A method for preparing a porous silicon-carbon composite material in one step using polysiloxane as a raw material

Abstract

The present invention provides a method for directly preparing a porous silicon-carbon composite material from a polysiloxane as a raw material. In the method for preparing the silicon-carbon composite material, Mg2Si and the polysiloxane are used for pyrolysis reaction at a high temperature to directly prepare the porous silicon-carbon composite material. This method has the advantages of high efficiency, environmental protection and economy. The porous silicon-carbon composite material has an in-situ formed carbon coating layer and porous silicon formed, has the advantages of high Coulomb efficiency, high cycle stability, etc., greatly improves the electrochemical performance, and at the same time, due to the simplicity and high efficiency of this method, it has broad market application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of anode materials for lithium-ion batteries. Specifically, a method for directly preparing a porous silicon-carbon composite material from polysiloxane as a raw material is provided. Technical Background

[0002] With the continuous development of today's society, environmental and resource problems have become increasingly prominent, seriously affecting the sustainable development of humanity. Therefore, the development of clean and sustainable new energy has become the focus of attention. However, due to the instability of new energy, high-efficiency energy storage devices are required when using new energy. Since current lithium-ion batteries are difficult to meet the needs, it is very important to develop a lithium-ion battery that meets the requirements.

[0003] In the anode of lithium-ion batteries, carbon materials are currently mostly used as the anode, but the capacity of carbon materials is low. For example, the theoretical capacity of graphite is 372 mAh / g. Therefore, traditional graphite-based anodes are difficult to meet the needs of today's development. Another material, silicon, in the anode material of lithium-ion batteries has been widely studied because of its high specific capacity, low lithium deintercalation potential, and rich resources. However, due to the instability of the SEI film and large volume expansion during charge and discharge of silicon, the initial Coulombic efficiency of silicon anodes is low, the cycle attenuation is fast, and the conductivity is poor. Therefore, it is crucial to select suitable raw materials and modify them to improve the initial Coulombic efficiency, cycle stability, and conductivity.

[0004] Patent CN115602821A discloses a method in which silane and hydrogen are used as reaction gases for PECVD reaction, and then nano-silicon and a carbon source are mixed in ethanol, dried, and sintered in a high-temperature furnace filled with argon. Finally, a porous silicon-carbon composite material is obtained. Although this method can obtain a porous silicon-carbon anode with good performance, the use of silane and hydrogen during production makes it very unsafe during production, and the use of the PECVD process is costly. CN109167031A discloses a multi-stage structure with a silicon nanoparticle core, an amorphous carbon middle layer, and a carbon fluoride outer shell. This structure effectively improves the electrochemical performance of the porous silicon-carbon anode.

[0005] Currently, the main silicon raw materials are silane, silicate minerals, and commercial micro-nano silicon. Among these raw materials, silane has been difficult to apply due to its danger; the high reaction required for silicate minerals in the preparation of silicon causes unnecessary waste of resources. And the preparation of silicon using polysiloxane is low-cost and safe.

[0006] Due to the existing problems of the above raw materials and silicon-based anodes, an environmentally friendly and economical raw material and modification method are particularly important for the preparation of porous silicon-carbon composites. The present invention proposes a preparation method for directly generating porous silicon-carbon composites by pyrolysis reaction of polysiloxane and Mg2Si at high temperature. Summary of the Invention

[0007] To solve the above deficiencies, the present invention innovatively proposes a preparation method for directly generating porous silicon-carbon composites by reacting polysiloxane and Mg2Si at high temperature.

