Vanadium niobium carbide (VNbCTx) bimetallic MXene derived V5S8-Nb2O5@MXene heterostructures for efficiently boosting the adsorption and catalytic performance of lithium polysulfide.

Abstract

To alleviate the shuttle effect in lithium-sulfur (Li-S) batteries, the electrocatalytic conversion of polysulfides serves as a vital strategy. However, achieving a synergy that combines robust adsorption with high catalytic activity continues to pose significant challenges. Herein, a simple solid-state sintering method is employed to transform vanadium-niobium carbide MXene (VNbCT_x) into a heterogeneous structure of V₅S₈-Nb₂O₅@VNbCT_x MXene (denoted as V₅S₈-Nb₂O₅@MX). The Nb₂O₅ component immobilizes lithium polysulfides (LiPSs) at the electrode through its strong chemical affinity, while the V₅S₈ fraction serves as an outstanding electrochemical catalyst, enhancing the reaction kinetics of sulfur precipitation. Furthermore, the VNbCT_x MXene precursor scaffold is preserved through the conversion and uniformly distributed throughout the composite, exhibiting excellent electrical conductivity. Thanks to the synergistic "capture-adsorption-catalysis" action on LiPSs, the V₅S₈-Nb₂O₅@MX composite effectively restrains the shuttle effect. The as-prepared Li-S battery demonstrates a significant increase in specific capacity, reaching 1508 mA h g^-1 at 0.1C and maintaining a capacity decay of approximately 0.027% per cycle after 500 cycles at 1C and 766.1 mA h g^-1 at 5C. Even under a high sulfur loading of 5.75 mg cm^-2, the battery can maintain a specific capacity of 596.6 mA h g^-1 and exhibit significant cycling stability after 100 cycles. DFT calculations indicate that the V₅S₈-Nb₂O₅@MX heterostructure exhibits a higher binding energy of 5.34 eV and a lower decomposition barrier energy of 0.68 eV, presenting potential advantages in accelerating the conversion reactions of LiPSs. Our research offers a straightforward approach for designing metal oxide-sulfide heterostructured catalysts that deliver superior performance and enhance the electrocatalytic conversion of LiPSs, clearing the path for high performance Li-S batteries.