Effect of Mn-to-Fe Substitution on the Dehydration Mechanism and Electrochemical Properties of Prussian White Materials for Na-Ion Batteries

Abstract

In this study, we investigated the impact of partial Mn-to-Fe substitution on the dehydration mechanism and electrochemical performance of Mn-hexacyanoferrates (Prussian White) as positive electrode active materials for sodium-ion batteries. In situ synchrotron temperature experiments revealed similar phase transitions during drying for both materials, though with different kinetics, with the substituted compound requiring more severe drying conditions to achieve the dehydrated phase. Electrochemical characterization showed that Mn-to-Fe substitution significantly improved capacity retention, while preserving high initial capacity. Operando and ex situ diffraction experiments revealed that both materials transition from a rhombohedral to a distorted phase during charge, with higher bond distance anisotropy in the Mn-PW. Finally, the substituted compound demonstrated excellent cycling stability in full cells versus hard carbon, retaining nearly 84% of capacity after 400 cycles at 1 C. These findings underscore the improvements stemming from Mn-to-Fe substitution and optimized dehydration in Prussian White materials for high-performance sodium-ion batteries.