Lithium-ion Polymer Batteries--general info.

[Reid Welch]

EDIT: To set the record straight.
These RC guys know lithium polymer inside out
http://www.rcgroups.com/forums/showpost.php?p=3066606&postcount=8
Check that RC groups resource out.
It supercedes anything speculative found in the thread below.




I'd like to put links to lithium battery stuff all in one thread
even if it's duplicate stuff or links from other threads

Please add your personal expertise

Yes, please quote as you like from old threads or any other sources.

Links are great, but hey, but text quotes and your words right here are even better.

Intent: tutorial for lithium-innocent newbies
like me.

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Theodore Gray on the basic metal and its reactive properties

 

[Reid Welch]

Isidor Buchmann on The high-power lithium-ion battery

(minimal quote of long article)

...Battery experts agree that the longevity of lithium-ion is shortened by other factors than charge and discharge rates. Even though incremental improvements can be achieved with careful use, our environment and the services required are not always conducive for optimal battery life. In this respect, the battery behaves much like us humans - we cannot always live a life that caters to achieve maximum life span.
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Created: March 2006, Last edited November 2006

 

[patrick_mahoney]

My list of safety concerns for Lithium chemistry batteries

A list of all safety-related issues with lithium ion (cobalt) and lithium polymer batteries that I am aware of - at least every one that doesn't involve manufacturer problems (like the Sony's that were recalled) are:

overcharging - charging to a voltage in excess of rated voltage (4.2V, usually)
overdischarging - discharging to a voltage below the rated discharge voltage (3V usually)
high discharge rate - discharging at a rate above the specifications (1.5C for lithium-ion, 2-40C for lithium polymer, where "C" indicates the capacity in "ampere-hours" usually, so 1.5C on a 2Ah would be 2Ah * 1.5 = 3A)
high charging rate - charging at a rate above the specifications (1C usually for both lithium ion and lithium polymer)
puncturing - like drilling a hole in the cell wall. Or sticking a nail through it.
high temperature - letting the cell get above the specified rate (usually >45 Celsius).

And then add to this list two things that are a subset of the list above:
balancing issues - leads to a subset of overcharging or overdischarging.
short-circuiting the battery - a subset of high discharge rate.

For more details the datasheet for an LG 3.7V 2.6Ah 18650-sized lithium ion cell:
http://www.all-battery.com/datasheet/18650B2%20TI.pdf

The list above is, to the best of my knowledge, a complete list. So if you can guard against these problems, the cells should behave in a safe (and non-pyrotechnic) manner.

There is a pretty comprehensive list of lithium ion/lithium polymer issues reported by radio control enthusiasts located here:
http://www.rcgroups.com/forums/showthread.php?t=209187

Bear in mind, however, that if you look at this list, damaged packs and incorrect charger configuration dominate the list looking at the incident counts. The R/C guys usage model is different from the e-biker's. R/C's usually have several different packs - often different sizes, they use no safety equipment on their packs (too heavy), they are in a hurry to charge them, they put them into delicate planes and fly them fast and hard in all types of weather and then frequently slam these packs into the ground a high speed, pick them up and hope they work just fine.

We, as e-bikers, have a different usage model. We will probably only have one pack, we will probably not be changing our charging configuration frequently, we will hopefully not slam our battery pack into the ground at high rates of speed (or we have other problems than fires to worry about), we are not in a massive hurry to charge the packs and we have space (and weight) to spare for safety circuitry.

 

[patrick_mahoney]

A bit about lithium ion battery balancing

The idea of balancing is to try to keep all of the batteries at the same level of charge. This could be considered the goal of any charging system - except that nearly all multi-cell battery chargers don't actually try to directly achieve this goal. Nearly all multi-cell chargers out there charge the battery pack until an "end goal" is met that indicates the battery is fully charged. They don't spend any effort trying to make sure that each cell is charged, they just watch the pack overall to detemine if the cells are charged or not. So if the pack appears to be charged by the charger, then it is assumed that all of the cells are charged... even if not all of them are. The goal of a balancer is to make sure that each cell is charged to a similar level as all the other cells in the pack.

Balancers are useful with all battery types, but they are particularly important in lithium-based battery systems that don't have battery management systems (BMSs) because out of balance cells can lead to safety concerns.

The way that lithium ions batteries charge is pretty straightforward - particularly compared to nickel-based batteries - you apply a constant current, until a voltage threshold is met, usually 4.2V per cell, at which point the charger switches to a constant voltage mode where the current is modulated downwards to hold the voltage at 4.2V. Imagine a scenario where you get a pack of 20 3.7V lithium-ion cells and you hook them all end-to-end (20 cells in series) to create a 74V pack. In a 74V lithium ion charger you would apply a constant current to the pack - usually 1C - until the pack reaches 84V at which point, the charger would modulate the current to hold the voltage at 84V until the current drops to a small value and the charger deems the battery to be charged.

