Zero‐Strain Sodium Nickel Ferrocyanide as Cathode Material for Sodium‐Ion Batteries with Ultra‐Long Lifespan

Abstract Prussian blue analogues are recognized as one of the most promising cathode materials for sodium‐ion batteries (SIBs) owing to the open 3D framework structure with large interstitial sites and developed Na‐ion diffusion channels. However, high content of anion vacancy and poor structural stability have hampered the prospect of their application. In this work, sodium nickel ferrocyanide (Na 1.34 Ni[Fe(CN) 6 ] 0.92 , NNHCF) is proposed as cathode material for SIBs. N‐coordinated Ni‐ion can boost NNHCF to possess less Fe[(CN) 6 ] 4− defect, low Na‐ion migration barrier, and more negative formation energy compared with Na 0.91 Cu[Fe(CN) 6 ] 0.77 (NCHCF), thus exhibiting more active sites, fast electrochemical kinetics behavior and great structure stability. It is confirmed that NNHCF undergoes a solid solution mechanism without phase evolution for reversible Na‐ion intercalation/deintercalation, employing Fe associated with C atom as redox center for charge compensation. Therefore, NNHCF contributes a high initial energy density of 180.94 Wh·g −1 at 10 mA·g −1 , excellent rate capability, superior cycling stability with ultra‐long lifespan of 13 000 cycles, and low fading rate of 0.0027% per cycle at 500 mA·g −1 . This work sheds light on the construction of low‐defect PBA cathodes with outstanding dynamics and stability.