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 μm Si 20 /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. The particle size and porosity of porous silicon are simultaneously optimized to obtain silicon-graphite composite with superior electrochemical properties. • The particle size and porosity of porous Si in Si-graphite composite are optimized. • More pores and smaller particle sizes of porous Si result in better performance. • Pre-lithiation improves the ICE and cycle stability of Si-graphite composite.