Preparation method and application of cellulose-based hard carbon anode material

Abstract

This invention provides a method for preparing cellulose-based hard carbon anode materials and their applications, belonging to the field of sodium-ion battery anode material preparation technology. The method includes: preparing a strong oxidizing acid solution, adding cellulose-based raw materials to the solution, ultrasonically vibrating and stirring until homogeneous; subsequently adding long-chain molecular compounds and stirring until uniformly mixed to obtain a mixed solution; then transferring the solution to a hydrothermal reactor for hydrothermal treatment; after the reactor cools to room temperature, centrifuging, washing, and drying the hydrothermal product; finally, transferring the hydrothermal product to a high-temperature tube furnace for high-temperature pyrolysis carbonization under an inert atmosphere to obtain the cellulose-based hard carbon anode material. This invention constructs a hard carbon precursor containing a large number of carbonyl groups and nitrogen doping through a hydrolysis competition mechanism, and then prepares the hard carbon anode material through high-temperature pyrolysis carbonization, solving problems such as low reversible capacity, poor first-cycle coulombic efficiency, and performance optimization under extreme high and low temperature conditions in biomass-derived hard carbon.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode material preparation technology, and in particular to a method for preparing and applying a cellulose-based hard carbon anode material. Background Technology

[0002] With the global shortage of lithium resources and the rising cost of battery raw materials, sodium-ion batteries have become a research focus for new energy storage systems due to the abundance and wide distribution of sodium resources. Hard carbon materials, as anodes in sodium-ion batteries, are widely recognized as the sodium battery anode materials with the greatest industrialization potential due to their unique disordered microcrystalline structure, tunable interlayer spacing, and abundant nanopores.

[0003] However, hard carbon materials still face challenges in practical applications, such as low initial coulombic efficiency, insufficient long-cycle stability, and significant degradation of electrochemical performance under extreme high and low temperatures. Traditional hard carbon materials lack precise control over pore distribution and functional group modification, making it difficult to simultaneously achieve high sodium storage sites and low interfacial impedance. While existing biomass-derived hard carbons (such as cellulose-based materials) offer cost and environmental advantages, their insufficient structural disorder and uneven functional group distribution limit reversible capacity and initial efficiency improvement. Although current technologies improve performance through precursor screening, micro / nanostructure control, and surface functional group modification, they have not yet overcome the kinetic limitations across a wide temperature range.

[0004] Therefore, providing a method for preparing and applying cellulose-based hard carbon anode materials that can maintain excellent electrochemical performance under extreme high and low temperature conditions, possess both high first-cycle coulombic efficiency and long-cycle stability, and have widely available and low-cost raw materials is of great practical significance for promoting the large-scale application of sodium-ion batteries in wide-temperature energy storage scenarios. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a method for preparing cellulose-based hard carbon anode materials and their applications. A hard carbon precursor containing a large number of carbonyl groups and nitrogen doping is constructed through a hydrolysis competition mechanism, and then the hard carbon anode material is prepared by high-temperature pyrolysis carbonization. This solves the problems of low reversible capacity, poor first-cycle coulombic efficiency, and battery performance optimization under extreme high and low temperature conditions in biomass-derived hard carbon.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] A method for preparing a cellulose-based hard carbon anode material includes the following steps:

[0008] S1. Prepare a strong oxidizing acid solution, add the cellulose raw material to the strong oxidizing acid solution, and stir with ultrasonic vibration to obtain an initial solution;

[0009] S2. Add the long-chain molecular compound to the initial solution and stir until the mixture is homogeneous to obtain a mixed solution;

[0010] S3. The mixed solution is transferred to a hydrothermal reactor for hydrothermal treatment. After the hydrothermal reactor cools to room temperature, the hydrothermal product is centrifuged, washed and dried in sequence.

[0011] S4. The treated hydrothermal products are transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis and carbonization treatment under an inert atmosphere to obtain cellulose-based hard carbon anode material.

[0012] Preferably, in S1, the strong oxidizing acid solution is a sulfuric acid solution or a nitric acid solution with a concentration of 0.2-1.0M; the cellulose raw material is a cellulose powder or a biological raw material containing cellulose in wood powder, bamboo powder, or straw powder, and the added mass of the cellulose raw material is 2-10g.

[0013] Preferably, in S1, the ultrasonic vibration time is 10 min and the stirring temperature is 60°C; in S2, the stirring temperature is 60°C and the stirring time is 3 h.

