Advancing Zn-Bromine Batteries: A Multifunctional Hydrated Deep Eutectic Solvent for Comprehensive Anode and Cathode Optimization

Abstract

The stationary Zn-bromine battery is emerging as a promising technology for next-generation energy solutions. However, its path to commercialization is hindered by notable challenges including Zn metal instability at the anode and redox-active bromide cross-diffusion at the cathode. In this work, we present a comprehensive strategy that concurrently addresses issues at both the cathode and anode, utilizing a hydrated deep eutectic solvent electrolyte that incorporates tetrabutylammonium bromide (TBABr). TBABr plays a pivotal dual role: it modifies the surface of the Zn anode by creating a protective hydrophobic layer, thereby stabilizing the Zn metal, and simultaneously forms solid complexes with Br3- ions at the cathode, effectively minimizing cross-diffusion-triggered self-discharge. Recognizing the critical importance of TBABr's solubility, we optimized the HDES composition by adjusting the Zn to halide ratio, the amount of water, and the addition of ethylene glycol. This electrolyte demonstrated superior performance, enabling a Zn anode to maintain stability for 3300 hours at 0.5 mA/cm2 and 0.5 mAh/cm2 in a symmetric cell setup. In a full-cell configuration, the cell displayed outstanding long-term cycling stability, exceeding 11,500 cycles with a 99% coulombic efficiency at a current density of 5 A/g. This innovative approach in electrolyte engineering effectively addresses challenges associated with both electrodes, paving the way for advanced Zn-bromine technology.