A novel polymer alloy made from common plastics demonstrates exceptional high-temperature performance, opening new possibilities for advanced applications.
In the quest for lighter, safer, and more efficient electronics—ranging from electric vehicles to large-scale energy systems—one component plays a crucial role: the polymer capacitor. These capacitors are essential for delivering quick bursts of energy and stabilizing power, unlike batteries, which provide slower, steady energy. However, conventional polymer capacitors struggle to operate at temperatures above 212°F, which can easily occur near car engines in summer or in heavily loaded data centers.
A team of researchers at Penn State has now developed a new polymer material that can store four times the energy of standard capacitors and withstand temperatures up to 482°F. The findings were published on February 18 in Nature.
“Progress in electric vehicles, data centers, space technologies, and other applications is often limited by the performance of polymer capacitors,” said Li Li, a postdoctoral researcher in Penn State’s Department of Electrical Engineering. “Traditional capacitors require cooling to function reliably. Our design solves this problem while delivering four times the energy—or the same energy in a device one-fourth the size.”
Capacitors differ from batteries in that they store less energy but can release it almost instantaneously. For instance, a smartphone relies on its battery for continuous power, but extra features like the camera flash need a rapid energy surge, which is provided by a capacitor.
The challenge with conventional polymer capacitors is that their polymer chains have relatively low glass-transition temperatures. Above this temperature, the polymer becomes brittle, leading to failure. Polymers are versatile materials, found naturally or synthesized for uses ranging from thin films to thick plastics. At the molecular level, the structure of mixed polymers can create interfaces that allow charge leakage, a problem that worsens at higher temperatures.
The Penn State team addressed this by combining two high-performance, commercially available polymers: PEI, often used in pharmaceuticals and originally developed by General Electric, and PBPDA, a polymer known for high thermal resistance and electrical insulation. By carefully controlling the mixing process, the polymers self-assembled into three-dimensional structures that formed stable thin films. The key was managing the polymers’ immiscibility—their natural tendency not to mix—similar to oil and water separating into distinct layers.
“Adjusting the ratios changes performance, much like how metal alloys behave,” said Guanchun Rui, a postdoctoral researcher in electrical engineering and materials science at Penn State. “By optimizing immiscibility, we created the first polymer alloy with these exceptional properties.”
The result is remarkable: while each polymer individually had a dielectric constant (K) below 4, the alloy achieved a K of 13.5, remaining stable from -148°F to 482°F. The improved performance comes from the nanostructure of the material, which allows the polymer chains to flex and accommodate energy without breaking. The self-assembled interfaces reduce charge leakage, enhancing the capacitor’s efficiency.
“This approach uses inexpensive, commercially available materials and can be scaled up easily,” Li explained. “It offers a cost-effective solution to energy challenges, enabling either more compact devices or higher power in existing sizes.”
The team is now working to commercialize the technology and has filed a patent for the polymer capacitors. Other Penn State contributors include Wenyi Zhu, Zitan Huang, Yiwen Guo, Zi-Kui Liu, Ralph H. Colby, Seong H. Kim, and Qing Wang. Collaborators from Brookhaven National Laboratory and North Carolina State University also contributed.
This research received support from the Office of Naval Research, the U.S. National Science Foundation, Axalta Coating Systems, and the Harvey F. Brush Chair endowment at Penn State College of Engineering.