Prismatic and cylindrical LiFePO4 cells.

[Mattb4]

Recently I noticed that there seems to be 2 styles of LiFePO4 battery cells. There is the block style (with blue plastic) that I have used in a battery build, it seems fairly common. However I now notice that there is a cylindrical tube style that seems mostly used by the scooter, electric bike crowd. One oddity I am noticing is both are sometimes called prismatic in some listings so I am not sure what that means. Is prismatic a designation for block and to use it for cylindrical an error?

I could see some advantages to using cylindrical cells if they work the same as the blocks. There seems to be a fair amount of selection when it comes to amp-hour ratings. I looked at 100ah cells and found this listing: https://www.evlithium.com/LiFePO4-Battery/100ah-cylindrical-lifepo4-battery.html I also saw several suppliers over on Alibaba.

Advantages/disadvantages? Anyone working with the cylindrical for solar battery storage and their impressions?

 

[SparkyJJO]

I honestly have no idea why they call the rectangular ones prismatic.

pris·mat·ic
/prizˈmadik/

adjective

Relating to or having the form of a prism or prisms.
"a prismatic structure"

Doesn't sound right to me, but...

 

[sunshine_eggo]

I honestly have no idea why they call the rectangular ones prismatic.



Doesn't sound right to me, but...

Gotta go to the definition of a prism:

A prism is a polyhedron comprising an n-sided polygon base

A polyhedron is a three-dimensional figure with flat polygonal faces, straight edges and sharp corners or vertices.

The typical shape of "prismatic" cell is a "rectangular prism."

"Cylindrical" describes, "in the shape of a cylinder"

When you jumble all that together, "prismatic" describes a "rectangluar prism" and is analogous to "cylindrical" when referring to cylinders.

 

[rogerheflin]

Recently I noticed that there seems to be 2 styles of LiFePO4 battery cells. There is the block style (with blue plastic) that I have used in a battery build, it seems fairly common. However I now notice that there is a cylindrical tube style that seems mostly used by the scooter, electric bike crowd. One oddity I am noticing is both are sometimes called prismatic in some listings so I am not sure what that means. Is prismatic a designation for block and to use it for cylindrical an error?

I could see some advantages to using cylindrical cells if they work the same as the blocks. There seems to be a fair amount of selection when it comes to amp-hour ratings. I looked at 100ah cells and found this listing: https://www.evlithium.com/LiFePO4-Battery/100ah-cylindrical-lifepo4-battery.html I also saw several suppliers over on Alibaba.

Advantages/disadvantages? Anyone working with the cylindrical for solar battery storage and their impressions?

The major advantage is you can get 20ah cylindrical cells that are rated for 3-4C for 30seconds. So the 100Ah cells you have above can do 300a for 30 seconds, and the 20ah cells can do 60A for 30sec. Basically they have a higher current to capacity hence them being used in high draw applications (scooters, wheelchairs, autos).

They cost more per Kwh because of the design changes needed to sustain higher currents.

They might have a use in a solar system when you really just need/want minimal batteries to sustain power for a short term a lack of solar (or an MPPT sweep). In a min battery setup they might make sense to be there to stabilize power output across short solar blips.

 

[Mattb4]

Gotta go to the definition of a prism:

A prism is a polyhedron comprising an n-sided polygon base

A polyhedron is a three-dimensional figure with flat polygonal faces, straight edges and sharp corners or vertices.

The typical shape of "prismatic" cell is a "rectangular prism."

"Cylindrical" describes, "in the shape of a cylinder"

When you jumble all that together, "prismatic" describes a "rectangluar prism" and is analogous to "cylindrical" when referring to cylinders.

Uh... could you repeat that slower using smaller words?

 

[SparkyJJO]

Gotta go to the definition of a prism:

A prism is a polyhedron comprising an n-sided polygon base

A polyhedron is a three-dimensional figure with flat polygonal faces, straight edges and sharp corners or vertices.

The typical shape of "prismatic" cell is a "rectangular prism."

"Cylindrical" describes, "in the shape of a cylinder"

When you jumble all that together, "prismatic" describes a "rectangluar prism" and is analogous to "cylindrical" when referring to cylinders.

