On the incorporation of extra Li in lithium cobaltate Li1 + xCo1 − xO2

Novel Li1 + xCo1 − 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 Li1 + xCo1 − xO2 compositions with x ~ 0.12. The structure and cationic distribution in Li1 + xCo1 − xO2 were monitored by XRD powder analysis, TEM analysis and 6Li MAS NMR spectroscopy. Pure Li1 + xCo1 − 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 Li1 + xCo1 − 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.

Research Highlights
► High-pressure synthesis enables to accommodate extra lithium in LiCoO2.
► Extra lithium is incorporated into the spinel modification of LiCoO2.
► Layered modification of LiCoO2 remains rigid.
► Solid state 6Li MAS NMR reflects the distribution of lithium in the oxides.