B/N co-doping rGO/BNNSs heterostructure with synergistic adsorption-electrocatalysis function enabling enhanced electrochemical performance of lithium-sulfur batteries

Abstract

The practical applications of lithium-sulfur (Li-S) batteries are obstructed by low sulfur utilization and poor cycling stability caused by notorious shuttle effect of soluble lithium polysulfide (LiPSs) and sluggish redox reaction kinetics. Herein, a creative B/N co-doping reduced graphene oxide/boron nitride nanosheets (B/N co-doping rGO/BNNSs) heterostructure prepared by a facile in-situ pyrolysis reaction strategy, is rationally designed as a multifunctional coating for high-performance Li-S batteries. The modified separator with B/N co-doping rGO/BNNSs displays excellent flexibility, thermal conductivity and electrolyte wettability. The superior shielding effect to LiPSs provided by the high density of B-N, B-C and C-N polar bonds and hierarchical pore structures, not only enhance the utilization of sulfur but also prevent the Li-anode from corrosion by LiPSs. Meanwhile, the improved electrochemical kinetics resulting from B/N co-doping sites and rGO/BNNSs heterostructure, effectively promote Li-ions diffusion and catalyze the redox kinetics of Li2S and LiPSs. Encouraged by the synergistic effect, the Li-S battery with B/N co-doping rGO/BNNSs coating shows a reversible capacity of 966.6 mAh g−1 at 1C. Upon increased current density of 4C, a desirable initial discharge capacity of 741.5 mAh g-1can be acquired with ultralow capacity decay of 0.015% per cycle after 500 cycles. Even under high sulfur areal loading configuration, the cell still has remarkable cycling stability. The fundamental explorations on inhibiting LiPSs shuttle and promoting various sulfur species conversion demonstrate the great potential of B/N co-doping rGO/BNNSs in practical Li-S batteries.