Electrolyte Solvation Chemistry and Systemic Safety in Potassium‐Ion Batteries

Potassium‐ion batteries (KIBs) are a leading candidate for low‐cost energy storage, yet their commercial viability hinges on full cell stability and thermal safety rather than the half cell metrics that dominate the literature. Both are governed by the electrolyte. This review examines recent KIB progress through electrolyte solvation chemistry and its control over the solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI), showing how salt and solvent selection dictate sheath composition and whether an anion‐ or solvent‐derived interphase forms. Studies are sorted by whether the solvation structure was characterized, separating electrolytes that are adopted, formulated for a bulk property, or engineered at the sheath. The division is sharpest among the anodes: every solvation‐engineered study uses unmodified commercial graphite, while adopted‐electrolyte studies reach for modified carbons and conversion anodes, placing their engineering on opposite sides of the interface. Thermal safety proves interfacial rather than a bulk‐solvent problem, as nonflammable electrolytes still drive a low‐temperature anode‐initiated exotherm that interphase stabilization delays more effectively than nonflammability alone. That conclusion rests on a narrow base, since all available calorimetry uses potassiated graphite. We identify the half cell‐to‐full cell gap and interphase‐mediated capacity loss as the central obstacles to practical KIBs.