[0008] The present invention provides a method for directly preparing porous silicon-carbon composites using polysiloxane as a raw material, which is characterized by the following steps: First, weigh a certain amount of Mg2Si (particle size 100-1000 nm), ball mill it in a ball mill for 1 h, and then add a certain amount of polysiloxane (PSO) and ball mill for another 1 h after ball milling. Then, place the ball mill tank in a blast drying oven in a fume hood and cure it at 100-150 °C for 1 h; put the cured material back into the ball mill and ball mill for 2 h, then put it into a tubular furnace filled with argon, the temperature is 650-850 °C, the heating rate is 5 °C / min, and the time is 0.5-2 h, and then cool it with the furnace. Finally, take out the material and wash it with 2M hydrochloric acid to remove magnesium oxide to obtain the porous silicon-carbon composite.

[0009] Preferably, in the above steps, the particle size of the Mg2Si is 100-1000 nm.

[0010] Preferably, in the above steps, the addition amount of PSO is 1-3 times the addition amount of Mg2Si.

[0011] Preferably, in the above steps, the active functional groups of PSO are at least two of silanol (Si-OH), silane (Si-H), methylsilane (Si-CH3), and vinyl (-C2H4).

[0012] Preferably, in the above steps, the molecular weight of PSO is 4000-7000.

[0013] Preferably, in the above steps, the temperature of the atmosphere furnace is 650-850 °C and the time is 0.5-2 h.

[0014] Compared with the prior art, the outstanding benefits of the present invention are as follows:

[0015] (1) The present invention innovatively proposes a method for directly synthesizing porous silicon-carbon composites using polysiloxane and Mg2Si. This preparation method is simple, efficient, and environmentally friendly.

[0016] (2) The use of polysiloxane to neutralize the pyrolysis reaction of Mg2Si proposed by the present invention can effectively inhibit the agglomeration and growth of silicon, and can form an amorphous carbon layer on the surface to prevent the oxidation of silicon. At the same time, it can improve the initial Coulomb efficiency of the porous silicon-carbon composite material, and efficiently prepare a porous silicon-carbon composite material with good electrochemical performance.

[0017] (3) The porous silicon obtained in the present invention alleviates the expansion of silicon during charge and discharge to a certain extent, and improves the cycle stability. Brief Description of the Drawings

[0018] Figure 1 It is the X-ray diffraction pattern of the porous silicon-carbon composite material in Example 1 of the present invention.

[0019] Figure 2 It is the scanning electron micrograph of the porous silicon-carbon composite material in Example 1 of the present invention. Detailed Embodiments

[0020] In order to further illustrate the present invention, the following is a detailed description of a preparation method for a porous silicon-carbon composite material that uses polysiloxane and Mg2Si to react at high temperature to generate a porous silicon-carbon composite material in one step provided by the present invention in combination with embodiments.

[0021] Example 1

[0022] The porous silicon-carbon composite material is prepared according to the following steps

[0023] First, weigh 3 g of 200 nm Mg2Si and ball mill it in a ball mill for 1 h. After the ball milling is completed, add 5.25 g of polysiloxane with a molecular weight of 4000 and containing silicon hydride (Si-H) and silicon methyl (Si-CH3), and then ball mill for 1 h. Then put the ball mill tank into a forced air drying oven in a fume hood and cure it at 150 °C for 1 h; put the cured material back into the ball mill and ball mill for 2 h. After grinding, put it into a tubular furnace filled with argon, with a temperature of 650 °C, a heating rate of 5 °C / min, and a time of 2 h, and then cool it with the furnace. Finally, take out the material, pickle it with 2 M hydrochloric acid, and dry it to obtain the porous silicon-carbon composite material.

[0024] The XRD of the material is as Figure 1 shown. It can be seen from the porous silicon-carbon negative electrode prepared by this method that a broad peak near 20° is the amorphous carbon peak obtained by the pyrolysis of polysiloxane, indicating that this method can deposit a layer of conductive carbon on the surface of nano-silicon well. There is a weak SiC peak in the XRD, which is due to the local overheating during the reaction, resulting in the formation of SiC. The SEM characterization is as Figure 2 shown.

