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

A sustainable aqueous potassium-ion battery was developed using manganese hexacyanoferrate and other cost-efficient materials, achieving high energy density and longevity enabled by Fe-doping, crystallinity improvement, and electrolyte optimization. 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(NO 3 ) 2 + 1.5 M KNO 3 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.