But imagine that in these 20 cells, a couple self-discharge a bit faster than the others. So the charger charges until 84V, but for a couple of cells that are not as charged as the rest because they lost more due to self-discharge, they are a bit under charged at 84V, and the rest are a bit overcharged at 84V. The pack reaches 84V, but some of the cells are at 4.1V and some others are at 4.3V. Over time, these cells become more and more "out of balance". The BMS will disable overcharging at 4.35V, but still you can have much of the pack at 4.35V - overcharged - and a handful of other cells at 3.75V and the charger thinks this pack is fully charged (15 * 4.35V + 5 * 3.75 = 84V).

So, the BMS stops the pack from overcharging a cell, but then when you discharge the pack, the BMS will disable the pack when it is overdischarged (typically any cell drops below 2.3V). So you have some cells that are only getting charged to 50% capacity at 3.75V and then the whole pack shuts down if any cell reaches 3.0V. So, now your effective pack capacity is 50% of it's rated capacity. But this effect isn't permanent. All you need to do is "balance" them and you'll be back close to 100% capacity again.

A balancer essentially looks at each cell individually and compares it against all of the other cells and then adjusts the voltage of them to equalize to the same voltage value (and hopefully to the same state-of-charge). The way that they work is they compare the voltages of the cells and then for all of the cells that are higher than the lowest cell, they shunt in a variable resistance in parallel with the cell to drain it faster (or charge it slower). This can be done while charging or discharging. More advanced techniques use charge shuttling to charge - or discharge - cells by connecting cells together.

Any easy way to balance a pack is to switch to parallel charging them as individual 3.7V cells periodically. So you take your hypothetical 20 series pack and charge it all in parallel as one 20-cell parallel pack. This takes a long time though. Another alternative is to do what Xyster does and always charge them as individual cells.

There's a paper on the subject here (found with Google "lithium ion balancer"):
http://www.americansolarchallenge.org/tech/resources/SAE_2001-01-0959.pdf

 

[Mathurin]

Plug the charger in a timer so the batteries stay partially discharged until only a few hours before you need them to go to work. This should increase your lithium battery's lifespan. Thus suggest the Velectris dilithium crystal gurus.

 

[fechter]

This thread has been stickified

If I look at this fairly typical multi-cell BMS, I can see it has resistors to dissipate excess energy during charging, but during discharge, I don't see how draining cells is going to help anything.

Also visible are two large FETs which look like they can break the circuit if the current goes too high or if one of the cells gets too high or too low.

 

[Reid Welch]

Thanks Patrick and fechter and Mathurin.

Say, at this time of writing I'm investigating the Battery Space lithium battery pack, 37V 8AH
which hasthe illustrated unit piggybacked inside the heatshrinked pack of ten flat cells.
Have now quick-read the PDF that Patrick provided link for.

(wondering which genre of the SAE article's classifications this regulator belongs to)


This regulator purports to balance on charge and only limit the discharge of the cells to their rated 40A max.

The self proposed-for-my-purchase Battery Space pack is shown in this thread.
NCM chemistry? More likely Manganese? (so thought because of B.S's allowable discharge rate for this cell, of 5C; ref: Buchmann's chart atop this page)

 

[Reid Welch]

Battery Space offers a technical discussion forum

__________________


As recently as last July, a question was asked of Battery Space,
why aren't lithium-ion polymer packs available yet for e-bikes?


_________________
I will pose a new question or two at their forum,
specifically about their new 40A rate 8AH/37V pack
and edit-in a link here in this form.

edit:
http://forums.batteryspace.com/forums/viewtopic.php?t=8315

 

[TylerDurden]

I have followed in the foosteps of jondoh, and made a significant investment in 24V li-ion batttery packs for power tools made by Ridgid.

The packs feature a charge indicator and a lifetime guarantee.

I also purchased a number of tools to use with the packs as well.

Many of the packs came with a hammer-drill kit. After selling the excess drills, my cost for batteries wil be about $50 for each 24V 3ah battery.

(previously mentioned here:
http://endless-sphere.com/forums/viewtopic.php?t=355)

8)

 

[Reid Welch]

Can't beat that with a stick, Tyler. And they'll be safe to use too.

__________________
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What, though, of cobalt-chemistry pouch cells?
Xyster taught me that these are still popular with the RC people because they are the most energy dense and power capable of Li, pound for pound.

