Jiayang Han,Fuxing Zhai,Dingyu Zheng,Lixin Xu,Huijian Ye
High-temperature film capacitor with large energy density and charge-discharge efficiency is urgent to be developed to fulfill the requirement of energy storage system. In this work, a semi-crystal polyimide (PI) with the fluorine-containing pendant group has been synthesized, and the high-temperature electrical displacement and breakdown behavior of PI film are investigated systematically. The evolution of crystal structure in PI film is evaluated by XRD and density function theory simulation. The lattice distortion caused by the large pendant group contributes to the free volume inside PI bulk. The optimized PI film demonstrates an energy density of 8.0 J cm-3 with a charge-discharge efficiency of 90% at 500 MV m-1 and 150 °C. The ultrahigh energy storage capability under high temperature is attributed to the combination of broad bandgap and free volume effect in the condense state. The presence of –CF3 effectively hinders the diffusion of charge carriers under the action of the applied field, which results in the enhanced dielectric reliability. This semi-crystal PI film with fluorinated pendant group illustrates the improved high-temperature energy storage performance, which sheds a light on the exploration of the depression of energy loss for polymer film capacitor.
Yang Zheng,Changbo Wang,Wei Liu,Xinfang Zhang,Shuangkun Zhang,Zhanpeng Wu
Poly(diaryloxy)phosphazene (PDAP) possesses good ablative resistance properties, owing to unique charred layers formed during ablation, showing promising applications in aerospace thermal protection. However, the high glass-transition temperature (Tg) of PDAP insulations limits the application in elastomeric heat-shielding materials (EHSMs) that is a need for meeting the growing requirements of solid rocket motors such as low-temperature storage and application. In this work, we focused on improving the low-temperature resistance and ablation resistance of polyphosphazene composites. A class of ablative-resistant poly(octafluoropentyloxy/butoxy/aryloxy)phosphazene (PFBAP) with low Tg was prepared by introducing flexible octafluoropentyloxy side groups into poly(butoxy/aryloxy)phosphazene (PBPP). The results showed that the octafluoropentyloxy side groups could improve the thermal oxidative stability, flame retardancy, and interfacial interaction of polyphosphazene. Compared with PBPP composites, the values of linear ablation rate, mass ablation rate, and charring ablation rate of PFBAP 2 (containing 11.86% octafluoropentyloxy side groups) composites were reduced by 65, 34, and 25%, respectively. The study on the ablation mechanism of PFBAP composites shows that the introduction of fluorinated side groups can not only improve the charring degree of insulations during ablation but also exert a flame-retardant effect in the gaseous phase, resulting in a denser and more coherent charred layer. This work demonstrates a way to develop low-temperature and ablation-resistant polyphosphazene materials for potential thermal protection in the aerospace industry.
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