Preparation method of closed-pore-rich high-performance cellulose / chitosan hard carbon negative electrode material

Abstract

The invention relates to a preparation method of a closed-pore-rich high-performance cellulose / chitosan hard carbon negative electrode material, and belongs to the field of advanced sodium ion battery negative electrode materials. The preparation method mainly comprises the following steps: (1) completely dissolving microcrystalline cellulose in an alkaline system, regenerating, washing, filtering and freeze-drying to obtain a regenerated cellulose solid; (2) oxidizing the solid with sodium periodate, washing, filtering and freeze-drying to obtain aldehyde cellulose; and (3) dispersing the aldehyde cellulose into the amino-activated chitosan solution, reacting, washing, filtering and freeze-drying to obtain a chitosan grafted cellulose solid. And (4) carrying out dehydration, ball milling, screening and carbonization treatment on the obtained chitosan grafted cellulose solid to obtain the closed-pore-rich high-performance cellulose / chitosan hard carbon negative electrode material. The hard carbon material prepared by the invention has an adjustable pseudo-graphitization domain structure and a rich closed-pore structure, mainly stores sodium in a closed-pore manner in a platform region, and has outstanding electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode material technology, specifically to a method for preparing a high-performance cellulose / chitosan hard carbon anode material rich in closed pores. Background Technology

[0002] In recent years, sodium-ion batteries have been considered a highly promising energy storage technology for large-scale secondary energy storage systems due to the abundance of sodium resources in the Earth's crust, lower manufacturing costs than lithium-ion batteries, and similar working principles. However, the commercialization of sodium-ion batteries still faces certain challenges due to the limited reversible capacity of the anode materials, low initial coulombic efficiency, and low voltage plateau capacity. Currently, anode materials suitable for sodium-ion batteries are mainly classified into several categories, including carbon-based materials, titanium-based materials, alloy materials, and metal compound materials. Among them, carbon-based materials are the most promising anode materials for research. However, the practical development and application of carbon-based anodes still face challenges.

[0003] Hard carbon is one of the more ideal anode materials among carbon-based materials. Biomass-derived hard carbon materials, with their advantages of abundant resources, low cost, and high utilization rate, have become a focus of current research. Hard carbon materials are resistant to graphitization at high temperatures, possessing a unique structure composed of multi-layered stacked pseudo-graphitized regions, forming a closed-pore structure formed by the bending and stacking of nano-carbon layers. This material exhibits high charge-discharge specific capacity, excellent rate performance and cycle stability, as well as a low sodium storage potential, making it considered one of the preferred anode materials for sodium-ion batteries. However, traditional biomass-derived hard carbon suffers from diverse precursor types and difficulty in controlling the crystallinity of the material. This results in structural differences such as a large number of micro-mesoporous structures, a large specific surface area, and a small number of closed pores, leading to problems such as low coulombic first-efficiency and insufficient plateau capacity, severely restricting its development in commercial applications. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention discloses a method for preparing a high-performance cellulose / chitosan hard carbon anode material rich in closed pores, relating to the field of novel sodium-ion battery anode material synthesis technology. This method uses microcrystalline cellulose as raw material, modifying the molecular chain arrangement of the microcrystalline cellulose by grafting chitosan molecules. A two-step grafting process of oxidation followed by grafting is employed. Subsequently, a process of pre-carbonization and dehydration, ball milling, sieving, and re-carbonization is used to regulate the ratio of graphitized carbon and pseudo-graphitized carbon domains in the microstructure of the hard carbon material, adjusting the pore structure, reducing particle size and specific surface area, resulting in a more uniform particle size distribution and better contact between the anode material and the electrolyte. The prepared hard carbon has a larger closed-pore volume and increased interlayer spacing, improving plateau capacity, coulombic first-efficiency, and cycle stability, providing a new approach for the research of high-closed-pore sodium-storage hard carbon anode materials.

