LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[john61ct]

Originally Posted by nebster

They're so far superior now in density (essentially, 2x)

Are you trying to say that LFP chemistry batts are themselves at a higher energy density (or power density) now compared to say five years ago?

Or that cell construction techniques have allowed the case / "packaging overhead" to be reduced in that time?

The former is definitely true for the **other** LI chemistries, is why LFP is no longer used in consumer EVs outside DIY builds.

And the latter is definitely the case with soft-sided pouch cells and LiPo packaging of those other LI chemistries.

But I haven't seen any significant density increase (in any of the four definitions) within LFP hard-case prismatics.

A bit yes in the round cells, but really A123 is the only credible LFP vendor there, well maybe Headway.

[john61ct]

Originally Posted by newhaul

Or would it be better to get aluminum cased cells.

Actually that's a good point, I have seen some claimed to be CALB in aluminium.

But I would be skeptical about them preventing swelling without any compression plate / strapping.

If someone really was concerned about intra-pack cooling, then aluminium plates between each cell, extending outward from the side planes to act as heatsinks, maybe active fans triggered by temp sensors for extra ventilation

that could work.

But IMO really overkill for sub-C use cases and ambient conditions averaging under say 30°C

[john61ct]

aluminium plates between each cell, extending outward from the side planes

Would also facilitate faster / more even heating in contexts where that was needed, without getting into the complexities of circulating fluids.

[CatNewBee]

Originally Posted by rgleason

Very interesting theory. Maybe the compression case needs to be a little bigger with compression spacers some thickness (1/4"-1/2") and some distance apart (1 1/2"?) at the sides and bottom to allow air flow?

Not really, the cell cases have vertical bars / ribs as spacers for airflow. How you want to compress and leave space around btw?

[nebster]

Originally Posted by john61ct

The need for compression plates / strapping is critical

This is objectively false for many cell types.

No one "compresses" cylindrical LFP. Others fall on a continuum of mechanical stability and within a performance envelope where expansion may not be the driving concern.

You want to suppress any bulging at all, and it can occur in normal use even coddling care optimizing longevity.

It doesn't occur on mine in normal use. Maybe my manufacturer engineered enough room in the enclosure to accommodate normal shifting.

The temperature "imbalance" issue IMO is a red herring.

It's a good thing it's just YO.

I think it's no surprise at all that interior cells in tightly-packed batteries tend to show more wear over time. They are getting hotter and staying that way longer.

[nebster]

Originally Posted by john61ct

Brand names are absolutely necessary, critical if getting good longevity is an important goal.

Objectively false, again. You're on a roll today.

Of course 5-10 years from now, the "top-notch shortlist" of known-good quality LFP cell makers may well have a couple more names on it

I'm sure they're all eager to make it onto your gilded list.

We've seen a huge decline in that aspect, even within the top-notch shortlist, likely more a supply chain issue than their QA processes.

Can you share your data?

[nebster]

Originally Posted by john61ct

Are you trying to say that LFP chemistry batts are themselves at a higher energy density (or power density) now compared to say five years ago?

Or that cell construction techniques have allowed the case / "packaging overhead" to be reduced in that time?

I'm not sure how much of the gain comes from the former versus the latter.

My suspicion is that almost all of it is "macro/mechanical" improvements -- better packing densities, better electrode topologies, etc. -- rather than low level electrochemical breakthroughs where the underlying chemistry is being tweaked.

But I haven't seen any significant density increase (in any of the four definitions) within LFP hard-case prismatics.

Then you're simply not looking?

My worksheet has about 100 cells in it today, and the energy densities have dramatically improved.

This seems like something you'd be good at: you don't even have to buy anything, John. Just go look at what's for sale and run the numbers.

It is why I always laugh when you rattle off your list of "trusted vendors", all of whom only produce large-scale prismatics using the old, inefficient plastic shell design.

Those of us looking for density performance care a lot more about that than having some "trusted name" factory giving us overpriced, underperforming technology from ten years ago.

[nebster]

Originally Posted by john61ct

Actually that's a good point, I have seen some claimed to be CALB in aluminium.

But I would be skeptical about them preventing swelling without any compression plate / strapping.

Aluminum shell packs are built with no compression, by design. If there is swelling (I can't measure any in real life in a normal battery), it must be happening inside the casing.

I think exotic compression schemes are an old-fashioned idea that we will see fade away quickly going forward. Manufacturers need to leave room inside their shells for day-to-day expansion. And pack builders should use other techniques to avoid the edge-of-envelope operating conditions that produce gross bulging and venting in the first place.

If those conditions can be met, then it makes sense to talk about reducing the temperature gradient across the battery as a follow-on optimization.

[Maine Sail]

Originally Posted by nebster

My worksheet has about 100 cells in it today, and the energy densities have dramatically improved.

This seems like something you'd be good at: you don't even have to buy anything, John. Just go look at what's for sale and run the numbers.

It is why I always laugh when you rattle off your list of "trusted vendors", all of whom only produce large-scale prismatics using the old, inefficient plastic shell design.
.

+1! I would most likely not be buying the plastic shell case technology of 12 years ago, if I were building myself a new pack today. It would most likely be aluminum shell, and they would be much smaller than my Winston cells..

[john61ct]

Originally Posted by nebster

No one "compresses" cylindrical LFP

Nor does anyone afaik use them for house banks. Obviously I was referring to the plastic-shelled prismatics, usually 20Ah and up.

Aluminum cased, I dunno.

[newhaul]

Originally Posted by john61ct

Nor does anyone afaik use them for house banks. Obviously I was referring to the plastic-shelled prismatics, usually 20Ah and up.

Aluminum cased, I dunno.

Did you even watch the video i posted of will prowse when he toured the battleborn factory?

They are made with cylindrical lfp cells

[nebster]

Originally Posted by john61ct

Nor does anyone afaik use them for house banks.

Lolwut?

Battle Born uses them exclusively in their batteries. And they have a HUGE deployed base in the USA RV self-install/DIY market now.

[john61ct]

Interesting.

What brand / model cells?

No wonder they're careful about C-rates!

[newhaul]

Originally Posted by john61ct

Interesting.

What brand / model cells?

No wonder they're careful about C-rates!

Go back a few pages and actually watch the video i posted . It answers all of your questions about battleborn.

http://www.cruisersforum.com/forums/...ml#post3050340

[john61ct]

Not that one