............

k I'm calling it a blue box

 

[Mattb4]

The major advantage is you can get 20ah cylindrical cells that are rated for 3-4C for 30seconds. So the 100Ah cells you have above can do 300a for 30 seconds, and the 20ah cells can do 60A for 30sec. Basically they have a higher current to capacity hence them being used in high draw applications (scooters, wheelchairs, autos).

They cost more per Kwh because of the design changes needed to sustain higher currents.

They might have a use in a solar system when you really just need/want minimal batteries to sustain power for a short term a lack of solar (or an MPPT sweep). In a min battery setup they might make sense to be there to stabilize power output across short solar blips.

I noticed that the price for 100ah ones was pretty low ~$27 per cell (even more so in quantity). Does being able to deliver higher amperage hurt them when delivering lower amperage over longer periods?

 

[Frugal Devonian]

Cylindrical cells basically roll off the production line,no compression debate either.

 

[sunshine_eggo]

The major advantage is you can get 20ah cylindrical cells that are rated for 3-4C for 30seconds. So the 100Ah cells you have above can do 300a for 30 seconds, and the 20ah cells can do 60A for 30sec. Basically they have a higher current to capacity hence them being used in high draw applications (scooters, wheelchairs, autos).

They cost more per Kwh because of the design changes needed to sustain higher currents.

They might have a use in a solar system when you really just need/want minimal batteries to sustain power for a short term a lack of solar (or an MPPT sweep). In a min battery setup they might make sense to be there to stabilize power output across short solar blips.

This isn't a cylindrical vs. prismatic thing. It's a construction/IR thing. I have some Navitas/Topband 25Ah prismatic cells rated for 3C continuous.

 

[rogerheflin]

I noticed that the price for 100ah ones was pretty low ~$27 per cell (even more so in quantity). Does being able to deliver higher amperage hurt them when delivering lower amperage over longer periods?

I would not think it would.

That comes to about the same price as a 305ah prismatic, but with a lot more smaller cells (when targeting large capacity) assembly gets to be more parts/labor (and possibly increases costs), and you would have to end up doing multiple cells in parallel which has risks.

 

[RCinFLA]

To optimize cell to maximize AH for size and weight you build cell with thick electrodes (graphite for neg anode, LFP for positive cathode). Disadvantage of this is the thicker electrodes increase the overpotential voltage drop at higher cell current, making the cell have a lower maximum current capability due to increased cell voltage slump at high current.

To optimize for high current performance, you build a cell with many thin layers of electrodes. This means more metal foil layers that takes up room so there is a bit less AH's for same size cell. But you get lower cell impedance giving a higher peak current capability on cell.

There is a limit on how thick the electrode can be and roll it up into a cylindrical form factor without electrode cracking.

Other advantage of the cylindrical form is you have better heat dissipation to outside of cell which is also something you want for high current capable cells.

Thick electrode prismatic cells have lower manufacturing cost per AH.

 

[Frugal Devonian]

I'd guess cylindrical are more energy efficient to produce too so greener?

 

[MrSparkle]

k I'm calling it a blue box

Don't say "blue box" in the presence of @sunshine_eggo , or our in-house-smurf will be all over the place like bees on the honey, considering his penchant to "blue boxes" from a known brand...

One oddity I am noticing is both are sometimes called prismatic

Well... people say Watts when they talk about Whatt-Hours.
... say clay roof tiles when speaking of cement tiles.
The list is huge.
We live in an age of overwhelming information flow, when even "educated" journalist seemingly do not reflect over what they are writing even though self-sensor is mandatory.

 

[yabert]

This isn't a cylindrical vs. prismatic thing. It's a construction/IR thing. I have some Navitas/Topband 25Ah prismatic cells rated for 3C continuous.

I second.
LEV60F 3.2v 74ah Lifepo4 cells are another example of prismatic high discharge cells: https://jag35.com/products/clearanc...0jS9gU92t89jutC2NOj78U61trZtaHJvTxXzMhX4Y4vlh

 

[sunshine_eggo]

To optimize cell to maximize AH for size and weight you build cell with thick electrodes (graphite for neg anode, LFP for positive cathode). Disadvantage of this is the thicker electrodes increase the overpotential voltage drop at higher cell current, making the cell have a lower maximum current capability due to increased cell voltage slump at high current.

