Dielectric polymer nanocomposites with high energy density and high charge-discharge efficiency 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 is related to the dielectric breakdown strength and energy storage density. 

Researchers from the Shenzhen Institutes of Advanced Technology (SIAT) of the Chinese Academy of Sciences developed novel nanoparticles by substituting part of S element in ZnS by O (ZnS:O) which creates isoelectronic traps due to different diameters and electronegativity between S and O. The isoelectronic traps could confine charge carriers and suppress their movement throughout the polymer matrix., resulting in a reduced conductivity and electric breakdown strength.  

The study was published in Composites science and Technology (Vol. 195, 2020, 108201). 

The composites achieved a breakdown strength as high as 6000 kV/cm and an energy density of 14.4 J/cm3 with 2.5 vol% ZnS:O nanoparticles, which are nearly twice and over three times respectively compared with those of the pure polyvinylidene fluoride (PVDF) (Eb ~3183 kV/cm, 4.6 J/cm3), and also much higher than those of ZnS filled PVDF. 

In addition, finite element simulation was employed to explicate the confinement of charge carriers and suppression of electrons' movement. 

Their results proved that the isoelectronic traps in the proposed ZnS:O nanoparticles could effectively inhibit the increase of free carriers and leakage current density in the nanocomposites under high electric field, improving breakdown strength and charge-discharge efficiency. 

This work promotes the electrical and dielectric performance of the polymer based composites and provides a unique idea to control the distribution of charge carriers in the polymer composites in the future. 

Schematic diagram of the motion of space charges in the crystal lattice. (Image by YU Shuhui)

Media Contact:
ZHANG Xiaomin
Email: xm.zhang@siat.ac.cn