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 by high-energy ballmilling and then electrochemically inserted with lithium using cells. The charge/discharge properties for the ballmilled composite anode were found to be very sensitive to the weight ratio of MWNT to Si. The highest and lowest of the composite anode were measured to be and , respectively, at the ratio of . During charging/discharging processes, most of the Li ions were inserted into the ballmilled composites by alloying with Si particles at potentials positive to vs Li and extracted from the ballmilled composites by dealloying with Si particles at potentials positive to vs Li. The good capacity and cycle performance of the 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 compound during Li insertion.