Flexible cellulose/alumina (Al2O3) nanocomposite films with enhanced energy density and efficiency for dielectric capacitors

Flexible dielectric materials with high energy density and remarkable charge–discharge efficiency are currently in great demand for the field of energy storage. On the other hand, it is also urgent to develop renewable, biodegradable and environmentally friendly dielectric materials. In this work, Al2O3 nanoparticles (AO) with a diameter of ~ 10 nm were incorporated into regenerated cellulose matrix (RC) without extra treatment to fabricate environment-friendly RC–AO dielectric nanocomposites via a simple dissolution/regeneration pathway. Effects of Al2O3 nanoparticles on the structure and dielectric properties of RC–AO nanocomposite films were systemically investigated. The results showed that the RC–AO films exhibited excellent comprehensive performance, including increased dielectric constant, reduced dielectric loss, improved breakdown strength and high energy storage density. Particularly, the high energy density of 5.7 J cm−3 was achieved at the breakdown strength of 380 MV m−1 when the Al2O3 content was 5 wt%. Furthermore, the composites possessed excellent thermal conductivity, stability and mechanical property. This work provides a good choice for the development of high-performance and ‘green’ natural polymer-based dielectric materials.