Assembly - December 2008 - (Page 46) ASSEMBLY Leak Testing Batteries Behaving Badly Evenly a tightly sealed battery can emit toxic gases. W Researchers test batteries in harsh environments to see when they leak electrolyte. Photo courtesy Sandia National Laboratories By Austin Weber Senior Editor hether Santa delivers toys, games, cameras, electric razors, power tools or the latest electronic gizmos this time of the year, chances are the devices will run on some type of battery. The technology is also extremely popular in the auto industry these days as manufacturers around the world scramble to develop a new generation of batteries that are lightweight, powerful, robust, safe and easy to mass-produce. Whether they’re lithium-ion, nickelmetal hydride, nickel-cadmium, silverzinc, thin-film, or the good old alkaline or lead-acid variety, batteries contain a wide variety of volatile chemicals and inherently unstable materials that can potentially create toxic gases. Fortunately, battery manufacturers use a variety of proprietary assembly processes to ensure that their products don’t leak in day-to-day use. They go to great lengths to seal potentially harmful cells with laser welding, ultrasonic welding and crimping processes. Some manufacturers also use epoxy to attach steel plates, gaskets and end caps. So, as long as stringent production parameters are followed, there is often little or no need for leak testing before a product is packaged and shipped. “The best cells typically feature laser-welded caps, which rarely leak,” says Peter Roth, lead researcher in the power sources R&D group at Sandia National Laboratories (Albuquerque, NM), which is actively engaged in a major project for the U.S. auto industry. “Crimp seals can develop leaks. Adhesive seals can create problems if a battery gets too hot.” Lithium-ion is currently the darling of the battery industry, because it allows manufacturers to reduce weight and volume by more than 30 percent. But, lithium, which is the lightest metal, is very unstable. Unlike a lead-acid battery, a lithium-ion battery contains a gelatinlike material rather than a liquid. The batteries can pose a threat if they are used in a product that is exposed to extreme heat or is involved in an accident. Several years ago, lithium-ion batteries used in cell phones and laptop computers were scrutinized because of some wellpublicized explosive incidents. Since then, battery manufacturers have made great strides producing, safe, long-lasting and affordable batteries. For instance, significant effort has been devoted to improve the safety of lithium-ion batteries. In particular, new electrode materials, separators and cell designs have improved safety. Battery manufacturers are also using more nickel manganese cobalt cathodes and lithium iron phosphate cathodes. “The Achilles heel of lithium-ion technology is the electrolyte, which is flammable,” says Chris Turner, director of battery technology at Nexergy Inc. (Columbus, OH), a battery pack systems integrator that works with several different battery cell manufacturers. “Under abuse conditions, such as high voltage or high temperature, the electrolyte can react with the anode or cathode to create an unstable and potentially hazardous condition inside the cell, leading to 46 ASSEMBLY / December 2008 www.assemblymag.com http://www.assemblymag.com
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