【作者】 李磊；

【导师】 张密林；

【作者基本信息】 哈尔滨工程大学 ， 材料科学与工程， 2016， 博士

【摘要】 由于高速增长的能源需求和日益严峻的环境问题,寻求高效可再生的储能装置在近几年成为研究领域的热点问题。在众多的储能器件中,超级电容器（同时也称为电化学电容器）由于其高功率密度,良好的倍率性能以及较长的循环周期,被看作是最具有前景的储能器件。而电容器的性能往往是由电极材料决定的。这就要求电极材料不仅具有经济安全、环境友好等特点,而且还需要兼顾良好的电化学性能。但是,单一的电极材料（碳材料、过渡金属氧化物和导电聚合物）由于自身难以克服的缺陷很难满足实际应用的需求。而构建复合材料,利用不同材料在电化学反应中的协同作用,可以有效提高电极材料的电化学性能。本文的目的就是设计合成过渡金属氧化物与碳基的复合材料,并研究它们作为超级电容器的电极材料时的电化学性质。同时,希望文中所述的合成方法将会为制备改性其他电极材料的提供新的思路。本论文主要研究内容如下:通过水热法和原位生长法的结合,合成新型核壳结构的Fe₃O₄@C@Ni-Al LDH（包覆碳层的四氧化三铁外再包覆一层镍铝水滑石）。这种特殊多层包覆的修饰方法促进这种复合物拥有了花状的壳核结构,并且具有较高的比表面积以及特有的孔径分布。当把合成的微米级Fe₃O₄@C@Ni-Al LDH作为电极材料应用到超级电容器体系中时,通过循环伏安,恒流充放电,交流阻抗等测试,这个电极材料表现出了较高的比电容（767.6 F/g）,良好的倍率性能以及优越的循环稳定性。因此,这种新颖的合成高效电容器的方法将会为改性其他电极材料的电化学性能提供更多的手段。通过高效的方法制备了一种还原氧化石墨烯负载四氧化三铁纳米颗粒复合材料（Fe₃O₄/rGO）,合成过程中使用的葡萄糖分别充当了Fe₃O₄纳米颗粒组装的粘合剂和氧化石墨烯的还原剂,通过一步简单的水热法就实现了Fe₃O₄/rGO复合材料的制备。Fe₃O₄/rGO复合材料具有高比表面积和介孔结构,具有优异的超级电容器性能。得益于rGO良好的导电性和Fe₃O₄优异的比电容,使得Fe₃O₄/rGO作为电极材料具有高达241F/g的比电容,在循环1000次后,依然具有79.8%的比电容保持率,显示了其优异的循环稳定性。这一合成方法为增加材料的电化学特性提供了新型的设计和合成路径,并在能量存储系统领域展现出良好的发展潜力。利用水热法和煅烧还原法,成功合成了中空碳层包覆二元金属氧化物纳米片的复合材料。这种新颖花状结构的C@MnCo₂O₄纳米复合物,由导电性优异的碳层和良好交联的纳米片组成,有利于电解质的渗透,为粒子和电子运输提供通路。值得关注的是,这种复合物具有大的比表面积（347 m²/g）,可以提供大量的活性位点,可以缓解循环过程中材料形貌的变化。得益于这种良好的结合和适宜的介孔结构,复合物C@MnCo₂O₄的比电容可以达到728.4 F/g。此外,复合物C@MnCo₂O₄具有良好的倍率性能和极好的循环稳定性。在8 A/g高电流密度下经历1000次循环后,仍有95.9%的比电容保留。这些优异的电化学性能使得这种材料成为一种非常有潜力的电极材料应用于超级电容器领域中。我们提出了一种通过原位聚合反应和水热处理结合的方法合成一种多孔多层的CNTs@NCS@MnO₂复合物。复合物中间的掺氮碳层是由间苯二酚和甲醛作为碳源,半胱氨酸作为氮源而制得的,拥有介孔结构和良好的化学稳定性。得益于这种特有的结构及新颖的组合,复合物具有很好的电化学性能:包括较高的比电容（在1 A/g电流密度下比电容为312.5 F/g）,良好的电容保持率（从1 A/g到10 A/g具有76.8%的保留）,及优异的循环可逆性。为了提高复合物的能量密度及电势窗口,还通过采用CNTs@NCS@MnO₂作为正极材料,活性炭作为负极材料组成不对称电容器。得到的不对称电容器的最高电压能够达到1.8 V并且具有较高的能量密度。这种合成超级电容器电极材料的方法能够极大的激发双电层电容器与赝电容器的协同作用,从而获得高性能的电极材料。在葡萄糖分子的参与下,通过简单的水热方法,合成了一种多孔的复合材料g-C₃N₄/rGO（CNRG）。该复合材料可以作为一种有效的固定基底来支撑Ni（OH）₂纳米片的生长。同时,g-C₃N₄片可以均匀地包覆在还原石墨烯的两侧,形成一种有层次的三明治结构的复合物。值得关注的是,g-C₃N₄的加入能够有效提高Ni（OH）₂的分散性避免团聚,显著提高综合的电容性能。由于独特的结合和结构,CNRG/Ni（OH）₂复合物拥有大的比表面积和适当的孔径分布,因此可以有效地容纳电解质离子迁移并且加速电子转移。当用作超级电容器的电极时,复合材料表现出极高的超级电容器的性能,例如极好的比电容（1785 F/g,电流强度2 A/g）,优异的电容保持率（在16 A/g时保持1106 F/g）和良好的循环持久性（在8 A/g循环1000次后保持87.6%）。以上优异的性能证明了CNRG/Ni（OH）₂复合材料在超级电容器的应用中可以成为一种有前景的电极材料。更多还原

【Abstract】 With the ongoing demands for increasing energy and environmental benignity,the development of energy storage device with sustainable,renewable and efficient properties has become a pressingly essential need in scientific area.supercapacitors(ECs,also known as electrochemical capacitors),which are considered as a promising candidate to power the next generation of energy storage device,have been widely investigated to meet the increasing requirements owing to their high power density,long cycling life and high rate capacity.The performance of the supercapacitor depends on the properties of the electrodes.This means that the electrode should not only have the features of low-cost and environmental friendly character,but also possess high electrochemical capability.However,single material cannot meet the requirements of practical application due to the intrinsic defects.Thus,the design of the composites,taking full advantage of their synergic effect,can achieve the purpose of developing high electrochemical electrode for supercapacitors.In