Nanoparticles with rationally designed isoelectronic traps as fillers significantly enhance breakdown strength and electrostatic energy density of polymer composites

Dielectric polymer nanocomposites with a high energy density and high charge-discharge efficiency are urgently in need which enable miniaturization of both electrical and electronic systems. One critical challenge for achieving a high energy density is the suppression of space charge movement in the composites which relates to the dielectric breakdown strength and thus energy density. Herein ZnS:O nanoparticles, in which a part of S in ZnS was substituted by O, were synthesized. The difference of electronegativity (Delta EN = 0.86) between S and O creates isoelectronic traps in the nanoparticles, which can to some extent bind space charges and suppress their movement. As a result, with ZnS:O as fillers and polyvinylidene fluoride (PVDF) as a host, the composites achieved a breakdown strength as high as 6000 kV/cm and an energy density of 14.4 J/cm(3) with 2.5 vol% ZnS:O nanoparticles, which are nearly twice and over three times respectively of those of the pure PVDF (E-b similar to 3183 kV/cm, 4.6 J/cm(3)), and also much higher than those of ZnS filled PVDF. Moreover, the dielectric loss and leakage current were effectively suppressed, leading to a high charge-discharge efficiency of up to 97%. The present work provides an efficient approach of modulating the dielectric and electric performance of nanocomposites by confining charge carriers in the isoelectric traps. The effect was investigated by calculation of electric field threshold and electron hopping distance. Finite element simulation was employed to understand the mechanism which vividly interprets the above phenomenon.