With the cross-regional electric network development and the voltage level improvement, the construction of ultra-high-voltage (UHV) electricity transmission is inseparable from the insulation support devices. Meanwhile, threatened by global climate change, renewable energy power generation and applications are being vigorously developed around the world, such as offshore wind power and electric vehicles, which have become important strategic emerging industries. In this context, rising challenges and tasks are posed for high-voltage dielectric materials. Insulators require higher electrical breakdown strength, which can greatly reduce the size and weight of power equipment. Electrostatic energy storage devices require dielectric materials with higher energy density, efficiency, stability, etc.
Since the concept of nano-dielectrics is first proposed by T. J. Lewis in 1994, numerous efforts have shown that the incorporation of nanoparticles could significantly improve the electrical, thermal, and mechanical properties of dielectric materials due to its nano “interface" effect is more vital than itself structure. Nano-dielectrics are one of the most promising candidates for the advanced functional insulation and electrostatic energy storage dielectrics. However, the performance modification mechanism is not sufficiently clear due to the lack of advanced and refined characterization methods, , especially for the intricate electrical breakdown behavior. The dispersibility conundrum in large-scale production is a major obstacle to its practical applications since its high surface activity is prone to agglomeration. Performance improvement in one aspect performance is inevitably at the expense of other aspects. In one word, the lack of systematic exploration and cognition of the change laws and physical mechanism has led to a failure to achieve rational construction, regulation and prediction.
In response to this problem, Prof. Yu Wang, State Key Laboratory of Power Transmission Equipment & System Security and New Technology, and the School of Electrical Engineering, Chongqing University, carry out a series of work on the application of Co3O4 nanomaterials in liquid and solid dielectric, and innovatively proposed P(VDF-HFP)-based nanosieves composites film. The electric filed cavity array and sub-macro potential trap array are induced by the unique mesoporous structure of nano-sieves in the outer interface layer under a high external electric field modulating the free carriers’ transport. The combination of sub-macro potential trap array with intrinsic defect traps on the Co3O4 active surface diminishes high-speed moving ions or electrons in the insulating dielectric, hinders the discharge channels’ formation, and hugely improves the breakdown resistance of the nanocomposite films. This resulted in a breakdown strength of 803 MV/m for the nanosieves/P(VDF-HFP) film, an 80% increase relative to the pure film of 445 MV/m. The breakdown modification effect is superior to other state-of-art nano-dielectrics, and by some distance. The corresponding energy storage density reaches 41.6 joules per cubic centimeter, with an efficiency of 90%. The distribution and size of the sieve holes can regulate the trap scatter and electric field distortion. This work can provide a certain reference and experience for other investigators on nanodielectrics, especially in the aspect of nanomaterial structure design. The combination of density functional theory and finite element simulation is beneficial to reveal the intricate continuous breakdown behavior mechanism from macroscopic to microscopic. It is beneficial to develop advanced materials for next-generation high-voltage dielectrics.
Related work was funded by the National Natural Science Foundation of China, the Thousand Young Talents Program of the Chinese Central Government and Project 111, as well as the support of the Department of Chemistry and Centre for Scientific Modeling and Computation (Chinese University of Hong Kong) and the School of Chemistry and Chemical Engineering (Chongqing University).
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