NCM vs lifepo4?

[999zip999]

I love the smaller size and can live with 800 cycles ( NCM ). Just looking for a 5c battery to be used at 2-3c. The worst thing about A123 is the weight and triing to fit the size of the pack on a bike. I guess I love 20ah for a pack to much.

 

[etriker]

I what ways are they safer or more stable? And why would GM use A123 cells for the Spark if the Volt's cells are superior? I heard a different story about why A123 wasn't in the Volt, and while I can't say for sure if it's true, it's very plausible in the context visible from my perspective.

LFP has been putting out misinformation about batteries ever since I have been reading this forum.

He is for sure the worst guru on our forum.

He bragged up using hk lipo for a long time and when I was a newbee I bought some.

Worst batteries I ever bought and wasted money.

I should have never read any of his posts.

He is bad for the ebike movement. A total joker that does not help people understand but confuses people.

Somebody linked me to this thread for the LOL value, which is fantastic, thank you.

RC LiPo isn't for n00bs, morons, or people who aren't willing to keep the battery in a safe place for it to burn etc (this seemed to be something made painfully clear by this entire forum and the various painful experiences etc). It's for people looking to make the highest performance EV's at the cost of most every non-performance attribute a battery can have. There is a place for that, kinda like using Nitro-methane for fuel, there is no match for it if your goal is to haul-ass, but just because you see top-fuel dragster pro's using and delivering the results they want back doesn't mean you're going to have much luck just filling your family sedan's tank with it and hoping for the best.

It would nice if before you could click "add to cart" you had to pass some IQ test minimum.

For a commuter pack, it's not the chemistry that plays the big role in how it will perform over time. It's cells that are made right from quality materials, QC processes that filter out the duds/hazards, and finally a pack design and architecture and management to keep the cells happy over time. Look at the Tesla Roadster, Lithium Cobalt cells (same chemistry in RC LiPo), I've never heard of one burning, and the packs have been lasting a long time. Look at the Fiskar Karma, many fires, and A123 LiFePO4 cells. It's because they obviously didn't do some things right, I've got no doubt a safe pack can be made with either.

NMC/NCM (same thing) is currently about the top of the pile as something to base building a safe cell around and still have good energy density. This means you can still make a super crappy NCM cell if you like, because as mentioned above, the chemistry choice is a pretty small piece of the big picture on a cells safety and performance. NCA makes a better cathode material in most attributes than NCM, and as the material tech and processes are better refined you will see it replacing many other chemistry choices soon.

The fundamental issue with a thread like this (not that I don't like this thread, I got many good belly-laughs from it), is comparing chemistry to chemistry is pointless and misses the big picture.

What cell makes a pack that suits your needs is the real question to ask. Do you need to draw 200A from a high voltage tiny pack that weighs just a few lbs? Better start looking at RC LiPo if those are your needs. If you want to pull 30A from a 25lbs low voltage battery, but have it last thousands of cycles, now RC LiPo seems like an absurd choice to make.

Different horses for different courses. Seems weird you even have to say it.

I guess ? If you really want to haul-ass get a Honda 350 ? They sure hold their value !

http://www.ebay.com/sch/Motorcycles-/6024/i.html?_from=R40&_vxp=mtr&_nkw=honda+cb350&LH_Complete=1&LH_Sold=1&rt=nc

Glad you got some laughs ! Means a lot coming from a person that has brought so much humor to our forum !

 

[etriker]

Is this still a NCM vs lifepo4 thread. Or blow my trumpet thread. Get the train back on track. Why is this thread so frock up ?

They are lighter but do less cycles so I hear and keeping the weight down on a ebike is important.

Putting the weight low on the ebike helps.

Now on an etrike the weight difference makes little difference at all in the ride or handling of the etrike.

It was my etrike that replaced my car. Not an ebike. Ebike still tends to be an offroad toy for me.( the rugged A123m1 cells sure will take off road beatings !)

So for toys I guess any battery is fun to play with but for a serious ev that will really replace a car an etrike with rugged tested tried and true A123m1 cells and waterproof electrical setup is the ticket for me.

