NSRRC Activity Report 2023

058 NSRRC ACTIVITY REPORT 2023 (OCV) state (LFP@OCV + C) and in the fully charged state (LFP@100% SOC + C). The pre-edge at 7112.8 eV in the OCV state indicates a Fe 2+ state, while in the fully charged state, it increases to 7114.7 eV, signifying a Fe 3+ valence state. These results for LFP are consistent with the general understanding of Fe valence states in both pristine and charged states. In contrast, Figs. 1(c) and 1(d) reveal that, when LPSC is surrounded by LFP in the OCV state (LFP@OCV + LPSC), the pre-edges at the LFP/S interface and center remain at 7112.8 eV, corresponding to Fe 2+ . Interestingly, in the fully charged state (LFP@100% SOC + LPSC), the pre-edge at the interface with less contact with LPSC remains at 7114.7 eV (Fe 3+ ), but at the interface with LPSC, it reduces back to Fe 2+ . The iron valence state mapping in Fig. 2 was analyzed from n-XAS mapping data. In Figs. 2(a) and 2(b) , green, red, and darker shades represent Fe 2+ and C in LFP@OCV + C and LFP@100% SOC + C, showing no significant differences in iron valence distribution between the two states. In the mixture with LPSC, green and blue represent Fe and S in LFP@OCV + LPSC ( Fig. 2(c) ). White, red, and blue represent Fe 2+ , Fe 3+ , and S in LFP@100% SOC + LPSC ( Fig. 2(d) ). When fully charged LFP@100% SOC is combined with LPSC, the valence states at the particle’s center and edge differ significantly. An interface layer between LFP and LPSC undergoes a significant reduction from Fe 3+ to Fe 2+ , indicating intense decomposition and reduction reactions at the interface and potentially compromising the LFP structure. In conclusion, the combination of n-XRF spectra and n-XAS mapping provides a comprehensive and in-depth understanding of interface reactions at the electrode– electrolyte interface. It is important to note that, despite LFP being a highly stable cathode material in traditional liquid- based lithium-ion batteries, severe interface reactions can occur at the inter- and intra-granular levels. The application of n-XRF and n-XAS, and even XND tools for decoupling interface reactions at the nanoscale in cathodes/sulfides is a groundbreaking approach that opens up a new avenue for understanding interface phenomena in solid-state batteries. (Reported by Ching-Yu Chiang) This report features the work of Bing Joe Hwang and his collaborators published in J. Phys. Chem. C 127 , 14336 (2023). TPS 21A X-ray Nanodiffraction • n-XRF, n-XAS • Materials Science, Interface Chemistry, All-solid-state Batteries References 1. W. Y. Hsu, S. C. Yang, Y. Yi. Lin, W. Z. Hsieh, K. N. Tu, W. L. Chiu, H. H. Chang, C. Y. Chiang, C. Chen, Nano- mater. 13 , 2448 (2023). 2. C. Wang, K. Adair, X. Sun, Acc. Mater. Res. 3 , 21 (2022). 3. C. Wang, R. Yu, H. Duan, Q. Lu, Q. Li, K. R. Adair, D. Bao, Y. Liu, R. Yang, J. Wang, S. Zhao, H. Huang, X. Sun, ACS Energy Lett. 7 , 410 (2022). 4. Y. Kato, S. Hori, T. Saito, K. Suzuki, M. Hirayama, A. Mitsui, M. Yonemura, H. Iba, R. Kanno, Nat. Energy 1 , 1 (2016). 5. P. J. Lian, B. S. Zhao, L. Q. Zhang, N. Xu, M. T. Wu, X. P. Gao, J. Mater. Chem. A 7 , 20540 (2019). 6. D. H. S. Tan, E. A. Wu, H. Nguyen, Z. Chen, M. A. T. Marple, J. M. Doux, X. Wang, H. Yang, A. Banerjee, Y. S. Meng, ACS Energy Lett. 4 , 2418 (2019). 7. T. K. Schwietert, V. A. Arszelewska, C. Wang, C. Yu, A. Vasileiadis, N. J. de Klerk, J. Hageman, T. Hupfer, I. Kerkamm, Y. Xu, E. van der Maas, E. M. Kelder, S. Gana- pathy, M. Wagemaker, Nat. Mater. 19 , 428 (2020). 8. L. Li, H. Duan, J. Li, L. Zhang, Y. Deng, G. Chen, Adv. Energy Mater. 11 , 2003154 (2021). 9. B.-Y. Tsai, S.-K. Jiang, Y.-T. Wu, J.-S. Yang, S.-H. Wu, P.- C. Tsai, W.-N. Su, C.-Y. Chiang, and B. J. Hwang, J. Phys. Chem. C 127 , 14336 (2023).