Theoretical Study On The Anchoring Effect Of Modified Graphene-based Materials In Lithium Sulfur Batteries

Recently,with the depletion of limited fossil fuels,the global industrialization has caused serious pollution problems and global warming.Therefore,the surge in demand for efficient,portable and economical power storage systems has greatly promoted the development of rechargeable batteries.In this case,lithium-sulfur?Li-S?batteries have greater advantages than the well-known Ni-Cd battery system,for example,higher theoretical specific capacity?1672 mAh/g?,higher energy density?2600 Wh/kg?,lower cost and environmental friendliness.Thus,Li-S batteries are one of the most promising candidates for high-efficiency energy storage devices in the modern electrochemical field,due to the above advantages.However,its large-scale industrial application are still severely limited by the high internal resistance,large changes in volume,uncontrolled growth of lithium crystals,and high consumption of bipolar materials in the charing and discharing process.Particularly,the generated polysulfide easily dissolves into organic solutions?i.e.,shuttle effect?,which results in serious consumption of bipolar materials,thus greatly limiting the application prospect of Li-S batteries.To address it,a feasible strategy is to use anchoring materials to effectively fix polysulfides.Therefore,it is very necessary to design and develop anchoring materials with high stability and high chemical activity to suppress the shuttle effect in Li-S batteries.In this paper,by means of density functional theory?DFT?computations,we evaluated that surface interface modification promotes the anchoring effect of graphene materials on polysulfides,thereby minimizing the shuttle effect faced in Li-S batteries.The results are as follows:?1?we investigated the potential application of experimentally available metal-N₄/graphene?e.g.,Cr,Mn,Fe,Co,Ni,and Cu?,as anchoring materials in the field of Li-S batteries.Our results showed that Cr-,Mn-,Fe-,Co-and Cu-N₄/graphene can moderately interact with long-chain Li₂S_n species,with the adsorption energies between0.95-1.92 eV,while remaining good conductivity.Therefore,introducing suitable metal-N₄ groups in graphene for modification treatment can greatly enhance its anchoring effect on Li-S batteries,thereby suppressing unnecessary shuttle effects.?2?We theoretically designed heterostructure materials,namely monolayer transition metal disulfide or diselenide?i.e.,MoS₂ and MoSe₂?and the B or N doped graphene stack,as the promosing anchoring candidates for Li-S batteries.Our redults revealed that designed heterostructures exhibit excellent anchoring properties for soluble long-chain Li₂S_n species,with the adsorption energies ranging from 1.20 to 2.05eV,avoiding the dissolution of Li₂S_n species into the electrolyte and ensuring structural integrity.Therefore,the as-designed heterostructure materials are a new class of promising Li-S battery anchoring materials.