Influences of mechanical and structural properties of carbon aerogels on specific capacity in lithium-sulfur batteries

Abstract

Carbon aerogels (CA) are highly porous, electrically conductive materials with tunable micro- and mesoporosity, as well as surface area and envelope density. Their properties are defined by the sol-gel process of their organic precursors and the carbonization conditions. Due to their well tunable properties they are very attractive as a cathode material for lithium-sulfur batteries. One of the challenges in lithium-sulfur batteries is the capacity loss induced by the polysulfide shuttle effect. Ultramicroporous (pores smaller 1 nm) carbon aerogels as conductive matrices embedding sulfur are able to suppress the polysulfide shuttle effect, maintaining 80% (about 1000 mA·h·g(S)−1) and 70% (about 800 mA·h·g(S)−1) of the initial discharge capacity after 200 cycles at a rate of 0.3C in carbonate and ether-based electrolytes, respectively. The conversion reaction of sulfur 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. Flexible carbon aerogels with tailored microstructure can accommodate volume expansion due to their ability for reversible deformation up to a certain degree during cycling. In this work, we synthesized and investigated highly microporous CAs with different degree of flexibility and particle sizes to study their influences on the capacity in lithium-sulfur batteries. The investigations show that the mechanical and structural properties play a key role in the performance of lithium-sulfur batteries.