Physical and electrochemical characterization of nanocrystalline LiMn2O4 prepared by a modified citrate route

Nanocrystalline LiMn2O4 spinel oxides have been synthesized successfully by using a modified citrate route with ethanol dehydration of a Li–Mn–citrate complex solution. The effects of sintering temperature and atmosphere on the physicochemical properties of the LiMn2O4 powders have been carefully examined by means of X-ray diffraction, electron microscopy, BET measurement, and X-ray absorption spectroscopy. It becomes clear that an oxidative atmosphere induces a partial agglomeration of particles at high temperature, but gives rise to an effective decomposition of the citrate precursors at low temperature. It is also found that a lowering of the sintering temperature enhances the average oxidation state of manganese with an increase in surface defects. The electrochemical property of the present LiMn2O4 nanocrystals has also been measured to compare with that of lithium manganate prepared by a solid-state reaction, which confirms the effectiveness of the present modified citrate route. The evolution of geometrical and electronic structures during the charging process has also been investigated with X-ray absorption spectroscopy, and reveals shortening of the (Mn–O) bond distances induced by lithium de-intercalation.