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.

Automated summary

Graphite anodes face challenges in potassium-ion batteries due to volume fluctuation and dendrite growth. In this study, an anion-derived interphase with high strength and conductivity is created using an amide-based electrolyte. The interphase buffers volume change, suppresses dendrite propagation, and facilitates ion diffusion. Stable plating and stripping of symmetric K//K cells with low polarization is achieved. The graphite electrode shows highly reversible phase transition and high discharge capacity, and the assembled full battery exhibits high energy density. This work emphasizes the importance of interfacial structure and provides a new strategy for designing high-performance electrolytes.