Highly microporous carbon aerogels encapsulating sulfur as cathodes for lithium-sulfur batteries

Abstract

Electrochemical energy storage devices such as lithium-sulfur batteries offering high gravimetric energy density are prerequisite for the realization of the long-range operating and cost-efficient electric vehicles. However, the commercialization of Li-S batteries is left challenged by the capacity loss due to the polysulfide shuttle effect. Encapsulating the active material in the cathode matrix is one of the many implemented approaches inhibiting the polysulfide shuttle effect [1]. Carbon aerogels (CA) are a highly promising material to be used as matrix for sulfur to produce cathodes for metal-sulfur batteries. Resulting from organic resorcinol-formaldehyde aerogels, carbon aerogels exhibit highly porous structure with porosity up to 97%, high surface area about 500-3500 m²·g-1, large pore volume about 0.1-2.5 cm³·g-1, and good electronic conductivity of about 80-150 S/m [2, 3]. Additionally, the important advantage of carbon aerogel is its tunable porous structure and pore size distribution. The microstructure can be adjusted while synthesis and carbonization of organic aerogels. Moreover, flexibility of carbon aerogels allows elimination of crack formation during volume change of sulfur. Herein we synthesized and investigated highly microporous CA as conductive matrix embedding sulfur for cathodes in Li-S batteries [4]. The carbonization procedure is improved leading to increase in micropore volume. Thus, the amount of active material sulfur in micropores is maximized. The possibility and mechanism of retaining active material in the cathode via confinement of the short chain S from the gas phase in the micropores are probed. It is shown that S-infiltrated microporous CA cathodes are able to suppress the polysulfide shuttle effect, resulting in longer cycle stability. Furthermore, the impact of chemical and physical properties of various carbon aerogels, including the density and size of the pores, on the electrochemical performance of the cell is discussed.