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The miniaturization of electronic devices and the structural optimization of power systems put forward a strict size requirement for passive components such as capacitors. The thickness reduction of dielectric polymer films becomes a necessary and urgent measure for future technology development. This advance leads to a higher capacitance density, less raw resource consumption, and lightweight modules and systems. However, the thickness change inevitably challenges the dielectric properties, the surface condition, and their relationship with the fabrication method of the dielectric films. This review primarily discusses: (1) the influence of polymer film thickness on the dielectric properties, (2) film quality issues in thinner polymer films with different filler contents, (3) high-temperature dielectric polymer engineering, and (4) the major processing methods in decreasing polymer film thickness. In addition, the polymer films also require scalability, processibility, and industrial feasibility in film and component manufacturing. The perspective of future investigations and concerns of dielectric polymer films are shared. It is interesting to see the favorable effect of multilayer polymer films on enhancing the dielectric strength.

Designing the mesopore-dominated activated carbon electrodes has witnessed a significant breakthrough in enhancing the electrolyte breakdown voltage and energy density of supercapacitors. Herein, we designed N-doped mesoporous-dominated hierarchical activated carbon (N-dfAC) from the dragon fruit peel, an abundant biomass precursor, under the synergetic effect of KOH as the activating agent and melamine as the dopant. The electrode with the optimum N-doping content (3.4 at. %) exhibits the highest specific capacitance of 427 F g–1 at 5 mA cm–2 and cyclic stability of 123% capacitance retention until 50000 charge–discharge cycles at 500 mA cm–2 in aqueous 6 M KOH electrolytes. We designed a 4 V symmetric coin cell supercapacitor cell, which exhibits a remarkable specific energy and specific power of 112 W h kg–1 and 3214 W kg–1, respectively, in organic electrolytes. The cell also exhibits a significantly higher cycle life (109% capacitance retention) after 5000 GCD cycles at the working voltage of ≥3.5 V than commercial YP-50 AC (∼60% capacitance retention). The larger Debye length of the diffuse ion layer permitted by the mesopores can explain the higher voltage window, and the polar N-doped species in the dfAC enhance capacitance and ion transport. The results endow a new path to design high-capacity and high-working voltage EDLCs from eco-friendly and sustainable biomass materials by properly tuning their pore structures.

Designing high voltage (>3 V) and stable electrochemical supercapacitors with low self‐discharge is desirable for the applications in modern electronic devices. This work demonstrates a 4 V symmetric supercapacitor with stabilized cycling performance through atomic layer deposition (ALD) of alumina (Al2O3) on the surface of activated carbon (AC). The 20‐cycle ALD Al2O3 coated AC delivers 84 % capacitance retention after 1000 charge/discharge cycles under 4 V, contrary to the bare AC cells having only 48 % retention. The extended cycling life is associated with the thickened Stern layer and suppressed oxygen functional group. The self‐discharge data also show that the Al2O3 coating enables AC cells to maintain 53 % of charge retention after 12 h, which is more than twice higher than that of bare AC cells under the same test protocol of 4 V charging. The curve fitting analysis reveals that ALD coating induced slow self‐discharge dominated by ion diffusion mechanism, thus enhancing the AC surface energy., 4 V symmetric supercapacitors are stabilized through optimizing Atomic Layer Deposition of Al2O3 on activated carbon electrodes. The thickened Stern layer and suppressed oxygen functional group extend the cycling life at 4 V. The additional aluminum oxide layer enhances the energy barrier for ion desorption, thereby resulting in a decreased rate of self‐discharge. Too thick oxide coating blocks the nanopores and lower the cycling performance.

In this work, the electromagnetic interference (EMI) shielding properties of an MXene interlayered crosslinked conducting poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) polymer film are investigated. The introduction of a crosslinker into PEDOT:PSS makes PEDOT:PSS water insoluble. An average EMI shielding effectiveness (SE) of ∼41 dB (corresponding to 99.999% blockage) was obtained for a solution coated 6 ± 0.2 μm thick optimized crosslinked PEDOT:PSS-Ti3C2Tx MXene (XPM50) nanocomposite film. Electrodynamic modelling and simulation also suggest an excellent SE for this nanocomposite system. From an application point of view, the specific EMI SE (SSE)/thickness (t) or absolute EMI SE is the most useful factor. The absolute EMI SE of the XPM50 film is observed to be 89 924 dB cm2 g−1, which is nearly nine times higher than that of the pristine PEDOT:PSS film and more than three times higher than that of the Ti3C2Tx MXene film. Mechanistically, the superior EMI shielding due to absorption (SEA) is intrinsically predominant. The crosslinked PEDOT:PSS interconnects with the Ti3C2Tx MXene flakes, generating more absorption sites and enhanced electrical conductivity which is responsible for the high SEA value. The XPM50 film also fulfils many commercial requirements, especially solution processability and outstanding absolute EMI SE, which makes it an attractive EMI shield for real time applications such as telecommunications, health care systems, detective systems, defence, and aerospace applications.

