Functional Fertilizers: Potash‐Tuned Prussian Blue Analogues for Potassium‐Ion Battery Cathodes

Potassium‐ion batteries (KIBs) are an exciting alternative to lithium‐ion batteries (LIBs) due to the global abundance of potassium resources and subsequent cost‐effectiveness, especially for applications such as grid‐scale storage where energy density requirements are not as strict. The most promising cathode material for KIBs are Prussian blue analogues (PBAs), though their electrochemical performance with respect to specific capacity and especially cyclability can be improved. Herein, three industrial potash salt precursors (two different purity grades of KCl and langbeinite) are incorporated into the synthesis of PBAs to improve their electrochemical storage properties. The addition of the higher purity KCl during synthesis increases the attainable specific capacity of the PBA cathodes, whereas the addition of langbeinite greatly increases the capacity retention over cycling from 22% to 86% after 75 cycles at C/10. The langbeinite‐modified PBA is also found to possess an external layer of MgO, which contributes to the cyclability of the PBA cathodes and increases thermal stability. With these findings, the potash modification of PBA cathodes is introduced and can be tailored for a variety of applications for the future of KIBs.