Scalable Polyimide-Organosilicate Hybrid Films for High-Temperature Capacitive Energy Storage.

High-temperature polymer dielectrics have broad application prospects in next-generation microelectronics and electrical power systems. However, the capacitive energy densities of dielectric polymers at elevated temperatures are severely limited by carrier excitation and transport. Herein, a molecular engineering strategy is presented to regulate the bulk-limited conduction in the polymer by bonding amino polyhedral oligomeric silsesquioxane (NH2 -POSS) with the chain ends of polyimide (PI). Experimental studies and density functional theory (DFT) calculations demonstrate that the terminal group NH2 -POSS with a wide-bandgap of Eg ≈ 6.6 eV increases the band energy levels of the PI and induces the formation of local deep traps in the hybrid films, which significantly restrains carrier transport. At 200 °C, the hybrid film exhibits concurrently an ultrahigh discharged energy density of 3.45 J cm-3 and a high gravimetric energy density of 2.74 J g-1 , with the charge-discharge efficiency >90%, far exceeding those achieved in the dielectric polymers and nearly all other polymer nanocomposites. Moreover, the NH2 -POSS terminated PI film exhibits excellent charge-discharge cyclability (>50000) and power density (0.39 MW cm-3 ) at 200 °C, making it a promising candidate for high-temperature high-energy-density capacitors. This work represents a novel strategy to scalable polymer dielectrics with superior capacitive performance operating in harsh environments.

Tailoring Poly(Styrene-co-maleic anhydride) Networks for All-Polymer Dielectrics Exhibiting Ultrahigh Energy Density and Charge-Discharge Efficiency at Elevated Temperatures.

Polymer film capacitors have been widely used in electronics and electrical power systems due to their advantages of high power densities, fast charge-discharge speed, and great stability. However, the exponential increase of electrical conduction with temperature and applied electric field substantially degrades the capacitive performance of dielectric polymers at elevated temperatures. Here, the first example of controlling the energy level of charge traps in all-organic crosslinked polymers by tailoring molecular structures that significantly inhibit high-field high-temperature conduction loss, which largely differs from current approaches based on the introduction of inorganic fillers, is reported. The polymer network with optimized crosslinking structures exhibits an ultrahigh discharged energy density of 7.02 J cm-3 with charge/discharge efficiencies of >90% at 150 °C, far outperforming current dielectric polymers and composites. The charge-trapping effects in different crosslinked structures, as the origins of the marked improvements in the high-temperature capacitive performance, are comprehensively investigated experimentally and confirmed computationally. Moreover, excellent cyclability and self-healing features are demonstrated in the polymer film capacitors. This work offers a promising pathway of molecular structure design to scalable high-energy-density polymer dielectrics capable of operating under harsh environments.

Electrostatic Adhesion Clutch with Superhigh Force Density Achieved by MXene-Poly(Vinylidene Fluoride-Trifluoroethylene-Chlorotrifluoroethylene) Composites.

Electrostatic adhesion (EA) clutches are widely applied in robots, wearable devices, and virtual reality, due to their compliance, lightweight, ultrathin profile, and low power consumption. Higher force density has been constantly perpetuated in the past decades since EA was initially proposed. In this study, by composing terpolymer poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] and two-dimensional Ti3C2Tx nanosheets (MXene), nanocomposite films with high dielectric constant (δr' > 2300) and low loss tangent are achieved. The force representative index δr'Ebd2 (the relative dielectric constant times the square of breakdown electric field) is enhanced by 5.91 times due to the charge accumulation at matrix-filler interfaces. Superhigh shear stress (85.61 N cm-2) is generated, 408% higher than the previous maximum value. One of the EA clutches fabricated in this study is only 160 µm thin and 0.4 g heavy. Owing to the low current (<1 µA), the power consumption is <60 mW/cm2. It can hold a 2.5 kg weight by only 0.32 cm2 area and support an adult (45 kg) (Clinical Trial Registration number: 20210090). With this technology, a dexterous robotic hand is displayed to grasp and release a ball, showing extensive applications of this technique.

