Yes, it's the chemistry that results in slower ion transfer. But that
results in an electrical effect. I believe that effect is lower voltage
across the cell. Thus, how do you explain the fact that higher current,
I**R, means more heat ?
Peri
------ Original Message ------
From: "paul dove" <[email protected]>
To: "Peri Hartman" <[email protected]>; "Electric Vehicle Discussion
List" <[email protected]>
Sent: 09-Sep-19 2:59:54 PM
Subject: Re: [EVDL] li ion battery in cold weather
You are confusing electric current with a chemical process.
Ohms law does not apply in a chemical process.
Low temperatures slow the chemical reaction and charge transfer
velocity, which leads to the decrease of ionic conductivity in the
electrolytes and lithium-ion diffusion within the electrodes
<https://www.sciencedirect.com/science/article/pii/S1002007118307536#bib53>.
Such decrease will result in the reduction of energy and power
capability, and sometimes even performance failure.
Sent from my iPhone
On Sep 9, 2019, at 12:38 PM, Peri Hartman via EV <[email protected]>
wrote:
Hi,
Does anyone have a more in-depth explanation why li ion cells perform
poorly in cold weather ? It's well known that your range goes down
when the battery is cold. Lots of writers talk about the phenomena and
advise you about it but fail to give any real explanations. I think
this conversation may have come up a long while ago but it's hard to
search for.
I did a bit of research. Some authors talk about "intercalation",
which happens below freezing. Intercalation is when the anode becomes
plated with lithium ions instead of the ions being absorbed into the
anode. Obviously, that permanently ruins the battery. So, this is
irrelevant regarding poor range in cold weather.
I did find one article that might be relevant, though.
https://cen.acs.org/articles/96/i10/Rechargeable-battery-weathers-extreme-cold-conditions.html
They claim the electrolyte becomes viscous, slowing down the ion
movement. That's about all they say. But, I'll add my thoughts.
If the electrolyte is viscous, then I suspect the voltage potential
drops. Since watts-hours (energy) is V * Ah, you have less energy
available, assuming that the Ah is constant. But, what about internal
resistance ? For the same driving behavior, you'll need higher amps at
a lower voltage. Resistance loss is I^2 * R, so that loss should go up
significantly. I'm getting into a trap here: why doesn't the increased
resistance loss heat up the battery ? The nominal resistance is
extremely low, so maybe even at an elevated state there isn't enough
heat to affect the electrolyte's viscosity. Don't know.
Here's another article that talks about electrolyte. They talk about
preventing decomposition of electrolyte.
https://spectrum.ieee.org/energywise/green-tech/fuel-cells/lithium-additives
Obviously, the other major factors are cabin heat and defrost.
Peri
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