Kinetic square scheme in oxygen-redox battery electrodes

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 − ↔ O 2− (4.4 V vs. Li/Li + ) and polarizing O 2 2− → O 2− (3.3 V vs. Li/Li + ) coexist and kinetically compete in O2-type Li 1.12- y Ni 0.17 Mn 0.71 O 2 . The oxygen-redox reaction is described as a square scheme, involving bond-forming 2O − → O 2 2− and bond-cleaving O 2 4 → 2O 2− processes, where preventing the formation of O 2 2− is essential to realize non-polarizing and energy-efficient oxygen-redox reactions. Kinetic formation of the peroxo-like O 2 2− dimer is identified as the origin of a voltage hysteresis in oxygen-redox battery electrodes.