A silicon-carbon negative electrode / current collector composite structure material, its preparation method and application

Abstract

The present invention discloses a silicon-carbon negative electrode / current collector composite structure material, a preparation method thereof, and an application thereof. The silicon-carbon negative electrode / current collector composite structure material provided by the present invention comprises nano-silicon and a carbon matrix, and the nano-silicon is dispersed in the carbon matrix. The preparation method provided by the present invention comprises: 1) using a cellulose paper as a matrix precursor; 2) soaking the matrix precursor in a sodium salt-containing solution to obtain a second precursor; 3) performing laser etching on the second precursor to obtain the silicon-carbon negative electrode / current collector composite structure material. The silicon-carbon negative electrode / current collector composite structure material provided by the present invention is used as a negative electrode material for a sodium-ion battery, does not require the use of a current collector during the battery assembly process, and has a high initial Coulomb efficiency and good cycling performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and particularly relates to a silicon-carbon negative electrode / current collector composite structure material, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of human civilization and the progress of technology, the demand for energy has been increasing day by day. The current major energy sources come from fossil fuels. Due to the non-renewability of fossil fuels and the damage to the environment, humans have made great efforts in searching for new energy storage technologies. Among the existing and efficient energy storage devices, secondary batteries are a high-energy-density storage system and are also highly compatible with clean and renewable energy, making them an ideal choice for portable electronic devices, hybrid electric vehicles, and large industrial equipment. Lithium-ion batteries are the most common rechargeable batteries on the market and are widely used in the storage of clean energy such as wind power, photovoltaic power, and hydropower, reducing the human dependence on fossil fuels. However, the abundance of lithium in the earth's crust is limited and unevenly distributed worldwide. Compared with lithium, sodium has the characteristics of higher abundance, wide distribution, and low price, and thus becomes an element of a new energy storage material that is promising for large-scale energy storage systems. Currently, developing materials with low cost and high performance is the core of the development of sodium-ion battery energy storage technology.

[0003] Currently, the negative electrodes of commercially available rechargeable batteries mainly use graphitized carbon materials. Specifically, they exhibit short-range order and long-range disorder, with a structure that has many defects formed by the intricate stacking and overlapping of graphite sheets. This structure shows a relatively large graphite layer spacing, allowing sodium ions with a relatively large ionic radius to achieve good intercalation and deintercalation. Moreover, the active sites at the defect sites can also store sodium well. However, the performance of graphitized carbon materials has approached a bottleneck in current applications. Its theoretical specific capacity in lithium-ion batteries is 372 mAh / g, and in sodium-ion batteries it is 333.4 mAh / g. Currently, commercially available carbon materials generally can reach a specific capacity of 280 mAh / g, and it is very difficult to further improve the performance. Therefore, exploring other negative electrode materials with higher theoretical specific capacities is very important for improving battery performance. The theoretical specific capacity of pure silicon negative electrodes is as high as 4200 mAh / g, making it a promising negative electrode material. However, the problems currently faced by sodium-ion batteries with silicon as the negative electrode are as follows: First, the structural strength of pure silicon negative electrodes is limited, and the sodium ions are relatively large. During the repeated intercalation and deintercalation of sodium ions, the volume of the negative electrode changes greatly, resulting in a limited number of charge-discharge cycles for the silicon negative electrode. Second, the conductivity of pure silicon negative electrodes is insufficient, which limits the speed of ion intercalation and deintercalation. Third, sodium-ion batteries require a large amount of aluminum to make current collectors to improve conductivity and stability. In the paper "Hierarchically Designed Nitrogen-Doped MoS2 Silicon Oxycarbide Nanoscale Heterostructure as High-Performance Sodium-Ion Battery Anode" (ACS Nano 2021, 15, 7409 - 7420), the authors doped elements such as MoS2, Si, and C as the negative electrode of sodium-ion batteries. At a small current of 50 mA / g, after 200 cycles, it maintained a specific capacity of approximately 600 mAh / g. This literature has the disadvantages of inconvenient preparation, fewer cycle times, and the need for a metal as the current collector. Summary of the Invention

[0004] Aiming at the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a silicon-carbon negative electrode / current collector composite structure material, its preparation method and application. The application is to use the silicon-carbon negative electrode / current collector composite structure material to assemble sodium-ion batteries, which has the advantages of simple preparation, more cycle times, and no need for a metal as the current collector.

