High-donor electrolyte endows graphite with anion-derived interphase to achieve stable K-storage

Graphite anodes are expected to be applied in potassium-ion batteries, but it is limited by uncontrolled volume fluctuation and dendrite growth during cycles. Herein, an anion-derived interphase with high mechanical strength and ionic conductivity is constructed to address the aforementioned issues using an amide-based electrolyte. The high-donor number for an amide molecule can strengthen the solvation with K+, ensuring more anions enter the primary solvation sheath. The shortened distance is in favor of the electron transfer from the solvated K+ to the anion and subsequently motivates the anion reduction. The obtained inorganic-rich interphase buffers volume change, suppresses K dendrite propagation, and facilitates ion diffusion. Based on these, symmetric K//K cells could operate stable plating and stripping with a small polarization of 0.15 V for over 2800 h. The graphite electrode achieves a highly reversible phase transition of C↔KC60↔KC48↔KC36↔KC24↔KC8. A high discharge capacity of 217.6 mA h g−1 with retention of 86.9% is obtained after 100 cycles. The assembled full battery also exhibits a high energy density of 52.5 W h kg−1. This work highlights the importance of the interfacial structure and provides a brand-new strategy for designing high-performance electrolytes.