Origin of the irreversible plateau (4.5Â V) of Li[Li0.182Ni0.182Co0.091Mn0.545]O2 layered material

Layered LiNi0.4Co0.2Mn0.4O2, Li[Li0.182Ni0.182Co0.091Mn0.545]O2, Li[Li1/3Mn2/3]O2 powder materials were prepared by rheological phase method. XRD characterization shows that these samples all have analogous structure to LiCoO2. Li[Li0.182Ni0.182Co0.091Mn0.545]O2 can be considered to be the solid solution of LiNi0.4Co0.2Mn0.4O2 and Li[Li1/3Mn2/3]O2. Detailed information from XRD, ex situ XPS measurement and electrochemical analysis of these three materials reveals the origin of the irreversible plateau (4.5 V) of Li[Li0.182Ni0.182Co0.091Mn0.545]O2 electrode. The irreversible oxidation reaction occurred in the first charging above 4.5 V is ascribed to the contribution of Li[Li1/3Mn2/3]O2 component, which maybe extract Li+ from the transition layer in Li[Li1/3Mn2/3]O2 or Li[Li0.182Ni0.182Co0.091Mn0.545]O2 through oxygen release. This step also activates Mn4+ of Li[Li1/3Mn2/3]O2 or Li[Li0.182Ni0.182Co0.091Mn0.545]O2, it can be reversibly reduced/oxidized between Mn4+ and Mn3+ in the subsequent cycles.