Layered KMnO·0.15HO as a Cathode Material for Potassium-Ion Intercalation.

Here, we present KMnO·0.15HO, which has a two-dimensional open framework, as an intercalation host for potassium ions. KMnO·0.15HO has a layered structure consisting of edge-sharing MnO octahedra with a large basal spacing of ∼7.3 Å, which facilitates K-ion mobility. Water molecules in the interlayers between the MnO 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 KMnO·0.15HO cathode delivers a high reversible capacity of 150 mA h g over 100 cycles at a rate of 0.1 C (15 mA g), with acceptable power capability up to 5 C-rates.