Lithiation-Assisted Strengthening Effect and Reactive Flow in Bulk and Nanoconfined Sulfur Cathodes of Lithium–Sulfur Batteries

Lithiation of electrode
materials can lead to significant microstructural
evolution and changes in their mechanical behaviors in lithium batteries.
Lithium–sulfur (Li–S) batteries have recently attracted
extensive attention, where carbon matrices have been utilized to retain
S content by restricting the dissolution of polysulfide into electrolytes.
Here we systematically investigate S cathode upon unconfined and nanoconfined
lithiation using reactive molecular dynamics simulations. We demonstrate
the great ductility of lithiated amorphous S cathode (a-LixS) governed by overcoordination sites, as well as
the resulting strengthening effect of a-LixS due to the formation of stronger Li–S bonds upon lithiation.
Fracture and cavitation studies also indicate the dominant role of
shear banding, which is facilitated by overcoordinated S “plastic
carriers”, in accommodating the plastic deformation of a-LixS under tensile loading. Based on a chemo-mechanical
yield function, we confirm two-dimensionally nanoconfined lithiation
reaction can facilitate the out-of-plane inelastic deformation (“reactive
flow”) of a-LixS at a much lower
level of biaxial stress. The atomistic understanding of lithiation
behaviors of S cathodes provides fundamental insight into the optimal
design of carbon-based S composite cathode with outstanding mechanical
integrity, as well as the prediction of lithiation behavior of other
electrode materials, such as silicon, metal oxides, and graphite.