Compact Si/C anodes fabricated by simultaneously regulating the size and oxidation degree of Si for Li-ion batteries

Abstract

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 (SiO_x) 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 SiO_x 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 LiNi_0.5Co_0.2Mn_0.3O₂/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.