Theoretical probing of monolayer BiI as an electrolyte separator and 3d-TM-doped BiI as electrocatalysts toward high-performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are regarded as one kind of promising energy storage system, but the present challenge is to achieve the desired energy density through resolving the shuttle effect and sluggish electrochemical process. In this work, pristine two-dimensional (2D) BiI 3 with intrinsic atomic pore structures and its corresponding 3d transition metal (TM) doped systems have been proposed and examined to solve the above issues based on first-principles calculations. Due to its unique atomic pores, the 2D BiI 3 monolayer can serve as an electrolyte separator to block dissolved lithium polysulfides (LiPSs) while ensuring ultra-fast transport of Li ions. More significantly, the 3d-TM (TM = Ti, V) doped BiI 3 systems show extremely lower overpotentials of 0.16-0.17 V for the sulfur reduction reaction and decreased energy barriers of 0.29-0.44 eV for decomposing insoluble Li 2 S, indicating the promotion of the electrochemical process of LiPS conversion by 3d-TM doping. Electronic structure analysis shows that the charge redistribution on monolayer TM/BiI 3 triggered by the hybridization of I-5p and TM-3d states is crucial to improve the adsorption and conversion of LiPSs for TM/BiI 3 through stronger Li-I bonds. These findings potentially provide the key electrolyte separator and electrocatalyst and open up the possibility of multifunctional materials with similar structures to apply in high-performance Li-S batteries. 2D Multifunctional BiI 3 has been proposed to serve as an electrolyte separator to block soluble LiPS diffusion with ultrafast Li + transport channels and as a promising electrocatalyst for improving LiPS conversion by 3d transition metal atom doping.