In the presented study, a sulfur infiltrated ultra-microporous carbon aerogel as a composite cathode for lithium sulfur batteries is developed and investigated.

While the characteristics of the macroscopic mechanical behavior of organic aerogels are well known, the mechanisms responsible for the substructural evolution of their networks under mechanical deformation are not fully understood. Herein, organic aerogels from the aqueous sol−gel polymerization of resorcinol with formaldehyde are first prepared. Specifically, the resorcinol to water (R:W) molar ratio is varied for obtaining diverse highly open‐cellular porous structures with mean pore sizes ranging between 30 and 50 nm. The corresponding network structures are then characterized and exhibit different morphological and mechanical properties. Furthermore, a micromechanical constitutive model based on the pore‐wall kinematics is proposed. While the arrays of particles forming the pore walls are moderately connected, the pore walls are considered to behave as solid beams under mechanical deformation. Moreover, the damage mechanisms in the pore walls that result in the network collapse are defined. All model parameters are shown to be physically derived, and their sensitivity to the macroscopic network behavior is analyzed. The model predictions are shown to be in good agreement with the experimental stress−strain data of the different aerogels.

Carbon aerogels find application in many fields. In most of the applications, they are used as powders and thus need to be pulverized. However, the pulverization could induce various changes in the microstructure of carbon aerogels. The extent of changes depends not only on the dominant forces of used technique, but also on the mechanical and structural properties of initial monolithic samples. In the present work, we discuss the influence of grinding, milling in shaker cryo-mill, and planetary ball mill on stiff, ductile and flexible carbon aerogels. Scanning electron microscopy and transmission electron microscopy images, gas sorption techniques, wide-angle X-ray scattering, and Raman spectroscopy show a strong dependency of the introduced energy amount while pulverization on the structure modification. Results show that stiff carbon aerogels do not undergo noticeable changes. In contrast, ductile carbon aerogels are very sensitive to friction forces. Soft and flexible carbon aerogels undergo drastic changes in the microstructure.

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).