Synthesis of dielectric polystyrene via one-step nitration reaction for large-scale energy storage

It is a great challenge to achieve ultrahigh discharge energy density (Ue) via improving simultaneously permittivity and breakdown strength of polymer dielectrics. In this work, it is first found that nitrated polystyrene films possess excellent dielectric and energy storage properties. The mechanism for the permittivity and breakdown strength of nitrated polystyrene were investigated. On one hand, substituent group of dipolar nitro can increase the glass transition temperature and permittivity of polystyrene. On the other hand, nitro substituent group can not only construct charge traps to reduce the carrier mobility under high fields, but also effectively destroy the carrier channel formed by the accumulation of pi-pi between the benzene rings under high field, both which favor the enhancive breakdown strength of polystyrene. As a results, the maximum Ue of 6.32 J cm−3 at 640 MV m−1 was obtained in nitrated polystyrene with a substitution degree of 15%, which is 2.38 times than that of neat polystyrene. Furthermore, at 200 MV m−1 and 100 °C, nitrated polystyrene with a substitution degree of 66% produced Ue of 1.1 J cm−3 with 88% efficiency. This study demonstrates that the nitration can significantly promote permittivity and breakdown strength of polystyrene, and provides a guidance for preparing high-performance and large-scale polymer dielectrics.