Power Electronics

Thin-film Technology May Benefit Battery Performance

Advances in rechargeable thin-film lithium battery technology at Oak Ridge National Laboratory could potentially improve battery performance. Traditional alkaline batteries can be short-lived in some devices—costly over the life of the device and inconvenient to replace. Rechargeable batteries made from highly toxic heavy metals can pollute the environment. Others have a short storage life (a rapid "self-discharge" rate). If used improperly, some lose the ability to hold a full charge, a problem known as the "memory effect."

Nancy Dudney, group leader of the Ceramic Thin Films Group in ORNL's Condensed Matter Sciences Division, said thin-film lithium batteries last longer; hold their charge better during storage; recharge faster with no memory effects; can be recharged many times and can be made much smaller, lighter and more flexible than traditional batteries. In addition, because they are entirely solid and contain no liquids, potential problems and hazards due to leakage, corrosion and freezing are eliminated. According to Dudney, current applications for thin-film rechargeable lithium batteries include implantable medical devices, remote sensors, miniature transmitters, smart cards and microelectronic devices.

Supported by the Department of Energy's (DOE) Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, and Laboratory Technology Transfer Research Program, ORNL has developed materials for thin-film lithium batteries that withstand temperatures from below 0° to 250°C (480°F), Dudney said. This opens the door to different product designs, such as soldering the batteries into integrated circuits to power microelectronic devices. ORNL also is working to make thin-film lithium power sources smaller, lighter and more flexible.

A drawback of thin-film lithium batteries is that they are more expensive than other small capacity batteries because they are more complex to manufacture and because they are still manufactured in much smaller numbers. Furthermore, they are not available in standard cell sizes.

John Bates, former head of the Ceramic Thin Films Group and chief technical officer and founder of Oak Ridge Micro-Energy, a local thin-film lithium battery technology firm, said companies are interested in the technology as backup power for computer memory chips and to power sensors embedded in tire sidewalls. These applications require the batteries to survive temperatures up to 280°C during assembly. When the thin-film lithium batteries are in the discharged state, they meet this requirement.

Bates said progress is being made toward a lower-priced, mass-produced, thin-film lithium power source that is practical for a broader range of applications. In September 2005, his firm announced a successful first manufacturing run of thin-film lithium and lithium-ion batteries with better than expected yields.

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