High-crystallinity and high-rate Prussian Blue analogues synthesized at the oil–water interface

Prussian blue (PB) and its analogues (PBAs) are considered to be cathode materials for practical applications in sodium-ion batteries due to their open three-dimensional structure and low cost. However, PBAs synthesized by traditional methods generally have poor crystallinity and a high content of [Fe(CN)6] vacancy defects and coordinate water, which not only affect the Na+-storage capacity of PBAs, but also hinder Na+ transportation in the bulk phase and lead to a deterioration in electrochemical performance. Therefore, we propose an unconventional two-phase method to synthesize PBAs. Due to the unique reaction environment of the two-phase method, the reaction time lasts long, which is advantageous to control the synthesis of PBAs to ensure high crystallinity, low defects, and a suitable size. The as-prepared PBA at optimal condition delivers a high initial discharge specific capacity of 152 mA h g−1 at 0.2 C (1 C = 170 mA h g−1), 110 and 105 mA h g−1 even at high current densities of 10 C and 20 C,respectively, as well as a capacity retention of 84% after 200 cycles at 2 C. In particular, superior electrochemical performances also suggested that the two-phase method could be extended to the synthesis of other types of PBAs, such as Mn-PBAs and Co-PBAs, or even more materials with poor crystallinity due to rapid nucleation and growth.