Effect of pore structures on the electrochemical performance of porous silicon synthesized from magnesiothermic reduction of biosilica

Two kinds of porous silicon (PS) were synthesized by magnesiothermic reduction of rice husk silica (RHS) derived from the oxidization of rice husks (RHs). One was obtained from oxidization/reduction at 500 °C of the unleached RHs, the other was synthesized from oxidization/reduction at 650 °C of the acidleached RHs. The structural difference of the above PS was compared: the former had a high pore volume (PV, 0.31 cm3/g) and a large specific surface area (SSA, 45.2 m2/g), 138 % and 17 % higher than the latter, respectively. As anode materials for lithium ion batteries, the former had reversible capacity of 1 400.7 mAh/g, 987 mAh/g lower than the latter; however, after 50 cycles, the former had 64.5 % capacity retention (907 mAh/g), which was 41.2 % higher than the latter (555.7 mAh/g). These results showed that the electrochemical performance of PS was significantly affected by its pore structures, and low reduction temperature played the key role in increasing its porosity, and therefore improving its cycling performance.