Energy storage improved in dielectric capacitors

Researchers from Queen Mary University of London, seeking to solve a sustainable energy storage problem, have found inspiration in the most unlikely of places: the humble croissant.

Renewable and sustainable energy sources such as solar and wind are intermittent, meaning that efficient, low-cost and environmentally friendly electric energy storage systems are needed to make them of wider practical use. As noted by lead researcher Dr Emiliano Bilotti, “Storing energy can be surprisingly tricky and expensive, and this is problematic with renewable energy sources which are not constant and rely on nature.”

Currently, there are three main energy storage options: batteries, electrochemical capacitors and dielectric capacitors. Dielectric capacitors typically have ultrahigh power density, making them suitable for high-power and pulse-power technologies that require the quick release of accumulated energy. Examples of this include motor drives, mobile power systems, space-vehicle power systems and electrochemical guns.

Dielectric capacitors are limited by the low amounts of energy they can currently store; the new research tackles this limitation. Inspired by the croissant-making technique of pressing and folding dough to create a layered pastry, the researchers pressed and folded a polymer film capacitor — a capacitor with an insulating plastic film — to store 30 times more energy than the best-performing commercially available dielectric capacitor, biaxially oriented polypropylene (BOPP).

Writing in the journal Nature Communications, the study authors describe pressing and folding as an iterative process in which the pressing and folding cycle can be applied an arbitrary number of times. Each cycle involves a folding step, in which an approximately rectangular poly(vinylidene fluoride) (PVDF) film, produced by hot pressing, is folded, followed by a pressing and annealing step around the melting point of PVDF.

The study results are reported to be the highest energy density ever reported in a polymer film capacitor. While expensive and complex synthesis and processing routes are normally necessary to achieve high energy density in polymer film capacitors, the newly developed processing, pressing and folding is unique for its simplicity, record-high energy density and potential to be adopted by industry.

“With this technique we can store large amounts of renewable energy to be used when the sun is not shining and it is not windy,” Dr Bilotti said.

Study author Professor Mike Reece added, “This finding promises to have a significant impact on the field of pulse-power applications and could produce a step change in the field of dielectric capacitors, so far limited by their low energy storage density.”

Image credit: ©stock.adobe.com/au/Richard Griffin

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