[0014] Preferably, in S2, the long-chain molecular compound is one or more of polyvinylpyrrolidone, polyethyleneimine, or polydimethyldiallylammonium chloride, and the mass of the long-chain molecular compound is 2-10g.

[0015] Preferably, in S3, the temperature of the hydrothermal treatment is 150-300℃, and the holding time is 12-24h.

[0016] Preferably, in step S3, the hydrothermal product is centrifuged and washed at least three times, and the drying temperature is 60-100°C.

[0017] Preferably, in S4, the inert atmosphere is nitrogen or argon.

[0018] Preferably, in S4, the heating rate of the high-temperature pyrolysis carbonization treatment is 2-10℃ / min, the temperature is 1000-1800℃, and the holding time is 2-10h.

[0019] The present invention also provides an application of the cellulose-based hard carbon anode material prepared by the above-mentioned method in sodium-ion batteries.

[0020] Preferably, in preparing the hard carbon anode sodium-ion battery according to the present invention, the cellulose-based hard carbon negative electrode material is ground into a uniform slurry with the conductive agent acetylene black and the binder sodium carboxymethyl cellulose at a mass ratio of 8:1:1, coated onto copper foil using a coater, and cut into 12mm battery electrode sheets, wherein the active material of the battery electrode sheet has a mass of 1-1.5g / cm³. 2.

[0021] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0022] (1) This invention introduces a large number of carbonyl groups (C=O) into the hard carbon precursor through a competitive mechanism between strong oxidizing acid pretreatment and hydrolysis of long-chain molecular compounds, and constructs a disordered carbon framework rich in closed pores and defect structures. The presence of carbonyl groups provides additional chemisorption sites for sodium ions, while the defect structures and nanopores can shorten the ion transport path and increase the active sites for sodium storage. At the same time, the conjugated structure formed by nitrogen doping stabilizes the electron cloud distribution near the carbonyl groups, reduces the interfacial impedance, and optimizes the electron transport path, enabling the material to exhibit a reversible specific capacity of 369 mAh / g at room temperature (25℃) and 0.1 A / g, with a first-cycle coulombic efficiency of 87.9%, which is significantly improved compared to traditional hard carbon materials, and the capacity retention during cycling is excellent.

[0023] (2) This invention reduces the sodium ion diffusion barrier by optimizing the micro- and nanoporous structure of the material and increasing the interlayer spacing, while the carbonyl functional group retains ion adsorption activity at low temperatures, and nitrogen doping further improves the charge transport dynamics over a wide temperature range. According to experimental data, the material retains 76% of its capacity after 1000 cycles at -25℃ and 1.0 A / g, and shows no capacity decay after 200 cycles at 70℃. The full cell assembled with Na3V2(PO4)3 cathode shows no capacity decay after 100 cycles at an extreme low temperature of -45℃, breaking the performance decay bottleneck of traditional hard carbon in wide temperature range applications and meeting the energy storage requirements under extreme environments.

[0024] (3) This invention uses cellulosic biomass (such as wood flour, bamboo flour, straw powder, etc.) as a precursor. The raw materials are widely available and inexpensive, reducing costs compared to traditional phenolic resin or asphalt precursors, and possessing green and environmentally friendly characteristics. The preparation method combines hydrothermal method with high-temperature pyrolysis, which is simple and controllable. The drying temperature only needs to be 60-100℃, and the pyrolysis temperature can achieve efficient carbonization at 1000-1800℃. The equipment requirements are low, and the energy consumption is controllable, making it suitable for large-scale industrial production. This provides a low-cost and highly reliable technical path for the industrialization of sodium-ion battery anode materials. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1This is a flowchart of a method for preparing a cellulose-based hard carbon anode material according to the present invention;

[0027] Figure 2 This is a SEM image of the cellulose-based hard carbon anode material prepared in Example 1 of the present invention;

[0028] Figure 3 The charge-discharge curve of the cellulose-based hard carbon anode material prepared in Example 1 of the present invention at room temperature (25°C) and a current density of 0.1 A / g is shown.

[0029] Figure 4 The capacity retention rate of the cellulose-based hard carbon anode material prepared in Example 1 of this invention after 1000 cycles at a low temperature of -25°C and a current density of 1.0 A / g.

[0030] Figure 5 The capacity retention rate of the cellulose-based hard carbon anode material prepared in Example 1 of this invention after 200 cycles at a high temperature of 70°C and a current density of 1.0 A / g.

