Preparation of multilayer core-shell WS2@CZIF-8@CZIF-67 and application in lithium-sulfur batteries

To address the challenges of rapid reversible capacity decay and significant volumetric expansion during charge-discharge cycles in lithium-sulfur (Li-S) batteries, this study designed a hierarchical core-shell composite material. Carbon material C_ZIF-8, derived from the metal-organic framework (MOF) ZIF-8, was used as the crystalline core. A rhombic dodecahedral ZIF-67 structure, possessing a similar configuration, was introduced on its surface, and carbonization resulted in the formation of a core-shell composite carbon material, C_ZIF-8@C_ZIF-67. Subsequently, nanoscale layered tungsten disulfide (WS₂) was synthesized in situ on the surface of the C_ZIF-8@C_ZIF-67 carbon polyhedron via a hydrothermal method. The obtained materials were characterized using X-ray diffraction, scanning electron microscopy, Raman spectroscopy, nitrogen adsorption-desorption analysis, and electrochemical performance tests. The results indicated that the formation of the hierarchical core-shell structure C_ZIF-8@C_ZIF-67 facilitated the expansion of the interlayer spacing of WS₂, exposing more active adsorption sites and enhancing the wettability of the electrode material with the electrolyte. Furthermore, the C_ZIF-8@C_ZIF-67 composite carbon material, featuring abundant pore structures and a high specific surface area, demonstrated superior adsorption capability for lithium polysulfides compared to single MOF-derived carbons, effectively mitigating volumetric expansion of sulfur electrodes during charge-discharge cycles. The synergistic effects between WS₂ and C_ZIF-8@C_ZIF-67 conferred outstanding cycling stability to the material. At a high current density of 2 C, it exhibited a capacity decay rate of only 0.040 % per cycle over 200 cycles. After 500 cycles, the capacity decay rate further decreased to 0.020 % per cycle.