LAUSR

A major challenge regarding the incorporation of Li-ion batteries into the large-scale applications is the safety concerns, that arise from non-equilibrium service conditions such as temperature rise, high cut-off voltage charging or mechanical damage. Under these circumstances, the oxide cathode decomposes and releases oxygen which then reacts exothermically with the decomposed organic electrolyte and can ignite the combustible components of the Li-ion battery [1]. Considering the significance of this issue, O2 evolution from oxide cathodes has been studied with various experimental and computational techniques. Overall, it is understood that the extraction of Li ions from the cathode unit cell results in the formation of under-coordinated oxygen atoms, which destabilizes the structure. At elevated temperatures, these oxygen atoms break the bonds with the transition metals and form O2 molecules leaving the structure. As a result, the layered structure will transform to spinel and rock salt phases, which contain less oxygen in their unit cell. Utilizing in-situ heating STEM/EELS analysis together with ab-initio molecular dynamic (AIMD) we have shown that the extent of oxygen-release and the phase transitions are dependent on the surface fraction and facet termination of the individual particles [2].