Controlling the Phase Separation of Dimethyl Carbonate Solvents Using a Dual-Cation System: Applications in High-Power Lithium Ion-Based Hybrid Capacitors

To achieve lithium ion-based energy storage devices having high power densities and stabilities, the use of a low-viscosity and low-dielectric-constant solvent [such as dimethyl carbonate (DMC)] as well as a chemically stable BF4 –-based salt (such as LiBF4 or quaternary ammonium salts [spiro-(1,1)-...

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Bibliographic Details
Published in:	Journal of physical chemistry. C Vol. 126; no. 34; pp. 14389 - 14398
Main Authors:	Chikaoka, Yu, Ochi, Riko, Fujii, Kenta, Ariga, Takaaki, Sakurai, Masato, Matsumoto, Ayuna, Ueda, Tsukasa, Iwama, Etsuro, Naoi, Katsuhiko
Format:	Journal Article
Language:	English
Published:	American Chemical Society 01-09-2022
Subjects:	C: Energy Conversion and Storage
Online Access:	Get full text
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Summary:	To achieve lithium ion-based energy storage devices having high power densities and stabilities, the use of a low-viscosity and low-dielectric-constant solvent [such as dimethyl carbonate (DMC)] as well as a chemically stable BF4 –-based salt (such as LiBF4 or quaternary ammonium salts [spiro-(1,1)-bipyrrolidinium tetrafluoroborate (SBPBF4))] is promising for application in next-generation electrolytes. However, these combinations are impractical for several reasons, including the low ionic conductivity of LiBF4/DMC and the phase separation of SBPBF4/DMC systems. Thus, we developed a DMC-based dual-cation system (1 M LiBF4 + 1 M SBPBF4/DMC) possessing a higher ionic conductivity (5.7 mS cm–1) than that of single-cation systems (1 M LiBF4/DMC, 0.5 mS cm–1) and realizing a stable single-phase solution. Raman measurements suggest that the dual-cation system constitutes one DMC and two or three BF4 – complexes (not neutral-charged states), which should result in high ionic conductivity. Furthermore, the DMC-based dual-cation system exhibited a higher power performance in a Li4Ti5O12//activated carbon hybrid capacitor than the single-cation system (88 and 13% capacity retention at 50 mA cm–2, respectively) and demonstrated high Li+ conductivity (dual-cation: 1.6 mS cm–1, single-cation: 0.2 mS cm–1). Therefore, the dual-cation strategy could aid the development of diverse electrolyte combinations involving salts and solvents that have been considered impracticable.
ISSN:	1932-7447 1932-7455
DOI:	10.1021/acs.jpcc.2c03004