Hi Drake, What chemistry of li-ion batteries are you talking about? Some, like LiFePO4, are far less prone to thermal runaway as they have superior thermal characteristics. Other chemistries should be avoided unless you have significant cell level monitoring and control.
As with all batteries, when any one cell in series with other cells becomes fully intercalated (think of a lead acid cell in saturation), that cell voltage will rise above the others that are still absorbing current. With lead batteries this means off gassing and heat buildup of that cell. With Li-ion cells, especially at high charge rates, this can produce a fast temperature buildup. Some Li cells have pressure valves built in, much like valve regulated lead batteries do. High temperature will cause pressure from boiling the electrolyte. The vent opens to release pressure and lower the internal temperature, hopefully. This stopgap greatly improves safety but may not be sufficient to prevent thermal runaway. If all cells are matched for capacity and balanced, a good practice is to under charge them. There is no reason ever to fully charge a lithium battery and stopping short is a good practice for any Li chemistry. But this alone is not enough. If you want to be more safe, monitor each cell voltage AND temperature and turn off charging before any 1 cell exceeds the specification for that battery type. This is done with a BMS. Our systems all have BMS controls which I believe makes Li-ion batteries safer than lead acid. In lead acid battery systems I have seen thermal run away and several explosions. Beware: Notice above I said “more safe”. There are conditions that can make a Li cell very dangerous, especially with a used battery, that you can’t tell from any non-destructive testing method. Study the formation of dendrites. This subject is too vast to discuss in an email, so I recommend that you study much before you proceed. Many others have been where you are now and have paid a very high price for assumed understanding. Larry Crutcher Starlight Solar Power Systems (4+ years studying, designing and installing Li-ion energy storage systems) On Oct 5, 2017, at 6:45 AM, Drake <drake.chamber...@redwoodalliance.org> wrote: Hello Wrenches, I've been contacted by a group who will be taking apart lithium ion battery packs that have been retired, finding the bad cells and recombining the remainder, then putting them in larger configurations for use in PV systems and electric vehicles. How can thermal runaway be avoided? Is there any information that could be of use in making these systems safe and effective? Thanks, Drake _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
