Ask REVOLECTRIX battery guy - RC Groups
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Jul 05, 2017, 09:35 AM
REVOJohn's Avatar
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Ask REVOLECTRIX battery guy


Hello All

I have been asked to start a discussion room about LiPO batteries topics to focus will be.

1. Production Processes
2. Cell Design & Raw materials
3. Cell Design parameters effecting performances
4. Safety by Design or Process
5. Root causes of failures or performance variances
6. Performance improvement techniques


Feel free to ask and we'll try get back to the forum asap, maybe even with a video
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Jul 05, 2017, 10:36 AM
Registered User
Sounds interesting.
Jul 05, 2017, 12:16 PM
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brushless55's Avatar
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Jul 05, 2017, 01:50 PM
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vimy g eaou's Avatar
Hello John,

Can I add another topic to your list?

From a manufacturer's point of view, what are the recommended practices for handling, storing and maintenance of LiPo batteries, and when is a battery considered past the point of safe use?

If a battery has mechanical or structural damage, when is that considered unsafe to keep using it?

It's understandable that due to cost, modellers don't want to just chuck out batteries that, despite their appearance, may still be perfectly safe and serviceable.

After reading various discussions, there seems to be no definitive information on the above issues from any other manufacturers.

If you have anything John, with photos, it would be much appreciated.

Thanks mate.
Last edited by vimy g eaou; Jul 05, 2017 at 01:59 PM.
Jul 05, 2017, 02:07 PM
Registered User
Good idea for a thread, here's a few questions to get things started:

- What is the process that allows for higher/lower C ratings? Is there a hard upper limit. I appreciate the definition of "X"c differs manufacturer to manufacturer but presumably you are all working under similar chemical/physical constraints that mean beyond a certain point it becomes impossible.

- We know we shouldn't go below 3-3.3 voltage at rest. Does this value change for high current applications when the voltage sags?

- Is there a sweet spot where C rating/capacity/weight/voltage are optimal for power delivery? Like with an amps per gram type measurement?
Jul 05, 2017, 07:55 PM
REVOJohn's Avatar
See below
Quote:
Originally Posted by vimy g eaou
Hello John,

Can I add another topic to your list? OK

From a manufacturer's point of view, what are the recommended practices for handling, storing and maintenance of LiPo batteries, and when is a battery considered past the point of safe use?

Handling. Treat them nice. LiPO cells but pure design is unstable, that is if triggered will lead to thermal runaway. Internally there is a fine balance of electrochemical reactions that to be honest is still not 100% understood and some trial and error is still required when designing cells for any application. Electrolyte additives are continuously modified for change in performances but this takes much time to realize the results and time plays allot of part in the real performance, as does usage pattern and enviro conditions.

Look at Nissan Leaf. They released their EV few years ago and did battery cell simulations and cycle life in accelerated form to mimic sales in hotter climates. Then when they released there was a big product recall. What was discovered was the customers don't actually use batteries in continuous charge asnd discharge conditions as moist cars are sitting in driveways. They found that at certain SOC storage and hotter temperatures the chemicals started to have adverse effects that could not be simulated.....................just too many variables to try to control





If a battery has mechanical or structural damage, when is that considered unsafe to keep using it?
NO. NO. No. One has damaged the sacred internal safety mechanisms, especially for RC packs that are stacking electrode format unlike cell phones and EV which are winding and more structualy sound. You damage that very thin separator, you are just that bit closer to an internal short.

It's understandable that due to cost, modellers don't want to just chuck out batteries that, despite their appearance, may still be perfectly safe and serviceable.
If unsure...............charge outside at least !

After reading various discussions, there seems to be no definitive information on the above issues from any other manufacturers.

If you have anything John, with photos, it would be much appreciated.

Thanks mate.
Last edited by REVOJohn; Jul 05, 2017 at 09:24 PM.
Jul 05, 2017, 08:23 PM
REVOJohn's Avatar
See below

Quote:
Originally Posted by fernandodlc2011
Good idea for a thread, here's a few questions to get things started:

- What is the process that allows for higher/lower C ratings? Is there a hard upper limit. I appreciate the definition of "X"c differs manufacturer to manufacturer but presumably you are all working under similar chemical/physical constraints that mean beyond a certain point it becomes impossible.

Oh you started with a tough one.
C rating cell capability is a trade off within a trade off.

1st Trade off: Cell Design vs Production Capability

Cathode Particle size must be small enough allot high ion transfer out but that adds $
Anode Particle side and shape must be good enough to allot high ion transfer in (more important that cathode) but that adds $
Electrolyte my be high ion transfer capable but not too high to seep though the cathode and start cathode degradation process
Factory coating process must be thin and consistent enough to coat the thin coating design and wind the separator without shorting or breaking

Facility Humidity Level RH during processing should be as low as possible to mitigate swelling and improve cycle life, but that adds to operational costs


2nd Trade off: C rate vs Self Discharge vs Safety Level vs Weight vs Cost vs Cycle Life


Separator must be thin enough to allow high ION transfer but not too thin to cause safety issues and self discharge of cells
Smaller active material particles adds cost but improves performance
Better internal conductors allot better Amp transfer but adds weight and cost
Design Overlap of Anode/Cathode Ratio need to be high enough to give good cycle life but not too high that it adds size and weight. Higher P/N ratio gives better cycle life and safety buffer
Separator overlap increases batter size but also increases safety margins



- We know we shouldn't go below 3-3.3 voltage at rest. Does this value change for high current applications when the voltage sags?
Much life the Nissan leaf story above there are too many variables to answer this one perfectly and distinctively as everyones design is difference and how you charge is also plays an effect. But for RC cells, 3.3 would be a nice safe spot especially under high C. We tested some 1300 FPV cells last year on low rate applications from 4.,2 to 2.9V and they cycled for 3000+ cycles with no issue. But once you start C rating it heat comes to play the cycle life trade off game

- Is there a sweet spot where C rating/capacity/weight/voltage are optimal for power delivery? Like with an amps per gram type measurement?

