Lithium-ION-Poly Batteries.... etc.

Hi All,
Not been here for sometime! Most of my project seem to be things? that move, etc. I have for years always used rechargeable cells usually in the form of AA's. I have some old Nicads on their last leg and some new NimH! I think 2700mA being the highest I have.

But I have been taken by the Lithium 18650 cell a bit longer and fatter (but lighter?) then an AA at 65mmx18 but 3.7v and 3600mA is tempting, the other thing I notice is some are protected (by a small PCB, in the base) for over changing/discharging, over voltage, etc) and some are not...

It would be good to hear from someone who uses or has used these cells, the protected are more expensive as you would imagine, could you recharge the un-protected one's then with a good bench PSU with constant voltage and current limit?? it seems you must never use more then 4.2volts for the single celled 3.7v ones.

There again I could be wrong

Regards

Mel.

PS. Yes I know Lith-ion and Lith-poly are not quite the same!

You don't necessarily need a bench PSU (unless you have one), you could use a hobby Lithium Ion/Polymer charger to charge them as well. The charging algorithm is constant current constant voltage. The current you can charge at depends on the cell, and is usually given as a C rating, C being the capacity of the cell. i.e. 2000 mAh cell, 1C would be 2000 mA charge rate, .5C 1000 mA charge rate, etc. Max voltage for both li-ion and li-poly is typically 4.2 volts per cell.

cactusface said:

could you recharge the un-protected one's then with a good bench PSU with constant voltage and current limit??

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You could, but there is so much to go wrong with this approach, I would not risk it, use a proper charger.

And those protection cirsuits are there for safety reasons only, they are not proper charge controllers at all, DO NOT use them to charge Lithium batteries.

Hi,

Another factor to consider is that many cells on ebay and/or direct from China are of very low quality, "fakes", or have a wildly "optimistic" energy rating. They're also very probably being shipped "illegally" by air mail and/or our Royal Mail (which bans all Lithium cells, except if assembled into equipment).

Reasonable quality cells should be about 2,500 mAhr and genuine "branded" cells perhaps a little over 3,000 mAhr. I've seen some ebay listings claiming over 5,000 mAhr, but In practice they're probably less than 20% of that value (if they work at all).

A few weeks ago somebody (manuka?) posted a link to a comparative test of many branded cells of the 18650 size.

As for charging control, it's possible to buy small, assembled Lithium cell charge controller PCBs for little more than a Pound, so why take a risk?

Cheers, Alan.

AllyCat said:

As for charging control, it's possible to buy small, assembled Lithium cell charge controller PCBs for little more than a Pound, so why take a risk?

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Yep, and very useful they are for buildng into projects too.

I just extracted 28x 18650 cells from my oldest ebike battery pack as I replaced them with new ones over the weekend, they were originally rated for 2200mAh so I tested one using my Picaxe discharge test rig at around 300-400mA drain and got 800mAh which isn't too shabby for a cell that's over 5 years old. Don't know what to do with them as I also have some better ones extracted from an old laptop battery, and I'm not sure how to dispose of them properly.

Cactusface: I've mentioned this -sigh-many times already here, but you may want to consider LiFePO4 types.

Although less powerful than Li-ion they're near bullet proof! They've negligible self discharge, & a particular benefit is their VERY stable 3.2V supply, which holds until >80% discharged. Who needs voltage regulators!

I now use 14500 "AA" sized LiFePO4 to great effect in consumer appliances (shavers, torches, digital cameras, radio gear etc) that'd previously been picky when 1.2V NiCd or NiMH driven. Performance & reliability improvement has been absolutely wonderful -a feeble 3 x AA shaver now works brilliantly on a single 3.2V LiFePO4, & a 2 x AA Canon digital camera that was always dieing is now leaping up & snapping to perfection. Naturally dummies are fitted to suit empty cell holders.

Extra: Weary Li-Ion woes? Boeing's 2013 Dreamliner "787" battery experiences show you're not alone ...

On February 12, 2013 the Wall Street Journal reported that "Aviation safety investigators are examining whether the formation of microscopic structures known as dendrites inside the Boeing Co. 787's lithium-ion batteries played a role in twin incidents that prompted the fleet to be grounded nearly a month ago."

