A comprehensive review study on pure titanium niobium oxide as the anode material for Li-ion batteries

Li-ion batteries (LIBs) are in increasing demand due to their application in a large variety of fields such as portable electronic devices and electric vehicles. However, the development of high-performance electrode materials with a long lifetime, excellent rate capability, and high safety is considered as a significant challenge in the advancement of LIBs. Recently, titanium niobium oxide (TNO) compounds have been considered as one of the most promising intercalation-type anode materials and highly potential alternatives to commercial graphite and Li4Ti5O12 anodes. This family of materials possess high theoretical capacities (377–402 mAh/g) resulting from their multiple redox couples (Ti4+/Ti3+, Nb5+/Nb4+, Nb4+/Nb3+), high safety, low volume changes during cycling, high working potential, and excellent cyclic stability. However, their low electronic/ionic conductivities would result in their poor rate performance. Various strategies such as ion doping, composite preparation with conductive materials, dimensional/morphological controlling, and defective structure engineering design have been proposed to improve the rate performance of TNO materials. In this review study, dimensional/morphological controlling, and defective structure engineering approaches are reviewed for enhancing the electrochemical properties of pure TNO anodes. In this context, the detailed findings of the most important recent literature on TNO anode materials are reviewed, from their optimal synthesis parameters, and the obtained morphological/structural features to their electrochemical properties. Furthermore, the challenges to the practical use of TNO anodes in full-cell LIBs are presented. Finally, the research gaps and the future perspective are proposed.