Thermal conversion of gels prepared by the complex sol-gel process (CSGP) from Li+-Me2+-CH3COO--ascorbic acid (ASC)-NH4+-OH-H2O systems to LiMn2O4 and LiNixCo1-xO2

The spinel LiMn2O4 and layered oxides LiNixCo1-xO2 (x=1; 0.75; 0) have been prepared by Complex Sol-gel Process (CSGP). The appropriate sol compositions were obtained from acetate aqueous solution of metals containing ascorbic acid by alkalizing it with aqueous ammonia. Gels were produced from the systems by evaporation of water and other volatilies at elevated temperatures. A very intense foaming was observed during the heating at the temperatures higher than 140degreesC. To avoid foaming in the course of the final thermal treatment, a very long (lasting several days) soaking step was found necessary. However pretreated materials exhibit self-ignition at temperature range 320-500degreesC dependent on socking conditions. The dependence of self-ignition temperature on carbon content in bed as well as on specific surface has not been proved. Final thermal transformation of gel to solid was studied by TG, DTA, XRD, and IR methods. It was observed that final compounds are formed faster from precursors which did not contain Ni (e.g. LiMn2O4 and LiCoO2), while Li carbonate is not formed in these systems. In contrast, in Li-Ni(Co)-O the formation of Li(or Ni)CO3 was always proved. In addition, during the thermal treatment Ni species are partially reduced even to metallic phase. This effect evidently restrains the formation of pure layered oxides phase. Electrochemical properties of carbonate free compounds are definitely better than of those containing CO3.