Silicon-coated coal-based porous carbon composite material, method and application of silicon-coated coal-based porous carbon composite material as negative electrode of sodium-ion battery

Abstract

The invention discloses a silicon-coated coal-based porous carbon composite material, a method and application of the silicon-coated coal-based porous carbon composite material as a negative electrode of a sodium-ion battery. The method comprises the following steps: 1, selecting gasified slag and putting into a hydrochloric acid solution for acid leaching; stirring is performed; 2, pouring the uniformly mixed solution into a suction filtration device, separating, and drying in a drying oven to obtain a sample; step 3, adding the dried sample into an HF solution for secondary acid leaching; stirring is performed; performing separation; repeatedly washing the solid with deionized water until the solid is neutral; placing the solid which is washed to be neutral in a drying oven for drying; step 4, putting the finally dried sample into a tubular furnace; carrying out activating treatment in a tubular furnace in a carbon dioxide atmosphere; and preparing the silicon-coated coal-based porous carbon composite material by a CVD (Chemical Vapor Deposition) method under the conditions of argon shielding gas and reducing atmosphere of hydrogen. The method has the advantages of raw material greenization and cost, and has the characteristics of porous structure regulation and improvement of silicon-carbon synergistic effect to relieve volume expansion.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of negative electrode materials, and particularly relates to a silicon-coated coal-based porous carbon composite material and method and application as a negative electrode of a sodium ion battery. BACKGROUND

[0002] In recent years, lithium ion batteries (LIBs) have gradually become one of the most popular power sources to replace traditional fossil fuels. Due to their long service life, high energy density and light weight, lithium ion batteries have been used in various devices in daily life, such as electric vehicles and portable devices, including mobile phones, laptops and electric tools. However, LIBs still have their own shortcomings in the entire development process, the global lithium resources are limited, the cost of lithium batteries has increased significantly in recent years, and in addition, safety problems of lithium batteries occur frequently. For this reason, sodium ion batteries (SIBs) with advantages such as abundant reserves and low cost, high safety, etc. have received high attention from the industry and academia, and are considered to be an ideal candidate for the next generation of large-scale energy storage batteries.

[0003] Although sodium and lithium are similar in chemistry, there are still fundamental differences between the two alkali metal ions. For example, Na ions are larger and heavier than Li ions, resulting in poor diffusion dynamics and poor mass / volume capacity in most host materials. The electronegativity of sodium (0.93) is lower than that of lithium (0.98), and the redox potential of Na + is 0.33 V higher than that of Li + , which reduces the working voltage and energy density, but this does not easily cause decomposition of the electrolyte, improving the safety and long-term stability of the battery. In addition, unlike lithium ions that react with aluminum to form alloys, sodium ions do not react with aluminum, so aluminum can be used as the current collector of sodium ion batteries, instead of the heavier and more expensive copper current collector, which will further reduce the total cost of sodium ion batteries by about 20%.

[0004] Currently, sodium ion battery technology is still in the early stages of development, such as ZHONG S Y, LIU H Z, WEID H, et al. Long-aspect-ratio n-rich carbon nanotubes as anode material for sodium and lithium ion batteries [J]. Chemical Engineering Journal, 2020, 395:125054;

[0005] YING H J, HAN W-Q, et al. Metallic Sn-Based Anode Materials: Application in High-Performance Lithium-Ion and Sodium-Ion Batteries [J]. Advanced Science, 2017, 11: 1700298.

[0006] The challenges faced by the above prior art include small interlayer spacing of graphite that cannot accommodate sodium ions with large ionic radius, severe volume expansion, and low energy density. It is well known that electrode materials are the core components that determine the performance of batteries. Therefore, developing electrode materials with excellent rate performance, long cycle stability, high coulombic efficiency, and high specific capacity is one of the focuses of sodium-ion battery research. SUMMARY

[0007] In order to overcome the problems existing in the above prior art, the purpose of the present application is to provide a silicon-coated coal-based porous carbon composite material and method and application as a negative electrode of a sodium-ion battery, which has the characteristics of green raw materials, cost advantage, porous structure regulation, and increase of silicon-carbon synergistic effect to alleviate volume expansion

[0008] In order to achieve the above purpose, the technical scheme adopted by the present application is:

