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

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_1.34Ni[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_0.91Cu[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.