A123 FYI

[steveo]

I was browsing the net; & came accross a forum on rc universe talking about if you ever have ever discharged beyond 2v or overcharged beyond 3.6v... and i quote from Brian of a123racing systems:

"Low voltage cutoff should not be of great concern to the average user. We recommend a cut-off voltage of 2V / cell but they are tolerant of over and under voltage. The working range for the cells is: Charge to 3.6V / cell and discharge to 2.0V/cell. The tolerable range is 4.2V to 1.0V / cell. These characteristics can be applied to the packs as long as the individual cells in the pack remain balanced. For example a 2S1P (6.6V) pack can be brought up to 8.4V provided that it is not kept at that voltage for a long duration of time, and that the pack is balanced properly. If the cells in the pack were not balanced you could seriously damage your pack at 8.4V. If one of the cells was measuring 3.6V the other would be at 4.8V. In this situation it is certain that you would shorten the life of the pack, and very possible that you would permanently damage it. Even though the batteries are tolerable of 4.2V / cell we do not recommend that they be charged on a 4.1/4.2V Lithium charger because the charger will maintain the pack voltage at 4.2V for several minutes, which will degrade the life of your pack. Also because those chargers do not monitor and balance the cells during charging it is very possible to permanently damage the pack."

other specs

"ower; 30C continuous 60C pulse.
Safety; No thermal runaway / fire.
Mechanical durability; impact resistant laser welded aluminum canister, and up to 1000 cycles.
Electrical durability, voltage tolerant of 1V to 4.2V / cell.
Quick Charge, As little as 15 minutes with the Sonic Charge system. "

Vent hole for a123

"The venting system is on the positive side of the battery. The ring on the bottom is where the cell vents. If the cell is abused to the point of failure this area will break open and allow the gas to escape. We are currently testing the Solderless power tubes, but we do not have any definitive data yet.

You should definitely not butt solder the cells end to end. Applying the heat from the soldering gun directly to the cell is very bad for it. When the heat is applied the electrolyte inside the cell actually boils creating a gas behind the anode or the cathode. This will degrade the lifespan of your cell dramatically. This should also be noted when working with a Dewalt pack. When you get a Dewalt pack most people cut the straps that hold the battery together in half. This leaves you with a tab that is to short to do anything with. People wind up soldering the wire to this short tab, because they are soldering so closely to the cell that heat can cause the same problem discussed above. In regards to the price, a Dewalt pack retails in stores for $159.99 ($16 / cell), which is where we base our pricing for our cells.
There are deals on Ebay, but that is how Ebay is sometimes. In short you can get a Dewalt pack off of Ebay and save a few bucks, but you have to spend your time to get it apart and after that you typically wind up with cells that have been damaged while building your pack. If you get he loose cells from us they come with nickel tabs that are capable of 100+ amps continuous that are designed for use in series and parallel strings (even end to end) and the cell will not be damaged when you build it. If you do take a Dewalt pack apart the signs of damage will not be apparent immediately but after the pack has been cycled for a while.

The button on the negative end of the cell SHOULD NOTE BE ROTATED. If you rotate this you could very possibly create an internal short in the cell. The tab should not rotate freely. If you do notice that it rotates then you are probably putting a little bit of effort into turning it."


Here is the web site for further reference & more info


http://www.rcuniverse.com/forum/m_4667844/printable.htm

-steveo

 

[Jeff]

QUOTE " The working range for the cells is: Charge to 3.6V / cell and discharge to 2.0V/cell. The tolerable range is 4.2V to 1.0V / cell."

Remember, don't believe everything you read on the World Wide Waste of time.

Use the A123 published data for charge cutoff and depth of discharge profile.

Jeff

 

[safe]

How this happens is one guy does something like drain their cells too far and it doesn't completely kill the cells, so they deduce that everything is fine. What they don't know is that they aged their cells prematurely and maybe six months later they will realize that they will be near the end of the cells life rather than only part way through it.

Mistakes with LiFePO4 can be hidden until the capacity drops enough to notice it.

Just don't do dumb stuff... stick to the specs...

 

[Doctorbass]

Safe, What is more strange that that is :

when a cell goes unser 1V and left during few hours at this state...

AND that you measure this cell after recharging it at low rate (250mA) AND.. you get 2250mAh with a true internal resistance of 11miliohm!!! that is the normal cell!!

After playing mant month with these cells i'm just wondering if they could have third parameter that would indicate the cell age !??

Normally good low internal resistance and good high capacity mean a cell in good shape right....

But when you torture an A123 and that these parameter does'nt change anymore after that......hummmm :? what happened..

