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 (GSC) composite is designed in which the particle size and oxidation degree of Si can be regulated simultaneously by sand milling micro-Si particles. Optimal Si with a particle size of about 125 nm and an oxide layer (SiOx) thickness of about 8 nm is obtained by controlling the sanding time, and is further uniformly coated on the surface of graphite. The synergistic effects of nanocrystallization and the SiOx layer of Si can minimize the volume expansion to achieve optimum electrochemical performance. A carbon coating is further applied on the outermost surface of graphite/Si particles 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 mA h g−1 and the capacity retention reaches 87.3% after 200 cycles at 1C. When the charging rate increases to 10C, the GSC still delivers a capacity of 528.0 mA h g−1. Furthermore, a LiNi0.5Co0.2Mn0.3O2/GSC–graphite pouch cell with a capacity of 1869.3 mA h exhibits a high capacity retention of 90.1% even after 150 cycles under a high compaction density of 1.55 g cm−3 for GSC–graphite. The excellent performance demonstrates that the compact GSC composite is an attractive candidate for anode materials for next-generation Li-ion batteries.