Wednesday, April 09, 2008

Longer-Lasting Batteries for Laptops

Conventional lithium-ion batteries in laptops and cell phones quickly lose their ability to store energy and can catch fire if they're overcharged or damaged. Now researchers at Argonne National Laboratory in Argonne, IL, have developed composite battery materials that can make such batteries both safer and longer lived, while increasing their capacity to store energy by 30 percent.

The Argonne researchers have improved the performance of the positive electrodes by increasing the chemical and structural stability of the materials already used in laptop batteries. In conventional lithium-ion batteries, which have cobalt oxide electrodes, a small amount of overheating, caused by overcharging the material or by electrical shorts inside a battery, can lead to rapidly increasing temperatures inside the cell and, in some cases, combustion. That's because, as the material overheats, the cobalt oxide readily gives up oxygen, which reacts with the solvent in the battery's electrolyte and generates more heat, feeding the reactions. The Argonne researchers addressed this problem by replacing some of the cobalt oxide with manganese oxide, which is chemically more stable.

The researchers' next step was to replace some of the active metal oxide materials in the electrode with a related but electrochemically inactive material, forming a composite. This material does not store energy, because it does not release and take up lithium ions as the battery is charged and discharged. (Lithium-ion batteries create electrical current as lithium ions shuttle between positive and negative electrodes.) The inactive material makes the composite more stable than conventional electrode materials, which means it can last longer. One version of the material can last for 1,500 charges and discharges without losing much capacity, he says. That's more than double the life of conventional laptop batteries.

The electrode material can store 45 percent to 50 percent more energy than the best electrodes in laptop batteries. In terms of an entire battery cell--given that the positive electrode represents less than half of the total weight and volume of a battery cell--the total energy storage of the battery can be improved by 20 percent to 30 percent, Henriksen says.
via Technology Review

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