A catechol grafted polymer binder regulating cation storage behaviors in MnO₂ cathode for rechargeable aqueous Zn batteries

Abstract

MnO2 is a promising cathode material in aqueous zinc batteries because of its low cost and high capacity. However, the sluggish cation transport and generation of insulating by-products seriously hinder the rate performance. Previous studies mainly focused on engineering MnO2 compositions, which achieved inadequate regulations. Herein, the importance of binders in modulating cation storage behaviors is uncovered to address the above-mentioned challenges. A catechol grafted polymer binder of P-PPGD is demonstrated. The abundant polar sites allow effective binding with MnO2 active material to improve adhesion properties. More importantly, they provide unique interactions with cations in the system, which facilitate their desolvation at the interface and mobility in the bulk electrode. Meanwhile, protons are adsorbed from the electrolyte to suppress the generation of insulating basic salt by-products. Owing to these merits, the MnO2/P-PPGD cathode delivers a high capacity of 517 mAh g−1 at 0.1 A g−1 and retains 197 mAh g−1 at 5 A g−1, superior to 349 mAh g−1/128 mAh g−1 of the conventional MnO2/PVDF cathode. Moreover, the replacement of PVDF with P-PPGD boosts the capacity retention from 24.0% to 90.4% after 8000 cycles. This work sheds fresh insights into designing functionalized polymer binders for aqueous zinc batteries.