Improved Working Temperature and Capacitive Energy Density of Biaxially Oriented Polypropylene Films with Alumina Coating Layers

High-temperature dielectric energy-storage properties are crucial for polymer-based capacitors for harsh environment applications. However, biaxially oriented polypropylene (BOPP), a state-of-the-art commercial capacitor dielectric, can work only below 105 degrees C. Here, we present a versatile method to enhance its working temperature by depositing alumina (Al2O3) layers onto BOPP films via magnetron sputtering. Compared with a pure BOPP film, the sandwiched Al2O3/BOPP/Al2O3 structure shows a higher dielectric constant, a lower electrical conduction loss, stronger mechanical properties, higher thermal conductivity, and especially increased working temperature. As a result, the composite film delivers a high discharged energy density of 0.45 J/cm3 under 200 MV/m (the actual operating electric field in hybrid electric vehicles) at 125 degrees C. The discharged energy density and energy-storage efficiency (similar to 97.7%) are highly stable over 5000 cycles at 125 degrees C. This work provides an effective route to develop high-temperature polymer-based capacitors.

Automated summary

This study presents a method to enhance the working temperature of a polymer-based capacitor by depositing alumina layers onto biaxially oriented polypropylene films. The composite film shows improved dielectric properties, mechanical properties, and thermal conductivity, enabling high discharged energy density and stability over multiple cycles at high temperature.