Macro/Mesoporous Carbon/Defective TiO₂ Composite as a Functional Host for Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) hold great potential as next-generation electrochemical energy storage and conversion systems owing to their higher theoretical capacity (1675 mAh/g). However, the shuttling of soluble polysulfides with slow redox reaction kinetics has restricted the commercialization of LSBs. The design and synthesis of effective cathode hosts provide a promising solution to improving the electrochemical performances of LSBs. Herein, we report a composite of macro/mesoporous carbon (MMC) coupled with defective TiO2 nanoparticles as a novel functional cathode host for LSBs. The MMC/TiO2 composite has been synthesized using a template-based approach combining simple hydrothermal reactions. Experimental characterizations, electrochemical measurements, and first-principles density functional theory (DFT) calculations disclose that the combination of macro/mesoporous carbon and defective TiO2 (coexistence of oxygen vacancies and Ti3+) effectively suppresses the undesired polysulfide shuttling effect and promotes fast redox conversion of polysulfides during cycling. The resultant LSBs with MMC/TiO2@S as a composite cathode thus exhibit impressive electrochemical properties with high capacity (1420 mAh/g at 0.2C), good rate capability (522 mAh/g at 2C), and cycling ability (65.6% retention at 0.2C over 60 cycles). This work can present some new insights into the rational design and exploration of novel material systems and compositions for applications in LSBs.