Quantifying the power output and structural figure-of-merits of triboelectric nanogenerators in a charging system starting from the Maxwell's displacement current

Conversion of mechanical energy into electricity using triboelectric nanogenerators (TENGs) is a rapidly expanding research area. Although the theoretical origin of TENGs has been proven using the Maxwell's displacement current (I _D ), a profound quantitative understanding of its generation is not available. Moreover, a comprehensive analysis of the fundamental charging behavior of TENGs and building a standard to evaluate each TENG's unique charging characteristic are critical to ensure efficient use of them in practice. We present a thorough analysis of TENG's charging behavior through which a more complete evaluation of TENG charging is proposed by introducing the structural figure of merit (FOMCs) in a charging system (powering capacitors). The analysis is based on Maxwell's displacement current and results are verified experimentally. To achieve this, according to the distance-dependent electric field model, we provide a systematic discussion on the generation of I _D in TENGs, along with the derived analytical formula and numerical calculations. This work suggests a new way to deeply understand the nature of the I _D generated within the TENGs; and the modified FOMC _S can be used to predict the charging characteristics of TENGs in an energy storage system, allowing us to utilize the TENGs more efficiently towards different applications.