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Oct 03, 2019, 01:02 AM
ancora imparo
jj604's Avatar
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Lithium Polymer Battery Technology - English version


Lithium Polymer Battery Technology
An introduction
with special consideration of RC model lithium batteries

Dipl.-Ing. Frank Siegert


4 years ago, Ron van Sommeren posted a link in RCGroups to a presentation on “An Introduction to Lithium Polymer Battery Technology” that is on Gerd Giese’s home page.

Unfortunately that particular presentation by Dipl.-Ing. Frank Siegert was only available in German.
I did a very crude transliteration into English which is in this thread
https://www.rcgroups.com/forums/show...d-into-English
and then Ken Myers cleaned it up a bit and published it in Ampeer.

It was a slide show rather than a written document and I formatted it with the original slides followed by an additional one with the translation. It wasn't the very convenient but it was worth the effort if you are serious about understanding LiPo behaviour. It was an invaluable source of authoritative information from a qualified professional who knew what he was talking about.
It is a most useful summary of LiIon and LiPo technology if you are interested in how our flight packs work.

As I said at the time, it will clarify such questions as:

Why do my LiPos die in the Winter under the same conditions as Summer flying?
Will the new high rate and high voltage LiPos last as long as my current ones?
Is that smell dangerous?

The good news

Frank has very generously agreed to do a proper English version of his slide show which is much more readable and accessible. It's still not a light read and the slide show presentation format means you have to stop and think about the exact meaning occasionally. But this presentation will tell you more than you will find anywhere else in everyday English about how our LiPo packs are made, the chemistry of how they work, how they are affected by various conditions, how to get maximum life from them and what the dangers are.

The presentation of over 80 slides is attached below as a pdf file.

John


ADDENDUM:

1) This link goes to an interview in a drone forum that contains some good authoritative info from a manufacturer (Dinogy in this case) that is non-technical but complements the presentation.

https://www.drone-zone.de/interviewi...-dinogy-lipos/

2) The most comprehensive and authoritative thread on comparative practical test results on RCGroups is that by Joe (MSGUY) which starts here.

https://www.rcgroups.com/forums/show...91&postcount=1

The links in that first post are useful, particularly the "Cliff Notes" link if you want to know what brands to avoid. Read both the 2018 and 2019 Cliff Notes. Testing is almost exclusively of the 6S, 5000/6000mAh packs but nowhere else will you find a more comprehensive, carefully controlled set of test results done under practical (high drain EDF type) conditions. Joe's summary of the various brands is concise and accurate. His BS detector is of the highest quality.

The link to "Best Practice" is an excellent simplified summary in non-technical form of how to manage and look after your LiPos based on the information in Frank Seigert's presentation. Highly recommended to everyone.

https://www.rcgroups.com/forums/show...postcount=8346
Last edited by jj604; Dec 22, 2019 at 07:40 PM. Reason: Additional link to Joe's thread
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Oct 03, 2019, 02:32 AM
Registered User
Very enlightening. Just had a discussion with my wife about keeping all my batteries in the fridge - she wasn't keen.
Oct 03, 2019, 03:45 AM
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jj604's Avatar
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Hmmmm. ....this is a very unusual objection from an Australian. Normally the argument is about how much beer has to make way for the LiPos.
Quote:
Originally Posted by 1auriec
Very enlightening. Just had a discussion with my wife about keeping all my batteries in the fridge - she wasn't keen.
Oct 03, 2019, 05:25 AM
Blue Skies
hifinsword's Avatar
Quote:
Originally Posted by jj604
Hmmmm. ....this is a very unusual objection from an Australian. Normally the argument is about how much beer has to make way for the LiPos.
It was probably too much of a reduction in her beer supply that caused that reaction! Just guessing.
Oct 03, 2019, 05:32 AM
Registered User
John,

Thanks very much for your efforts on that.

Its pretty enlightening if you take the time to read it.
I was pleased to see that our empirical conclusion that the "Winter failure syndrome" does exist and is explained by cathode damage when a lipo is subjected to high currents at low temperatures.
The "winter failure syndrome" is so dangerous because when a flyer finds the power much lower than expected on takeoff, the obvious response is to open the throttle further, which is the worst possible action (apart from applying full down elevator ) as that greatly increases the current and damage.

I was also pleased to see that discharging to 3V/cell is ok as long as the lipo is recharged immediately and not left discharged. I have always done this during testing and never seen any obvious deleterious effect on a pack. It is necessary if you wish to accurately measure the actual capacity of a lipo and usually results in a capacity within a few percent of the claimed capacity - there are some exceptions I have seen lately.

Wayne
Oct 03, 2019, 05:55 AM
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jj604's Avatar
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Wayne, the one thing that was bit of an eye opener for me was Frank's advice about maximum temperatures. I had (fairly empirically) taken a 50C temperature rise as being acceptable based on the common 70C maximum surface temperature recommendations by Revolectrix, Hyperion and others and a standard 20C ambient. This was supported by the test results at very high C rates showing the Turnigy Graphene and Panthers exhibited no puffing at those 70C surface temperatures.

Franks' suggestion that you should always keep a LiPo below 55C in use (slide 22) is food for thought.
Mind you, in some parts of the world (not where you live) 55C is only 10C above ambient in summer!

