Society's growing demand for high-voltage electrical technologies - including pulsed power systems, cars and electrified aircraft, and renewable energy applications - requires a new generation of capacitors that store and deliver large amounts of energy under intense thermal and electrical conditions. Researchers at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and Scripps Research have now developed a new polymer-based device that efficiently handles record amounts of energy while withstanding extreme temperatures and electric fields. The device is composed of materials synthesized via a next-generation version of the chemical reaction for which three scientists won the 2022 Nobel Prize in Chemistry.
Polymer film capacitors are electrical components that store and release energy within an electric field using a thin plastic layer as the insulating layer. They make up 50% of the global high voltage capacitor market and offer advantages including light weight, low cost, mechanical flexibility, and robust cyclability. But state-of-the-art polymer film capacitors decrease dramatically in performance with increasing temperature and voltages. Developing new materials with improved tolerance for heat and electric fields is paramount; and creating polymers with near-perfect chemistry offers a way to do so.
"Our work adds a new class of electrically robust polymers to the table. It opens many possibilities to the exploration of more robust, high performing materials."
- Yi Liu
"Our work adds a new class of electrically robust polymers to the table. It opens many possibilities to the exploration of more robust, high performing materials," said Yi Liu, a chemist at Berkeley Lab and senior author on the Joule study reporting the work. Liu is the Facility Director of Organic and Macromolecular Synthesis at the Molecular Foundry, a DOE Office of Science user facility at Berkeley Lab.
In addition to remaining stable when subjected to high temperatures, a capacitor needs to be a strong "dielectric" material, meaning that it remains a strong insulator when subjected to high voltages. However, few known materials systems exist that deliver both thermal stability and dielectric strength. This scarcity is due to a lack of reliable and convenient synthesis methods, as well as a lack of fundamental understanding of the relationship between polymer structure and properties. "Improving the thermal stability of existing films while retaining their electrical insulating strength is an ongoing materials challenge," said Liu.
A long-term collaboration between researchers at the Molecular Foundry and Scripps Research Institute has now met that challenge. They used a simple and quick chemical reaction developed in 2014 that swaps out fluorine atoms in compounds that contain sulfur-fluoride bonds, to yield long polymer chains of sulfate molecules called polysulfates. This Sulfur-Fluoride Exchange (SuFEx) reaction is a next-generation version of the click chemistry reaction pioneered by K. Barry Sharpless, a chemist at Scripps Research and two-time Nobel laureate in Chemistry, along with Peng Wu, also a chemist at Scripps Research. The near-perfect yet easy-to-run reactions join separate molecular entities through strong chemical bonds that form between different reactive groups. Liu's team had originally used a variety of thermal analysis tools to examine the basic thermal and mechanical properties of these new materials.