Flexible dielectric polymer composites occupy a significant position in electronic devices. However, many investigations focus on complicated synthetic methods to enhance the energy density of dielectrics. Developing simple and feasible strategy is meaningful and urgent for their acceptance to various applications. Herein, we utilize the high thermal conductivity and electrical insulation characteristic of Boron nitride and Aluminum nitride (BN/AIN) as the hybrid fillers for polyetherimide (PEl) matrix to increase dielectric constant and breakdown strength. This combination resulted in a high discharged energy density of 8.39 J/cm3 at 500 kV/mm with a high efficiency of 90.5% at a low filler fraction. This strategy provides a feasible option for a scalable manufacturing of high performance composite films in the future.

High voltage electric double layer capacitors with reliable cycling performance are in high demand for energy storage applications. In this research, studies of the process-structure-property relations of commercial activated carbon electrode modified with atomic layer deposition (ALD) have been performed in terms of coating of various oxide compounds. These investigations have yielded similar enhancements of cycling performance at high voltages (3.5 V) enabled by the ALD coating of oxides on activated carbon surfaces. The commonalities are the phenomenal increase in capacitance retention of coin cell supercapacitors after 1,000 charge/discharge cycles regardless of the electric nature of ALD deposited oxides. Minor differences in coating morphologies and uniformities were observed between the aluminum oxide, titanium oxide, and manganese-cobalt oxide. ALD coating of these oxides of about 20-growth cycle (1–2 nm in thickness) was found to effectively result in reliable cycling performance, lower impedance, and significantly low leakage current. The authors proposed a modified Gouy-Chapman-Stern model to explain the remarkable increase in operating voltage and cycling performance by the increased Stern layer thickness due to the ALD oxide coating. These results demonstrate that the ALD oxide coating has excellent potential for activated carbons for high operating voltage and energy density supercapacitor.

MXene, the new family of two-dimensional materials having numerous nanoscale layers, is being considered as a novel microwave absorption material. However, MXene/functionalized MXene-loaded polymer nanocomposites exhibit narrow reflection loss (RL) bandwidth (RL less than or equal to −10 dB). In order to enhance the microwave absorption bandwidth of MXene hybrid-matrix materials, for the first time, macroscopic design approach is carried out for TiO 2 -Ti 3 C 2 T x MXene and Fe 3 O 4 @TiO 2 -Ti 3 C 2 T x MXene hybrids through simulation. The simulated results indicate that use of pyramidal meta structure of MXene can significantly tune the RL bandwidth. For optimized MXene hybrid-matrix materials pyramid pattern, the bandwidth enhances to 3–18 GHz. Experimental RL value well matched with the simulated RL. On the other hand, the optimized Fe 3 O 4 @TiO 2 -Ti 3 C 2 T x hybrid exhibits two specific absorption bandwidths (minimum RL value - −47 dB). Compared with other two-dimensional nanocomposites such as graphene or Fe 3 O 4 -graphene, MXene hybrid-matrix materials show better microwave absorption bandwidth in macroscopic pattern.

The primary strategy to increase dielectric constant and energy storage density is adding a high fraction of fillers with high dielectric constant to polymer matrix. Yet, it has not been very successful without encountering processing difficulties, lowered breakdown strength, and mechanical inflexibility. Herein, we introduce an unconventional approach using ultra-low fraction of zinc oxide core and boron nitride shell (ZnO@BN) filler with very high thermal conductivity dispersed in polyetherimide (PEI) for the same purpose. For the 0.1 vol% core-shelled fillers, the PEI composite film exhibits a superior dischargeable energy density of 10.8 J/cm3 and a high efficiency of 92.1% at an electric field of 500 kV/mm. The polarization responses under high electric fields and simulation reveal the association with the increased interfacial polarization of the thermally conductive core-shelled structure. This strategy lays out a new route to further investigate of high energy density composite and capacitor technologies.

Last two decades has witnessed various technical programs towards the development of new dielectric films for high temperature and high energy density capacitor technology. Yet, the organic polypropylene film still holds its top position for film capacitors required for electric and electronic power applications such as power grid, hybrid electric vehicles, oil and gas exploration, and aviation. However, its low temperature stability determined by its structural nature limits its further adoption for more rising markets. This work thus developed a creative method (ultrathin coating of inorganic compound using atomic layer deposition) to increase the high temperature stability and the dielectric strength of such a strategically important polymer film from below 105 °C to above 140 °C. Several techniques also confirmed the effective minimization of the dimensional change and crystallinity loss at higher temperatures, i.e., Thermomechanical analysis, Dynamic mechanical analysis, Dynamic Scanning calorimetry, x-ray diffraction and electron microscopy techniques. This breakthrough discovery adds a huge value to the commercial PP films and relevant capacitor industry and will extend the operation of high-performance PP film capacitors to various high standard applications.

This work focused on the interaction of polar ceramic particles with the hosting polymers to improve the distribution of particles and the dielectric properties of polymer composites. Polymers incorporating polar ceramic particles were shown to exhibit improved dielectric properties. Both computation and experimental observation were conducted to enhance the understanding of composite dielectric engineering. The electric field was found to be localized at the particle- polymer interface, likely contributing to the polarization of polar particles.