Enhanced High-Temperature Capacitive Energy Storage by 0.55Bi0.5Na0.5TiO3-0.45(Bi0.2Sr0.7)TiO3 Nanofibers in Polyetherimide Nanocomposites

The low discharge energy density and operation temperature of dielectrics limit the integration application of capacitors under extreme environment conditions. In order to reduce the dielectric loss of Bi0.5Na0.5TiO3, 0.55Bi0.5Na0.5TiO3-0.45(Bi0.2Sr0.7)TiO3 (BNT-BST) nanofibers with optimized diameter were synthesized and utilized to improve the high-temperature capacitive energy storage of polyetherimide (PEI) nanocomposites. Benefiting from the introduction of nanofibers, the leakage current is significantly reduced and charge migration is limited, contributing to the enhancement of the energy storage properties. For example, the leakage current density of the 3 wt % BNT-BST/PEI nanocomposite is suppressed from 0.136 μA/cm2 of PEI to 0.056 μA/cm2 at 250 kV/mm. The nanocomposite with 3 wt % BNT-BST achieves an excellent discharge energy density of 10.37 J/cm3 at 560 kV/mm, which is 65.4% higher than that of PEI. When the environment temperature is up to 100 °C, the discharge energy density of the nanocomposite maintains a high level of 4.76 J/cm3. Furthermore, the nanocomposite displays outstanding cycling stability and fast charge–discharge performance. For instance, after 106 charge–discharge cycles at 150 kV/mm, the discharge energy density and efficiency remain at 99 and 95% of the initial values, respectively. This work provides a feasible idea for achieving high-energy density nanocomposites under high environment temperature.