Concurrently Achieving High Discharged Energy Density and Efficiency in Composites by Introducing Ultralow Loadings of Core-Shell Structured Graphene@TiO2 Nanoboxes.

Polymer dielectrics have drawn tremendous attention worldwide due to their huge potential for pulsed power capacitors. Recent studies have demonstrated that linear/nonlinear layered composites, which can effectively balance energy density and efficiency, have huge potential for capacitive energy storage applications. However, further enhanced energy densities are strongly desired to meet the everincreasing demand for the miniaturization of electronic devices. Herein, a novel class of core-shell structured graphene@titanium dioxide nanoboxes is successfully synthesized and introduced into poly(vinylidene fluoride-hexafluoropropylene)-poly(ether imide) double-layer films. It is exciting to find that the introduction of merely 0.5 wt % nanoboxes results in a substantially enhanced energy density of 19.39 J/cm3, which is over 2.6 times that of the film without nanoboxes (7.44 J/cm3). Meanwhile, a high breakdown strength of 655 kV/mm and a high efficiency of 83% are achieved. Furthermore, the nanocomposites also show excellent power densities and cycling stabilities. These composites with excellent comprehensive energy storage performances have huge potential for advanced pulsed power capacitors.

Enhanced Thermal Conductivity and Dielectric Properties of Iron Oxide/Polyethylene Nanocomposites Induced by a Magnetic Field.

Iron Oxide (Fe3O4) nanoparticles were deposited on the surface of low density polyethylene (LDPE) particles by solvothermal method. A magnetic field was introduced to the preparation of Fe3O4/LDPE composites, and the influences of the magnetic field on thermal conductivity and dielectric properties of composites were investigated systematically. The Fe3O4/LDPE composites treated by a vertical direction magnetic field exhibited a high thermal conductivity and a large dielectric constant at low filler loading. The enhancement of thermal conductivity and dielectric constant is attributed to the formation of the conductive chains of Fe3O4 in LDPE matrix under the action of the magnetic field, which can effectively enhance the heat flux and interfacial polarization of the Fe3O4/LDPE composites. Moreover, the relatively low dielectric loss and low conductivity achieved are attributed to the low volume fraction of fillers and excellent compatibility between Fe3O4 and LDPE. Of particular note is the dielectric properties of Fe3O4/LDPE composites induced by the magnetic field also retain good stability across a wide temperature range, and this contributes to the stability and lifespan of polymer capacitors. All the above-mentioned properties along with the simplicity and scalability of the preparation for the polymer nanocomposites make them promising for the electronics industry.

Enhanced dielectric properties of poly(vinylidene fluoride) composites filled with nano iron oxide-deposited barium titanate hybrid particles.

We report enhancement of the dielectric permittivity of poly(vinylidene fluoride) (PVDF) generated by depositing magnetic iron oxide (Fe3O4) nanoparticles on the surface of barium titanate (BT) to fabricate BT-Fe3O4/PVDF composites. This process introduced an external magnetic field and the influences of external magnetic field on dielectric properties of composites were investigated systematically. The composites subjected to magnetic field treatment for 30 min at 60 °C exhibited the largest dielectric permittivity (385 at 100 Hz) when the BT-Fe3O4 concentration is approximately 33 vol.%. The BT-Fe3O4 suppressed the formation of a conducting path in the composite and induced low dielectric loss (0.3) and low conductivity (4.12 × 10(-9) S/cm) in the composite. Series-parallel model suggested that the enhanced dielectric permittivity of BT-Fe3O4/PVDF composites should arise from the ultrahigh permittivity of BT-Fe3O4 hybrid particles. However, the experimental results of the BT-Fe3O4/PVDF composites treated by magnetic field agree with percolation theory, which indicates that the enhanced dielectric properties of the BT-Fe3O4/PVDF composites originate from the interfacial polarization induced by the external magnetic field. This work provides a simple and effective way for preparing nanocomposites with enhanced dielectric properties for use in the electronics industry.