Controlled synthesis of nanosized Si by magnesiothermic reduction from diatomite as anode material for Li-ion batteries

Li-ion batteries (LIBs) have demonstrated great promise in electric vehicles and hybrid electric vehicles. However, commercial graphite materials, the current predominant anodes in LIBs, have a low theoretical capacity of only 372 mAh·g-1, which cannot meet the ever-increasing demand of LIBs for high energy density. Nanoscale Si is considered an ideal form of Si for the fabrication of LIB anodes as Si-C composites. Synthesis of nanoscale Si in a facile, cost-effective way, however, still poses a great challenge. In this work, nanoscale Si was prepared by a controlled magnesiothermic reaction using diatomite as the Si source. It was found that the nanoscale Si prepared under optimized conditions (800°C, 10 h) can deliver a high initial specific capacity (3053 mAh·g-1 on discharge, 2519 mAh·g-1 on charge) with a high first coulombic efficiency (82.5%). When using sand-milled diatomite as a precursor, the obtained nanoscale Si exhibited a well-dispersed morphology and had a higher first coulombic efficiency (85.6%). The Si-C (Si: graphite = 1:7 in weight) composite using Si from the sand-milled diatomite demonstrated a high specific capacity (over 700 mAhg”1 at 100 mAg”1), good rate capability (587mAh·g-1 at 500 mA·g-1), and a long cycle life (480 mAh·g-1 after 200 cycles at 500 mA·g-1). This work gives a facile method to synthesize nanoscale Si with both high capacity and high first coulombic efficiency.