Grass-like alumina nanoelectrodes for hierarchical porous silicon supercapacitors

With the development of microscale and standalone electronic devices the demand for microscale energy storage is increasing. Micro-supercapacitors are emerging as the candidate for microscale energy storage, especially when combined with energy harvesters. In this work, we enhance the capacitance of porous silicon (PS) supercapacitor electrodes up to 4x by adding a new high-surface-area nanoelectrode on the existing topography, thus forming a hierarchical 3D supercapacitor electrode that can be used in micro-supercapacitor applications. The nanoelectrode is based on grass-like alumina (GLA) - a recently reported conformal nanoporous coating - with two surrounding TiN films, all materials deposited by atomic layer deposition. The GLA nanoelectrode can be deposited conformally on complex topographies like here on PS, as the total thickness of the electrode structure does not exceed 200 nm allowing it to be fitted in existing electrodes. The GLA nanoelectrode increased the capacitance of the PS supercapacitors alone by up to fourfold or 4x and reduced the self-discharge to a mere 25% loss after 20 h compared to a TiN coated PS reference and state-of-the-art PS both with significantly higher losses. The GLA nanoelectrode showed remarkable stability for 10 000 galvanostatic cycles with a decrease in the capacitance only by 5% and no structural changes were identified from SEM images. Microelectronics compatible processing, the conformal deposition process and the nanoscale thickness of the GLA nanoelectrode allow it to enhance 3D electrodes commonly used in micro-supercapacitors. We demonstrate a new kind of conformal nanoelectrode for hierarchical supercapacitors made by ALD. This grass-like alumina (GLA) nanoelectrode increases the capacitance of PS supercapacitors fourfold or 4x and consists of a TiN-GLA-TiN stack.

Automated summary

With the development of microscale and standalone electronic devices, the demand for microscale energy storage is increasing. In this work, the capacitance of porous silicon (PS) supercapacitor electrodes was enhanced up to 4x by adding a new high-surface-area nanoelectrode. The grass-like alumina (GLA) nanoelectrode showed remarkable stability and increased the capacitance of PS supercapacitors fourfold.