Zinc chemistry regulated by chitosan-based poly(aprotic/protic ionic liquid)s with multi-anion–cation interactions for highly reversible Zn-ion batteries

Abstract

Aqueous Zn-ion batteries (AZIBs) provide an enticing option for energy storage with cost-effectiveness, integral safety, and environmental benignity. However, the reversibility and lifespan of AZIBs are constrained by the uncontrolled Zn chemistry occurring both within the bulk electrolyte and at the electrode/electrolyte interface. Herein, taking the particular structural feature of chitosan (CS), a series of robust CS-based poly(protic ionic liquid)s (CPPILs) and poly(aprotic/protic ionic liquid)s (CPAPILs) were firstly prepared to regulate Zn chemistry through synergistic anions and cations. The betaine hydrochloride-derived CPAPILs additive (CPAPILs-B) showed a better ability to reorganize the Zn²⁺ solvation structure and enhance ion transport via the carboxylate and chloride anions, while the protonated amine and quaternary ammonium cations in CPAPILs-B are effectively anchored to the Zn anode, providing ample zincophilic sites and a uniform electric field. Consequently, the CPAPILs-B with multi-anion–cation interactions endows Zn//Zn symmetrical cells with long-term cycling durability of 5925 h at 1 mA cm⁻²/0.5 mA h cm⁻² and an ultra-high cumulative plating capacity (CPC) exceeding 7550 mA h cm⁻² at 10 mA cm⁻²/1 mA h cm⁻². This study introduces an eco-friendly, sustainable CPAPILs-B additive and highlights the innovative molecular design and multi-anion–cation synergy as a promising strategy for developing green additives to enhance the reversibility of AZIBs.