Indium-Doped Rutile Titanium Oxide with Reduced Particle Length and Its Sodium Storage Properties.

We hydrothermally synthesized In-doped rutile TiO particles in an anionic surfactant solution and investigated the influences of In doping and the particle morphology on the Na storage properties. The solid solubility limit was found to be 0.8 atom % in In-doped TiO. In the case where no surfactant was used, the best anode performance was obtained for 0.8 atom % In-doped TiO electrode by the benefits of three doping effects: (i) expanded diffusion-path size, (ii) improved electronic conductivity, and (iii) reduced electron charge density in the path. Further enhancement in the performance was achieved for the In-doped TiO with a reduced particle length by the synthesis in the surfactant solution. This electrode exhibited a better cycle stability and maintained a high discharge capacity of 240 mA h g for 200 cycles. The reason is probably that Na can be inserted in the inner part of TiO particles because of its reduced particle length.