Dielectric capacitors are one of the most widely used electronic components in modern devices. Among the various types of capacitor elements, polymer film capacitors offer several advantages, including high output voltage, wide frequency range, high mechanical flexibility, strong charge-discharge cycling capability, and excellent self-healing properties.

In recent years, with the trend of integration and miniaturization in electromagnetic pulse weapons, energy and power systems, and transportation systems, there is an urgent need to develop polymer-based dielectric materials with high energy storage performance.

Chair Professor Hong Wang’s research team from the Department of Materials Science and Engineering (MSE) at the Southern University of Science and Technology (SUSTech) has recently made a breakthrough in the field of dielectric energy storage materials.

Their work, published in the journal Advanced Materials titled “Superior Capacitive Energy Storage Enabled by Molecularly Interpenetrating Interfaces in Layered Polymers”, offer innovative solutions to long-standing challenges in energy storage materials.

The intrinsic inverse relationship between the dielectric constant and breakdown strength of dielectric materials poses a limitation on the improvement of energy storage density. Polymer-based nanocomposites reinforced with high-k inorganic ceramics to enhance polarization often come at the expense of breakdown strength and face challenges in industrial-scale production. Linear, all-organic polymers exhibit low loss and high charge-discharge efficiency, and hold promise for large-scale manufacturing. However, their energy storage density is still constrained by low polarization and low breakdown strength.

Professor Wang’s team designed a novel type of bilayer polymer dielectric film with a heterogeneous molecular interpenetrating interface, based on ferroelectric and linear dielectric polymers, rather than the traditional laminated polymer structure. This design decouples the constraint between dielectric constant and breakdown strength, achieving ultra-high energy density and efficiency (Figure 1).

Figure 1. Theoretical simulation, characterization, and performance of the molecular interpenetrating interface in all-organic bilayer heterogeneous polymer.

The team enhanced the polar phase transition by regulating the heterogeneous molecular interpenetrating interface between the PVDF-based blended ferroelectric polymer and the linear dielectric PEI layer. This approach increased the content of polar β and γ phases, effectively enhancing the polarization of the polymer (Figure 2). The strong intermolecular interactions at the molecular interpenetrating interface reduced interchain spacing and grain size, increasing Young’s modulus and mitigating local stress distortions (Figure 3). Advanced techniques such as Thermally Stimulated Depolarization Current (TSDC), Pulsed Electro-Acoustic (PEA), and Kelvin Probe Force Microscopy (KPFM) demonstrated that this molecular interface design also enhanced the polymer film’s ability to trap free charges, resulting in a significant reduction in leakage current density and a substantial increase in breakdown strength (Figure 3).

Figure 2. Polar phase transition and intermolecular interactions induced by molecular interpenetrating interfaces

Figure 3. Charge trapping, mechanical properties, and breakdown strength of the molecular interpenetrating interfaces

Due to the synergistic enhancement of dielectric constant and breakdown strength, the polymer film achieved a high energy storage density of 29.89 J cm^-3 with an efficiency of 81.1% under an ultra-high electric field of 940 MV m^-1. Moreover, it maintained an energy storage density of 22.89 J cm^-3 at a charge-discharge efficiency of ≥90%, outperforming the currently reported polymer-based thin-film dielectric materials (Figure 4). Additionally, the polymer film exhibited excellent cycle stability and large-scale production capability.

Figure 4. Dielectric energy storage properties, fatigue properties, and stability of polymer films

Ph.D. candidate Liang Sun from the Department of MSE at SUSTech is the first author of the paper. Research Assistant Professor Fengyuan Zhang and postdoctoral researcher Li Li, both from the Department of MSE, are the co-first authors. Chair Professor Hong Wang serves as the lead corresponding author, while Professor Qing Wang from Pennsylvania State University and Li Li as the co-corresponding authors. SUSTech is the first affiliated institution of the paper.

Other contributors to this work include Professor Jiangyu Li from the Department of MSE, Associate Professor Qi Li from the Department of Electrical Engineering at Tsinghua University, and Professor Kai Wu from the School of Electrical Engineering at Xi’an Jiaotong University.

Paper link: https://doi.org/10.1002/adma.202412561

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