Interface-intimate and redox-stabilizing hydrophilic binder enables durable MnO2 cathodes for aqueous Zn-ion batteries

Abstract

Growing demand for sustainable and scalable energy storage systems has highlighted aqueous zinc-ion batteries (AZIBs) as safe and cost-effective alternatives to conventional storage devices. However, poly(vinylidene fluoride) (PVDF), a conventional binder used in AZIBs, suffers from poor internetwork and hydrophobic characteristics, which impair ion penetration and structural stability within the electrode. These issues remain practical challenges to realizing cell feasibility with high-loaded electrodes and long-term cycling stability. Herein, an amide-crosslinked hydrophilic polymer (ACHP) binder is presented, synthesized via thermal curing of watersoluble acrylate and amine-rich polymers. Abundant hydrogen bonding functionalities in ACHP form strong interactions with electrode components and suppress carbon-binder domain migration, enhancing the structural integrity of the electrode. In addition, amide and amine moieties in ACHP coordinate with dissolved Mn2+ near the manganese dioxide (MnO2) surface, which mitigate Mn2+ release and promotes interfacial stability. Notably, the combined effects of interfacial interaction and ion coordination facilitate efficient ion transport and enable facile redox reactions. Interestingly, the ACHP binder also improves the reversibility of MnO2 phase transitions during cycling. Consequently, the ACHP-based electrode retained 80.1% of its initial capacity after 1550 cycles. Furthermore, a 60 mAh-class Zn||MnO2 cell was fabricated to validate the practical applicability of the binder design.