A dilute fluorine-free electrolyte design for high-voltage hybrid aqueous batteries

Abstract

Fluorinated salts and/or high salt concentrations are usually necessary to produce protective films on the electrodes for high-voltage aqueous batteries, yet these approaches increase the cost, toxicity and reaction resistances of battery. Herein, we report a dilute fluorine-free electrolyte design to overcome this dilemma. By using the LiClO4 salt and polyethylene glycol dimethyl ether (PED) solvent and optimizing the LiClO4/PED/H2O molar ratio, we formulate a 1 mol kg−1 3 V-class hybrid aqueous electrolyte that enables reversible charge/discharge of 2.5 V LiMn2O4|Li4Ti5O12 full cell at both low (0.5C, 92.4% capacity retention in 300 cycles) and high (5C, 80.4% capacity retention in 2000 cycles) rates. This excellent performance is reached even without the generation of protective film on either anode or cathode as identified by in/ex situ characterizations. The selection of appropriate ingredients that have both high stability and strong interactions with water is critical to widen the potential window of electrolyte while suppressing parasitic reactions on the electrodes. This work suggests that expensive and toxic fluorinate salts are no longer necessary for 3 V-class aqueous electrolytes, boosting the development of low-cost, environmentally-friendly, high-power and high-energy-density aqueous batteries.