【作者】 李芳；

【导师】 钱昕晔；

【作者基本信息】 江苏大学 ， 材料科学与工程， 2021， 硕士

【摘要】 锂硫（Li-S）电池作为新型二次电池具有比容量高、环境友好、原材料储量丰富、成本低等优势引起了国际科研工作者的广泛关注,是下一代储能器件的理想选择。但其在面临商业化时仍存在活性物质导电性极差、反应前后的“体积效应”、反应中间产物的“穿梭效应”及锂枝晶生长等制约瓶颈。针对以上问题,对Li-S电池隔膜改性展开研究,高效提升电池电化学性能。金属有机框架（MOFs）作为一类新型纳米多孔材料,由于它拥有比表面积大、孔道结构有序、孔径及表面化学性质可调等优点已广泛应用于能量储存与转换系统。本文通过设计和制备基于ZIF-8前驱体的衍生多孔材料改性涂层来减缓“穿梭效应”,高效改善电池电化学性能。具体工作如下:（1）利用工业级碳纳米管（CNT）为载体,采用常温水溶液法在CNT上原位生成ZIF-8颗粒并高温碳化后得到N-C@CNT复合材料,将改性材料涂覆在聚乙烯隔膜（PE）一侧,研究其对电池电化学性能的影响。结果表明,硫负载量为3.3 mg cm^-2,N-C@CNT改性隔膜在0.5 C下首圈放电比容量为852.9 m Ah g^-1,在500圈长循环后,容量剩余424.4 m Ah g^-1。良好的循环性能主要归因于长线状CNT的高导电性为电子及Li离子传输提供有效路径,丰富的介孔与大孔缓解反应前后体积效应,与MOFs衍生碳的微介孔协同高效阻挡多硫化物,此外N原子掺杂催化电池内部氧化还原反应的进行。（2）采用常温水溶液法在CNT上原位生成ZIF-8颗粒以及Mn-MOF并高温碳化后得到Mn O/N-C@CNT改性材料,将Mn O/N-C@CNT涂覆于聚乙烯隔膜（PE）一侧,组装电池进行电化学性能测试。测试结果表明Mn O/N-C@CNT改性涂层的性能在N-C@CNT的基础上继续提升,硫负载量3.3 mg cm^-2时,0.5C下的首圈放电比容量达920.3 m Ah g^-1,在500次循环后容量保持为500.2 m Ah g^-1。这得益于纳米Mn O的极性表面锚定多硫化物形成强烈的化学吸附,此外金属氧键及氧空位还有利于S-S键的解离降低反应势垒,催化电池内部的氧化还原反应。（3）采用共沉淀法制备了Mn₃[Fe（CN）₆]₂·n H₂O前驱体,作为模板和Mn源,通过溶剂热法制备纳米片状的Mn S负载于研究内容（1）中的N-C@CNT复合材料上得到Mn S/N-C@CNT,将其涂覆于聚乙烯隔膜（PE）一侧并组装电池研究该改性涂层对电池电化学性能的影响。结果显示,硫负载量3.3 mg cm^-2时,0.5 C下首次放电比容量为923.9 m Ah g^-1,500圈长循环后,容量保持在500.8 m Ah g^-1;倍率测试中在2 C的高倍率下放电容量为498 m Ah g^-1,并具有良好的可逆性。这归因于Mn S颗粒对多硫化物具有很强的亲和性,促进多硫化物的成核生长,改善氧化还原动力学,对电化学反应具有更好的催化作用。更多还原

【Abstract】 Lithium-sulfur（Li-S）batteriy,as a new type of secondary battery,has been widely concerned at home and abroad for its high specific capacity,environment-friendly,natural abundance,low cost and so on.It is an ideal choice for the next generation of energy storage devices.However,the commercialization of Li-S batteriy faces some bottlenecks,such as the insulation of sulfur,the“volume effect”of sulfur after lithiation,the“shuttle effect”of the reaction intermediate products and the growth of lithium dendrites.In view of the above problems,it is an effective method to modify the separator of lithium sulfur battery.Metal organic frameworks（MOFs）,as a new type of nano porous materials,have been widely used in energy storage and conversion systems due to their large specific surface area,ordered pore structure,adjustable pore size and surface chemical properties.In this paper,we designed and prepared a modified coating of derived porous materials based on ZIF-8 precursor to suppress the“shuttle effect”and efficiently improve the electrochemical performance of the battery.The specific work is as follows:（1）Using industrial-grade carbon nanotubes（CNT）as a carrier,ZIF-8 particles are generated in situ on CNT by the normal temperature aqueous solution method and carbonized at high temperatures to obtain N-C@CNT composite materials,which is coated on the side of separator polyethylene（PE）to study the effect on the electrochemical performance of the battery.The results show that when sulfur loading of 3.3 mg cm^-2 and the initial discharge capacity of N-C@CNT modified separator is852.9 m Ah g^-1 at 0.5 C.Even after 500 cycles,a steady reversible capacity of 424.4m Ah g^-1can be obtained.This is mainly attributed to the high conductivity of long linear CNT,which provides an effective path for electronic and Li ion transport,the abundant mesopores alleviate the“volume effect”before and after the reaction,cooperate with MOF micropores to block polysulfides efficiently,and N atom doping promotes the redox reaction.（2）ZIF-8 particles and Mn-MOF were generated in situ on CNT by the normal temperature aqueous solution method and carbonized at high temperature to obtain the Mn O/N-C@CNT modified material,which was coated on the side of separator polyethylene（PE）to assemble the battery for electrochemical performance test.The test results show that the performance of the Mn O/N-C@CNT modified coating continues to improve on the basis of N-C@CNT,and the initial discharge capacity reaches 920.3 m Ah g^-1at the sulfur loading of of 3.3 mg cm^-2at the rate of 0.5 C.After500 cycles,the capacity is maintaining at 500.2 m Ah g^-1.This is attributed to the strong chemisorption formed by the polarity surface anchoring polysulfide of nano-Mn O.At the same time,the metal oxygen bond and oxygen vacancy are also conducive to the dissociation of S-S bond,which accelerates the transformation of polysulfide lithium and catalyzes the redox reaction inside the battery.（3）Mn₃[Fe（CN）₆]₂·n H₂O precursor was prepared by co-precipitation method as template and Mn source.Nano-sheet Mn S was prepared by the solvothermal method and loaded on the N-C@CNT composite prepared in the research（1）to obtain Mn S/N-C@CNT.And coated it on the separator polyethylene（PE）and assembles into a battery to study the influence of the modified coating on the electrochemical performance of the battery.The results show that the first discharge specific capacity is 923.9 m Ah g^-1at sulfur content of 3.3 mg cm^-2 at the rate of 0.5 C,and after 500 cycles the capacity maintain 500.8 m Ah g^-1;the discharge capacity at high rate of 2 C is 498 m Ah g^-1,and it shows the good reversibility.It is owing to the strong affinity of Mn S particles for polysulfide-containing sulfur,the promotion of polysulfide nucleation growth improves the oxidation-reduction kinetics and has a better catalytic effect on electrochemical reactions.更多还原