Surface-substituted Prussian blue analogue cathode for sustainable potassium-ion batteries

While lithium-ion batteries still dominate energy storage applications, aqueous potassium-ion batteries have emerged as a complementary technology due to their combined advantages in cost and safety. Realizing their full potential, however, is not without challenges. One is that among the limited choices of cathode materials, the more sustainable Prussian blue analogues suffer from fast capacity fading when manganese is present. Here we report a potassium manganese hexacyanoferrate K1.82Mn[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 the current cathode with a 3,4,9,10-perylenetetracarboxylic diimide anode yields a full potassium-ion cell that delivers an energy density 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 unprecedented electrochemical performance could be attributed to the suppressed manganese dissolution as a result of the shielding surface layer. This work may open an avenue for the rational design of high-performance cathode materials with redox-active manganese for rechargeable batteries.