Layered K_0.28MnO₂·0.15H₂O as a Cathode Material for Potassium-Ion Intercalation

Here, we present K0.28MnO2·0.15H2O, which has a two-dimensional open framework, as an intercalation host for potassium ions. K0.28MnO2·0.15H2O has a layered structure consisting of edge-sharing MnO6 octahedra with a large basal spacing of ∼7.3 Å, which facilitates K+-ion mobility. Water molecules in the interlayers between the MnO2 layers play an important role as a pillar to support the structure during repetitive de/potassiation cycles, as confirmed by an operando X-ray diffraction study. As a result, the large K+ ions readily migrate into the crystal structure, resulting in satisfactory electrochemical performance in K-cells. With the aid of the structural pillar, the K0.28MnO2·0.15H2O cathode delivers a high reversible capacity of 150 mA h g–1 over 100 cycles at a rate of 0.1 C (15 mA g–1), with acceptable power capability up to 5 C-rates.