The lithium-sulfur battery is a promising next generation battery (NGB) technology, but with a common major complication of irreversible loss of active material (S) from the composite cathode (C/S). Elemental sulfur and polysulfides (Li₂S_x, 4 ≤ x ≤ 8, PS) generated during the charge/discharge process are both dissolved into the electrolyte and the PS shuttle between the anode and the cathode without performing useful work. This shuttling results in low Coulombic efficiency, low cycling capacity, and increased internal cell resistance.^{1, 2}

One way to reduce the PS shuttling is to employ electrolytes that only sparsely dissolve sulfur and PS.^{3, 4} Here we have employed several such electrolytes based on fluorinated carbonates and ethers and studied the resulting performance including the cycle life of the Li-S battery cells made. By combining physico-chemical characterization, electrochemical performance assessments, and operando confocal Raman spectroscopy we gain a better understanding of the PS formation. The overall outcome can be used to guide the selection of solvents for more performant Li-S batteries.

The research presented has received funding through the HELIS project (European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 666221).

References

1 Q. Pang, X. Liang, C. Y. Kwok and L. F. Nazar, Nat. Energy, 2016, 1, 1–11.

2 P. Bonnick, E. Nagai and J. Muldoon, J. Electrochem. Soc., 2018, 165, A6005–A6007.

3 S. Drvarič Talian, S. Jeschke, A. Vizintin, K. Pirnat, I. Arčon, G. Aquilanti, P. Johansson and R. Dominko, Chem. Mater., 2017, 29, 10037–10044.

4 S. Gu, R. Qian, J. Jin, Q. Wang, J. Guo, S. Zhang, S. Zhuo and Z. Wen, Phys. Chem. Chem. Phys., 2016, 18, 29293–29299.