Solvation engineering decouples bulk and interfacial chemistry for robust potassium-ion batteries

The development of high-performance potassium-ion batteries is constrained by the intrinsic trade-off between bulk and interfacial electrolyte properties, a dilemma exacerbated under harsh operating conditions. Here we report a solvation structure engineering strategy to decouple these conflicting factors, breaking this trade-off while enabling non-flammability, stable, and fast-cycling performance in batteries. By incorporating a 2,2,2-trifluoroethyl trifluoromethanesulfonate solvent into a flame-retardant trimethyl phosphate-based electrolyte, we created a dynamic, weakly bound anion-K+ solvation structure that is regulated by anion-solvent interactions, while maintaining adequate anion participation in the solvation sheath. This configuration exhibits interface stabilization and low desolvation barriers, with a kinetic compensation mechanism yielding a higher K⁺ transference number. When assembled in potassium batteries, it achieves highly reversible K plating/stripping with a Coulombic efficiency of 98.9% in K||Cu cells, 85% capacity retention over 1600 cycles in a graphite electrode, and stable, fast-cycling performance in both K||Prussian blue analogue half-cells and graphite||Prussian blue analogue full-cells over a wide working temperature range of −20 to +45 °C. This work establishes a viable approach for tailoring specific electrolyte properties by precisely tuning microscopic solvation structures through anion-solvent interaction. Potassium-ion batteries face a trade-off between bulk and interfacial electrolyte properties. Here, the authors report a solvation structure engineering strategy that decouples these factors, enabling safe, stable, and fast-cycling batteries across a wide temperature range.