Hydrogel electrolytes with an electron/ion dual regulation mechanism for highly reversible flexible zinc batteries

Abstract

Hydrogel electrolytes have been extensively developed for flexible zinc-ion batteries (FZIBs) owing to their rich ion transfer channels, mechanical stability and intrinsic safety. However, single ion regulation in traditional hydrogel electrolytes still remains a great challenge to effectively inhibit the growth of Zn dendrites and the occurrence of side reactions, leading to limited performance levels in FZIBs. To address this, herein, a unique electron/ion dual regulation mechanism is established in a well-designed hydrogel electrolyte by integrating a polyacrylamide (PAM) network and carboxylated multi-walled carbon nanotubes (MWCNTs) for high-performance and stable FZIBs. The negatively charged carbonyl groups within PAM chains and the high conductivity of MWCNTs trigger an associated synergistic regulation mechanism to achieve a uniform ionic/electronic field for highly reversible Zn anodes. As a result, the well-designed hydrogel electrolyte shows a high Zn²⁺ ion transference number of 0.712 and a high ionic conductivity of 22.02 mS cm⁻¹ at room temperature as well as high battery performance, including a high Coulombic efficiency of 98.2%, over 3600 h of lifespan, and superior mechanical/electrochemical stability for flexible Zn//MnO₂ pouch cells. This electron/ion dual regulation strategy to challenge traditional hydrogel electrolytes and aqueous Zn chemistry may open up a new avenue for building better FZIBs and beyond.