voltammetry were performed using an electrochemical workstation (CHI660, China). All electrochemical tests were conducted within the voltage range of 0.01–2.5 V at room temperature (25°C).

[0021] Example 1

[0022] Weigh 0.75g of cellulose powder and measure 3ml of ionic liquid (1-butyl-3-methylimidazolium acetate). Add the cellulose to the ionic liquid and stir magnetically in a 70℃ water bath for 8 hours until the cellulose is completely dispersed. Transfer the sample to a quartz boat, spread it evenly, and place it in a tube furnace. Heat the tube furnace to 1400℃ at a heating rate of 5℃ / min and maintain it at this temperature for 1 hour. After carbonization, allow it to cool naturally to room temperature. Take out the hard carbon material, wash it repeatedly with deionized water and hydrochloric acid solution, and vacuum dry it at 80℃ for 12 hours.

[0023] Example 2

[0024] Preparation of HC-ILs-1400 materials

[0025] The mass of the cellulose powder is 1.0g, and other details are the same as in Implementation Case 1.

[0026] Example 3

[0027] The mass of the cellulose powder is 1.25g, and other parameters are the same as in Implementation Case 1.

[0028] Example 4

[0029] Weigh 1.0 g of cellulose powder and measure 3 ml of ionic liquid (1-butyl-3-methylimidazolium chloride). Add the cellulose to the ionic liquid and stir magnetically in a 70 °C water bath for 8 h until the cellulose is completely dispersed. Transfer the sample to a quartz boat, spread it evenly, and place it in a tube furnace. Heat the tube furnace to 1400 °C at a heating rate of 5 °C / min and maintain it at this temperature for 1 h. After carbonization, allow it to cool naturally to room temperature. Take out the hard carbon material, wash it repeatedly with deionized water and hydrochloric acid solution, and vacuum dry it at 80 °C for 12 h.

[0030] Example 5

[0031] Replace the ionic liquid with 1-butylpyridine chloride, and follow the same procedure as in Implementation Case 4.

[0032] Comparative Example 1

[0033] Preparation of HC-1400 material

[0034] Weigh 2.0g of cellulose powder and place it in a quartz boat. Heat the tube furnace to 1400℃ at a heating rate of 5℃ / min and maintain it at this temperature for 1h. After carbonization, allow it to cool naturally to room temperature. Remove the hard carbon material and wash it repeatedly with deionized water and hydrochloric acid solution. Then, vacuum dry it at 80℃ for 12h.

[0035] Comparative Example 2

[0036] Weigh 1.5g of cellulose powder and measure 3ml of ionic liquid (1-butyl-3-methylimidazolium acetate). Add the cellulose to the ionic liquid and stir magnetically in a 70℃ water bath for 8 hours until the cellulose is completely dispersed. Transfer the sample to a quartz boat, spread it evenly, and place it in a tube furnace. Heat the tube furnace to 1400℃ at a heating rate of 5℃ / min and maintain it at this temperature for 1 hour. After carbonization, allow it to cool naturally to room temperature. Take out the hard carbon material, wash it repeatedly with deionized water and hydrochloric acid solution, and vacuum dry it at 80℃ for 12 hours.

[0037] The test results for the examples and comparative examples are as follows:

[0038] As shown in Figure (1), at 0.025Ag -1 At a current density of [value missing], the HC-1400 achieved a specific capacity of 261.62 mAh g during its first charge cycle. -1 The HC-ILs-1400 has a first-cycle charge capacity of 285.6mAh g. -1 The first-charge specific capacity of HC-ILs-1400 is higher than that of HC-1400. This is likely due to the ionic liquid treatment of cellulose effectively disrupting the hydrogen bond network and crystalline regions of cellulose, transforming it into an amorphous state, thus facilitating the formation of a porous structure during carbonization. This porous structure provides more sodium ion storage sites, significantly improving the first-charge specific capacity.

[0039] As shown in Figure (2), in 1Ag -1 After 200 cycles at the specified current density, the capacity retention rate of HC-1400 was 72.48%, while that of HC-ILs-1400 was 89.44%, indicating that HC-ILs-1400 has better cycle stability.

[0040] As shown in Figure (3), the Ag values ​​are 0.025, 0.05, 0.1, 0.2, 0.5, 1, 2, and 5. -1 Under these conditions, the specific capacities of HC-ILs-1400 were 314.5, 275.7, 253.8, 238.9, 213.8, 182.9, 121.8, and 53.5 mAh g. -1 Furthermore, as can be observed from Figure (3), HC-ILs-1400 has a more significant increase in the multiplier than HC-1400.

Claims

1. A method for preparing a cellulose-derived hard carbon anode material based on ionic liquid processing, characterized in that, The steps are as follows: (1) Add cellulose to the ionic liquid and control the ratio of cellulose mass g to ionic liquid volume mL to be 6:24 to 100:

24. Place the mixture in a water bath at 60 to 80°C and stir continuously on a magnetic stirrer for 8 hours until the cellulose is completely dispersed in the ionic liquid to obtain a cellulose-ionic liquid mixture. (2) Transfer the above uniformly dispersed cellulose-ionic liquid mixture to a quartz boat, ensuring that the cellulose-ionic liquid mixture is evenly spread, and heat it to 1400°C at a heating rate of 5°C / min in an Ar gas environment, and keep it for 1 hour to obtain the carbonized hard carbon material. (3) Take out the carbonized hard carbon material, wash it repeatedly with detergent to remove residual ionic liquid and other impurities, and dry the washed material in a vacuum drying oven at 80°C for 12 hours to obtain hard carbon anode material HC-ILs-1400.

2. The preparation method according to claim 1, characterized in that, The detergent comprises hydrochloric acid solution and deionized water, and the hydrochloric acid solution and deionized water are used alternately for washing. The molar concentration of the hydrochloric acid solution is 0.5-1.2M.

3. The preparation method according to claim 1, characterized in that, In step (1), the ionic liquid is 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium chloride or 1-butylpyridinium chloride.

4. The hard carbon anode material obtained by any of the preparation methods described in claims 1-3 may be used as an anode material for sodium-ion batteries.

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