Improving Manganese Hexacyanoferrate’s Performance by Optimizing Processing Conditions and Adding Minuscule Amount of Ni
Authors: Deshmukh Jay , Zhang Libin , Zhang Ning , Dutta Animesh , Ye Ziwei , Hijazi Hussein , Yue Meng , Tulloch Meredith , Metzger Michael 
Published: December 2024

Intermittent energy generation from solar and wind demands a large deployment of energy storage systems (ESS), with 850 GWh expected by 2040 [1], in order to move away from fossil fuels. Na-ion cells are a fairly mature technology that could meet ESS demands. Among Na-ion cathode materials, Prussian Blue Analogs (PBAs) are promising because of their low cost, facile syntheses, long cycle life, and high-power performance associated with their open-framework structure. A high discharge voltage of ~3.5 V allows manganese hexacyanoferrate (MnHCF) to compete with LiFePO4-based Li-ion cells in Wh/kg and cost, but lacks in Wh/l. The latter may be acceptable for stationary ESS. However, PBAs’ open-framework structure enables them to absorb water rather easily, jeopardizing the longevity of the cell’s performance in organic electrolytes [2]. Moreover, rudimentary co-precipitation synthesis introduces vacancies in the structure, causing capacity loss due to limited redox sites [3].
In this study, we explore and optimize the synthesis and processing conditions of PBAs that lead to excellent calendar life performance of >2000 hours (~400 cycles) in Na half-cells. First, MnHCF and nickel hexacyanoferrate (NiHCF) were synthesized using a chelating agent-aided route to obtain the monoclinic phase, as shown by XRD, which indicates high Na content and minimal vacancies, showing cubic morphology. We also show that the water content of PBAs can be significantly reduced (<0.40 wt.% for MnHCF) with thorough drying at 170 °C as verified by TGA. Both analogs demonstrated their own distinctive characteristics, i.e., high specific capacity for MnHCF and stable capacity retention in the case of NiHCF (Figure 1). MnHCF’s lower cost and higher energy density make it a more viable candidate, but the Jahn-Teller distortion of Mn is suggested to cause performance decay over time. This prompted us to add a minuscule amount of Ni to MnHCF in order to alleviate some strain in the structure, as reported in other literature reports [4,5]. The resulting NiMnHCF showed a synergetic effect of both transition metals, outperforming MnHCF in terms of normalized capacity retention, as shown in Figure 1. We also validated the C-rate performance of these PBAs, showing > 80% capacity at 10C rate and compared their performance to our previously reported Na0.96Ca0.02Ni1/3Fe1/3Mn1/3O2 cathode [6] and vendor supplied LiFePO4 and PBA commercial active materials. We also saw that choice of carbon diluents is crucial in augmenting PBAs’ performance due to their relatively lower electronic conductivity than oxide-based cathodes.

References:

[1] Kebede, Abraham Alem, Theodoros Kalogiannis, Joeri Van Mierlo, and Maitane Berecibar. "A comprehensive review of stationary energy storage devices for large scale renewable energy sources grid integration." Renewable and Sustainable Energy Reviews 159 (2022): 112213.
[2] Song, Jie, Long Wang, Yuhao Lu, Jue Liu, Bingkun Guo, Penghao Xiao, Jong-Jan Lee, Xiao-Qing Yang, Graeme Henkelman, and John B. Goodenough. "Removal of interstitial H2O in hexacyanometallates for a superior cathode of a sodium-ion battery." Journal of the American Chemical Society 137, no. 7 (2015): 2658-2664.
[3] Liu, Yang, Gangya Wei, Mengyue Ma, and Yun Qiao. "Role of acid in tailoring Prussian blue as cathode for high‐performance sodium‐ion battery." Chemistry–A European Journal 23, no. 63 (2017): 15991-15996.
[4] Gebert, Florian, David L. Cortie, James C. Bouwer, Wanlin Wang, Zichao Yan, Shi‐Xue Dou, and Shu‐Lei Chou. "Epitaxial Nickel Ferrocyanide Stabilizes Jahn–Teller Distortions of Manganese Ferrocyanide for Sodium‐Ion Batteries." Angewandte Chemie 133, no. 34 (2021): 18667-18674.
[5] Xu, Zheng, Yu Sun, Jian Xie, Yang Nie, Xiongwen Xu, Jian Tu, Jie Zhang, Lvchao Qiu, Tiejun Zhu, and Xinbing Zhao. "Scalable preparation of Mn/Ni binary Prussian blue as sustainable cathode for harsh-condition-tolerant sodium-ion batteries." ACS Sustainable Chemistry & Engineering 10, no. 40 (2022): 13277-13287.
[6] Zhang, Libin, Jay Deshmukh, Hussein Hijazi, Ziwei Ye, Michel B. Johnson, Andy George, Jeff R. Dahn, and Michael Metzger. "Impact of Calcium on Air Stability of Na [Ni1/3Fe1/3Mn1/3] O2 Positive Electrode Material for Sodium-ion Batteries." Journal of The Electrochemical Society 170, no. 7 (2023): 070514.

Figure 1