Physisorption Mechanism of Solvated Polysulfide Chains on Graphene Oxides with Varied Functional Groups
AM Dive and MK Song and S Banerjee, JOURNAL OF PHYSICAL CHEMISTRY C, 121, 5089-5098 (2017).
Despite the high theoretical capacity (similar to 1675 mAh/g) and energy density, commercialization of the lithium sulfur (Li-S) batteries has been hindered primarily due to the loss of active material at the cathode through the "polysulfide shuttle" effect during repeated charge- discharge cycles. Graphene and graphene oxide (GO) are being explored as effective cathode supports to alleviate these problems. However, there is a lack in fundamental understanding of the physical interactions between polysulfide and graphene/GO substrates. In order to determine the dominant mechanisms for physisorption of polysulfides on GO, we employed molecular dynamics (MD) to simulate polysulfides (S-8(2-)) solvated in standard dimethoxy ethane (DME)/dioxalane (DOL) (1:1 v/v) solvent near a range of graphene and GO structures. The results indicate that the extent of physisorption of polysulfide is governed by Coulombic interactions with GO, solvent orientation near substrates, and steric factors that depend on the nature and surface density of functional groups on the GO. Based on physisorption, GO with hydroxyl functional groups is the most effective in anchoring polysulfides. These results can potentially pave the way for design of molecularly tailored cathode supports to mitigate polysulfide shuttle and therefore improve performance of Li-S batteries.
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