[0009] A silicon-coated coal-based porous carbon composite material preparation method, comprising the following steps:

[0010] Step 1: Select the gasification slag and put it into a hydrochloric acid solution for acid leaching; stir the acid leached solution on a magnetic stirrer to make it uniform;

[0011] Step 2: Then pour the solution into a filtration device, and the solid is deposited on the filter membrane to separate the solution; wash repeatedly with deionized water to make it neutral; then place it in an oven to dry;

[0012] Step 3: Add the dried sample to the HF solution for secondary acid leaching; stir the solution on a magnetic stirrer; then pour the solution into a filtration device, and the solid is deposited on the filter membrane to separate the solution; wash repeatedly with deionized water to make it neutral; place it in an oven to dry;

[0013] Step 4: Put the finally dried sample into a tube furnace; activate the sample in a tube furnace with a carbon dioxide atmosphere; prepare a silicon-coated coal-based porous carbon composite material by CVD method under the conditions of argon protection gas and hydrogen reducing atmosphere.

[0014] Select 2-4 g of gasification slag and put it into (~ 5 mol L -1) hydrochloric acid solution, (300-400 r / min) stirring 4-6 h.

[0015] In step 2, the solid with a particle size of 50-200 μm is selected by a filter membrane, and the filter membrane has a pore size of 0.45 μm and is resistant to strong acid environment with a pH of 0-2.

[0016] In step 2, the solid is dried in an oven at 60-80 °C.

[0017] In step 3, the HF solution is about 10 wt%, and (300-400) r / min stirring is performed for 4-6 h.

[0018] In step 3, the solid with a particle size of 50-200 μm is selected by a filter membrane, and the filter membrane has a pore size of 0.45 μm and is resistant to strong acid environment with a pH of 0-2.

[0019] In step 4, the temperature is increased to 700-900 °C at a rate of 5 °C / min. -1 The temperature is kept at 700-900 °C for 3-4 h.

[0020] The argon gas flow is set to 0.8 L / min. -1 The hydrogen gas flow is set to 0.1 L / min. -1 The sample is kept at 700-900 °C for 30-60 min for silicon deposition, and then cooled to room temperature in an argon atmosphere.

[0021] A silicon-coated coal-based porous carbon composite material has a yolk-shell structure, in which coal-based porous carbon gasification slag serves as the yolk, and silicon-based material serves as the shell to form a core-shell structure. The silicon material is deposited on the surface of the coal-based material to obtain a multi-layer composite material with a coal-based material as the core and silicon as the surface layer. The deposited silicon material has a specific structure that alleviates material failure caused by charging and discharging. The Si-C chemical bond and gradient pore structure enhance charge transport, alleviate volume effect, and accelerate the diffusion of sodium ions. At the same time, the composite material constructed by silicon and carbon avoids the low conductivity caused by single silicon, which limits the overall performance of the battery. Silicon stores sodium ions through reversible alloying reaction, and the reaction formula is:

[0022] The silicon layer provides high specific capacity, and the porous carbon matrix buffers the volume expansion of silicon through hierarchical pores (micropores + mesopores) and elastic structure. Silicon exists in a crystalline state on the surface of coal-based porous carbon. The pore structure of the carrier provides sites for silicon deposition, and the silicon and the coal-based porous carbon surface form a tight interfacial bond.

[0023] The silicon-coated coal-based porous carbon composite material is applied to a sodium ion battery negative electrode, and is suitable for large-scale energy storage systems, low-speed electric vehicles and portable electronic equipment fields.

[0024] The beneficial effects of the present application are:

[0025] The metal compound impurities in the gasification slag are intertwined with each other to form a complex structure. In the present application, the two pickling methods of hydrochloric acid and hydrofluoric acid can produce a synergistic effect to selectively dissolve and remove various metal compounds in the gasification slag. This combined pickling method can more comprehensively and efficiently remove impurities in the gasification slag, and has obvious advantages and innovation compared with single pickling agent or other conventional pickling methods.

[0026] Through CO2 activation, the advantages of low pollution and greenhouse gas utilization can be achieved in the environment. Compared with chemical reagent activation such as KOH and NaOH, harmful chemical substances are not introduced. In terms of material structure, CO2 activation often has a more uniform pore structure, while chemical reagent activation is more violent and may result in different pore sizes. Therefore, the CO2 activation method is a new way to prepare new carbon materials.

