Carbon aerogels for battery applications

Kurzfassung

Carbon aerogels are highly open-porous solid materials in which a gas occupies more than 90% of their volume. Therefore, they show a low density, a large surface area, a high pore volume and high electrical conductivity. These properties make carbon aerogels an excellent candidate for a cathode material for metal-sulphur batteries. Sulphur as active material in the positive electrode achieves theoretical gravimetric energy density and capacity of 2600 Wh kg-1 and 1675 Ah kg-1 by conversion reaction and formation of polysulfides. Furthermore, low cost of sulphur and high abundance make the metal-sulphur battery very attractive. Nevertheless, there are still several challenges, such as low sulphur utilization, polysulfide shuttle effect, lithium-dendrite formation, and enormous volume expansion. The conversion reaction of sulphur and the formation of Li2S cause a large volume expansion, which results in a reduction of electron transport paths and thus a decrease in kinetics [1]. In general, the cathode structure should be tolerant enough to stand the large volume expansion and contraction incurred by the discharging and charging of sulphur active material. Flexible carbon aerogels with tailored microstructure can accommodate volume expansion due to their ability for reversible deformation up to a certain degree during cycling, thereby resulting in highperformance cells. They showed high capacity and high Coulombic efficiency after 200 cycles if infiltrated in the gas phase compared to commercial available Ketjenblack . In this work, we present first experimental results on the synthesis and characterisation of sulphur-infiltrated carbon aerogels. First results on a first-of-its-kind molecular study on carbon aerogellike nanostructures will also be presented. Molecular dynamics (MD) studies present a detailed insight into the atomic-scale phenomena that underlie the formation of the porous network of carbon aerogels. The AIREBO potential, which is shown to accurately interpret carbon-carbon interactions, is used to simulate the nanoporous carbon network. The resulting pores in the structure are then incorporated with sulphur atoms and the behaviour of the system is studied under expansion of sulphur atoms mimicking the discharging and charging cycles.