Reservoir-Inspired Self-Circulating Instantaneous Discharge Triboelectric Nanogenerator (SCID-TENG) with Electrowetting-Enhanced Ultrahigh Power Density under Small Loads for Wireless Energy Delivery of Implantable Devices

Abstract Battery-free wireless energy delivery is highly desired for implantable medical devices (IMDs). Although triboelectric nanogenerators (TENGs) show promise, they often face challenges in delivering high power density under small loads, limiting their capability to drive extracorporeal transmitters. Herein, we propose a self-circulating instantaneous-discharge TENG (SCID-TENG) that decouples charge accumulation from instantaneous release. The SCID-TENG delivers 144.6 V and 20.9 W at 1 kΩ while maintaining a load-insensitive output from 1 kΩ to 1 MΩ. Integrating electrowetting-assisted charge injection (EWCI) with the SCID-TENG further boosts the output, yielding a peak power density of 3922 W/m2. With incorporation into a wireless transmission system, the device achieves a subcutaneous peak-to-peak voltage of 145.8 V, 1.9 times that before EWCI. The SCID-TENG generates negligible energy per pulse, confirming its safety for direct contact. Collectively, this work achieves ultrahigh power density under small loads, providing a viable pathway toward wireless energy delivery of IMDs.