【作者】 田地；

【导师】 王策；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2020， 博士

【摘要】 人类社会发展对化石燃料的高度依赖,引发了能源短缺、环境污染和气候变暖等一系列问题。为了改善这种局面,人们越来越重视对环境友好、可持续能源的利用,以及高效的能源转化和储存设备的开发。在众多储能设备中,超级电容器由于具备充放电速率快、循环寿命长、功率密度大以及环保安全等优点被研究者们所青睐。而电极材料作为超级电容器的重要组成部分,其组分和结构设计与超级电容器的电化学性能息息相关,因而成为了近年来的研究热点。从结构上看,纳米材料的出现为电极材料的发展寻找到了新的突破点,其中,一维静电纺纳米纤维因具有较高比表面积和较大长径比,有利于促进电子传输和离子扩散,而成为一种可塑性很强的结构类型。从其成分来看,除了碳材料、金属氧化物和导电聚合物等较为典型的电极材料外,金属硫化物/硒化物/磷化物、金属有机骨架化合物(MOF)和MXene等一系列电极材料也展现出巨大潜力。然而,单一材料在某些方面所呈现出的局限性,促使不同材料间的复合成为了构筑高性能电极材料的必然趋势。本论文以纳米纤维基复合材料为研究对象,将一维静电纺纳米纤维作为基底与多种赝电容材料进行复合,并通过对材料活性组分及形貌结构的调控,对电极材料的电化学性能进行改善。此外,通过构建对称性或非对称性超级电容器对电极材料的实际应用前景进行了探究。该研究为静电纺丝纳米纤维基复合电极材料的设计合成提供了有意义的参考。具体内容如下:1.碳纳米纤维(CNF)基金属氧化物及导电聚合物复合电极材料:金属氧化物与导电聚合物都是典型的赝电容材料,将其与CNF进行复合,不仅能实现赝电容与双层电容的协同作用,使材料具备较高的电容性能,还能构筑比表面积较高的一维同轴异质结构,促进电子的转移和离子的扩散。(1)锰(Mn)基氧化物和镍(Ni)基氧化物都是具有较高理论电容、资源丰富、成本低廉的赝电容活性材料。两者结合后得到的Mn-Ni氧化物展现出比单金属氧化物更为丰富的氧化还原活性位点、更强的导电性和更稳定的结构。在CNF上负载Mn-Ni氢氧化物,再结合煅烧能获得的CNF@Ni-Mn-O复合材料,其最高比电容可达368.6 F g-1(0.5 A g-1)。以CNF为核,双金属纳米片为壳的组分及形貌结构设计贡献了良好的导电性和较高比表面积,赋予了电极材料优异的倍率性能(电流密度扩大20倍,电容保持率为78.6%)。由该材料组成的对称性超级电容器的最高能量密度达20.4 Wh kg-1,且循环稳定性良好。(2)聚苯胺(PANI)是一种较为常见的导电聚合物,由于具有较高理论电容(2000 F g-1)、良好导电性能、低成本和易合成等优点而被广泛用作电极材料。通过原位聚合法将PANI与静电纺CNF进行复合,并利用Ni纳米颗粒和石墨烯等活性组分对电极材料的电化学性能进行改善。与纯CNF比,复合后电极材料的比电容大幅提升(从83.9 F g-1到318.0 F g-1),这源自PANI较高的赝电容贡献。而Ni和石墨烯的引入不仅增强了CNF的导电性和浸润性,还缓冲了充放电过程中电极材料发生的体积膨胀,进而提高了电极材料的循环稳定性能。通过对称性超级电容器的构建证明该电极材料还具有较好的实际应用价值。2.预氧化聚丙烯腈纳米纤维(PPNF)基MOF及其衍生物复合电极材料:除了较为典型的赝电容材料,MOF等多孔材料由于具有高比表面积、可控的孔结构和丰富活性位点等优点也被广泛应用于超级电容器领域。基于所选MOF的生长环境,官能团丰富且结构稳定的PPNF被作为基底材料来构建电化学性能良好的电极材料。(1)PPNF@MOF展现出较高的比电容(702.8 F g-1,0.5 A g-1)和良好循环稳定性,这既源于MOF所贡献的较高赝电容,又与复合材料呈现出的较多孔隙和高比表面积有关。此外,将PPNF@MOF煅烧后获得的Ni纳米颗粒掺杂的碳材料拥有良好的导电性和形貌特征,以及作为负极材料应用的潜能。由两种材料组成的非对称性器件展现出较高的能量密度(51.4 Wh kg-1)和极佳的应用潜力。(2)通过钴(Co)、锌(Zn)、铜(Cu)和铁(Fe)离子的引入对PPNF@MOF形貌与组分进行调控,进而改善其电化学性能。在这些材料中,PPNF@Co-Ni MOF表现出最佳的电容性能(1096.2 F g-1,0.5 A g-1)和倍率性能。这得益于Co离子引入对Ni MOF性能的增强,以及复合材料多种组分和多级结构间的协同效应。此外,由该材料与石墨烯修饰的活化CNF组成的非对称性固态超级电容器展现出良好的实际应用前景。3.CNF基MOF及其衍生物复合电极材料:MOF与PPNF材料较差的导电性,阻碍了电极材料整体电化学性能的表现。因此,尝试从两个角度构建了导电性能有所提高的CNF基Ni3S2及Co掺杂MOF电极材料,对其电化学性能进行进一步改善。(1)Ni3S2作为一种廉价的自然资源展现出丰富的价态、高理论电容和良好的电化学活性,因而被视为一种极具潜力的电极材料。我们以PPNF@MOF为前体和模板通过煅烧和硫化获得了Ni/Ni3S2/CNF多级复合材料。碳化和硫化分别提高了材料的导电性和赝电容活性,PPNF@MOF的模板作用使材料保持较大比表面积。Ni/Ni3S2/CNF呈现出较高比电容(830.0 F g-1,0.2 A g-1)和良好倍率性能。由Ni/Ni3S2/CNF和活性炭组成的非对称性固态超级电容器,具备较高能量密度(31.6 Wh kg-1)和循环稳定性能(5000圈,电容保持率为95.7%),展现出良好的应用前景。(2)鉴于金属的引入对CNF和MOF材料都带来的积极影响,我们将不同种类的金属或金属氧化物纳米颗粒引入CNF,并以此为基底生长Ni MOF,构建了一系列形貌和组分不同的电极材料。其中,C-Co@MOF材料展现出最高比电容(1201.63 F g-1,0.5 A g-1),这既与Co引入后对CNF导电性和与MOF结合力的增强有关,又源自多组分材料间的协同作用。由该材料与氮掺杂碳纳米管组成的非对称性固态超级电容器能量密度最高可达37.0 Wh kg-1,循环稳定性能优异,展现出了光明的应用前景。更多还原

【Abstract】 The high dependence of human society on fossil fuel has led to a series of issues,such as energy shortage,environmental pollution,and climate warming.In order to improve this situation,people pay more and more attention to the usage of green and renewable energy,as well as the development of efficient energy conversion and storage equipment.Among many energy storage devices,supercapacitors have been favored by researchers due to their features including fast charge and discharge rates,long cycle life,large power density,environment friendly and safety.Electrode material,as an important part of supercapacitor,has become a research focus in recent years,whose composition and structure are closely related to the electrochemical performance of supercapacitors.For structure,the emergence of nanomaterials has become a breakthrough point for the development of electrode materials.Among them,one dimensional electrospun nanofibers with high specific surface area and large