Review of: “Thermal management of lithium-ion batteries for electric vehicles”

I truly regret spending $ 35 to read the paper “Thermal management of lithium-ion batteries for electric vehicles” by G. Karimi and X. Li.

I’ll save you the $ 35: in just one sentence, this is what the paper says:

“To cool a battery, use air (the extra effort of liquid cooling is not worth the trouble) and make sure the air flow is evenly distributed in between each cell, otherwise you’ll only cool the ends of the battery, and get a temperature gradient, which is bad.”

Well, obviously!

To reach that obvious conclusion, the researchers did do a good job at modeling the effects of cooling. But they never bothered to actually try it in practice. Had they done so, they would have realized that two of the fundamental premises of their model were wrong:

  1. Cycling a battery with a thermal gradient will unbalance it (it doesn’t)
  2. The open circuit voltage of a Li-Ion cell is temperature dependent (it isn’t)

Specifically:

1) Temperature differences do result in differing self discharge currents; but the effect is secondary and long term, and is completely unaffected by whether the battery is cycled or is in storage. So, while a temperature differential does unbalance the battery over the long term, in the short term, cycling such a battery will not result in any more unbalance than if it were standing by.

2) Temperature differences do result in differing cell resistances; if under load, they result in differing terminal voltages. But the Open Circuit Voltage (OCV) is not affected: some time after the load is removed, the cell voltages will return all to the same voltages, even if they are at different temperatures; that’s because their SOC levels are all still all the same (the battery is still balanced)

On top of that:

What a pain it is to pay to access a paper for just 1 day, a paper that you don’t get to keep, using a font too small to read on a computer screen (they defeated the zooming function in my pdf reader).

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