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

Abstract

Lithium−sulfur batteries hold great promise as nextgeneration 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.

Yolk Double-Shell Cathode for Encapsulating Polysulfides and Initialing Redox Kinetics toward High-Performance Lithium–Sulfur Batteries

“…The era of energy diversification reflects the wisdom progress of human civilization, but limited earth resources need to be rationally allocated to maximize their utilization efficiency. − Faced with the rising demand for sharp energy density iteration, the exploitation of highly efficient energy storage devices becomes an urgent need. − Lithium–sulfur batteries (LSBs) have been widely studied because of these advantages, such as high energy density (especially up to 2600 Wh kg –1 ), high theoretical specific capacity of active sulfur (1675 mAh g –1 ), and abundant resources. − However, these issues perplex the research process of LSBs, including the unstable cathode frameworks caused by volume expansion/shrinkage for sulfur redox reaction (SRR) during charging/discharging cycles, the untimely transformation of lithium polysulfides (LiPSs), inferior conductivity of sulfur source (S 8 ) and low-order phase reaction products (Li 2 S 2 and Li 2 S), and the lithium dendrites on the anode, restricting its commercial exploration. − In particular, the shuttle effect of dissolvable LiPSs (mainly Li 2 S 8 –Li 2 S 4 ) not only injures the mass transfer reaction of SRR within the cathode (a mass of intermediates travel to the anode side) but also causes the out-of-order deposition/stripping of active substances lithium (inactive dead-sulfur and dead-lithium are clustered in microzones). − …”