Flexible, Wearable Wireless-Charging Power System Incorporating Piezo-Ultrasonic Arrays and MXene-Based Solid-State Supercapacitors

With the continuous development of wearable electronics, higher requirements are put forward for flexible, detachable, stable output, and long service life power modules. Given the limited capacity of energy storage devices, the integration of energy capture and storage is a viable approach. Here, we present a flexible, wearable, wireless-charging power system that integrates a piezoelectric ultrasonic array harvester (PUAH) with MXene-based solid-state supercapacitors (MSSSs) in a soft wristband format for sustainable applications. The MSSS as the energy storage module is developed by using Ti₃C₂T_<i>x</i> nanosheet-loaded inserted finger-like carbon cloth skeletons as electrodes and poly(vinyl alcohol)/H₃PO₄ gel as electrolytes, with high energy density (58.74 Wh kg^–1) and long cycle life (99.37%, 10,000 cycles). A two-dimensional stretchable piezoelectric array as a wireless-charging module hybridizes high-performance 1–3 composite units with serpentine electrodes, which allows wireless power via ultrasonic waves, with a maximum power density of 1.56 W cm^–2 and an output voltage of 20.75 V. The overall PUAH–MSSS wireless energy supply system is 2 mm thick and offers excellent energy conversion/storage performance, cyclic stability, and mechanical flexibility. The results of this project will lay the foundation for the development of next-generation wearable electronics.