Low temperature synthesis of gamma-LixMnO2 powders in ethylene glycol

The reaction of Electrolytic Manganese Dioxide (EMD gamma -MnO2) with anhyd rous LiOH in ethylene glycol (EG) was studied. It was found that this react ion proceeds in three steps while the reaction temperature increases: (1) c hemical insertion of lithium in gamma -MnO2, structure leading to gamma -Li xMnO2 phase, (2) progressive dissolution of this reduced phase and (3) prec ipitation of a Li-free organo-metallic compound Mn(OCH2CH2O) with lamellar structure (Mn-EG). If the reaction is performed at moderate temperature (T< 120<degrees>C), we can limit the dissolution reaction and completely avoid the precipitation of the organo-metallic phase. The x value in the resultin g LixMnO2 phases is found to be mainly linked to the temperature of the rea ction medium. Although a maximum value of x = 0.35 can be obtained at 30 de greesC, Li0.84MnO2 can be prepared at 120 degreesC. We showed that the LixM nO2 formation mechanism consists of a direct lithium insertion in the struc ture of MnO2 concomitant with Mn reduction by the organic medium. By changi ng the medium cationic content of the medium, we were able to prepare vario us reduced MnO2 compositions, such as HxMnO2, (Li,H)(x)MnO2, (Na,H)(x)MnO2, (K,H)(x)MnO2. These LixMnO2 phases, when rested in half Li-cells, show poo r cyclability but large first charge capacity (260 mAh/g for x=0.84) that t akes place at significantly higher voltage than observed for electrochemica lly inserted EMD. This finding was related to the presence of chemically in serted protons besides lithium ions. (C) 2000 Elsevier Science Ltd. All rig hts reserved.