[0031] Figure 6 The full cell assembled with the Na3V2(PO4)3 positive electrode using the cellulose-based hard carbon anode material prepared in Example 1 of this invention under low temperature of -45°C, after 100 cycles, retains its capacity. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0033] like Figure 1 As shown, the present invention provides a method for preparing a cellulose-based hard carbon anode material, comprising the following steps:

[0034] S1. Prepare a strong oxidizing acid solution, add the cellulose raw material to the strong oxidizing acid solution, and stir with ultrasonic vibration to obtain an initial solution;

[0035] S2. Add the long-chain molecular compound to the initial solution and stir until the mixture is homogeneous to obtain a mixed solution;

[0036] S3. The mixed solution is transferred to a hydrothermal reactor for hydrothermal treatment. After the hydrothermal reactor cools to room temperature, the hydrothermal product is centrifuged, washed and dried in sequence.

[0037] S4. The treated hydrothermal products are transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis and carbonization treatment under an inert atmosphere to obtain cellulose-based hard carbon anode material.

[0038] In the above steps, the strong oxidizing acid solution is a sulfuric acid solution or a nitric acid solution with a concentration of 0.2-1.0M; and the cellulose raw material is a cellulose powder or a biological raw material containing cellulose, such as wood powder, bamboo powder, or straw powder, with an added mass of 2-10g. The ultrasonic vibration time is 10min, and the stirring temperature is 60℃.

[0039] In step S2, the stirring temperature is 60°C and the stirring time is 3 hours. The long-chain molecular compound is one or more of polyvinylpyrrolidone, polyethyleneimine, or polydimethyldiallylammonium chloride, and the mass of the long-chain molecular compound is 2-10 g.

[0040] In S3, the hydrothermal treatment temperature is 150-300℃, and the holding time is 12-24h; the hydrothermal product is centrifuged and washed at least 3 times, and the drying temperature is 60-100℃.

[0041] In S4, the inert atmosphere is nitrogen or argon. The heating rate of the high-temperature pyrolysis carbonization treatment is 2-10℃ / min, the temperature is 1000-1800℃, and the holding time is 2-10h.

[0042] The present invention also provides an application of the cellulose-based hard carbon anode material prepared by the above-mentioned method in sodium-ion batteries.

[0043] Specifically, in preparing the hard carbon anode sodium-ion battery according to the present invention, the cellulose-based hard carbon negative electrode material is ground into a uniform slurry with the conductive agent acetylene black and the binder sodium carboxymethyl cellulose at a mass ratio of 8:1:1. This slurry is then coated onto copper foil using a coater and cut into 12mm battery electrode sheets. The active material of the battery electrode sheets has a mass of 1-1.5 g / cm³. 2 .

[0044] To make the above-mentioned features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] Example 1

[0046] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0047] Prepare 60 mL of 0.5 M sulfuric acid solution, add 5 g of cellulose powder to the 0.5 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0048] Add 2.5g of polyvinylpyrrolidone to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0049] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 200°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0050] Finally, the hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a rate of 5℃ / min and held for 3 hours to obtain cellulose-based hard carbon material.

[0051] Example 2

[0052] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0053] Prepare 60 mL of 1.0 M sulfuric acid solution, add 5 g of cellulose powder to the 1.0 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and stir continuously at 60 °C.

[0054] Add 2.5g of polyvinylpyrrolidone to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0055] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 200°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0056] Finally, the hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a rate of 5℃ / min and held for 3 hours to obtain cellulose-based hard carbon material.

[0057] Example 3

[0058] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0059] Prepare 60 mL of 0.5 M sulfuric acid solution, add 2 g of cellulose powder to the 0.5 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0060] Add 1g of polyvinylpyrrolidone to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0061] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 200°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0062] Finally, the hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a rate of 5℃ / min and held for 3 hours to obtain cellulose-based hard carbon material.

[0063] Example 4

[0064] In this embodiment, the preparation method of cellulose-based hard carbon material includes the following steps:

[0065] Prepare 60 mL of 0.5 M sulfuric acid solution, add 10 g of cellulose powder to the 0.5 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0066] Add 5g of polyvinylpyrrolidone to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0067] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 200°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0068] Finally, the hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a rate of 5℃ / min and held for 3 hours to obtain cellulose-based hard carbon material.

