Model-based electrolyte design for near-neutral aqueous zinc batteries with manganese-oxide cathodes

Abstract

Most modern zinc-ion batteries (ZIBs) with cathodes utilize near-neutral aqueous electrolytes based on a zinc sulfate (ZnSO4) salt. They achieve good cycling stabilities with high intrinsic safety, employ environmentally friendly materials, and deliver competitive volumetric energy densities. However, the limited solubility of zinc-sulfate species influences the performance and cycling mechanism of these cells. We examine the speciation and solubility limits of ZnSO4, zinc chloride (ZnCl2), and zinc triflate (Zn(CF3SO3)2) in aqueous solutions and simulate their intrinsic transport properties. We use our earlier developed and validated full-cell model to investigate the effects of several electrolytes on the two-phase cycling behavior. Previously, we reported that the origin of the second phase is based on an interaction mechanism between cathodic dissolution and a precipitation reaction at the cathode. We investigate this interplay between electrolyte stability and cathodic dissolution based on electrolyte choice. Our theory-based approach allows us to identify performance indicators of aqueous electrolytes and draws a consistent pathway to optimize electrolyte design for manganese-based ZIBs.