Rubbery conductors aim at better batteries.

Researchers eagerly want to build lightweight, durable, rechargeable batteries, especially for use in the mobile electronic consumer products - such as cellular telephones and lap-top computers-that are fast becoming integral parts of daily life. But finding electrolyte materials that can safely and efficiently conduct current between a battery's negatively charged anode and its positively charged cathode has proved difficult. Liquids leak out and catch fire. Highly conductive solid glasses crack apart under the stress of discharging and recharging. And rubbery polymers, while robust, have so far performed poorly as carriers of current.

Now, a group of physical chemists at Arizona State University in Tempe report that they've developed d new class of electrolytes that combines the high conductivity of glassy materials with the flexibility of rubbery polymers. "Our materials have the potential to carry higher current than any other polymer electrolyte," says lead scientist C. Austen Angell.

In the March 11 Nature, the team describes how they reversed the usual procedure for making "salt-in-polymer" electrolytes. Instead of dissolving a small amount of salt in polymers, they dissolved small amounts of the polymers polypropylene oxide and polyethylene oxide into a cocktail of lithium salts. The resulting "polymer-in-salt" material has the consistency of rubber cement, making it stretchy enough to withstand changes in volume during the discharging and recharging of a battery And it readily conducts lithium ions. indeed, the greater amount of salt in the material makes it 1,000 times more conductive at room temperatures than other polymer electrolytes developed so far. Angell's group tested the material using simple cells with a lithium anode and found that the current was carried predominantly by lithium ions. Electrolytes with single-ion conductors make the most efficient and powerful batteries, he explains.

"The incorporation of such electrolytes into high-energy high-power-density, rechargeable lithium cells could widen the use of batteries in sensing and energy storage and give a fresh impetus to the development of electric vehicles," writes Malcolm Ingram, a chemist at the University of Aberdeen in Scotland, in a commentary that accompanies the Nature report.

Scientists have long held high hopes for lithium batteries, but they haven't yet overcome the many practical obstacles, including the rapid degradation of the lithium anode (SN: 12/12/92, p.415). Terje Skotheim, president of Moltech Corp., a company based in Stony Brook, N.Y., that researches battery technologies, believes the new polymer-in-salt material may solve several problems at once. "With a new class of electrolytes, it's a new game," he says. "Perhaps the lithium anode will be more stable and better behaved. The possibilities look very exciting"

Angell notes that the new material could prove to be a useful electrolyte for many kinds of batteries. But first he and his colleagues must determine how well it performs in an actual battery prototype.