Magnéli Phase Titanium Oxide as a Novel Anode Material for Potassium-Ion Batteries.

Recently, K-ion batteries (KIBs) have attracted attention for potential applications in next-generation energy storage devices principally on the account of their abundancy and lower cost. Herein, for the first time, we report an anatase TiO-derived Magnéli phase TiO as a novel anode material for KIBs. We incorporate pristine carbon nanotube (CNT) on the TiO host materials due to the low electronic conductivity of the host materials. TiO transformed to Magnéli phase TiO after the first insertion/deinsertion of K ions. From the second cycle, Magnéli phase TiO/CNT composite showed reversible charge/discharge profiles with ∼150 mA h g at 0.05 A g. Ex situ X-ray diffraction and transmission electron microscopy analyses revealed that the charge storage process of Magnéli phase TiO proceeded via the conversion reaction during potassium ion insertion/deinsertion. The Magnéli phase TiO/CNT composite electrode showed long-term cycling life over 500 cycles at 200 mA g, exhibiting a capacity retention of 76% and a high Coulombic efficiency of 99.9%. These salient results presented here provide a novel understanding of the K-ion storage mechanisms in the extensively investigated oxide-based material for Li-ion batteries and Na-ion batteries, shedding light on the development of promising electrode materials for next-generation batteries.