Aromatic Polyurea for High Temperature High Energy Density Capacitors
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Aromatic Polyurea for High Temperature High Energy Density Capacitors Yong Wang1, Xin Zhou1, Minren Lin2, Sheng-Guo Lu2, Junhong Lin3, and Q. M. Zhang1,2 1
Department of Electricalal Engineering, The Pennsylvania State University, Materials Research Institute, The Pennsylvania State University, 3 Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802 2
ABSTRACT We investigate aromatic polyureas which can be fabricated in the form of thin films through CVD. It was found that the polymer possesses a flat dielectric response (k~ 4.2 and loss 800MV/m), high energy density (>12J/cm3) and high efficiency suggest this polymer can be a good candidate material for high temperature energy storage capacitors. Breakdown strength was analyzed with Weibull model over a broad temperature range (25oC ~180oC). Experimental results indicate that aromatic polyurea is more like a nonpolar linear dielectric material because of its highly cross-linked structures. The experiment results further show that this polymer maintains its high performance even at high temperatures. INTRODUCTION Capacitors with high electric energy density are highly desirable for a broad range of modern power electronic systems such as medical devices, hybrid electric vehicles (HEV), and power weapon systems [1]. Due to their high breakdown field and graceful failure, which lead to high device reliability, dielectric polymers are presently the primary choice for high energy density capacitors. Recently, very high energy density (>10J/cm3) have been achieved in polyvinylidene fluoride (PVDF) based copolymers and terolymers [2]. However, all these high energy density polymers can only work under temperatures below 125oC. They are not suitable for harsh environment applications such as HEVs, power electric weapons and aerospace systems which require operating temperature at least 150oC [3]. For high temperature polymer capacitors, polyimide is currently the most commonly used polymer material. Two other high temperature polymers Teflon perfluoroalkoxy (PFA) and poly-P-xylene (PPX), were also studied by some researchers for high temperature capacitors [4]. But all these high temperature materials do not have high energy density because of their low dielectric constants and low breakdown fields (
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