The massive employment of non-renewable fossil fuels has resulted in a rapid increase of greenhouse gas emission and global warming. The consequent excessive climate changes have triggered a new energy policy, mainly focused on clean and renewable sources.¹ Solar and wind energy conversion systems are the most suitable for large-scale diffusion, in particular in view of recent advances reflecting in cost reduction and economic advantages.¹ However, these discontinuous energy sources require side systems for energy storage and electrical grid stabilization.² Furthermore, electrified vehicles using high-energy storage systems matching the automotive market requirements may effectively mitigate the environmental pollution in large urban areas.² Thus, there is a large push for the development of high capacity energy storage technologies.

Lithium−sulfur battery appears as one of the most promising technologies due to its high theoretical capacity and energy density, i.e. 1672 mAh g⁻¹ and 3500 Wh kg⁻¹ basing on the sulfur weight, respectively, the natural abundance, the low toxicity of elemental sulfur, and the expected low cost.³ However, a sulfur electrode in a lithium battery shows several drawbacks, including poor electronic conductivity, high solubility of the polysulfides formed during the electrochemical process, large volume changes (approximately 80%) by operation, and precipitation of insoluble Li−S intermediates formed during the discharge process in the electrolyte solution. These remarkable issues, leading to severe capacity fading and Li−S cell deterioration upon cycling, have been already investigated in terms of the reaction mechanism.⁴

Herein, we reported a detailed study of an important aspect, i.e., the chemical−physical and electrochemical characterization of the electrode−electrolyte interphase. Indeed, we comparatively investigate the properties of the SEI film formed at the lithium electrode surface in tetraethylene glycol dimethyl ether (TEGDME)-based electrolytes containing different polysulfide species, namely Li₂S₂, Li₂S₄, Li₂S₆, and Li₂S₈, added within a constant concentration of 5% w/w.⁵

References

(1) Armand, M.; Tarascon, J.-M. Nature 2008, 451, 652−657.

(2) Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J.-M. Nat. Mater. 2012, 11, 19−29.

(3) Ji, X.; Nazar, L. F. J. Mater. Chem. 2010, 20, 9821−9826.

(4) Ryu, H.-S.; Guo, Z.; Ahn, H.-J.; Cho, G.-B.; Liu, H. J. Power Sources 2009, 189, 1179−1183.

(5) Agostini, M.; Shizhao, X.; Matic, A.; Hassoun, J. Chem. Mater 2015, 27, 4604−4611.