Commissioning charge for new cells

[Haxx]

Hey guys,

While browsing through older posts, I read that new cells, after a few gentle cycles, should be commissioned properly, by charging at minimum .5c for a few cycles. Something about avoiding building up favoured or strong/weak pathways in the battery.

For those of us with bigger cells (280/305/etc) this is sometimes not a simple task.

How important is this, and any experts able to explain it in simple terms for the rest of us?

 

[DIYrich]

I have not heard of that for LiFePO4. I'm interested to hear

 

[Steve_S]

Top Balancing new Cells is standard. This is done with new cells or with those that have been in storage for an extended period.

Here's one of our references on the subject.

Top Balancing LiFePo4 Cells using a low cost benchtop power supply.

To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...

diysolarforum.com

 

[Haxx]

Top Balancing new Cells is standard. This is done with new cells or with those that have been in storage for an extended period.

Here's one of our references on the subject.

Top Balancing LiFePo4 Cells using a low cost benchtop power supply.

To get the paper, click on the orange at the top of this page. This is a tutorial with detailed steps on how I top-balance my LiFePO4 Cells using a low-cost benchtop power supply. To get the tutorial, click on the orange "Download" button...

diysolarforum.com

I'm very familiar with top balancing, but if you re-read my original post, you'll see i'm asking about minimum charge amps.

While reading through an older thread regarding LiFePO4 cell capacity, someone had mentioned something regarding about not accessing the full capacity unless you run some higher-amp (e.g. half c-rate) charge cycles once the batteries have been gently broken in.

It sounds like they are saying that under low-amp i/o, the cell will favour the same pathway(s) with the least resistance, and that some sections of the cell see little use. By pushing significantly more amps through, it results in current being spread out more, and promotes development of more 'easy' pathways inside the cell.

I'm going to look around the interweb for more info, but was hoping some experts could weigh in here, as well.

 

[mikefitz]

I read that new cells, after a few gentle cycles, should be commissioned properly, by charging at minimum .5c for a few cycles.

Should not the manufactures QA test create this condition ?

 

[Haxx]

Should not the manufactures QA test create this condition ?

It sounded like this was supposed to be done after the cells are broken in a bit.

I'll see if i can find the post again and quote the original on this thread.

 

[Haxx]

Found it. Posts #47 and #48 in this thread:

Disappointing EVE 280K Results

Real world: nobody is going to pay attention to a 5% reduction in stated capacity going from 280 to 266ah. That's actually not bad for consumer level. "But then they should sell them as 265ah!" If you were in business, a competitor with same cells would clean your clock by selling as 280ah...

diysolarforum.com

By user @Substrate

This is a link shared in that thread which describes the general processes of creating a lithium cell.
Some interesting info there too.

Li-ion cell manufacturing: A look at processes and equipment

The production of the lithium-ion battery cell consists of three main stages: electrode manufacturing, cell assembly, and cell finishing. Each of these stages has sub-processes, th...

etn.news

 

[toms]

Initial charge regime is critical, it forms the SEI (solid electrolyte interface/interphase).

After the very initial charge the cell is scanned under an electron microscope and if the SEI isn’t forming correctly the cell is rejected. These cells make up the majority of cells sent to brokers for resale (marked ‘B’ if it’s an EVE).

Immediately putting a cell at this stage of SEI formation into low current high voltage situation (eg parallel top balance) guarantees the SEI will not finish formation correctly.

Terminating charge at a higher current or lower voltage has less effect on the SEI.

When I got my first LiFePO4 cells I spoke at length with my manufacturer regarding the requirements of the cells.

 

[Haxx]

Is this something I should be doing with my LF280K batteries - Aiming for a few (how many?) charge cycles at 140-150 amps?

Will it do anything for cells a hundred cycles in, or does it need to be done early on?

Any idea what real world difference there is in doing it vs not doing it?

 

[toms]

Is this something I should be doing with my LF280K batteries - Aiming for a few (how many?) charge cycles at 140-150 amps?

Will it do anything for cells a hundred cycles in, or does it need to be done early on?

Any idea what real world difference there is in doing it vs not doing it?

If you purchased cells new from the manufacturer you only need to follow thier charge regime.

If you purchased cells from a broker and aren’t 100% certain of their status after the manufacturers QA process, then you should assume they have only had an initial charge (typically around 0.2C to 3.65V)
The next few charge cycles should be ramping down from 0.2C (56A).

Keep in mind the manufacturer SEI formation charges are hard cut. ie- the cell current is kept constant at a fixed value (eg 0.2C), then the instant the voltage reaches its preset (eg 3.65V) the charge cycle is terminated. The cell voltage instantly drops. No manufacturer holds a cell at its full voltage.

There has been a huge amount of manufacturer investment and research into electrolyte composition and SEI formation charge regimes. I doubt you will find anything published other than white papers by university students that often miss the mark.

What hasn’t changed is that if you start off the initial charge regime with too low current, you will get dendrite seeding. If you have too high current you will end up with a porous SEI layer.

 

[Haxx]

If you purchased cells new from the manufacturer you only need to follow thier charge regime.

If you purchased cells from a broker and aren’t 100% certain of their status after the manufacturers QA process, then you should assume they have only had an initial charge (typically around 0.2C to 3.65V)
The next few charge cycles should be ramping down from 0.2C (56A).

Keep in mind the manufacturer SEI formation charges are hard cut. ie- the cell current is kept constant at a fixed value (eg 0.2C), then the instant the voltage reaches its preset (eg 3.65V) the charge cycle is terminated. The cell voltage instantly drops. No manufacturer holds a cell at its full voltage.

There has been a huge amount of manufacturer investment and research into electrolyte composition and SEI formation charge regimes. I doubt you will find anything published other than white papers by university students that often miss the mark.

What hasn’t changed is that if you start off the initial charge regime with too low current, you will get dendrite seeding. If you have too high current you will end up with a porous SEI layer.

Interesting. Thanks for the info!

Am I understanding it right, in that usually by the time we start using the cells (from a reputable seller, like 18650batterystore, CurrentConnected, etc) we shouldn't have to worry about this at all?

 

[toms]

Interesting. Thanks for the info!

Am I understanding it right, in that usually by the time we start using the cells (from a reputable seller, like 18650batterystore, CurrentConnected, etc) we shouldn't have to worry about this at all?

That’s correct, a cell that has passed manufacturer QA process has a fully formed SEI.