Fully exploited imidazolium bromide for simultaneous resolution of cathode and anode challenges in zinc–bromine batteries

Abstract

Aqueous zinc–bromine (Zn–Br₂) batteries feature operational safety and high-energy and high-power densities, but suffer from polybromide dissolution in the cathode and the low reversibility of Zn metal in the anode. Here, we demonstrate that these challenges can be simultaneously tackled by using a fully exploited imidazolium bromide (MPIBr). An in-depth analysis demonstrates that MPIBr enhances both the reversibility and kinetics of Zn anodes. This enhancement arises from MPI⁺ cations participating in the formation of an H₂O-scarce inner Helmholtz plane, suppressing water-associated side reactions. Additionally, electron-donating Br⁻ ions contribute to the Zn²⁺-solvation sheath, forming [Zn(H₂O)₅Br]⁺ that promotes Zn²⁺ migration and faster interfacial kinetics. Furthermore, the robust chelation between the MPI⁺ cation and Br_x⁻ species significantly impedes shuttling. Notably, the Br⁻ anion and Zn²⁺ cation in the electrolyte can construct a dual-plating Zn–Br₂ battery, eliminating the necessity for active materials on both the cathode and anode. The as-prepared dendrite-free and shuttle-free dual-plating Zn–Br₂ batteries demonstrate stable cycling for 1000 cycles even under 100% depth of discharge. This work deepens the understanding of electrolyte composition on electrode interfaces, driving the advancement of high-performance and cost-effective Zn-halogen batteries.