Research On Preparation Of Molybdenum-based Metal Compound And Its Applications In Lithium Sulfur Batteries

Lithium-sulfur batteries are regarded as one of the best candidates for next-generation energy storage devices due to low cost and high theoretical specific capacity.However,the commercialization application of Li-S batteries still has some critical issues that need to be solved.Among them,the sluggish electrochemical reactions and severe polysulfide shuttling effects resulting in low active material utilization and poor cycling stability are the biggest obstacles limiting its commercial application.In this thesis,molybdenum-based metal compounds with different morphological structures are designed and prepared as functional sulfur host materials to address the challenges of lithium-sulfur batteries.The details of the study and the results are as follows:（1）The MoO₃ nanorods were synthesized by hydrothermal method.MoO₃@ZIF-8materials were further obtained by in-situ growth to make the MOFs uniformly dispersed on the surface of MoO₃ nanorods.The target products Mo₂C nanorods were obtained by high temperature carbonization treatment.The rod structure can not only shorten the electron and ion transport pathways,but also physically hinder the diffusive dissolution of polysulfides.In addition,Mo₂C,as the transition metal carbide,has strong polar adsorption for polysulfides to suppress the shuttle effect.At a current density of 0.1 C,the initial discharge specific capacity of Mo₂C/S cathode reaches 1091.5 m Ah g^-1 and remains at414.2 m Ah g^-1 after 200 cycles,which proves the great advantage of Mo₂C as the host materials for lithium-sulfur batteries.（2）The Mo₂C-C/Fe₃C composites with synergistic effect serving as a promising host material for Li-S batteries are reported.The strong polar chemical adsorption capacity of Mo₂C and its synergistic catalytic effect with Fe₃C nanoparticles effectively inhibit the shuttle effect and improve the utilization of active substances.Meanwhile,the carbon substrate acts as a conductive network to achieve rapid charge transfer.Mo₂C-C/Fe₃C electrode material combining high electrical conductivity,valid catalytic activity and strong polar chemisorption ability,which exhibits excellent electrochemical performance when applied to Li-S battery systems.Accordingly,the Mo₂C-C/Fe₃C cathodes deliver a high initial discharge capacity of 1203.4 m Ah g^-1 at 0.1 C and 587.1 m Ah g^-1 even at 2 C.（3）The Zn S-MoS₂ heterostructures were prepared by in-situ sulfurization of MoO₃@ZIF-8 as the cathode materials for lithium-sulfur batteries.The synergistic effect of the unique layered structure of MoS₂ and the catalytic capability of Zn S is realized.More importantly,the excellent ion/electron transfers and rapid redox reaction kinetics were realized by the strong build-in electric field and abundant active sites formed by heterostructures.Benefiting from the above characteristics,the Zn S-MoS₂ electrodes show excellent rate performance(508 m Ah g^-1 at 0.5 C)and the superior cycling stability(620m Ah g^-1 at 0.1 C after 200 cycles).