Synthesis of hollandite-type Li xMnO 2 by Li + ion-exchange in molten salt and lithium insertion characteristics

Abstract

The Li + ion-exchange reaction of K +-type α-K 0.14MnO 1.93· nH 2O containing different amounts of water molecules ( n = 0–0.15) with a large (2 × 2) tunnel structure has been investigated in a LiNO 3–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-MnO 2 were exchanged by Li + ions in the molten salt, resulting in the Li +-type α-MnO 2 containing different amounts of Li + ions and lithium oxide (Li 2O) 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-MnO 2 samples have been investigated as insertion compounds in the search for new cathode materials for rechargeable lithium batteries. The Li + ion-exchanged α-MnO 2 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 Li 2O in the (2 × 2) tunnels.