[0069] Example 5

[0070] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0071] Prepare 60 mL of 0.5 M nitric acid solution, add 5 g of cellulose powder to the 0.5 M nitric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0072] Add 2.5g of polyvinylpyrrolidone to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0073] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 200°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0074] Finally, the hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a rate of 5℃ / min and held for 3 hours to obtain cellulose-based hard carbon material.

[0075] Example 6

[0076] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0077] Prepare 60 mL of 0.5 M sulfuric acid solution, add 5 g of cellulose powder to the 0.5 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0078] Add 2.5g of polyethyleneimine to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0079] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 200°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0080] Finally, the hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a rate of 5℃ / min and held for 3 hours to obtain cellulose-based hard carbon material.

[0081] Example 7

[0082] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0083] Prepare 60 mL of 0.5 M sulfuric acid solution, add 5 g of cellulose powder to the 0.5 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0084] Add 2.5g of polydimethyldiallylammonium chloride to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0085] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 200°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0086] Finally, the hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a rate of 5℃ / min and held for 3 hours to obtain cellulose-based hard carbon material.

[0087] Example 8

[0088] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0089] Prepare 60 mL of 0.5 M sulfuric acid solution, add 5 g of cellulose powder to the 0.5 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0090] Add 2.5g of polyvinylpyrrolidone to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0091] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 150°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0092] Finally, the hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a rate of 5℃ / min and held for 3 hours to obtain cellulose-based hard carbon material.

[0093] Example 9

[0094] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0095] Prepare 60 mL of 0.5 M sulfuric acid solution, add 5 g of cellulose powder to the 0.5 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0096] Add 2.5g of polyvinylpyrrolidone to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0097] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 250°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0098] Finally, the hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a rate of 5℃ / min and held for 3 hours to obtain cellulose-based hard carbon material.

[0099] Example 10

[0100] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0101] Prepare 60 mL of 0.5 M sulfuric acid solution, add 5 g of cellulose powder to the 0.5 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0102] Add 2.5g of polyvinylpyrrolidone to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0103] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 300°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0104] Finally, the hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a rate of 5℃ / min and held for 3 hours to obtain cellulose-based hard carbon material.

[0105] Example 11

[0106] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0107] Prepare 60 mL of 0.5 M sulfuric acid solution, add 5 g of cellulose powder to the 0.5 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0108] Add 2.5g of polyvinylpyrrolidone to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0109] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 200°C for 10 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0110] Finally, the hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a rate of 5℃ / min and held for 3 hours to obtain cellulose-based hard carbon material.

[0111] Example 12

[0112] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0113] Prepare 60 mL of 0.5 M sulfuric acid solution, add 5 g of cellulose powder to the 0.5 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0114] Add 2.5g of polyvinylpyrrolidone to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0115] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 250°C for 20 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0116] Finally, the hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a rate of 5℃ / min and held for 3 hours to obtain cellulose-based hard carbon material.

[0117] Example 13

[0118] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0119] Prepare 60 mL of 0.5 M sulfuric acid solution, add 5 g of cellulose powder to the 0.5 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0120] Add 2.5g of polyvinylpyrrolidone to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0121] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 200°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0122] Finally, the hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a rate of 2℃ / min and held for 3 hours to obtain cellulose-based hard carbon material.

[0123] Example 14

[0124] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0125] Prepare 60 mL of 0.5 M sulfuric acid solution, add 5 g of cellulose powder to the 0.5 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0126] Add 2.5g of polyvinylpyrrolidone to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0127] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 200°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0128] Finally, the hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a rate of 10℃ / min and held for 3 hours to obtain cellulose-based hard carbon material.

[0129] Example 15

[0130] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0131] Prepare 60 mL of 0.5 M sulfuric acid solution, add 5 g of cellulose powder to the 0.5 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0132] Add 2.5g of polyvinylpyrrolidone to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0133] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 200°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0134] Finally, the treated hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1000℃ at a heating rate of 5℃ / min and held for 3 hours to obtain cellulose-based hard carbon material.

[0135] Example 16

[0136] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0137] Prepare 60 mL of 0.5 M sulfuric acid solution, add 5 g of cellulose powder to the 0.5 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0138] Add 2.5g of polyvinylpyrrolidone to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0139] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 200°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0140] Finally, the hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1800℃ at a rate of 5℃ / min and held for 3 hours to obtain cellulose-based hard carbon material.

[0141] Example 17

[0142] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0143] Prepare 60 mL of 0.5 M sulfuric acid solution, add 5 g of cellulose powder to the 0.5 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0144] Add 2.5g of polyvinylpyrrolidone to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0145] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 200°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0146] Finally, the treated hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a heating rate of 5℃ / min and held for 1 hour to obtain cellulose-based hard carbon material.

