基于离子液体的超级电容在3 V及65℃老化条件下的铝碳界面效应

Carbon-Al Interface Effect on the Performance of Ionic Liquid-Based Supercapacitor at 3 V and 65℃

相比于传统乙腈电解液体系的超级电容器,离子液体基超级电容器具有工作窗口电压高,能量密度大,不可燃等优点,适用于碳中和时代清洁但不稳定电力领域的大规模储能。然而,目前的工作主要集中在对纽扣型离子液体-超级电容器的研究上,有关软包式离子液体-超级电容器的长循环寿命评测的报道较少。构建可靠的超级电容器用于长时间测试或在高温下开展加速老化测试,应考虑集流体/电极界面的良好接触,以最小化电荷转移电阻。本文以包覆不同碳层的泡沫铝为集流体,研究了超级电容器新系统中的碳-铝界面效应。通过环氧树脂薄膜碳化得到的均匀无定形碳层,相比通过PVDF粘附石墨烯碳层,赋予了铝相和碳相更强的相互作用。此外,为了充分挖掘大离子尺寸的离子液体电解液的潜力,本文采用介孔碳电极实现离子在介孔间的快速扩散。因此,本工作首次制备了由介孔碳电极、离子液体电解液和覆碳三维泡沫铝集流体组成的新结构软包式超级电容器。以自制的容量为37 F的不同软包式超级电容器件,通过3 V、65℃、500 h加速老化试验,研究了其时间依赖性的电化学性能,包括CV测试、恒流充放电测试、电容值、接触电阻、电化学阻抗谱等。相比石墨烯包覆的泡沫铝基器件,无定形碳层包覆的泡沫铝基器件表现出更高的电容保持率。此外,我们还对ESR进行了等效电路拟合,并深入分析了接触电阻、电荷转移电阻、韦伯电阻,研究了C-Al界面对高能量密度超级电容器的高性能和稳定性的影响。500小时老化测试前后的极片表征证实了上述结果。高温、高压条件使粘附石墨烯碳层的泡沫铝界面结构不可靠。而泡沫铝表面原位包覆的碳层在老化过程中表现出较强的相互作用和稳定的结构。这些坚实的数据为面向高能量密度、高功率密度和长循环寿命,进一步优化高窗口电压超级电容器提供了充足的信息。

Ionic liquid(IL)electrolyte-based supercapacitors(SCs)have advantages of high operating voltage window,high energy density and nonflammability,as compared to conventional acetonitrile-based organic electrolyte SCs,and are typically suitable for the large-scale energy storage in the era of carbon neutrality full of renewable,but unstable electricity.However,current efforts were concentrated on the study with coin-cell type of IL-SCs,and less has been reported on the pouch type of IL-SCs for a long cycling time yet.To fabricate a reliable SC for the life time test or for the accelerated aging test under high temperature,one should concern the excellent contact in the current collector/electrode interface to minimize the charge transfer resistance.In the present work,the carbon-Al interfacial effect was studied in the new SC system with Al foam as a current collector coated or painted by different carbon layers.Uniform amorphous carbon layer on Al foam was obtained from carbonization of epoxy resin film,giving a strong interaction of Al and carbon phase,as compared to that of the Al foam adhered with graphene by PVDF.In addition,to fully explore the potential of ILs electrolyte with large ion size,mesoporous carbon electrode was adopted here for a rapid ion diffusion across mesopores.Thus,the new structure SCs pouch consisting of mesoporous carbon electrode,ILs electrolyte and carbon coated-3D Al foam current collector was for the first time fabricated in the present work.Based on the as-made different pouches with capacity of 37 F,their time dependent electrochemical properties,including cyclic voltammetric(CV)response,galvanostatic charge and discharge behaviors,capacitance,contact resistance,and electrochemical impedance spectroscopic(EIS)characteristics were studied by accelerating aging test at 65 oC for 500 h at 3 V.The former pouch of Al foam coated with amorphous carbon layer exhibited far higher capacitance retention as compared to the pouch of Al foam adhered with graphene layer.Detailed fitting of ESR was made,and the contact resistance,charge transfer resistance,and Warburg resistance were analyzed thoroughly,providing deep insight into the strong C-Al interface effect on the high and stable performance of SCs with high energy density.Characterization of electrode sheet before and after 500 h aging test confirmed the above results.The high temperature and high voltage condition made the graphene-pasted Al foam unreliable.But the in situ coated carbon layer on Al foam exhibited relatively strong interaction and a reliable structure for the stable operation of the SCs pouch during the aging test.These solid data provide sufficient information for the further optimization of the high voltage SCs toward high energy density,high power density and long cycling time.