A Hofmeister effect induced hydrogel electrolyte–electrode interfacial adhesion enhancement strategy for energy-efficient and mechanically robust redoxcapacitors

Abstract

How to realize tough interface adhesion between a hydrogel electrolyte and electrode is one of the keys to endow flexible energy storage devices with both high energy efficiency and mechanical durability, but still challenging. Herein, we present a hydrogel electrolyte–electrode interfacial adhesion enhancement strategy based on a polyacrylic acid–Fe³⁺–chitosan hydrogel with a double crosslinked network structure. Enhanced adhesion is provided by the Hofmeister effect occurring with the precipitation and folding of chitosan macromolecular micelles interpenetrated in the polyacrylic acid crosslinked network, on impregnating with ZnCl₂/NH₄Cl electrolyte rich in well-hydrated Cl⁻/NH₄⁺ ions. As a demonstration, an MXene-based flexible Zn-ion redoxcapacitor (ZRC) has been fabricated by integrating the proposed hydrogel electrolyte with a Zn plated anode and an MXene/Ag-nanowires&bacterial cellulose hybrid cathode. The ZRC not only achieves a high area energy density (278.6 μW h cm⁻²) and output power stability (46.1% of the energy from a battery-type plateau), but also excellent mechanical durability (enabling a capacity retention of over 89.19% after 1000 continuous bending cycles or dozens of destructive hammering and needle poking). The proposed hydrogel electrolyte–electrode interfacial engineering strategy, along with unprecedented performance demonstrated by the ZRC, represents a new design methodology towards energy storage devices with simultaneously high energy efficiency and mechanical durability.