Researchers at South Korea's Ulsan National Institute of Science and Technology have developed a lithium-ion battery so flexible that it can be tied in a knot.

Traditional batteries use liquefied electrolytes in hard cases. These hard casings prevent flexibility and create a risk of explosion should heat melt the film that separates electrolytes.

In a paper with the cumbersome title "Imprintable, Bendable, and Shape-Conformable Polymer Electrolytes for Versatile-Shaped Lithium-Ion Batteries", the researchers point out that the solution is to use a solid, but flexible, electrolyte rather than a fluid.

The electrolyte tested consisted of Al2O3 nanoparticles in a UV-cured polymer matrix. As well as being flexible and more stable, the batteries are easier to manufacture because the material can be "spread like jam on bread".

The development follows Samsung's recent demonstration of flexible screens for phones and tablets.