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A new polymer chain clears a major hurdle for the future of energy storage. 

A team of chemists at the University of Massachusetts Amherst has developed the polymer-based system that can yield energy storage density—the amount of energy stored—more than two times higher than previous systems.

The new system is able to reach an average of 510 Joules per game with a maximum of 690, while the previous high-energy storage density achieved in a polymeric system was in the range of 200 Joules per gram.

“Theory says that we should be able to achieve 800 Joules per gram, but nobody could do it,” Dhandapani Venkataraman said in a statement. “This paper reports that we've reached one of the highest energy densities stored per gram in a polymeric system, and how we did it.”

According to the researchers, if energy storage density improves, applications for the new technology include possibly solar pads that collect energy from the Sun by day and then store it for heating food, living spaces, clothing or blankets at night. This could be particularly impactful in areas with no access to a power grid.

“We understood the idea of controlling the arrangement, but we thought What if we use a flexible polymer, not a rigid tube?” he said. “Something like a string of Christmas lights, where the lights are the azobenzene molecules.

“Because what you cannot do with a carbon nanotube is reduce the distance between the molecules,” he added. “We thought that the structure of a polymer chain would let the azobenzene groups get closer to each other and interact, which is when they gain energy and become more stable.”

Venkataraman said the finding was unexpected, which led them to conduct more experiments.

“The twist in the story is that we thought that the distance between the lights in the string was the most important,” he said. “It is important, but what is more important is the way that multiple strings and their lights are carefully arranged.

“It turns out that the processing solvent we used acts to arrange and regulate the architecture, so the azobenzene molecules attached to the polymer are arranged very neatly and compactly,” he added. “It basically acts to ensure that there can be maximum packing density.”

The researchers used the solvent tetrahydrofuran (THF) for processing because it is a good solvent for the polymer system.

“This paper talks about how, on the molecular level, the THF affects the energy we see on the macro scale,” Venkataraman said. “It starts out with how the solvent molecule interacts with the polymer and it turns out that that is related to the molecular packing, how they are arranged in space.

“When the molecules are packed properly they can gain more energy. It took two years of work, but we finally were able to show that it's true.”

The study was published in Scientific Reports.

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