The role of carbon electrodes pore size distribution on the formation of the cathode-electrolyte interphase in lithium-sulfur batteries

The use of sulfur is advantageous in next generation lithium batteries replacing scarce metals and leading to enhanced specific energy compared to established energy storage devices. Herein, the utilization of microporous (d<2 nm) carbon/sulfur composites using a carbonate‐based electrolyte is studied to obtain more insights into the formation of a solid‐electrolyte interphase (SEI) layer on the cathode surface in Li‐S cells. The sulfur was confined in model carbide‐derived carbon (CDC) system with uniform micropores as well as in commercial microporous activated carbon materials. The molecular structure of sulfur in the pores is characterized by means of EXAFS spectroscopy. The electrochemical evaluation of confined sulfur cathodes revealed quasi solid‐state transformation mechanism as well as the generation of a protective SEI layer on the cathode surface. This cathode‐electrolyte interphase (CEI) allows common microporous carbon/sulfur cathodes to reversibly cycle in carbonate‐based electrolyte, while mesoporous systems show rapid capacity fade due to leaky CEIs. Based on this result, the influence of the porosity of the porous carbon host materials on the essential cathodic SEI layer formation is discussed for carbonate‐based electrolytes in Li‐S batteries.