In Situ Electrochemical Incorporation of La ³⁺ 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.