Layered K0.28MnO2•0.15H2O as a Cathode Material for Potassium-Ion Intercalation

Here, we present K0.28MnO2 center dot 0.15H(2)O, which has a two-dimensional open framework, as an intercalation host for potassium ions. K0.28MnO2 center dot 0.15H(2)O has a layered structure consisting of edge-sharing MnO6 octahedra with a large basal spacing of similar to 7.3 angstrom, 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 center dot 0.15H(2)O 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.