High-Performance Energy Storage Materials Based on Polypropylene/Bacterial Cellulose Multilayered Composite Films

Polymer-based dielectric materials exhibit broad application prospects in next-generation capacitive energy storage systems, but their poor thermal stability and low energy density limit their use in extreme environments. In this study, a flexible multilayer composite film was designed and fabricated by introducing bacterial cellulose (BC) as a functional interfacial layer into a polypropylene (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{P} \mathbf{P}$</tex>) matrix to improve its dielectric properties and energy storage capability. The composite material adopts a PP/BC/PP sandwich structure, achieving a high energy density of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$6.23 \mathrm{J} / \text{cm} 3$</tex> at room temperature, and maintaining stable performance of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5.83 \mathrm{J} / \text{cm} 3$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$4.93 \mathrm{J} / \text{cm} 3$</tex> at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$85^{\circ} \mathrm{C}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$125^{\circ} \mathrm{C}$</tex>, respectively. The introduction of the BC functional layer significantly suppressed charge migration, reducing leakage current by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$82.98 \% \sim 93.67 \%$</tex> and increasing the breakdown strength by up to 8.43 %. In addition, the combined effect of bandgap difference and interfacial trapping brought by the BC functional layer inhibited the migration of free electrons within the material, thereby maintaining excellent dielectric properties and stability at high temperatures.