Enhanced Cycling Stability of Rechargeable Li-O2 Batteries Using High-Concentration Electrolytes

Abstract

The stability of electrolytes against highly reactive, reduced oxygen species is crucial for the development of rechargeable Li-O2 batteries. In this work, the effect of lithium salt concentration in 1,2-dimethoxyethane (DME)-based electrolytes on the cycling stability of Li-O2 batteries is investigated systematically. Cells with highly concentrated electrolyte demonstrate greatly enhanced cycling stability under both full discharge/charge (2.0-4.5 V vs Li/Li+) and the capacity-limited (at 1000 mAh g-1) conditions. These cells also exhibit much less reaction residue on the charged air-electrode surface and much less corrosion of the Li-metal anode. Density functional theory calculations are used to calculate molecular orbital energies of the electrolyte components and Gibbs activation energy barriers for the superoxide radical anion in the DME solvent and Li+-(DME) n solvates. In a highly concentrated electrolyte, all DME molecules are coordinated with salt cations, and the C-H bond scission of the DME molecule becomes more difficult. Therefore, the decomposition of the highly concentrated electrolyte can be mitigated, and both air cathodes and Li-metal anodes exhibit much better reversibility, resulting in improved cyclability of Li-O2 batteries. Superior performance of rechargeable Li-O2 batteries based on high-concentration Li bis(trifluoromethanesulfonyl)imide (LiTFSI)-1,2-dimethoxyethane (DME) electrolyte is related to enhanced stability of the Li-metal anode and air electrode in this electrolyte. This finding provides a significant insight into the fundamental mechanism of high-concentration electrolytes in enhancing the stability of air cathodes and Li-metal anodes in rechargeable Li-O2 batteries.