Oxygen content and electrochemical activity of LiCoMnO4–δ

LiCoMnO4−δ is one of the materials first reported as a 5 V cathode in prototype lithium batteries, but as-prepared material has a residual 4 V plateau in addition to the main 5 V plateau. A combination of thermogravimetry on samples prepared under various conditions, high temperature X-ray powder diffraction and electrochemical testing, shows the 4 V plateau to depend on the extent of oxygen deficiency, δ, and to, therefore, correlate with the Mn3+ content. A complex reaction sequence occurs upon oxygen loss, including formation of oxygen-deficient spinel, precipitation of Li2MnO3 and change in cation composition of the spinel but remarkably, these reactions show a high degree of reversibility upon oxygen uptake.