Ultrastable Fe-based Prussian Blue Analogs Cathode for Sodium-Ion Battery

Low-cost Iron-based Prussian blue analogs (PBAs) with ultra-high cycling performance is a promising cathode material for sodium-ion batteries. However, the presence of vacancies occupied by crystal water in the structure of PBA prepared by the traditional co-precipitation method leads to rapid capacity decay of the battery, which significantly limits its practical application. In the present work, we use a modified co-precipitation method to synthesize Fe-based PBAs, which has a cubic structure and offers a large Na+ insertion/extraction channel. The results show that 99.9% of the capacity (108.9 mAh g−1) retained after 100 cycles of tests for the sample with the most outstanding cycling stability (PB-15). In addition, the samples are heat-treated to remove the crystal water from the acquired PBAs. The freshly prepared PB-15 sample is further treated at 180 °C. Phase transformation from the cubic structure to the monoclinic phase of the samples is probed after heat treatment. The initial specific capacity of HT-PB-15 is higher than that of PB-15 by 10.2 mAh g−1 and the capacity remained at 117.6 mAh g−1 after 100 cycles, which is the most outstanding cycling performance in the reported results.