Kinetic square scheme in oxygen-redox battery electrodes

Abstract

Integrating an anionic-redox (or oxygen-redox) capacity with a conventional cationic-redox capacity is a promising strategy for large-capacity battery cathodes exceeding present technical limits. However, most oxygen-redox cathodes exhibit a large charge/discharge voltage hysteresis (>0.5 V), resulting in poor energy efficiency and impractical implementation. Here, we show that nonpolarizing O− ↔ O2− (4.4 V vs. Li/Li+) and polarizing O22− → O2− (3.3 V vs. Li/Li+) coexist and kinetically compete in O2-type Li1.12-yNi0.17Mn0.71O2. The oxygen-redox reaction is described as a square scheme, involving bond-forming 2O− → O22− and bond-cleaving O24− → 2O2− processes, where preventing the formation of O22− is essential to realize non-polarizing and energy-efficient oxygen-redox reactions.