[0005] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing a high-performance cellulose / chitosan hard carbon anode material rich in closed pores is provided, comprising the following steps: (1) Microcrystalline cellulose is completely dissolved in an alkaline system under mechanical stirring. After multiple washing, filtration, freeze drying, and grinding, regenerated cellulose solid is obtained. (2) The regenerated cellulose solid obtained in step (1) is partially oxidized under mechanical stirring to generate aldehyde cellulose. After multiple washing, filtration, freeze drying, and grinding, oxidized cellulose solid is obtained. (3) Disperse the oxidized cellulose solid obtained in step (2) in an amino-activated chitosan solution system, react for a period of time under mechanical stirring, and after multiple washing, filtration, and vacuum drying, obtain chitosan-grafted cellulose solid. (4) The chitosan-grafted cellulose solid obtained in step (3) is pre-carbonized and dehydrated in a tube furnace under an argon atmosphere, and then ball-milled and sieved to obtain solid powder. (5) The solid powder obtained in step (4) is carbonized in a tube furnace under an argon atmosphere, and then ball-milled and sieved to obtain cellulose / chitosan hard carbon anode material.

[0006] Furthermore, in step (1), the alkaline system is prepared by dissolving sodium hydroxide or ammonia and urea or alkaline urea in deionized water.

[0007] Furthermore, in step (1), the ratio of microcrystalline cellulose: sodium hydroxide: alkali urea: water is 15g: 20g: 25g: 250mL.

[0008] Furthermore, in step (1), 70-80 wt% ethanol solution is added to the system and stirred to regenerate cellulose.

[0009] Furthermore, in step (2), sodium periodate is used as an oxidant, and the mass ratio of sodium periodate to regenerated cellulose is 13g:10g.

[0010] Furthermore, in step (2), the oxidation temperature is 50℃ and the oxidation time is 5~6h.

[0011] Furthermore, in step (2), the reaction is terminated with ethylene glycol after the reaction is complete.

[0012] Furthermore, in step (2), the reaction is terminated at a time of 1.5 h.

[0013] Furthermore, in step (3), the mass ratio of oxidized cellulose to chitosan is 1:1 and 1:2.

[0014] Furthermore, in step (3), the reaction time is 5 hours and the reaction temperature is 50°C.

[0015] Furthermore, in steps (4) and (5), the argon purity is 99.99%.

[0016] Furthermore, in step (4), the dehydration temperature is 350℃. First, the temperature is raised from 25℃ to 200℃ at 3℃ / min, held at 200℃ for 60min, then raised to 350℃ at 3℃ / min, held at 350℃ for 4h, and then cooled to 50℃ in one step at 3℃ / min, and then naturally cooled to room temperature.

[0017] Furthermore, in step (5), the carbonization temperature is 1400℃. First, the temperature is increased to 1400℃ in one step at 25℃ at 3℃ / min and maintained for 2h. Then, the temperature is reduced to 200℃ at 3℃ / min and then naturally cooled to room temperature.

[0018] The present invention has the following beneficial effects: 1. The present invention provides a method for preparing a high-performance cellulose / chitosan hard carbon anode material with rich closed pores. Microcrystalline cellulose is used as the main raw material, and chitosan molecules penetrate the cellulose molecular network, reducing the original high crystallinity of cellulose. An advanced process is employed, consisting of low-temperature pre-carbonization and dehydration, followed by ball milling and sieving, and then high-temperature polycondensation and carbonization. This two-step carbonization process results in more thorough cross-linking and rearrangement of the molecules.

[0019] 2. Compared with the original cellulose hard carbon, the cellulose / chitosan hard carbon of the present invention has an increased proportion of amorphous carbon, and the growth of long-range ordered graphitized carbon domains is restricted, promoting the formation of abundant vortex closed pores. The closed pore volume and number are both superior to those of unmodified cellulose hard carbon.