[0005] The present invention achieves the above purpose through the following solutions.

[0006] The present invention provides a method for preparing a silicon-carbon negative electrode / current collector composite structure material. The material is a silicon-carbon composite material, the preparation raw materials are paper and silicon-containing inorganic salts, and the preparation method is laser etching. The silicon-carbon negative electrode / current collector composite structure material prepared by the present invention can directly replace the negative electrode and the current collector.

[0007] The present invention provides a method for preparing a silicon-carbon negative electrode / current collector composite structure material, which specifically includes the following steps:

[0008] (1) Prepare a sodium salt solution with a certain concentration: Heat and dissolve the sodium salt in a solvent, and stir to form a colorless and transparent sodium salt solution;

[0009] (2) Immerse the raw material paper in the sodium salt solution in step (1) for a certain period of time;

[0010] (3) Dry the paper soaked in step (2) in a blast drying oven, and cut it into appropriate size and shape;

[0011] (4) Perform laser etching on the paper cut in step (3) to obtain a silicon-carbon negative electrode / current collector composite structure material.

[0012] Preferably, the sodium salt in step (1) includes one or more of sodium silicate and sodium carbonate.

[0013] Preferably, the sodium salt in step (1) includes sodium silicate with a modulus of 2.

[0014] Preferably, the concentration of the sodium salt solution in step (1) is 1 g / L to 10 g / L.

[0015] Preferably, the soaking time in step (2) is 6 to 24 hours.

[0016] Preferably, the paper in step (2) is cellulose paper.

[0017] Preferably, the drying condition in step (3) is drying at 40 °C to 70 °C.

[0018] Preferably, the drying time in step (3) is 1 - 3 hours.

[0019] Preferably, the initial process parameters of the laser etching in step (4) are: the scanning speed is 30 - 100 mV / s, and the current is 12 - 25 A.

[0020] Preferably, the pattern of the laser etching in step (4) is a rectangle.

[0021] Preferably, for the laser etching in step (4), the etched pattern is a rectangle of 8 cm * 8 cm.

[0022] Preferably, in step (4), the laser etching carbonizes the paper, and silicon elements are doped into the carbon material at the same time.

[0023] Preferably, the material after etching in step (4) is punched according to the size of the battery case, and the size of the battery case is the 2032 model.

[0024] Preferably, the silicon-carbon negative electrode / current collector composite structure material in step (4) needs to be tableted.

[0025] The present invention provides a silicon-carbon negative electrode / current collector composite structure material prepared by the preparation method.

[0026] Preferably, the silicon-carbon negative electrode / current collector composite structure material includes nano-silicon and a carbon matrix, and the nano-silicon is dispersed in the carbon matrix.

[0027] Preferably, the particle size of the nano-silicon is 10-100 nm.

[0028] Preferably, the carbon matrix contains pores.

[0029] Preferably, the mass fraction of the carbon matrix in the silicon-carbon negative electrode / current collector composite structure material is 35%-80%.

[0030] Preferably, the particle size of the silicon-carbon negative electrode / current collector composite structure material is 10-100 nm.

[0031] Preferably, the silicon-carbon negative electrode / current collector composite structure material in step (4) is used to assemble a sodium ion battery.

[0032] The present invention also provides a sodium ion battery, including a silicon-carbon negative electrode / current collector composite structure material, an electrolyte and an organic solvent, wherein the solute of the electrolyte contains a sodium salt selected from sodium perchlorate CAS No. 7601-89-0, sodium hexafluorophosphate CAS No. 21324-39-0, sodium bis(fluorosulfonyl)imide CAS No. 100669-96-3, sodium bis(trifluoromethylsulfonyl)imide CAS No. 91742-21-1, and sodium trifluoromethanesulfonate CAS No. 2926-30-9, and the solvent of the electrolyte is selected from one or more of propylene carbonate CAS No. 108-32-7, ethylene carbonate CAS No. 96-49-1, diethyl carbonate CAS No. 105-58-8, dimethyl carbonate CAS No. 616-38-6, and ethyl methyl carbonate CAS No. 623-53-0.

[0033] Preferably, the negative electrode of the sodium ion battery is the silicon-carbon negative electrode / current collector composite structure material, and there is no need to use aluminum foil as a current collector separately.

