Tuning of interactions between cathode and lithium polysulfide in Li-S battery by rational halogenation

Li–S batteries have aroused intense interests as one of the most promising high-energy-density storage technology. However, the complex undesired shuttle effect induced by dissolution and diffusion of lithium polysulfide intermediates remains the major setback of this technology. Chemical modification of carbon cathode through heteroatom-doping is widely accepted as an effective method to inhibit the shuttle effect in Li-S battery cathode. Herein, using first principle calculations, we systematically examined the interaction between halogenated graphene and lithium polysulfide species. It is found that the halogen dopants (F, Cl, Br, I) significantly modify the local electronic structure of adsorption site and further induce a polarization to trap the polysulfides. Interestingly, a concave curve is observed from F to I for lithium polysulfide adsorption rather than a linear relation. The exceptions demonstrated from iodine dopant is carefully analyzed and attributed to its unique charge state. Moreover, boron as second dopant further strengthens the interaction between halogenated graphene and polysulfide molecule. Based on halogenation strategy, lithium polysulfide/cathode interactions are tuned in a wide range, which can also be of great importance to accelerate redox reaction in Li-S battery. Overall, an effective method by halogenation is verified to regulate the adsorption of lithium polysulfide and also enhance the reaction kinetics of the Li-S battery system.