In view of recent Li-ion battery failures, I found this article to be a reasonable explanation of the failure mechanism.
>From an article by Damon Darlin and Barnaby J. Feder, NEW YORK TIMES NEWS SERVICE: "The potential for fire in a lithium-ion battery is a result of its chemical composition. Contained in that small package are all the elements needed for a fierce blaze: carbon, oxygen and a flammable fluid. The battery is made of a thin layer of lithium cobalt oxide, which serves as the cathode, and a strip of graphite, the anode. These are separated by a porous insulator and surrounded by fluid, a lithium salt electrolyte that happens to be highly flammable. "When the battery is charged, lithium ions on the cathode migrate to the anode. As the battery is used, the ions migrate back to provide the energy. In the charged state, the cathode without most of its ions is highly unstable. If a spark occurs, the temperature of the cathode can exceed 275 degrees. "That is hot enough to cause the cathode to decompose and release oxygen. A fire starts, and as heat builds the battery begins what scientists call a "thermal runaway." In the case of the Sony-made batteries recalled by Dell, a microscopic metal particle that contaminated the electrolyte during manufacturing caused the spark." Richard Nute Product Safety Consultant San Diego - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
