Nanostructure under pressure: Molecular Insights into the Mechanical Behavior of Aerogel Cathodes

Kurzfassung

Goal: Carbon aerogels, are promising cathode materials for metal-sulphur batteries due to their low density, high conductivity, large specific surface area and large micropore volume (pore sizes < 2 nm)1-3. However, the ≈80% volume expansion during the sulphur conversion reaction poses a significant risk of carbon network failure4, 5. Therefore, this work aims to investigate the nonlinear and inelastic mechanical behaviour of nanostructured porous carbon, resembling carbon aerogel morphology, at the microstructure level. Methodology: Molecular dynamics (MD) is employed as a method to develop nanoporous carbon structures. The nanostructured porous carbon models of different densities are developed using the methodology described in Patel et al6. Their structural and morphological validation is done using experimental studies to mimic the behavior of carbon aerogels. Models were subjected to cyclic compressive deformation as well as tensile deformation up to fracture for un-notched and notched systems. Results: Mechanical properties, Elastic modulus, E, Fracture strength, σf, Fracture toughness, KIC and strain energy release rate, GC are highly dependent on the density of the material at the molecular level. Tensile deformation leads to structural failure once the applied stress exceeds the σf signifying a loss of elastic integrity within the material framework. High density structures show higher dependency on the crack length to height ratio of the material for KIC and GC before showing convergence behaviour. The simulated structures show stability up to 20% cyclic compressive deformation. Discussion: Experimental studies on carbon aerogels concentrate on the bulk mechanical properties of the material and provide little to no information about the mechanical behaviour of the material at a particle level or microstructure level. Models developed here exhibit excellent resistance to mechanical stresses at molecular level. Study of the damage, residual deformation under cyclic deformation and crack propagation mechanisms informs the mechanical design and enhance the long-term efficacy of carbon aerogel-based cathodes.