【作者】 李诚；

【导师】 吴玉程； 张琪；

【作者基本信息】 合肥工业大学 ， 材料学， 2021， 硕士

【摘要】 锂硫电池是新一代高能量密度、环境友好、安全价廉的电池体系。金属有机框架（MOFs）及其衍生材料因高比表面,强锚定作用和高催化活性被广泛用于锂硫电池以限制其“穿梭效应”。本文针对典型MOFs材料ZIF-8,ZIF-67和MOF-5以及MOFs衍生钴基碳化物Co₂C和Co₃C在锂硫电池中的应用,探究了MOFs材料基于锚定作用抑制穿梭效应的机理以及MOFs衍生Co₂C和Co₃C基于锚定和催化作用应用于锂硫电池的潜在可能性。全文基于理论计算方法开展研究,主要取得以下研究结果:1)ZIF-8,ZIF-67和MOF-5是三种应用于锂硫电池正极和隔膜的典型MOFs材料,揭示它们对于多硫化物的锚定效应的规律有助于开发新型MOFs材料。本文计算了三种MOFs材料对于多硫化物的吸附能和电荷转移等性质。基于ZIF-8和ZIF-67的对比,发现不同的金属中心通过改变配体上与多硫化物分子成键原子的电荷密度,间接影响吸附效果。基于ZIF-8和MOF-5的对比发现有机配体通过原子电负性和三维骨架结构两个方面影响多硫化物成键强弱和成键数量,从而直接影响吸附能力。基于此总结具有低电负性金属中心,高电负性配体杂原子和足够的配体骨架空间的MOFs材料具备优异的吸附效果。2)MOFs衍生钴基碳化物Co₂C和Co₃C已被证实在电催化领域具备优异表现。以在锂硫电池中具备优异性能表现的单原子催化材料Co-N₄-C作为对比,从电子/离子传输能力、多硫化物吸附和转化能力等角度探索MOFs衍生Co₂C和Co₃C作为锂硫电池高效催化剂的应用潜力。能带结构和锂离子迁移动力学计算结果表明三者均具备优异的电子和离子传输能力。多硫化物吸附结果显示Co₂C和Co₃C相比于Co-N₄-C均具有更强的吸附能力。充放电过程自由能变化结果表明Co₂C相比于Co₃C和Co-N₄-C具有最低的充电过电势,具备更优的催化能力,可实现多硫化物高效转化。基于此,MOFs衍生钴基碳化物Co₂C具备优异的电子/离子传输能力以及多硫化物吸附和转化能力,是锂硫电池中具有应用潜力的催化材料。更多还原

【Abstract】 Lithium-sulfur（Li-S）battery is a promising next generation battery system due to its high energy density,environment-friendly,safe and low-cost.Metal organic frameworks（MOFs）and their derivatives are widely used in Li-S batteries to mitigate the"shuttle effect"thanks to their high specific surface area,strong anchoring effect and high catalytic activity.Aiming at the application of typical MOFs ZIF-8,ZIF-67and MOF-5,as well as MOFs-derived cobalt-based carbides Co₂C and Co₃C in Li-S batteries,this work explores the mechanism of MOFs materials for shuttle effect suppression via surface anchoring and the potential of MOFs-derived Co₂C and Co₃C applied as catalysts in Li-S battery.In this paper,based on DFT（density functional theory）calculation,the main research results are as follows:1)ZIF-8,ZIF-67 and MOF-5 are three typical MOFs materials which are widely applied in the cathode and separator of Li-S batteries.Revealing their anchoring rule towards polysulfide is conductive to develop new MOFs materials.Herein,the adsorption energies and charge transfer properties of the three MOFs have been investigated.Based on the comparison between ZIF-8 and ZIF-67,the metal center is found to indirectly affect the adsorption effect by changing the charge density of the coordination heteroatom of the ligand.Based on the comparison between ZIF-8 and MOF-5,it is found that organic ligands regulate the bonding with Li PSs via coordination atoms and three-dimensional framework structure,which directly affects the adsorption capacity.It is concluded that MOFs materials with low electronegativity metal center,high electronegativity ligand heteroatom,and sufficient ligand framework space would have great anchoring effect.2)Cobalt-based carbides Co₂C and Co₃C derived from MOFs have been proven to have excellent performance in the field of electrocatalysis.Herein,taking the excellent single-atom catalytic material Co-N₄-C as a comparison,the application potential of Co₂C and Co₃C as catalysts for Li-S batteries was explored from the perspectives of electron/ion transport,Li PSs adsorption and conversion.The calculation results show that all the three have excellent electron and ion transport capabilities based on the electronic band structure and lithium ion migration kinetics.Both Co₂C and Co₃C have stronger adsorption capacity than Co-N₄-C according to Li PSs adsorption results.The free energy profiles of the charge-discharge process show that Co₂C has lower charging overpotential than Co₃C and Co-N₄-C,indicating that Co₂C has better catalytic ability to realize the efficient Li PSs conversion.Accordingly,MOFs-derived Co₂C has excellent electron/ion transport,Li PSs adsorption and conversion ability,which is predicted to be a potential catalytic material for Li-S batteries.更多还原