 

[etriker]

Those ncm nmc or whatever they are 18650 cells may make great extender packs to back up A123m1 cells.

Maybe NCM and lifepo4?

I think every ebike needs an A123m1 cell main pack and it may not need to be very large.

They are almost like super caps on the input to the controller.

What other cells can do that ? ? ?

 

[johnrobholmes]

The C-rate (discharge rate) does not change at all regardless of the size of the battery.
.

:wink:

Technically true, but heat buildup does reduce the continuous discharge rate of a pack vs a single cell in the test environment. Thermal management can get it back if the size and weight penalty is acceptable.

 

[SamTexas]

The C-rate (discharge rate) does not change at all regardless of the size of the battery.
.

:wink:

Technically true, but heat buildup does reduce the continuous discharge rate of a pack vs a single cell in the test environment. Thermal management can get it back if the size and weight penalty is acceptable.

Agreed. But if we have to explicitly describe every nuances, however obvious, then a battery specifications would not be one page long. It could be the size of War and Peace.

Ex: XYZ battery: 3.7V, 2200mAh capacity at 1C. But only 2150mAh at 1.000035C discharge and 2206mAh at 0.999654C discharge.... When does it end?

 

[wb9k]

The C-rate (discharge rate) does not change at all regardless of the size of the battery.
.

:wink:

Technically true, but heat buildup does reduce the continuous discharge rate of a pack vs a single cell in the test environment. Thermal management can get it back if the size and weight penalty is acceptable.

Agreed. But if we have to explicitly describe every nuances, however obvious, then a battery specifications would not be one page long. It could be the size of War and Peace.

Ex: XYZ battery: 3.7V, 2200mAh capacity at 1C. But only 2150mAh at 1.000035C discharge and 2206mAh at 0.999654C discharge.... When does it end?

You're right. The full spec for the A123 20 Ah pouch cell is some 60 pages long--and that's without splitting hairs anywhere near as finely as your example does. That's what it takes for a complete characterization--of any cell. I'm not suggesting this become SOP here, but can't we at least properly define the most fundamental spec a battery has? Why allow total confusion to reign? It's counterproductive.

 

[johnrobholmes]

It never ends around here, the analysis paralysis is ....... Endless...

 

[SamTexas]

It never ends around here, the analysis paralysis is ....... Endless...

Don't blame me. You started it.

 

[nicobie]

I'm sorry, but you dillweeds are boring me to death.

Read the old posts... they are better than these new posts.

If you don't know what "C" is, you don't deserve or should own, an electric anything that needs a battery.

 

[drebikes]

edit: some of my misunderstanding may stem from the well-known rule-of-thumb that drawing high amps from a pack will provide less capacity, while drawing low amps for a longer time will provide a higher capacity. The C-Rate of the chemistry doesn't change, but the capacity is conditional?

Yes, but it's simple. The capacity is the amount of energy that can be used. It is dependent on the load. For example a 10Ah 16s 48V Lifepo4 battery:
*If no voltage drop on the pack: at 100% SOC it's at 58.4V; at 0%SOC 48V; To simplify we can consider linear voltage throughout SOC discharge, so average of 53.2V. The capacity is thus E=I*t*U so 53.2x10 = 532Wh
*When you apply a load you'll have a voltage sag due to the internal resistance.
**Let's say @1C you have 8mohm/cell and 16S1P - resistance of pack (neglecting connectors) is 0.128ohm; you discharge at 10Amps (1C) so the lost energy in the course of an hour is 10^2x0.128 so 12.8Wh; So your usable capacity is 532-12.8Wh
**same for 10C. Let's say 12mohm/cell. Energy lost 16sx0.012ohm*100A^2, but the battery will last for 6 minutes in stead of 60 so divide by 10 ==> energy lost is 192Wh. Total usable at 10C: 532-192Wh. You loose almost half.

