High-voltage Zn||monoclinic Prussian blue analog batteries enabled by a low-concentration, flame-retardant, and water-retaining electrolyte

Manganese-based Prussian blue analogues (MnFePBAs), renowned for their high redox potential and dual redox-active sites, often fail to fully realize their intrinsic performance in zinc-ion batteries (ZIBs). In this work, the underlying causes of the instability of monoclinic K+-containing MnFePBA (KMnFePBA) cathodes in aqueous electrolytes were investigated. To prevent irreversible phase transitions, a low-concentration, flame-retardant organic electrolyte operable under open-air conditions was developed. Utilizing triethyl phosphate (TEP) as the electrolyte solvent, the KMnFePBA cathode exhibited two distinct redox peaks at approximately 1.83 and 1.70 V, coupled with a high reversible capacity of ∼130 mA h g−1. The TEP electrolyte offers not only flame-retardant and anti-drying properties but also benefits from the inclusion of trace amounts of water, which enhances the redox kinetics. The optimized electrolyte enables Zn||KMnFePBA batteries to operate reversibly without structural degradation, function effectively across a wide temperature range, and suppress Zn dendrite formation by modulating the zinc-ion solvation structure and interfacial environment. This study presents a practical electrolyte engineering strategy for stabilizing monoclinic MnFePBA cathodes while simultaneously extending the lifespan of Zn anodes in ZIBs.