Electrochemical lithium intercalation in nanosized manganese oxides

Abstract

Abstract X-ray amorphous manganese oxides were prepared by reduction of sodium permanganate by lithium iodide in aqueous medium (MnO x -I) and by decomposition of manganese carbonate at moderate temperature (MnO x -C). TEM showed that these materials are not amorphous, but nanostructured, with a prominent spinel substructure in MnO x -C. These materials intercalate lithium with capacities up to 200 mAh/g at first cycle (potential window 1.8–4.3 V) and 175 mAh/g at 100th cycle. Best performances for MnO x -C are obtained with cobalt doping. Potential electrochemical spectroscopy shows that the initial discharge induces a 2-phase transformation in MnO x -C phases, but not in MnO x -I ones. EXAFS and XANES confirm the participation of manganese in the redox process, with variations in local structure much smaller than in known long-range crystallized manganese oxides. X-ray absorption spectroscopy also shows that cobalt in MnO x -C is divalent and does not participate in the electrochemical reaction.