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

Noncrystalline solids with LiCoC 6 H 5 O 7 ·5H 2 O and (NH 4 ) 3 LiCo(C 6 H 5 O 7 ) 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 LiCoC 6 H 5 O 7 ·5H 2 O one triionized citrate ion chelates Co 2+ while two triionized citrate ions surround Co 2+ in (NH 4 ) 3 LiCo(C 6 H 5 O 7 ) 2 . Lithium−cobalt citrates were used as precursors in the formation of lithium−cobalt mixed oxides. At 400 °C, thermal decomposition of LiCoC 6 H 5 O 7 ·5H 2 O yields a mixture of pseudo-spinel and rhombohedral LiCoO 2 . From (NH 4 ) 3 LiCo(C 6 H 5 O 7 ) 2, monophase powders of rhombohedral LiCoO 2 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 LiCoO 2 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.