Silicon @ carbon composite material with egg yolk shell structure and preparation and application thereof
A technology of carbon composite materials and egg yolk shells, applied in nanotechnology for materials and surface science, structural parts, final product manufacturing, etc., can solve problems such as structural volume changes and poor conductivity
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Embodiment 1
[0078] Preparation of mesoporous silicon-carbon composite (Si@C) anode material with egg yolk shell structure
[0079] Step 1): Mix the SBA-15 precursor into Mg powder (99%) and sodium chloride according to the molar ratio (SBA:Mg:NaCl=1:1.05:4), mix and grind by hand for 30 minutes in a dry method. In an argon atmosphere with 5% hydrogen, the temperature is raised to 300°C at a rate of 5°C / min and kept for 2h, and then the temperature is raised to 650°C at a heating rate of 5°C / min and the temperature is kept for 6h. The product after roasting is diluted with hydrochloric acid Carry out multiple times of cleaning and centrifugal drying to obtain mesoporous silicon nanomaterials;
[0080] Step 2): Next, ultrasonically disperse 1g of mesoporous silicon nanomaterial in 5mL of water to obtain a nanosilica dispersion, and then mix the polyvinyl alcohol solution to obtain mixed solution A (the mass ratio of mesoporous silicon nanomaterial / polyvinyl alcohol is 2 :1), and then mix the mi...
Embodiment 2
[0095] Compared with Example 1, the only difference is that in step 1), the temperature is raised to 300° C., and after holding for 2 hours, the temperature is then raised to 550° C. for 6 hours.
[0096] Assembled into a button according to the method of Example 1. The measured electrical performance is that the specific discharge capacity of the first, second, fifth, and tenth charge and discharge cycles are 834, 612, 503, 407 mAh g, respectively -1 Compared with Example 1, its cycle performance is very poor. After the 100th cycle, the capacity decays to 335mAh g -1 , At a current density of 1A g -1 Hourly discharge specific capacity is 391mAh g -1 , At 2A g -1 Hourly discharge specific capacity is 347mAh g -1 According to Example 1 and Example 2, it is found that the reaction is not complete under these conditions, and there is a layer of white silicon oxide that has not been reduced, so that the product mesoporous nano-silicon material is reduced. And because the material conta...
Embodiment 3
[0098] Compared with Example 1, the only difference is that in step 2), the ratio of mesoporous nano-silicon material, surfactant, and aluminum salt is 1:1:2.
[0099] According to the method of Example 1, it is assembled into a button, and the electrical performance is measured. After the 90th cycle, the capacity quickly decays to 183mAh g -1 Compared with Example 1, the increase in AC impedance is increased by 400%. From Example 1 and Example 3, it is found that if too much surfactant is added, these excessive surfactant molecules will be disorderly in the solution and cannot form a colloid in the solution. Therefore, it is impossible to prepare a silicon carbon negative electrode material with an egg yolk shell structure, and cannot withstand the expansion of the silicon core. So the optimal ratio of adding silicon powder, surfactant and aluminum salt is 2:1:4. Similarly, if the ammonia is added in excess, it will produce aluminum hydroxide precipitation.
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