[0034] Compared with the prior art solutions, the advantages of the technical solution of the present invention are as follows:

[0035] 1. The present invention is applied to sodium-ion batteries. Compared with the currently mainstream lithium-ion batteries, the crustal content of sodium is much higher than that of lithium and is more evenly distributed, making it easier to obtain in China.

[0036] 2. The silicon-carbon negative electrode / current collector composite structure material prepared by the present invention is both a negative electrode material and a component of the current collector of the battery, eliminating the need for additional aluminum foil and effectively saving metal resources. The synthesis process of the present invention has the advantages of simple process, no waste pollutants, and no need for high-temperature oxygen isolation calcination.

[0037] 3. The silicon-carbon negative electrode / current collector composite structure material prepared by the present invention has excellent electrochemical properties such as high initial Coulomb efficiency and good cycle stability, making it very suitable for application in sodium-ion batteries.

[0038] 4. The silicon-carbon negative electrode / current collector composite structure material provided by the present invention, as the negative electrode material of a sodium-ion battery, does not require the use of a current collector during the battery assembly process and has a high initial Coulomb efficiency and good cycle life. Description of the Drawings

[0039] Figure 1 It is a schematic diagram of battery assembly.

[0040] Figure 2 It is a schematic diagram of constant current cyclic charge and discharge of a sodium-ion half battery assembled with the silicon-carbon negative electrode / current collector composite structure material prepared in Example 1.

[0041] Figure 3 It is a scanning electron microscope (SEM) image of the silicon-carbon negative electrode / current collector composite structure material prepared in Example 1. Detailed Embodiments

[0042] In the following embodiments, the technical solution of the present invention will be further described in detail. The specific embodiments described herein are only for explaining the present invention and are not used to limit the present invention. In addition, the technical features involved in the following specific embodiments can be combined with each other as long as they do not conflict with each other.

[0043] The paper used in the following examples was purchased from DuPont (Nomex T 411 model paper).

[0044] Example 1

[0045] A preparation method of a silicon-carbon negative electrode / current collector composite structure material and its application in a sodium-ion battery

[0046] Step 1: Dissolve sodium silicate and sodium carbonate in deionized water by heating to 50 °C, and stir to form a colorless and transparent liquid to obtain an aqueous solution of sodium silicate and sodium carbonate, with the concentration of sodium silicate being 1 g / L and the concentration of sodium carbonate being 0.1 g / L. Then add paper and soak it at room temperature for 6 hours.

[0047] Step 2: Take out the paper from the aqueous solution of sodium silicate and sodium carbonate, dry it in a blast drying oven at 40 °C for 3 hours, and then cut it into a square with a size of 8 cm * 8 cm.

[0048] Step 3: Conduct laser etching on the 8 cm * 8 cm square paper obtained in Step 2. The initial process parameters of laser etching are set as follows: the scanning speed is 30 mV / s and the current is 20 A.

[0049] Step 4: Process the laser-etched material with a punching machine to obtain a silicon-carbon negative electrode / current collector composite structure material, and then press it to obtain a negative electrode / current collector composite structure electrode sheet.

[0050] Step 5: Prepare an electrolyte with sodium perchlorate as the solute, propylene carbonate and ethyl methyl carbonate (the volume ratio of propylene carbonate to ethyl methyl carbonate is 1:1) as the solvent, and the concentration is 1 M.

[0051] Step 6: Weigh the negative electrode / current collector composite structure electrode sheet using a five-digit balance and record the corresponding mass of the active material; use a sodium sheet as the positive electrode. Under the condition that the water and oxygen content are both less than 0.01 ppm, successively assemble the positive electrode shell, negative electrode shell, glass fiber separator, sodium sheet, electrolyte, gasket, and spring sheet together, and finally seal the assembled battery with a button cell sealer. Then take it out from the glove box and let it stand for 12 hours to obtain an assembled sodium-ion half cell.

[0052] Step 7: Conduct electrochemical performance tests on the assembled sodium-ion half cell. The specific test conditions are as follows: at a large current density of 1 A / g, perform constant current charge and discharge cycling on the battery for 1000 cycles. The test results are as Figure 2 shown. It can be Figure 2 seen that the sodium-ion half cell assembled with the silicon-carbon negative electrode / current collector composite structure material prepared in Example 1 has a high initial Coulomb efficiency of 73.8%, and the battery maintains a specific capacity of about 180 mAh / g, with excellent cycling performance.

