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 m Ah·g, which cannot meet the everincreasing 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 m Ah·gon discharge, 2519 m Ah·gon 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 m Ah·gat 100 m A·g), good rate capability(587 m Ah·gat 500 m A·g), and a long cycle life(480 m Ah·gafter 200 cycles at 500 m A·g). This work gives a facile method to synthesize nanoscale Si with both high capacity and high first coulombic efficiency.