Evaluating silicene as a potential cathode host to immobilize polysulfides in lithium-sulfur batteries

The internal shuttle effect caused by polysulfides dissolution and migration negatively impacts lithium-sulfur battery performance. In this work, a mesoscale simulation strategy, which involves atomistic calculation and coarse-grained molecular modeling, is employed to evaluate silicene as a potential cathode host material to immobilize polysulfides. Adsorption energies of insoluble polysulfides (Li2Sx with x=1, 2) and soluble polysulfide Li2S4 on pristine and doped silicene sheets are calculated. Results show that the adsorption is thermodynamically favorable and N-doped silicene is helpful in trapping intermediate discharge products, Li2S2 and Li2S4. The dissociation and reduction of long-chain polysulfides to short-chain polysulfides are observed. Electronic structure analysis shows that Li2Sx molecules interact with silicene via strong chemical bonds. The atomistic structure evolution of Li2S layer formation on silicene is also investigated in this study. It is found that Li2S (110) layer forms first, and then, it is converted to Li2S (111) layer by introducing more Li2S molecules to the substrate. Li2S (111)/silicene interfacial structure is thermodynamically stable, and the interaction is dominated by Li-Si bonds. A coarse-grained model is developed to study and compare the growth of Li2S on silicene and graphene. Li2S-induced surface coverage is faster on silicene than on graphene, which indicates that a silicene-based cathode host will experience more acute surface passivation, which will adversely affect cathode performance. [GRAPHICS]