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 TiO₂-derived Magnéli phase Ti₆O₁₁ as a novel anode material for KIBs. We incorporate pristine carbon nanotube (CNT) on the TiO₂ host materials due to the low electronic conductivity of the host materials. TiO₂ transformed to Magnéli phase Ti₆O₁₁ after the first insertion/deinsertion of K ions. From the second cycle, Magnéli phase Ti₆O₁₁/CNT composite showed reversible charge/discharge profiles with ∼150 mA h g^-1 at 0.05 A g^-1. Ex situ X-ray diffraction and transmission electron microscopy analyses revealed that the charge storage process of Magnéli phase Ti₆O₁₁ proceeded via the conversion reaction during potassium ion insertion/deinsertion. The Magnéli phase Ti₆O₁₁/CNT composite electrode showed long-term cycling life over 500 cycles at 200 mA g^-1, 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.