Electrochemical lithium intercalation in nanosized manganese oxides

摘要

X-ray amorphous manganese oxides were prepared by reduction of sodiumpermanganate by lithium iodide in aqueous medium (MnOx-I) and by decompositionof manganese carbonate at moderate temperature (MnOx-C). TEM showed that thesematerials are not amorphous, but nanostructured, with a prominent spinelsubstructure in MnOx-C. These materials intercalate lithium with capacities upto 200 mAh/g at first cycle (potential window 1.8-4.3 V) and 175 mAh/g at 100thcycle. Best performances for MnOx-C are obtained with cobalt doping. Potentialelectrochemical spectroscopy shows that the initial discharge induces a 2-phasetransformation in MnOx-C phases, but not in MnOx-I ones. EXAFS and XANESconfirm the participation of manganese in the redox process, with variations inlocal structure much smaller than in known long-range crystallized manganeseoxides. X-ray absorption spectroscopy also shows that cobalt in MnOx-C isdivalent and does not participate in the electrochemical reaction.