Organic Solvothermal Method Promoted Monoclinic Prussian Blue as a Superior Cathode for Na-Ion Batteries

Prussian blue (PB) is recognized as a promising cathode material for sodium-ion batteries due to its rigid open framework and low cost. The electrochemical performance of PB is largely determined by the lattice structure, which is greatly affected by the preparation process. Herein, an organic-based solvothermal strategy is developed to prepare monoclinic PB (M-PB). During the solvothermal process, ethylene glycol not only acts as a natural insulating layer to hinder the contact of Fe-II and [Fe(CN)(6)](4-), further slowing the crystal growth process, but also functions as a mild reducing agent to prevent Fe-II from oxidizing, leading to a stable lattice structure. The critical effects of the water/glycol ratio, reaction temperature, and reaction time on the growth of PB are investigated in detail. Benefiting from the stable structure and limited lattice defects, the M-PB exhibits much improved Na+-ion storage performance. Furthermore, the storage mechanism behind the electrochemical process is revealed. This study highlights the importance of the preparation process to the material structure and hence its electrochemical performance, which provides the insight into the rational design of PB-based cathode materials.