Fabrication of LiCoO2/helical nanocarbon composites and their effect on lithium cell performance

Abstract

We fabricate LiCoO[2]/helical nanocarbon (HCN) composites by forming HCNs on LiCoO[2] on which iron oxides (Fe[2]O[3] or Fe[3]O[4]) are dispersed (LiCoO[2](Fe[2]O[3]) or LiCoO[2](Fe[3]O[4])) as catalysts for HCN formation, and estimate their electrochemical properties. Granular nanocarbons form on LiCoO[2](Fe[2]O[3]) and LiCoO[2](Fe[3]O[4]) at 350 °C although HCNs of about 100 nm in diameter form on LiCoO[2](Fe[2]O[3]) at 450 °C. Transmission electron microscopy and energy dispersive X-ray spectroscopy measurements show that HCNs consist of stacked graphene layers for LiCoO[2](Fe[2]O[3])/HCN composites fabricated at 450 °C. On the other hand, several-nm-thick tetragonal layer exists on the LiCoO[2] substrate and amorphous nanocarbons form on the tetragonal layer for LiCoO[2](Fe[2]O[3])/HCN and LiCoO[2](Fe[3]O[4])/HCN composites fabricated at 350 °C. X-ray diffraction measurements suggest that Fe[2]O[3] and Fe[3]O[4] do not completely inhibit LiCoO[2] decomposition. Cathodes containing LiCoO[2](Fe[2]O[3])/HCN or LiCoO[2](Fe[3]O[4])/HCN fabricated at 350 °C improve rate capability of lithium cells. However, this rate capability is not better than that of cathodes containing a mixture of LiCoO[2] and acetylene black.