Highly Crystalline Sodium Manganese Ferrocyanide Microcubes for Sodium Batteries

The abundant sodium resources inspired research efforts in developing cost-effective sodium-based batteries as an alternative to Li-ion batteries. Nonaqueous sodium batteries that allow fast charging and low-temperature operation holds the promise to completement available Li-ion batteries used in electric cars and power tools. Highly crystalline sodium manganese ferrocyanide microcubes (Mn-HCF) have emerged as a leading candidate. [1−3] The Mn-HCF features a double perovskite framework, consisting of interconnected Mn─N 6 and Fe─C 6 octahedra, which ensures facile Na + mobility and allows for adaptive volume changes during cycling. [4] However, the open framework faces several challenges. Firstly, the interstitial water within these frameworks reduces the availability of Na + ions and obstructs ion channels. [5] Secondly, metal ions leaching from these structures compromise their structural integrity. [6] Thirdly, the poor electronic conductivity of the crystal structure restricts charge transfer. [7, 8] To address these issues, modifications such as modulating crystal structure, coating organic polymers (pyrrole), and incorporating carbon additives (acetylene black, graphene, carbon nanotubes) have been explored respectively. The crystal structure modulation method can significantly suppress the content of interstitial water and coordinated water, thereby ensuring sufficient Na + ions transfer and high specific capacity. Organic polymer coating not only improves the structural integrity of the cathode material but also contributes to improved interfacial stability that protects the active material from attacking by electrolyte decomposition products. Carbon additives enhance the electronic conductivity of the microcubes, facilitating better charge transfer during operation. This work presents the synthesis and characterization of these modified Mn-HCF microcubes, emphasizing their unique crystal structure and morphology. Utilizing an aqueous synthesis method, we achieve uniform microcubes with high crystallinity, which are systematically analyzed through X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Electrochemical testing reveals that the sodium manganese ferrocyanide microcubes exhibit a high specific capacity, and prolonged cycling stability, underscoring their suitability for practical sodium batteries applications. This research highlights the potential of sodium manganese ferrocyanide microcubes as a viable cathode material, contributing to the advancement of sustainable and cost-effective sodium batteries for future energy storage solutions. References: [1] P. Hong, C. F. Xu, C. Z. Yan, Y. L. Dong, H. P. Zhao, Y. Lei, Prussian blue and its analogues for commercializing fast-charging sodium/potassium-ion batteries. ACS Energy Lett. 2025 , 10 , 750−778. [2] H. Wu, J. N. Hao, Y. L. Jiang, Y. R. Jiao, J. H. Liu, X. Xu, K. Davey, C. S. Wang, S.-Z. Qiao, Alkaline-based aqueous sodium-ion batteries for large-scale energy storage. Nat. Common. 2024 , 15 , 575. [3] A. Bauer, J. Song, S. Vail, W. Pan, J. Barker, Y. H. Lu, The scale-up and commercialization of nonaqueous Na-ion battery technologies. Adv. Energy Mater. 2018 , 8 , 1702869. [4] Y. Shang, B. Ren, R. X. Wu, J. Lin, X. X. Li, J. X. Shen, D. Yan, H. Y. Yang, Building robust manganese hexacyanoferrate cathode for long-cycle-life sodium-ion batteries. Small 2025 , 21 , 2408018. [5] Z. Y. Li, Y. Wang, F. Rabuel, M. Deschamps, G. Rousse, O. Sel, J.-M. Tarascon, Na 2− x Mn[Fe(CN) 6 ] Prussian blue analog cathodes for Na-ion batteries-From fundamentals to practical demonstration. Energy Storage Mater. 2025 , 76 , 104118. [6] H. Zhang, J. Y. Li, J. H. Liu, Y. Gao, Y. M. Fan, X. H. Liu, C. F. Guo, H. X. Liu, X. D. Chen, X. Q. Wu, Y. Liu, Q. F. Gu, L. Li, J. Z. Wang, S.-L. Chou, Understanding capacity fading from structural degradation in Prussian blue analogues for wide-temperature sodium-ion cylindrical battery. Nat. Commun. 2025 , 16 , 2520. [7] S. Jia, K. Liao, M. J. Zhou, X. Xin, Y. J. Luo, Y.-J. Cheng, R. Liu, X. F. Yan, J. Lee, S.Papović, K. Zheng, K. Świerczek, Prussian white/reduced graphene oxide composite as cathode material to enhance the electrochemical performance of sodium-ion battery. Langmuir 2024 , 40 , 20485−20494. [8] J. Zhang, J. L. Zhang, H. H. Wang, V. W.-H. Lau, G.-H. Lee, K. Zhang, M. H. Park, Y.-M. Kang, Solid-solid interfacial charge storage of Prussian blue/rGO mixed-conductor cathode for high-power Na ion batteries. ACS Energy Lett. 2022 , 7 , 4472−4482.