Decoupling Electrode Environments with a pH-Asymmetric Biphase Electrolyte for High-Voltage Aqueous Rocking-Chair Batteries

Aqueous batteries demonstrate promising application prospects in large-scale energy storage and portable electronics due to their high safety, environmental friendliness, and low cost. However, their practical application still faces challenges, such as low operating voltage and insufficient energy density. Herein, a pH-asymmetric biphase electrolyte, composed of an alkaline aqueous electrolyte (AE) and an ionic liquid-hydrofluoroether electrolyte (ILE), was designed to decouple the anode and cathode environments. This design caters to the distinct needs of each electrode and enables the successful construction of a high-voltage aqueous rocking-chair lithium-ion battery. This phase-separated electrolyte (PSE) design breaks through the performance limitations of traditional homogeneous electrolytes, achieving a wide electrochemical stability window of 4.1 V and enabling the application of high-potential LiMn₂O₄ cathode materials. Benefiting from the anode potential negative shift effect dominated by the high-pH value of the alkaline aqueous electrolyte, this dual-phase electrolyte system exhibits significant advantages over conventional single-phase electrolytes, delivering an average discharge voltage of 1.72 V (a 0.35 V enhancement) and an initial specific capacity as high as 220 mAh g^-1 (based on the anode). By overcoming the potential limitations of both electrodes, this study provides an innovative technical pathway for developing high-voltage, high-energy-density aqueous batteries.