Stereoisomerically enhanced polynorbornene-imide dielectric energy storage performance

Developing dielectric polymers with different stereoisomers may provide a novel strategy to improve electrostatic energy storage performance under harsh environments. However, there is still little research about the effect of polymer stereoisomerism on capacitive energy storage so far. Here, we report a new class of cycloaliphatic polynorbornene-imide (PNC) dielectric with two different spatial configurations and demonstrate that flexural configuration significantly improves the energy storage performance at room temperature and high temperature. ENDO-PNC with flexural configuration possesses slightly higher dielectric constant, comparably large bandgap and dramatically improved thermal properties with respect to EXO-PNC with near-planar configuration. Notedly, ENDO-PNC exhibits dramatically inhibited leakage current density and hopping distance, substantially improved activation energy, electrical resistivity and breakdown strength. Consequently, ENDO-PNC exhibits an ultrahigh discharged energy density (U_d) of 11.10 J/cm³, 9.11 J/cm³ and 6.77 J/cm³ at 25 °C, 150 °C and 200 °C respectively, as high as 1.4 times, 2.0 times and 2.8 times that of EXO-PNC. Moreover, ENDO-PNC delivers a maximum U_d of 6.0 J/cm³ and 3.3 J/cm³ above 90 % efficiency respectively at 150 °C and 200 °C, superior to neat polymers and highly competitive in reported polymer composites. The stereoisomerism effect on dielectric energy storage is further demonstrated in other dielectric polymers, revealing this strategy is universally applicable and particularly meaningful to design and exploit polymer dielectrics working under harsh environments.