[0027] The present application uses solid waste (gasification slag) generated during the coal gasification process as raw material to prepare a deposited carrier; through a carbon dioxide activation process, the porosity and specific surface area are greatly improved;

[0028] Through chemical vapor deposition (CVD) technology, a silicon layer is deposited on the surface of the coal-based porous carbon to form a silicon-carbon composite material with a yolk-shell structure. The silicon layer provides high specific capacity, while the porous carbon matrix buffers the volume expansion of silicon (expansion rate from 300% to <50%) through hierarchical pores (micropores + mesopores) and elastic structure, and enhances the electrical conductivity. The diffraction peaks of the present application correspond to the crystal structure of silicon, indicating that silicon exists in a crystalline state on the surface of the coal-based porous carbon; the pore structure of the carrier provides sites for the deposition of silicon, allowing it to form a tight interfacial bond with the coal-based porous carbon surface. This structural design significantly improves the electrochemical performance of the composite material.

[0029] The present application improves the overall electrochemical performance of the composite material, and the Si-C composite material after compounding has a first discharge capacity of 422.47mA h g -1 at a current density of 0.05A·g -1 , a charge capacity of 259mA h g -1 , and a corresponding first coulombic efficiency of 62.2%. After 100 cycles, it still maintains a capacity of 249mAh·g -1 , and the corresponding capacity retention rate is 97%, which is attributed to the stability of the silicon-carbon interface and the structural support of the porous carbon, showing excellent cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 X-ray diffraction characterization graph of the silicon-coated coal-based porous carbon composite negative electrode material.

[0031] Figure 2 Cycle efficiency graph of the silicon-coated coal-based porous carbon composite negative electrode material in its electrochemical performance.

[0032] Figure 3 SEM graph of the Si-C composite negative electrode material provided for Example 1 at 20,000 times.

[0033] Figure 4 SEM graph of the Si-C composite negative electrode material provided for Example 2 at 20,000 times.

[0034] Figure 5 SEM graph of the Si-C composite negative electrode material provided for Example 3 at 10,000 times.

[0035] Figure 6 Charge-discharge curve graph of the Si-C composite negative electrode material provided for Example 1.

[0036] Figure 7 Charge-discharge curve graph of the Si-C composite negative electrode material provided for Example 2.

[0037] Figure 8 Charge-discharge curve graph of the Si-C composite negative electrode material provided for Example 3. DETAILED DESCRIPTION

[0038] The application will be further described in detail below with reference to the accompanying drawings.

[0039] The application provides a preparation method of a silicon-coated coal-based porous composite negative electrode material, comprising the following steps:

[0040] Example 1:

[0041] 4g of gasification slag was weighed and placed into a mixed solution of 18ml of 36% HCL and 22ml of H2O for acid leaching, and was stirred on a magnetic stirrer at 350r / min for 4h, and then the solid was separated from the solution by suction filtration, and was washed with distilled water to be neutral, and was placed in an oven at 60℃ for 12h for drying. Subsequently, the dried sample was placed into a mixed solution of 10ml of 40% HF and 30ml of H2O for secondary acid leaching, and was stirred on a magnetic stirrer at 350r / min for 4h, and then the solid was separated from the solution by suction filtration, and was washed with distilled water to be neutral, and was placed in an oven at 60℃ for 12h for drying.

[0042] The second dried sample was placed in an activation tube and the activation tube was placed in a tube furnace for activation treatment. The tube furnace was vacuumed by a vacuum pump and then filled with nitrogen to normal pressure, which was repeated for 3 times. The parameters of nitrogen flow rate and heating rate were set as 60 ml·min -1 and 5 ℃·min -1 , respectively. The temperature was raised to the set value of 700 ℃. After the temperature reached the set value, the nitrogen was switched to carbon dioxide gas, and the flow rate was adjusted to the set value of 100 ml·min -1 . The sample was kept in the carbon dioxide atmosphere for 3 h, and then cooled to room temperature with the furnace.

