Effects of Phase Change and Cu Doping on the Li Storage Properties of Rutile TiO₂ (Supporting Information)

The crystal structure and Li storage properties of Cu-doped rutile TiO₂ after a phase change caused by lithiation were investigated for the first time. Structural analysis results confirmed that undoped rutile TiO₂ was transformed to a disordered layered rock-salt Li<i>_x</i>TiO₂ structure with a small volume expansion of only 1 % when cycled in a potential range of 1.0–3.0 V vs. Li⁺/Li. A substitutional solid solution of Cu²⁺ was formed in layered Li<i>_x</i>TiO₂. The Cu doping increased both the interlayer distance and electronic conductivity of the layered Li<i>_x</i>TiO₂. As an Li-ion battery anode, a Cu-doped TiO₂ electrode exhibited a long cycle life, maintaining a reversible capacity of 120 mAh g⁻¹ over 10000 cycles at 5C and an excellent rate capability of 108 mAh g⁻¹ at 50C. Furthermore, this electrode could also be potentially used as a Na storage material. These attractive properties demonstrate high applicability of Cu-doped rutile TiO₂ as a novel anode material.<br>