Research On The Properties Of 2D Materials As Anchoring Materials For Lithium/Sodium-Sulfur Batteries

In recent years,metal-sulfur batteries（M-S,M=Li and Na）are expected to be one of the next generations of excellent storage devices due to their high theoretical specific capacity(～1672 m A h·g^-1).However,the commercial application of M-S batteries is still restricted,which ascribes to the poor conductivity of the S cathode,the shuttle effect,and the sluggish reaction kinetics.One of the most troubling problems is the shuttle effect caused by the easy dissolution of higher-order polysulfides（MPSs,M=Li and Na）in organic electrolytes during the discharging process.Therefore,developing the anchoring material（AM）on the S cathode is identified as one of the efficient methods to suppress the shuttle effect.In this work,the properties of 2D materials as AMs for M-S batteries are investigated by means of the first-principles calculation method based on the density functional theory.The main findings are listed as follows:The potential of the BNP₂ monolayer as an AM for Li-S batteries was first studied.Compared with the adsorption energies between 1,3-dioxolane（DOL）&1,2-dimethoxyethane（DME）solvent molecules and Li PSs,BNP₂ with adequate adsorption energies can adsorb higher-order Li PSs without causing them decomposition,which effectively suppresses the shuttle effect and avoids the loss of active substances.The projected density of states（PDOS）of the adsorption systems reveals that BNP₂ exhibits metallic characteristics after the adsorption of Li PSs,which is conducive to improving the electronic conductivity of the system.In addition,the BNP₂ monolayer acts as a catalyst in the conversion process of Li₂S₂ into Li₂S and the decomposition process of Li₂S.The corresponding cleavage and catalytic decomposition energy barriers were reduced to-1.02 e V and 0.25 e V,respectively.This not only promotes the conversion efficiency between lower-order Li PSs but also improves the multiplier performance of Li-S batteries.In the second work,the properties of pristine borophosphene（BP）and doped BP as AMs for Na-S batteries were investigated.It was found that the BP substrate doped with N or C atoms could improve the adsorption energies to Na PSs more effectively than the pristine BP,and reduce the vd W action share,which is beneficial to suppress the shuttle effect.Meanwhile,the PDOS suggests that the metallic properties of the three substrates are still well preserved.The excellent electrocatalytic properties of the three substrates are exhibited by reducing the catalytic decomposition energy barriers of Na₂S,in which 0.27/0.79/1.02 e V is found on the pristine/N_P/C_P-BP,respectively.The cycle performance and multiplier performance of Na-S batteries are ultimately improved.After calculation and analysis,both BNP₂ monolayer and BP have good prospects for application as AMs in Li/Na-S batteries.Meanwhile,in addition to the influence of doping modulation on the material properties,this study provides a theoretical basis for the subsequent problems of shuttle effect and sluggish reaction kinetics in Li/Na-S batteries.