Polymer dielectrics sandwiched by medium-dielectric-constant nanoscale deposition layers for high-temperature capacitive energy storage

Polymer film capacitors are usually limited to relatively low working temperatures due to the large conduction loss of polymer dielectrics under high thermal stress. Here, a polymer dielectric sandwiched by medium-dielectric-constant nanoscale deposition layers is reported, which exhibits significantly suppressed conduction loss and outstanding capacitive performance at high temperatures. A series of deposition materials with distinct band structures and dielectric properties are investigated. It is found that well-balanced bandgap, dielectric constant and electrical conductivity of the nanoscale deposition layer is desirable for suppressing charge injection. The substantial performance improvements are demonstrated to result from the slow decay of barrier height with increasing electric field and the reduced electric field in the deposition layers. The optimized design using a polyetherimide film sandwiched by 150-nm-thick Al₂O₃ deposition layers gives rise to a concurrent high discharged energy density (2.8 J cm⁻³) and charge-discharge efficiency (90%) up to 200 °C, which are significantly higher than those of previously reported surface-coated polymer dielectrics, and are even comparable to the maximum values achieved with expensive, less productive solution-based composite approaches.