Recently, the team of Meng Guowen and Han Fangming, researchers of the Institute of Solid State Physics of the Chinese Academy of Sciences Hefei Institute of Physical Sciences, cooperated with Wei Bingqing, professor of the University of Delaware in the United States, designed and prepared a three-dimensional interconnection array of multi shell coaxial carbon tubes similar to the "Russian doll" structure on the basis of the high-performance filter capacitor based on the structural integration three-dimensional interconnection carbon tube grid film in the early stage, Furthermore, it was used as the electrode of a symmetrical double-layer capacitor to construct a new type of filtering supercapacitor. The multi shell coaxial carbon nanotube array with similar nesting structure not only improves the electrode area and specific capacitance, but also does not affect the transmission speed and response frequency of electrolyte ions. Therefore, the filtering supercapacitor based on nesting structure carbon nanotubes has a smaller volume and is expected to provide miniaturized power supply solutions for integrated circuits and chips. The relevant research results are published in Joule.

Filter capacitors have the function of smoothing ripple in AC/DC conversion signals and are crucial for the stable operation of high-end power electronic equipment. Aluminum electrolytic capacitors (AECs) dominate the majority of the market in this field. AECs have small capacity and large volume, and are usually one of the largest components in circuits, but they restrict the miniaturization development of electronic devices. The specific capacitance of double layer supercapacitors (EDLCs) is several orders of magnitude higher than that of commercial aluminum electrolytic capacitors (AECs). If EDLCs can be used for filtering, it is expected to meet the needs of miniaturization development of electronic devices. However, traditional double layer supercapacitors (EDLCs) have high capacity due to the bending and complex pore structure in porous carbon based electrodes, but their response frequency is generally below 1Hz and cannot filter the mains power for use in electronic devices.

In order to improve the frequency response performance of double-layer supercapacitors, scientists investigated filtering double-layer capacitors constructed with various carbon based nanomaterials with vertically oriented large pore structures as electrodes. However, they found that the area and volume of the device were lower than the capacitance at the mains frequency, and the ripple after mains filtering was still large, which could not provide a smooth and stable power supply for electronic devices. Therefore, the development of electrodes with high orientation, fast response frequency, large specific surface area, and high capacity is crucial for miniaturizing filtering supercapacitors.

The team used the previously created three-dimensional interconnected porous anodized aluminum oxide as a template, and alternately deposited carbon layers and atomic layers of AlOx sacrificial layers under the confinement induction of template pores. After selectively etching the aluminum oxide template and sacrificial layer AlOx, they constructed a three-dimensional framework consisting of coaxial structure of two-layer and three-layer carbon tube interconnection. Analysis shows that in this coaxial multi shell three-dimensional interconnected carbon nanotube grid film, all carbon nanotubes are similar to the "Russian nesting doll" structure, and the inner layer carbon nanotubes are uniformly filled inside the outer layer of the coaxial carbon nanotubes; This three-dimensional interconnected nesting carbon nanotube grid film not only has a larger surface area for storing charges, but also has highly oriented large pore structures between the vertical carbon nanotubes, which is conducive to the rapid transfer of electrolyte ions.

This study constructed a symmetrical double-layer capacitor using a three-dimensional interconnected nesting carbon nanotube grid film as the electrode. Research has shown that devices constructed with three-layer nesting carbon tube electrodes exhibit an impedance phase angle of -80.1 ° and a shorter resistance capacitance time constant of 0.25 milliseconds at a frequency of 120 Hz. This indicates that the electrode resembles an ordered and smooth ion fast transport channel, promoting the rapid distribution of ions. The area to capacitance ratio of the device reaches 3.08 mF cm-2, which is two orders of magnitude higher than commercial AECs and also higher than the reported sandwich configuration of water-based filtering supercapacitors so far. In addition, the study also found that the loss factor of the device is low and the energy storage efficiency is high.

In order to verify the AC filtering function of the device, this work targets a 10 volt commercial aluminum electrolytic capacitor and connects ten identical new devices in series to expand the working voltage of the device filtering. Research has found that the series connected device group still exhibits excellent frequency response performance, and a filtering circuit has been built to verify the filtering performance of the series connected device group on AC lines; After rectification and device filtering, the 60 Hz AC mains signal can output a stable and smooth constant DC signal to power DC appliances; The device can filter various types of input signals (such as square waves, triangular waves, and arbitrary waveforms) into smooth output electrical signals. Furthermore, in order to visually demonstrate the filtering function of the device, researchers conducted demonstration experiments using device groups to filter the pulse voltage emitted by the nanogenerator and light up the light-emitting diode. Research has found that the light-emitting diode keeps flashing until the filtering capacitor is connected; After connecting the filtering capacitor, the light-emitting diode emits stable light, indicating that the device group has a good function of smoothing pulse voltage.

In summary, supercapacitors based on nesting carbon tube three-dimensional interconnected grid membrane electrodes have high specific capacitance, low equivalent series resistance, and fast frequency response performance, opening up a new way for the development of next-generation miniaturized filtering capacitors that combine high capacity and fast frequency response performance.

The research work has received support from the National Natural Science Foundation of China and the Dean's Fund of Hefei Research Institute.

Paper link：论文链接



Preparation process of a coaxial multi shell carbon tube three-dimensional interconnect framework similar to the "Russian nesting doll" structure