[0020] 3. The high-closed-pore cellulose / chitosan hard carbon material provided by this invention exhibits excellent electrochemical performance. This material has a low specific surface area and small particle size. With the growth of pseudo-graphitized carbon domains, the interlayer spacing increases, and the closed-pore structure is abundant, providing more ample space and favorable kinetic conditions for sodium ion storage. This hard carbon primarily stores sodium through a closed-pore mechanism, thereby improving reversible specific capacity and exhibiting excellent rate performance and cycling stability. Attached Figure Description

[0021] Figure 1 Figure 1 shows the scanning electron microscope (SEM) images of the hard carbon obtained in Examples 1-2 and Comparative Example 1; Figure 2a is the SEM image of the hard carbon prepared in Example 1, Figure 3b is the SEM image of the hard carbon prepared in Example 2, and Figure 4c is the SEM image of the hard carbon prepared in Comparative Example 1. Figure 2 Fourier transform infrared absorption spectra (a) and XRD patterns (b) of the grafted products obtained in Examples 1-2 and Comparative Example 1. Figure 3 Nitrogen isothermal adsorption / desorption curves of hard carbon obtained in Examples 1-2 and Comparative Example 1; Figure 4 Examples include high-magnification transmission electron microscope (TEM) images of the hard carbon obtained in Examples 1-2 and Comparative Example 1; Figure a is a high-magnification TEM image of the hard carbon prepared in Example 1, Figure b is a high-magnification TEM image of the hard carbon prepared in Example 2, and Figure c is a high-magnification TEM image of the hard carbon prepared in Comparative Example 1. Figure 5 Figure 1 shows the constant current charge-discharge curve of the half-cell assembled in Example 2; Figure 2a shows the constant current charge-discharge curve of the hard carbon assembled half-cell prepared in Example 1; Figure 3b shows the constant current charge-discharge curve of the hard carbon assembled half-cell prepared in Example 2; and Figure 4c shows the constant current charge-discharge curve of the hard carbon assembled half-cell prepared in Comparative Example 1. Figure 6 Comparison of ramp capacity / plateau capacity in the second cycle of constant current charge-discharge cycling for the preparation of hard carbon; Figure 7 Rate performance diagram for preparing hard carbon; Figure 8 Long-cycle performance diagram for the preparation of hard carbon; Figure 9 The constant current intermittent titration curve for preparing hard carbon. Detailed Implementation

[0022] The principles and features of this invention are described below. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0023] Example 1: A high-performance cellulose / chitosan hard carbon anode material rich in closed pores is prepared by the following steps: (1) Weigh 20g of sodium hydroxide and 25g of alkali urea, and measure 250mL of water to prepare an alkaline system. Dissolve 15g of microcrystalline cellulose in the alkaline system under mechanical stirring. After complete dissolution, add 200mL of 70% ethanol solution and continue stirring until the cellulose is regenerated. Filter, wash three times with ethanol and deionized water until neutral, filter again, and dry the obtained solid in a freeze dryer for 24h. Ball mill to obtain regenerated cellulose solid powder.

[0024] (2) 10 g of the regenerated cellulose solid powder obtained in step (1) was uniformly dispersed in 500 mL of deionized water by mechanical stirring at room temperature. Then, 13 g of sodium periodate was added under light-protected conditions at 50 °C, and the reaction was allowed to proceed for 5 h. After the reaction was completed, excess ethylene glycol was added to terminate the reaction and stirring was continued for 1.5 h to dissolve the residual sodium periodate. The resulting product was washed and filtered 3 to 5 times with ethanol and deionized water until the filtrate was neutral. Then, it was freeze-dried for 24 h and ball-milled to obtain powdered oxidized cellulose solid.

[0025] (3) Dissolve 10g of the oxidized cellulose solid powder obtained in step (2) in a chitosan solution system containing 10g of amino-activated cellulose. Stir mechanically and react at 30°C for 5h. After washing and filtering multiple times until the pH is neutral, dry under vacuum to obtain chitosan-grafted cellulose solid MCCTs1-1.

[0026] (4) Take 10g of the chitosan-grafted cellulose solid MCCTs1-1 obtained in step (3) and place it in a crucible. Dehydrate it in a tube furnace under a 99.99% argon atmosphere. First, raise the temperature from 25℃ to 200℃ at 3℃ / min, hold at 200℃ for 60min, then raise the temperature to 350℃ at 3℃ / min, hold at 350℃ for 4h, and then lower the temperature to 50℃ in one step at 3℃ / min. Then, cool it naturally to room temperature to obtain pre-carbonized cellulose / chitosan solid a.

