Electrochemical insertion of lithium into multiwalled carbon nanotube/silicon composites produced by ballmilling

Multiwalled carbon nanotube (MWNT)/silicon composite with different weight ratios were produced from purified MWNTs and Si powder with a maximum particle size of 45 mu m by high-energy ballmilling and then electrochemically inserted with lithium using Li/(MWNT/Si) cells. The charge/discharge properties for the ballmilled MWNT/Si composite anode were found to be very sensitive to the weight ratio of MWNT to Si. The highest C-rev and lowest C-irr of the composite anode were measured to be 1770 mAh/g and 469 mAh g(-1), respectively, at the ratio of MWNT0.5/Si-0.5. During charging/discharging processes, most of the Li ions were inserted into the ballmilled MWNT/Si composites by alloying with Si particles at potentials positive to 0.25 V vs Li and extracted from the ballmilled MWNT/Si composites by dealloying with Si particles at potentials positive to 0.5 V vs Li. The good capacity and cycle performance of the MWNT0.5/Si-0.5 composite anode is due primarily to the fact that MWNTs encapsulating fine Si particles by strong contact prevent Si particles from electrical insulation caused by the crumbling of the Si particles as well as buffer the volume expansion caused by the formation Li-Si compound during Li insertion.