Energy band-engineered solid electrolyte interphase for stable potassium-ion batteries

The solid electrolyte interphase (SEI) critically governs the performance of potassium-ion batteries (PIBs). However, present-day SEIs cannot prevent persistent parasitic reactions between the electrode and electrolyte due to SEI’s low energy band gap and high ion migration energy barrier. Here, we propose an SEI energy band engineering strategy by screening the band-gap width and migration energy barrier of various SEI components, and we found that the Si-O-SEI simultaneously increases SEI’s energy band gap and lowers the ion migration energy barrier to enable good electron-blocking capability and high K + ion diffusion. Our Si-O-SEI prepared in situ on the electrode surface, using a simple additive, enables carbonate-based electrolytes to achieve a highly reversible potassium plating and stripping with a Coulombic efficiency (CE) of 99.2%, together with the upgraded reversibility of the graphite anode. SEI composition and structural modulation through a simple and generic strategy provide a valuable research platform for developing high-performance PIB electrolytes.