A new polymer could be the final link needed to make lithium-sulphur batteries possible, bringing about a world with high-powered, long-lasting, flexible and strong portable power supplies.

Lithium-sulphur batteries could easily store four to five times as much energy as today’s best lithium-ion batteries, but have been unworkable for some time due to a limited amount of charges.

“Lithium-ion batteries can last 1,000 charge cycles, but lithium-sulphur batteries tend to fail before they’re charged 100 times,” says Dr Jeffrey Pyun, a chemist at the University of Arizona.

But this may be about to change, the chemical engineer says.

He says electrodes made from sulphur polymers, like other plastic products, should be inexpensive to manufacture on a large scale. The raw material is good supply as well, with around 60 million tonnes of elemental sulphur produced each year.

Sulphur polymer electrodes would solve the problem plaguing the design, which is that the batteries’ cathode reacts with lithium ions in the electrolyte to form lithium sulphur salt deposits. These build up on the electrodes, depleting the cathode of its sulphur, decreasing the storage capacity of the battery and causing structural problems for the electrodes.

In their most recent study, a team from the US wanted to find the best cathode material recipe and test it in batteries.

They tested 2,032 copolymers, each with different amounts of sulphur, in coin-cell batteries. The batteries resemble those used in wristwatches and are the standard method for researchers test new battery designs.

The best performing copolymer consisted of 90% sulphur by mass. Batteries using this copolymer had an initial storage capacity of 1,225 mAh per gram of material.

After 100 charge-discharge cycles, the capacity dropped to 1,005 mAh/g, and after 500 cycles it fell to about 635 mAh/g. In comparison, a lithium-ion battery typically starts out with a storage capacity of 200 mAh/g but maintains it for the life of the battery.

To become a commercial product, a battery made with the sulphur polymer will need to have a steady storage capacity throughout its lifetime and be able to last the 1,000 cycles of today’s batteries. To get there, researchers will continue experimenting with other kinds of sulphur copolymers that may have better properties.

Dr Jodie Lutkenhaus, a fellow chemical engineer working on similar polymer batteries says the design has many advantages.

Besides high storage capacity; polymer batteries are likely to be cheaper and lighter, and they could enable flexible storage devices for portable electronics. They could even perform double duties as a structural material - for example, as an airplane wing or a car door that also an energy source.

More details are available in the full report, published by the journal ACS Macro Letters.