Solid electrolyte interface (SEI) is crucial for the electrochemical performance of potassium-ion batteries. Conventional strongly solvating electrolyte can form stable SEI, but most of the components are organic, resulting in the SEI structure being thick and soft, and causing co-intercalation behaviour of anion with the solvent. Here, we found that weakening the interaction between anion and solvent can change the cation solvation sheath structures , leading to the inorganic components derived from anions can also participate in the formation of SEI, to form a uniformly shaped SEI with good mechanical properties, and thus to improve the performance of the potassium-ion batteries. Hence, tetrahydrofuran (THF)-based weakly solvating electrolyte exhibits K⁺ intercalation behaviour at the graphite anode (capacity retention of 98.9%) and highly stable plating/stripping of potassium metal (average Coulombic efficiency of 96.5%). The cation solvation sheath structure modification strategy provides a promising approach for the development of high-performance electrolytes and beyond.

Potassium ion batteries; Electrolyte; Weak solvation; Solid electrolyte Interface; Cycling performance