A low-cost and high-energy aqueous potassium-ion battery

To address challenges related to the intermittency of renewable energy sources, aqueous potassium-ion batteries (AKIBs) are a promising and sustainable alternative to conventional systems for large-scale energy storage. To enable their practical application, maximizing energy density and longevity while minimizing production and material costs is a key goal. In this work, we propose an AKIB consisting only of abundant and cost-efficient materials, which delivers a high energy density of more than 70 Wh kg⁻¹. We combine simple strategies to stabilize the Mn-rich Prussian blue analog cathode by Fe-doping, improving the crystallinity, and tuning the electrolyte composition without employing expensive water-in-salt electrolytes. Using a mixed 2.5 M Ca(NO₃)₂ + 1.5 M KNO₃ electrolyte, we assemble a novel AKIB with a Fe-doped manganese hexacyanoferrate cathode and an organic poly(naphthalene-4-formyl-ethylenediamine) anode. Besides a high energy density, the full cell delivers a specific capacity of approximately 60 mA h g⁻¹, a power density of 5000 W kg⁻¹, and 80% capacity retention after 600 cycles.