Preparation method of lignite-derived hard carbon negative electrode material for sodium ion battery

Abstract

The application discloses a preparation method of a lignite-derived hard carbon negative material of a sodium ion battery, and the method comprises the following steps: step (1), lignite powder is sequentially washed by deionized water and anhydrous ethanol through ultrasonic washing, and after the ultrasonic washing is completed, the lignite powder is dried and crushed to obtain a lignite precursor powder; step (2), the lignite precursor powder is placed in a microwave reaction kettle, a sulfuric acid solution is added for microwave reaction, and the lignite precursor powder is taken out, cooled to room temperature, filtered, washed and dried; step (3), the material treated in step (2) is placed in a tube furnace, and high-temperature pyrolysis is carried out in a protective atmosphere, and the tube furnace is cooled to room temperature to obtain the lignite-derived hard carbon negative material. The method modifies the lignite through microwave assistance and chemical treatment, and controls the hard carbon structure, so that the sodium ion battery negative material with excellent electrochemical performance is obtained, and the prepared hard carbon material has high specific capacity and excellent rate performance as the sodium ion battery negative electrode.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion secondary batteries and relates to a method for preparing lignite-based hard carbon material and its application in the negative electrode of sodium-ion batteries. Background Technology

[0002] Sodium-ion batteries possess excellent low-temperature performance and safety, making them the most promising next-generation energy storage battery. Under current conditions, due to the relative scarcity of lithium resources, developing next-generation energy storage batteries has become a crucial strategy. Sodium, with its high abundance, widespread global distribution, and low price, along with similar physicochemical properties to lithium, has become the most promising new rechargeable battery energy storage technology for large-scale energy storage systems. However, compared to lithium ions, sodium ions, due to their larger ionic radius, cannot form a stable thermodynamic structure in graphite, and therefore cannot use graphite as the negative electrode like lithium ions. Thus, a larger interlayer spacing is required for reversible sodium ion storage. Hard carbon, as a difficult-to-graphitize carbon material, has a large interlayer spacing exceeding 0.37 nm, making it the most ideal material for the negative electrode of sodium-ion batteries.

[0003] Currently reported biomass hard carbon materials generally include coconut shells, starch, straw powder, and resin-based materials. However, these biomass-derived hard carbons all exhibit low coulombic efficiency, poor cycle stability, and rate performance. Resin-based materials, in particular, are limited in development due to their high cost and environmental pollution. Lignite, as a low-rank coal, is abundant, inexpensive, and has a high carbon content, but its direct carbonization easily produces partially graphitized structures, which are unfavorable for sodium ion storage. Conventional processing methods involve complex procedures, further increasing its production costs. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing high-capacity, high-rate, low-cost, and environmentally friendly lignite-derived hard carbon anode materials for sodium-ion batteries. This method modifies lignite through microwave-assisted chemical treatment, controlling the hard carbon structure to obtain a sodium-ion battery anode material with excellent electrochemical performance. The prepared hard carbon material, as a sodium-ion battery anode, exhibits high specific capacity and excellent rate performance. The microwave-assisted chemical treatment method of this invention can efficiently and rapidly pretreat precursor materials, enabling controllable adjustment of the content of fixed carbon, volatile matter, ash, and other components in lignite, significantly shortening preparation time, reducing costs, and improving material consistency. Furthermore, the wide distribution, ease of collection, and extremely low cost of lignite also give it excellent development potential.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for preparing a lignite-derived hard carbon anode material for sodium-ion batteries involves first pretreating the lignite to remove surface impurities; then, a one-step carbonization method using microwave-assisted chemical treatment is employed to obtain a lignite-based hard carbon anode material with good electrochemical performance. The method specifically includes the following steps:

[0007] Step (1) The lignite powder is ultrasonically washed with deionized water and anhydrous ethanol for 0.5-2 h to remove impurities from the surface of the material. After ultrasonic washing, it is dried in a forced-air drying oven. The dried lignite is crushed in a crusher to obtain lignite precursor powder. The ultrasonic washing time is 0.5-2 h; the drying temperature is 60-80℃ and the time is 6-12 h.

[0008] Step (2) Place the lignite precursor powder in a microwave reactor, add sulfuric acid solution for microwave reaction, remove and cool to room temperature, filter, wash and dry. The solid-liquid ratio of lignite precursor powder to sulfuric acid solution is 1:15~1:30, the lignite precursor powder is sieved through a 30~50 mesh sieve, the concentration of sulfuric acid solution is 0.5~2.0 mol / L, preferably 1.0~1.5 mol / L; the microwave reaction temperature is 120~200℃, preferably 160~180℃, and the time is 5~30 min, preferably 10~20 min. The sulfuric acid solution is prepared by the following steps: add deionized water to a volumetric flask, add 98% concentrated sulfuric acid to the volumetric flask, and make up to volume to obtain a sulfuric acid solution with a concentration of 0.5~2.0 mol / L. Let it cool to room temperature before use.

