Metal Organic Frameworks Derived Hierarchical Composite Materials for High Performance Lithium Sulfur Batteries


Student thesis: Doctoral Thesis

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Award date6 Jan 2022


Considered asone of the most promising next-generation energy storage battery systems, lithium-sulfur (Li-S) batteries have received considerable critical attention in the past decade due to their high theoretical specific capacity and energy density of elemental sulfur, outperforming by far existing Li-ion batteries. Although significant advances have been made in optimizing Li-S batteries through rational design of compositions and structures, they still face daunting challenges including: (1) insulation properties of sulfur and lithium sulfides, (2) shuttle effect of polysulfides, (3) dramatic volume changes during charge/discharge, (4) sluggish polysulfide conversion kinetics. So, considerable research efforts, such as fabricating superior new cathode materials, optimizing functional electrolytes, modifying separator, developing new binders and protecting Li metal anodes, should be devoted to promoting the overall performance of Li-S systems.

This thesis presents three continuous researches concerning separator modification and cathode materials for Li-S batteries based on metal organic frameworks (MOFs) derived hierarchical composite materials. To begin with, Co-based MOF (ZIF-67) derived hollow NiCo-LDH polyhedrons were synthesized firstly followed by coating a thin layer of MnO2 nanosheets. The hierarchical hollow NiCo-LDH@MnO2 hybrid materials were finally coated on the Celgard separator. The modified separator showed higher specific discharge capacity and more stable cycling performance, which proved the effectiveness of relieving the shuttle effect of polysulfides and enhancing the polysulfide conversion kinetics. Following the success in the preparation of modified separator, two other researches focus on the synthesis of host materials for sulfur cathode. The first one developed a hybrid nanostructure with Co and CoP nanoparticles embedded in a N-doped carbon and CNTs hollow polyhedron (Co-CoP@NCHP) through a pyrolysis-phosphating strategy derived from core-shell ZIF-8@ZIF-67. Benefiting from the synergistic effects between highly active Co-CoP nanoparticles and N-doped carbon hollow polyhedron,the Co-CoP@NCHP hybrid exhibited outstanding bifunctional electrocatalytic performances as the sulfur host for Li-S batteries. The strong cycling stability is attributed to the chemisorption and electrocatalysis of CoP and good conductivity of the N-doped carbon and CNTs. The second one fabricated a hollow porous ZnCo@NCHP precursor from bimetallic ZnCo-MOF. After that, the sulfurization and sulfur infusion of ZnCo@NCHP precursor was conducted in one step at low temperature. Due to the uniform distribution of ZnS and CoS2 nanoparticles in N-doped carbon polyhedrons, the ZnS-CoS2@NCHP hybrid materials exhibit quite stable cycling performance. Besides, the homogeneous distribution of ZnS and CoS2 nanoparticles can provide more active catalytic sites and stronger chemisorption for polysulfides.

    Research areas

  • Lithium-sulfur batteries, Metal-Organic Frameworks, Hierarchical structures, Metal sulfides