Synthesis, crystal structure, and electrochemical properties of hollandite-type KxTi1 − yMnyO2

Single phase specimens of hollandite-type MnO2, TiO2, and KxTi1 − yMnyO2, were synthesized, and their electrochemical properties and crystal structures were investigated. The chemically prelithiated MnO2 and sufficiently K+-extracted TiO2 specimens exhibited good charge-discharge properties. The initial Li insertion capacities were about 160 mAh/g for TiO2 and about 230 mAh/g for MnO2. In contrast, the partially K+-extracted solid solution, K0.055Ti0.75Mn0.25O2, showed a poor charge-discharge property. The small amount of residual K+ ions in the tunnel structure affected significantly the charge-discharge property. Electron density distribution images obtained from X-ray powder diffraction data elucidated that stabilizing O atoms locate at the tunnel space of lithiated MnO2 but the tunnel space of TiO2 was essentially empty.