[0147] Example 18

[0148] In this embodiment, the preparation method of the cellulose-based hard carbon material includes the following steps:

[0149] Prepare 60 mL of 0.5 M sulfuric acid solution, add 5 g of cellulose powder to the 0.5 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0150] Add 2.5g of polyvinylpyrrolidone to the homogeneous solution formed above, and stir at 60°C for 3 hours to mix the two evenly, thus obtaining a mixed solution.

[0151] The resulting mixed solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 200°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0152] Finally, the processed hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a heating rate of 5℃ / min and held for 5 hours to obtain cellulose-based hard carbon material.

[0153] Comparative Example 1

[0154] In this comparative example, 5g of cellulose powder was transferred to a high-temperature tube furnace without any treatment and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a heating rate of 5℃ / min and held for 3h to obtain the hard carbon material of Comparative Example 1.

[0155] Comparative Example 2

[0156] This comparative example includes the following steps:

[0157] Prepare 60 mL of 0.2 M sulfuric acid solution, add 5 g of cellulose powder to the 0.2 M sulfuric acid solution, sonicate for 10 min to form a homogeneous solution, and continuously stir at 60 °C.

[0158] The homogeneous solution was transferred to a hydrothermal reactor for hydrothermal treatment at a temperature of 200°C for 15 hours. After the reaction was completed and cooled to room temperature, the hydrothermal reaction product was centrifuged and washed at least three times and then dried at 80°C.

[0159] Finally, the treated hydrothermal reaction product was transferred to a high-temperature tube furnace and subjected to high-temperature pyrolysis carbonization under an argon atmosphere. The temperature was increased to 1400℃ at a heating rate of 5℃ / min and held for 5 hours to obtain the hard carbon material of Comparative Example 2.

[0160] Based on Examples 1-18 and Comparative Example 1 provided above, the hard carbon material prepared therefrom was applied to sodium-ion batteries. The prepared hard carbon material was used as the negative electrode active material of sodium-ion batteries to prepare electrode sheets. Sodium-ion coin cells were prepared in an inert atmosphere in a glove box, and the electrochemical performance of the coin cells was tested. The results are shown in Table 1.

[0161] Table 1 Electrochemical performance test results

[0162]

[0163]

[0164] As shown in Table 1, compared with Comparative Examples 1-2, Examples 1-18 exhibit higher reversible capacity and first-cycle coulombic efficiency. This is because acid-catalyzed hydrolysis of cellulose can form a uniform carbon sphere structure with a particle size of 50-500 nm, as shown in Table 1. Figure 2 As shown. This micro / nano structure is beneficial for optimizing pore distribution and increasing the number of closed pores during subsequent high-temperature carbonization, thereby improving sodium ion transport efficiency. On the other hand, cellulose and long-chain macromolecules form a hydrolysis competition mechanism during acid hydrolysis, which may introduce functional groups such as hydroxyl (-OH) and carbonyl (C=O) groups onto the surface of the hard carbon precursor. These functional groups can enhance the reactivity of the material and the adsorption / diffusion capacity of sodium ions, thus having a positive impact on the electrochemical performance of hard carbon materials.

[0165] In addition, refer to Figure 3 The results show that the cellulose-based hard carbon prepared in Example 1 achieved a high reversible capacity of 369 mAh / g and an ultra-high first-cycle coulombic efficiency of 87.9% under a current of 0.1 A / g. Furthermore, to further improve the application prospects of the battery under extreme temperature conditions (-45°C to 70°C), high and low temperature tests were conducted on the sodium-ion battery assembled from the cellulose-based hard carbon material. The results are as follows... Figure 4 and Figure 5As shown, under the low-temperature test condition of -45℃, the capacity retention rate of the cellulose-based hard carbon sodium-ion battery reached 76% after 1000 cycles. Under the low-temperature test condition of 70℃, the cellulose-based hard carbon sodium-ion battery showed no capacity decay after 200 cycles. This result fully demonstrates the adaptability of cellulose-based hard carbon under high and low temperature conditions. The optimized micro-nanoporous structure and large interlayer spacing of cellulose-based hard carbon reduce the diffusion barrier of sodium ions. At the same time, the large number of carbonyl functional groups introduced by the hydrolysis competition mechanism can still maintain activity at low temperatures, promoting ion intercalation kinetics. These advantages make cellulose-based hard carbon materials an ideal anode candidate for sodium-ion batteries under extreme temperature environments, especially showing significant potential in low-temperature capacity retention and high-temperature cycling stability. To further verify its commercial application prospects, the cellulose-based hard carbon anode was assembled with sodium vanadium phosphate (Na3V2(PO4)3) cathode to form a full cell, and tested under the extreme low-temperature test condition of -45℃. The results are shown below. Figure 6 As shown, the capacity retention rate is as high as 100% after 95 cycles, which proves the excellent electrochemical performance of cellulose-based hard carbon anode materials and has significant advantages in application scenarios with stringent environmental adaptability requirements.

