Hydrophobic-unit-regulated hydrogel electrolytes with high water content and low salt concentration for high-voltage aqueous batteries

Common aqueous electrolytes with extended electrochemical stability windows (ESWs) have a low water content; thus, water molecules are well confined. However, confinement to metal cations of these aqueous electrolytes, which leads to poor compatibility with available metal-ion charge carriers, has been overlooked. We demonstrated that hydrogel electrolytes with high water content and low salt concentration exhibit wide ESWs through effective water interactions. Moreover, these electrolytes have well-suppressed confinement to metal cations, leading to high battery performance and excellent compatibility with charge carriers. The fabricated hydrophobic-unit-regulated hydrogel electrolyte (HHE) features trace amounts of hydrophobic moieties, which disperse evenly in the HHEs. The hydrophobicity in the vicinity of hydrophilic groups enhances their hydrogen bond strength with water molecules, resulting in an ESW of 3.3 V at a water concentration of 68 wt %. The 2.3, 1.9, and 1.75 V discharge plateaus were observed in aqueous Li₄Ti₅O₁₂||LiMn₂O₄, Zn||MnO₂, and potassium-ion batteries, respectively.