Bin Liu,† Wu Xu,†,* Pengfei Yan,‡ Sun Tai Kim,∥ Mark H. Engelhard,‡ Xiuliang Sun,§ Donghai Mei,§ Jaephil Cho,∥ Chong-Min Wang,‡ Ji-Guang Zhang†,*
† Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, WA 99354, United States
‡ Environmental and Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99354, United States
§ Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99354, United States
∥ Department of Energy Engineering, School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 689-798, South Korea.
*E-mails: jiguang.zhang@pnnl.gov; wu.xu@pnnl.gov
The conventional DMSO-based electrolyte (1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in DMSO) is unstable against the Li metal anode and therefore cannot be used directly in practical Li-O2 batteries. Here, we demonstrate that a highly concentrated electrolyte based on LiTFSI in DMSO (with a molar ratio of 1:3) can greatly improve the stability of the Li metal anode against DMSO and significantly improve the cycling stability of Li-O2 batteries. This highly concentrated electrolyte contains no free DMSO solvent molecules, but only complexes of (TFSI–)a-Li+-(DMSO)b (where a+b=4), and thus enhances their stability with Li metal anodes. In addition, such salt-solvent complexes have higher Gibbs activation energy barriers than the free DMSO solvent molecules, indicating improved stability of the electrolyte against the attack of superoxide radical anions. Therefore, the stability of this highly concentrated electrolyte at both Li metal anodes and carbon-based air electrodes has been greatly enhanced, resulting in improved cyclic stability of Li-O2 batteries. The fundamental stability of the electrolyte with free-solvent against the chemical and electrochemical reactions can also be used to enhance the stability of other electrochemical systems.
Acknowledgement
This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies, of the U. S. Department of Energy (DOE) as part of Battery Materials Research (BMR) program.
