Water-in-Bisalt Electrolytes with Enhanced Transport Properties and Electrochemical Stability

This study introduces a binary salt approach for achieving high K+ concentration with tunable solvation sphere composed of acetate (Ac⁻) and trifluoromethane sulfonate (OTf⁻) anions, and water, suited for potassium-ion batteries. By the elimination of the free water molecules from the electrolyte through the judicious selection of the hydrophobic and hydrophilic anions and the solvation disproportion resulting from the bi-salt approach, very high K+ concentration was achieved while simultaneously maintaining good transport properties and widened electrochemical stability window.