Investigation of Potassium Storage in Layered P3‐Type K 0.5 MnO 2 Cathode

Novel and low‐cost batteries are of considerable interest for application in large‐scale energy storage systems, for which the cost per cycle becomes critical. Here, this study proposes K 0.5 MnO 2 as a potential cathode material for K‐ion batteries as an alternative to Li technology. K 0.5 MnO 2 has a P3‐type layered structure and delivers a reversible specific capacity of ≈100 mAh g −1 with good capacity retention. In situ X‐ray diffraction analysis reveals that the material undergoes a reversible phase transition upon K extraction and insertion. In addition, first‐principles calculations indicate that this phase transition is driven by the relative phase stability of different oxygen stackings with respect to the K content.