Effect of charge profile on the lithium battery

[zee123king]

What is the effect of charge profile on the health of lithium battery pack?
For example, if soc is 0-5%, we charge with 4 Amperes, if SoC is 5-10%, then we charge with 5A, similarly we increase the current to max. 10A for 80% SoC then decrease the current to 6A at full charge.

Is this method feasible or possible for a lithium ion battery charger? Would this have any negative effect on the health of the battery? Is there any provision in the charger for this feature?

 

[Korishan]

That's similar to the way most Lithium battery chargers function. It's called CC/CV.

When the voltage is below a certain threshold, then only a small amount of current is applied. Once this is reached, current is ramped up to a predefined max until the battery reaches a certain voltage threshold again, and the charger switches to CV mode and holds the voltage and allows the current to slowly trickle down to 0 amps.

This method is actually what helps keep Lithium batteries healthy

 

[zee123king]

Actually what I wanted to implement is to not use the constant current routine (CC) but replace it by current steps of fixed or variable duration. So it's different from the conventional CC-CV routine generally used by chargers. A rough diagram I have attached. So what is the effect of such type of routine on health of battery or any charger already using such type of routine? Is it feasible?

 

[Korishan]

Actually what I wanted to implement is to not use the constant current routine (CC) but replace it by current steps of fixed or variable duration. So it's different from the conventional CC-CV routine generally used by chargers. A rough diagram I have attached. So what is the effect of such type of routine on health of battery or any charger already using such type of routine? Is it feasible?

Sure it's feasible, if your charger is able to be programmed that way.
Curious as to why you'd want to do it that way though? I doubt using a more complex charging method is gong to yield a much longer life span on the cells.

I have an RD6018 with the custom firmware installed, with that I can connect it via usb/wifi and send a charging script to the power supply to follow particular patterns. So if something like that can do that, then there are other ways. Thing is, you either need a charger that can be controlled via serial or other means by an external source, or build one yourself.

 

[zee123king]

Actually I am looking at various ways to improve the state of health of a lithium battery. So if we vary the charging profile, how much can we improve the lifespan of the battery that is the main objective of the study. I have looked at various charging profiles like pulse charging, multistage constant current. So I wanted to see if custom current profiles could yield a better result.

 

[Korishan]

Almost sounds like you're preparing a Thesis

Would be interesting if there's any difference. Problem is getting used cells that are practically identical in degradation and do the test study on some, and normal on the others, and see which batch lasts longer.

Definitely not a short term experiment.

 

[zee123king]

Yes.. not exactly but similar scale experiment It will take some time

 

[OffGridInTheCity]

Actually I am looking at various ways to improve the state of health of a lithium battery. So if we vary the charging profile, how much can we improve the lifespan of the battery that is the main objective of the study. I have looked at various charging profiles like pulse charging, multistage constant current. So I wanted to see if custom current profiles could yield a better result.

I understand there is more than just solar systems, but perhaps you could clarify the type of lithium battery operation you're thinking of.

Off-grid Solar....
As one who operates a large NMC powerwall to support an off-grid solar power generation system targeted for extra long battery life......

Charging is primarily about...
1) low stress environment - modest temps, no moisture, etc....
2) low stress charge (and discharge) current per cell - lower ma/cell is better and one way to achieve this is by having a larger battery. Specifically, I'm running somewhere in the ~100ma/cell average on 18650 cells in the 2000mah-3000mah capacity range.
3) low stress DOD - operating in the middle range of the battery at lifetime average of 37% DOD.

**This means that CV never even comes into play as the top ranges of charge never come into play. So for me, as a logic experiment, CC coupled with a good environment, low stress, low DOD, and avoiding both extreme ends of the voltage range is perfectly adequate.

 

[italianuser]

Hi there @zee123king, nice to hear about your project.

You should keep the cell's specifications in mind. Normally if you charge or discharge a cell at currents higher than the ones in the datasheet will result in a lower capacity. You can see this on the datasheets. I mainly use ICR cells (not power cells) so the examples I'll bring are for Samsumg and Panasonic cells.

(Ref. Samsung ICR18650-22F.pdf Datasheet)

You can see the difference when charging at 0.2C (440mA) in respect to 1.0C (2200mA).

Same happens when discharging:

(Ref. PANASONIC_CGR18650EA.pdf)

Discharging at 0.2C (490mA) gives the best performance. That's why I always say that Liitokala 500s discharging at max.500mAh may be an advantage respect to Opus' 1000mAh discharge, as for what capacity goes (not for time factor!).

I show both charge and discharge curves because a complete capacity measurement is done using a Charge-Discharge-Charge (CDC) cycle.

Keep us updated with your project!

[EDIT: all tests at 25°C, at different temperatures you'll obviously get different capacity results]

 

[zee123king]

Yes...@italianuser Thanks for the wonderful insight. I will keep updating any new information