High performance lithium ion battery anodes based on carbon nanotube–silicon core–shell nanowires with controlled morphology

We report a carbon nanotube (CNT)–silicon core–shell nanowire for lithium ion battery anodes. In this material, the core consists of vertically aligned CNTs synthesized through plasma enhanced chemical vapor deposition. The CNTs exhibit quite large diameters and large inter-wire spacing and are advantageous in strain accommodation and electrolyte access. The silicon shell is tailored with a thickness gradient along its length to eliminate excessive strain accumulation at the nanowire roots and cater for free space distribution in the CNT core array. In addition, the silicon shell exhibits a unique vertically opened pore structure, which is expected to have further improved strain accommodation and Li+ transport. As a result, the CNT–silicon anode demonstrates excellent cyclability with a capacity retention of more than 90% over 100 cycles. It also shows remarkable rate performance that is to our knowledge, the best among all core–shell nanowires reported.