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.