Extended Electrochemical Window Via Interfacial Microdomain Regulation by a Bicontinuous Microemulsion-Based Heterogel Electrolyte

Abstract

Regulating the freedom and distribution of H₂O molecules has become the decisive factor in enlarging the electrochemical stability window (ESW) of aqueous electrolytes. Compared with the water in a bulk electrolyte, H₂O molecules at the electrode–electrolyte interface tend to directly split under bias potential. Therefore, the composition and properties of the interfacial microenvironment are the crux for optimizing ESW. Herein, we developed a heterogel electrolyte with wide ESW (4.88 V) and satisfactory ionic conductivity (4.4 mS/cm) inspired by the bicontinuous architecture and surfactant self-assembly behavior in the ionic liquid microemulsion-based template. This electrolyte was capable of expanding the ESW through the dynamic oil/water/electrode interface ternary structure, which enriched the oil phase and assembled the hydrophobic surfactant tails at the interface to prevent H₂O molecules from approaching the electrode surface. Moreover, the surfactant Tween 20 and polymer network effectively suppressed the activity of H₂O molecules through H-bond interactions, which was beneficial in expanding the operating voltage range and improving the temperature tolerance. The prepared gel electrolyte demonstrated unparalleled adaptability in various aqueous lithium-based energy storage devices. Notably, the lithium-ion capacitor showed an extended operating voltage of 2.2 V and could provide a high power density of 1350.36 W/kg at an energy density of 6 Wh/kg. It maintained normal power output even in the challenging harsh environment, which enabled 11,000 uninterrupted charge–discharge cycles at 0°C. This work focuses on the regulation of the interfacial microdomain and the restriction of the degree of freedom of H₂O molecules to boost the ESW of aqueous electrolytes, providing a promising strategy for the advancement of energy storage technologies.

Keywords

bicontinuous microemulsion / electrochemical window / heterogel electrolyte / interfacial microdomain / lithium-ion capacitor

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