Mechanisms that decrease the Lifespan of Lithium-Ion batteries and how to avoid them

[karrak]

I think that the biggest problem is that the S/N ratio is so high, that NOBODY is getting any value from the debate, be it right or wrong or in total agreement.

I have given up on getting any useful information on the subject of this thread from this forum. The thread has been hijacked and I think it is important to discuss the points that Sunking has bought up.

Simon

[karrak]

Assumptions made by Sunking

Sunking, one of your main arguments for not doing top balancing or not charging above is it 80% or 90% is that it will cause a huge decrease in the lifespan of an LFP battery, to quote you

It is well know if you charge any of the Lithium batteries near or to 100%, you cut your cycle life in half.

Could you provide me with information to back up this claim.

In this study http://www.researchgate.net/publicat...teLiFePO4_cell which I have mentioned before in this thread on page 298 is the following.

Fig. 2(a) shows that, after 240 days (8 months) of storage, the capacity increased by 1.8%, 1.07%, and 1% for SOC nom 30%, 65%, and 100%, respectively. Meanwhile, Fig. 2(b) and (c) shows that the capacity fade is fairly linear as a function of storage time and at a specified temperature, more capacity fade is experienced at higher storage SOC. At 45◦C, after nearly 214–247 days of storage, the capacity has decreased by 2.1%, 4.9%, and 5.7% for SOC nom 30%, 65%, and 100%, respectively. This decrease becomes much more substantial for the cells stored at 60◦C for which the capacity fade percentages of the cells (∼155–188 days of aging) are about 18.1%, 23.7%, and 26.9% for SOC nom 30%, 65% and 100%, respectively.

The other cornerstone of your argument is that if you if you bottom balance you don't need to have a BMS. I can see this would work if the balance at the bottom and top does not change with time. This is not the case. If the capacity of the individual cells vary relative to each other the top balance will change, if the coulomb efficiency of the cells is not identical the bottom balance will change. All this has already been covered before in this thread http://www.solarpaneltalk.com/showth...-Solar-amp-BMS

Simon

[Sunking]

If Sunking puts forward some credible evidence to support his claims them I might change my mind on his credibility regarding Lithium batteries and particularly Lithium batteries being charged by solar energy.

I have done that many times for you Simon, you just do not want to hear it. Start with this written by my peers.

Topologies[edit]

BMS technology varies in complexity and performance:

• Simple passive regulators achieve balancing across batteries or cells by bypassing charging current when the cell's voltage reaches a certain level. The cell voltage is a poor indicator of the cell's SOC (and for certain Lithium chemistries such as LiFePO4 it is no indicator at all), thus, making cell voltages equal using passive regulators does not balance SOC, which is the goal of a BMS. Therefore, such devices, while certainly beneficial, have severe limitations in their effectiveness.

More facts you cannot deny and is well known.

• Limiting SOC to 80% doubles the calendar and cycle life. Which begs the question is why would you ever go to 100%. That is a Pb left over and mentality period.
• You Inverter and Charge Controller already has the protection you need to protect you from Over Charging and Over Discharging. When you Bottom Balance makes it impossible to Over Discharge a LFP cell
• We are talking only about NiFePO4 cells. NOT ANY OTHER TYPE.
  
• We are only talking about very low Charge and Discharge Rates in a controlled environment of room temps.
• Many battery Manufactures make 12 volt LFP batteries as drop in replacements for Pb and most do not have any type of BMS other than a LVD Relay. That includes the almighty A123 LFP 12 Volt Car Battery. Why would a manufacture do that without a BMS? Because it is NOT NEEDED.

You cannot deny anything I have said as not true and factual. You just do not want to hear it. The other thing you have not heard and do not want to hear is I never said: You Should Not Use BMS on a LFP solar system.

I say: A BMS is not required or necessary Everyone else has heard that except you. You do not even understand the concept of Bottom Balancing. It mimics matching cells accurately. You can use a BMS, I do not care, it is your money you are pissing away, not mine. Go spend it, all of it.

[Sunking]

OK, what if you get distracted when you have your bleed resistor hooked across one of your cells when doing a bottom balance.

I have a tool all Bottom Balancers use a PowerLabs 8 hobby charger. Impossible to over discharge. Even using a resistor would be incredible hard to over discharge.

You connect all 16 100 AH cells in parallel. With a .080 Ohm 100 watt resistor gives you a big wide window of a few hours to remember. With a Powerlabs 8 drawing 30 amps, you walk away, go to bed, and by morning you are balanced perfectly at 2.4 to 2.6 volts per cell. You can go to 2 volts but not recommended.

