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 Fe 3 O 4 nanoparticles capable of entrapping soluble lithium polysulfides while synergistically facilitating their rapid conversion into Li 2 S. 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@CoNiFe 3 O 4 /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 Fe 3 O 4 , facilitated by charge transfer between the polysulfides and the substrate.