Qibin Yuan

Significantly Enhanced Breakdown Strength and Energy Density in Sandwich‐Structured Barium Titanate/Poly(vinylidene fluoride) Nanocomposites

Sandwich-structured BaTiO3 /poly(vinylidene fluoride) (PVDF) nanocomposites are successfully prepared by the solution-casting method layer by layer. They possess both high breakdown strength and large dielectric polarization simultaneously. An ultra-high energy-storage density of 18.8 J cm(-3) can be achieved by adjusting the volume fraction of ceramic fillers: this is almost three times larger than that of pure PVDF.

Compositional tailoring effect on electric field distribution for significantly enhanced breakdown strength and restrained conductive loss in sandwich-structured ceramic/polymer nanocomposites

Compared to conventional single-layered thin films, spatial organization of the polymer matrix and ceramic nanofillers into three-dimensional sandwich structures is a promising route to dielectric materials for enhanced energy storage properties (ESPs) that enable the dielectric capacitors for a number of applications in advanced electronic and electrical power systems. In this study, a systematic study of the sandwich-structured ceramic/polymer nanocomposites composed of pristine poly(vinylidene fluoride) (PVDF) as the middle layer and barium titanate (BT)/PVDF nanocomposites as two outer layers has been presented. Experimental results indicate that the ESP of the sandwich BT/PVDF composites, including breakdown strength, discharge efficiency, and energy density, can be significantly improved by tailoring the BT content. As verified by finite element simulations, the ESP of sandwich films is mainly governed by the electric field distribution owing to the introduction of high-dielectric-constant BT into the layered structures. The rational design of BT content leads to the electric field distribution capable of enhancing the dielectric strength and reducing the electrical conductivity for high energy density and improved discharge efficiency. An ultrahigh energy density of 16.2 J cm−3 has been achieved at the breakdown strength of 410 MV m−1 in the optimized sandwich-structured nanocomposites. The understanding of the influence of filler content on electric field distribution achieved in this work provides a viable way for exploiting novel layered dielectrics with exceptional ESPs for energy storage devices.

Ultrahigh electric displacement and energy density in gradient layer-structured BaTiO3/PVDF nanocomposites with an interfacial barrier effect

Negative environmental consequences of non-renewable energy resources and limited reserves of fossil fuel supplies have spurred the development of renewable and environmentally friendly energies as well as advanced energy conversion and storage technologies. Among the currently available electrical energy storage devices, electrostatic capacitors possess highest power density because of their fast charge–discharge capability. However, their low energy densities limit their applications. Herein, we demonstrated a remarkable improvement in the breakdown strength and energy density of a group of three-tiered ferroelectric polyvinylidene fluoride (PVDF) films with the content of barium titanate (BT) nanoparticle fillers gradually increasing layer by layer. It was found that a weak electric field region could be formed as an efficient insulating barrier to hamper the development of electrical trees via tailoring of the gradient of filler contents. Optimization of the composite compositions guided by simulation studies resulted in a greatly enhanced breakdown strength of 390 MV m−1 with an ultrahigh maximum polarization of 12.5 μC cm−2, and thus, an impressive discharged energy density of 16.5 J cm−3 was achieved. This successful structural design provides a new paradigm to explore polymer nanocomposites having excellent dielectric and capacitive properties, which can also be applied to other materials in electric and electrical applications.

Relaxor ferroelectric 0.9BaTiO3–0.1Bi(Zn0.5Zr0.5)O3 ceramic capacitors with high energy density and temperature stable energy storage properties

A relaxor ferroelectric ceramic for high energy storage applications based on 0.9BaTiO3–0.1Bi(Zn0.5Zr0.5)O3 (0.9BT–0.1BZZ) was successfully fabricated via a conventional solid-state method. The sintered samples have a perovskite structure with a pseudocubic phase, showing a moderate dielectric constant (500–2000), low dielectric loss (tan δ < 0.15) and highly diffusive and dispersive relaxor-like behavior. The weak dielectric nonlinearity exhibits a dielectric constant change of ∼10% as the bias electric field increases from 0 kV cm−1 to 40 kV cm−1. Extra slim polarization–electric field loops accompanying the slow decrease of breakdown strength from 266.5 kV cm−1 to 217.7 kV cm−1 are observed in a measured temperature range of 30–150 °C. A maximum energy density of 2.46 J cm−3 was obtained at the electric field of 264 kV cm−1 close to the breakdown strength at ambient temperature. Temperature stability of both energy density and energy efficiency exists in a wide temperature range, which makes BT–BZZ ceramics promising candidates for high power electric applications.

Tuning conductivity and magnetism of CuFe2O4 via cation redistribution

Copper ferrite polycrystalline samples with different cation distributions are prepared via different thermal treatments. Combined studies including X-ray diffraction, PPMS, Mossbauer spectroscopy, and complex impedance spectroscopy show both conductivity and magnetism keep increasing, accompanied by an obvious phase transition from tetragonal symmetry (I41/amd) to cubic symmetry (Fdm) as Cu2+ ions migrate from Oh sites to Td sites. The changes of structural, electrical and magnetic properties due to the cation redistribution are also investigated by spin-polarized density functional theory. The simulated results indicate that the semiconducting band structure gradually transforms into a metallic band structure as Cu2+ ions migrate from Oh sites to Td sites. The conductivity and magnetism will increase during the same process, which matches well with the experimental observations. This work demonstrates that the cation redistribution in copper ferrite is effective in controlling both conductivity and magnetism, which can be further exploited in applications using interacting electron/spin systems.

Microstructure and dielectric properties of Ti0.995(In0.5Nb0.5)0.005O2/SrO-B2O3-SiO2 glass-ceramics for energy storage

The Ti0.995(In0.5Nb0.5)0.005O2/SrO-B2O3-SiO2 glass-ceramics for dielectric energy storage applications were prepared and investigated. The optimal microstructure of the glass-ceramics has been achieved by adopting Ti0.995(In0.5Nb0.5)0.005O2 with colossal dielectric constant as grains and SrO-B2O3-SiO2 glass with high resistivity as grain boundaries. After the introduction of SrO-B2O3-SiO2 glass, it was found that the breakdown strength increased several times higher than that of pristine Ti0.995(In0.5Nb0.5)0.005O2 ceramics. Meanwhile, the energy density increased more than four times and energy efficiency is more than one time. An outstanding energy density of 1.55 J/cm3 and a high energy efficiency of 70% for Ti0.995(In0.5Nb0.5)0.005O2 ceramic with 2 wt%% SrO-B2O3-SiO2 glass were obtained at an electric field of 328.3 kV/cm, suggesting that this kind of glass-ceramic could be an attractive candidate for energy storage applications.

Nanocomposites: Significantly Enhanced Breakdown Strength and Energy Density in Sandwich‐Structured Barium Titanate/Poly(vinylidene fluoride) Nanocomposites (Adv. Mater. 42/2015)

On page 6658, H. Wang and co-workers report a sandwich-structured BaTiO3 /poly(vinylidene fluoride) (PVDF) nanocomposite with an ultrahigh energy density of 18.8 J cm(-3) . The electric field distribution and polarization in this structure can be optimized by adjusting the volume fraction of the ceramic fillers in different layers, resulting in a high breakdown strength and large dielectric polarization simultaneously.