Ming-Sheng Zheng

1D/2D Carbon Nanomaterial‐Polymer Dielectric Composites with High Permittivity for Power Energy Storage Applications

With the development of flexible electronic devices and large-scale energy storage technologies, functional polymer-matrix nanocomposites with high permittivity (high-k) are attracting more attention due to their ease of processing, flexibility, and low cost. The percolation effect is often used to explain the high-k characteristic of polymer composites when the conducting functional fillers are dispersed into polymers, which gives the polymer composite excellent flexibility due to the very low loading of fillers. Carbon nanotubes (CNTs) and graphene nanosheets (GNs), as one-dimensional (1D) and two-dimensional (2D) carbon nanomaterials respectively, have great potential for realizing flexible high-k dielectric nanocomposites. They are becoming more attractive for many fields, owing to their unique and excellent advantages. The progress in dielectric fields by using 1D/2D carbon nanomaterials as functional fillers in polymer composites is introduced, and the methods and mechanisms for improving dielectric properties, breakdown strength and energy storage density of their dielectric nanocomposites are examined. Achieving a uniform dispersion state of carbon nanomaterials and preventing the development of conductive networks in their polymer composites are the two main issues that still need to be solved in dielectric fields for power energy storage. Recent findings, current problems, and future perspectives are summarized.

Enhanced breakdown strength of poly(vinylidene fluoride) utilizing rubber nanoparticles for energy storage application

A kind of rubber nanoparticles, methyl methacrylate-butadiene-styrene (MBS), was applied into poly(vinylidene fluoride) (PVDF) matrix to fabricate MBS/PVDF composite films. Uniform dispersion and good compatibility of MBS in the matrix were observed. We found that the entanglement state between MBS nanoparticles and random chains of PVDF could diminish gaps in the matrix, which is helpful for high breakdown strength. The composite film with 12 vol. % MBS showed the maximum breakdown strength of 535 MV/m and the high energy density of 9.85 J/cm3, which were 1.7 times and about 2.2 times higher than pure PVDF film, respectively.

Polyurethane induced high breakdown strength and high energy storage density in polyurethane/poly(vinylidene fluoride) composite films

A series of composites blending thermoplastic polyurethane (TPU) with poly(vinylidene fluoride) (PVDF) were prepared in this work to realize a high energy storage density. Low loading of TPU (<3 vol. %) shows a uniform dispersion state in the PVDF matrix. We demonstrate that the incorporation of TPU induces high breakdown strength which results in promoted energy storage performance. In addition, the influence of the different TPU hardnesses (65, 75, and 85) on the breakdown strength of TPU/PVDF composites was also investigated. Finally, a maximum value up to 537.8 MV/m at 3 vol. % TPU with a hardness of 65 was obtained, which led to a high energy density of 10.36 J/cm3.

Nonlinear electrical conductivity of ionic liquid modified WS2/EPDM field grading material

In this work, a small amount of ionic liquids (ILs, 1-vinyl-3-ethylimidazolium tetrafluoroborate) was used to modify tungsten disulfide (WS2), and then, the modified WS2 was mixed with ethylene propylene diene monomer (EPDM) to obtain IL-WS2/EPDM composites with different IL contents. The content of WS2 in composites was determined from the result of our previous work. The nonlinear electrical conductivity of composites at 25 °C, 50 °C, and 80 °C was measured and analyzed subsequently. A small amount of ILs has an influence on the nonlinear property of composites, and the inflection point of the ternary composite can be controlled by changing IL contents. The direct current (DC) breakdown strength and thermal conductivity of composites were also measured and researched. Addition of ILs would decrease the breakdown strength of IL-WS2/EPDM composites.In this work, a small amount of ionic liquids (ILs, 1-vinyl-3-ethylimidazolium tetrafluoroborate) was used to modify tungsten disulfide (WS2), and then, the modified WS2 was mixed with ethylene propylene diene monomer (EPDM) to obtain IL-WS2/EPDM composites with different IL contents. The content of WS2 in composites was determined from the result of our previous work. The nonlinear electrical conductivity of composites at 25 °C, 50 °C, and 80 °C was measured and analyzed subsequently. A small amount of ILs has an influence on the nonlinear property of composites, and the inflection point of the ternary composite can be controlled by changing IL contents. The direct current (DC) breakdown strength and thermal conductivity of composites were also measured and researched. Addition of ILs would decrease the breakdown strength of IL-WS2/EPDM composites.

Research of nano WS 2 filled composite used as field grading material

Nano size semiconducting particles are the most commonly used fillers in field grading material to homogenize the inner electric field distribution. In this work, commercially purchased WS2 and the exfoliated ones were used as filler into EPDM to fabricate WS2/EPDM composites with different WS2 loading. Nonlinear electric conductivities were measured at 25 50 and 80 respectively. The influence of temperature on the conductivity was introduced to analysis the conductivity changes of the WS2/EPDM composite at higher temperature. Direct current breakdown strength was also studied. Tests result shown that the properties of exfoliated WS2 filled composite had more regular change and the best performance. It turned out that uniform size and morphology of filler will be helpful for the properties of composite. The nonlinear conductivity performance created the possibility of using WS2 as nonlinear conductivity filler in field grading material.

Enhanced dielectric properties of polyvinylidene fluoride nanocomposites via calcium copper titanate nanofibers

Polymer matrix nanocomposites with high permittivity attract more and more attention due to their flexibility, easy processing, low cost and wide applications of electronic industry. However, the permittivity of the majority of polymers are quite low. The most effective method is combining polymers and high-permittivity inorganic ceramics (such as TiO2, barium titanate, lead zirconate titanate and etc.). Calcium copper titanate (CCTO) is a promising candidate for fabrication high dielectric constant composites owing to its giant (>105) and stable permittivity over a very wide temperature range from 100 K to 500 K. In this research, the one-dimensional CCTO nanofibers (CCTO-NFs) with high aspect ratio were prepared by a novel strategy combining sol-gel method and electrospinning technology. The diameter of CCTO nanofibers is less than 300 nm. The morphology of CCTO nanofibers was researched by thermogravimetry-differential thermal analysis (TG-DTA) and scanning electron microscope (SEM). Based on the CCTO nanofibers, a novel composite with polyvinylidene fluoride (PVDF) matrix was prepared via the solution casting method. The permittivity of CCTO-NFs/PVDF composites was measured depending on different fillers loading. The results showed that CCTO nanofibers can improve the dielectric property of the PVDF composites effectively and the permittivity of composites increased with the increasing CCTO nanofibers loading. The PVDF nanocomposite with a low loading (7 vol%) exhibits good dielectric property. In addition, the permittivity of 22, which is about 2.4 times of neat PVDF, was obtained with 20 vol% loading of CCTO nanofibers/PVDF composite. This work indicates that CCTO nanofibers are potential fillers to develop the dielectric property of polymer composites and provide a new possibility to fabricate high-permittivity polymer nanocomposites.