Dielectric nanocomposites with superb high-temperature capacitive performance based on high intrinsic dielectric constant polymer

Advancements in power electronics necessitate dielectric polymer films capable of operating at high temperatures and possessing high energy density.Although significant strides have been achieved by integrating inorganic fillers into high-temperature polymer matrices,the inherently low dielectric constants of these matrices have tempered the magnitude of success.In this work,we report an innovative nanocomposite based on sulfonylated polyimide(SPI),distinguished by the incorporation of sulfonyl groups within the SPI backbone and the inclusion of wide bandgap hafnium dioxide(HfO_(2))nanofillers.The nanocomposite has demonstrated notable enhancements in thermal stability,dielectric properties,and capacitive performance at elevated temperatures.Detailed simulations at both molecular and mesoscopic levels have elucidated the mechanisms behind these improvements,which could be attributed to confined segmental motion,an optimized electronic band structure,and a diminished incidence of dielectric breakdown ascribed to the presence of sulfonyl groups.Remarkably,the SPI-HfO_(2)nanocomposite demonstrates a high charge-discharge efficiency of 95.7%at an elevated temperature of 150℃and an applied electric field of 200 MV/m.Furthermore,it achieves a maximum discharged energy density of 2.71 J/cm^(3),signalling its substantial potential for energy storage applications under extreme conditions.

Polymer nanocomposite dielectrics with high electrocaloric effect for flexible solid-state cooling devices

Nanocomposite dielectrics show great promising application in developing next generation wearable all-solidstate cooling devices owing to the possessed advantages of high cooling efficiency, light-weight and small volume without the induced greenhouse effect or serious harm to ozone layer in the exploited refrigerants. However, low electrocaloric strength in nanocomposite dielectric is severely restricting its wide-spread application because of high applied operating voltage to improve electrocaloric effect. After addressing the chosen optimized ferroelectric ceramic and ferroelectric polymer matrix in conjunction with the analysis of crucial parameters, recent progress of electrocaloric effect(ECE) in polymer nanocomposites has been considerably reviewed. Subsequently, prior to proposing the conceptual design and devices/systems in electrocaloric nanocomposites, the existing developed devices/systems are reviewed. Finally, conclusions and prospects are conducted, including the aspects of materials chosen, structural design and key issues to be considered in improving electrocaloric effect of polymer nanocomposite dielectrics for flexible solidstate cooling devices.

Improved energy storage performance of nanocomposites with Bi_(4.2)K_(0.8)Fe_(2)O_(9+δ) nanobelts

Modern electronics and electric power grids require high performance polymer-based dielectric nanocomposites.To realize large-scale applications,the energy density of nanocomposites needs to be further increased.Here,we demonstrate a remarkable improvement in energy density of poly(vinylidene fluoride)(PVDF)matrix upon the incorporation of high-k Bi_(4.2)K_(0.8)Fe_(2)O_(9+δ)(BKFO)nanobelts.High aspect ratio BKFO nanobelts can enhance the Young's moduli of the nanocomposites and increase the path tortuosity of electrical trees,which are favorable for increasing the breakdown strength of the system.Thus,the dielectric constant and breakdown strength increase simultaneously at a low volume fraction(0.35 vol%)of BKFO nanobelts,and an ultrahigh recoverable energy density of 25.4 J/cm^(3) is achieved.These results provide a strategy to develop high performance flexible high-energy-density devices.

Preparation and improved energy storage capability of nanocomposites utilizing ultrathin 2D HfO_(2)@TiO_(2)nanosheets

Polymer-based dielectrics play an important role in electrostatic capacitor by their high energy density(U_(e))and flexibility.Herein,we designed a simple high Ue polymer-based dielectrics by controlling the morphology and surface modification of inorganic fillers.To decrease the difference in dielectric properties between fillers and matrix of the nanocomposites,HfO_(2)acting as the buffer layer with high insulation and appropriate permittivity coated onto the surface of TiO_(2)nanosheets(TiO_(2)Ns)to form a core–shell structure.The introduction of HfO_(2)@TiO_(2)nanosheets(HfO_(2)@TiO_(2)Ns)makes the nanocomposite with higher dielectric permittivity and lower dielectric loss than poly(vinylidene fluoride-co-hexafluoropropylene)(P(VDF-HFP))matrix.In addition,the HfO_(2)@TiO_(2)Ns can establish an efficient barrier to limit the space charge conduction,hamper the growing electric trees,and the HfO_(2)layer with high insulation could hinder the mobility of charge carriers.The breakdown strength(Eb)of nanocomposite is superior to that of polymer matrix.A small addition of 3 wt.%HfO_(2)@TiO_(2)Ns into P(VDF-HFP)matrix can raise the Eb to 480.7MV/m and present a maximum discharged Ue of 13.9 J/cm3.This work demonstrates that it is an effective strategy to improve the Ue via designing the structure and surface state of inorganic filler simultaneously.

Compositional Effect of ZrO_2 Nanofillers on a PVDF-co-HFP Based Polymer Electrolyte System for Solid State Zinc Batteries

Composite polymer electrolytes（CPEs） comprising poly（vinilydene fluoride-hexafluoro propylene）, PVDF-coHFP and zinc triflate, Zn（CF3SO3）2 with varying concentrations of ZrO_2 nanofillers were prepared by solution casting technique with N,N-dimethyl formamide（DMF） as the common solvent. The polymer electrolyte specimen with the particular composition 75 wt% PVDF-co-HFP： 25 wt% Zn Tf ＋ 7 wt% Zr O2 showed the highest conductivity of 4.6 × 10-4 S/cm at 298 K as confirmed from impedance measurements and favored by the rich amorphous phase of the CPE revealed from room temperature X-ray diffraction analysis（XRD）. The electrical conductivity relaxation time and its distribution within the materials have been evaluated from the electric modulus M 2 and impedance Z＂ data which showed the occurrence of non-Debye type of relaxation phenomenon. The changes in the surface morphology of the CPEs were examined using scanning electron microscopy（SEM）. The electrochemical stability window of CPE is found to be 2.6 V with a thermal stability up to 300 °C. An electrochemical cell has been fabricated based on Zn/MnO_2 electrode couple under a constant load of 1 MΩ and its discharge characteristics have been evaluated.