Sustainable Biopolymer Binder Enables High-Performance β-MnO₂ Cathodes for Aqueous Zinc-Ion Storage

Abstract

Rechargeable aqueous zinc-ion batteries (ARZIBs) have gained considerable attention as sustainable energy storage systems due to their inherent safety, environmental friendliness, and low cost. Among various cathode candidates, β-MnO2 is particularly attractive owing to its structural stability and abundance. However, its practical application is hindered by the dissolution of Mn2+ ions during cycling, which leads to poor long-term performance. In this study, β-MnO2 was synthesized via a hydrothermal method and integrated into electrodes using both conventional PVdF and a novel water-based, cross-linked binder system composed of xanthan gum and citric acid (c-XG-CA). The c-XG-CA binder, abundant in hydroxyl, carboxyl, and acetyl groups, was shown to enhance Mn2+ adsorption capacity, improve electrode adhesion, and increase hydrophilicity compared to PVdF. The formation and stability of the cross-linked structure, along with its manganese ion adsorption behavior, were verified through FTIR and DFT analyses. Electrochemical evaluations revealed that the β-MnO2-c-XG-CA cathode achieved superior cycling stability (73% capacity retention after 200 cycles at C/2) and higher diffusion coefficients. Post-cycling XRD and SEM characterizations indicated the formation of reversible Zn-buserite and Znx(OTf)y(OH)2x–y·nH2O phases. These findings demonstrate that the c-XG-CA binder offers significant structural and electrochemical advantages, making it a promising alternative to conventional binders for high-performance ARZIBs.