How to make the silicon-based anode material of lithium ion battery porous and nanometer?

For the modification of elemental silicon, the Si-M alloy is formed by incorporation of the second component, the volume expansion coefficient of the silicon alloy is reduced, or the silicon is made porous and nanosized by various engineering techniques, and the volume expansion of silicon is reserved. Space, reducing the effect of silicon volume effect on material cycle stability.

Porosity of Silicon

On the one hand, the porous Silicon can increase the specific surface area of the Silicon main material in contact with the electrolyte, improve the transport efficiency of lithium ions into the material, enhance the conductivity of the material, and on the other hand, it can be used for Silicon in the process of charging and discharging. The volume expansion reserved space, The effect of reducing Silicon volume effect on Polar films. The porous Silicon has been widely regarded as an effective means to solve the Silicon volume effect. Fig. 1 shows the SEM morphology of porous silicon.

Tang et al. prepared porous Si/C composite negative electrode materials by means of PVA carbon coating, HF acid etching and bitumen secondary coating. The results show that when the secondary coated asphalt content is 40 %(mass fraction), the discharge capacity of the charge and discharge cycle in the second week of the sample reaches 773 mAh/g at a current density of 100 mA/g, After 60 weeks of circulation, the specific capacity remained at 669 mAh/g, and the capacity loss rate was only 0.23 % per week. The material showed good cyclic stability.

Han et al. combined electrochemical etching with high-energy ball grinding method. P-type Si was used as the base plate, HF solution was used as the etching fluid, porous Silicon thin film material with a porosity of 70 % was obtained, and then the ball was ground and heat treated in PAN. A porous Silicon negative electrode material coated with carbon was prepared. The reversible specific capacity of the sample after 120 cycles under 0.1 C is 1179 mAh/g, which has a good electrochemical performance. The method is cheap and suitable for large-scale preparation of porous Silicon materials.

Nanocrystallization of silicon

Researchers of silicon-based anode materials generally believe that when the scale of silicon is small to a certain extent, the effect of silicon volume effect can be relatively reduced, and the silicon of small particles is matched with the corresponding dispersion technology, and it is easy to reserve enough for the silicon particles. The expansion space, so the nanocrystallization of silicon is considered to be an important way to solve the commercialization of silicon-based anode materials.

Wang et al. used the ZnO nanowires template method to grow Silicon nanotube arrays on carbon matrix and compared the effects of carbon coating on Silicon nanotube arrays. The results showed that the Silicon nanotube array after carbon coating showed good cyclic stability, and the discharge capacity reached 3654mAh/g after 100 cycles.

Sun et al. used a plasma-assisted discharge method to prepare Si/graphite nanosheets from nano-silicon and expanded graphite, and used them as anode materials for lithium-ion batteries. The results show that the synthesized Si/C composite sample has good cycle stability, and the specific capacity of lithium intercalation is 1000 mAh/g. There is no capacity loss until the cycle of 350 weeks, and the coulombic efficiency is above 99%.

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