Copper-based redox flow batteries (CuRFBs) are promising candidates for large-scale energy storage, exploiting the Cu(I)/Cu(II) redox couple in aqueous electrolytes. A key challenge is the stabilization of Cu(I), which requires halide ligands; while chloride-based systems have been studied, copper–bromide complexes are emerging as attractive alternatives, offering higher open-circuit voltages and greater solubility, directly enhancing energy density. This project aims to elucidate the coordination structures of Cu(I) and Cu(II) in bromide-rich media and to establish how copper-bromide speciation governs electrochemical behavior. Results will be correlated with those for chloride electrolytes, providing a comprehensive overview of copper–halide electrochemistry. Since speciation and kinetics evolve with state of charge (SoC), the work combines ex situ investigations of coordination numbers and bond distances with operando XANES and EXAFS at the Cu K-edge, directly informing the design.