[0027] (5) Place the solid a obtained in step (4) into a ball mill and grind for 1.5 hours. Then, vibrate and sieve it through a 300-mesh sieve to obtain solid powder a1.

[0028] (6) Place the pre-carbonized cellulose / chitosan solid a1 obtained in all steps (5) in a crucible, and under a 99.99% argon atmosphere, first raise the temperature to 1400℃ in one step at 25℃ at 3℃ / min, maintain for 2h, then lower the temperature to 200℃ at 3℃ / min, and then let it cool naturally to room temperature to obtain cellulose / chitosan hard carbon solid a2. (7) Place the cellulose / chitosan hard carbon solid a2 obtained in step (6) into a ball mill and grind for 3 hours to obtain solid powder a3.

[0029] (8) The solid powder a3 obtained in step (7) is vibrated and sieved to obtain cellulose / chitosan hard carbon solid (labeled as: GCHC1-1).

[0030] Example 2: (1) Weigh 20g of solid sodium hydroxide and 25g of alkali urea, and measure 250mL of water to prepare an alkaline system. Dissolve 15g of microcrystalline cellulose in the alkaline system under mechanical stirring. After complete dissolution, add 200mL of 70% ethanol solution and continue stirring until the cellulose is regenerated. Filter, wash three times with ethanol and deionized water until neutral, filter again, and dry the obtained solid in a freeze dryer for 24h. Ball mill to obtain regenerated cellulose solid powder.

[0031] (2) 10 g of the regenerated cellulose solid powder obtained in step (1) was uniformly dispersed in 500 mL of deionized water by mechanical stirring at room temperature. Then, 13 g of sodium periodate was added under light-protected conditions at 50 °C, and the reaction was allowed to proceed for 5 h. After the reaction was completed, excess ethylene glycol was added to terminate the reaction and stirring was continued for 1.5 h to dissolve the residual sodium periodate. The resulting product was washed and filtered 3 to 5 times with ethanol and deionized water until the filtrate was neutral. Then, it was freeze-dried for 24 h and ball-milled to obtain powdered oxidized cellulose solid.

[0032] (3) Dissolve 10g of the oxidized cellulose solid powder obtained in step (2) in a chitosan solution system containing 20g of amino-activated cellulose. Stir mechanically and react at 30°C for 5h. After washing and filtering multiple times until the pH is neutral, dry under vacuum to obtain chitosan-grafted cellulose solid MCCTs1-2.

[0033] (4) Take 10g of the chitosan-grafted cellulose solid MCCTs1-2 obtained in step (3) and place it in a crucible. Dehydrate it in a tube furnace under a 99.99% argon atmosphere. First, raise the temperature from 25℃ to 200℃ at 3℃ / min, hold at 200℃ for 60min, then raise the temperature to 350℃ at 3℃ / min, hold at 350℃ for 4h, and then lower the temperature to 50℃ in one step at 3℃ / min. Then, cool it naturally to room temperature to obtain pre-carbonized cellulose / chitosan solid b.

[0034] (5) Place the solid b obtained in step (4) into a ball mill and grind for 1.5 hours. Then, vibrate and sieve it through a 300-mesh sieve to obtain solid powder b1.

[0035] (6) Place the pre-carbonized cellulose / chitosan solid b1 obtained in all steps (5) in a crucible, and under a 99.99% argon atmosphere, first raise the temperature to 1400℃ in one step at 25℃ at 3℃ / min, maintain for 2h, then lower the temperature to 200℃ at 3℃ / min, and then allow it to cool naturally to room temperature to obtain cellulose / chitosan hard carbon solid b2. (7) Place the cellulose / chitosan hard carbon solid b2 obtained in step (6) into a ball mill and grind for 3 hours to obtain solid powder b3.

[0036] (8) The solid powder b3 obtained in step (7) is vibrated and sieved to obtain cellulose / chitosan hard carbon solid (labeled as GCHC1-2).

