Improved Li-Ion Transport by DME Chelation in a Novel Ionic Liquid-Based Hybrid Electrolyte for Li-S Battery Application

摘要

Current Li-S battery technology has yet to reach the promise of high capacity and suffers rapid capacity fade due in large part to the dissolution and diffusion of polysulphide intermediates. The electrolyte plays a significant role here as well as in stabilizing the Li metal anode electrochemistry. In this work, a novel hybrid electrolyte system is investigated based on varying composition of N-methyl, N-propyl pyrrolidinium bisfluorosulfonimide (C(3)mpyrFSI) ionic liquid (IL) and 1,2-dimethoxy ether (DME) at the saturated concentration of LiFSI salt, demonstrating a most favorable performance for an 80:20 IL/DME composition (by weight). This electrolyte presented higher ionic conductivity and diffusivity while simultaneously improving the electrochemical behavior of Li metal plating and stripping. The ionic interactions among different species of the electrolyte have been studied by NMR spin lattice relaxation time (T-1) measurements, which indicated that Li-DME is likely to form chelation compounds, thereby breaking down the larger ionic aggregates and resulting in smaller solvation shell and higher ionic mobility. An ex situ polysulphide dissolution study indicated that the hybrid electrolyte is also efficient in eliminating polysulphide dissolution. Therefore, due to its ability to suppress polysulphide dissolution and enhance Li transport properties, while minimizing the volatile organic solvent component, the hybrid electrolyte system is an excellent candidate to further explore for future Li-S systems.