Heat in a lithium ion battery is from two sources electrochemical operation and
Joule heating. A way to calculate the battery heat is using a thermodynamic
energy balance shown in equation below where the first term is the heat
generation due to Joule heating and the second term is the heat generation due
to entropy changes.
q= I(U-V) - I(T(dU/dV)
Bernadi D, Powlikowski E and Newman J 1985 A general energy balance for battery
systems J.
Electrochem. Soc. 132 5-12
Sent from my iPhone
> On Sep 9, 2019, at 5:23 PM, Peri Hartman via EV <[email protected]> wrote:
>
> 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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