[0043] The activated sample was placed in a special jig and placed in a tube furnace. Under the condition of argon protection gas, the temperature was raised from room temperature to 700 ℃ at a rate of 5 ℃ / min per minute. When the temperature reached 700 ℃, the gas path was changed, the argon flow rate of the main gas path was set to 0.8 L / min, the hydrogen flow rate of the branch gas was set to 0.2 L / min, and the nitrogen flow rate of the carrier gas was set to 0.1 L / min. Under these conditions, the sample was kept at 700 ℃ for silicon deposition, and kept for 30 minutes. The sample was cooled to room temperature in an argon atmosphere to obtain a Si / C composite material with core-shell structure. As Figure 3 It can be seen from the SEM image that the surface is rough and uneven at this temperature, and the silicon film is not completely coated on the surface of the substrate. The electrochemical performance is as shown in Figure 6 , the first discharge capacity at a current density of 0.05 A·g -1 was 403.62 mAh g -1 , and the charge capacity was 245 mAh g -1 , corresponding to a first coulombic efficiency of 60.8%.

[0044] Example 2:

[0045] 4 g of gasified slag was weighed and placed in a mixed solution of 20 ml of 36% HCL and 20 ml of H2O for acid leaching. After stirring for 4 h on a magnetic stirrer at 350 r / min, the solid was separated from the solution by suction filtration, washed with distilled water to neutralize, and placed in an oven at 60 ℃ for 12 h for drying. Subsequently, the dried sample was placed in a mixed solution of 12 ml of 40% HF and 28 ml of H2O for secondary acid leaching. After stirring for 4 h on a magnetic stirrer at 350 r / min, the solid was separated from the solution by suction filtration, washed with distilled water to neutralize, and placed in an oven at 60 ℃ for 12 h for drying.

[0046] The second dried sample was placed in an activation tube and the activation tube was placed in a tube furnace for activation treatment. The tube furnace was vacuumed by a vacuum pump and then filled with nitrogen to normal pressure, which was repeated for 3 times. The parameters of nitrogen flow rate and heating rate were set as 60 ml·min -1and 5℃·min -1 Heat the gas to the set temperature of 800℃. Once the temperature reaches the set value, switch the nitrogen gas to carbon dioxide gas and adjust the flow rate to the set value of 100 ml / min. -1 It was kept at a temperature of 3 hours in a carbon dioxide atmosphere, and then cooled to room temperature with the furnace.

[0047] The activated sample was placed in a specific fixture and then placed in a tube furnace. Under an argon protective gas atmosphere, the temperature was increased from room temperature to 800°C at a rate of 5°C / min. Upon reaching 800°C, the temperature was held for 10 min, and the gas path was changed. The argon flow rate in the main gas path was set to 0.8 L / min, the hydrogen flow rate in the branch gas path was set to 0.2 L / min, and the nitrogen flow rate in the carrier gas path was set to 0.1 L / min. Under these conditions, the sample was held at 800°C for silicon deposition, held for 30 minutes, and then cooled to room temperature in an argon atmosphere to obtain a Si / C composite material with a core-shell structure. Figure 4 As shown in the SEM image, free silicon forms nuclei at substrate defect sites and deposits on the substrate surface in a uniform nucleation manner. Electrochemical performance is as follows... Figure 7 As shown, 0.05 A·g -1 The initial discharge capacity at the current density is 422.47 mAh g. -1 The charging capacity is 259mA hg -1 The corresponding initial Coulomb efficiency is 62.2%.

[0048] Example 3:

[0049] Weigh 4g of gasification residue and place it in a mixed solution of 22ml of 36% HCl and 18ml of H2O for acid leaching. Stir on a magnetic stirrer at 350r / min for 4h, then separate the solid from the solution by vacuum filtration. Wash with distilled water until neutral, and dry in an oven at 60℃ for 12h. Subsequently, place the dried sample in a mixed solution of 14ml of 40% HF and 26ml of H2O for a second acid leaching. Stir on a magnetic stirrer at 350r / min for 4h, then separate the solid from the solution by vacuum filtration. Wash with distilled water until neutral, and dry in an oven at 60℃ for 12h.

