Bimetallic organic framework nanocages enhance polysulfide trapping and redox kinetics in lithium–sulfur batteries

Abstract

The shuttle effect and slow redox kinetics of soluble lithium polysulfides (LiPSs) are two serious obstacles to the practical application of lithium–sulfur (Li–S) batteries. Herein, conductive bimetallic metal–organic framework hollow nanocages of CoZn-hexaiminotriphenylene (CoZn-HTP) were carefully designed and synthesized to serve as an efficient sulfur host for Li–S batteries. The unique hollow nanostructures of CoZn-HTP improved sulfur loading and accelerated charge/mass transfer. The doped Zn atoms optimized d-orbital energy levels and induced more active unpaired electrons in CoZn-HTP, effectively enhancing adsorption energy and conversion kinetics for LiPSs. The resulting Li–S batteries with CoZn-HTP showed a high initial capacity of 1184.9 mA h g⁻¹ at 0.1C and a prolonged lifespan of over 1000 cycles at 2C with an ultralow capacity decay of 0.019% per cycle. Notably, the CoZn-HTP@S electrode retained a high specific capacity of 828 mA h g⁻¹ after 100 cycles, with 92% capacity retention, even at high sulfur loading and in poor electrolytes.