As a promising technology to harvest different forms of mechanical energy from environment, triboelectric nanogenerators (TENGs) have great potential application in self-powered sensor, Internet of Things, and large-scale renewable blue energy. For application it is important to further enhance the output power density and efficiency, which depend on the triboelectric charge density quadratically. In this paper, we briefly introduce the approach to improve the charge density and review the progress of achieving ultrahigh triboelectric charge density. In addition, the restricting factors and limitation of triboelectric charge density are investigated by taking Cu-PTFE as the contact surface of TENG as an example, which could provide a research direction for achieving ultra-high charge density of TENG.

charge density  /  triboelectric nanogenerator  /  figure-of-merits  /  surface modification  /  structure optimization