Surface passivation of NaxFe[Fe(CN)6] cathode to improve its electrochemical kinetics and stability in sodium-ion batteries

Prussian blue analogs (PBAs) are considered as promising cathode materials in sodium-ion batteries. However, PBAs usually suffer from low electrical conductivity and high humid sensitivity, which results in the poor electrochemical kinetics and stability. In this work, a passivation strategy is proposed to solve these problems. The sodium iron hexacyanoferrate (PB) passivated by acetate ligands exhibits significantly improved electrochemical kinetics. It delivers a specific capacity of 128 mAh g(-1) at 25 mA g(-1). Even at 2 A g(-1), the capacity still retains 94.6 mAh g(-1). Most impressively, the passivated PB can maintain excellent electrochemical stability when exposed in the humid air for 7 days. Further investigations show that the strong physical interaction between the acetate ligands and the exposed Fe atoms can inhibit the readsorption of water and induce the electron transfer between low spin Fe and high spin Fe in PB. Thus, the surface passivation can efficiently enhance the electrical conductivity and electrochemical stability of PB.