Surface-Substituted Prussian Blue Analog Cathode for Sustainable Potassium-Ion Batteries

Abstract

While lithium-ion batteries still dominate energy storage applications, aqueous potassium-ion batteries have emerged asa complementary technology due to their combined advantages in cost and safety. Realizing their full potential, however, isnot without challenges. One is that among the limited choices of cathode materials, the more sustainable Prussian blue analogssuffer from fast capacity fading when manganese is present. Here we report a potassium manganese hexacyanoferrateK1.82Mn[Fe(CN)6]0.96·0.47H2O cathode featuring an in situ cation engineered surface where iron is substituted for manganese.With this engineered surface, the cathode design exhibits a discharge capacity of 160 mAh g−1 and 120 mAh g−1 at 300 mA g−1 and 2,500 mA g−1, respectively, and sustains 130,000 cycles (more than 500 days) with negligible capacity loss. Pairing thecurrent cathode with a 3,4,9,10-perylenetetracarboxylic diimide anode yields a full potassium-ion cell that delivers an energydensity as high as 92 Wh kg−1 and retains 82.5% of the initial capacity after 6,500 cycles at 1,500 mA g−1. The unprecedentedelectrochemical performance is attributed to the suppressed manganese dissolution as a result of the shielding surfacelayer. This work is expected to open an avenue for the rational design of high-performance cathode materials with redox-active manganese for rechargeable batteries.