Say Goodbye to Your Charger with a Flexible/Wearable Self-Powered Energy Unit

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A self-powered unit refers to a system that can simultaneously harvest, store and deliver energy without external chargers. However, its development is still handicapped by the inefficient bulky connections between functional modules. In our Nature Communications article, we innovatively designed a flexible solar charging self-powered unit based on printed Mg ion micro-supercapacitors and commercial solar cells. The integrated system demonstrates a new record for overall energy conversion and storage efficiency and favorable flexibility. This research work is led by Jingyu Sun at Soochow University, Yuanlong Shao at King Abdullah University of Science & Technology, and Richard Kaner at the University of California, Los Angeles.

The Internet of Things (IoT) and flexible electronics have spurred demand for self-powered systems. Typically, a self-powered system encompasses two components, an energy harvesting module and an energy storage module. Solar energy is a renewable, sustainable and non-polluting source of energy. As such, solar cells can directly harvest and transform solar radiation into electricity thanks to the photovoltaic effect. Thus-derived electrical energy can be stored in an energy storage device. Nevertheless, daunting challenges still exist in the development of high-performance flexible self-powered energy units. For instance, the hybrid system, by integrating a rigid solar cell, still lacks mechanical robustness. In addition, the adaptability of fluctuating charging currents and voltages for the energy storage module need to be improved to match the electric output capability of the solar cells.


In our latest Nature Communications report, an innovative flexible solar charging self-powered unit is developed by integrating Mg-ion interdigitated micro-supercapacitors and GaAs solar cells, as illustrated in the schematic. The Mg-ion micro-supercapacitor is fabricated by screen-printing technology, which harvests an extended output voltage through an asymmetric design. The overall energy conversion and storage efficiency of the self-powered unit reaches a new record of 17.57%. Such a flexible self-powered unit demonstrates an excellent stability of 98.7% capacitance retention after 100 cycles, as evidenced by solar-charging/discharge cycling tests.


Furthermore, the printed micro-supercapacitors afford high energy densities of up to 13.1 mWh cm−3 via a Mg-ion intercalation pseudocapacitive charge storage mechanism. The mechanism is systematically investigated by in-depth operando X-ray diffraction and ex situ XPS analysis. Our findings pave the way for a practical route toward the design of future self-powered systems favorably harnessing safety, long life, and high energy.


For more information please see: Zhengnan Tian et al. “Printable Mg-ion quasi-solid-state asymmetric supercapacitors for flexible solar-charging integrated units” Nature Communications. 2019, DOI: 10.1038/s41467-019-12900-4.

Yuanlong Shao

Professor, Soochow University