storage performance of the coated films.
1.8 Conclusion
Advances in the nanomaterials and nanotechnology have promoted the development of polymer composites for electrical energy storage application. The field of dielectric polymer composites has witnessed great progress, and the progress is still accelerating continuously. The discharged energy density achieved in the polymer composites has already exceeded 20 J/cm3, which is comparable to other energy storage methods, such as electrochemical capacitors. Various innovative material structure designs and processing methods, such as nanofiller morphology control, nanofiller surface modification, nanofiller alignment, and multilayer‐structured composites, have been proposed to improve the performance of the dielectric polymer composites.
To further improve the performance of the dielectric polymer composites to meet the increasing demand from application, the following points should be addressed in the future studies. The majority of the high discharged energy density dielectrics are based on PVDF‐based polymers with high dielectric constant. However, these polymer composites suffer from the high energy loss, i.e. >20% in most PVDF‐based polymer composites at high electric field, which is not acceptable in many applications. So efforts should be made to improve the charge/discharge efficiency of the high‐energy‐density polymer composites. The charge/discharge efficiency should be comparable to the benchmark of biaxially oriented polypropylene (BOPP) film. It should be noted that the current high‐energy‐density polymer composites are mostly designed for room temperature application because of the relatively low thermal stability of the polymer matrix. However, the emerging applications under extreme conditions require polymer dielectrics capable of high temperature application. Although great achievements have been made in high temperature polymer dielectrics, the discharged energy density is still relatively low, i.e. <5 J/cm3 at 150 °C. To further improve the performance of the polymer composites, fundamental understanding of the interfacial properties should be advanced, which would assist the rational design of the material structure. Moreover, the application of big data and machine learning technologies should be explored in the material structure design and optimization to guide the development of dielectric polymer composites. Last but not least, the low‐cost, scale‐up film processing method should be developed to produce the high‐quality, large‐scale polymer composite films. All these efforts together would push the field of dielectric polymer composites to a new stage to meet the emerging demand for electrical energy storage in various industrial applications.
Figure 1.12 (a) Illustration of the fabrication process of sandwich‐structured films (P stands for the PVDF layer, and B denotes the BNNSs layer); (b) cross‐sectional SEM pictures of PBP1, PBP3, PBP5, and PBP7, respectively (all scale bars are 2 μm); (c) Weibull breakdown strength; and (d) maximum discharged energy density and charge/discharge efficiency of the series films, comparison of electric field distribution, and electrical tree propagation path of (e) PBP3 and (f) PVDF/BNNS composites.
Source: Zhu et al. [94]. Reproduced with permission of John Wiley & Sons.
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