[0025] Example 2

[0026] Prepare the porous silicon-carbon composite material according to the following steps

[0027] First, weigh 3 g of 500-nm Mg2Si and ball-mill it in a ball mill for 1 h. After the ball milling is completed, add 6.3 g of a polysiloxane with a molecular weight of 4000 and containing silicon hydride (Si-H) and silicon methyl (Si-CH3), and then ball-mill for another 1 h. Then, place the ball mill jar in a forced-air drying oven in a fume hood and cure it at 120 °C for 1 h. Put the cured material back into the ball mill and ball-mill for 2 h. After grinding, place it in a tubular furnace filled with argon, with a temperature of 650 °C, a heating rate of 5 °C / min, and a time of 2 h, and then cool it with the furnace. Finally, take out the material, perform pickling with 2 M hydrochloric acid, and dry it to obtain the porous silicon-carbon composite material.

[0028] Example 3

[0029] Prepare the porous silicon-carbon composite material according to the following steps

[0030] First, weigh 3 g of 200-nm Mg2Si and ball-mill it in a ball mill for 1 h. After the ball milling is completed, add 4.2 g of a polysiloxane with a molecular weight of 6000 and containing silicon hydride (Si-H) and silicon methyl (Si-CH3), and then ball-mill for another 1 h. Then, place the ball mill jar in a forced-air drying oven in a fume hood and cure it at 150 °C for 1 h. Put the cured material back into the ball mill and ball-mill for 2 h. After grinding, place it in a tubular furnace filled with argon, with a temperature of 700 °C, a heating rate of 5 °C / min, and a time of 2 h, and then cool it with the furnace. Finally, take out the material, perform pickling with 2 M hydrochloric acid, and dry it to obtain the porous silicon-carbon composite material.

[0031] The above-described cases are only preferred implementation cases of the present invention and are not used to limit this application. The preparation method of the present invention is simple to operate, novel in configuration, and stable in performance. For those skilled in the art, without departing from the principle of the present invention, various changes and modifications can be made to this application. Any modifications, substitutions, improvements, etc. should be included within the protection scope of this application.

Claims

1. A method for one-step preparation of a porous silicon-carbon composite material using polysiloxane as a raw material, characterized in that, In the method for preparing the silicon-carbon composite material, polysiloxane and Mg2Si are used to prepare the porous silicon-carbon composite material in one step at high temperature; The preparation method includes the following steps: First, weigh a certain amount of Mg2Si with a particle size of 100 - 1000 nm, ball mill it for 1 h with a ball mill, add a certain amount of polysiloxane PSO after ball milling and then ball mill for 1 h, and then put the ball mill pot into a blast drying oven in a fume hood for curing at 100 - 150 °C for 1 h; Put the cured material into the ball mill again for ball milling for 2 h, put it into a tubular furnace filled with argon after grinding, the temperature is 650 - 850 °C, the heating rate is 5 °C / min, the time is 0.5 - 2 h, and then cool it with the furnace. Finally, take out the material and perform pickling with 2M hydrochloric acid to remove magnesium oxide to obtain the porous silicon-carbon composite material.

2. The method for one-step preparation of a porous silicon-carbon composite material using polysiloxane as a raw material according to claim 1, characterized in that, In the step described, the addition amount of PSO is 1 - 3 times the addition amount of Mg2Si.

3. A method for preparing a porous silicon-carbon composite material from polysiloxane as a raw material in one step, characterized in that, In the step described, the active functional groups of PSO are at least two of silanol (Si-OH), silane (Si-H), trimethylsilyl (Si-CH3), and vinyl (-C2H4).

4. A method for preparing a porous silicon-carbon composite material from polysiloxane as a raw material in one step, characterized in that, In the step described, the molecular weight of PSO is 4000 - 7000.

5. A method for preparing a porous silicon-carbon composite material from polysiloxane as a raw material in one step, characterized in that, In the step described, the temperature of the atmosphere furnace is 650 - 850 °C and the time is 0.5 - 2 h.

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