John
Oct 03, 2019, 07:21 AM
Registered User
The fact is, propulsion use cases generally require sacrificing **a lot** of longevity.

Most especially those involving flying.
Oct 03, 2019, 08:03 AM
Registered User
Quote:
Originally Posted by jj604
Wayne, the one thing that was bit of an eye opener for me was Frank's advice about maximum temperatures. I had (fairly empirically) taken a 50C temperature rise as being acceptable based on the common 70C maximum surface temperature recommendations by Revolectrix, Hyperion and others and a standard 20C ambient. This was supported by the test results at very high C rates showing the Turnigy Graphene and Panthers exhibited no puffing at those 70C surface temperatures.

Franks' suggestion that you should always keep a LiPo below 55C in use (slide 22) is food for thought.
Mind you, in some parts of the world (not where you live) 55C is only 10C above ambient in summer!

John
Yes, I thought the same.
I have found the same as you in testing and only get ready to run when the temperature exceeds 70*C.
It could well be that he is being conservative, being wary of suggesting higher temperatures are OK when the world is so litigious now.

Wayne
Oct 03, 2019, 08:26 AM
4.2V of pure Kraut power
bzfrank's Avatar
I see the question came up why 60 degree C is the top limit of the temperture range. Well....

LiPF6 starts decomposition to LiF and PF5 around this tempetarure. Then PF5 reacts with organic solvents to form a variety of decomposition products including carbon dioxide (CO2), ethers, alkylfluorides, fluorophosphate, .... Nothing you want to have in the cell, quickly adding to the SEI layer with all consequences and/or create irreversable puffing.

In fact LiPF6 stability is usually still sufficient from a safety aspect until around 70 degree C but elevated cycle degeneration already sets in at lower temps. Another problem is the possible decomposition of the SEI layer at elevated tempetures, see graph from

https://www.sciencedirect.com/scienc...6943321831448X

There are additives that improve the stability at higher tempetarures, but in the RC world you never know what is exactly is in the battery you purchase. If the battery distributor allows for such high temperatures, they may just use cells specified and prepped for it. Or they may just hope for the best.

- Frank
Last edited by bzfrank; Oct 03, 2019 at 08:54 AM.
Oct 03, 2019, 10:24 AM
Frankenstein recycled packs
rampman's Avatar
Quote:
Originally Posted by jj604
...Franks' suggestion that you should always keep a LiPo below 55C in use (slide 22) is food for thought.
Mind you, in some parts of the world (not where you live) 55C is only 10C above ambient in summer!

John
Very interesting.
When I cycled that first 1300 4S Turnigy Graphene over 1100 cycles I never reached 140F / 60C. Granted, at the time no other pack could have taken the abuses we give them today.
I stand behind my statement to buy the highest true C pack money can by for the longest cycle life as long as you can take the weight penalty. I just did not connect the dots to be directly heat related.

Rick
Oct 03, 2019, 12:01 PM
Registered User
Quote:
Originally Posted by rampman
I stand behind my statement to buy the highest true C pack money can by for the longest cycle life as long as you can take the weight penalty
Yes, that "energy density" is opposed to "power density" is clear, and RC batteries have become very specialized towards the latter.

Given a "normally abusive" hobby use case, your reco very likely holds.

But if high C-rates are not at all needed, then price vs longevity value may very well be best served by going with cells that are **not** so tuned for that factor.

Does not mean going for extreme energy density either though.

I think high-longevity at lower C-rates really needs its own standardized testing regime, but it is not easy, and it seems not so much in demand.
Oct 03, 2019, 02:16 PM
Frankenstein recycled packs
rampman's Avatar
I bought a couple 6S 15C 12,000 packs for that exact reason. Longevity when used lightly.

I was charging 2 packs earlier this week and one was very warm to the touch at end of charge. I did this at work so no way to measure pack temperature but guessing 130+ .
Having finally read all 78 pages I will suspect that one pack is damaged beyond repair and use. Of course I will use it more but it has a very RED BAD written across the front of it so I can monitor and check for any other tell-tell signs showing damage. It scared me pretty good as I was not taking precautions in case it lit off.

Rick
[Add] The two packs were 1800, NOT the 12,000 packs but still...
Last edited by rampman; Oct 03, 2019 at 05:06 PM.
Oct 03, 2019, 03:52 PM
Space Coast USA
hoppy's Avatar
Oops, sorry boss....that smoke will clear up in just a couple of hours. By the way, that cough won't last long but, I'd check with your Doc just as a precaution.

Wow, you dodged a bullet there.
Oct 03, 2019, 10:56 PM
The 6 P principle works for me
elecfryer's Avatar
Downloaded and read it tonight, Awesome! Lots of information, great explanations and loads of references (SEI, EC, DMC, ect..). Love the summation at the end, Long Life and Even Longer Life! A great big thank you to whomever did the translation!

Michael (if your not frying, your not tryin!)
Oct 04, 2019, 08:27 AM
ancora imparo
jj604's Avatar
Thread OP

Updated version


I have uploaded a slightly revised version. There are no substantial changes - just a few minor corrections.

John


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