If by chance I should ever need to re balance which is unlikely because I know around 100 people with EV's that BB and have done so for at least 3 years have never ended to re balance, I would drive my EV until it stopped and would use my PowerLab 8 discharging 8 cells at a time until the reach 2.5 vpc again. No driving my EV until it stops will not hurt the batteries because I designed it so it cannot hurt the batteries. They will still be setting around 2.7 to 2.9 volts per cell if out of balance. Right now if I drive until the EV quits all cells rest at 2.8 volts as designed. If they were Top Balanced and I drove my EV until it quits would likely end with a destroyed cell, the weakest one.

[wb9k]

I heartily welcome WB9K, and no matter what happens, I have gotten a LOT from you just lurking over the last few years.

So much so, that I cut open many NEW powersports batteries a few years ago just to work with A123 cells, which got me enough hands-on to brave large prismatics from other companies and compare notes - although there are obviously some differences.

I'm actually amazed that anyone working in the industry even steps foot inside a forum, considering the large target it puts on your back. It isn't much different than the hammering I saw "Optima Jim" (Jim McIlvane) go through when he just really wanted to help people understand and improve their setups, and not try to be a salesman or company shill - just a tech trying to help people out. Unfortunately, you don't find much of him anymore in the forums, and I think I know why - like not wanting to get gray hair prematurely.

So please understand that even when threads get contentious, there is STILL VALUE in what is debated, especially for those of us that can look beyond the drama. Basically THANK YOU from a lurker.

Thanks for the kind words. It's gratifying to know that folks are reading and benefiting from my efforts to share useful information. See you around!

dh

[solar pete]

please argue nicely

Hi All,

I was a bit worried about this thread but I am very pleased that the argument can continue in a civil manner. People will disagree on many things, lets face it there is more than one way to skin a rabbit. I, like some of the other posters think these things need to be debated but in the most civil and polite way, cheers all

[wb9k]

Like I said you are a manufacture and only have one point of view. The claim that Top Balance and a BMS must be used is completely false and made up by manufactures with BMS and Top Balance products.

I work for a company that is a cell maker first and foremost. The company does also make BMS systems, but they are not for sale to the general public, and I don't expect A123 to ever sell any electronics to any member of the GP. So, I reject the idea that I'm on some kind of sales shill mission regarding control systems. I never said packs MUST be top balanced, but I think there are plenty of good reasons for opting for that arrangement. Bottom balancing requires compromising performance and control over certain aspects that I think are not worth any perceived benefits. Others in this thread and the one at ES have covered most of these things already.

There is nothing dangerous with Bottom Balancing, it is safer than Top Balance. As to responding I would have loved to continue a debate, but you shut the thread down. So do not give us that crap I would not answer questions. You do not want questions answered unless it is you are th eone giving answers. You cannot have your way here. Now you come here hoping to shut the debate down here. Simon like like you are manufactures, you have to tow the company line. Simon couldn't win the debate here, so went crying to you looking for help. I expect you and Simon both to say exactly what you are saying. As manufactures if you said anything else is Conflict of Interest. You are here to protect your Invested Interest. I am here to tell floks there is another way and you do not like it.

You're teetering off the rails here. I am not a moderator at ES, or any other forum nor have I ever been. I had nothing at all to do with the temporary locking of that thread, in fact when I saw it was locked, I sent a note to the moderator (Ypedal in this case) to make sure I wasn't the one being complained about (I wasn't). I have no idea who complained or what exactly they complained about, and I don't really care. As Simon (who you falsely accuse of being a mfg.) pointed out, the thread is open again, and if you look, you'll see an unanswered question from me about what you actually mean by when you say "BMS". This is needed before any debate can continue there, which I'm open to. I suspect the locking of the thread was about the acidic comments of one member there, but I don't know for sure. I'm confident it had nothing to do with technical content...where several posters (not just me, not just people in the industry) expressed a feeling that you were deficient on that front.

Fact is EV manufactures do not Top Balance, they all Middle Balance never touching 100% and never getting close to 0%. Exact same thing I do with my NEV. I charge up to 80/90%, and only discharge down to 20/30%.

