Disordering and electronic state of cobalt ions in mechanochemically synthesized LiCoO2

Mechanical activation (MA) combined with heat treatment at moderate temperatures was used to prepare disordered and highly dispersed LiCoO2 starting from the mixtures of various cobalt precursors (CoOOH, Co(OH)(2), and Co) and LiOH. X-ray powder diffraction and IR spectroscopy were used to investigate the phase composition and the crystal structure of as-prepared samples, while the electronic state of cobalt ions was characterized by diffuse reflectance electron spectroscopy. MA of the LiOH + CoOOH mixture led to the formation of LT-LiCoO2 with a cubic spinel-related structure. Heat treatment at 600 degreesC of the latter resulted in the formation of HT-LiCoO2 with a hexagonal layered structure similar to ceramic LiCoO2, However, as-prepared HT-LiCoO2 is characterized by Co octahedra less perfect than those of ceramic LiCoO2. All MA-LiCoO2 samples are exclusively described by localized d electrons. (C) 2002 Elsevier Science (USA).