Lithium−Cobalt Citrate Precursors in the Preparation of Intercalation Electrode Materials

Noncrystalline solids with LiCoC6H5O7·5H2O and (NH4)3LiCo(C6H5O7)2 compositions were obtained by ethanol dehydration of concentrated lithium−cobalt citrate solutions. Electron spectroscopy of solutions and solid citrates, as well as IR spectroscopy of solid citrates, reveals that in LiCoC6H5O7·5H2O one triionized citrate ion chelates Co2+ while two triionized citrate ions surround Co2+ in (NH4)3LiCo(C6H5O7)2. Lithium−cobalt citrates were used as precursors in the formation of lithium−cobalt mixed oxides. At 400 °C, thermal decomposition of LiCoC6H5O7·5H2O yields a mixture of pseudo-spinel and rhombohedral LiCoO2. From (NH4)3LiCo(C6H5O7)2, monophase powders of rhombohedral LiCoO2 were obtained at 400 °C, which consist of hexagonal individual particles with a diameter of 80−120 nm. This product can be annealed up to 800 °C without marked structural changes. The rhombohedral LiCoO2 was used as active cathode material in lithium cells. Cyclic voltammogams showed little changes in the main cathodic and anodic peaks with synthesis temperature. The loss of cell capacity is limited in electrodes prepared at 400 °C from citrate precursors as compared with products of low-temperature synthetic procedures previously reported.