【作者】 徐娟；

【导师】 陈超；

【作者基本信息】 广东工业大学 ， 化学工程（专业学位）， 2023， 硕士

【摘要】 随着当前新能源供应趋势的发展,电池技术已成为可持续能源转换和储存的关键问题。目前,锂离子电池由于能量密度有限,已逐渐无法满足实际应用的要求。具有高理论比能量(2600 Wh kg^-1)、丰富的硫储量和对环境友好性的锂硫电池,被认为是下一代电池系统中最有前途的候选者之一。由于其固有的缺点如硫的绝缘性、电极在充放电过程中巨大的体积变化、多硫化物的穿梭效应等,锂硫电池商业化仍然受到严重限制。近年来,通过构建功能性隔膜夹层已被证明是缓解上述问题的可行且有效的方法。金属有机框架材料（MOFs）具有可调的孔隙结构、高的比表面积以及简单的表面官能化等优点。根据对MOFs基隔膜夹层的研究报道,MOFs材料可以通过“离子筛效应”、金属和杂原子（O,N）与多硫化物的物理和化学相互作用以及引入的官能团来有效抑制穿梭效应。同时,通过煅烧MOFs材料可形成具有高比表面积的多孔金属钴/碳复合材料,丰富的Co纳米颗粒作为多硫化物固定化和快速转化的活性位点,赋予了锂硫电池优异的电化学性能。本文通过制备具有活性位点的Co基MOF材料及其衍生物金属/碳复合材料用于缓解多硫化物的穿梭,进而改善锂硫电池的电化学性能。主要的工作概括如下:（一）通过构建基于水稳定性好、轻质的MOF材料的隔膜夹层作为一种高效的多硫化物屏障,进而改善锂硫电池的电化学性能。该隔膜夹层是由一种富氮、柱层状结构的钴基MOF材料和石墨烯混合,后通过抽滤的方法得到的一层薄膜（PLMOF（Co）@G/PP）。PLMOF（Co）@G/PP通过丰富的金属（Co）离子和杂原子（N,O）锚定多硫化物,并促进硫的反应动力学,从而显著缓解穿梭效应。采用PLMOF（Co）@G/PP隔膜的锂硫电池具有良好的循环稳定性（在2 C下的300次循环中容量衰减率仅为0.086%）。即使在超低的夹层负载量(0.08 mg cm^-2)下,Li-S电池也表现出优异的电化学性能(在0.5 C下100次循环后放电比容量保持在705 m Ah g^-1)。（二）合成了一种易于制备的金属有机框架衍生的纳米多孔碳,其具有嵌入的钴纳米颗粒（NPCo/C）,用于缓解多硫化物的穿梭。具有高比表面积和丰富Co纳米颗粒的NPCo/C是通过直接碳化Co基MOF材料简单制备而来,该材料与石墨烯结合以构建坚固的隔膜（NPCo/C@G/PP）。采用NPCo/C@G/PP隔膜的锂硫电池具有良好的循环稳定性(在0.5 C下300次循环后放电比容量保持在707 m Ah g^-1)和倍率性能（在2C下的300次循环中容量衰减率为0.18%）。即使NPCo/C@G/PP隔膜在超低负载量(0.08 mg cm^-2)下,也表现出优异的电池性能。这主要归因于NPCo/C中大量暴露的Co活性位点,可以固定多硫化物并加速硫反应动力学,以及NPCo/C@G优异的导电性以提高硫的利用率。更多还原

【Abstract】 With the development of current trends in new energy supply,battery technology has become a key issue for sustainable energy conversion and storage.At present,lithium-ion batteries are gradually unable to meet the requirements of practical applications due to their limited energy density.Lithium-sulfur（Li-S）batteries have emerged as promising can-didates for next generation energy storage systems due to their high theoretical energy density(2600Wh kg^-1),plentiful sulfur resources,and environmental friendliness.However,practical Li-S battery performance can be severely limited by several intrinsic issues including the insulation of sulfur,huge volume variation in the electrochemical reaction process,and particularly their shuttle effect,which is the most limiting key issue faced by the Li-S battery system at present.In recent years,construction of functional separators has attracted much attention and been proved a viable and effective means to tackle the polysulfide shuttle effect.Metal-organic framework materials（MOFs）possess several attractive properties including tunable pore structures,large surface areas and pore volumes,as well as facile surface functionalization.Based on reported work on MOF-based interlayers,the shuttle effect can be effectively suppressed using MOF materials through a“molecular sieve effect”,or through physical and chemical interactions of polysulfides with metals,heteroatoms（O,N）,and introduced functional groups.At the same time,porous metal cobalt/carbon composites with high specific surface area can be formed by calcining MOFs materials.Rich Co nanoparticles,as active site for polysulfide immobilization and rapid conversion,endow Li-S batteries with excellent electrochemical performance.In this thesis,Co-based MOF materials with active site and their derivatives metal/carbon composites were prepared to alleviate the shuttle of polysulfides,thereby improving the electrochemical performance of Li-S batteries.The main tasks are summarized as follows:Firstly,by constructing a membrane interlayer based on water stable and lightweight MOF materials as an efficient polysulfide barrier,the electrochemical performance of Li-S batteries can be improved.The diaphragm interlayer is a thin film（PLMOF（Co）@G/PP）obtained by mixing a nitrogen rich,columnar structured cobalt-based MOF material with graphene and then using suction filtration.PLMOF（Co）@G/PP anchors polysulfides through abundant metal（Co）ions and heteroatoms（N,O）,and promotes the reaction kinetics of sulfur,thereby significantly alleviating the shuttle effect.The Li-S battery using PLMOF（Co）@G/PP separator has good cycle stability（with a capacity decay rate of only 0.086%in 300 cycles at2 C）.Even at an ultra-low interlayer load(0.08 mg cm^-2),Li-S batteries exhibit excellent electrochemical performance(maintaining a discharge specific capacity of 705 m Ah g^-1 after100 cycles at 0.5 C).Secondly,a metal-organic framework derived nano porous carbon with embedded cobalt nanoparticles（NPCo/C）has been synthesized,which is easy to prepare,to alleviate the shuttle of polysulfides.NPCo/C with large specific surface area and abundant Co nanoparticles is simply prepared by directly carbonizing Co-based MOF materials,which combine with graphene to construct a sturdy membrane（NPCo/C@G/PP）.The Li-S battery with NPCo/C@G/PP separator has good cycle stability(with a discharge specific capacity of 707m Ah g^-1 after 300 cycles at 0.5 C)and rate performance（with a capacity decay rate of 0.18%after 300 cycles at 2 C）.Even if NPCo/C@G/PP separator also exhibits excellent battery performance at ultra-low load(0.08 mg cm^-2).This is mainly due to the large number of Co active site exposed in NPCo/C,which can immobilize polysulfides and accelerate the sulfur reaction kinetics,and the excellent conductivity of NPCo/C@G to improve the utilization of sulfur.更多还原