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Charge On!, Issue #014: Lithium Battery Chemistry and Garage Fires
December 16, 2011
Hi,!

Happy Holidays!

I've been working on sorting out the different lithium ion battery types that are available for electric cars today, and thinking about all the lithium electric car battery packs involved in mysterious garage fires that have been in the news.

Disclaimer: I don't have inside information, I'm just thinking about it and bouncing those thoughts off a couple of other people who are also thinking about it.

So we - the fellow thinkers and I - talked about...

I wrote up the conversations, which you can find on the website at the links above.



Here's what I think I've got...

The basic EV lithium chemistries are lithium polymer, li ion ("ion" is the cathode, and is usually cobalt oxide or manganese oxide spinel), or LiFePO4.

  • Lithium polymer means the electrolyte is trapped in a structure. Absolutely require good management.

  • Lithium ion batteries have free liquid electrolyte. Also absolutely require good management, except LiFePO4, which is a li-ion battery, but better behaved. See next item.

  • LiFePO4 does NOT tend to catch fire, unless you put a battery management system on it that doesn't function correctly. LiFePO4 is better off with NO management than bad management.

  • Li ion polymer means the electrolyte is liquid, but the anode, instead of being graphite, is some variety of silicon polymer. There's polymer involved, that's pretty much all these have in common with lithium polymer; )

  • When you hear "spinel" and lithium ion batteries in the same sentence...it's referring to lithium manganese oxide spinel. That's a particular crystal form of Mn2O4 that is the cathode material in the Volt and Leaf's lithium ion batteries which have liquid electrolyte.

  • Tesla uses about 7000 small lithium cobalt oxide (LiCoO2) cells.


    • Comparison of Different Lithium Chemistries

    Many thanks to Wikipedia for the data. Hope they got it right; )

    LiCoO2 3.7 V 140 mA·h/g 0.518 kW·h/kg
    LiMn2O4 4.0 V 100 mA·h/g 0.400 kW·h/kg
    LiFePO4 3.3 V 150 mA·h/g 0.495 kW·h/kg


    Lithium Batteries and Fires

    I talked about lithium EV batteries and mysterious garage fires with Mike Collier from Lithium Storage and Jack Rickard from EVTV in the articles I linked to above, but I thought I'd share with you a little extra on EV battery fires I talked about with Jack Rickard that's NOT in the articles.

    Jack: The earliest fire problems were reported with laptops and cellphones using Lithium Cobalt Oxide cells. These were mostly replaced with Lithium Manganese Oxide cells to alleviate the problem.

    Both types of cells have a negative temperature coefficient and give off free oxygen at fairly low temperatures.

    What this means is that if they are overheated, they will tend to heat further and at some temperature, the cathode material will give off oxygen feeding the fire and in fact making it almost impossible to put the fire out.

    Lithium Iron Phosphate cells tend NOT to go into thermal runaway, and the temperature at which they DO give off oxygen is much higher. So I think LiFePo4 cells are inherently so much safer than any lithium metal oxide cell that they are the only choice for automotive use. The problem is the metal oxide cells DO give a bit better energy density - range.

    Lynne: A bit, maybe, but who cares? 100 miles on a charge is good enough for me.

    That's it for me.

    Hope you're all staying safe and warm and dry this holiday season!

    Best regards,
    Lynne Mason

    Electric Cars are for Girls
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