High Energy Storage Performance of Random Norbornene Copolymer Containing Oligothiophene as Side-chain for Dielectric Capacitors Applications

Abstract

Modern energy storage systems impose stringent demands on polymer dielectrics, requiring both high discharged energy density (Ue) and high charge-discharge efficiency (𝜂) under harsh operating conditions. Among various intrinsic polymer dielectrics, polynorbornene-based materials offer notable advantages, including high breakdown strength (Eb) and elevated glass transition temperature (Tg). However, they suffer from substantial energy loss (Ul), leading to poor 𝜂 under concurrent electric field extremes and elevated temperatures. Herein, an innovative strategy is proposed to synergistically enhance Ue and 𝜂 through the introduction of easily polarized, rod-like π-conjugated oligothiophenes. Random copolymers based on poly(oxanorbornene-imide), incorporating varying amounts of terthiophene as side chains (PTA-TP), were synthesized. The incorporation of TP units simultaneously increases the dielectric constant and facilitate β relaxation. Meanwhile, the introduction of TP unit effectively modulates the local frontier-orbital alignment and creates deep traps of 0.91 eV, as revealed by density functional theory analysis (DFT) and thermally stimulated depolarization current (TSDC) characterization, thereby capturing free charge carriers and suppressing electronic loss. As a result, the optimized copolymer (PTA-TP-3) exhibits a Ue of 8.50 J cm-3 at 700 MV m-1 and 150 oC along with a remarkable 𝜂 of 91%, while at 750 MV m-1, it achieves a Ue of 9.75 J cm-3 with an efficiency of 89%. This strategy demonstrates applicability and effectiveness across other poly(oxanorbornene-imide) dielectrics, establishing a generalized framework for the design of high-performance dielectric materials under extreme conditions.