LFP Charge, Discharge, Storage vs Temperature

[rgleason]

Battery U - Charging at High and Low Temperatures

LiFePO4 Optimal Operation Temperature Range
Analysis for EV/HEV

Lithium Iron Phosphate (LiFePO4) Battery - BatterySpace.com


Preliminary Summary

• Storage -20°c to 0°c (-4°F to 32°F) - no charge and no discharge
• Slow Charge 0°c to 5°c
• Charge 5°c to 45°c (32°F to 113°F) - varying performance
• Discharge 0°c to 45°c (32°F to 113°F) - varying performance

1. "40°c is determined to be the upper limit of operation temperature range to maintain the performance and prevent aging caused by high temperature." One source above.
2. "No charging is permitted at freezing temperatures ...because of the reduced diffusion rates on the anode leads to plating of metallic lithium can occur on the anode during a sub-freezing charge. This is permanent and cannot be removed with cycling." Another source above.
3. "At −20 °C, LiFePO4 cathode only retains less than 50% of the discharge capacity obtained at 20 °C." another source
4. "Finally,the optimal operation temperature range is proved to be 10℃ to 40℃ according to the experimental results.- yet another source.

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Will a LiFePo4 battery charged to 50% SoC that is isolated (no charge or discharge) survive in a covered boat in Rhode Island where temperatures can drop down to -27c (-17 degreesF) for brief periods? RI lowest recorded temperature is –25f –32c https://www.infoplease.com/science-h...eratures-state

Daily average temperatures for RI http://www.intellicast.com/Local/His...ation=USRI0050

Judging from MaineSail's experiences, I believe it is possible, but it could be a big mistake to assume accordingly without really knowing for sure.

I would rather not have to disconnect all the cells and move them.


If I must do it, I could rig up some SolarPV connected to a resistance heating mat and stuff some insulation around the batteries.

[john61ct]

Yes. I think 8-)

Especially below the waterline, huge buffering delays compared to outside air temps

how often does the water freeze there?

No mains available, bilge pumps?

Could rig a polyiso enclosure with cheap silicon pads under the cells to be "sure", reliable thermostat control is key.

Def check on them regularly.

Or configure packs for portability, take them off the boat.

[rgleason]

Sorry, boat is hauled and has a deck cover. No cords to boats allowed. River freezes over some winters. Wind blows hard and cold.


Boats are packed together, sun warms the covers.


I should put a max min thermometer in there.

[john61ct]

You mean you're not allowed to visit and charge your batteries?

Change yards.

Or take the cells home.

[john61ct]

New factoid

You know how fast charging LFP at high C-rates is harmful to longevity?

Well turns out, that issue is **very** dependent on internal cell temperature.

As long as well over say 25°C, then 0.6-.8C charging is fine.

Getting around 30°, even a bit over 1C should be no problem.

Obviously sticking to 0.3-4C by default overall is that bit better for those really prioritizing maximum longevity.

But when minimizing runtime on an ICE charge source is also important, trying to get back to Full in under an hour should not cause a lot of stress.

[john61ct]

Something to consider now for those can afford it, not just for freezing weather

https://www.google.com/search?q=LiFeBlue+300ah+LiFePO4

[rgleason]

Originally Posted by john61ct

New factoid

You know how fast charging LFP at high C-rates is harmful to longevity?
Well turns out, that issue is **very** dependent on internal cell temperature.

As long as well over say 25°C, then 0.6-.8C charging is fine.
Getting around 30°, even a bit over 1C should be no problem.
Obviously sticking to 0.3-4C by default overall is that bit better for those really prioritizing maximum longevity.

But when minimizing runtime on an ICE charge source is also important, trying to get back to Full in under an hour should not cause a lot of stress.

Thanks John, where did you find this info?


So > 30°C (86°F) and less than 35°C(95°F) can be charged at 1C with ICE alternator?

[john61ct]

Extrapolating from googled threads in EV and battery forums discussing translated presentations and technical papers.

All technical research docs assume 1C charging is just completely unrealistically slow, 45C and even higher charge rate targets are the norm.

The key question is framed as "how can we reduce the longevity hit? assuming fast as possible charging is required not an option".

And sophisticated thermal management systems are apparently the key at the cutting edge, within current chemistries and manufacturing methods.

I had thought mainly oriented toward accommodating freezing ambients, and removing internally generated heat, but lot more too it than that, basically keeping cells within a tight temp band optimal for the current usage (vs just sitting) mode.

Assumptions that LFP has similar chemical reactions, correlation with temperature trends as the more mainstream LI chemistries in that high C-rate world, make tight quantifications like you propose unrealistic to expect hard evidence, except by our experimenting ourselves.

Bottom line for longevity conclusions:

Low charging C-rates by default, especially when temps are cool do **not** go to high rates,

pre-warm the cells when fast charging, only if short charge times are really needed, still a longevity hit, the higher temp just reduces it.

Warmer temps also make a huge difference for high-C discharge rates, but more of a performance issue there, not as big a longevity hit.

Go cool as possible, and low SoC, while **not** cycling, only allow high temps and charge up to higher SoC ranges just before discharging is required.


Purity of chemistry is also critical QA build quality factor, impurities drastically cut cycling longevity,

I think this is a huge difference between the big respected brands and random / generic cells, besides just cell consistency in general.