You keep repeating that first point as though it is gospel, and I know for certain that it is a totally incorrect statement. I know of several programs (mostly hybrid buses) that do in fact allow packs to go to 0% and will allow brief excursions ABOVE 100%. Every plug-in car I'm familiar with takes the pack to 100% or very close to it on every charge cycle that runs to completion. "Middle balancing" doesn't even exist. LFP cells must be balanced at either top or bottom of charge to be balanced at all. If you're not at one of the extreme ends of the charge curve, you cannot discern SOC using voltage with any hope of accuracy. NEV is a mighty highfalutin' term for a souped up golf cart. Is it even street legal in any sense? Regardless, in a purely recreational vehicle, you can afford to not use 30-40% of your battery capacity. In a real car, this would be considered an enormous waste of resources and no OEM I am aware of operates this way to my knowledge. Perhaps if you could share how you come by this belief, we could discuss it more detail.

What you guys did on EP is distort what I said. Batteries are not Bottom Balanced every cycle as was implied by yourself and others. They are only Bottom Balanced initially when assembled like any dang battery assemble has to be done. Does not matter if it is Top, Middle, or Bottom because any will work once you pick the end means. . Any lithium battery must be equalized with his mates before assembly. You know that as well as I do. I just do it at the bottom when the cells arrive. Wire then all in Parallel and drain then down to 2.5 vpc resting over night. All it takes is a real simple cheap circuit made from a dollars worth of parts and nichrome wire.

I never said you bottom balanced every cycle. In fact, I think the lack of regular resetting of balance is the single largest liability in your system. You have no means of dealing with developing imbalance, except by leaving margins for error wide enough to drive a truck through at both the top and bottom of charge--putting over 1/3 of capacity permanently off limits. Yes, it's cheap to bottom-balance cells just before assembling a pack, but it is any cheaper than paralleling the cells and charging them to exactly 3.6 Volts? I see no reason to trumpet this virtue for this part of the process because so far, you've gained nothing at all.

You say it has to be at the top 100% where you only really know voltage, but AH is unknown. I reference at the Bottom where I Know exactly where 0% and 00 amp hours are located. From there once charged they never see anything below 20% or above 90% which is spot on for maximum lithium battery life. Everything I said has been factual.

In a pack made of decent cells, there should be very little difference in capacity from cell to cell. This is one good reason for paralleling smaller cells when building a pack....the capacity difference between cell groups tends to get averaged out and be less of an issue than if you use one giant cell for each series element. Your system seems to be targeted very specifically at fixing this problem which you really shouldn't have in the first place, unless you're building from recycled/recovered used cells.

Your method is to charge lithium cells to 100% every time, and it is well know that is not good on for lithium batteries and can cut battery cycle life down some 50%. That is good practice from a manufacture POV as it generates more battery replacement sales. Me I never go above 90%, so not something I have to worry about is over charging, I eliminated the possibility, where Top Balance does it every cycle if set to 3.6 volts.

I'd like to see data showing that 50% loss of lifespan vs charging to 80% with LFP. This would need to include specific details on the charging and usage routines to be really meaningful. My own experience and the data I'm familiar with suggests a difference of more like 5 or 10%. Top SOC isn't the only thing that affects this. Charge rates and soak voltages are important to consider as well. A cell that loses half it's life for going to top of charge is not fit for automotive use, IMO, and I think the OEM's feel much the same way.

With Top Balance you also set the batteries up for a over discharge and reversing a battery cell polarity. With Bottom Balance I eliminated the possibility because all cells arrive at 0 at the same time. No adjacent cells have any energy left in them to drive a cell into reversal. Cell Reversal is the most destructive thing you can do to a lithium and you know it.

Top or bottom balance has nothing at all to do with robust protection against overcharge or overdischarge. Those things can only be properly addressed with cell-level voltage monitoring and controls that stop the show before a cell can be destroyed. Yes, I say all the time that overdischarge is bad, there has never been any argument about that. Apart from gross overcharge, it is the most dangerous thing you can do with an LFP cell.

Is Bottom Balance for everyone. Nope especially the uniformed public. For them, I send them to you to lighten their pockets with Automation and not a thought in their head. . That is good for both if us.

See the deal is I do not represent any company or technology. I got nothing to sell you or anyone else. Just 35 years as a professional electrical engineer in battery plants and power transmission. Retired and giving something back to the public. Endless Sphere is a commercial site, that was my only mistake. You guys do not want anyone there that does not have a commercial product solution and I understand and respect that.

