【作者】 李勇；

【导师】 闫小琴；

【作者基本信息】 北京科技大学 ， 材料科学与工程， 2018， 博士

【摘要】 随着人们对智能电子设备性能要求的提高,新一代便携式、柔性、可穿戴、可折叠电子设备相继出现,开发能为之提供能量的轻、薄、柔性的高性能储能器件成为当前学术界和产业界的研究热点。其中超级电容器是一种介于传统电容器和电池之间的新型电化学储能器件,它具有充放电速度快、循环寿命长且环境友好等优势,被认为是未来柔性电源的一个重要选择。其中,纤维状超级电容器不仅具有超级电容器的固有优势,还可以满足微型化、集成化和柔性化的可穿戴要求。然而,对纤维状超级电容器的研究还处于起始阶段,其相对较低的能量密度严重制约了其实际应用。如何在不牺牲其较高的功率密度、优异的循环稳定性的前提下,制备出既具有优异机械稳定性又具有较高能量密度的纤维状超级电容器是一项严峻的考验。本论文旨在研究具有高能量密度、高功率密度和优异机械稳定性的纤维状超级电容器。首先通过电极材料的可控制备、结构优化以及储荷机理研究,实现了 MnO2@ZnO-NWs@CNT、PANI/Graphene@CNT、PANI/3DCS 和CNT-aerogel纤维状电极的设计与构建,改善了电极材料的电化学性能,提高纤维电极的电容性能。在此基础上,通过器件结构优化构建非对称结构超级电容器,且通过采用新型电解液来拓宽器件的工作电压窗口。具体研究内容如下:1.采用水热法在CNT纤维表而生长ZnO纳米线阵列,然后在其表面生长MnO2薄膜层,制得复合纳米结构的MnO2@ZnO-NWs@CNT电极材料。利用ZnO纳米线阵列的高比表面积可提高活性物质的负载量,从而提升复合电极的电容量,在0.5 mA电流下的比电容值最高为386.1 μF/cm3。根据正负电极材料不同的电压窗口,设计构建了MnO2@ZnO-NWs@CNT//CNT纤维状非对称超级电容器(FASC),器件的电压窗口扩宽至0～1.8V,并具有13.25μWh/cm2的高能量密度。另外,FASC具有出色的机械稳定性,在可穿戴储能器件应用领域具有明显的优势。2.采用电化学聚合的方法在CNT纤维表面沉积PANI/graphene多孔复合薄膜,成功制得PANI/graphene@CNT纤维状复合电极。graphene对复合电极的电化学性能的改善(如倍率性能、循环稳定性等)效果明显。根据正负电极不同的电压窗口,构筑了 PANI/graphene@)CNT//CNT-film全固态纤维状非对称超级电容器,电压窗口能扩展到1.6 V。器件最大能量密度为160.5μWh/cm2,最高功率密度为13mW/cm2。3.利用电化学活化法和原位电聚合法制备了纤维状多孔复合电极材料PANI/3DCS,赝电容活性物质PANI与3DCS内部的CNT束均匀复合,不仅仅存在于纤维电极的表面,还充斥在3DCS内部的大量空间,在很大程度上提高了活性物质的负载量。PANI/3DCS内部的大量微纳孔洞有利于电解质离子的传输,缩短了活性物质与电极液之间的传输距离,同时3DCS是优异的电输运骨架,两者结合保证离子的快速传输。根据正负电极材料不同的电压窗口,设计构建了 PANI/3DCS//3DCS纤维状非对称超级电容器,最高能量密度为30.92μWh/cm2,最高功率密度为1.78 mW/cm2。经过1000次充放电循环后,依然可保持初始电容量的94%,说明了其优异的电化学稳定性。而经过1000次180。弯折测试后,器件可保持初始电容量的90.2%,说明了其优异的机械稳定性。4.采用电化学活化和冻干法处理,将CNT纤维转变为连续、多孔的纤维状CNT气凝胶材料,该材料具有高比表面积、高机械强度、导电性优异和高电容量(0.5 mA电流下为160.8 F/g)等特点,是用作纤维状超级电容器理想的电极材料。使用CNT气凝胶纤维为电极,(EMIM)BF4/[P(VDF-HFP)]离子液凝胶为电解液组装对称型纤维状超级电容器。离子液凝胶电解液的使用可将器件的电压窗口提高至3 V,室温下的能量密度与功率密度最高可达29.6 Wh/kg和27331 W/kg。器件具有优异的机械稳定性(经过2000次弯折试验后依然可保持初始电容的92.9%)和热稳定性(在0～80℃的环境下正常运行)。更多还原

