Featured Dr. Prius Packs Less Than A Year Away?

Here's one paper giving a ballpark:

Rickman et al., Considerations for the Thermal Modeling of Lithium-Ion Cells for Battery Analysis, 48th International Conference on Environmental Systems, 10–14 July 2016, Vienna.

Of course that's for Li-ion, maybe a little different from LiFePO4, and a closer value would really depend on details of construction. So yeah, what I'm doing here is back-of-an-envelope scribbling just to get a ballpark, not pinpoint accuracy, but somebody else could.

I'll also scribble on this envelope that I've heard the Project Lithium packs are about half the weight of the NiMH ones, which I'll take to be "about a hundred pounds", so I'll call the lithium ones "about fifty", and someone who knows a closer number can step in with that.

So about fifty pounds of stuff, or 23,000 grams, at 0.9 J/g-℃, works out to a thermal mass around 21,000 J/℃.

The electric car blanket I have is around 40 watts. So I could use that to warm up this battery in (optimistically) around nine minutes per celsius degree I needed the temperature raised.

("Optimistically" assuming the blanket perfectly applied to the battery so all the 40 watts go to heating the battery, and also disregarding the ongoing heat loss to the environment as the battery warms. Hard to fit all that stuff on the back of an envelope.)

For the 12-volt capacity required, that'd be about six watthours, or half an amphour from a 12-volt battery, for each celsius degree of warming needed.

Somebody wanting to do the work of building an actual thing could either do much more careful work to get more accurate numbers, or just start with those and double or quadruple them and say "probably good enough".

 

Yes, that's what the paper cited in #121 is getting at when it talks about estimating the thermal mass from "the effective specific heat of the constituent materials". That's another one of those things that has been thought of before, and "often reported to be close to 0.9 J/g-℃". An example of a "back of the envelope" calculation.

Yes, that's the experimental way to approach it, and that's the way (if the experiment is designed and conducted well enough) to get a less-approximate answer, one that more closely accounts for all the details of how the Prius battery is constructed.

But even there, the ability to do a quick back-of-the-envelope usually figures in, even just for designing the experiment: around how many hours do you expect it to take, and budget for the experiment, times the number of different temps to try, and how many socks (or what wattage of socks or blankets or similar items) should be used to conduct the experiment in a reasonable time, and how much 12 V capacity should be available to power them?

Those are all the kinds of questions that you can get closer answers for by experiment, but where you'd typically use back-of-the-envelope at first to quickly find the ballpark and design a practical experiment.

That is a nice article. Have to read pretty much to the end to see what's the wattage of the battery heaters they use. They "draw 6 amps each during operation", so they're using a pair of 72-watt heaters, or 144 watts total.

When I google around for heated socks, I'm seeing listings in the neighborhood of "9 Watts of Heat ... in each sock", or 18 watts a pair. So the article is using heat equivalent to about 8 pairs of heated socks, or about 3½ heated blankets like the one I've got.

The article also mentions "leaving them on constantly isn’t a realistic option with a 6 amp consumption for each pad. Make sure you have enough amp hours available in the battery to pre-heat and to keep the batteries warm during charging."

So the article isn't quite offering a worked-out, turnkey solution. Coming up with a workable power budget is still an exercise for the reader. If it were realistic to leave the heaters on constantly, you would only need enough power to keep the battery temperature from dropping too low (though you'd need it constantly). But if the power budget forces you to let the battery cool down and then preheat it just for charging, then you need to think about how many degrees of warming that preheat will have to accomplish, and how many watthours that'll require, and how long it'll take (or, how much heating wattage will be needed so it doesn't take longer than you're willing to wait).

Those all are the kinds of questions where back-of-the-envelope skills come in handy.

 

One important aspect of a new product is ensuring there is sufficient demand to warrant the manufacture of the product.....

 

This might be a bit radical, but if you need a new hybrid battery in an area that regularly sees below freezing temps, maybe you should consider NiMH.

 

Battery chemistry operating temperatures:

Lithium Ion: -20C to 60C
LiFePO4: -20C to 60C
NiMH: –20 to 45 °C

Tesla is ready to go LiFePo4:

https://electrek.co/2022/04/22/tesla-using-cobalt-free-lfp-batteries-in-half-new-cars-produced/

From what I read. The IP owners of LiFePO4 strictly and only allowed China to be the producers. But that patent has expired this year. Any battery producer can start producing LiFePO4 cells.

 

There is a big gap between ‘can’ and ‘does’.

Bob Wilson

 

American Battery Factory (ABF) announced today that it would build its first lithium iron phosphate (LFP) Gigafactory cell production site in Tuscon, Arizona, with a total annual capacity of 3 GWh.

ABF lands in Arizona for its first LFP Gigafactory in the U.S.

 

We don’t have enough chemical and systems engineers. But it may be an opportunity for petroleum engineers to escape.

