Enhancing sulfur cathode process via a functionalized complex molecule

Lithium-sulfur batteries are regarded as promising next-generation energy storage batteries for their ultra-high theoretical energy density. However, the complex sulfur electrode process with sluggish sulfur conversion reactions is a critical issue for lithium-sulfur batteries, in which catalytic interfacial reactions and accelerated lithium-ion diffusion are the key factors. Our previous work has shown that implanting functional molecules with multiple redox properties in the electrode can break through the conventional diffusion layer constraints and achieve forced convection. In this work, a functionalized complex molecule, methylene blue anthraquinone-2-sulfonate (MB-AQ), with multiple redox activities as well as abundant active sites, was synthesized and introduced into the sulfur cathode. In addition to accelerating the transport of lithium ions by reversible inhaling and exhaling lithium ions, the MB-AQ can combine polysulfides by its active sites to accelerate sulfur conversion reactions. Benefiting from two functions of accelerating ion diffusion and catalyzing interfacial reactions, MB-AQ/reduced graphene oxide (rGO)/S cathode can achieve high initial capacities of 884 and 674 mAh·g −1 with stable cycling of 700 and 1,000 times at 1 and 4 C, respectively. It is worth mentioning that the capacity of 462 mAh·g -1 can be achieved even at a high current density of 6 C. This work provides a new approach to enhancing the sulfur cathode process.