Achieving synergetic anion-cation redox chemistry in freestanding amorphous vanadium oxysulfide cathodes toward ultrafast and stable aqueous zinc-ion batteries

Flexible aqueous zinc-ion batteries (AZIBs) with high safety and low cost hold great promise for potential applications in wearable electronics, but the strong electrostatic interaction between Zn${}^{2+}$ and crystalline structures, and the traditional cathodes with single cationic redox center remain stumbling blocks to developing high-performance AZIBs. Herein, freestanding amorphous vanadium oxysulfide (AVSO) cathodes with abundant defects and auxiliary anionic redox centers are developed via in situ anodic oxidation strategy. The well-designed amorphous AVSO cathodes demonstrate numerous Zn${}^{2+}$ isotropic pathways and rapid reaction kinetics, performing a high reversible capacity of 538.7 mAhg${}^{-1}$ and high-rate capability (237.8 mAhg${}^{-1}$@40Ag${}^{-1}$). Experimental results and theoretical simulations reveal that vanadium cations serve as the main redox centers while sulfur anions in AVSO cathode as the supporting redox centers to compensate local electron-transfer ability of active sites. Significantly, the amorphous structure with sulfur chemistry can tolerate volumetric change upon Zn${}^{2+}$/H${}^{+}$ insertion and weaken electrostatic interaction between Zn${}^{2+}$ and host materials. Consequently, the AVSO composites display alleviated structural degradation and exceptional long-term cyclability (89.8% retention after 20 000 cycles at 40 Ag${}^{-1}$). This work can be generally extended to various freestanding amorphous cathode materials of multiple redox reactions, inspiring development of designing ultrafast and long-life wearable AZIBs. (© 2023 Wiley-VCH GmbH)