So the same battery at the same Ah has a different capacity Wh as a function of the discharge rate. Function of the chemistry, as you discharge faster (more Cs) you have more or less of a rise in internal resistance (see below), but the one inescapable fact is that the internal losses in the battery are squared with the current, so at higher discharge rate you'll have less usable capacity. How much less depends on the value of the IR, if you find a cell that does reliably 1mohm it's obviously going to be less of an issue than an 8mohm (any chemistry that may be).

Cell impedance changes with discharge rate. I believe this is usually a function of electrochemistry, not a purely electrical phenomenon. Higher cell impedance means more heat and more loss across the cell itself. Hence, lower capacity.

True, and it's a measure of electrochemical efficiency. In general terms impedance (for a given chemistry and cathode / anode layout technique) goes up with the C-rate. If the C-rate is pushed high enough the impedance goes up with time. The more capacity-oriented the cell is designed, the more impedance rises with C-rate. On the other hand power-focused cells like with titanium in stead of graphite cathode are going to be less sensitive to C-rate.

On-topic: This is a very useful thread. I was curious of the debate between NCM and Lifepo4 in an ebike context since I'm going to build one soon. I'd just add that only a few weeks back I've assisted to some destructive tests of various chemistry among which NCM, Lifepo, Lipo with cobalt and even oddities like Li-metal. Every one bar the Lifepo4 (A123 26550) blew up spectacularly; we were told that the presence of cobalt in the chemistry increases the voltage (so more Wh for a given Ah, so more energy), but these batteries vent oxygen when the mechanical integrity is broken and self-ignite. Lifepo4-s don't vent oxygen when cracked/squished, only the electrolyte leaks. Electrolytes aren't very flammable in general, but when exposed to pressurized oxygen like in Cobalt chemistry they do go off, in Lifepo they don't because there's no pressurized oxygen source. Lifepo-s burn like any other if cracked and exposed to fire, but if there's no spark they just smoke a bit.

 

[dnmun]

you seem to have a scholarly interest in the lipo. i am under the impression that the thermal runaway that leads to the intense heating of the cobalt oxide type cell begins when the SEI is disrupted and spalls off the anode when the charging voltage exceeds a voltage in the 4.3-4.5V range. as the SEI layer breaks off it exposes the bare carbon surface and the immediate reaction of the LiF6 and ethyl and diethyl carbamiles with the carbon surface results in an exothermic reaction of these species with the carbon and the growth of a new surface layer and the heat released from the exothermic reaction causes more of the adjacent SEI to spall off and continue the self perpetuating reaction which we call thermal runaway. of course i don't know anything so maybe the super experts will jump on me some more here about how i don't know what i am talking about. maybe we will learn something from that.

 

[major]

The capacity is the amount of energy that can be used.

The capacity of a battery or cell is a measure of electric charge. Electric charge is different than energy. Although you can find some references to battery energy capacity, the common and accepted meaning of capacity is electric charge and measured in Ampere hours (Ah) and that charge is abbreviated with the symbol C. Take a look at a cell specification like this: http://www.enerdel.com/ce175-360-moxie-prismatic-cell/ The Nominal Capacity is stated as 17.5 Ah. 17.5 Ah is a quantity of electric charge, not energy.

 

[eva-michael]

Some 24V ebike will use NCM with a case to hold cells inside and keep them more safety. NCM has higher voltage and power density then LiFePO4. So it looks nice in a slim bicycle.
They are dangerous if it's over heat, short circuit or over charged.

 

[SamTexas]

They are dangerous if it's over heat, short circuit or over charged.

Is there a battery that is NOT dangerous when overheated, short circuited or overcharged?

Or you just want to post something, anything, however meaningless to get more exposure for your business link in the signature?

 

[wb9k]

you seem to have a scholarly interest in the lipo. i am under the impression that the thermal runaway that leads to the intense heating of the chrome oxide begins when the SEI is disrupted and spalls off the anode when the charging voltage exceeds a voltage in the 4.3-4.5V range. as the SEI layer breaks off it exposes the bare carbon surface and the immediate reaction of the LiF6 and ethyl and diethyl carbamiles with the carbon surface results in an exothermic reaction of these species with the carbon and the growth of a new surface layer and the heat released from the exothermic reaction causes more of the adjacent SEI to spall off and continue the self perpetuating reaction which we call thermal runaway. of course i don't know anything so maybe the super experts will jump on me some more here about how i don't know what i am talking about. maybe we will learn something from that.

drebikes,

Thanks for the excellent post.

