The power of Nb-substituted TiO2 in Li-ion batteries: Morphology transformation induced by high concentration substitution

This study aims to investigate the power potential of Li-ion batteries using a hydrothermal process to synthesize nanoscale Nb-TiO2 with high surface area. By substituting Nb into anatase TiO2, the rate capability of Li-ion batteries is improved with the formation of nanoplate Nb-TiO2 containing (001) facets and NbOx species. In addition, the high solubility of Nb promotes the transformation of TiO2 from hollow-like to plate-like morphology, accelerating the Li-ion surface transportation over a large contact area. With respect to rate capability, Nb-TiO2 displays a high capacity of 220 mAh g(-1) at 0.5C and retains 127 mAh g(-1) at 10C. Additionally, the cyclability test exhibits less degradation after 10,000 cycles. In order to investigate the mechanisms of capability improvement, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) are applied to measure the Li-ion diffusivity and surface chargetransfer resistance. The results demonstrate that both Li-ion diffusivity and surface charge-transfer ability are enhanced, leading to pseudocapacitance. Thus, it can be concluded that nanoplate Nb-TiO2 exhibits superior rate capability by the improvement of pseudocapacitance. This study derives a novel process to synthesize nanoplate TiO2 and should provide a potential approach for industrial fabrication of high power Li-ion batteries. (C) 2015 Elsevier B.V. All rights reserved.