 The charge flowing into TENG1 and the voltage across TENG1 was measured at the same time, in which the charge was measured by coulometer Q2, and the voltage was obtained by multiplying the resistance R with the current flowing through it as measured by current meter I, as detailed in Methods.The turning points obtained in this (Q, V) were considered as the breakdown points.And then, if xmax was achieved to finish the experimental measurement part.