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| Powerful particles: New lithium-ion battery electrode materials, shown here under an electron microscope, can store more energy, and so do more safely, than conventional lithium-ion batteries in laptops and cell phones. Credit: Courtesy of Argonne National Laboratory |
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.
Last month, the researchers took a significant step toward commercializing the technology by licensing it to a major materials supply company, Toda Kogyo, based in Japan. The company has the capacity to make the materials for about 30 million laptop batteries a year, says Gary Henriksen, who manages electrochemical storage research at Argonne.
The new materials are one example of a new generation of lithium-ion electrode chemistries that address the shortcomings of conventional lithium-ion batteries. Each has its own trade-offs. For example, another material called lithium iron phosphate has better safety and durability than Argonne's materials, but it stores somewhat less energy than conventional lithium-ion batteries. Argonne's materials improve on the safety and reliability of today's laptop batteries, while also storing more energy.
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.
What's more, reducing the amount of active, energy-storing material has the counterintuitive effect of increasing the composite's storage capacity. If too much lithium is removed from conventional cobalt oxide materials, the material degrades and quickly loses its ability to fully charge and discharge. The inactive material makes it possible to use much more of the lithium without damaging the material.
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.
The researchers' next step is improving the rate at which the composite material can be charged and discharged so that it can be used in hybrid vehicles. As it's made now, the Argonne material can be completely discharged in about three hours--fast enough for laptops but far too slow for a car. Discharging rates will need to be at least three times faster, and likely more, for the technology to work in plug-in hybrids, vehicles in which the battery can be recharged from a conventional electrical outlet.
Yet-Ming Chiang, a professor of laptop batteries and engineering at MIT, says the new material is "a significant improvement over lithium cobalt oxide" for laptop batteries. "If you think about it in terms of a field that grows 8 to 9 percent per year, you just saved yourself three years. You may have leapfrogged the competition," he says. "I'm sure that anybody who makes cell phone and laptop batteries would be very happy to have that kind of an edge."
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