Recently, the research group of associate professor Bi of Beijing University of Posts and telecommunications has made progress in the field of nano heterostructure enhanced dielectric properties and energy storage density of PVDF nanocomposites by CO loading of BaTiO3 and CoFe2O4 Nanoparticles "is published in the journal advanced composites and hybrid materials. The first author of the thesis is Wang Qingmin, a doctoral student of Beijing University of Posts and telecommunications, and the corresponding author is associate professor Bi Ke.
The dielectric properties of composite materials, especially flexible polymer materials, play an important role in various applications of optical and electrical devices. How to control the dielectric properties of flexible materials has been the focus of researchers for many years. In addition, in the field of energy storage films, the introduction of dielectric materials with high dielectric constant can improve the breakdown and dielectric properties of polymers at the same time. At the same time, the composite film made of polymer matrix filled with dielectric material has the advantages of flexibility, easy processing and low cost. Therefore, the preparation of composite films with appropriate dielectric constant is a research hotspot in the field of energy storage films. At present, composite films are mostly composed of single or multiple dielectric particles and polymers such as PVDF. Few researchers use heterostructure to study the dielectric and energy storage properties of flexible polymers.
The research group of associate professor BICO compounded a small amount of CoFe2O4 (CF) nanoparticles on the surface of BaTiO3 (BT) nanoparticles to form the center satellite heterostructure of bt-cf, and introduced the heterostructure into PVDF polymer materials. Due to the interface polarization and permeation, the dielectric constant and energy storage density of PVDF polymer materials are enhanced without additional loss. Schematic diagram of bt-cf / PVDF composite film preparation (Fig. 1).
Figure 1 process flow for fabric of bt-cf / PVDF nanocomposite films
A small amount of CF nanoparticles were attached to BT surface by hydrothermal synthesis to form center satellite heterostructure. Bt-cf / PVDF nanocomposite films were prepared by solution casting (Fig. 2). In the bt-cf / PVDF nanocomposite film, the bt-cf heterostructure is evenly distributed in the PVDF polymer matrix (Fig. 3), where the size of BT is 100 nm and the size of CF is 30 nm.
Figure 2 (a) TEM images of bt-cf nanocomposites. (b) SEM images of bt-cf nanocomposites. (c) cross sectional SEM images of the bt-0.07cf/pvdf film. Size distributions of (d) CF and (E) BT particles
Fig. 3 EDS element mapping images of the bt-cf / PVDF nanocomposites with 7wt.% CF fillers
The dielectric constant of bt-cf / PVDF nanocomposite film is closely related to the amount of CF nanoparticles. The fine adjustment of the dielectric constant of the flexible film is realized by controlling the amount of CF nanoparticles. Moreover, the addition of CF nanoparticles did not increase the dielectric loss (Fig. 4). The relationship between the energy storage density of bt-cf / PVDF film and the electric field proves that a small amount of CF nanoparticles increases the energy storage density. The relationship between the energy storage efficiency of bt-cf / PVDF film and the electric field proves that the energy storage efficiency is enhanced by adding a small amount of CF nanoparticles (Fig. 5).
Figure 4 (a) dielectric constant and (b) dielectric loss of the bt-cf / PVDF nanocomposite films with variable CF mass fractions
Figure 5 (a) discharged storage energy density and (b) efficiency under different external electric field for bt-cf / PVDF nanocomposite films with variable CF mass fractions
The relationship between the breakdown strength and energy storage density and the addition amount of CF nanoparticles proves that the addition of a small amount of CF nanoparticles increases the breakdown field strength and energy storage density of the composite films. This is because the introduction of CF nanoparticles with dielectric constant values between BT and PVDF improves the compatibility between BT and PVDF polymers, improves the dielectric constant and breakdown field strength of composite films, and thus improves the energy storage density of composite films (Fig. 6).
Figure 6 breakdown strength and discharged storage energy density of bt-cf / PVDF nanocomposite films with variable CF mass fragments
Therefore, by controlling the amount of CF in the bt-cf center satellite heterostructure, the dielectric constant of the flexible film can be adjusted. At the same time, the energy density and efficiency of the composite film are improved by adding a small amount of CF nanoparticles. Due to the addition of magnetic CF particles, further research on the composite films with heterogeneous nanostructures is expected to achieve the magnetic control of dielectric properties. This work provides a new idea for the design of flexible materials for wearable optoelectronic devices.
Paper link:
https://doi.org/10.1007/s42114-020-00138-4
Brief introduction of the research group:
The main research directions of the research group are functional composite materials and electromagnetic metamaterials. Relevant research results are published in advanced functional materials, nano energy, advanced optical materials, photonics research, scripta materials, applied physics letters and other domestic and foreign journals.
1. Jianchun Xu, Ke Bi*, Ru Zhang, Yanan Hao, Chuwen Lan, Klaus Mcdonald-Maier, Xiaojun Zhai, Zidong Zhang*, Shanguo Huang*, “A Small-divergence-angle Orbital Angular Momentum Metasurface Antenna”, Research, 2019, 2019: 9686213.
2. Limin Guo, Caifu Zhong, Jinqing Cao, Yanan Hao, Ming Lei, Ke Bi*, Qijun Sun*, Zhonglin Wang*, “Enhanced photocatalytic H2 evolution by plasmonic and piezotronic effects based on periodic Al/BaTiO3 heterostructures”, Nano Energy, 2019, 62: 513-520.
3. Chuwen Lan, He Ma, Manting Wang, Zehua Gao*, Kai Liu, Ke Bi*, Ji Zhou, and Xiangjun Xin*, “Highly Efficient Active All-Dielectric Metasurfaces Based on Hybrid Structures Integrated with Phase-Change Materials: From Terahertz to Optical Ranges”, ACS Applied Materials & Interfaces, 2019, 11(15): 14229-14238.
4. Ke Bi, Daquan Yang, Jia Chen, Qingmin Wang, Hongya Wu, Chuwen Lan*, Yuping Yang, “Experimental demonstration of ultra-large-scale terahertz all-dielectric metamaterials”, Photonics Research, 2019, 7(4): 457-463.
5. Limin Guo, Caifu Zhong, Li Shi, Licheng Ju, Xiaohui Wang, Daquan Yang, Ke Bi*, Yanan Hao*, Yang Yang*, “Phase and Defect Engineering of MoS2 Stabilized in Periodic TiO2 Nanoporous Film for Enhanced Solar Water Splitting”, Advanced Optical Materials, 2019, 7(5): 1801403.
6. L. M. Guo, J. N. Deng, G. Z. Wang, Y. N. Hao, K. Bi*, X. H. Wang*, Y. Yang*, “N, P-doped CoS2 Embedded in TiO2 Nanoporous Films for Zn-Air Batteries”, Advanced Functional Materials, 2018, 28(42): 1804540.
7. K. Bi, M. H. Bi, Y. N. Hao*, W. Luo, Z. M. Cai, X. H. Wang*, Y. H. Huang*, “Ultrafine core-shell BaTiO3@SiO2 structures for nanocomposite capacitors with high energy density”, Nano Energy, 2018, 51: 513-523.
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