[Oeva-list] Lithium Ion Batteries

Gary Graunke gary at whitecape.org
Fri Dec 9 11:02:11 PST 2011


All,

There are many kinds of Li batteries, so it is important, especially for us
amateurs, to be very selective when considering Li batteries for our
conversions. Since major companies have more resources, they may mitigate
some of the dangers by careful design, cooling systems, etc. However, even
then in an accident is should be common sense that one should carefully
dismantle damaged packs and remove the energy source from charged batteries
and, more importantly, damaged cells and interconnects.

Many advanced batteries require redundant, reliable thermal management for
safety reasons. These are not for amateurs, and might be wise to avoid by
consumers as well.

Li cells with Cr have the highest energy density, but are subject to thermal
runaway, and the electrolyte is explosive when in contact with air. 

I have been using A123 LiFePO4 cells for 4.5 years now in my Insight
conversion, and again in a plug-in Prius. They are extremely safe, and
require no thermal management. Initially, I had cooling and logged
temperature before concluding that I did not need those systems. My cells
are cylindrical, and this permits air cooling of the cells. They also have
expansion room in case a cell pops as required by A123 guidelines. 

The A123 systems cells lost out to the LG Chem cells because A123 did not
make prismatic (rectangular) cells to permit less pack volume, and perhaps
other reasons. However, the Navistar truck uses newer prismatic A123 cells,
so they may be more suitable for the Volt. 

In another case, the OSU solar racing team lost their vehicle due to a fire
which may have originated in the batteries--the driver, who escaped with 2nd
degree burns, reported a popping sound and quickly exited the vehicle. The
OSU solar racing team in their first vehicle used A123 LiFePO cells upon my
advice for their successful race from Austin to Calgary, and after the fire
approached A123, who is now their battery sponsor.  

So unless you really know what you are doing (more than GM), stick with lead
or LiFePO cells!
Pay attention to thermal issues and monitor pack temperatures, and design
your battery boxes to mitigate battery fires or starting adjacent materials
on fire when the batteries are extremely hot, such as when you have a loose
connection!
I have melted plastic on lead battery cases due to an over-tightened
interconnect that stripped the nut on my S10. If I had had a temperature
sensor, I would have stopped in time to prevent further damage. Now I check
the pack after a first short run with an infrared thermometer to verify
connections are tight. Someday I'll get one that provides an image.
Even aging lead batteries may do thermal runaway when charging, so this is
not an issue restricted to lead. I have also had this happen in my Insight
conversion when I used old lead batteries, but no consequential damage due
to good battery box thermal isolation. Best to have a system to shut off
charging for hot batteries!

Generally, if you are paying attention to battery care issues, you will have
a good start on the safety issues as well.

And, of course, it is best practice and worth repeating ad-nausea to isolate
both plus and minus leads from the pack with appropriate contactors for an
emergency disconnect, and use only DC-rated high voltage fuses, such as the
Bussman FWH or Littlefuse KLKD in the pack itself to prevent plasma fires.
Keep in mind there is enough energy there to move a heavy vehicle a long
distance--we don't want it to be released quickly!  

Electricity is much safer than gasoline in many ways, but has its own
issues. These deserve our respect and attention.

Gary

-----Original Message-----
From: oeva-list-bounces at oeva.org [mailto:oeva-list-bounces at oeva.org] On
Behalf Of gfifield at onlinenw.com
Sent: Friday, December 09, 2011 7:32 AM
To: oeva-list at oeva.org
Subject: [Oeva-list] Lithium Ion Batteries

Bloomberg Businessweek article
GM Buys Batteries Less Volatile Than Volt's for Spark Model
http://www.businessweek.com/news/2011-12-09/gm-buys-batteries-less-volatile-
than-volt-s-for-spark-model.html



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