[0037] Comparative example: (1) Place 20g of microcrystalline cellulose solid powder in a crucible and dehydrate it in a tube furnace under a 99.99% argon atmosphere. First, raise the temperature from 25℃ to 200℃ at 3℃ / min, hold at 200℃ for 60min, then raise the temperature to 350℃ at 3℃ / min, hold at 350℃ for 4h, and then lower the temperature to 50℃ in one step at 3℃ / min. Finally, let it cool naturally to room temperature to obtain pre-carbonized microcrystalline cellulose c.

[0038] (2) The solid c obtained in step (1) is placed in a ball mill and ground for 1.5 hours. It is then sieved through a 300-mesh sieve to obtain solid powder c1.

[0039] (3) Place all the solids c1 obtained in step (2) in a crucible, and in a 99.99% argon atmosphere, first heat it to 1400℃ in one step at 25℃ at 3℃ / min, maintain it for 2h, then cool it down to 200℃ at 3℃ / min, and then cool it down to room temperature naturally to obtain pure cellulose hard carbon solid c2. (4) Place the pure cellulose hard carbon solid b2 obtained in step (3) into a ball mill and grind for 3 hours to obtain solid powder c3.

[0040] (5) The solid powder c3 obtained in step (4) is vibrated and sieved to obtain pure cellulose hard carbon solid (labeled as rHC).

[0041] Experimental Example 1: Scanning electron microscope (SEM) images of the hard carbon anode materials obtained in Examples 1 and 2 were obtained respectively, as follows: Figure 1 As shown; the infrared spectrum and XRD pattern of chitosan-grafted cellulose solid are as follows. Figure 2 As shown; nitrogen adsorption / desorption images of cellulose / chitosan hard carbon anode materials are shown below. Figure 3 As shown; transmission electron microscope image as shown Figure 4 As shown, rHC represents cellulose hard carbon.

[0042] Depend on Figure 1 Scanning electron microscopy (SEM) images of the cellulose / chitosan hard carbon anode materials show that all hard carbon materials treated with the same carbonization process exhibit irregular blocky particles with surface texture. rHC hard carbon particles are unevenly distributed, have large particle sizes, and show obvious particle adhesion. The surface roughness of GCHC1-1 and GCHC1-2 hard carbons after grafting reaction increases, and their particle size distribution is more uniform with smaller particle sizes, which is beneficial for electrolyte penetration.

[0043] Depend on Figure 2It can be seen that, compared with r-MC, chitosan-grafted cellulose materials MCCTs1-1 and MCCTs1-2 have a higher growth rate at 1579 cm⁻¹. -1 The infrared vibrational absorption peak of the C=N group appears. This indicates that the grafting method leads to the dissociation of the comprehensive hydrogen bond network within the cellulose chain, while the chitosan macromolecules achieve three-dimensional interpenetration through covalent β-(1,4)-glycosidic bonds. XRD results show that after the grafting reaction, the 001 peak intensity of MCCTs1-1 and MCCTs1-2 is significantly lower than that of r-MC. This is due to the breaking of the hydrogen bond network caused by intermolecular crosslinking, and the lower crystallinity is conducive to the formation of pseudo-graphitized carbon domains.

[0044] Depend on Figure 3 The nitrogen adsorption / desorption results of the cellulose / chitosan hard carbon anode material show that the specific surface areas of rHC, GCHC1-1, and GCHC1-2 are 68.04, 8.22, and 7.74 m², respectively. 2 / g, the grafting strategy effectively reduced the specific surface area of ​​the hard carbon. Pore size distribution shows that GCHC1-1 and GCHC1-2 have a uniform pore size distribution, mainly composed of micro-mesopores in the range of 2~5nm. The reduction in specific surface area is beneficial to reduce irreversible reactions between electrolyte and active material, avoid excessive irreversible capacity loss, and improve coulombic first efficiency.

