The high temperature cyclic voltammetric performances of various LiMnO spinel materials were investigated. A split of the second reduction peak at x>0.5, in Li x Mn2O4, during insertion was found at temperatures higher than 70°C, which is a characteristic of Li-stoichiometric LiMnO spinel. The disproportionation dissolution of stoichiometric spinel intensified by the elevated temperature in slightly acidic electrolyte is considered responsible for the occurrence of the phenomenon. The electrochemical characteristics and dependence of the peak split on material natures, preparation temperatures, scan rates, electrolyte solvents and salts species are also presented.