Elevating the Performance of the Prussian Blue Analogue Cathode for Sodium-Ion Batteries by Adjusting the Low Spin Fe Redox

Prussian blue and its analogues (PB and PBAs) belong to a group of metal–organic frameworks that are ideal cathodes in sodium-ion batteries (SIBs) due to their open framework, which is kinetically suitable for intercalating ions and the ease of large-scale production with low cost. However, vacancies are generated during the coprecipitation methods, and driving the interstitial water to occupy these spaces adversely affects the electrochemical performance of SIBs. In this work, we synthesized iron hexacyanoferrate (Fe[Fe(CN)6]) PBA via the self-decomposition method under a protective environment, suppressing vacancy formation. Further, a one-step ion exchange process was developed to introduce cobalt ions into the Fe[Fe(CN)6] crystal structure. The synthesized material was utilized as a cathode for a SIB, which delivered a specific capacity of 160 mAh g–1 at a current rate of 10 mA g–1. Benefiting from structural advantages the cell successfully shows a stable performance up to 300 cycles with 89% retention of its first capacity.