To optimize for high current performance, you build a cell with many thin layers of electrodes. This means more metal foil layers that takes up room so there is a bit less AH's for same size cell. But you get lower cell impedance giving a higher peak current capability on cell.

The above is analogous to deep cycle vs. starter lead acid batteries... deep cycle have thick plates and can better handle deep cycles.

Starter batteries have multiple thinner plates for higher current.

There is a limit on how thick the electrode can be and roll it up into a cylindrical form factor without electrode cracking.

Other advantage of the cylindrical form is you have better heat dissipation to outside of cell which is also something you want for high current capable cells.

I'm going to disagree and say this is dependent on the actual geometry of "identical" cells. "identical" in terms of capacity, IR and C rate.

Case in point... NiMH "D" cells vs. thin prismatic cells of same height, but about 40% thickness. 6.5Ah, 1mΩ, 20C. Same manufacturer (Panasonic EV Energy, Primearth EV Energy).

The "D" cells exhibited horrific cooling characteristics due to their substantially 2X thickness, and lower surface to volume ratio. Essentially, cooling ability is proportional to the center to cooling surface distance and ratio of volume to total cooling area. Cylindrical cells are also an aerodynamics nightmare for forced convective cooling.

As evidenced by hundreds of thousands of Honda hybrids vs. even more Toyota hybrids. Hondas had dramatically higher failure rates with some models as high as 16-30% in 4-7 years where prismatic failures were in the low single digits in the same timeframe.

It's worth noting that the battery cooling fans of the Hondas were like leaf blowers, and the cooling fan of a Toyota is like a hairdryer on cool. Dramatically higher CFM in the Hondas.

In the extreme cases (30%), this was predominantly due to a completely asinine cooling system design change that created 132 hot spots within the pack (one per cell). At the lower end (16%), these were NOT the result of cooling system design issues, but attributable to the cells running at a higher core temperature with a large thermal gradient from center to surface. This gradient also contributed to degradation and failure.

If you look at what is typical of the existing cylindrical (low capacity) vs. prismatic cells (notably higher capacity), cylindrical may cool better simply due to their smaller size with higher surface area to volume ratio, but you're going to need more cells. Same for same, I do not agree that two LFP cells with identical performance specs will see better cooling performance for cylindrical vs. prismatic.

 

[Mattb4]

It might be fun to put together a battery from the larger ah cylindrical cells if they start being available in the US. In my searching so far I seem to find only Alibaba as a place to find them. Probably show up on Aliexpress at some point.

 

[tinyt]

It might be fun to put together a battery from the larger ah cylindrical cells if they start being available in the US. In my searching so far I seem to find only Alibaba as a place to find them. Probably show up on Aliexpress at some point.

S168 55AH assembled in july 2022, still working but probably 1C or less loading only. Bought from ebay then (maybe removed from equipment), seems to be un-available now even from aliexpress.

 

[MrSparkle]

@tinyt That is one nice, tidy, clean build of battery-pron!

 

[tinyt]

@tinyt That is one nice, tidy, clean build of battery-pron!

Look for the nut that has burn marks. That was before I insulated the wrench handles.

 

[MrSparkle]

Look for the nut that has burn marks. That was before I insulated the wrench handles.

Aaah, that's what those markings are from...! Well, even sun have its spots?
Also, been thinking. Would it not been slightly more advantageous to connect cells this way?
I
O
I........I
O O-O
I...I
O O-O
I........I
O O-O
I...I
O O-O
I........I
O-O-O
So that both end terminals would be on the top hence shorter cables?

Btw, "Wrench"? You mean "torque-wrench" huh?

 

[tinyt]

Aaah, that's what those markings are from...! Well, even sun have its spots?
Also, been thinking. Would it not been slightly more advantageous to connect cells this way?
I
O
I........I
O O-O
I...I
O O-O
I........I
O O-O
I...I
O O-O
I........I
O-O-O
So that both end terminals would be on the top hence shorter cables?

Btw, "Wrench"? You mean "torque-wrench" huh?

Will figure out that arrangement later, too confused right now.
Also, this is what I have just recently assembled. And still one cable is long.