CoB and BN composites enabling integrated adsorption/catalysis to polysulfides for inhibiting shuttle-effect in Li-S batteries

Abstract

The integrated structure of CoB/BN@rGO facilitates the remarkable increase of adsorption/catalytic sites and enhances its catalytic capability to LPS conversion, that leads to improved electrochemical performances of LSB. • CoB/BN@rGO with catalytic ability was used as the modification layer of separator to inhibit shuttle effect. • BN alone shows preferred adsorption capacity for LPS through LiSnLi + ⋯N bond. • CoB itself has important impacts on LPS electro-catalytic conversion that occurs mainly on Co 2+ active sites. • The integrated structure can double the adsorption/catalytic sites to expedite catalytic conversions. Lithium-sulfur (Li-S) batteries are hampered by the infamous shuttle effect and slow redox kinetics, resulting in rapid capacity decay. Herein, a bifunctional catalysis CoB/BN@rGO with integrated structure and synergy effect between adsorption and catalysis is proposed to solve the above problems. The integrated CoB and BN are simultaneously and uniformly introduced on the rGO substrate through a one-step calcination strategy, applied to modify the cathode side of PP separator. The transition metal borides can catalyze the conversion of lithium polysulfides (Li 2 S n , n ≥ 4), whereas the bond of B-S is too weak to absorb LPS. Thus BN introduced can effectively restrict the diffusion of polysulfides via strong chemisorption with LiS n Li + ⋯N, while the rGO substrate ensures smooth electron transfer for redox reaction. Therefore, through the integrated adsorption/catalysis, the shuttle effect is suppressed, the kinetics of redox reaction is enhanced, and the capacity decay is reduced. Using CoB/BN@rGO modified PP separator, the Li-S batteries with high initial capacity (1450 mAh g −1 at 0.35 mA cm −2 ) and long-cycle stability (700 cycles at 1.74 mA cm −2 with a decay rate of 0.032% per cycle) are achieved. This work provides a novel insight for the preparation of bifunctional catalysis with integrated structure for long-life Li-S batteries.