[0045] Depend on Figure 4 The HRTEM images reveal distinct structural features of the hard carbon materials. It can be seen that the graphitization degree of the cellulose / chitosan hard carbon materials GCHC1-1 and GCHC1-2 is significantly lower than that of pure cellulose hard carbon (rHC), and they exhibit numerous closed-pore structures composed of multiple layers of short-range nanographite sheets rolled and stacked. Furthermore, the interlayer spacing also shows significant changes. The average interlayer spacing (d002) of GCHC1-1 and GCHC1-2 are 0.383 nm and 0.388 nm, respectively. Compared to pure cellulose (d002 = 0.358 nm), the interlayer spacing is significantly increased. This indicates that the reduced crystallinity is conducive to a lower degree of graphitization, modulating the ratio of graphitized and pseudo-graphitized carbon domains, and increasing the interlayer spacing of the hard carbon. The larger interlayer spacing and the presence of closed-pore structures promote the reaction kinetics between sodium ions and the electrolyte, improving sodium ion storage efficiency and further enhancing the capacity of the closed-pore sodium-dominant platform.

[0046] Experimental Example 2: The specific steps for assembling and testing a half-cell are as follows: (1) Preparation of negative electrode sheet: Weigh 0.8 g of cellulose / chitosan hard carbon GCHC1-2 and GCHC1-2 solid powder, 0.1 g of conductive carbon black (hereinafter referred to as Super P), and 3.33 g of 3.0 wt% polyvinylidene fluoride / N-methylpyrrolidone solution (PVDF / NMP) in the order of 8:1:1 in Example 1. Grind them thoroughly in a mortar to form a cement-like black slurry. Coat the mixed slurry onto the smooth aluminum foil surface with a 100 μm thick four-sided coating and vacuum dry at 80 ℃ for 12 h. Finally, cut it into circular pieces with a 13 mm diameter cutting machine to obtain the negative electrode sheet required for button battery. (2) Preparation of positive electrode sheet: Using metallic sodium as the standard positive electrode, small pieces of metallic sodium are pressed into sheets with a roller press to a thickness of 0.8 mm, and then cut into small circular sodium sheets with a diameter of 12 mm. (3) Assembling the coin cell: Place the positive electrode shell, spring, gasket, sodium plate, and glass fiber separator in the following order, with the top facing up. Add approximately 1 mL of 1 mol / L sodium hexafluorophosphate electrolyte, the negative electrode, and the negative electrode shell. After assembly, seal the coin cell with a hydraulic press to obtain a coin cell with a complete circuit. All assembly processes were carried out in a glove box continuously filled with argon gas (O2 concentration ≤ 0.5 ppm, H2O concentration ≤ 0.1 ppm).

[0047] The above half-cell was subjected to constant current charge-discharge, rate performance, cycle performance, and mass transfer kinetics tests. The constant current charge-discharge results are as follows: Figure 5 As shown, the slope / platform capacity ratio analysis is as follows: Figure 6 As shown, the rate performance is as follows Figure 7 Cyclic performance such as Figure 8 As shown, the results of the constant current intermittent titration are as follows: Figure 9 As shown.

[0048] Depend on Figure 5 The results show that after 10 cycles at a current density of 20 mA / g, the initial coulombic efficiencies of the cellulose / chitosan hard carbon anode materials GCHC1-1 and GCHC1-2 reached 81.79% and 87.37%, respectively, and the reversible capacities reached 328.89 mAh / g and 341.01 mAh / g, respectively. These represent a 10%–15% improvement in initial coulombic efficiency compared to pure cellulose hard carbon rHC.

[0049] Depend on Figure 6The slope capacity / plateau capacity ratio analysis results show that the plateau capacities of the cellulose / chitosan hard carbon anode materials GCHC1-1 and GCHC1-2 increased to 237.78 mAh / g and 247.53 mAh / g, respectively, which is 40-50 mAh / g higher than that of rHC. This indicates that the high closed-pore hard carbon materials prepared by this grafting method are beneficial to improving sodium storage performance. Furthermore, GCHC1-2 has a higher closed-pore content, resulting in superior electrochemical performance.

[0050] Depend on Figure 7 , Figure 8 It can be seen that the prepared cellulose / chitosan hard carbon exhibits good rate performance and cycling performance. With increasing rate, the melt volume decrease rate is smaller than that of rHC, and it still maintains a high capacity retention rate at high rates. The long-cycle curves show that the cellulose / chitosan hard carbon has good cycling stability; after 300 cycles at a current density of 300 mA / g, the capacity retention rate is approximately 78.07%.

