Performance Metrics of Triboelectric Nanogenerator toward Record-High Output Energy Density

The state-of-the-art studies have promoted the output energy density of the triboelectric nanogenerator (TENG) to be 10^5 J m^-3 level, while the current major barrier lies on the breakdown discharge limit. The universal performance metrics to reveal the maximized energy output ability of TENG approaching the breakdown limit are highly desirable, yet remaining a major challenge. Herein, this work proposed performance metrics for charge density and output energy density, quantitatively characterizing the output performance based on sliding-freestanding TENG with charge excitation strategy. A series of parameters of different dielectric materials were systematically investigated to reveal their impacts on the performance metrics. Consequently, the maximum output energy density of 10 kinds tribo-dielectrics were evaluated based on voltage-charge (V-Q) curve, validating the proposed performance metrics. Guided by this new standard, we developed a stretched P(VDF-TrFE) film with synergistically improved permittivity and breakdown strength, achieving record-high charge density and output energy density of 2.8 mC m^-2 and 6.2×10^5 J m^-3, respectively. Furthermore, a self-driven charge excitation system is explored in rotary-mode TENGs, showing excellent output capability to light up 15 series bulbs directly. This work establishes a basic standard and guideline for improving the TENG’s energy output, highlighting TENG’s potential applications for energy harvesting.