Understanding the anchoring effect of Graphene, BN, C_2N and C_3N_4 monolayers for lithium-polysulfides in Li-S batteries

摘要

Graphical abstractNon-metallic monolayer materials containing rich pyridinic N active sites are more available to trap lithium-polysulfides (LiPSs) and retard the shuttle of LiPS species during cycling of Li–S batteries. The molecular distortion and charge transfer reveal that among the Graphene, BN, C2N and C3N4monolayers, the C3N4or C2N can serve as an electrocatalyst, which effectively accelerates the redox reaction kinetics of LiPSs during the charging and discharging process.Display OmittedHighlights•The non-metallic monolayer material (N-MMLM) containing N can provide more active sites to alleviate the shuttle effect.•The molecular distortion and charge transfer reveal that C3N4and C2N can accelerate the redox kinetics of LiPSs.•Multiple Li2S molecules are uniformly dispersed on C3N4and C2N rather than nucleation into larger Li2S clusters.•The adsorption/desorption of multiple Li2S molecules can be controlled by modifying the charged state of the N-MMLMs.AbstractRecently, Li−S batteries with a high theoretical specific energy have attracted significant attention. However, their practical application is still seriously hindered by the shuttling effect of lithium polysulfides (LiPSs) in the Li−S batteries system. Introducing anchoring materials into the cathode or separator, which can strongly attract LiPSs because of advisable binding energies, has been demonstrated as an effective strategy to alleviate the shuttling effect for achieving the excellent cycling performance of Li−S batteries. In this work, the complete mechanistic understanding of the interaction between non-metallic monolayer materials (N-MMLMs, including Graphene, BN, C2N and C3N4) and LiPSs is given in detail with the aid of density functional theory. The calculation results show that N-MMLM can combine the chemical interaction and the physical entrapment of sulfur species to suppress the shuttling effect. C3N4and C2N are predicted to trap LiPSs via stronger interfacial interaction and alleviate the interactions between LiPSs and solvents as well as the consequent dissolution. The strong anchoring effect of C3N4/C2N comes from the bonding of Li−N/C−S and charge transfer. Further charge transfer study reveals that the C3N4/C2N can serve as an electrocatalyst, which effectively accelerates the kinetics of LiPSs redox reactions.