STUDIES ON LI-MN-O SPINEL SYSTEM (OBTAINED FROM MELT-IMPREGNATION METHOD) AS A CATHODE FOR 4-V-LITHIUM BATTERIES .2. OPTIMUM SPINEL FROM GAMMA-MNOOH

The mechanism for the formation of a spinel compound from the reaction of LiNO3 with a high density gamma-MnOOH is extensively investigated in terms of pore-size distribution, X-ray diffraction, thermal and che mical analyses. The reaction of MnOOH with LiNO3 at about 300 degrees C yields a product that consists of domains of lithiated MnO2 phase wi th an approximate composition of Li0.3MnO2. This product ultimately tr ansforms to a disordered spinel phase of composition LiMn2O4+y at 300- 400 degrees C. The disordered spinel is converted to a well-ordered sp inel as the temperature is raised above 550 degrees C. The oxygen cont ent depends on the final heating temperature and atmosphere. Compounds obtained at high temperature, or in N-2, have a large capacity and un stable rechargeability. By contrast, some compounds prepared at low te mperature, or with a slightly high lithium content in the starting mat erials, exhibit an improvement in rechargeability. The possible cause for the differences in electrochemical characteristics of both types o f compound is proposed.