K2Ti4O9: A Promising Anode Material for Potassium Ion Batteries

Potassium tetratitanate (K2Ti4O9) has been synthesized by solid state method using K2CO3 and TiO2, and studied as an anode material for potassium ion batteries for the first time. A discharge capacity of 80 mAh g−1 has been obtained at a current density of 100 mA g−1 (0.8 C rate) and 97 mAh g−1 at 30 mA g−1 (0.2 C rate), initially. The discharge capacity is stable at low rates of cycling. The uptake of K+ on charging K2Ti4O9 electrodes is quantitatively studied. The proposed mechanism of charging involves reduction of two Ti ions from 4+ oxidation state to 3+ oxidation state, which facilitates insertion of two K+ ions per formula unit. The rate capability experiments suggest that K2Ti4O9 is capable of undergoing charge-discharge cycling at high rates (up to 15 C rate), but with a low discharge capacity. Thus K2Ti4O9 is a promising anode material for future K-ion batteries.