Sodium salt assisted room-temperature synthesis of Prussian blue analogues as high-performance cathodes for sodium-ion batteries

Abstract

Prussian blue analogues (PBAs) are widely used as cathodes for sodium-ion batteries (SIBs) due to their stable framework structure, simple synthesis method, and low fabrication cost. However, during the synthesis process, a large number of [Fe(CN)6]4− vacancies are easily caused, which leads to the destruction of crystal structure and the rapid decay of discharge capacity. In this work, the effect of sodium salts on lattice defects and electrochemical properties of iron hexacyanoferrates (FeHCF) was studied by adding different sodium salts (Na2SO4, NaCl, C6H5Na3O7, and EDTA-2Na) in the room-temperature coprecipitation method. It was found that the synthesis of FeHCF by adding Na2SO4 based on the chelating agent can not only increase the atomic ratio of Na+ but also effectively reduce [Fe(CN)6]4− vacancy defects and significantly increase the capacity contribution of low-spin Fe redox reaction. Due to the reduction of [Fe(CN)6]4− vacancy defects, the crystal structure is not easy to be destroyed during the cycle process, and the cycle stability of FeHCF is significantly improved. The sample shows good electrochemical performance, with a discharge capacity of 130.8 mAh g−1 in the first cycle and 114.3 mAh g−1 after 100 cycles. This work provides a new way to synthesize PBAs with low [Fe(CN)6]4− vacancy defects.