Enhancing the high-temperature energy storage performance of sandwich-structured cellulose acetate composite films via multi-scale breakdown-resistant gradient distribution structure

Abstract

The ability to store energy at high temperature is essential for polymer dielectric films operating in harsh environments. However, the energy storage performance of dielectrics degrades sharply at elevated temperature because of increased leakage current. Here, a facile strategy was reported to address this issue by designing sandwich-structured composite films with multi-scale breakdown-resistant gradient distribution structure. Specifically, cellulose acetate (CA) was served as the intermediate layer, while a poly (methyl methacrylate)/poly (vinylidene fluoride-hexafluoropropylene) (PMMA/(P(VDF-HFP)) (MF) blend was functioned as the creation of the breakdown-resistant outer layers. The hydrogen bonding interaction between layers promotes the redistribution of PMMA molecular chains in outer layers, forming the sublayers enriched in P(VDF-HFP) and PMMA, respectively. The outer layers construct energy barriers to restrict charge injection, while the interfaces between layers are responsible for the creation of deep traps to capture mobile charges and suppress conduction loss. These effects collectively decrease the leakage current, enabling the 2MF-CA-2MF to achieve the discharge energy density ($U_d$) of 6.48 J/cm³ (307 % of pure CA) and the high charge-discharge efficiency ($\eta$) of 76.78 % at 600 MV/m and 150 °C. This work demonstrates that CA-based dielectric films can be a viable candidate for high-temperature energy storage in next-generation power electronics.