this paper,we have designed and synthesize the composites combining carbon-based materials and transition metal oxides,and explore the electrical performance as supercapacitive electrode.Meanwhile,we believe that these synthetic routes can provide new ideas to prepare other materials with admirable electrochemical properties.The studying contents of this paper are summarized as follows:A novel core-shell structured Fe3O4@C@Ni-Al LDH composite containing carbon-coated Fe3O4 magnetic core and a layered double hydroxide(LDH)had been successfully prepared by a combination of the hydrothermal method and a facile in situ growth process.Owing to the unique layered feature,the composite displays core-shell structure with flower-like morphology,high surface area(792 m2/g)and specific pore size distribution.Moreover,the as-synthesized Fe3O4@C@Ni-Al LDH microsphere as an electrode material was fabricated into a supercapacitor and characterized by cyclic voltammetry(CV),electrochemical impedance spectroscopy(EIS),and galvanostatic charge-discharge measurements.It turned out that the Fe3O4@C@Ni-Al LDH exhibits specific capacitance of 767.6 F/g,good rate capability,and remarkable cycling stability(92% after 1000 cycling).Therefore,such novel synthetic route to assemble the high-performance electrochemical capacitor may open a new strategy to synthesize other materials with largely enhanced electrochemical property,which can be of great promise in energy storage device applications.We also present a facile and efficient process for the preparation of Fe3O4 nanoparticles(about an average diameter of 5 nm)grown on reduced graphene oxide(Fe3O4/r GO)with high supercapacitive properties.The novel composite with high surface area and mesoporous structure are prepared by a one-step hydrothermal method with the help of glucose,which can serve as a binder for the assembly of Fe3O4 nanoparticles(NPs)and a reducing agent for the reduction of graphene oxide simultaneously.Benefiting from the combined r GO and Fe3O4 in such a unique structure,the Fe3O4/r GO electrode material possesses a high specific capacitance of 241 F/g at 1 A/g within the potential range from-1 to 0 V and an excellent cycling stability of 79.2 % after 1000 cycles at a high current density of 10 A/g.These results demonstrate that such synthetic route may open a new pathway to design and fabricate other materials with largely enhanced electrochemical properties,which can be of great potential in the development of energy-storage systems.Binary metal oxides Mn Co2O4 nanosheets wrapped on hollow activated carbon shell(C@Mn Co2O4)has been successfully synthesized through a facile hydrothermal method followed by a calcination process.The novel flower-like C@Mn Co2O4 composite with good conductive carbon shell and well interconnected nanosheets can efficiently facilitate the electrolyte penetration and offer expedite transport path for ion and electron.Notably,the large surface(347 m2/g)of the hybrid composite can endow large amount of active sites,which evidently accommodate the strain during cycling.Benefited from this elegant combination and the effectively mesoporous structure,the specific