While they have shown tremendous influence on electrochemical performance of Li-S batteries, solid electrolyte interphase (SEI) layers on sulfur cathodes still largely remain ambiguous in terms of their functionality, chemical nature and mechanisms of formation. Combining direct detection of SEI layer components on different types of sulfur cathodes in Li/Na-S batteries and chemical reactions between various (poly)sulfides and carbonate electrolyte, this work identifies two distinct chemical routes for the formations of two types of components in SEI layers. One reaction route is unique to a cathode of a Li-S battery fabricated by microporous carbon/sulfur (MC/S) composite, while the formation of SEI layers in a Na-MC/S battery contains both routes. The different types of SEI layers on Na-S and Li-S batteries may have significant meanings in battery performance. The critical roles of Li+ cations and solvent structures of Li+/Na+ cations in steering chemical routes of SEI formation are identified. Based on experimental results, the existence of small sulfur molecules (such as S2), instead of the normal S8, in the micro-pores is proposed. The corrosion reactions between various (poly)sulfides and electrolyte components are investigated in details and important conclusions are drawn regarding to capacity loss in Li-S batteries. This work intends to illustrate fundamental issues in terms of SEI formation and functionalities in Li/Na-S batteries, which demonstrate determining effects in the retaining or degradation of battery capacity.

Solid electrolyte interphase layers on sulfur cathodes in Li/Na-S batteries: Chemical compositions, functionality, the critical role of Li+ and cation solvation structures

254th National Meeting (2017)

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