[0051] Depend on Figure 9 It can be seen that GCHC1-1 and GCHC1-2 exhibit small voltage hysteresis and relatively uniform sawtooth amplitude during charge and discharge processes, indicating that the materials possess excellent ion diffusion kinetics and low electrochemical polarization, which is beneficial for rapid charge and discharge. The curves are highly symmetrical and have very long and flat low-voltage plateaus, suggesting that they have abundant and appropriately sized nanopores, enabling efficient and reversible sodium ion filling. The sodium ions are minimally lost during insertion and extraction, thus contributing to high specific capacity.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-performance cellulose / chitosan hard carbon anode material rich in closed-pores, characterized in that, Includes the following steps: (1) Microcrystalline cellulose is completely dissolved in an alkaline system under mechanical stirring. After multiple washing, filtration, freeze drying, and grinding, regenerated cellulose solid is obtained. (2) The regenerated cellulose solid obtained in step (1) is partially oxidized under mechanical stirring to generate aldehyde cellulose. After multiple washing, filtration, freeze drying, and grinding, oxidized cellulose solid is obtained. (3) Disperse the oxidized cellulose solid obtained in step (2) in an amino-activated chitosan solution system, react for a period of time under mechanical stirring, and after multiple washing, filtration, and vacuum drying, obtain chitosan-grafted cellulose solid. (4) The chitosan-grafted cellulose solid obtained in step (3) is pre-carbonized and dehydrated in a tube furnace under an argon atmosphere, and then ball-milled and sieved to obtain solid powder. (5) The solid powder obtained in step (4) is carbonized in a tube furnace under an argon atmosphere, and then ball-milled and sieved to obtain cellulose / chitosan hard carbon anode material.

2. The preparation method of the high-performance cellulose / chitosan hard carbon anode material rich in closed pores as described in claim 1, characterized in that, In step (1), the amount of dissolved cellulose is 20g.

3. The preparation method of the high-performance cellulose / chitosan hard carbon anode material rich in closed pores as described in claim 1, characterized in that, In step (2), the mass and volume ratio of cellulose: sodium periodate: deionized water: ethylene glycol in the oxidation system is 10g: 13g: 1000mL: 20mL.

4. The preparation method of the high-performance cellulose / chitosan hard carbon anode material rich in closed pores as described in claim 1, characterized in that, In step (2), the product is washed 3 to 5 times with ethanol and deionized water, and then freeze-dried under vacuum for 24 hours.

5. The preparation method of the high-performance cellulose / chitosan hard carbon anode material rich in closed pores as described in claim 1, characterized in that, In step (3), the pH of the grafting reaction is controlled at 4.0~5.0, and the grafting mass ratio of chitosan to cellulose is 10g:10g and 10g:20g, respectively.

6. The preparation method of the high-performance cellulose / chitosan hard carbon anode material rich in closed pores as described in claim 1, characterized in that, In step (4), the temperature of the pre-carbonization and dehydration treatment is 300~350℃, and the holding time is 4h.

7. The preparation method of the high-performance cellulose / chitosan hard carbon anode material rich in closed pores as described in claim 1, characterized in that, In step (4), the ball milling time is 1.5h and the particle size range is 40~50μm. The large particles after sieving are then ball milled a second time for 1.5h.

8. The method for preparing the high-performance cellulose / chitosan hard carbon anode material with rich closed-pore structure as described in claim 1, characterized in that, In step (5), the carbonization temperature is 1400℃. First, the temperature is increased from 25℃ to 1400℃ in one step at 3℃ / min and maintained for 2h. Then, the temperature is reduced to 200℃ at 3℃ / min and then naturally cooled to room temperature.

9. The method for preparing the high-performance cellulose / chitosan hard carbon anode material with rich closed-pore structure as described in claim 1, characterized in that, In step (5), the ball milling time is 3 hours and the particle size range is 10~20μm.

10. The high-performance cellulose / chitosan hard carbon anode material rich in closed pores obtained by the preparation method of the high-performance cellulose / chitosan hard carbon anode material rich in closed pores according to any one of claims 1-9.

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