Superior high-temperature energy storage performance of PEI-based nanocomposite with ultralow loading of nn-heterojunction ZnO-SnO₂ nanofiber

Polymer-based dielectric capacitors are considered as important energy storage components in the electronic devices and power system owing to their high power density, fast charge–discharge speed, and good reliability. However, the increment of leakage current density at elevated temperature and electric field significantly descends the breakdown strength (E_b) and energy storage density, restricting their application in harsh environments. Herein, we selected ZnO and SnO₂ n-type semiconductors to construct nn-heterojunction ZnO-SnO₂ nanofibers and introduced them into PEI matrix to fabricate the ZnO-SnO₂/PEI nanocomposite films via solution casting method. By constructing potential barrier at the interface of ZnO and SnO₂, charge carrier can be captured and constrained in the potential barrier well during the process of carrier transport, effectively hindering the charge conduction in the nanocomposites, and thus suppressing the leakage current density and boosting the E_b and energy storage density. As a consequence, nanocomposite film with 0.50 wt% nanofibers demonstrates high E_b of 647 MV/m and large discharge energy density (U_d) of 8.24J/cm³ at 25 ℃. Even at 150 ℃, superior U_d of 6.02 J/cm³, high charge–discharge efficiency (η) of 83.5 %, high E_b of 593 MV/m are realized in the nanocomposite, which are significantly enhanced than that of pure PEI (U_d ∼ 1.98 J/cm³, η ∼ 57.5 %, E_b ∼ 438 MV/m). The work provides a novel and feasible strategy for developing high-performance polymer-based dielectric capacitors at elevated temperature.