Dual functionality of an organic co-solvent for enhancing stability and efficiency in static zinc bromine batteries

Abstract

The flammability of conventional lithium-ion batteries poses significant safety concerns, driving interest in safer alternatives. Static zinc bromine batteries (ZBBs) offer a promising solution due to their non-flammable aqueous electrolyte and low cost. However, their widespread adoption is hindered by self-discharge reactions caused by polybromide (pBr − ) crossover, along with hydrogen evolution and uncontrolled Zn metal deposition. In this study, we address these issues by introducing N,N-dimethylacetamide (DMA) as a dual-functional co-solvent. DMA acts as an efficient pBr − -capturing agent to form a condensed DMA-pBr complex, effectively suppressing pBr − crossover by decreasing its mobility. Beyond pBr − crossover management, DMA partially replaces H 2 O molecules in the Zn 2+ solvation shell and adsorbs at the negative electrode, mitigating corrosion and promoting uniform and planar Zn metal deposition. This dual functionality enables static ZBBs with exceptional cycle life and enhanced Coulombic efficiency, retaining capacity for 350 cycles at 20 mA cm −2 and 20 mAh cm −2 with negligible performance degradation. These findings highlight the untapped potential of dual functionality of co-solvents to simultaneously address crossover and reversibility challenges in ZBBs.