A sustainable biopolymer binder enables the fabrication of 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 characterization studies indicated the formation of reversible Zn–buserite and Zn_x(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.