Where we left our conversation before you had it turned off is, I said is some level of monitoring is required and a Strategy is needed with LFP. You replied calling that BMS. That is when I said you cannot define what a BMS is other than something you sell or recommend as a manufacture. We get it. You sell lithium batteries. As a manufacture you can only warrant your product if a BMS of your approval is used.

Have I missed anything?

I think you've missed plenty and added some things as well. ES, as far as I know, is NOT a commercial site, any more than this forum or DIY EC. You're strawmanning me and Simon by painting us as having agendas that we don't have. I am not a sales guy. I sometimes go to bat for the company on forums when I see misinformation or sabotage by certain individuals, but that's as far as it goes. A123 has already sold every cell it can possibly make through 2017...I really don't care whose cells you use, and you can't buy an A123 BMS, so this is just noise on your part. You're oddly narrow definition of "BMS" makes me wonder what product you may have waiting in the wings and how you plan to differentiate it in the market. Just a hunch...trying to make sense of your odd assertions.

[wb9k]

[*]Many battery Manufactures make 12 volt LFP batteries as drop in replacements for Pb and most do not have any type of BMS other than a LVD Relay. That includes the almighty A123 LFP 12 Volt Car Battery. Why would a manufacture do that without a BMS? Because it is NOT NEEDED.

WHOA That statement is complete BS....totally untrue. How to you pretend to know what is inside that battery? Tell you what....you tell us what's in there, and then I'll post a picture of one torn down and we can all see how full of it you really are. Your trousers are ablaze.

dh

[Sunking]

WHOA That statement is complete BS....totally untrue. How to you pretend to know what is inside that battery? Tell you what....you tell us what's in there, and then I'll post a picture of one torn down and we can all see how full of it you really are. Your trousers are ablaze.

dh

Lets see it, nothing in the documentation that indicates there is anything inside. . Then IJ wil show you dozens of 12 volt Lithium batteries with no form of BMS. There are more than I can count. A 12 volt 4S battery is kind of a waste having any BMS. If a cell failed you would be in the 9 volt output range. That woul dtake catastrophic failure and gross negligence on the user.

[wb9k]

Lets see it.

Oh no...you first, Mr Expert. A relay, you say? Running LVC? Any other capabilities in this thing at all? Tell us, what are the real-world requirements for this battery. I'll even give you this...that's the same battery we have been selling to Daimler and Ferrari for a couple years now. So...what's needed in such a battery?

[Edit:] Those "no BMS" 12V batteries are unreliable, dangerous pieces of crap that will eventually be illegal. Search the ES forum for "Ballistic" for my posts regarding one example. Are you consulting for these guys?

dh

[wb9k]

Lets see it, nothing in the documentation that indicates there is anything inside. . Then IJ wil show you dozens of 12 volt Lithium batteries with no form of BMS. There are more than I can count. A 12 volt 4S battery is kind of a waste having any BMS. If a cell failed you would be in the 9 volt output range. That woul dtake catastrophic failure and gross negligence on the user.

The more you edit this post, the worse it gets for you. Selling a product that can kill somebody for being negligent or ignorant...IS NEGLIGENT! There's nothing stopping the user from the possibility of burning his house down if he accidentally puts his 12V battery on a 24 V charger.....or a "12V" charger that really makes up to 17 Volts. Now you really are advocating no supervisory electronics on an LFP pack. If this were my forum, you'd be on vacation for advocating dangerous practices and banned if you repeated. But of course, it's not. The moderators here can do as they please, but to me, you smell like a saboteur.

dh

[Sunking]

you'll see an unanswered question from me about what you actually mean by when you say "BMS". This is needed before any debate can continue there, which I'm open to.

I answered that already here because the other thread is locked. But to recap any system that uses Balance Boards or By-Pass Charging. It is the vampire boards I take issue with.

I know of several programs (mostly hybrid buses) that do in fact allow packs to go to 0% and will allow brief excursions ABOVE 100%. Every plug-in car I'm familiar with takes the pack to 100% or very close to it on every charge cycle that runs to completion. "Middle balancing" doesn't even exist. LFP cells must be balanced at either top or bottom of charge to be balanced at all. If you're not at one of the extreme ends of the charge curve, you cannot discern SOC using voltage with any hope of accuracy.

Sure you want to stick with that statement? Because Tesla and Nissan do not allow owners to have access to all the battery capacity. In fact Tesla just upgraded all their Roadster mileage from 240 to 400 miles with nothing more than a Over The Air Up Grade to firmware to allow customers to access more capacity that was always there to start with. Tesal sends out alerts to customers warning them not to charge to more than 90%.

