On 11/17/2015 7:47 AM, dovepa via EV wrote:
Jack Richard came to this conclusion years ago. He said Li-Ion batteries work better hot. It's in one of his videos I watched. I don't remember details but it was during all the Leaf problems in Arizona.
Almost all batteries have increased specific power (higher power output) when warmer than room temperature. Li-ion batteries have a chemistry-dependent optimal temperature which results in greater peak power output. With elevated temperature, the internal resistance goes down and the chemical diffusion goes up which results in better immediate performance, but there is a limit as to how far you can push this. Often the separators or the case will start to melt or the electrolyte will boil at some maximum temperature.
However, this short-term benefit of increased performance and power comes at a hefty price; decreased lifespan, often drastically decreased lifespan. Almost all batteries will age more quickly as you elevate the temperature. The higher the temperature, the shorter the lifespan. Typically, the lifespan decrease is _exponential_ with increased temperature. Thus, the lifespan at 60 Celsius might be shortened to days when the battery would last for many years at 25 Celsius. Also, self-discharge increases drastically with elevated temperature in a similar manner, which will tax the ability of the BMS to hold the pack in balance, causing further degradation.
Batteries are complicated electro-chemical beasts. Bill Dube _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