length diameter ratio are conducive to charge transfer and ion diffusion.In terms of composition,in addition to the typical electrode materials including carbon materials,metal oxides and conductive polymers,a series of electrode materials such as metal sulfide/selenide/phosphide,metal organic framework compounds,and MXene have also been used in supercapacitor field.However,the obvious limitations of a single material in some aspects have promoted the combination of different materials,which become a feasible strategy to construct a high-performance electrode material.In this thesis,composite electrode materials are selected as the research object.One-dimensional electrospun nanofibers are used as the substrates to combine with a variety of pseudocapacitive materials,and meanwhile the electrochemical behaviors of the electrode materials are improved by adjusting their active components and morphologies.In addition,the practical application prospect of electrode materials is explored by assembling symmetrical or asymmetric supercapacitors.This paper provides a meaningful reference for the design and synthesis of electrospun nanofiber based composite electrode materials.The details are as follows:1.Carbon nanofiber(CNF)based metal oxide and conductive polymer electrode materials: Both metal oxide and conducting polymer are typical pseudocapacitor materials.Combination them with CNF can not only realizes the synergistic effect of pseudocapacitor and double-layer capacitor,contributing to a high capacitance,but also constructs the one-dimensional coaxial heterostructure with high specific surface area,which can promote electron transfer and ion diffusion.(1)Manganese(Mn)-based oxides and nickel(Ni)-based oxides display high theoretical capacitance,abundant resources and low cost,serving as promising pseudocapacitor active materials.Mn-Ni oxides show more redox active sites,stronger conductivity and more stable structure than single metal oxide.The maximum specific capacitance of CNF@Mn-Ni oxides could reach 368.6 F g-1(0.5 A g-1).The design of component and morphology,using CNF as core and bimetallic nanosheets as the shell,brought about the superb conductivity and high specific surface area of electrode materials,contributing to the excellent rate performance(when current density increases 20 times,capacitance retention rate is 78.6%).The symmetrical supercapacitor asembled by CNF@Mn-Ni oxides delivered an energy density of 20.4 Wh kg-1 and good cycling behaviors.(2)Polyaniline(PANI)as a common conductive polymer is widely used as an electrode material owing to its high theoretical capacitance(2000 F g-1),good conductivity,low cost,and easy synthesis.Polyaniline and electrospun CNF were combined by in-situ polymerization,and its electrochemical performance were improved by introducing Ni nanoparticles and graphene(G)into CNF.Compared with the pure CNF,the specific capacitance of the composite increased significantly(from 83.9 F g-1 to 318.0 F g-1),due to the higher pseudocapacitance contribution of PANI.Furthermore,the introduction of Ni and G not only enhanced the conductivity and wettability of CNF,but also moderated the expansion of electrode material volume during the charging and discharging process,thus improving the cycling stability.The electrode material displayed a bright application prospect through the construction of symmetrical supercapacitor.2.Preoxidized polyacrylonitrile nanofiber(PPNF)-based MOF and its derivative electrode materials: in addition to the typical pseudocapacitor materials,MOF as a porous material has been widely used in supercapacitor filed because of its advantages of high specific surface area,controllable pore structure and rich active sites.Based on the growth environment of a selected MOF,PPNF with rich functional groups and stable structure was used as the substrate material to fabricate the electrode materials with good electrochemical performance.