Inhibiting Graphite Co-Intercalation through Weak Solvating Ether Electrolytes for Stable Cycling in Potassium-Ion Batteries

Ether-based electrolytes are widely acknowledged for their potential to form stable solid electrolyte interfaces (SEIs) for stable anode performance. However, conventional ether-based electrolytes have shown a tendency for cation–solvent co-intercalation phenomena on graphite electrodes, resulting in lower capacity and higher voltage platforms compared to those of neat cation insertion in ester-based electrolytes. In response, we propose the development of weakly solvating ether solvents to weaken the interaction between cations and solvents, thereby suppressing co-intercalation behavior. In this study, theoretical calculations first demonstrate that tetrahydrofuran (THF) exhibits a smaller binding energy (−0.89 eV) with K+ in comparison to 1,2-dimethoxyethane (DME, −1.37 eV) and ethylene carbonate (EC, −1.26 eV). Consequently, solvent co-intercalation, electrolyte decomposition, and graphite exfoliation are suppressed in a 1 M solution of K salt in THF. Simultaneously, a uniform and robust SEI is formed to improve the K+ storage stability of the graphite anode (99% capacity retention after 200 cycles at 0.1 A g–1). Meanwhile, such a THF-based K-ion electrolyte also exhibits good adaptability when applied to both hard and soft carbonaceous anodes. This work addresses the challenges associated with achieving high capacity and stable graphite anodes in ether-based electrolytes, offering a solution to the problem of cation–solvent co-intercalation. The findings also promote the application of graphite anodes in potassium-ion batteries, emphasizing the significance of weakly solvating ether electrolytes in enhancing battery performance and stability.