High sulfur content in microporous carbon aerogels for lithium-sulfur batteries

Kurzfassung

Lithium-Sulfur (Li-S) batteries are currently one of the attractive systems among next generation of the batteries offering high theoretical specific capacity of 1675 mAh/g and high specific energy density of 2500 Wh/Kg. In addition, sulfur is abundant on earth and inexpensive. These advantages of Li-S battery make it the promising candidate for the realization of cost and performance- efficient electro-mobility. However, the commercialization of Li-S batteries is challenged by the capacity loss induced by the so-called polysulfide shuttle effect. The encapsulation of the active material in the cathode matrix is one of the many strategies impeding the polysulfide shuttle effect [1]. Due to the adjustable microporous structure and pore size distribution, carbon aerogels are highly promising material to be used as user-defined porous matrix for sulfur. Starting from organic resorcinol-formaldehyde (RF) aerogels, recently developed carbon aerogels exhibit porous structure with huge porosity up to 97 %, high surface area about 500-2000 m²/g, large micro pore volume about 0.1-0.6 cm³/g, and good electrical conductivity [2,3]. Moreover, flexibility of carbon aerogels allows elimination of crack formation during volume change of sulfur. In the presented study, we synthesized and investigated highly microporous carbon aerogel as conductive matrix embedding up to 32 wt-% of sulfur for cathodes in Li-S batteries [4]. New aerogel based battery exhibits high cyclic stability and high specific capacity of 1000 mAh/g(S) after 150 cycles. The innovative gas-phase sulfur infiltration of the carbon aerogels and the resulting confinement of the short sulfur-chains in the microspores (< 2 nm) are demonstrated employing complementary characterization techniques such as TGA, XPS, and elemental analysis. It is shown that S-infiltrated microporous carbon aerogel cathodes are indeed able to suppress the polysulfide shuttle effect, resulting in longer cycle stability of the cell in both ether and carbonate-based electrolyte.