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Energy Storage Microdevices
Energy Storage Microdevices
The Internet of Things, based on large quantities of distributed microelectronics, is revolutionizing human life. However, a sustainable solution for their excessive energy demand is yet to be found. Self-powered microelectronics involving integrated energy harvesters is a promising candidate, and energy storage microdevices are inevitable in such systems for ensuring stable operation during intermittent energy supply and for buffering power fluctuations.
At PULSE Lab, we aim to develop innovative energy storage microdevices that feature high storage efficiency, high operation speed, long lifetime, and easy integration with microelectronics. On-chip micro-supercapacitors (MSCs) are of our particular interest since they can be charged and discharged rapidly and have an almost unlimited lifetime. Among various aspects, we mainly focus on investigating novel electrode designs, including creating 3D internal structures for improving the ion transportation, and developing the optimal manufacturing processes to integrate them with energy harvesters and electronics seamlessly.
Illustration of a typical configuration of a planar MSC. The basic components in an MSC are two electrodes separated by an electrolyte. The electrodes can consist of an active material and a current collector or one material for both purposes. The charge storage capability of an active material can be attributed to two processes occurring at the electrode-electrolyte interfaces: (1) the accumulation of ions and (2) the electron-charge transfer. Optimal electrode designs are critical to the efficient interaction of ions carrying electricity and the active material storing the electricity.
An energy harvesting system consisting of a droplet-based electricity generator (DEG) and an MSC array we designed and fabricated using inkjet printing and ultrafast laser micromachining. The right figure shows the measured energy stored by MSC arrays with different numbers of cells. It can be seen that the energy collection efficiency increased with increasing cell numbers. What is special about this system is that it achieved a record-high energy collection efficiency of over 60%. The challenge mainly results from the pulsed output of DEG with peak voltages over 100 V, which are impossible to collect using batteries or a single MSC. We addressed it by fabricating MSCs with high operation speed, enabling the collection of pulsed electricity, and integrating them in series to enlarge the working voltage window. [Chen, Shiqian, et al. Advanced Science 11.22 (2024): 2400697., https://doi.org/10.1002/advs.202400697]
A 3D-printed glass micro-supercapacitor. Using the approach we developed for efficient 3D printing of hierarchical glass structures based on ultrafast laser-induced crosslinking and self-formation of nanogratings in HSQ, we fabricated skeletons featuring a large surface-area-to-volume ratio. The skeletons were then coated with TiN using atomic layer deposition to serve as the electrodes for the MSC. What is special about this device is that the discrete nanogratings form channels that enable the efficient transportation of ions, in addition to providing a large surface area. As shown in the measured performance (particularly, the b value staying very close to 1), the energy storage efficiency of the device was not limited by ion transportation impedance up to an extremely high scan rate of 100 V/s. [Huang, P.-H., et al. ACS nano 18.43 (2024): 29748-29759., https://doi.org/10.1021/acsnano.4c09339]
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