[0053] Figure 3 is the scanning electron microscope (SEM) image of the silicon-carbon negative electrode / current collector composite structure material prepared in Example 1. It can be Figure 3 seen that the particle diameter of this material is 10 - 20 nm, and the uniformity is good.

[0054] Example 2

[0055] Preparation Method of a Silicon-Carbon Anode / Current Collector Composite Structure Material and Its Application in Sodium-Ion Batteries

[0056] Step 1: Heat sodium silicate in deionized water to 50 °C for dissolution, stir to form a colorless and transparent liquid, and obtain a sodium silicate aqueous solution with a concentration of 1 g / L. Then add paper and soak it at room temperature for 12 hours.

[0057] Step 2: Take out the paper from the sodium silicate aqueous solution, dry it in a blast drying oven at 50 °C for 2 hours, and then cut it into a square with a size of 8 cm * 8 cm.

[0058] Step 3: Perform laser etching on the 8 cm * 8 cm square paper obtained in Step 2. The initial process parameters of laser etching are set as follows: the scanning speed is 80 mV / s, and the current is 12 A.

[0059] Step 4: Process the material after laser etching with a punching machine to obtain a silicon-carbon anode / current collector composite structure material, and then press it into a sheet to obtain a negative electrode / current collector composite structure electrode sheet.

[0060] Step 5: Prepare the electrolyte. The solute is sodium hexafluorophosphate, the solvent is ethylene carbonate and ethyl methyl carbonate (the volume ratio of ethylene carbonate to ethyl methyl carbonate is 1:1), and the concentration is 1 M.

[0061] Step 6: Weigh the negative electrode / current collector composite structure electrode sheet using a five-digit balance and calculate the corresponding mass of the active material. Using a sodium sheet as the positive electrode, under the condition that the water and oxygen content are both less than 0.01 ppm, successively assemble the positive electrode shell, negative electrode shell, glass fiber separator, sodium sheet, electrolyte, gasket, and spring sheet together. Finally, seal the assembled battery with a button cell sealer, then take it out of the glove box and let it stand for 12 hours to obtain an assembled sodium-ion half cell.

[0062] Step 7: Perform electrochemical performance tests on the assembled sodium-ion half cell. The specific test conditions are as follows: at a current density of 1 A / g, perform constant current charge and discharge cycling on the battery for 1000 cycles.

[0063] Example 3

[0064] Preparation Method of a Silicon-Carbon Anode / Current Collector Composite Structure Material and Its Application in Sodium-Ion Batteries

[0065] Step 1: Heat sodium silicate in deionized water to 40 °C for dissolution, stir to form a colorless and transparent liquid, and obtain a sodium silicate aqueous solution with a concentration of 1 g / L. Then add paper and soak it at room temperature for 12 hours.

[0066] Step 2: Take out the paper from the sodium silicate aqueous solution, dry it in a blast drying oven at 60 °C for 1 hour, and then cut it into a 10 cm * 10 cm square.

[0067] Step 3: Perform laser etching on the 10 cm * 10 cm square paper obtained in Step 2. The initial process parameters of the laser etching are set as follows: the scanning speed is 80 mV / s, and the current is 20 A.

[0068] Step 4: Process the laser-etched material with a punching machine to obtain a silicon-carbon negative electrode / current collector composite structure material, and then press it to obtain a negative electrode / current collector composite structure electrode sheet.

[0069] Step 5: Prepare the electrolyte. The solute is sodium perchlorate, the solvents are propylene carbonate and diethyl carbonate (the volume ratio of propylene carbonate to diethyl carbonate is 1:1), and the concentration is 1 M.

[0070] Step 6: Weigh the negative electrode / current collector composite structure electrode sheet using a five-digit balance and record the corresponding mass of the active material. Using a sodium sheet as the positive electrode, under the condition that the water and oxygen content are both less than 0.01 ppm, successively assemble the positive electrode shell, negative electrode shell, glass fiber separator, sodium sheet, electrolyte, gasket, and shrapnel together. Finally, seal the assembled battery with a button cell sealer, then take it out of the glove box and let it stand for 12 hours to obtain the assembled sodium-ion half cell.

[0071] Step 7: Perform electrochemical performance tests on the assembled sodium-ion half cell. The specific test conditions are as follows: at a current density of 1 A / g, perform constant current charge and discharge cycling on the battery for 1000 cycles.

