Lithiation-Assisted Strengthening Effect and Reactive Flow in Bulk and Nanoconfined Sulfur Cathodes of Lithium-Sulfur Batteries
MC Wang and JG Yu and SC Lin, JOURNAL OF PHYSICAL CHEMISTRY C, 121, 17029-17037 (2017).
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.
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