But they can go bad in a bad way.
This is why BatterySpace would want me to put a prismatic cell pack into a metal or other fire and water-resistant container.

edit: obsolete, faulty speculation, grayed out:

Now, what is needed for a lithium fire? Oxygen.
Water as an extinguisher is no good for us because the metal will get oxygen from the water.

Metallic lithium is safely stored in petroleum oil.
Oil can be made to be anhydrous (no water to speak of).

I can't immerse my proposed-purchase of a lipoly pack in oil, though;
at least, I don't know that would be OK for the pouches, etc. Perhaps silicone oil. Ah, but that might be a source of oxygen for the metal too?
OK, petroleum oil, were it not for the unknown effects it might have on the pouches or an integrated BMS over time. Ruled out for now.

Here is a government document with good info on metal fire controls


Excerpted:

Inert Gases
In some cases, inert gases (such as argon and helium) will control zirconium fires if they can be used under conditions that will exclude air. Gas blanketing with argon has been effective in controlling lithium, sodium, and potassium fires. Caution should be exercised when using the agent in confined spaces because of the danger of suffocation of personnel.


Water
When burning metals are spattered with limited amounts of water, the hot metal extracts oxygen from the water and promotes combustion. At the same time, hydrogen is released in a free state and ignites readily. Since small amounts of water do accelerate combustible metal fires (particularly where chips or other fines are involved), use of common portable extinguishers containing water is not recommended except to control fires in adjacent Class A materials.

Water, however, is a good coolant and can be used on some combustible metals under proper conditions and applications to reduce the temperature of the burning metals below the ignition point. The following paragraphs discuss the advantages and limitations of using water on fires involving various combustible metals.


Water on Sodium, Potassium, Lithium, NaK, Barium, Calcium, and Strontium Fires
Water must not be used on fires involving these metals. Water applied to sodium, potassium, lithium, sodium-potassium alloys (NaK), barium, calcium, and strontium will induce chemical reactions that can lead to fire or explosion even at room temperatures.

Conclusions I draw: If the pack/s are placed in a metal box, airtight, flooded with argon gas, then there can be no lithium fire.

What sort of metal box? To my mind, only steel or stainless steel is unimpeachable.

If the packs are in a hermetic box, which has a metal bellows or other buffer to allow for thermal expansion, plus, preferably, a tube leading to a dessicant medium (an auto AC receiver-drier comes to mind), and if this part has a low-pressure blow-off seal of say, tin foil, by which to both exclude air, plus serve as a tell-tale in case a cell vents (the pressure will rend the seal)...
and so, by purging the battery box of moisture and oxygen via an inlet and outlet, will ensure that no lithium fire can result, period.

This could make any amount of lithium, even metallic form, safe to reside with under roof.

--raw thoughts. mediate. don't burn on my account.

 

[Reid Welch]

faulty speculation cleared away

 

[patrick_mahoney]

The lithium in a lithium ion (or lithium polymer) battery is not in metallic form. It is in a "salt" form - LiMnO2 or LiCoO2 for the cathode, LiPF6 along with others for the electrolyte, and LiC (lithium-carbon) typically for the anode.

In a lithium polymer fire, due to overcharge or short-circuiting, the battery heats up, the heat breaks down the electrolyte producing a flammable gas (hydrogen?) which can then ignite from an external source, of if the battery is hot enough, self-ignite. This sets off a self-sustaining reaction that leads to a very, very hot fire.

I have said in the past that this type of fire required a class-D fire extinguisher - one that doesn't contain any form of oxygen and that essentially smothers the fire. From what I have read more recently - which is based on manufacturer's datasheets - I was wrong. The fire is hot, but it's not as hot as a metallic lithium or magnesium fire. The composition of a lithium ion or lithium polymer battery is not metallic lithium.

According to Material Safety Data Sheets, a class B or class C (or BC) extinguisher is sufficient.

That said, according to the manufacturers the fire emit flourine gas, which is very toxic. So, on the one hand you don't need a $400 fire extinguisher to put it out (a standard BC extinguisher should do), but on the other hand, you need to vent the area thoroughly and be very careful about breathing the fumes.

http://www.monmouth.army.mil/cecom/safety/sys_service/b_cobalt.pdf
http://app.rayovac.com/cm/groups/public/documents/msds/007125.pdf

 

[Reid Welch]

I didn't know that (Maxwell Smart voice)

Thank you Patrick!

edit: faulty speculation cleared away.

 

[xyster]

Some "Water Proof / Fire Retardant" battery pack enclosures:
http://www.batteryspace.com/index.asp?PageAction=VIEWCATS&Category=1032

Don't know how "fire retardant" ABS plastic is...

