Oriented single-crystalline TiO₂ nanowires on titanium foil for lithium ion batteries

A simple and environmentally benign three-step hydrothermal method was developed for growing oriented single-crystalline TiO₂-B and/or anatase TiO₂ nanowire arrays on titanium foil over large areas. These nanowire arrays are suitable for use as the anode in lithium ion batteries; they exhibit specific capacities ranging from 200-250 mAh/g at charge-discharge rates of 0.3 C where 1 C is based on the theoretical capacity of 168 mAh/g. Batteries retain this capacity over as many as 200 charge-discharge cycles. Even at high charge-discharge rates of 0.9 C and 1.8 C, the specific capacities were 150 mAh/g and 120 mAh/g, respectively. These promising properties are attributed to both the nanometer size of the nanowires and their oriented alignment. The comparable electrochemical performance to existing technology, improved safety, and the ability to roll titanium foils into compact three-dimensional structures without additional substrates, binders, or additives suggest that these TiO₂ nanowires on titanium foil are promising anode materials for large-scale energy storage.