(1)PPNF@MOF exhibited high specific capacitance(702.8 F g-1,0.5 A g-1)and good cycling stability,which not only stemmed from the higher pseudocapacitance provided by MOF,but also was related to the porosity and large specific surface area of the composite.In addition,Ni nanoparticles doped carbon materials were derived from PPNF@MOF via a calcination process,whose good conductivity and morphology characteristics endowed them with the potential to be used as negative electrode materials.The asymmetric device composed of these materials showed high energy density(51.4 Wh kg-1)and excellent application prospect.(2)In order to improve the electrochemical performance of PPNF@MOF,its morphology and component were adjusted by introducing cobalt(Co),zinc(Zn),copper(Cu)and iron(Fe)ions.Among them,PPNF@Co-Ni MOF displayed the best capacitive performance(1096.2 F g-1,0.5 A g-1)and rate performance,which were attributed to the enhanced electrochemical properties of Ni MOF by the introduction of Co ions,as well as the synergistic effect between various components and hierarchical structure of the composite.Furthermore,the asymmetric solid-state supercapacitor asemled by this material and activated CNF-G showed a bright practical application prospect.3.CNF based MOF and its derivative electrode materials:The poor conductivity of both MOF and PPNF limits the overall electrochemical performance of electrode materials.Therefore,from two perspectives,CNF based Ni3S2 and C-Co@Co doped MOF were prepared as electrode materials to further improve their electrochemical performance(1)Ni3S2,as a kind of rich and cheap natural resource,exhibits abundant valence states,high theoretical capacitance and good electrochemical activities,indicating a promising electrode material.PPNF@MOF was used as a precursor and template to obtain a hierarchical Ni/Ni3S2/CNF composite through calcination and vulcanization.The conductivity and pseudocapacitive activities of the material were increased by Carbonization and vulcanization,respectively,and meanwhile PPNF@MOF as template endowed the composite with high specific surface area.The material demonstrated a high specific capacitance(830.0 F g-1,0.2 A g-1)and improved rate performance.The asymmetric solid-state supercapacitor constructed by Ni/Ni3S2/CNFs and activated carbon delivered high energy density(31.6 Wh kg-1)and good cycling stability(5000 cycles,capacitance retention rate of 95.7%),revealing a good application prospect.(2)In view of the possible positive influence of metals on the electrochemical performance of CNF and MOF,different kinds of metal or metal oxide nanoparticles were introduced into CNF,and thus a series of composite electrode materials with different morphology and components were achieved.Among them,CCo@MOF materials exhibited the highest capacitance(1201.63 F g-1,0.5 A g-1),which was not only related to the enhanced conductivity of CNF and the adhesion after the introduction of Co,but also stemmed from the synergistic effect among multicomponent materials.The asymmetric solid-state supercapacitor built by this material and nitrogen doped carbon nanotubes yielded a maximum energy density of 37.0 Wh kg-1 and excellent cycle stability,showing a brilliant poractical application prospect.更多还原