Water-in-bisalt electrolytes with mixed hydrophilic and hydrophobic anions for enhanced transport and stability for potassium-ion batteries.

Water-in-salt electrolytes provide an expanded electrochemical potential window, thus enabling a wide range of battery chemistries based on readily available salts and water. This study introduces a binary salt approach for achieving high K concentration with a tunable solvation sphere composed of acetate (Ac) and trifluoromethane sulfonate (OTf) anions, and water. Combining the hydrophilic low-cost potassium acetate with hydrophobic potassium trifluoromethane sulfonate salts, 36 molal liquid electrolyte, K(Ac)(OTf)·1.