Sodium Manganese Hexacyanoferrate: Characterization as Sodium-Ion Battery Cathode Material, Full Cell Cycling with Hard Carbon and Post-Mortem Analyses

Sodium manganese hexacyanoferrate Na₂Mn[Fe(CN)₆] (NaMnHCF) is a promising cathode material for sodium-ion batteries, owing to its voltage profile similar to that of lithium iron phosphate (LFP) and its use of abundant, inexpensive resources. This study presents full cell cycling data for NaMnHCF against hard carbon (HC) anodes with various common carbonate-based electrolytes across different voltage windows. Post-mortem analyses indicate that, in addition to NaMnHCF degradation, Na⁺-ion inventory loss significantly contributes to capacity decline during cycling. Surprisingly, an ICP-OES analysis of the post-mortem anodes show that the correct electrolyte choice can entirely prevent the commonly cited manganese dissolution of NaMnHCF during cycling. This work also highlights methods for characterizing and processing NaMnHCF and the broader Prussian White family of materials, helping to introduce these materials to a wider audience. Finally, a comparison between NaMnHCF/HC and LFP/graphite is provided, examining both cost and electrochemical performance.