[0009] Step (3) The material processed in step (2) is placed in a tube furnace and subjected to high-temperature pyrolysis in a protective atmosphere using a graphite crucible as the support. After the tube furnace cools to room temperature, a lignite-derived hard carbon anode material with a reasonable graphitized structure after composition control is obtained. The protective gas is nitrogen or argon. The high-temperature pyrolysis temperature is 1200~1500℃, the time is 2~4 h, and the heating rate is 5~10℃ / min below 1000℃ and 3~8℃ / min above 1000℃. By controllably adjusting the carbon source composition of the precursor, the lignite-derived hard carbon anode material is obtained. The 002 interlayer spacing is calculated to be 0.375~0.395 nm by Bragg equation, which allows for reversible insertion and extraction of sodium ions. Furthermore, Raman spectroscopy is used to determine the I of the lignite-derived hard carbon anode material. D / I G It has a value of 1.6 to 1.9, and possesses a reasonable graphitized structure.

[0010] Application of a lignite-derived hard carbon anode material prepared by the above method in the anode of sodium-ion batteries.

[0011] Compared with the prior art, the present invention has the following advantages:

[0012] 1. This invention uses a microwave-assisted chemical treatment combined with a one-step carbonization method to modify lignite, which has a short reaction time and yields lignite-derived hard carbon materials with good electrochemical performance.

[0013] 2. This invention uses natural lignite as raw material, which is inexpensive and readily available, low in cost, simple and easy to implement, and highly efficient in preparation. Furthermore, it requires no templates or surfactants, enabling the high-value comprehensive utilization of low-rank coal resources. It solves the problems of high price and environmental pollution associated with traditional carbon material preparation methods, and has significant research value.

[0014] 3. The sodium-ion battery anode material prepared by this invention effectively reduces the specific surface area, increases the curvature of the carbon layer, increases the disorder of the material, and forms more closed pore structures and reversible sites, which is beneficial to the insertion and extraction of sodium ions.

[0015] 4. The half-cell assembled from the hard carbon material prepared in this invention has a high specific capacity. The maximum specific capacity can reach 330~350 mAh / g at a current density of 20 mA / g. After 2000 cycles at a current density of 1 A / g, the average coulombic efficiency is above 99.5% and the capacity retention is >88%. Attached Figure Description

[0016] Figure 1 The data represents the charge-discharge curves of lignite-based hard carbon structures as anode materials for sodium-ion batteries, regulated by different microwave reaction times, at current densities of 0–2.5 V and 20 mA / g.

[0017] Figure 2 The data represents the charge-discharge curves of lignite-based hard carbon structures used as anode materials for sodium-ion batteries, with different sulfuric acid concentrations, under current densities ranging from 0 to 2.5 V and 20 mA / g.

[0018] Figure 3 This is a transmission electron microscope (TEM) image of a lignite-based hard carbon anode material for sodium-ion batteries, prepared by microwave 1 M sulfuric acid solution for 10 min. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0020] Example 1:

[0021] This embodiment provides a method for preparing high-performance sodium-ion battery energy storage materials by regulating the hard carbon structure through microwave-assisted chemical treatment. The method includes the following steps:

[0022] Step S1: Soak 2.5 g of lignite precursor (raw lignite, crushed to 30-50 mesh before use) in 50 mL of 1.2 mol / L sulfuric acid solution and place it in a microwave reactor to react for 15 min.

[0023] Step S2: The material obtained in step S1 is supported in a graphite crucible and carbonized at 1400℃ for 3 h under a nitrogen atmosphere to obtain a lignite-based hard carbon material regulated by microwave-assisted chemical treatment.

[0024] Step S3: After thoroughly grinding the carbonized powder, mix it with hard carbon, conductive carbon black, and sodium carboxymethyl cellulose in a mass ratio of 80:10:10. Grind the mixture thoroughly in a mortar, then add an appropriate amount of deionized water using a pipette and grind again until homogeneous, obtaining a uniform slurry. Coat the slurry onto aluminum foil and dry it in a 90℃ vacuum drying oven for 12 hours until the solvent is completely evaporated. Then, use a cutting machine (MSK-T10) to cut it into circular electrode sheets with a diameter of 10 mm. After weighing, the mass of the active material is calculated to be 0.8~0.9 mg.

[0025] Electrochemical performance testing of the microwave-assisted combined chemically treated lignite-based hard carbon material prepared in this embodiment:

[0026] A C2032 coin cell was assembled using metallic sodium as the counter electrode, 1 mol / L NaPF6 (DEGDME) as the electrolyte, and glass fiber (GF / C) as the separator, within a glove box filled with argon (Ar) gas. Charge-discharge performance was tested using a battery testing system from Shenzhen Xinwei Electronics Co., Ltd.