The only action that would degrade a cell age and both RI and C parameter is when reversing it... after that you can measure the difference...

That's what i conclude after tested more than 650 of these A123!

Doc

 

[steveo]

Safe, What is more strange that that is :

when a cell goes unser 1V and left during few hours at this state...

AND that you measure this cell after recharging it at low rate (250mA) AND.. you get 2250mAh with a true internal resistance of 11miliohm!!! that is the normal cell!!

After playing mant month with these cells i'm just wondering if they could have third parameter that would indicate the cell age !??

Normally good low internal resistance and good high capacity mean a cell in good shape right....

But when you torture an A123 and that these parameter doesn't change anymore after that......hummmm :? what happened..

The only action that would degrade a cell age and both RI and C parameter is when reversing it... after that you can measure the difference...

That's what i conclude after tested more than 650 of these A123!

Doc

I have to agree with doc on this one; I've tested about 120+ a123's and alot of cells i'd say 1v+ - 2v have had good mah & internal resistance .. i don't believe there live has been affected at all . there are other cells that have dropped below 1v and also have good rating except for a few i guess you could say have lost mahs.. but none the less internal resistance is ok still and they are still usable, i should post a pic of my bad cells and how they came threw on testing ..it may settle things a bit here .. i might when i got some time...

-steveo

 

[slayer]

YES OK MAYBE THE CELL CAN GO DOWN MORE THAN 2 VOLTS AND NOT BE AFFECTED ...BUT TRY ONLY ONCE TO GO OVER 4.2 VOLTS ...AND TELL ME MORE

 

[Doctorbass]

YES OK MAYBE THE CELL CAN GO DOWN MORE THAN 2 VOLTS AND NOT BE AFFECTED ...BUT TRY ONLY ONCE TO GO OVER 4.2 VOLTS ...AND TELL ME MORE

I seen a report from a guy over the web that had tested a a123 cell up to 5.6V!

....that was the break point.....


bOo Oom ! !!.. no fire.. just a black/grey powder and cooper spiral and alluminium can....

What is incredible is that the 24480 Joules (6.8Wh) stored inside this cell does not appear to be liberated when poping... like the li-co cells that burst in flames...


SO WHERE THIS ENERGY GOES ????

Does it still stay in the black powder... cathode... anode
combinaison of both?



Doc

 

[Doctorbass]

This should also be noted when working with a Dewalt pack. When you get a Dewalt pack most people cut the straps that hold the battery together in half. This leaves you with a tab that is to short to do anything with. People wind up soldering the wire to this short tab, because they are soldering so closely to the cell that heat can cause the same problem discussed above

I doesn't agree!

First: that's easy to solder a 50A + connection to these half straps and to avoid to overheating these.

Also: Between the straps and the cell tab the heat conductors are only the 4 small spotweld of around half mm diameter..

They are too small to heat up the tab to a boiling point if the guy that solder them have a decent soldering technic...

In the other hand,

A bad electrical contact on the tab WILL produce heat and will certainly degrade the cell performance and life.

Doc

 

[Doctorbass]

QUOTE "

Use the A123 published data for charge cutoff and depth of discharge profile.

Jeff

I TOTALLY AGREE ABOUT THAT

Doc

 

[slayer]

it appears the chemistry is not exploding...

 

[slayer]

but the chemistry if you go over 4.2 volts ...just a little...will be over, they will be pemantly damaged 0 volts

 

[steveo]

As promised ....

cells discharged passed to volts; showing there mah & resistance, sorry about my bad writing lol

 

[steveo]

QUOTE " The working range for the cells is: Charge to 3.6V / cell and discharge to 2.0V/cell. The tolerable range is 4.2V to 1.0V / cell."

Remember, don't believe everything you read on the World Wide Waste of time.

Use the A123 published data for charge cutoff and depth of discharge profile.

Jeff

this is the tolerable range ... it is obviously not recommended loll .. if you kept the cell at 4.2 for 5mins .. then yes it most likely would be destroyed ..

that is a representative from a123 racing systems.

-steve

 

[CGameProgrammer]

After building my third and final 10s6p subpack, I decided to insulate it by spraying PlastiDip over it. It's a rubber-like compound you spray on like spray-paint, and it leaves a very thin but insulative rubber coating. But the vent caps got sprayed too, and I'm not sure if the popping would break the rubber and allow the gas to escape. It might; I'm just not sure. Anyway, what are the odds of the cells venting? I never run them down much, not even to 3V (measured without load), and I use the DeWalt BMS and charger to charge/balance.

