Poster

Li-ion Transport Related to LiTFSA Cluster Size in Localized High-Concentration Electrolytes Using Molecular Dynamics Simulations

Yuki Ito, Taiki Shiba, Kaoru Dokko, Kazushi Fujimoto
1. Department of Chemistry and Materials Engineering, Graduate School of Science and Engineering,
Kansai University, 3-3-35 Yamate-cho, Suita, Osaka 564-8680, Japan.
2. Department of Chemistry and Life Science, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan.
3. Department of Chemistry and Materials Engineering, Faculty of Chemistry, Materials and
Bioengineering, Kansai University, 3-3-35 Yamate-cho, Suita, Osaka 564-8680, Japan.
k-fuji@kansai-u.ac.jp

Abstract

Figure from Ito1.docx

Figure from Ito1.docx

Efficient Li+ transport is essential for the performance of lithium batteries. Localized high-concentration electrolytes (LHCEs) exhibit heterogeneous salt-rich and diluent-rich regions. Therefore, clarifying how this heterogeneous structure affects Li+ diffusion is important for understanding Li+ transport in LHCEs.

In our previous study, we investigated an LHCE composed of FEC (solvent), TTE (diluent), and LiTFSA (salt), and showed that Li⁺ species in diluent-rich regions significantly contribute to the overall Li⁺ transport [1]. In this study, we examined two LHCEs composed of FEC, LiTFSA, and either nBME or tBME as the diluents, focusing on how differences in LiTFSA cluster structures affect Li+ transport. The molar ratio was LiTFSA:FEC:BME = 1:6:3.7.

Figure from Ito1.docx

Figure from Ito1.docx

Cluster analysis revealed that the nBME and tBME systems formed different LiTFSA cluster structures (Figure 1). The cluster volume distribution showed that larger LiTFSA clusters were preferentially formed in the nBME system, whereas many smaller clusters were formed in the tBME system. This difference is likely related to the different coordination abilities of nBME and tBME toward Li⁺. tBME coordinates more readily with Li+ than nBME, which suppresses LiTFSA aggregation. As a result, the tBME system contains smaller LiTFSA clusters and more non-clustered Li+ species.

MSDs calculated separately for clustered and non-clustered Li⁺ showed that non-clustered Li⁺ diffused faster than clustered Li⁺ (Figure 2), indicating that Li⁺ species in diluent-rich regions enhance the overall Li⁺ transport. In addition, the center-of-mass MSD of LiTFSA clusters larger than 1 nm³ revealed that cluster translational motion also contributes to Li⁺ transport. By further analyzing the diffusion behavior for different cluster sizes, we discuss size-dependent Li⁺ transport involving non-clustered Li+ species, medium-sized LiTFSA clusters, and large LiTFSA clusters.

These results suggest that suppressing excessive LiTFSA aggregation and forming mobile small-to-medium-sized clusters are important for promoting Li+ diffusion in LHCEs.

References

[1] Y. Ito, Y. Yasuda, Y. Konishi, T. Shiba, K. Dokko, K. Fujimoto, J. Phys. Chem. C, 130, 1327-1337 (2026).