[0072] Example 4

[0073] A preparation method of a silicon-carbon negative electrode / current collector composite structure material and its application in a sodium-ion battery

[0074] Step 1: Heat sodium silicate in deionized water to 40 °C for dissolution, stir to form a colorless and transparent liquid to obtain a sodium silicate aqueous solution with a sodium silicate concentration of 1 g / L. Then add the paper and soak it at room temperature for 24 hours.

[0075] Step 2: Take out the paper from the sodium silicate aqueous solution, dry it in a blast drying oven at 60 °C for 2 hours, and then cut it into a 10 cm * 10 cm square.

[0076] Step 3: Perform laser etching on the 10 cm * 10 cm square paper obtained in Step 2. The initial process parameters of the laser etching are set as follows: the scanning speed is 100 mV / s, and the current is 25 A.

[0077] Step 4: Process the laser-etched material with a punching machine to obtain a silicon-carbon negative electrode / current collector composite structure material, and then press it into a sheet to obtain a negative electrode / current collector composite structure electrode sheet.

[0078] Step 5: Prepare the electrolyte. The solute is sodium perchlorate, the solvent is propylene carbonate and diethyl carbonate (the volume ratio of propylene carbonate to diethyl carbonate is 1:1), and the concentration is 1 M.

[0079] Step 6: Weigh the negative electrode / current collector composite structure electrode sheet using a five-digit balance and record the corresponding mass of the active material. Using a sodium sheet as the positive electrode, under the condition that the water and oxygen content are both less than 0.01 ppm, successively assemble the positive electrode shell, negative electrode shell, glass fiber separator, sodium sheet, electrolyte, gasket, and spring piece together. Finally, seal the assembled battery with a button cell sealer, then take it out of the glove box and let it stand for 12 hours to obtain the assembled sodium-ion half cell.

[0080] Step 7: Conduct electrochemical performance tests on the assembled sodium-ion half cell. The specific test conditions are as follows: at a current density of 1 A / g, perform constant current charge and discharge cycling on the battery for 1000 cycles.

[0081] Based on the above preparation process and test results, it can be seen that the silicon-carbon negative electrode / current collector composite structure material prepared by this method has many advantages when applied to sodium-ion batteries. Its synthesis process has the advantages of simple process, no waste pollutants, and no need for high-temperature oxygen isolation calcination. The test results also show that the battery has excellent long-term cycling ability at high currents.

[0082] The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the specific embodiments disclosed and described above. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A preparation method of a silicon-carbon negative electrode / current collector composite structure material, characterized in that, It includes the following steps: (1) Heat and dissolve the sodium salt in a solvent, stir to form a colorless and transparent liquid, and then add paper for soaking; the sodium salt includes one or more of sodium silicate and sodium carbonate and at least includes sodium silicate; the paper is cellulose paper; (2) Dry and cut the paper soaked in step (1); (3) Laser etch the paper cut in step (2) to obtain a silicon-carbon negative electrode / current collector composite structural material.

2. The preparation method of the silicon-carbon negative electrode / current collector composite structural material according to claim 1, characterized in that, The soaking time in step (1) is 6-24 hours.

3. The preparation method of the silicon-carbon negative electrode / current collector composite structure material according to claim 1, characterized in that The process parameters of the laser etching in step (3): the scanning speed is 30-100 mV / s, and the current is 12-25 A.

4. The preparation method of the silicon-carbon negative electrode / current collector composite structure material according to claim 1, wherein The pattern of the laser etching in step (3) is rectangular.

5. The silicon-carbon negative electrode / current collector composite structural material prepared by the preparation method according to any one of claims 1-4.

6. The silicon-carbon negative electrode / current collector composite structural material according to claim 5, characterized in that The particle size of the silicon-carbon negative electrode / current collector composite structural material is 10-100 nm.

7. A sodium-ion battery, characterized in that, It includes the silicon-carbon negative electrode / current collector composite structural material according to claim 5, an electrolyte, and an organic solvent, wherein the solute of the electrolyte contains a sodium salt selected from one or more of sodium perchlorate, sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, and sodium trifluoromethanesulfonate, and the solvent of the electrolyte is selected from one or more of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate.

8. The sodium ion battery according to claim 7, characterized in that, The negative electrode of the sodium ion battery is the silicon-carbon negative electrode / current collector composite structural material according to claim 7.

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