Mott‐Schottky MXene@WS2 Heterostructure: Structural and Thermodynamic Insights and Application in Ultra Stable Lithium−Sulfur Batteries

Abstract

AbstractDue to the “shuttle effect” and low conversion kinetics of polysulfides, the cycle stability of lithium sulfur (Li−S) battery is unsatisfactory, which hinders its practical application. The Mott‐Schottky heterostructures for Li−S batteries not only provide more catalytic/adsorption active sites, but also facilitate electrons transport by a built‐in electric field, which are both beneficial for polysulfides conversion and long‐term cycle stability. Here, MXene@WS2 heterostructure was constructed by in‐situ hydrothermal growth for separator modification. In‐depth ultraviolet photoelectron spectroscopy and ultraviolet visible diffuse reflectance spectroscopy analysis reveals that there is an energy band difference between MXene and WS2, confirming the heterostructure nature of MXene@WS2. DFT calculations indicate that the Mott‐Schottky MXene@WS2 heterostructure can effectively promote electron transfer, improve the multi‐step cathodic reaction kinetics, and further enhance polysulfides conversion. The built‐in electric field of the heterostructure plays an important role in reducing the energy barrier of polysulfides conversion. Thermodynamic studies reveal the best stability of MXene@WS2 during polysulfides adsorption. As a result, the Li−S battery with MXene@WS2 modified separator exhibits high specific capacity (1613.7 mAh g−1 at 0.1 C) and excellent cycling stability (2000 cycles with 0.0286 % decay per cycle at 2 C). Even at a high sulfur loading of 6.3 mg cm−2, the specific capacity could be retained by 60.0 % after 240 cycles at 0.3 C. This work provides deep structural and thermodynamic insights into MXene@WS2 heterostructure and its promising prospect of application in high performance Li−S batteries.