A research team led by Prof. MENG Guowen from the Institute Solid State Physics, Hefei Institutes of Physical Science (HFIPS) of Chinese Academy of Sciences (CAS), cooperating with Prof. WEI Bingqing of the University of Delaware, Newark, USA, successfully developed a structurally integrated, highly-oriented carbon tube (CT) grids as electrodes of electric double-layer capacitors (EDLCs), to significantly improve in the frequency response performance and the areal and volumetric capacitances at the corresponding frequency. It is expected to be used as a high-performance small-sized alternating current (AC) line-filtering capacitor in electronic circuits, providing the essential materials and technology for the miniaturization and portability of electronic products.
The results were published in Science on August 26, 2022.
Converting AC into direct current (DC) is vital for powering electronics. In the process, filter capacitors play a pivotal role in smoothing the voltage ripple in the rectified DC signal, ensuring the quality and reliability of electrical and electronic equipment. Aluminum electrolytic capacitors (AECs) are widely used in this field. Still, they are always the largest electronic component due to their low volumetric capacitances, which seriously restricts the development of miniaturized and portable electronic products.
EDLCs, usually with carbon materials as electrodes, are considered potential candidates for AC line-filtering to replace AECs due to their higher specific capacitance, in line with the trend of device miniaturization, but restricted by their low operating frequency (~1 Hz). Although the operating frequency can be enhanced by using highly-oriented carbon nanomaterials as electrodes, the specific capacitance is very limited. Meanwhile, the physical contacts between adjacent carbon nanotubes or graphene sheets would not only increase the resistance, further slowing the frequency response, but also make it difficult to increase the mass loadings of the carbon nanomaterials and thus obtain a large capacitance. There is an urgent need to develop newly-structured materials to increase the fast frequency response while maintaining high specific capacitance.
Since 2015, the research team has been working on this topic. After unremitting efforts, a new three-dimensional (3D) structure-integrated and highly-oriented CT array with laterally interconnected CTs by chemical bonds has been successfully developed. The 3D CT grid with truly-interconnected and structurally-integrated vertical and lateral CTs (denoted as 3D-CT) can provide highly oriented, high structural stability, superior electrical conductivity, and effective open porous structure (Figure 1), which is expected to meet the requirements of the electrode materials of the small-sized high-performance AC line-filtering EDLCs.
In order to obtain this unique structure, the researchers firstly anodized an aluminum sheet containing a small amount of Cu impurity, to obtain the highly ordered vertical porous anodic aluminum oxide (AAO) template containing Cu-impurity nanoparticles on the pore walls. Subsequently, a 3D interconnected porous AAO template (3D-AAO, upper-left corner in Figure 1) was obtained by selectively etching the Cu-containing nanoparticles on the pore walls with phosphoric acid.