[0050] After the second drying, the sample was placed in an activation tube, which was then placed in a tube furnace for activation. The tube furnace was evacuated using a vacuum pump, and nitrogen gas was introduced until atmospheric pressure was reached; this process was repeated three times. The nitrogen flow rate and heating rate were set to 60 ml / min. -1 and 5℃·min -1 Heat to the set temperature of 900℃. Once the temperature reaches the set value, switch from nitrogen to carbon dioxide gas and adjust the flow rate to the set value of 100 ml / min. -1It was kept at a temperature of 4 hours in a carbon dioxide atmosphere, and then cooled to room temperature with the furnace.

[0051] The activated sample was placed in a specific fixture and then placed in a tube furnace. Under an argon protective gas atmosphere, the temperature was increased from room temperature to 900°C at a rate of 5°C / min. Upon reaching 900°C, the temperature was held for 10 min, and the gas path was changed. The argon flow rate in the main gas path was set to 0.8 L / min, the hydrogen flow rate in the branch gas path was set to 0.2 L / min, and the nitrogen flow rate in the carrier gas path was set to 0.1 L / min. Under these conditions, the sample was held at 900°C for silicon deposition, held for 40 minutes, and then cooled to room temperature in an argon atmosphere to obtain a Si / C composite material with a core-shell structure. Figure 5 As shown in the SEM image, the surface is composed of numerous aggregated silicon particles, resulting in an uneven distribution. Electrochemical performance is as follows... Figure 8 As shown, 0.05 A·g -1 The initial discharge capacity at the current density is 400.47 mA hg. -1 The charging capacity is 244mA hg -1 The corresponding initial Coulomb efficiency is 61%.

[0052] Figure 1 The characterization pattern of the silicon-coated coal-based porous carbon composite anode material by X-ray diffraction shows a carbon peak at ≈24deg and a band at ≈43deg, which may be attributed to the reflection of the graphite-like material at (002) and (101). The diffraction peaks at its crystal planes (110), (220), and (311) correspond to the crystal structure of silicon, indicating that silicon exists in a crystalline form on the surface of the coal-based porous carbon.

[0053] Figure 2 The graph shows the cycle efficiency of the silicon-coated coal-based porous carbon composite anode material at 0.05 A·g. -1 The initial discharge capacity at the current density is 422.47 mAh g. -1 The charging capacity is 259mAh g. -1 The initial coulombic efficiency was 62.2%. After 100 cycles, it remained at 249 mAh·g. -1 The capacity has a corresponding capacity retention rate of 97%.

[0054] like Figure 3 The image shown is a SEM image of the Si-C composite anode material provided in Example 1 at 20,000x magnification. The Si coating layer is not uniformly coated on the substrate surface, leaving part of the substrate surface exposed.

[0055] like Figure 4The image shown is a SEM image of the Si-C composite anode material provided in Example 2 at 20,000x magnification. The Si coating layer is uniformly covered on the surface of the gasification slag matrix without obvious large-area cracks or peeling. The matrix surface is relatively rough, which may be due to the pore structure of the gasification slag itself, causing the coating layer to exhibit micron-level undulations.

[0056] like Figure 5 The image shown is a SEM image of the Si-C composite anode material provided in Example 3 at 10,000x magnification. Excess silicon precursor is rapidly deposited during the reaction, causing the surface composed of numerous aggregated silicon particles to be unevenly distributed.

[0057] like Figure 6 The figure shows the charge-discharge curve of the Si-C composite anode material provided in Example 1, at 0.05 A·g -1 The initial discharge capacity at the current density is 403.62 mA hg. -1 The charging capacity is 245mAh g -1 The corresponding initial Coulomb efficiency is 60.8%.

[0058] like Figure 7 The figure shows the charge-discharge curve of the Si-C composite anode material provided in Example 2, at 0.05 A·g -1 The initial discharge capacity at the current density is 422.47 mAh g. -1 The charging capacity is 259mAh g. -1 The corresponding initial Coulomb efficiency is 62.2%.

[0059] like Figure 8 The figure shown is the charge-discharge curve of the Si-C composite anode material provided in Example 3, at 0.05 A·g -1 The initial discharge capacity at the current density is 400.47 mAh g. -1 The charging capacity is 244mAh g. -1 The corresponding initial Coulomb efficiency is 61%.

