Role of 57Fe Mössbauer spectroscopy in understanding the reaction mechanism of electrode materials: case study of MFeIIIOPO4 (M: Co, Ni) and Li3.27FeIII 0.81FeII 0.19V(PO4)3 for Lithium-ion batteries

57Fe Mössbauer spectroscopy consists of the resonant absorption of gamma rays from the excited states of a nucleus. This characterization technique is highly sensitive for studying the local atomic environments of materials, including redox ratios, spin and valence states, and the occupation sites of atoms [1]. 57Fe Mössbauer spectroscopy was applied by several research groups to investigate the reaction mechanism of electrode materials in the field of electrochemical energy storage [2-5]. In our case, 57Fe Mössbauer spectroscopy was conducted on MFeIIIOPO4 (M: Co, Ni) anode [4] and Li3.27FeIII0.81FeII0.19V(PO4)3 cathode [5] materials at different states of charge and discharge. Surprisingly, our findings on MFeIIIOPO4 (Fig. 1a-b). reveal that that Fe is partially reduced to divalent and metallic Fe at the first steps of discharge then to 100 % Fe0 at the end of discharge. Furthermore, Fe was detected in both oxidation states FeII and FeIII at the end of charge. In the study on the Li3.27FeIII0.81FeII0.19V (PO4)3 cathode material for LIBs, the target chemical composition was Li4FeIIV(PO4)3. However, when conducting 57Fe Mössbauer spectroscopy on the pristine powder, Fe was partially oxidized (Fig. 1c). More details about insightful findings driven from 57Fe Mössbauer spectroscopy analysis will be communicated during this conference. Recent Publications 1. Y. Liu, J. Li, Q. Shen, J. Zhang, P. He, X. Qu, Y. Liu, eScience 2022, 2, 1, 10-31. 2. J. Cong, S. H. Luo, Y. C. Lin, P. Y. Li, L. X. Qian, S. X. Yan, X. Liu, X. F. Lei, Chem Eng J. 2024, 502, 157939. 3. J. Peng, A. Sarapulova, Q. Fu, H. Li, H. Liu, O. Dolotko, T. Bergfeldt, K. Kleiner, B. Ying, Y. Wu, V. Baran, E. Welter, P. Nagel, S. Schuppler, M. Merz, M. Knapp, H. Ehrenberg, Q. Indris, Chem Mater 2024, 36, 9, 4107-4120. 4. H. Aziam, S. Indris, H. Bem Youcef, R. Witte, A. Sarapulova, H. Ehrenberg, I. Saadoune, J. Alloys Compd 2022, 906, 164373. 5. H. Aziam, A. Mahmoud, D. Mikhailova, M. Harfouche, I. Saadoune, H. Ben Youcef, J Power Sources 2023, 575, 233190.