The full utilization of affordable potassium-ion batteries (PIBs) based on all-aluminum current collectors is hindered by low specific energy, limited lifespan, and safety concerns, primarily due to the lack of suitable electrolytes for high-capacity electrodes. This work introduces new molecular insights, from bulk solvation chemistry to interfacial behaviors, for designing compatible electrolytes. Fluorinated triethyl phosphate (FTEP) of tris(2,2,2-trifluoroethyl) phosphate was strategically selected as a low-polarity solvating solvent to create an anion-rich solvation sheath, albeit with reduced ion mobility at moderate concentration (1.0 mol·L⁻¹). The deficiency of solvating-solvent molecules in the primary solvation sheath facilitates the formation of a protective layer derived from bis(fluorosulfonyl)imide anion decomposition, ultimately inhibiting undesirable side reactions at electrode/electrolyte interfaces. Moreover, FTEP as the sole solvating solvent endows the electrolyte with exceptional flame retardancy. The results provide crucial insights into the role of solvation chemistry on solvation structure and interfacial transport dynamics, critical for advancing the development of compatible electrolytes for high-performance PIBs.