I'll explain my understanding of the thermal runaway phenomenon, but keep in mind that I'm no chemist.

Metal oxide and LFP chemistries all contain oxygen. Metal oxide chemistries surrender their oxygen atoms much more readily than LFP does with temperature rise. The stripped oxygen feeds the thermal reaction and it elevates out of control. A123 cells will burn, just like most anything else, but they don't experience this severe runaway reaction. Thus, temperatures of a burning cell are some 1200 to 1800 degrees C cooler than a metal oxide cell burning. This is the reason I don't like metal oxide chemistries for motive applications except for maybe on a race track. The risk of spectacular fire is just too great.

That said, I don't have any real experience with NCM, but some have touted it's safety in this thread. I had always associated the presence of Co and Mn with this thermal runaway issue, but perhaps NCM is better in this regard?

 

[dnmun]

my point was that it is not the presence of oxygen in the chrome oxide that causes the cell to go into thermal runaway. the oxygen can be released in the chemical reaction as the chrome oxide heats up and the solvents in the electrolyte ignite from the heat by combining with the oxygen from the chrome oxide.

i would never expect lifepo4 to release the oxygen from the po4 unless the temperature exceeds the 600o mark.

but what do i know? i just read the literature. i am not an expert. i am always wrong, i know that because the experts all tell me so.

 

[eva-michael]

They are dangerous if it's over heat, short circuit or over charged.

Is there a battery that is NOT dangerous when overheated, short circuited or overcharged?

Or you just want to post something, anything, however meaningless to get more exposure for your business link in the signature?

Yes, Anything has dangerous and we should take good care.
But I will said that's different in level. People will like to know that.
You may not have the feeling which I went through in workshop of pack building. There are most LiFePO4 packs which are building there but I saw two NCM fire and burn very fast. if you always be nearby then you will get a deep impression in your mind. For LiFePO4, I only saw swelling and no experience for a burning.
For NCM, make special notice to tips below.
1, Over heat of soldering tin will be also a very dangerous factor
2, make sure use a proper rated current of BMS are installed(if you use BMS) and it match well with max current of controller.

 

[drebikes]

you seem to have a scholarly interest in the lipo. i am under the impression that the thermal runaway that leads to the intense heating of the chrome oxide begins when the SEI is disrupted and spalls off the anode when the charging voltage exceeds a voltage in the 4.3-4.5V range. as the SEI layer breaks off it exposes the bare carbon surface and the immediate reaction of the LiF6 and ethyl and diethyl carbamiles with the carbon surface results in an exothermic reaction of these species with the carbon and the growth of a new surface layer and the heat released from the exothermic reaction causes more of the adjacent SEI to spall off and continue the self perpetuating reaction which we call thermal runaway. of course i don't know anything so maybe the super experts will jump on me some more here about how i don't know what i am talking about. maybe we will learn something from that.

This is quite an insight, I'm not that gifted in chemistry to understand everything, but I'll try I'm interested also for work because I do hybrid powertrain design. Up until 2 months ago batteries were for me a voltage source in Pspice with an IR of 8mohm/cell, boy was I wrong. Anyway, the end effect of thermal runaway as far as I grasp it is quite something like what wb9k says below. I think in the norms there are a few tests that are required to do on a commercialized cell: overcharge, undercharge, short-circuit, piercing, squashing (is this a technical term?), etc. Not all lead to thermal runaway. For an ebike what I care most are overcharge and all the mechanicals as there's always the possibility of falling into a ditch or being hit by a car (happen to me both, not only once and not very often happily)

Metal oxide and LFP chemistries all contain oxygen. Metal oxide chemistries surrender their oxygen atoms much more readily than LFP does with temperature rise. The stripped oxygen feeds the thermal reaction and it elevates out of control. A123 cells will burn, just like most anything else, but they don't experience this severe runaway reaction. Thus, temperatures of a burning cell are some 1200 to 1800 degrees C cooler than a metal oxide cell burning. This is the reason I don't like metal oxide chemistries for motive applications except for maybe on a race track. The risk of spectacular fire is just too great.

