Studies on Li---Mn---O spinel system (obtained from melt-impregnation method) as a cathode for 4 V lithium batteries Part II. Optimum spinel from γ-MnOOH

The mechanism for the formation of a spinel compound from the reaction of LiNO3 with a high density γ-MnOOH is extensively investigated in terms of pore-size distribution, X-ray diffraction, thermal and chemical analyses. The reaction of MnOOH with LiNO3 at about 300°C yields a product that consists of domains of lithiated MnO2 phase with an approximate composition of Li0.3MnO2. This product ultimately transforms to a disordered spinel phase of composition LiMn2O4 + y at 300–400°C. The disordered spinel is converted to a well-ordered as the temperature is raised above 550°C. The oxygen content depends on the final heating temperature and atmosphere. Compounds obtained at high temperature, or in N2, have a large capacity and unstable rechargeability. By contrast, some compounds prepared at low temperature, or with a slightly high lithium content in the starting materials, exhibit an improvement in rechargeability. The possible cause for the differences in electrochemical characteristics of both types of compound is proposed.