Sandwich-structured cellulose acetate dielectric films toward high-temperature energy storage application

Common sandwich-structured dielectric films are typically confined to comparatively low operating temperatures because of the significant conduction loss of polymer under high thermal stress that originated from the relatively weak interfacial interaction between adjacent layers. Here, all-organic sandwich-structured dielectric films were fabricated based on cellulose acetate (CA) and poly(methyl methacrylate) (PMMA) by solution casting method. Specifically, CA with high dielectric constant was designed as the intermediate polarizing layer, while PMMA with good insulation property was taken for the breakdown-resistant out layers. The good interlayer interaction endows the sandwich-structured films with a dense structure, while the difference in interlayer conductivity effectively suppresses electric field distortion. Consequently, the maximal discharge energy density ($U_d$) of M-CA4-M composite film reaches 6.64 J/cm³ (i.e., 223 % of pure CA) at 752.66 MV/m, along with an excellent charge-discharge efficiency ($\eta$) of 83.45 %. Importantly, the composite film also displays prominent capacitive performance still at 150 °C, with $U_d$ of 4.72 J/cm³ and $\eta$ of 76.65 % at 644.92 MV/m, which are much better than the commercially available dielectric films. This work illustrates the possible application of CA-based dielectric films in high-temperature energy storage field.