Synthesis of hollandite-type LiMnO2 by Li+ ion-exchange in molten salt and lithium insertion characteristics

The Li+ ion-exchange reaction of K+-type alpha-K0.14MnO1.93 center dot nH(2)O containing different amounts of water molecules (n=0-0.15) with a large (2 x 2) tunnel structure has been investigated in a LiNO3-LiCl molten salt at 300 degrees 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 x 2) tunnels of alpha-MnO2 were exchanged by Li+ ions in the molten salt, resulting in the Li+-type alpha-MnO2 containing different amounts of Li+ ions and lithium oxide (Li2O) in the (2 x 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 alpha-MnO2 samples have been investigated as insertion compounds in the search for new cathode materials for rechargeable lithium batteries. The Li+ ion-exchanged alpha-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 x 2) tunnels. (c) 2007 Elsevier Ltd. All rights reserved.