New polysulfate compounds could find use in electronics components

A new type of polysulfate compound that can form thin, flexible films has properties that could make it suitable for many high-performance electrical components, according to a study from scientists at Scripps Research and the Lawrence Berkeley National laboratory (LBNL). In the study, published in Joule, the scientists found that the new polysulfates can be used to make polymer film capacitors that store and discharge high density of electrical energy while tolerating heat and electrical fields beyond the limits of existing polymer film capacitors.

Study co-senior author Peng Wu, PhD, said the research findings suggest that energy-storing capacitors and other devices based on these new polysulfates could see wide applications, including in electric vehicle power systems. The other senior authors were K Barry Sharpless, PhD, and Yi Liu, PhD. The Sharpless and Wu labs recently synthesised many previously inaccessible polysulfates using the sulfur fluoride exchange (SuFEx) reaction. SuFEx is part of a growing set of molecule-building methods known as click chemistry for their high efficiency and easy reaction requirements.

In investigations at Liu’s lab at LBNL’s Molecular Foundry, the researchers found that some of the new polysulfates have superior ‘dielectric’ properties. Dielectric materials are electrical insulators in which positive and negative charges separate — storing energy, in effect — when the materials are exposed to electric fields. They are used in capacitors, transistors and other ubiquitous components of modern electronic circuits.

Many of the dielectric materials in contemporary use are lightweight, flexible, plastic-like materials called polymers. The new polysulfates are also polymers, but have improved properties compared to commercial dielectric polymers. The researchers found that capacitors made from one of the new polysulfates, when enhanced with a thin film of aluminium oxide, could discharge a high density of energy, while withstanding electric fields (more than 700 million volts per metre) and temperatures (150°C) that would destroy widely used polymer film capacitors. It was noted that the heat sensitivity of standard polymer capacitors often necessitates expensive and cumbersome cooling measures in systems that use them — such as some electric car models. Therefore, adoption of the new polysulfate dielectrics could lead to cheaper, simpler, more durable power systems in electric cars and other applications.

“I was very surprised at first, and still am — I think we all are. How can a classic force from the domain of physics, like the electric field force, be modulated by a thin chemical-polymer film in its path? The results speak for themselves though, and now seems a good time to share this puzzle,” Sharpless said.

The researchers continue to synthesise and investigate new polysulfates to find some that have better properties.

“The polysulfate polymers we examined in this study can do very well at 150°C, but we think we can find related polysulfates that can handle 200 to 250°C with little or no loss of function,” Liu said.

Image caption: A new type of polysulfate compound can be used to make polymer film capacitors that store and discharge high density of electrical energy while tolerating heat and electric fields beyond the limits of existing polymer film capacitors. Image credit: Scripps Research