Effect of combination methods for nanosilicon and graphite composites on the anode performance of lithium batteries

Nanosilicon materials are hardly used as anode materials of lithium batteries for the serious volume expansion during charging and discharging. Carbon-coated materials can reduce the volume effect of the silicon-improving cycle stability. In this paper, silicon/graphite (Si/G) composites were prepared by directly compounding silicon nanoparticles with graphite during size mixing, and (Si/G)@C composites were prepared by coating sucrose cracked carbon on the surface of silicon nanoparticles and graphite, and then spray drying the mixture and carbonized at 900 °С for 3 h under vacuum condition. The morphology and properties of the composites were compared by means of microstructure analysis and electrochemical performance tests. The results show that the improved electrochemical properties can be obtained by both composite methods. The Si/G composite delivers a high initial discharge capacity of approximately 597.9 mA h/g, with initial coulombic efficiency of 84.95%, and the reversible charge capacity is 423.5 mA h/g after 300 cycles with corresponding capacity retention ratio of 70.83%. The (Si/G)@C composite has better cycle life and coulombic efficiency with a discharge capacity of 572.9 mA h/g, and a capacity retention rate of 82.77% after 300 cycles. Coating carbon with silicon nanoparticles and graphite can improve the electrochemical properties of the (Si/G)@C composite electrode by preventing the crushing of active material particles, reducing the formation of SEI films, and enhancing the electrical conductivity of the particles.