Hydrogenated Anatase and Rutile TiO₂for Sodium-Ion Battery Anodes

Defective transition metal oxides prepared via a hydrogenation treatment have attracted growing attention for use as electrode materials of batteries and supercapacitors due to their improved electrochemical properties. In this work, two TiO2 phases, namely, rutile (TiO2-R) and anatase (TiO2-A), and their hydrogenated phases (denoted with the prefix "H") are investigated as anodes for sodium-ion batteries. The charge-discharge properties of both phases can be enhanced via a high-pressure hydrogenation treatment. For example, H-TiO2-A exhibits exceptional high-rate performance (100 mA h g-1 at 10,000 mA g-1 vs 5 mA h g-1 at the same current rate for TiO2-A) and great cycling stability (80% capacity retention after 4500 cycles). The introduction of oxygen vacancies increases the electronic and ionic conductivity of TiO2 and the disordered structure offers more active sites for electrochemical reactions. The H-TiO2-R and H-TiO2-A electrodes are compared for sodium-ion battery applications. The superior performance of the former electrode is supported by the generalized gradient approximation Perdew-Burke-Ernzerhof density functional calculation.