Stabilization of Li Metal Anode in DMSO-Based Electrolytes via Optimization of Salt-Solvent Coordination for Li-O2 Batteries

The conventional electrolyte of 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in dimethyl sulfoxide (DMSO) is unstable against the Li metal anode and therefore cannot be used directly in practical Li-O-2 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-O-2 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 cycling performance of Li-O-2 batteries. The fundamental stability of the electrolyte in the absence of free-solvent against the chemical and electrochemical reactions can also be used to enhance the stability of other electrochemical systems.