Ionic Liquid-Assisted Prussian Blue for Stable Sodium-Ion Battery Cathodes

Sodium-ion batteries (SIBs) are bright competitors for large-scale energy storage owing to infinite global reserves and the low cost of sodium. Prussian blue (PB) and its analogues are up-and-coming cathodes for SIBs due to their environmental friendliness, open framework, and facile preparation process. However, PB synthesized through traditional methods shows several vacancies and structural defects, which results in structure collapse and inferior cycling performance. In this work, an ionic liquid is introduced into the PB structure (denoted as IL-PB), which greatly reduces the nucleation rate. Thus, IL-PB delivers a high specific capacity of 134 mAh g-1 at 50 mA g-1 and stable cycling performance with a capacity retention of 77.3% at 100 mA g-1 after 500 cycles. The good property originates from the fewer vacancies and coordinated water in IL-PB materials. The reversible transformation mechanism of the IL-PB materials was further revealed by in situ characterizations. The introduction of ionic liquid provides an idea for the preparation of high-quality PB materials.