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A new polymer jelly could be the next big step forward for lithium batteries.

The jelly replaces the volatile and hazardous liquid electrolyte currently used in most lithium batteries.

Researchers from the University of Leeds hope their development leads to smaller, cheaper and safer gadgets.

Once on the market, the lithium jelly batteries could allow lighter laptop computers, and more efficient electric cars.

In 2006, Dell recalled four million laptop batteries because of concerns that they might catch fire. Dell replaced them with batteries that used lower-performance electrodes, but these batteries were significantly larger.

Battery size still dictates the size and weight of most laptops, say the developers of the new battery.

Electronics manufacturer Apple got around the safety problem for their lightweight laptops with a solid polymer electrolyte, but in doing so, the power output of the computers suffered.

Overheating is also an issue for electric cars. Developers have had to use reinforced, steel-clad battery housings, multiple fuses and circuits to protect the battery during charging. All of these contribute to the cost and weight, and hence efficiency, of electric cars.

Thermal runaway

The newly developed jelly batteries should prevent "thermal runaway", during which batteries can reach hundreds of degrees and catch fire.

The Leeds-based researchers are promising that their jelly batteries are as safe as polymer batteries, perform like liquid-filled batteries, but are 10 to 20% the price of either.

The secret to their success lies in blending a rubber-like polymer with a conductive, liquid electrolyte into a thin, flexible film of gel that sits between the battery electrodes.

"The polymer gel looks like a solid film, but it actually contains about 70% liquid electrolyte," explained the study's lead author, Professor Ian Ward from the University of Leeds.

"The remarkable thing is that we can make the separation between the solid and liquid phase at the point that it hits the electrodes.

"Safety is of paramount importance in lithium batteries. Conventional lithium batteries use electrolytes based on organic liquids; this is what you see burning in pictures of lithium batteries that catch fire. Replacing liquid electrolytes by a polymer or gel electrolyte should improve safety and lead to an all-solid-state cell," said Professor Peter Bruce from the University of St Andrews, who was not involved in the study.

Professor Ian Ward spoke to Quentin Cooper about his battery breakthrough on ����ý Radio 4's Material World.