Investigation of Ether-Based Ionic Liquid Electrolytes for Lithium-O2 Batteries

Abstract

The growing global energy demand of modern society is urging to find large-scale sources, which are more sustainable and environmentally friendly than the oil-based ones. At present, the capacity of the state-of-the-art lithium ion battery is limited and therefore, radically different approaches are required in order to fulfil the very demanding requests of energy storage. Rechargeable Li-O2/air batteries can potentially represent an interesting solution because they theoretically can store more energy than Li-ion batteries. At present numerous aspects of Li-O2 batteries deserve to be carefully investigated before becoming a commercial reality and among them the electrolyte is one of the main challenges.1 Ether based electrolytes have attracted a lot of interest because they combine several beneficial attributes; they are safe, low cost, stable up to 4.5V and they are of low volatility. Tetra(ethylene) glycol dimethyl ether (TEGDME) has been recently employed in Li-O2 batteries and with very good electrochemical performances.2 Hydrophobic ionic liquids (ILs) have been largely employed in case of the conventional Li-ion cells, however a few details on their behaviour in Li-O2batteries are still available.In this work, we investigated the potential use as electrolytes of mixtures of TEGDME and ether functionalized ionic liquids (ILs). We show the results of the characterization of mixtures having different ratio TEGDME-ILs and containing LiCF3SO3 or LiTFSI salt by means of thermal analysis, conductivity and electrochemical stability measurements. In addition, their application in Li-O2 batteries has been assessed, investigating Li/TEGDME-IL/O2 cells by means of cycling voltammetry (CV) and galvanostatic charge-discharge tests. Oxygen reduction and evolution reactions (ORR and OER) have been studied in TEGDME-ILs mixtures to address the mechanism and reversibility of ORR and OER. Our results demonstrate that oxygen reduction and evolution take place in a reversible way and that ether-based electrolytes containing ionic liquids worthwhile of being further investigated for rechargeable Li-O2cells.[1] D. Capsoni, M. Bini, S. Ferrari, E. Quartarone, P. Mustarelli J. Power Sources(2012) 220, 253.[2] H.-G. Jung, J. Hassoun, J.-B. Park, Y.-K. Sun, B. Scrosati Nat. Chem. (2012) 4, 579