Abstract Triboelectric nanogenerators (TENGs) have garnered increasing attention due to their exceptional ability to convert mechanical energy into electricity. Previous understanding is that the electric performance of TENGs is primarily restricted by contact electrification, air breakdown, and dielectric breakdown effects. Here, we have discovered the occurrence of field emission arising from contact electrification and identified its limitation on surface charge density, subsequently impacting the output performance of TENGs. More importantly, we reveal that field emission occurs prior to dielectric breakdown, introducing a new limitation for TENGs performance. By suppressing the field emission effect, an ultrahigh charge density in contact electrification, reaching up to 2.816 mC m−2, is achieved, significantly exceeding previous reports. Additionally, we show that by regulating the field emission effect, TENGs could produce an energy density over 10 J m−2. These findings are crucial for improving TENG’s performance and enhancing the understanding of contact electrification.