Partial Replacement of Manganese in Sodium Manganese Hexacyanoferrate for Long-Life Sodium-Ion Cathode Materials

Abstract

Among the various cathode active materials for Na-ion batteries Prussian Blue Analogs (PBA) are a promising candidate. From a cost and sustainability perspective, Na2Mn[Fe(CN)]6 (NaMnHCF) is of particular interest due to its high potential and superior electrochemical performance.[1] However, it suffers from poor cycling stability which is believed to be partly due to structural distortions caused by the Jahn-Teller effect of oxidized Mn3+ and dissolution of Mn in the electrolyte.[1,2] An alternative PBA like Na2Fe[Fe(CN)]6 (NaFeHCF) does not have these issues, but operates at a lower average potential of about 3.15 V versus Na+/Na during discharge (versus 3.45 V for NaMnHCF).[3] Therefore, in this study, the systematic replacement of Mn is investigated to find an optimum of high potential and good cycling stability.[4] As an example, Figure 1 shows the voltage curves for the first C/20 cycle in sodium half cells with Na2Mn[Fe(CN)]6 (green) or Na2Mn0.8Fe0.2[Fe(CN)]6 (blue). The material with the higher Fe content clearly shows a second, lower plateau and an overall lower potential.The materials were compared in terms of their electrochemical properties and characterized by SEM, XRD, ICP-OES and TGA. References Song, J., Wang, L., Lu, Y., Liu, J., Guo, B., Xiao, P., ... & Goodenough, J. B. (2015). Journal of the American Chemical Society, 137(7), 2658-2664.Xu, C., Ma, Y., Zhao, J., Zhang, P., Chen, Z., Yang, C., ... & Hu, Y. S. (2023). Angewandte Chemie International Edition, 62(13), e202217761.Wang, L., Song, J., Qiao, R., Wray, L. A., Hossain, M. A., Chuang, Y. D., ... & Goodenough, J. B. (2015). Journal of the American Chemical Society, 137(7), 2548-2554.Chen, X., Xia, Y., Fang, X., Zhang, K., Xiong, Y., & Jian, Z. (2022). Journal of Materials Science, 57(29), 14015-14025. Figure 1