Chemical\nInhibition Method to Synthesize Highly Crystalline\nPrussian Blue Analogs for Sodium-Ion Battery Cathodes

Abstract

The nucleation rate plays a critical\nrole in the synthesis of Prussian\nblue analogs. Rapid precipitation may lead to a large number of vacancies\nand a large amount of interstitial water in the material, resulting\nin poor electrochemical performance in batteries. Hence, sodium citrate\nis used to compete with [Fe­(CN)₆]^4– to\nslow down the coordination rates of Ni²⁺ and Mn²⁺ ions with ferrous cyanide ions. The feasibility of the experiment\nis also confirmed by theoretical analysis. Benefiting from stable\ncrystal structure and the removal of interstitial water, the as-prepared\nNa₂Ni_<i>x</i>Mn_<i>y</i>Fe­(CN)₆ sample exhibits a high reversible capacity\nof 150 mA h g^–1. In addition, a high rate performance\nof 77 mA h g^–1 is achieved at a current density\nof 1600 mA g^–1. Most noteworthy, the Coulombic efficiency\nand specific capacity gradually increase in the first few cycles,\nwhich can be ascribed to the formation of a passivation layer on the\nsurface of the electrode. Continuous testing in an electrolyte solution\nof 1 M NaPF₆ dissolved in sulfone reveals that the presence\nof a passivation film is very important for the stability of the electrode.