[0027] Example 2:

[0028] The difference between this embodiment and Embodiment 1 is that the concentration of the sulfuric acid solution is 0.5 mol / L.

[0029] Example 3:

[0030] The difference between this embodiment and Example 1 is that the concentration of the sulfuric acid solution is 1.0 mol / L.

[0031] Example 4:

[0032] The difference between this embodiment and Embodiment 1 is that the concentration of the sulfuric acid solution is 1.5 mol / L.

[0033] Example 5:

[0034] The difference between this embodiment and embodiments 1-4 is that the microwave reaction time is 15 minutes.

[0035] Example 5:

[0036] The difference between this embodiment and embodiments 1-4 is that the microwave reaction time is 5 minutes.

[0037] Example 6:

[0038] The difference between this embodiment and embodiments 1-4 is that the microwave reaction time is 10 minutes.

[0039] Example 7:

[0040] The difference between this embodiment and embodiments 1-4 is that the microwave reaction time is 20 minutes.

[0041] Figure 1 The figures show the charge-discharge curves of lignite-based hard carbon structures used as anode materials in sodium-ion batteries at current densities of 20 mA / g and varying microwave reaction times. Figure 1 As can be seen, the first coulombic efficiency of the prepared coal-based hard carbon material is ≥85%, and the first-cycle reversible specific capacity is ≥300 mAh / g.

[0042] Figure 2 These are the charge-discharge curves of lignite-based hard carbon structures used as anode materials in sodium-ion batteries, adjusted by varying sulfuric acid concentrations, at current densities of 0–2.5 V and 20 mA / g. Figure 2 It can be seen that the prepared coal-based hard carbon material has a first coulombic efficiency of up to ≥85% and a first-cycle reversible specific capacity of up to ≥310 mAh / g.

[0043] Figure 3 Transmission electron microscopy (TEM) image of a lignite-based hard carbon anode material for sodium-ion batteries, prepared by microwave 1 M sulfuric acid solution for 10 min. Figure 3 As shown, the material exhibits a typical amorphous structure, composed of randomly stacked graphite microcrystals, rich in defects and closed pores. Its carbon interlayer spacing, measured to be approximately 0.395 nm, combined with the abundant microstructure, provides numerous active sites for the reversible storage of sodium ions.

Claims

1. A method for preparing a lignite-derived hard carbon anode material for sodium-ion batteries, characterized in that... The method includes the following steps: Step (1) The lignite powder is ultrasonically washed with deionized water and anhydrous ethanol respectively. After ultrasonic washing is completed, it is dried and crushed to obtain lignite precursor powder. Step (2) Place the lignite precursor powder in a microwave reactor, add sulfuric acid solution for microwave reaction, remove and cool to room temperature, filter, wash and dry; Step (3) Place the material processed in step (2) into a tubular furnace and perform high-temperature pyrolysis in a protective atmosphere. After the tubular furnace cools to room temperature, lignite-derived hard carbon anode material is obtained.

2. The method for preparing the lignite-derived hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that... In step (1), the ultrasonic washing time is 0.5~2 h.

3. The method for preparing the lignite-derived hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that... In step (1), the drying temperature is 60~80℃ and the time is 6~12 h.

4. The method for preparing the lignite-derived hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that... In step (2), the solid-liquid ratio of lignite precursor powder to sulfuric acid solution is 1:15 to 1:30, the lignite precursor powder is sieved through a 30 to 50 mesh sieve, and the concentration of sulfuric acid solution is 0.5 to 2.0 mol / L; the temperature of the microwave reaction is 120 to 200℃, and the time is 5 to 30 min.

5. The method for preparing the lignite-derived hard carbon anode material for sodium-ion batteries according to claim 4, characterized in that... The concentration of the sulfuric acid solution is 1.0~1.5 mol / L, the microwave reaction temperature is 160~180℃, and the time is 10~20 min.

6. The method for preparing the lignite-derived hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that... In step (3), the protective gas is nitrogen or argon.

7. The method for preparing the lignite-derived hard carbon anode material for sodium-ion batteries according to claim 1, characterized in that... In step (3), the temperature of high-temperature pyrolysis is 1200~1500℃, the time is 2~4 h, the heating rate is 5~10℃ / min below 1000℃, and 3~8℃ / min above 1000℃.

8. A lignite-derived hard carbon anode material prepared by the method of any one of claims 1-7.

9. The application of a lignite-derived hard carbon anode material prepared by the method of any one of claims 1-7 in a sodium-ion battery anode.

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