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Mainly I'm using 2x 18650 lion cells in my projects. problem with those cells are when you are using 5volt regulators and cell's voltage drop under 3 volt. 7805 regulator drop voltage about 2V...so 6V-2V = 4V->not good for some devices ex. ultrasonic sensors etc. Nowdays I'm using LDO regulators which have around 0,2V dropout voltage with protection. They have served me well.

I use 18650 cells from old laptop battery packs for picaxe projects. I charge them using a bench psu, but at a low current rate (C/10 or so i.e. say 100mA) and also set a voltage limit. A lot can go wrong with lithium cells, after all, the laptop pack has temperature sensors, cutouts, and some serious chippery to control it all. But at a low charge rate nothing even gets warm. Remember when in original service the charge rate was probably C (i.e. 1-2 amps or more) and when pumping that amount of energy at that speed things can go very wrong.

I generally run chips at 3.3v using an ldo reg on the 3.7+ that the cell provides.

You can get 18650 holders from our Chinese friends.

LiFePO4 is a bit like Rocking Horse manure here in the UK !

Hence the Li-Ion popularity.

The other reason is that 18650s from laptops are free and usually only one or two cells in a dud pack are actually dud! Sometimes even none are dud if the problem is over-discharge and then the 'logic' prevents recharge.

The terminology in this thread is mighty confusing!

All lithium ion cells are lithium polymer, the two are the same and the terms describe the charge mechanism (ion transfer) and the electrolyte (a polymer film that allows ion transfer).

There are many lithium ion/lithium polymer cell chemistries in use, ranging from the original lithium cobalt oxide cells (still often seen in radio control model packs, because of their high energy density) through to lithium iron phosphate (slightly safer, but lower energy density due to the lower terminal voltage).

So, any lithium secondary cell is going to be a lithium ion (Li Ion) cell, or a lithium polymer (Li Po) cell if you prefer, and the major differences are basically the electrode chemistry. You can currently get around a dozen different variations on electrode chemistry, all with varying qualities. Laptop cell chemistry tends to be optimised for safety, so the cells are now deliberately designed to have a fairly high internal resistance, to limit the max discharge current, and can tolerate a fair bit of abuse (these changes came about primarily because of the Sony laptop problem years ago).

Lithium iron phosphate LiPo/Li Ion cells are relatively uncommon in small sizes, but are slightly safer in high current form as the chemistry tends to be a little bit more tolerant of over-charge and over-discharge that the various other chemistries, such as lithium cobalt, lithium manganese, etc, etc. They are the odd ones out in having a low max charge voltage of around 3.7 V and a terminal voltage of around 3.2 to 3.3 V, whereas most of the other Li Ion/Li Po chemistries tend to have a max charge voltage of around 4.2 V and a terminal voltage of around 3.7 V. Probably the best known Lithium iron phosphate Li Po cells are the A123 type, used in portable tool backs.

Overall, for low current hobby use (as in low power Picaxe projects) then good brand name 18650 cells from laptop packs are probably best. Most are now very safe, with a cell chemistry that is far safer than the original plain lithium cobalt that caused so many problems in the early days. As already pointed out, there are millions of fake cells available on well-known auction sites, and as it is dead easy to make lithium cells (you can literally do it in a garage it's that simple) it is easy for the fakers to knock up potentially dangerous rubbish.

Worth noting that no lithium cells (of whatever electrode chemistry) actually contain any metallic lithium, so there is no risk of a lithium fire as such. The lithium is in the form of a lithium salt in the electrolyte within the polymer layer and a lithium oxide on one of the electrodes. The other electrode is a thin layer of carbon usually. The fire risk is from the polymer and organic solvent carrier, and it is the latter that causes abused cells to swell and perhaps burst and smoke, or, rarely, catch fire. The latter only happens under really severe abuse with modern cells, and laptop cells (from a known to be good manufacturer) are remarkably tolerant of abuse (although they will be damaged and may still vent and fume a bit if seriously abused).

manuka said:

Cactusface: I've mentioned this -sigh-many times already here, but you may want to consider LiFePO4 types.

