Verify battery chemistry...

[Mark-]

Hello,

A rack mount 16 cell, 100 Amp hour battery, that is sold as a (website, specification sheets claim it) LiFePO4/Lithium Ferrous Phosphate battery but, the user manual from the manufacture does not contain the words “LiFePO4” or “Lithium Ferrous Phosphate”, what is the best way to verify the chemistry? Opening the battery case for inspection, what conclusively, proves the chemistry is or is not as advertised? Is it possible?

 

[MisterSandals]

If you reveal what secret battery you are talking about, somebody here might know and be able to answer your question.

 

[Mark-]

If you reveal what secret battery you are talking about...

Thanks for the response.

I did not provide the name to prevent unnecessary troubles for the seller due to a possible slight error on the manufactures side of the ledger. Plus I have purchased another brand (rack mount 16 cell, 100 Amp hour battery, etc.) from AliExpress and it is in transit. So the data on how to determine the chemistry via a visual inspection, if possible, would be used to also examine that battery.

If either turns out not to be what is sold, I will publish the battery information (with pictures).

 

[LydMekk]

No reason to hold that back...
Otherwise this is like guessing next weeks Lotto numbers ^^

 

[ejfluhr]

The maximum charge voltage should be able to confirm the chemistry. 16s LiFePO4 would peak at roughly 57.6v. Lower voltages should still be unique enough to identify the chemistry.

 

[Nobodybusiness]

No reason to hold that back...
Otherwise this is like guessing next weeks Lotto numbers ^^

I do that quite often to no avail.

 

[russc25]

Do the instructions mention other battery chemistries or do the directions involve voltages that would indicate different chemistries?

 

[Mark-]

The maximum charge voltage should be able to confirm the chemistry. 16s LiFePO4 would peak at roughly 57.6v. Lower voltages should still be unique enough to identify the chemistry.

Thanks for the response.

The manual has: Charging cutoff voltage 58.4.

 

[Mark-]

Do the instructions mention other battery chemistries or do the directions involve voltages that would indicate different chemistries?

Thanks for the response.

The user manual has "Lithium-ion" and "Lithium" battery.

 

[RCinFLA]

LFP across their SoC range have rested open circuit cell voltage of 3.25v to 3.43v.

Battery voltage is cathode material potential minus anode material potential. In the graphs below it is the 'blue' line.

Most lithium-ion cells use graphite for negative anode. LTO is an exception. Some NCA and NMC cells have a small amount of silicon added to graphite to increase capacity but silicon fractures in a low number of charge cycles which reduces capacity quickly over charge cycles.

 

[Mark-]

LFP across their SoC range have rested open circuit cell voltage of 3.25v to 3.43v.

Battery voltage is cathode material potential minus anode material potential. In the graphs below it is the 'blue' line.

Most lithium-ion cells use graphite for negative anode. LTO is an exception. Some NCA and NMC cells have a small amount of silicon added to graphite to increase capacity but silicon fractures in a low number of charge cycles which reduces capacity quickly over charge cycles.

Thanks for the response.

 

[ejfluhr]

>The manual has: Charging cutoff voltage 58.4.

58.4v/16 cells = 3.65v per cell

That indicates LiFePO4. Different manufacturers stop at 3.60v or 3.65v, depends on how aggressive they are with specs and maybe balancing.

The other major form of lithium, often called Li-NMC for its constituent elements, has Vmax of 4.2v per cell. So a 14s battery would peak at 58.8v, which is rather close to LiFePO4 16s max and can confuse some. Verify the cell count and you should have your answer.

 

[Mark-]

>The manual has: Charging cutoff voltage 58.4.

58.4v/16 cells = 3.65v per cell

That indicates LiFePO4. Different manufacturers stop at 3.60v or 3.65v, depends on how aggressive they are with specs and maybe balancing.

The other major form of lithium, often called Li-NMC for its constituent elements, has Vmax of 4.2v per cell. So a 14s battery would peak at 58.8v, which is rather close to LiFePO4 16s max and can confuse some. Verify the cell count and you should have your answer.

Thanks for the response.

 

[RCinFLA]

All batteries have overpotential terminal voltage with cell current. It is overhead required to drive the kinetics of cell. In lithium-Ion cells it drives the lithium-ion migration through the cell to support the demanded electrode current, either charge (bump up) or discharge current (voltage slump).

The 3.65v maximum charge voltage is just a set voltage limit at which a slight increased rate of electrolyte damage begins. The amount of necessary overpotential depends on how high the charge current pushed through cell. At low charging current 3.45v will achieve full charge on LFP, just takes longer to fully charge.

At full charge with sustained overpotential there is also an inter-layer surface charge build up, like a super-capacitor, that builds up mostly in graphite that artificially raises terminal voltage over the inherent 3.43v full charge of LFP cell voltage. The surface charge has insignificant amount of capacity compared to actual cell lithium-ion driven capacity, amounting to less than 0.02% of cell capacity. This surface charge will bleed off in a few hours to a couple of days of time if cell if left open circuited after taking off charge. Many misinterpret this as cells not being balances after doing a 3.65v top balance when it is just the different cells bleeding off their surface charge at different rates. Cells are fully charged and balanced at full charge as long as no cell drops below about 3.45v of open circuit terminal voltage.

 

[Mark-]

All batteries have overpotential terminal voltage with cell current. It is overhead required to drive the kinetics of cell. In lithium-Ion cells it drives the lithium-ion migration through the cell to support the demanded electrode current, either charge (bump up) or discharge current (voltage slump).

...

Thanks for the response.