In Situ Electrochemical Incorporation of La3+ into Prussian Blue Frameworks: A Facile Strategy for Enhanced Structural Integrity and Crystalline Water Management

Prussian blue (PB) cathode materials, renowned for their structural adaptability and cost‐effectiveness, encounter significant degradation issues stemming from lattice distortion and residual crystalline water during electrochemical cycling. This study proposes a trivalent‐cation doping strategy to enhance PB stability through in situ electrochemical incorporation of La3+ from the electrolyte into the Na+ sites. The high charge density of La3+ facilitates strong interaction with the framework, meanwhile, preventing its extraction during the charging/de‐sodiation process, thereby ensuring continuous structural reinforcement. Additionally, La3+ exhibits strong binding energy with water molecules, effectively stabilizing both interstitial and coordinated water within the framework. Diverging from the conventional Na‐site doping techniques that aim to reduce crystalline water content, the in situ electrochemical incorporation of La3+ dynamically immobilizes water molecules, thereby avoiding the lattice distortion caused by hydrated Na+ migration and suppressing water‐induced side reactions in the electrolyte. The optimized PB‐La cathode achieves an exceptional capacity retention of 86.1% after 1500 cycles at 1 A g−1. Furthermore, this strategy demonstrates broad applicability: even in a pre‐dehydrated PB configuration, it delivers a high capacity of 114.2 mAh g−1 with 92.6% capacity retention after 200 cycles, showcasing its universality in enhancing structural stability across diverse PB architectures.