K₂Ti₄O₉: A Promising Anode Material for Potassium Ion Batteries

Potassium tetratitanate (K 2 Ti 4 O 9 ) has been synthesized by solid state method using K 2 CO 3 and TiO 2 , 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 K 2 Ti 4 O 9 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 K 2 Ti 4 O 9 is capable of undergoing charge-discharge cycling at high rates (up to 15 C rate), but with a low discharge capacity. Thus K 2 Ti 4 O 9 is a promising anode material for future K-ion batteries.