Nano Si-Based Anode Materials

Besides carbon materials, the most promising candidate for anode material is silicon (Si). It has a theoretical capacity as high as Li4.4Si (4200 mAh/g).In addition to its outstanding capacity. Si is the second most abundant element on earth. Therefore, Si attracts high attention for researchers. 

The main problem of Si is its volume expansion during Li insertion-extraction process, that is, 400% volume expansion of the Si lattice occurs after insertion. This volume expansion causes poor electronic contact between the Si particles and finally, large irreversible capacity and continuous capacity fading. When increasing the pressure of the cell or the amount of the conductive additives, the electrochemical performance could be improved. Amorphous Si shows better electrochemical performance than crystalline Si, due to the homogeneous expansion of volume of amorphous Si. 

Reducing the Si particle size to nanoscale is a most widely studied method to solve this problem. When the particle size is nanoscale, the volume expansion is reduced. The discharge capacity is 2775 mAh/g and reversible capacity is 2097 mAh/g, after 10 cycles. 

Fabricating composites of Si and conductive materials is quite effective to improve the capacity retention ability of nano-Si. The conductive materials include Li inactive materials and Li active materials.  

TiN is inactive Li. It has high electronic conductivity and high mechanical strength to withstand the volume change of Si on cycling. TiN-Si nanocomposites prepared by ball-milling for 12 h exhibit a stable capacity of 300 mAh/g, indicate a promising future of this method. 

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