Theoretical prediction of B/Al-doped black phosphorus as potential cathode material in lithium-sulfur batteries

摘要

Benefiting from the high electronic conductivity, good flexibility, and the capacity of polysulfides immobilization and conversion, black phosphorus (BP) has been widely used in lithium-sulfur batteries. However, high loading electrochemically inert BP reduces the energy density advantage of the batteries. To reduce the BP loading, the present theoretical study was performed to predict the "surface strategy" by heteroatom doping of BP to enhance its performance. With Lewis acidic B-doped, Al-doped BP, Lewis basic N-doped BP and pristine BP as objects, the adsorption and the catalytic conversion of polysulfide were carefully investigated. Based on calculation results, even though all the N, B and Al-doping elevate adsorption capacity, N-doping hinders the polysulfide conversion whereas B and Al-doping promote the conversion. Therefore, it is predicted that B and Al-doping are promising "surface strategy". The facility is two-fold: First, in addition to Li-P interaction between polysulfide and the surface, B/Al-doping creates S-B/Al interaction, leading to the greater adsorption. Second, the Lewis acidic B/Al and the P atom of the surface construct "B/Al-P frustrated Lewis pair" system, which promotes kinetics of polysulfide conversion. It is hoped that our findings could provide insights into improving the surface properties of BP and reducing the loading.