Bob Wilson

 

Once Jack gets his patent, he has huge potential to license out his battery packs to any battery producer. He needs high quality production that can produce good packs at a good price. There are millions of Toyota NiMH cells ready to be replaced world wide. Maybe Toyota will buy him out.

 

LFP was discovered in the USA but somehow strictly given over to China royalty free. Does anyone smell something...fishy/corrupt?

China and vehicle batteries vying dominance estimated 24 trillion market | Quantumrun

"The invention of a battery formulation in the 90s called lithium-iron-phosphate (LFP) by John Goodenough, an American professor, has been integral in China’s prolific production of batteries. Furthermore, thanks to a decision by a Swiss-based patent-holding consortium that restricted China’s use of LFP batteries to their local market, China maximized the opportunity to manufacture these batteries without paying exorbitant licensing fees."

Batteries: The true drivers behind LFP demand - new safety standards, costs, IP rights, ESG & simplified battery pack designs — Roskill

"IP rights kept LFP confined to the Chinese market; this will change after 2022

LFP cathode producers explained to Roskill that the consortium managing LFP’s IP rights reached an agreement with the Chinese battery industry a decade ago in which, as long as LFP was produced and used within China, the consortium would not charge Chinese manufacturers a licensing fee. As a result, the price of Chinese LFP batteries has always been considerably lower than non-Chinese LFP batteries. However, the patents’ restrictions over LFP will start to expire in 2022. Simultaneously, the limitation of LFP exports on Chinese producers will be largely removed, along with the licensing fee for non-Chinese LFP cell producers. The removal of this IP barrier could become the largest opportunity for LFP-based Li-ion batteries to rapidly gain market share in the EV market outside China."

 

Why LFP batteries are poised to bring down entry-level EV prices • TechCrunch

"A slew of patents for lithium-iron-phosphate (LFP) chemistries due to expire in 2022 could shift the face of battery production in the U.S. and Europe.

China has owned the market for nearly a decade due to an agreement with patent holders — a consortium of universities in the U.S. and Canada — that let Chinese manufacturers use them to supply local markets. Meanwhile, manufacturers outside China have focused on developing other lithium-ion chemistries to power their EVs because their higher energy density translates into longer range on the road."

Tesla looks to pave the way for Chinese battery makers to come to U.S. | Reuters

"China dominates the production of iron-based batteries thanks to a series of key patents, which have allowed the country to make 95% of the world’s Lithium Iron Phosphate (LFP) batteries.

However, these patents expire soon and Tesla said it plans to adopt LFP batteries in its fleet of standard-range vehicles globally and move battery production here closer to its factories."

 

Is that glacier monitoring equipment being charged out in the field, or are the batteries or equipment being swapped for fresh units, and being taking back to base for charging at warmer temperatures?

Li-ion, including LFP, doesn't have an issue discharging at below freezing temps, beyond the usual reduced output. The issue is with charging. If the cell is at or below 0C, irrevesible lithium plating occurs at the anode when charged, which isn't good for the useful life of the battery.. On start up, a hybrid goes through a warm up cycle for the ICE. Excess output from the ICE during this time goes to charging the battery. If the battery is at 0C, which is likely on first start up in the winter, then you are damaging the battery.

For those concerned about that possibly, then NiMH is a better option because it doesn't have the no charging at freezing temperature restriction.

 

NiMH is also not supposed to be charged below freezing. So maybe that is already factored into the Toyota hybrid system to wait until the battery is at charging temps before attempting to charge.

As more Nexcell users run into freezing temps, hopefully we can get more feedback about performance and health of the batteries. Running the Dr. Prius app can help us see if the hybrid system attempts to charge below freezing or not.

NiMH and LFP both discharge at -20C and in the process release heat. So maybe we can get more users to monitor how discharging below freezing increases temps high enough to accept normal charging.

 

I'm out in Denver and would love to work with Jack or @PriusCamper to develop more data sets around these potential issues. I was just skiing in the mountains over the weekend and its easy to see overnight temperatures below zero, combined with a few days of parking my car in a parking lot, cold soak on the components becomes real.

 

I don't think you are suppose to charge any battery chemistry below freezing. Too cold and too hot aren't ideal conditions for a battery in use. So you aren't suppose to use them then.

Lithium plating permanently reduces the battery capacity. I'm not finding info on whether NiMH suffers such permanent damage when charged at such low temperatures. Just the general too high and too low warning that such aren't good for any battery.

Toyota has stated they use NiMH in the AWD Prius because of the chemistry's better cold performance. Panasonic has at least one product that can be charged down to -10C. https://industrial.panasonic.com/cdbs/www-data/pdf2/ACG4000/ACG4000C13.pdf

 

Also once the engine fires up. The heat from the exhaust immediately begins heating up the underbelly which runs under the hybrid battery. More data set to factor in.