An Ionic Liquid Assisted Prussian Blue for High-Capacity and Stable Sodium-Ion Battery Cathodes

Sodium-ion batteries (SIBs) are suitable candidates for the field of large-scale energy storage due to infinite global reserves and low-cost of sodium. Prussian blue (PB) and its analogues are promising cathode materials for SIBs because of their environmental friendliness, open framework, and facile preparation process. However, the PB synthesized through traditional methods shows numbers of 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 (donated as IL-PB), which greatly reduces the nucleation rate. Thus, the IL-PB delivers a high specific capacity of 118 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 excellent electrochemical performance is attributed to the less vacancies and coordinated water in PB materials. The reversible transformation mechanism of the IL-PB materials was further revealed by in-situ characterizations. Moreover, when matched with NaTi 2 (PO 4 ) 3 anode, the IL-PB // NaTi 2 (PO 4 ) 3 full cell shows stable electrochemical performance