Electrochemical Effects of the Hollow Structure Co₃O₄/MWCNT Interlayer Derived through ZIF-67 in Lithium-Sulfur Batteries

The self-standing ZIF-67 derived Co₃O₄@MWCNT interlayer is prepared without a binder and conductor. The hollow structure of ZIF-67 derived Co₃O₄ is confirmed through SEM and TEM analysis. XRD analysis confirms the synthesis of ZIF-67 and the subsequent formation of ligand-free Co₃O₄ after thermal decomposition. BET analysis also confirms a specific surface area of approximately 139.72 m² g⁻². Through polarization measurements, Co₃O₄ effectively reduces polarization by more than 22% compared to when it is not used. After 10 cycles, the capacity of the Co₃O₄@MWCNT cell is 1120.65 mAh g⁻¹, which is 315 mAh g⁻¹ higher than that of an MWCNT cell (805 mAh g⁻¹). The Co₃O₄ promotes the conversion from Li₂S₄ to Li₂S₂ and Li₂S, which leads to higher capacity. Moreover, the cycle stability improves by more than 28% by adsorbing more polysulfide through the hollow structure. Furthermore, it is confirmed that Co₃O₄@MWCNT exhibits approximately 33% less polarization compared to MWCNT even under high C-rate conditions (2 C rate). Various electrochemical characteristics and X-ray photoelectron spectroscopy (XPS) reveal that the hollow Co₃O₄ physically and chemically suppresses the shuttling phenomenon.