Ti2Nb2xO4+5x anode materials for lithium-ion batteries: a comprehensive review

Lithium-ion batteries (LIBs) have achieved great success in portable electronics, but their applications in electric vehicles (EVs) are still very challenging owing to the lack of high-performance electrode materials with high specific capacities, safety, rate capability and cycling stability. Recently, intercalating Ti2Nb2xO4+5x anode materials have received intensive attention owing to their high specific capacities (388–402 mA h g−1), high safety, prolonged cycling stability, easy state-of-charge evaluation and significant pseudocapacitive behavior. Their limited rate capabilities can be significantly improved by various modifications, including crystal structure modification, formation of a composite conductive phase, particle size reduction, and combined methods. These modified Ti2Nb2xO4+5x materials can be promising and practical anode materials for LIBs in EVs. Here, the research history, crystal structures, characteristics, working mechanisms and various modifications of Ti2Nb2xO4+5x are comprehensively reviewed. The relations between the material composition, material fabrication, material structure, material properties and LIB performance are emphasized. An insight into future directions in this research community is also provided.