Carbon nanotubes (CNTs) as a buffer layer in silicon/CNTs composite electrodes for lithium secondary batteries

A core/shell type silicon/carbon nanotubes (Si/CNTs) composite is prepared and its anodic performance in lithium secondary batteries is examined. For the growth of CNTs, a Ni catalyst is loaded on a Si surface by electroless deposition. The growth is performed by chemical vapour deposition at 600 °C using C2H2/H2 but is successful only on smaller and thinner Ni deposits. This is probably due to an easier transformation to small droplets that initiate the growth reaction. The anodic performance of a Si/CNTs composite electrode is superior to that observed with bare Si and Si/CNTs mixed electrodes. This beneficial feature is ascribed to the conductive buffering role of the CNTs layer. It is likely that the void space and the flexible characteristics in the CNTs buffer layer on the Si surface allow volume expansion of the Si core without severe electrode swelling. Because of this, the electric conductive network made among Si particles, carbon network and current-collector is well maintained, which reduces the charge-transfer resistance.