Entropy Engineering Constrain Phase Transitions Enable Ultralong‐life Prussian Blue Analogs Cathodes

Abstract Prussian blue analogs (PBAs) are considered as one of the most potential electrode materials in capacitive deionization (CDI) due to their unique 3D framework structure. However, their practical applications suffer from low desalination capacity and poor cyclic stability. Here, an entropy engineering strategy is proposed that incorporates high‐entropy (HE) concept into PBAs to address the unfavorable multistage phase transitions during CDI desalination. By introducing five or more metals, which share N coordination site, high‐entropy hexacyanoferrate (HE‐HCF) is constructed, thereby increasing the configurational entropy of the system to above 1.5R and placing it into the high‐entropy category. As a result, the developed HE‐HCF demonstrates remarkable cycling performance, with a capacity retention rate of over 97% after undergoing 350 ultralong‐life cycles of adsorption/desorption. Additionally, it exhibits a high desalination capacity of 77.24 mg g −1 at 1.2 V. Structural characterization and theoretical calculation reveal that high configurational entropy not only helps to restrain phase transition and strengthen structural stability, but also optimizes Na + ions diffusion path and energy barrier, accelerates reaction kinetics and thus improves performance. This research introduces a new approach for designing electrodes with high performance, low cost, and long‐lasting durability for capacitive deionization applications.