Urchin-like Li4Ti5O12–carbon nanofiber composites for high rate performance anodes in Li-ion batteries

Abstract

A facile strategy is developed based on a sol–gel method to prepare lithium titanate (Li4Ti5O12, LTO)–carbon nanofiber (CNF) composites as anode in Li-ion batteries (LIBs). Depending on the conductive CNF and carbon black (CB) additive contents added in the electrode, the resultant composite particles present either an urchin-like or a corn-dog structure with largely different electronic conductivities and associated electrochemical properties. When small amounts of both one-dimensional CNF and zero-dimensional CB particles, 5.0 wt% each, are present, conductive networks are established within the urchin-like LTO secondary particles by the penetrating multiple CNFs, whereas the CB particles attached onto the surface of the LTO particles connect the gaps between them, being able to form extensive three-dimensional conductive networks across the whole composites. The electrodes made from this composite deliver a remarkable capacity of 123 mA h g−1 when charged/discharged at 15 C, which is much higher than 91 mA h g−1 for those made from the neat LTO powders, a reflection of significant improvements in both the conductivity and Li ion diffusion coefficient in the composite electrode. When the CNF content is increased to 10 wt%, corn-dog shaped composites are formed consisting of individual CNFs penetrating the elongated LTO secondary particles along the axial direction with limited conductive networks. The electrodes made from this composite present much poorer capacities at all current rates than those with an urchin-like structure. These intriguing observations verify that both the structure of the active material and the conductivity of the electrode play important roles in delivering high capacities and rate capabilities.