Long-Range Ion-Ordering in Salt-Concentrated Lithium-Ion Battery Electrolytes: A Combined High-Energy X‑ray Total Scattering and Molecular Dynamics Simulation Study

• Published in: Journal of physical chemistry. C 2017-10, Vol.121 (41), p.22720-22726
• Main Authors: Fujii, Kenta, Matsugami, Masaru, Ueno, Kazuhide, Ohara, Koji, Sogawa, Michiru, Utsunomiya, Takashi, Morita, Masayuki
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.7b08243

Herein, we report on a structural study for characterizing unique solution structures in the salt-concentrated electrolytes, which are promising new lithium (Li)-ion battery electrolytes. A combination of high-energy X-ray total scattering (HEXTS) experiments with all-atom molecular dynamics (MD) simulations was performed on the salt-concentrated electrolytes that were based on Li bis­(trifluoromethanesulfonyl)­amide (LiTFSA) and N,N-dimethylformamide (DMF). The radial distribution functions obtained from the HEXTS and MD approaches were in good agreement in the current LiTFSA/DMF solutions. We found that in the local structure: (1) the Li-ions were coordinated with both the DMF molecules and the TFSA anions in the concentrated solutions and (2) specific Li+···Li+ correlations were present in the radial distribution function over the r range of 3 Å–15 Å. The Li+···Li+ correlations originated from the extended multiple Li-ion complexes, that is, polymerized [Li+···TFSA–···Li+] n complexes so that they were highly structurally ordered. We concluded that this type of an ion-ordered structure plays a crucial role in the electrochemical stability and the ion-conducting mechanism, resulting in a unique LIB performance employing these salt-concentrated electrolytes.