Rutile TiO2 Creates Advanced Na-Storage Materials

Rutile-type titanium oxide (TiO2) is a resource-rich and inexpensive material with a one-dimensional ion-diffusion path along the c-axis. However, it has received no attention as an anode material for Na-ion batteries because of its low electronic conductivity and limited ion diffusion in the ab-plane direction. We have revealed for the first time the reversible Na insertion–extraction reaction of rutile TiO2 and have recently reported the improvement in the anode performances by doping with various impurity elements such as Nb5+, Ta5+, and In3+. In this Review, we introduce a material chemistry methodology to enhance the anode properties of the rutile TiO2 electrode by impurity doping, introduction of oxygen vacancies, formation of single-crystalline particles, and reduction of their aspect ratio. The knowledge is remarkably effective for creating advanced high-performance anode materials with not only using rutile TiO2 but also using anatase TiO2 and other titanium-based oxides.