The optimization of porosity and particle size for micron-size porous silicon in high energy pre-lithiated silicon-graphite composite for Li-ion batteries

To improve the capacity and energy density for Li-ion batteries, the composite of silicon and graphite has been regarded as the most promising alternative for next-generation anodes. However, the utilization of silicon has been limited by its large volume change and high manufacturing cost of nano silicon. Herein, the micron-size porous silicon is coated on the graphite and then encapsulated in carbon to form p-Si/G@C composite, in which the porosity and particle size of porous silicon are regulated by the element ratio and particle size of AlSi alloy. We find that the porous silicon with higher porosity and the smaller particle size shows better cycle stability and rate performance for p-Si/G@C electrode. Especially, by optimizing the porosity and particle size for porous silicon in the composite, the obtained p-0.8 mu m Si20/G@C exhibits an initial reversible capacity of 649.4 mA h/g, the initial coulombic efficiency (ICE) of 81.85% and the outstanding cycle stability with the capacity retention of 83.1% after 500 cycles. With simple pre-lithiation, the ICE could be significantly increased to 97.16% and the cycle capacity becomes more stable. This rationally designed p-Si/G@C possesses the advantages of low production cost, simple synthesis process, which shows significant potential for practical use.

Automated summary

To improve the performance of Li-ion batteries, researchers synthesized a p-Si/G@C composite, in which porous silicon was coated on graphite and encapsulated in carbon. It was found that porous silicon with higher porosity and smaller particle size displayed better cycle stability and rate performance in the electrode. With optimized design, the p-Si/G@C composite exhibited excellent cycle stability and high capacity retention.