Multiple Electron Transfers Enable High‐Capacity Cathode Through Stable Anionic Redox

Abstract

Single‐electron transfer, low alkali metal contents, and large‐molecular masses limit the capacity of cathodes. This study uses a cost‐effective and light‐molecular‐mass orthosilicate material, K2FeSiO4, with a high initial potassium content, as a cathode for potassium‐ion batteries to enable the transfer of more than one electron. Despite the limited valence change of Fe ions during cycling, K2FeSiO4 can undergo multiple electron transfers via successive oxygen anionic redox reactions to generate a high reversible capacity. Although the formation of O‒O dimers in K2FeSiO4 occur upon removing large amounts of potassium, the strong binding effect of Si on O mitigates irreversible oxygen release and voltage degradation during cycling. K2FeSiO4 achieves 236 mAh g−1 at 50 mA g−1, with an energy density of 520 Wh kg−1, which can be comparable with commercial LiFePO4 materials. Moreover, it also exhibits 1400 stable cycles under high‐current conditions. These findings enhance the potential commercialization prospects for potassium‐ion batteries.