Ultra-Microporous Carbon Aerogel Encapsulating Sulfur As Cathode for Lithium-Sulfur Batteries

Abstract

The operating range and cost effectivity of electric vehicles are significantly compromised by the low energy density of state-of-the-art lithium-ion batteries. For the realization of electro-mobility, chemistries beyond Li-ion such as lithium-sulfur batteries offering high gravimetric energy density are requisite. However, the commercialization of Li-S batteries faces challenges such as severe capacity fade induced by the so-called polysulfide shuttle effect. Encapsulating and trapping the active material in the cathode matrix are among many approaches inhibiting polysulfide dissolution and shuttle effect [1-3]. Herein, we synthesized and investigated highly porous carbon aerogels (CA) as conductive matrix embedding sulfur for cathode in Li-S batteries [4]. Resulting from organic resorcinol-formaldehyde aerogels, the synthesised carbon aerogels exhibit highly porous structure with porosity up to 97%, high surface area of 500-2000 m²·g-1 and large micropore volume of 0.1-0.6 cm³·g-1. The gas-phase sulfur infiltration of the carbon aerogels and the resulting confinement of the short-chain sulfur in the micropores are demonstrated using complementary characterization techniques including TGA, XRD, and XPS. It is shown that S-infiltrated microporous carbon aerogel cathodes are able to suppress the polysulfide shuttle effect, maintaining 80% (1100 mAh/g(S)) of initial discharge capacity after 100 cycles at 0.3C in carbonate-based electrolyte. The cyclability and compatibility of the ether and carbonate-based electrolyte with such composite cathode are explicitly discussed. Additionally, the influence of chemical and physical properties of different synthesized carbon aerogels including pore density, size and morphology on the electrochemical behavior of the cell is investigated in detail. 1. S. Evers, & L. F. Nazar, New approaches for high energy density lithium–sulfur battery cathodes. Acc. Chem. Res. 46, 1135–1143 (2012). 2. Y. Yang, G. Zheng, Y. Cui, Nanostructured sulfur cathodes. Chem. Soc. Rev. 42, 3018–3032 (2013). 3. R. Fang, K. Chen. L. Yin, Z. Sun, F. Li, HM Cheng, The regulating role of carbon nanotubes and graphene in lithium-ion and Lithium-sulfur batteries, Advanced Materials, 31(9) 1800863 (2019) 4. Schwan und L. Ratke, "Flexible Carbon Aerogels" J. Carbon Res. 2, 22 (2016).