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The next time you eat a croissant you can enjoy not only the buttery deliciousness but the knowledge the treat in your hands gave engineers the idea for a solution to one of the biggest obstacles to keeping the world habitable. A prototype pastry-inspired capacitor stores 30 times as much energy as the best commercial model, opening up new options for storing pollution-free energy.

Solar and wind power have become so much less expensive in recent years that one or both is now cheaper than using fossil fuels across most of the world, even without including environmental costs in the price. Aside from political will, the only thing stopping us from removing the single largest source of greenhouse gases is the challenge of storing renewable energy for days of cloud and little wind.

Options for storage exist of course, and batteries are getting better all the time, but the cost still represents a major impediment. Dielectric capacitors offer an alternative, and Dr Emiliano Bilotti is attempting to make them commercially feasible. He found inspiration in an unexpected place.

Capacitors are one of the most efficient methods of storing electricity and have the advantage over competitors that they can release their stored energy exceptionally quickly when needed. Billions are used in electronic devices across the world for that very purpose, but these store only tiny amounts of charge. To cleanly power a city through a windless night capacitors are currently far behind batteries for cost, and further behind pumped hydro where suitable sites exist.

However, Bilotti realized these limitations in part reflect design inefficiencies. Polymer film capacitors, a variety of dielectric capacitors that place the film between two electrodes, prevent electrons jumping between the electrodes storing charge.

Bilotti, who after a PhD in Naples surprisingly chose Queen Mary University, London, over French institutions, thought about the way dough is pressed and folded to create a croissant prior to the actual baking. He realized the same technique applied to the polymer films should boost the storage capacity of capacitors.

In Nature Communications Bilotti describes using the same technique to make a β-poly(vinylidene fluoride) film, noting the process works “without the need of any hazardous gases, solvents, electrical, or chemical treatments.” The product is enormously more energy-dense than existing capacitors, although still far behind batteries, and doesn’t compromise on the speed of release. However, the prototype is only 74 percent efficient, where many capacitors manage 95 percent, so further work is required, and the energy density could still be improved. 

Initially, the technology could displace existing capacitors in applications such as electric cars’ regenerative braking. If widespread use of Bilotti’s idea brings costs down, however, croissant-inspired capacitors may eventually compete with batteries for much larger scale storage requirements.

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