Asymmetric Anions for enhanced Ionic Liquid-based Electrolytes in O2ǁLi-Batteries


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To satisfy the need for high-energy batteries, which are for example used for electric vehicles, ongoing research is necessary and new cell chemistries beyond lithium-ion are required. The lithium-oxygen (O2ǁLi) battery is a promising candidate to enable high energy density batteries because of their high theoretical specific energy, if oxygen storage is excluded. However, the small electrochemical stability window as well as the high volatility and flammability of most commercially used electrolytes hinders an application in O2ǁLi batteries. Ionic liquids (ILs) are regarded promising candidates, since they offer beneficial properties like hydrophobicity, low volatility and high stability (thermal and electrochemical). Furthermore, ILs with asymmetric anions enable low-melting and low-viscous electrolytes while offering relatively high ionic conductivities. Additionally, mixtures with ethers/glymes decrease the electrolyte viscosity and increase ionic conductivity.1–3
In this work, widely known ILs, such as Pyr13TFSI and PYR13FSI, and less known ILs, like Pyr13TFSAM, Pyr13FTFSI and Pyr13TSAC, in combination with their respective lithium salts and mixtures thereof with TEGDME are compared. For IL benchmarking tests, as well as for O2ǁLi battery evaluation linear sweep voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic constant current cycling (CCC) of half and full cell setups are used. Further, the benchmarked electrolyte properties are correlated with wetting properties, as determined through contact angle measurements. It is shown, that solvent-electrolyte mixtures of ILs with TEGDME resulted in optimized cell performances and partially prolonged cycle life.

1. Ara, M., Meng, T., Nazri, G.-A., Salley, S. O. & Simon Ng, K. Y. Ternary Imidazolium-Pyrrolidinium-Based Ionic Liquid Electrolytes for Rechargeable Li-O 2 Batteries . J. Electrochem. Soc. 161, A1969–A1975 (2014).
2. Lai, J. et al. Electrolytes for Rechargeable Lithium–Air Batteries. Angew. Chemie Int. Ed. 59, 2974–2997 (2020).
3. Rüther, T., Bhatt, A. I., Best, A. S., Harris, K. R. & Hollenkamp, A. F. Electrolytes for Lithium (Sodium) Batteries Based on Ionic Liquids: Highlighting the Key Role Played by the Anion. Batter. Supercaps 3, 793–827 (2020).

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