Constructing a continuous gradient structure significantly enhances the high-temperature energy storage performance of cellulose acetate multilayer composite films

Abstract

Developing environmentally friendly and renewable biobased dielectric materials is particularly important in the coming AI era in relation to requirements for high energy storage and application as well as high integration and flexibility. Here, a five-layer continuous gradient structure of a cellulose acetate (CA)-based dielectric composite film is proposed. In the design rules, the multistage gradient interfaces are constructed by sequentially increasing the content of alumina (AO) particles from top to bottom. Specifically, the middle three layers are designed as AO/CA polarization layers, and the outer layers are breakdown layers consisting of a poly(methyl methacrylate)/poly(vinylidene fluoride-hexafluoropropylene) (PMMA/(P(VDF-HFP)) blend combined with a molecular semiconductor (NTCDA). The results demonstrate the effectiveness of the gradient structure in reducing leakage current density and enhancing breakdown strength, while simultaneously inducing high polarization. This synergistic effect endows the composite film with a discharge energy density of 11.09 J cm⁻³ and 86.86% efficiency at 25 °C. Importantly, the composite film also displays prominent capacitive performance at 150 °C, with a discharge energy density of 8.96 J cm⁻³ and an efficiency of 81.65%, thus offering a productive guideline for high-temperature applications of CA-based dielectric films.