Abstract

Novel Li_1 + xCo_1 − xO₂ compositions were prepared by two synthesis methods: solid-state reaction between Li₂O₂ and Co₃O₄ under high pressure and mechanochemically assisted reaction between CoOOH and LiOH.H₂O. Variation of the Li-to-Co ratio in the precursor mixture from 1.0 to 1.5 resulted in the formation of Li_1 + xCo_1 − xO₂ compositions with x ~ 0.12. The structure and cationic distribution in Li_1 + xCo_1 − xO₂ were monitored by XRD powder analysis, TEM analysis and ⁶Li MAS NMR spectroscopy. Pure Li_1 + xCo_1 − xO₂ with Li₂Ti₂O₄-type spinel structure was obtained under high pressure only. Mechanochemically assisted synthesis at 400 °C yielded layered LiCoO₂ with a small amount of spinel-type Li_1 + xCo_1 − xO₂. The spinel modification of LiCoO₂ is able to accommodate extra Li, so that the Li-to-Co ratio is higher than 1. The layered modification of LiCoO₂ is more rigid with respect to the accommodation of more than one lithium atom.