Although less powerful than Li-ion they're near bullet proof! They've negligible self discharge, & a particular benefit is their VERY stable 3.2V supply, which holds until >80% discharged. Who needs voltage regulators!
I now use 14500 "AA" sized LiFePO4 to great effect in consumer appliances (shavers, torches, digital cameras, radio gear etc) that'd previously been picky when 1.2V NiCd or NiMH driven. Performance & reliability improvement has been absolutely wonderful -a feeble 3 x AA shaver now works brilliantly on a single 3.2V LiFePO4, & a 2 x AA Canon digital camera that was always dieing is now leaping up & snapping to perfection. Naturally dummies are fitted to suit empty cell holders.

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Hi Manuka,
I thought there was an AA version, but must have missed it along the way. Think I might go back and take a look!!

Thanks all for the info, keep it coming.

Regards

Mel.

That's quite an essay Jeremy. Thanks for your thoughts. Obviously, you've done your research.

I'm just starting to get interested in using Lithium cells - I've been scared off in the past by Boeing and Sony stories.

All of my small recent robots have used a single AA-sized 14500 Li-Ion with a tiny 5V USB booster circuit ($1) to power the sensors & electronics. 9-gram servos work fine directly powered by the 3.7-4 volt Li-Ion.

Looks as if there is a lot of great information about batteries in this thread. Maybe someone can help me satisfy my curiosity. I have an Implantable Cardioverter Defibrilator (ICD) that's been doing it's job for the past three years. A technician tests the device every 3-4 months. Checks if the leads are OK, reads-out and prints off many pages of logged data that's been time-stamped, and resets the device. During the last check-out he told me that there is about 5 to 7 years of battery life remaining before the battery will need to be replaced (that's a total of 8 to 10 years). It's quite a data logger and controller all in one small package. Can someone tell me what battery techology is used in these devices? Thank you, Jims

-no lithium cells (of whatever electrode chemistry) actually contain any metallic lithium, so there is no risk of a lithium fire as such.

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Jeremy: You may have meant to say "lithium ion cells"? Primary 1.5 Volt Lithium Iron disulfide types (LiFeS2) contain pure Lithium metal-diverse Youtube clips show how to extract it.

Jims: One trusts you're not going to PICAXE this! I was once gifted such a Li powered pacemaker as a teaching aid, & even 10 -15 years later a DMM showed it was still ticking away. Students were predictably a tad taken back to learn of it's function, but it certainly served to grab their attention about niche electronic careers.

All: Perhaps the best resource for this electrochemical topic is the esteemed Battery University

manuka said:

Jeremy: You may have meant to say "lithium ion cells"? Primary 1.5 Volt Lithium Iron disulfide types (LiFeS2) contain pure Lithium metal-diverse Youtube clips show how to extract it.

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No. I was referring to secondary cells, which seems to be the subject of this topic, rather than primary cells. Note this sentence from my post:

So, any lithium secondary cell is going to be a lithium ion (Li Ion) cell, or a lithium polymer (Li Po) cell if you prefer, and the major differences are basically the electrode chemistry.

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Primary cells can indeed contain metallic lithium, and are in a higher fire hazard category as a consequence. Around 20 or more years ago I worked on a safety mitigation strategy for carrying high capacity lithium primary cells in aircraft, as the fire that results from a mishap with these can be pretty hard to put out (you need graphite dry powder extinguishers and have to keep any water well away from the fire).

Thank you manuka. I understand that the device you have is powered with "Lithium ion" cell. I admire the work that you and other educators are doing by helping develop the minds of our young folk (and us older folks too by all the conversations on this FORUM). Please try not to discourage them from "niche" electronic careers. I'm sure that with nono-technologies, etc; there is still an need for advancements in medical devices that will generate, control, and deliver the 900 volts necessary to "coax" a fibrillating heart muscle back into normal rhythm. Thanks again...keep up the good work. Jims

manuka said:

Jeremy: You may have meant to say "lithium ion cells"? Primary 1.5 Volt Lithium Iron disulfide types (LiFeS2) contain pure Lithium metal-diverse Youtube clips show how to extract it.

Jims: One trusts you're not going to PICAXE this! I was once gifted such a Li powered pacemaker as a teaching aid, & even 10 -15 years later a DMM showed it was still ticking away. Students were predictably a tad taken back to learn of it's function, but it certainly served to grab their attention about niche electronic careers.

All: Perhaps the best resource for this electrochemical topic is the esteemed Battery University

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