Reversible Oxygen-Redox Reaction for High-Capacity Positive Electrodes

Lithium-rich oxides are an important class of high-capacity positive electrode materials that exhibit the redox reaction of oxide ions. Although the reaction mechanism of oxygen redox (or anionic redox) remained unclear by the early 2010s, decade research effort has successfully provided comprehensive understanding of how oxide ions in lithium-rich oxides undergo reversible and irreversible redox reactions. This chapter describes the oxygen-redox principle based on the molecular orbital theory as well as degradation mechanism during charge/discharge cycles. The overall oxygen-redox reaction is simply summarized using a square scheme involving both thermodynamic and kinetic factors. Furthermore, reversible oxygen-redox positive electrodes are exemplified by some specific layered oxides such as Na2Mn3O7 and O2–Li1.12Ni0.17Mn0.71O2, implicating an effective strategy for the rational design of practical high-capacity positive electrodes.