Compact Si/C Anodes Fabricated by Simultaneously Regulating the Size and Oxidation Degree of Si for Li-Ion Batteries

The large volume expansion during lithiation and poor conductivity of Si as anodes of Li-ion batteries limit their practical applications. Herein, a compact graphite/Si/C composite (GSC) is designed in which the particle size and oxidation degree of Si can be regulated simultaneously by sand milling the micro-Si particles. The optimal Si with a particle size of about 125 nm and oxide layer (SiOx) thickness of about 8 nm is obtained by controlling the sanding time, which is further uniformly coated on the surface of graphite. The synergistic effects of nanocrystallization and SiOx layer of Si can minimize the volume expansion to achieve optimum electrochemical performance. A carbon coating is further constructed on the outmost surface of graphite/Si particle to increase the conductivity, reduce the volume expansion, and stabilize the solid electrolyte interface (SEI) of nano-Si. The obtained GSC with a high tap density of 0.95 g cm-3 delivers an initial reversible capacity of 675 mAh g-1 and the capacity retention reaches 87.3% after 200 cycles at 1 C. When the charging rate increases to 10 C, the GSC still delivers a capacity of 528.0 mAh g-1. Furthermore, the LiNi0.5Co0.2Mn0.3O2/GSC-graphite pouch cell with a capacity of 1869.3 mAh exhibits a high capacity retention of 90.1% even after 150 cycles under a high compaction density of 1.55 g cm-3 for the GSC-graphite. The excellent performance demonstrates that the compact GSC composite is an attractive candidate of anode materials for the next-generation Li-ion batteries.