氧化物纳米夹层聚酰亚胺的原位制备与高温介电性能研究

IN-SITU PREPARATION AND HIGH-TEMPERATURE DIELECTRIC PROPERTIES OF OXIDE NANOSANWICH POLYIMIDE COMPOSITES

邓星磊

11849048

硕士

材料物理与化学

汪宏

2020-05-27

2020-07-01

哈尔滨工业大学

深圳

聚合物电介质以其柔性、轻质、高击穿强度、易于加工等众多优点而被广泛使用在介电储能领域。双向拉伸聚丙烯薄膜（BOPP）作为当下薄膜电容器最主要的介质材料，虽然具备优异的介电性能，但其允许的工作温度低于 105℃，远远无法满足当下电动汽车、航空航天等领域对于电容元器件的高温需求，故而研发可在高温下（≥150℃）稳定使用的介电薄膜材料已经迫在眉睫。本论文采用高效工艺——离子交换法，聚酰亚胺（PI）经过表面水解、离子交换、再亚胺化等步骤后，宽带隙氧化物被原位生长在 PI 的上下表面，制备出具有三明治结构的氧化物纳米夹层复合材料，该材料明显不同且优于以往三明治结构聚合物复合薄膜。分析 FTIR 谱可知，水解前后、亚胺化前后 PI 表面基团的吸收峰发生了明显的变化，证实了水解与亚胺化过程的发生。再通过 EDS、XPS 等表征手段，确认了所生长纳米层的物质属性，证实了金属离子均形成相应的氧化物。此外，SEM 表征表明氧化物层与聚合物基体结合紧密，自身致密，且厚度均匀可被精确调控。其后，本论文系统研究了氧化物纳米层的厚度与带隙宽度对复合材料的高温介电性能与储能性能的影响。可以发现，250℃时氧化物夹层 PI 复合材料介电常数随频率上升的同时，介质损耗明显下降。复合薄膜的介电性能随纳米夹层厚度增加先上升而后下降，存在明显的极值关系。值得注意的是，宽带隙的MgO（~7.8 eV）夹层可显著降低复合材料在高温下的漏电流，250℃、125 MV/m时复合薄膜的漏电流密度从 PI 对应的 1.75×10 -5 A/cm 2 下降到 7.65×10 -8 A/cm 2 。介电性能的全面提升使得复合薄膜的储能性能得到了极大的改善，如 250℃时MgO 夹层 PI 复合材料储能效率在 90%以上的最大储能密度达到了 4.65 J/cm 3 ，是相同情况下 PI 储能密度的 7.5 倍。此外，宽带隙的 ZrO 2 （~5.2 eV），SrO（~6.9 eV）也可显著降低 PI 基体在高温高场下的漏电流，从而提高复合薄膜在高温下的储能效率和密度。通过对比三种氧化物纳米夹层 PI 复合薄膜，可以发现，聚合物的高温电容性能与氧化物层的带隙宽度直接相关，其中带隙最宽的 MgO 对应的复合材料的绝缘性能最好，相应的储能性能也最好。宽带隙材料可以显著提高电极与介质之间的能级势垒，有效抑制高温高场下电极电荷的注入。综上所述，采用离子交换法制备的绝缘层夹层结构复合材料，实现了高温下储能密度和储能效率的同时大幅度提高，从而有望省略传统的冷却系统，更有利于器件轻量化和小型化。此外，这项工作也为制备应用于特种环境的高性能聚合物电介质提供了一种新的思路。

Polymer dielectrics are widely used in the field of dielectric energy storage due to their flexibility, lightweight, higher breakdown strength, ease of processing. Biaxially-oriented Polypropylene (BOPP) is the most important dielectric material for film capacitors. Although BOPP has excellent dielectric performance, its allowable operating temperature is lower than 105℃, which is far from meeting the current high temperature demand for capacitor components in electric vehicles, aerospace and other fields. Therefore, it is urgent to develop polymer dielectric which can be used stably at high temperature(≥150℃).In this paper, a unique process - Ion Exchange Method is utilized. After surface hydrolysis, ion exchange, heat treatment and reimination of polyimide (PI), wideband gap oxides are grown on the upper and lower surfaces of PI in situ. The oxide nanosandwich composite with sandwich structure was prepared, which was obviously different and better than the previous sandwich structure polymer composite films. Through the analysis of FTIR, it can be seen that the absorption peak of PI surface groups before and after hydrolysis and before and after imination has changed significantly, which confirms the occurrence of hydrolysis and imination. Then, EDS, XPS and other characterization methods were used to confirm the material properties of the growth nanolayer and confirm that the metal ions all formed corresponding oxides. In addition, the SEM images of the composite also confirmed that the oxide layer was tightly bound to the polymer matrix. The oxide layer is dense without hole defects and its uniform thickness can be exactly regulated. Subsequently, the effects of the thickness and band gap of the oxide nanolayer on the dielectric properties and energy storage properties of the composite film were systematically studied. It can be found that the dielectric loss of oxide nanosandwich PI composite films decreases obviously when the dielectric constant increases with frequency. The dielectric properties of the composite films increased first and then decreased with the increase of oxide thickness. What notable is the MgO (~ 7.8 ev) nanolayer with wide band gap can significantly reduce the leakage current of the composite material at high temperature. At 250℃ and 125 MV/m, the leakage current density of MgO nanosanwich PI composite decreases from 1.75×10 -5 A/cm 2 corresponding to PI to 7.65×10 -8 A/cm 2 . The comprehensive improvement of dielectric properties has greatly improved the energy storage performance of the composite film. At 250℃, the maximum discharge energy density of MgO nanosanwich PI composite with efficiency above 90% reaches 4.65 J/cm 3 , which is 7.5 times that of PI. In addition, wide band gap ZrO2 (~5.2 eV) and SrO (~6.9 eV) can also significantly reduce the leakage current of PI under high temperature and high field, thus improving the energy storage efficiency and energy storage density of composite films at high temperature. By horizontally comparing the three oxide nanosanwich PI composite, it can be found that the high-temperature capacitance performance of composites is directly related to the band gap width of the oxide layer. Among them, the composites applied MgO of widest band gap has the best insulation performance and the best energy storage performance. Wideband gap materials can greatly increase the energy level barrier between electrode and medium and effectively inhibit the injection of electrode charge at high-temperature and high electric field.In summary, the insulating layer nanosandwich polymer structure prepared by the ion exchange method achieves a significant increase in energy storage density and energy storage efficiency at high temperature, can omit the traditional cooling system, and is more conducive to light weight and miniaturization of devices. In addition, this work offers a new idea for the preparation of high-performance polymer dielectric used in special environments.

离子交换法 原位制备 高温 聚酰亚胺

Ion exchange In-situ High temperature Polyimide

中文

联合培养

南方科技大学

邓星磊. 氧化物纳米夹层聚酰亚胺的原位制备与高温介电性能研究[D]. 深圳. 哈尔滨工业大学,2020.