[0166] Therefore, by adopting the above-mentioned method for preparing and applying a cellulose-based hard carbon anode material, a hard carbon precursor containing a large number of carbonyl groups and nitrogen doping is constructed through a hydrolysis competition mechanism, and then the hard carbon anode material is prepared by high-temperature pyrolysis carbonization. This solves the problems of low reversible capacity, poor first-cycle coulombic efficiency, and battery performance optimization under extreme high and low temperature conditions of biomass-derived hard carbon.

[0167] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0168] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preparing a cellulose-based hard carbon negative electrode material, characterized by, It comprises the following steps: S1, configure a strong oxidizing acid solution, and add a cellulose raw material into the strong oxidizing acid solution, ultrasonic vibration, and stir to obtain an initial solution; S2, add a long-chain molecular compound into the initial solution, and stir until mixed evenly to obtain a mixed solution; The long-chain molecular compound is one or more of polyvinylpyrrolidone, polyethyleneimine or polydimethyl diallyl ammonium chloride; S3, transfer the mixed solution into a hydrothermal reaction kettle for hydrothermal treatment, and after the hydrothermal reaction kettle is cooled to room temperature, centrifuge, wash and dry the hydrothermal product in sequence; S4, transfer the treated hydrothermal product into a high-temperature tube furnace, and perform high-temperature pyrolysis carbonization treatment under an inert atmosphere to obtain a cellulose-based hard carbon negative electrode material.

2. The method for preparing a cellulose-based hard carbon anode material according to claim 1, characterized in that, In S1, the strong oxidizing acid solution is a sulfuric acid solution or a nitric acid solution, and the concentration is 0.2-1.0M; the cellulose raw material is cellulose powder or cellulose-containing biological raw materials such as wood powder, bamboo powder and straw powder, and the added mass of the cellulose raw material is 2-10g.

3. The method for preparing a cellulose-based hard carbon anode material according to claim 1, characterized in that, In S1, the ultrasonic vibration time is 10min, and the stirring temperature is 60℃; in S2, the stirring temperature is 60℃, and the stirring time is 3h.

4. The method for preparing a cellulose-based hard carbon anode material according to claim 1, characterized in that, In S2, the mass of the long-chain molecular compound is 2-10g.

5. The method for preparing a cellulose-based hard carbon anode material according to claim 1, characterized in that, In S3, the temperature of the hydrothermal treatment is 150-300℃, and the holding time is 12-24h.

6. The method for preparing a cellulose-based hard carbon anode material according to claim 1, characterized in that, In S3, the hydrothermal product is centrifuged and washed for no less than 3 times, and the drying temperature is 60-100℃.

7. The method for preparing a cellulose-based hard carbon anode material according to claim 1, characterized in that, In S4, the inert atmosphere is nitrogen or argon.

8. The method for preparing a cellulose-based hard carbon anode material according to claim 1, characterized in that, In S4, the temperature rising rate of the high-temperature pyrolysis carbonization treatment is 2-10℃ / min, the temperature is 1000-1800℃, and the holding time is 2-10h.

9. The application of a cellulose-based hard carbon negative electrode material prepared by the preparation method of the cellulose-based hard carbon negative electrode material according to any one of claims 1-8 in a sodium ion battery.

10. The application of the cellulose-based hard carbon anode material prepared by the preparation method of claim 9 in a sodium ion battery, characterized in that, In the preparation of the hard carbon anode sodium ion battery, the cellulose-based hard carbon negative electrode material is ground into a uniform slurry with a mass ratio of 8:1:1 of conductive agent acetylene black, binder sodium carboxymethyl cellulose, coated on a copper foil by a coater, cut into 12 mm battery pole pieces, and the battery pole piece active material mass is 1-1.5 g / cm 2 .

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