Selective Reduction of Multivariate Metal–Organic Frameworks for Advanced Electrocatalytic Cathodes in High Areal Capacity and Long-Life Lithium–Sulfur Batteries

Lithium–sulfur batteries hold great promise as next-generation high-energy-density batteries. However, their performance has been limited by the low cycling stability and sulfur utilization. Herein, we demonstrate that a selective reduction of the multivariate metal–organic framework, MTV-MOF-74 (Co, Ni, Fe), transforms the framework into a porous carbon decorated with bimetallic CoNi alloy and Fe3O4 nanoparticles capable of entrapping soluble lithium polysulfides while synergistically facilitating their rapid conversion into Li2S. Electrochemical studies on coin cells containing 89 wt % sulfur loading revealed a reversible capacity of 1439.8 mA h g–1 at 0.05 C and prolonged cycling stability for 1000 cycles at 1 C/1060.2 mA h g–1 with a decay rate of 0.018% per cycle. At a high areal sulfur loading of 6.9 mg cm–2 and lean electrolyte/sulfur ratio (4.5 μL:1.0 mg), the battery based on the 89S@CoNiFe3O4/PC cathode provides a high areal capacity of 6.7 mA h cm–2. The battery exhibits an outstanding power density of 849 W kg–1 at 5 C and delivers a specific energy of 216 W h kg–1 at 2 C, corresponding to a specific power of 433 W kg–1. Density functional theory shows that the observed results are due to the strong interaction between the CoNi alloy and Fe3O4, facilitated by charge transfer between the polysulfides and the substrate.