Weakly solvating electrolyte enabling solvent-free co-intercalation for stable potassium-ion storage in graphite

Ether electrolytes for potassium-ion batteries exhibit a broader electrochemical window and greater applicability, yet most of them are high-concentration electrolytes with elevated cost. In this study, we propose the use of a weakly solvating cyclic ether electrolyte with tetrahydropyran (THP) as the solvent. This approach induces the formation of a thin and dense inorganic-rich solid electrolyte interphase (SEI) film, which is accompanied by a decrease in the activation energy of electrode interfacial reactions due to the weak ligand binding of THP with K⁺. Density functional theory (DFT) simulations also corroborate the hypothesis that K⁺ has a lower binding energy with THP. During potassium storage process, the phenomenon of solvent co-intercalation of graphite does not occur, which greatly reduces the destruction of the graphite structure and enables a superior electrochemical performance and enhanced cycling stability at a lower concentration (2 M). At a current density of 0.2 C (55.8 mA·g^–1), the battery can be stably cycled for 800 cycles (approximately 8 months) with a specific capacity of 171.8 mAh·g^–1. This study provides a new ether-based electrolyte for potassium ion batteries and effectively reduces the electrolyte cost, which is expected to inspire further development of energy storage batteries.