 

[Reid Welch]

Some "Water Proof / Fire Retardant" battery pack enclosures:
http://www.batteryspace.com/index.asp?PageAction=VIEWCATS&Category=1032

Don't know how "fire retardant" ABS plastic is...

Isn't that a thermoplastic?
It just doesn't support combustion itself, I guess.

I think I recall them spec'ing a fire -proof- container for the lipo bike pack.
But they have no suitable product.
But they do emphasize these batteries are not for retail sale;
for "R&D" only. They just aren't big enough to offer full lines of ancillary products.

Still....



jeez louise

 

[Reid Welch]

I will prune, revise and clean my -speculative- posts in this thread, so that long-term, no garbage will remain.

I'm on a learning curve.

What I learned today by reading the RC group pages that Patrick referred on page one, I will summarize later on here.

And I stand for corrections. Corrections are vital.

 

[Reid Welch]

Not alarmist, but to ensure this is seen

HERE is a well-staged lipoly pack destruction by overcharging.

From my limited study so far, it appears that the fire cannot be prevented by argon blanketing
--I suspect that the battery components themselves provide sufficient oxygen to initiate the fire, and to carry on the fire.

edit: faulty plans, obsolete, now grayed out


A container should be steel
It must in no ways be clamped shut; it must freely vent.
Open-top venting would, undesirably, allow a more vigorous fire by allowing ingress of oxygen.

 

[EbikeMaui]

I think being able to replace bad cells would be a great option.

 

[Reid Welch]

Hi Randy!

Agreed.

I know nothing yet about this stuff.
These rigid cells--am I seeing a pouch cells each slipped into and sealed into a sturdy case?
That picture above looks like from the Forsen site.

I like that construction.
I suppose it's much sturdier for the rigors of e-bikes and scooters.

Do we have members here who have great experience with LiPo cells on e-bikes? Would be good to get your inputs
moreso than my newbie noodlings.

---

I'm off now to read more of the RC group's pages.
later,
r.

 

[Reid Welch]

http://www.rcgroups.com/forums/showthread.php?t=643192&page=4

Quote:
Originally Posted by cyclops2
The cells composition has a complete supply of chemical Oxygen mixed with the Lithium. That is why they ERUPT so violently.
Once a hot spot ignites the 2 chemicals. They burn in any atmosphere.

Can this be verified? I am not a chemical expert but I would be inclined to believe that the Lithium itself will not burn in the form it is used in batteries. Pure Lithium will burn in contact with Oxygen.

Here is a post from Hoppy claiming that the batteries are not a significant Oxygen source: http://www.rcgroups.com/forums/show...35&postcount=11. You may want to read the entire thread for opposing views.

DNA has done tests to see if a Nomex sock can prevent/limit fire:
http://www.rcgroups.com/forums/showthread.php?t=154257

Resolving this issue is of course important to our choice of methods to prevent, limit and extinguish lipo fires.

 

[Reid Welch]

To prospective lipoly users

Please read the entire thread
http://www.rcgroups.com/forums/showthread.php?t=355739

 

[Reid Welch]

screenshot from the second page




__________________________________


Kokam catalog/brochure (PDF)

screenshots from the Kokam catalog
note that they have metal boxed packs--indicating confidence that their batteries will not explode

 

[EbikeMaui]

The 48 volt 25 ah pack Kokam has would be good for 75 - 100 mile round trips just about in any conditions at above 20 mph average without pedaling on a efficient ebike system. I wonder where you can get them and at what price? So far I think Kokam is the best!

 

[Reid Welch]

Kokam is the industry leader.

Their range of cell types is wide.

"SLPB" is their trade acronym for "Superior Lithium Polymer Battery".
The RC group seems to agree.

These Kokam cells are of a chemistry less volatile than conventional Lipos.
They are relatively rugged and fire safe.

http://kokam.com/english/product/battery_main.html

The "High Power" range is what we'd most likely employ;
their being balanced in design between the mutually exclusive qualities
of superior capacity and superior discharge rate.

Inasmuch as the Kokams are theoretically available (who stocks though?) in high AH capacity cells, the construction of an e-bike battery is pretty straightforward: no paralleling need be done if large cells are chosen


For example,
an 11AH cell from the "High Power" range of Kokam Lipolys

screenshot from the PDF

 

[Reid Welch]

http://kokam.com/english/product/kokam_Lipo_01.html

Portion of the cited page; Kokam purports to offer superior cycle life.

How the cycle life relates to depth of discharge is made clear by the table:




__________________________


How rate of discharge relates to nominal capacity of a Kokam SLPB
http://kokam.com/english/product/kokam_Lipo_02.html

excerpt