OK Power Delivery with trades off on C rating:Capacity:Weight:Voltage

Actually i thing your trade off wold be purely on design not considering ability to process the design all tjings equal

Power Out: Trade off on; Cost of Cell (Raw ingredients) vs Weight vs Safety Level vs Cycle Life

Give you an example. We recently design a high capacity cell for a US military application. expected cycle count 1. C rate as large as we could get it (we had the 5200mAhr cell down at 0.6mohm per cell) and light as we could (`120g) but the trade off was cycle life
Last edited by REVOJohn; Jul 05, 2017 at 09:23 PM.
Jul 05, 2017, 08:51 PM
Registered User
I'd like to ask John to use (his choice) different color, font, or bold or a consistent format to set his answer off from the question. Readability issue. Thank you.
Jul 06, 2017, 08:28 AM
Registered User
Quote:
Originally Posted by REVOJohn
See below



OK Power Delivery with trades off on C rating:Capacity:Weight:Voltage

Actually i thing your trade off wold be purely on design not considering ability to process the design all tjings equal

Power Out: Trade off on; Cost of Cell (Raw ingredients) vs Weight vs Safety Level vs Cycle Life

Give you an example. We recently design a high capacity cell for a US military application. expected cycle count 1. C rate as large as we could get it (we had the 5200mAhr cell down at 0.6mohm per cell) and light as we could (`120g) but the trade off was cycle life
All very interesting, a lot to digest. Thanks
Jul 06, 2017, 09:36 AM
REVOJohn's Avatar
this is going to be tedious,
is there a way i can reply in video or maybe add the answer on our youtube packs and just link it to the question????? what you guys prefer?
Jul 06, 2017, 09:52 AM
Unregistered User
vimy g eaou's Avatar
Thanks John, for answering my questions. If I can come up with anything else, I'll post it.

Just thought of one...

I know there is always going to be a weight penalty with batteries used for anything to do with aircraft, that's a given.

Has anyone tried some sort of chemical contained in a membrane wrapped around the entire battery, that can be released to put out a fire?
Last edited by vimy g eaou; Jul 06, 2017 at 10:03 AM.
Jul 06, 2017, 10:18 AM
Registered User
Quote:
Originally Posted by REVOJohn
this is going to be tedious,
is there a way i can reply in video or maybe add the answer on our youtube packs and just link it to the question????? what you guys prefer?
I would like to see simple answers in text here, with the odd link to video for more extensive stuff.

Thanks for taking the time to talk with us.
Jul 06, 2017, 10:41 AM
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Mr.frankenjet's Avatar
I have heard from time to time of a break in process, is there actually one recommended for lipo and what performance - current and capacity- changes can be expected with the first few cycles and or break in. Thanks !
Jul 06, 2017, 10:59 AM
REVOJohn's Avatar
Quote:
Originally Posted by vimy g eaou
Thanks John, for answering my questions. If I can come up with anything else, I'll post it.

Just thought of one...

I know there is always going to be a weight penalty with batteries used for anything to do with aircraft, that's a given.

Has anyone tried some sort of chemical contained in a membrane wrapped around the entire battery, that can be released to put out a fire?
OK this is a bit out of scope but there is world there may be flame retardant separator but we have not been able to see anyone actually making it yet. One thermal runaway is triggered, its almost impossible to stop
Jul 06, 2017, 11:06 AM
REVOJohn's Avatar
Quote:
Originally Posted by Mr.frankenjet
I have heard from time to time of a break in process, is there actually one recommended for lipo and what performance - current and capacity- changes can be expected with the first few cycles and or break in. Thanks !
OK from the start did you ever hear of needing to break in your cell phone battery?? No
I believe some factories wanted to ask customers to break in packs as the factory production process of formation was shortened to save time and $. Formation is the process of waking up the cell to get its capacity and SEI layer activated. This takes time = $

personally we never asked anyone to do such breaking in but in a recent Singapore military project the customer had laid the packs for 24 months at a low SOC and when they tired to use them they failed quite quickly. When i tool some of the same remaining packs and broke them in first they were fine.
On the other hand some packs were left at 100% SOC for 24 months and there was nothing i could do, they failed very very early due to kathode degredation, normal to see this with very thin electrode formats for RC and at high SOC and long time the electroltye reacts with kathode and eats it away.

As a practice for high rate cell I think its a good idea anyway, especially after long periods of storage to reactivate the SEI later to either form it again or remove it if too big. We're thinking of putting this auto function into the Grand Touring series of chargers

Depending on how much the factory process was shortened you could see up to 10% but i would think 5% of so max capacity uplift. More important is the IR improvement you would get thus increasing cycle life


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