Synthesis of hollandite-type LixMnO2 by Li+ ion-exchange in molten salt and lithium insertion characteristics

The Li+ ion-exchange reaction of K+-type α-K0.14MnO1.93·nH2O containing different amounts of water molecules (n = 0–0.15) with a large (2 × 2) tunnel structure has been investigated in a LiNO3–LiCl molten salt at 300 °C. The Li+ ion-exchanged products were examined by chemical analysis, X-ray diffraction, and transmission electron microscopy measurements. The K+ ions and the hydrogens of the water molecules in the (2 × 2) tunnels of α-MnO2 were exchanged by Li+ ions in the molten salt, resulting in the Li+-type α-MnO2 containing different amounts of Li+ ions and lithium oxide (Li2O) in the (2 × 2) tunnels with maintaining the original hollandite structure.The electrochemical properties and structural variation with initial discharge and charge–discharge cycling of the Li+ ion-exchanged α-MnO2 samples have been investigated as insertion compounds in the search for new cathode materials for rechargeable lithium batteries. The Li+ ion-exchanged α-MnO2 samples provided higher capacities and higher Li+ ion diffusivity than the parent K+-type materials on initial discharge and charge–discharge cyclings, probably due to the structural stabilization with the existence of Li2O in the (2 × 2) tunnels.