Manganese-cobalt hexacyanoferrate cathodes for sodium-ion batteries

Mauro Pasta, Richard Y. Wang, Riccardo Ruffo, Ruimin Qiao, Hyun Wook Lee, Badri Shyam, Minghua Guo, Yayu Wang, L. Andrew Wray, Wanli Yang, Michael F. Toney, Yi Cui

    Research output: Contribution to journalArticle

    Abstract

    Prussian Blue analogues (PBAs) have shown promise as electrode materials for grid-scale batteries because of their high cycle life and rapid kinetics in aqueous-based electrolytes. However, these materials suffer from relatively low specific capacity, which may limit their practical applications. Here, we investigate strategies to improve the specific capacity of these materials while maintaining their cycling stability and elucidate mechanisms that enhance their electrochemical properties. In particular, we have studied the electrochemical and structural properties of manganese hexacyanoferrate (MnHCFe) and cobalt hexacyanoferrate (CoHCFe) in an aqueous, sodium-ion electrolyte. We also studied manganese-cobalt hexacyanoferrate (Mn-CoHCFe) solid solutions with different Mn/Co ratios that combine properties of both MnHCFe and CoHCFe. The materials have the characteristic open-framework crystal structure of PBAs, and their specific capacities can be significantly improved by electrochemically cycling (oxidizing and reducing) both the carbon-coordinated Fe and the nitrogen-coordinated Co or Mn ions. In situ synchrotron X-ray diffraction studies and ex situ soft X-ray absorption spectroscopy combined with an in-depth electrochemical characterization provide insight into the different electrochemical properties associated with the Fe, Co, and Mn redox couples. We show that cycling the C-coordinated Fe preserves the crystal structure and enables the outstanding kinetics and cycle life previously displayed by PBAs in aqueous electrolytes. On the other hand, the N-coordinated Co and Mn ions exhibit a slower kinetic regime due to structural distortions resulting from the weak N-coordinated crystal field, but they still contribute significantly towards increasing the specific capacity of the materials. These results provide the understanding needed to drive future development of PBAs for grid-scale applications that require extremely high cycle life and kinetics.

    Original languageEnglish (US)
    Pages (from-to)4211-4223
    Number of pages13
    JournalJournal of Materials Chemistry A
    Volume4
    Issue number11
    DOIs
    StatePublished - 2016

    ASJC Scopus subject areas

    • Chemistry(all)
    • Renewable Energy, Sustainability and the Environment
    • Materials Science(all)

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