Investigation of Potassium Storage in Layered P3-Type K0.5 MnO2 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 K0.5 MnO2 as a potential cathode material for K-ion batteries as an alternative to Li technology. K0.5 MnO2 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.