capacitance of the C@Mn Co2O4 composites can be achieved as high as 728.4 F/g,which is,to the best of our knowledge,the highest value so far reported for Mn Co2O4 based electrode.In addition,C@Mn Co2O4 composite exhibits enhanced rate capability and an excellent cycling stability of 95.9% retention after 1000 cycles at high current density of 8 A/g.Therefore,the desirable integrated electrical performance enables it to be a promising electrode material for supercapacitor application.We present a novel and rational strategy for preparing hierarchical porous CNTs@NCS@Mn O2 core-shell composite via a facile in situ chemical polymerization coating method,followed by a hydrothermal process.The intermediate nitrogen-doped carbon shell(NCS)with mesoporous structure and favorable chemical durability is obtained by utilizing resorcinol-formaldehyde resin as carbon source and L-cysteine as nitrogen source,respectively.Benefiting from unique structure and considerable combination,the composites possess high comprehensive electrochemical performance: high specific capacitance(312.5 F/g at a current density of 1 A/g),good rate capability(76.8% retention with charge-discharge rate increasing from 1 A/g to 10 A/g)and superior reversibility.In order to increase the energy density and voltage window,an asymmetric supercapacitor(ASC)was assembled using CNTs@NCS@Mn O2 and activated carbon(AC)as the positive and negative electrodes,respectively.The as-fabricated asymmetric supercapacitor achieved a high specific capacitance with a stable operational voltage of 1.8 V and admirable energy density.Such a synthetic route to prepare the capacitor materials can thoroughly motivate the synergistic effect between electrical double layer capacitors and pseudocapacitors for obtaining high comprehensive performance electrode in energy storage fields.A porous hybrid g-C3N4/r GO(CNRG)material has been fabricated through a facile hydrothermal process with the help of glucose molecules,and serves as an efficient immobilization substrate to support ultrathin Ni(OH)2 nanosheets under an easy precipitation process.It was found that the g-C3N4 flakes can uniformly coat both sides of the r GO,forming sandwich-type composites with a hierarchical structure.It is worth noting that the induction of the g-C3N4 can effectively achieve the highly dispersion and avoid the agglomeration of the nickel hydroxide,and significantly enhance the synthetically capacitive performance.Owning to this unique combination and structure,the CNRG/Ni(OH)2 composite possesses large surface area with suitable pore size distribution,which can effectively accommodate the electrolyte ions migration and accelerate efficient electron transport.When used as electrode for supercapacitor,the hybrid material exhibits high supercapacitive performance,such as an admirable specific capacitance(1785 F/g at a current density of 2 A/g),desirable rate stability(retain 1106 F/g at 16 A/g)and favorable cycling durability(maintaining 87.6 % capacity after 1000 cycles at 8 A/g).Such desirable properties signify that the CNRG/Ni(OH)2 composites can be a promising electrode material in the application of the supercapacitor.更多还原