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

Layered LiNi_0.4Co_0.2Mn_0.4O₂, LiLi_0.182Ni_0.182Co_0.091Mn_0.545]O₂, LiLi_1/3Mn_2/3]O₂ powder materials were prepared by rheological phase method. XRD characterization shows that these samples all have analogous structure to LiCoO₂. LiLi_0.182Ni_0.182Co_0.091Mn_0.545]O₂ can be considered to be the solid solution of LiNi_0.4Co_0.2Mn_0.4O₂ and LiLi_1/3Mn_2/3]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 LiLi_0.182Ni_0.182Co_0.091Mn_0.545]O₂ electrode. The irreversible oxidation reaction occurred in the first charging above 4.5 V is ascribed to the contribution of LiLi_1/3Mn_2/3]O₂ component, which maybe extract Li⁺ from the transition layer in LiLi_1/3Mn_2/3]O₂ or LiLi_0.182Ni_0.182Co_0.091Mn_0.545]O₂ through oxygen release. This step also activates Mn⁴⁺ of LiLi_1/3Mn_2/3]O₂ or LiLi_0.182Ni_0.182Co_0.091Mn_0.545]O₂, it can be reversibly reduced/oxidized between Mn⁴⁺ and Mn³⁺ in the subsequent cycles.