【Abstract】 The rapid development of portable and wearable electronics in recent years has boosted the demand for appropriate flexible and lightweight energy supply devices.Supercapacitors(SCs)have attracted significant interest during the past few decades because of their high power density,super-long cycling life and safe operation.By offering,rapid charging and discharging rates,and the ability to sustain millions of cycles.SCs bridge the gap between batteries and conventional electrolytic capacitors.As a new member of SCs,fiber SCs(FSCs)have attracted considerable attention since 2011 and have shown great potential in miniaturized consumer electronics,wearable electronics and smart textiles.Due to their unique wire-shaped structure.FSCs can be deformed into desired shapes and even knitted into wearable textiles/fabrics.Furthermore,compared with conventional bulk SCs,FSCs could be easily integrated with photovoltaic devices,detectors or sensors to form self-powered or multifunctional integrated systems.However,compared to conventional SCs.research on FSCs is still in its infancy and it remains challenging to increase the energy density without sacrificing power density and cycling life.A common research goal is to develop flexible FSCs while preserving or even surpassing their electrochemical characteristics as compared to conventional SCs.1.A fiber-shaped asymmetric supercapacitor(FASC)with high energy density has been developed successfully using CNT@ZnO-NWs@MnO2 fibers as the positive electrode and CNT fibers as the negative electrode.Due to the high capacitances and excellent rate performances of CNT@ZnO-NWs@MnO2 fibers and CNT fibers,such an asymmetric cell exhibits superior electrochemical performances.An optimized FASC can be cycled reversibly in the voltage range of 0-1.8 V,and exhibits a maximum energy density of 13.25 mWh cm-2,which is much higher than those reported for fiber-shaped supercapacitors.Owing to the rational structure design,the all-solid-state FASCs demonstrate excellent mechanical and electrochemical stability.Over 1000 bending cycles,96.7%of the initial capacitance can still be retained.2.The PANI/graphene porous composite film was deposited on the surface of CNT fibers by electrochemical polymerization,and the PANI/graphene@CNT fiber composite electrode was successfully prepared.Graphene is very helpful to improved the electrochemical performance of the composite electrode(eg.rate performance,cycle stability).Based on the charge balance principle,an asymmetric fiber-shaped supercapacitor was successfully constructed.It resulted in excellent performances including an extended operating voltage window of 1.6 V,a maximum energy density of 160 μWh cm-2 at power density of 13 mW cm-2.3.We first fabricated threedimensional CNT sponge(3DCS)by a facile electrochemical activation and freeze-drying method and then synthesized 3DCS/polyaniline nanocomposite fibers by in situ electro-polymerization.Through a rational nanoscale electrode engineering design,the resultant fibers show a specific capacitance as high as 242.9 F cm-1 in 1 M H2SO4.Furthermore,a fiber-shaped asymmetric supercapacitor(FASC)was assembled using 3DCS/P as the positive electrode and 3DCS as the negative electrode.After optimization,the FASC delivers a high energy density of 30.92 mWh cm-2,which is about 2 times higher than that of the highest reported previously,and maintains a maximum power density(1.78 mW cm-2)more than two orders of magnitude higher than those of micro-batteries and an outstanding mechanical stability with 90.2%specific capacitance retained after 1000 bending cycles.In view of the excellent electrochemical characteristics and the simple manufacturing of the highly conductive and flexible 3DCS/P,it offers new opportunities for designing long-life wearable FSCs with high energy density and high power density.4.We report a facile method to prepare a novel fibrous CNT-aerogel by electrochemical activation and freeze-drying.The fibrous CNT-aerogel electrode possesses large specific surface area,high mechanical strength,excellent electrical conductivity,as well as a high specific capacitance of 160.8 F g-1 at 0.5 mA and long cyclic stability.Then we assembled a non-faradaic FSC based on fibrous CNT-aerogel as electrodes and P(VDF-HFP)/EMIMBF4 ionogel as electrolyte.The introduction of the ionogel electrolyte increases the operating voltage of the FSC to 3V.and makes the device combine the intrinsic high power density(27.3 kW kg-1)of non-faradaic SCs with an ultrahigh energy density of 29.6 Wh kg-1.which has reached the level of lithium-ionbatteries.More importantly,the assembled FSCs show excellent flexibility and bending-stability,and can still operate normally within a wide working temperature window(0～80℃).The outstanding electrochemical performance and the mechanical/thermal stability indicate the assembled FSC device is a promising power source for flexible electronics.更多还原