If necessary, I could just scrape the rubber off the caps, but I'd only want to do that if really necessary.

 

[safe]

It's very likely that the A123 cells are more pure chemically and so they simply don't degrade as fast as the lower purity counterparts. It's like some poeple who have good genetics and live longer.

I just think that what you have is a simple liquid chemical and if it's really, really, really pure then whatever defects are in the liquid do less harm in degrading it. When you do things that stress the liquid then it will gradually change from one chemistry to another and eventually if you do enough bad things to it you get some other chemical that is no longer as usable.

With SLA, NiCad, and NiMh the technology is well understood because it's been around a long time and they all start out as one thing and end up as something else. (some sort of internal decay takes place)

All things in life degrade... I know that in my body every day I get up in the morning... :lol:

(I'm approaching 50 )

 

[tailwind]

CGameProgrammer,

"I decided to insulate it by spraying PlastiDip over it"....
"and it leaves a very thin but insulative rubber coating."

Steveo showed a couple of pictures of one of his cells that vented.

"I noticed the ends had bulged a bit"...
"my mom called me to tell me she heard a loud bang"

The pressure build up in the cell would be enough to break through a thin rubber coating.
Even a couple of layers of duct tape.

With people spot welding copper strips and soldering lengths of wire to the ends of the cells, this will make it harder for the vent seam to split. As the pressure further builds up in the cell, it will still fail at its weakest point, which is the vent seam. What you will get is a louder bang.

Greg

 

[safe]

Why LiFePO4 Wears Out

The cycling performance of low-cost LiFePO4-based high-power lithium-ion cells was investigated and the components were analyzed after cycling to determine capacity fade mechanisms. Pouch type LiFePO4/natural graphite cells were assembled and evaluated by constant C/2 cycling, pulse-power and impedance measurements.

From post-test electrochemical analysis after cycling, active materials, LiFePO4 and natural graphite, showed no degradation structurally or electrochemically.

The main reasons for the capacity fade of cell were lithium inventory loss by side reaction and possible lithium deposition on the anode.

http://www.osti.gov/bridge/product.biblio.jsp?osti_id=842964

So basically the material itself has no problem but it's whatever impurities that enter the system that cause the cell to degrade as well as cathode and anode interactions. More stress on the system would like contribute to the problem, but the main preventable "cause" is impurity.

This is actually the same problem you get with SLA and others in that the material itself is okay, but you get something like sulphation that builds up on the cathode or anode.

Maybe there will one day be "desulphation" like algorithms for LiFePO4 that will in the future shake off the buildup?

"Delithification"

 

[CGameProgrammer]

Oh, the entire end opens up? I thought it was just the small notch inside the tab! Well in that case, the rubber won't make a difference, although the wire I've soldered to the cell might. I think I'm in the clear though.

 

[PJD]

What is incredible is that the 24480 Joules (6.8Wh) stored inside this cell does not appear to be liberated when poping... like the li-co cells that burst in flames...SO WHERE THIS ENERGY GOES ????

The energy in the battery comes from the oxydation and reduction potentials of the anode and cathode materials respectively (the negative and positive poles respectively, when discharging), times the amount of available material to oxydize and/or reduce. This energy stays in electrical, not mechanical or thermal form, because the LiFePO4 cathode material is chemically stable enough that it cannot oxydize the other common way things oxidize - by reaction with oxygen (aka "burning" or even "exploding") unless you grind it up and put it in a fire.

The popping open of the cell is just from the overheated electrolye boiling - not related to the stored electchemical energy.

So you guessed right - the potential energy is still there, but gets thrown out around the room where it isn't in a usable form.

 

[OneEye]

Maybe there will one day be "desulphation" like algorithms for LiFePO4 that will in the future shake off the buildup?

"Delithification"

Probably the wrong thread for this, but interesting information all the same. The cycle life charts in the paper you posted may be indicative of what to expect from the duct tape pouch batteries from China.

Perhaps "delithification" is the wrong term, as the problem is the loss of free lithium to other (non-reversible) reactions. Instead, maybe you would need "relithification" -- add lithium ions back into the electrolyte to rejeuvenate the cells.

The cells in the report were "pouch type", labeled as "low cost" in the abstract, and were cycle tested at C/2. The cycle life chart had ~60% capacity after 400 cycles, the 80% capacity threshold was something short of 200 cycles (I'm guessing ~160).

 

[docnjoj]

Any chance that there has been an "improvement" in pouch technology in the 4+ years since that study was published?
David (Doc)

 

[OneEye]

One can certainly hope.