Controlled Functionalization of Carbonaceous Fibers for Asymmetric Solid-State Micro-Supercapacitors with High Volumetric Energy Density
Controlled Functionalization of Carbonaceous Fibers for Asymmetric Solid-State Micro-Supercapacitors with High Volumetric Energy Density
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DOI：
10.1002/adma.201403061
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发表时间：
2014-10-22
影响因子：
29.4
通讯作者：
Chen, Yuan
中科院分区：
文献类型：
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作者：
Yu, Dingshan;Goh, Kunli;Chen, Yuan
DOI：10.1002/adma. 201403061不对称微型SC，其中一个电容器型电极作为电源，另一个电池型法拉第电极作为能源。[5，6]这使得两种类型的电极的不同电化学窗口实现高工作电压，并且因此可以导致改进的能量密度。我们认为，在非对称SC中获得高能量密度的三个关键任务是：（1）设计合适的电容电极材料（2）选择合适的法拉第电极材料（通常是纳米结构的赝电容材料）;及（3）平衡收费（q= C m m ΔE）存储在两个有源电极（q+= q-）中，其中C m是电极材料的重量电容，m是电极的质量，ΔE是充电/放电过程中施加的电位差。[6]非对称SC设计已在传统的宏观SC中得到证实，其通常采用由两种不同的薄膜电极组成的三明治结构，碳材料作为负极，金属氧化物（例如MnO 2）或金属氢氧化物（例如Ni（OH）2）作为正极。正负极中的活性电极材料以块状粉末形式合成，通过调节两个电极中活性材料的质量比可以实现宏观尺度器件中的电荷平衡。相比之下，基于柔性纤维的非对称微太阳能电池的设计和制造则更加困难，因为：（1）纤维中电极材料的合成受到纤维几何形状和机械柔性要求的限制;（2）大部分用作宏观尺度太阳能电池中法拉第电极的赝电容材料不能制成柔性纤维电极，限制了法拉第电极材料的选择;（3）微SC尺寸的减小意味着每个纤维电极中活性材料的量减少。因此，很难通过简单地调节两个电极的质量来达到两个电极中的电荷平衡。由于上述困难，目前关于高压非对称光纤微SC的研究报道很少。我们认为，一个关键的使命，以解决这些困难是开发多功能的纤维电极材料与可调电容，同时保持理想的几何结构和机械灵活性。我们最近开发了一种在乙二胺（EDA）存在下使用毛细管硅胶柱作为一维微反应器的水热方法来合成氮掺杂的rGO/SWCNT纤维;然而，这些纤维仅用于制备工作电压限制为1.0 V的对称微SC。[21]在本研究中，为了设计和组装高效的非对称光纤微SC，
DOI: 10.1002/adma. 201403061 asymmetric micro-SCs with one capacitor-type electrode as power source and the other battery-type Faradic electrode as energy source.[5, 6] This renders different electrochemical windows of two types of electrodes to achieve a high working voltage, and thus could lead to an improved energy density. We envision that three key tasks to obtain high energy density in asymmetric SCs are:(1) to design suitable capacitive electrode materials (usually carbon materials);(2) to select proper Faradic electrode materials (usually nanostructured pseudocapacitive materials); and (3) to balance the charges (q= C m m ΔE) stored in two active electrodes (q+= q−), where C m is the gravimetric capacitance of the electrode material, m is the mass of electrode, ΔE is the applied potential difference for the charge/discharge process.[6]The asymmetric SC design has been demonstrated in conventional macroscale SCs, which usually employ a sandwich structure consisting of two different thin-film electrodes with carbon materials as negative electrodes and metal oxides (eg, MnO 2) or metal hydroxide (eg, Ni (OH) 2) as positive electrodes.[5, 6, 18–20] The active electrode materials in the positive and negative electrodes are synthesized in bulk powder forms, and the charge balance in macro-scale devices can be achieved by adjusting the mass ratio of the active materials in the two electrodes. In contrast, the design and fabrication of flexible fiberbased asymmetric micro-SCs are more difficult because:(1) the synthesis of electrode materials in fibers is constrained by the fiber geometry and mechanical flexibility requirements;(2) most of pseudocapacitive materials used as Faradic electrodes in macro-scale SCs cannot be fabricated into flexible fiber electrodes, limiting the choices of Faradic electrode materials;(3) the decrease in size of micro-SCs implies a diminishing amount of active materials in each fiber electrode. Thus, it is hard to reach charge balance in the two electrodes by simply adjusting their mass. Due to the aforementioned difficulties, there are few studies on high voltage asymmetric fiber micro-SCs reported so far. We consider that a critical mission to address these difficulties is to develop versatile fiber electrode materials with tunable capacitances while retaining desirable geometry structure and mechanical flexibility. We recently developed a hydrothermal method using capillary silica column as 1D micro-reactor to synthesize nitrogen-doped rGO/SWCNT fibers in the presence of ethylenediamine (EDA); however, these fibers were only used for fabricating symmetric micro-SCs with the working voltage limited to 1.0 V.[21] In this study, with the aim of designing and assembling highly-efficient asymmetric fiber micro-SCs, we hydrothermally