Claims

1. A method for preparing a silicon-coated coal-based porous carbon composite material, characterized in that, Comprise the following steps: Step 1: select the gasification slag into the hydrochloric acid solution for acid leaching; the solution after acid leaching is stirred on the magnetic stirrer, so that the mixture is uniform; Step 2: then pour the solution into the suction filtration device, the solid is deposited on the filter membrane so that the solution is separated from it; washed repeatedly with deionized water to neutral; then placed in an oven to dry; Step 3: the dried sample is added to the HF solution for secondary acid leaching; the solution is stirred on the magnetic stirrer; Then pour the solution into the suction filtration device, the solid is deposited on the filter membrane so that the solution is separated from it; washed repeatedly with deionized water to neutral; placed in an oven to dry; Step 4: the final dried sample is placed in a tube furnace; the sample is activated in a tube furnace under a carbon dioxide atmosphere; the activated sample is used as a matrix to prepare a silicon-coated coal-based porous carbon composite material by CVD method under the conditions of argon protection gas and hydrogen reducing atmosphere.

2. The method for preparing a silicon-coated coal-based porous carbon composite material according to claim 1, characterized in that, In step 1, 2-4 g of gasified slag is put into (~ 5 mol L -1 ) hydrochloric acid solution; magnetic stirrer 300-400 r / min) stirring 4-6 h.

3. The method for preparing a silicon-coated coal-based porous carbon composite material according to claim 1, characterized in that, In step 2, the solid with a particle size of 50-200 μm is selected through the filter membrane; the filter membrane has a pore size of 0.45 μm.

4. The method of claim 1, wherein the silicon-coated coal-based porous carbon composite is prepared by the steps of: In step 2, the oven is set at 60-80°C for drying.

5. The method of claim 1, wherein the silicon-coated coal-based porous carbon composite is prepared by the steps of: In step 3, the HF solution is about 10 wt%, and the magnetic stirrer is set at 300-400 r / min for stirring for 4-6 h.

6. The method of claim 1, wherein the silicon-coated coal-based porous carbon composite is prepared by the steps of: In step 3, the solid with a particle size of 50-200 μm is selected through the filter membrane, and the filter membrane has a pore size of 0.45 μm for filtering the impurity elements in the water-based filter membrane; the solid is dried in an oven set at 60-80°C.

7. The method of claim 1, wherein the silicon-coated coal-based porous carbon composite is prepared by the steps of: a) mixing coal-based porous carbon with a silicon source; b) heating the mixture to a temperature of 800-1200°C; and c) cooling the mixture to room temperature. In step 4, the temperature is increased to 700-900°C for 3-4 hours. -1 temperature to 700-900°C for 3-4 hours.

8. The method of claim 7, wherein the silicon-coated coal-based porous carbon composite is prepared by the steps of: The argon gas flow rate was set to 0.8 L / min -1 The shunt gas hydrogen flow rate was set to 0.1 L / min -1 The sample was kept at 700-900 °C for 30-60 min for silicon deposition in an argon atmosphere and then cooled to room temperature.

9. A silicon-coated coal-based porous carbon composite material prepared by the method of any one of claims 1-8, which has a yolk-shell structure, with the coal-based porous carbon gasification slag serving as the yolk and the silicon serving as the shell to form a core-shell structure. By depositing silicon material on the surface of the coal-based material, a multi-layer composite material is obtained, in which the core is the coal-based material and the surface layer is silicon. The deposited silicon material has a specific structure that alleviates material failure caused by charging and discharging. The Si-C chemical bond and gradient pore structure enhance charge transport, alleviate volume effect, and accelerate the diffusion of sodium ions. At the same time, the composite material constructed by silicon and carbon avoids the low conductivity caused by single silicon, which limits the overall performance of the battery. Silicon stores sodium ions through reversible alloying reaction. The silicon layer provides high specific capacity, and the porous carbon matrix alleviates the volume expansion of silicon through hierarchical porosity (micropores + mesopores) and elastic structure. Silicon exists in a crystalline state on the surface of the coal-based porous carbon. The pore structure of the carrier provides sites for silicon deposition, allowing it to form a tight interface with the coal-based porous carbon surface.

10. Use of a silicon-coated coal-based porous carbon composite material prepared according to the method of any one of claims 1 to 8, characterized in that, The silicon-coated coal-based porous carbon composite material is applied to the negative electrode of a sodium ion battery and is suitable for large-scale energy storage systems, low-speed electric vehicles, and portable electronic device fields.

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