Assembly - December 2008 - (Page 47) thermal runaway and often resulting in an explosion or fire.” Lithium-ion batteries have an inherent ability to become unstable at temperatures above 130 C. If a leak occurs, the electrolyte can be harmful to body tissue and electronic circuitry. Harsh Lab Testing Most leak testing applications take place in research labs that expose batteries to extreme conditions. To determine how safe batteries are, Roth tests them in harsh environments to see when they fail or leak their electrolyte. He uses mass spectrometry to examine the stability of the materials, their flame-retardant performance, and the high-temperature integrity of separators between the cathode and the anode, in addition to general thermophysical properties. “We look at fundamental chemistry to discover the kinds of gases they emit when they are heated and explode,” explains Roth. He says some of the newer devices on the market, such as lithium-iron phosphate batteries used in handheld power tools, are extremely resilient and less reactive when subjected to extreme conditions, unlike other types of batteries. Underwriters Laboratories Inc. (UL, Northbrook, IL) is another organization that tests batteries for leaks and other potential safety hazards that may create a fire or an explosion. Batteries are tested both individually and when used in consumer goods such as cameras, cell phones and laptop computers. “Leak testing is part of our standard test program to make sure batteries conform to the UL 1642 standard,” says John Drengenberg, consumer affairs manager. “We put batteries through a wide variety of test conditions, such as altitude, heat, cold and vibration.” Battery packs and cells are typically weighed during testing. Engineers at UL use electronic scales to measure the density of cells before and after testing. Any discrepancy indicates that a leak has occurred. According to Drengenberg, an engineer who has been studying batteries Battery manufacturers have made great strides producing safe, long-lasting batteries. Photo courtesy Nexergy Inc. and other products for more than 40 years, most problems occur because of a bad design or bad construction. “It’s often caused by ineffective crimping or by cracking,” he points out. In addition to the work being done by independent labs, battery manufacturers are doing more testing to ensure the safety of their products. “We don’t target battery or fuel cell testing specifically, but over the last year, we have seen an increase in customer demand for leak test and other process monitoring,” says Nathan Sheaff, CEO of Sciemetric Instruments Inc. (Ottawa, ON). His company focuses on air-based leak tests using pressure decay, vacuum or flow as the methodology. Most battery leak testing applications today have shifted to electronics and medical devices. For instance, back in the 1980s, InterTech Development Co. (Skokie, IL) was actively involved in testing eight-cell automotive batteries. “The issue was to determine if the plastic housing between compartments Battery manufacturers are doing more testing to ensure safety. Photo courtesy Johnson Controls Inc. www.assemblymag.com December 2008 / ASSE M B LY 47 http://www.assemblymag.com
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