I'd add only that lifepo4's electrolytes I've seen actually don't burn except if you have a spark or a concentrated oxygen source; we haven't heated them beforehand though, it is possible over 600 they release the oxygen. Once sparked is burns like diesel/oil a slow uptake and then it takes a while for it to go, unlike Mn or Co chemistry which go like gas. Afaik all chemistries are used on the racetrack, for better or worse; some go for safe, some go for light, packaging can go a long way to insure at least mechanical integrity. About the overhanging and s-c we've all seen the Dreamliner story, they should have taken Lifepo.

The capacity is the amount of energy that can be used.

The capacity of a battery or cell is a measure of electric charge. Electric charge is different than energy. Although you can find some references to battery energy capacity, the common and accepted meaning of capacity is electric charge and measured in Ampere hours (Ah) and that charge is abbreviated with the symbol C. Take a look at a cell specification like this: http://www.enerdel.com/ce175-360-moxie-prismatic-cell/ The Nominal Capacity is stated as 17.5 Ah. 17.5 Ah is a quantity of electric charge, not energy.

I guess I was trying to differentiate between SOC and SOE, which is state of charge and state of energy. I was arguing capacity is neither the initial Ah or the Wh, but the actual energy (joules) that can be used. The difference between the capacity SOC (as defined in Ah) and usable energy SOE (Wh) are the losses in the pack, be that chemical or electrical; losses can be computed per mission profile. I think Ah is the stock capacity and Wh is what we can use out of the initial charge: Wh=(Ah x Voltage)-Heat; so Ah is something that is in the supplier's datasheet and Wh is something I define per application at the DC battery plug.

They are dangerous if it's over heat, short circuit or over charged.

Is there a battery that is NOT dangerous when overheated, short circuited or overcharged?

...I'd say A123 26550 Lifepo. And no, I'm not paid by them or have any connection with them. We just destroyed an impressive amount of batteries just to see what happens. We have a very high possibility of overcharge, undercharge, mechanical and chemical damage, so aside from packaging that has to take lots of punishment, we have to make sure cells are as safe as reasonable. Well, we haven't managed to make those cells blow and not for lack of trying

That said, I think I'll get NCM for the bike, I'll handle it. For someone that is more of a beginner I'd get Lifepo just to be safe(r).

 

[SLC Tortfeasor]

Noob here. Just finished reading the whole thread. Now having serious doubts about whether I want to dip my toes into all of this. Technical confusion is the main reason, but another reason is that I'm afraid of becoming a wild-eyed, overly-opinionated, defensive, electical engineering know-it-all.

 

[Ypedal]

wild-eyed, overly-opinionated, defensive, electical engineering know-it-all.

i could add to the list.. but welcome to the group.. above all.. as long as you have fun.. it's a win win situation. 8)

 

[slacker]

should i upgrade from sla?welcome all expert opinion;s?

 

[999zip999]

YES.

 

[slacker]

the question was in jest as i find it amusing how people get so worked up and personal on this forum.good day all

 

[dogman dan]

:lol:

Something going on this summer. We moderators usually just prune out spammers, edit a few f bombs, and let the discussions rock and roll. This year we are having to put out fires every week. Just don't call other members names. Ridicule the idea all you want, but don't get personal. Got somebody here you hate, set your forum so you never read his comments.

As the years go by though, those of us into this since 2008, 2009, have gotten more solidified in our opinions of what works best. We can come off awfully strident.

Back in 08-09, battery stuff was changing so fast nobody had opinions that lasted much longer than 6 months. Now that you can get your hands on any chemistry you like, the polarization has begun. Each job has a tool that does that job best, so choose based on that. The other guys job may not be just like yours. Read it all, then choose the tool for your job. It doesn't matter if others don't like it. Even lead still has it's niche, where it works fine for the job to be done.