Chevy Volt uses a 16 Kwh battery and limits access to only 10.4 Kwh usable.

The Nissan Leaf uses a 24 Kwh and limits to 21 Kwh usable.

Between Tesla, Nissan, and Chevy make up the majority of the market.

I never said you bottom balanced every cycle. In fact, I think the lack of regular resetting of balance is the single largest liability in your system. You have no means of dealing with developing imbalance, except by leaving margins for error wide enough to drive a truck through at both the top and bottom of charge--putting over 1/3 of capacity permanently off limits. Yes, it's cheap to bottom-balance cells just before assembling a pack, but it is any cheaper than paralleling the cells and charging them to exactly 3.6 Volts? I see no reason to trumpet this virtue for this part of the process because so far, you've gained nothing at all.

You would be incorrect, I would use my Powerlab 8 to re balance if it ever became necessary like anyone who BB thier EV pack.

Not sure what Holes you are are talking about and loss of capacity. When I drop to 10 to 15% SOC all my cell voltages are equal all the way down to 2.5 vpc. I cannot see anyway hole sin those voltages.

My cells are 100 AH Prismatic, Chi Com Prismatic GBS to be exact. Their actual capacity ranges from 101 to 110 AH or about a 9% tolerance. Regardless the weak cell of pack means the pack is only 101 AH. That last 9% is not accessible like any battery pack be it Lithium or Pb. When I am fully charge (85 to 90 AH, I use Coulomb Counter Gas Gauge), my lowest cell voltage 3.36 and highest is 3.41. So I have no idea what holes of loss of capacity you are referring too.

In a pack made of decent cells, there should be very little difference in capacity from cell to cell.

That maybe true if you use a good manufacture, and have a manufacturing at either at the battery manufacture plant , or Auto Manufacturing to match cells. But what I have been trying to tell you a DIY Solar System is going to use inexpensive Chi-Com cells and only LFP. If cells were matched up as close as you imply, there would be no need for any monitoring needed outside what the charger and inverter already have built in. All that would be required is the initial Balance at either the Top or Bottom. Set your charger to say 3.45 vpc and set LVD to 2.9 vps and you would never even come remotely close to either edge making it a Middle Balanced system.

We are not talking about any other battery, only Chi-Com LFP in a DIY Off-Grid Solar System. The batteries get treated like babies and never see the extremes an EV will see. In a properly designed solar system, a LFP battery will never be fully charged. Just not enough sun hours in the day. Charging rates are relatively low in a Solar system and discharge rates are even lower. On the charge side it would would be rare to ever see a charge rate in excess of C5 with C/8 to C/10 being the norm. Discharge rates are similar. Couple that with a controlled environment of room temps and all the need for a BMS vanish.

Look I am not saying DO Not Use BMS. I am saying You Do Not Have Use a BMS. Regardless if you like it or not, there is a Market being born for BB. BMS manufactures are just now starting to offer equipment, but all one really needs is a Powerlab 8, and good strategy. Run Between the Sheets of either 10/90 or 20/80.

[Sunking]

The more you edit this post, the worse it gets for you. Selling a product that can kill somebody for being negligent or ignorant...IS NEGLIGENT! There's nothing stopping the user from the possibility of burning his house down if he accidentally puts his 12V battery on a 24 V charger.....or a "12V" charger that really makes up to 17 Volts. Now you really are advocating no supervisory electronics on an LFP pack. If this were my forum, you'd be on vacation for advocating dangerous practices and banned if you repeated. But of course, it's not. The moderators here can do as they please, but to me, you smell like a saboteur.

You are full of chit too. If anyone can say anything about me, Dangerous is not one of them. That is a fact that can get you in trouble here because every moderator and the site owner know for fact safety is my top priority. If anyone stinks it is you my friend as a Shrill.

No supervisory my foot. What the heck do you think any Inverter or Solar Charge Controller has built into it?

[wb9k]

You're changing the subject because you stepped in a pile of sh%t with claims you realize you can't back up, and in fact are in danger of being proven extremely wrong. What's inside that A123 battery...since you claimed to know? Put up, or STFU. I will not waste my time on a fraud any longer.

[Sunking]

You're changing the subject because you stepped in a pile of sh%t with claims you realize you can't back up, and in fact are in danger of being proven extremely wrong. What's inside that A123 battery...since you claimed to know? Put up, or STFU. I will not waste my time on a fraud any longer.

Like I said lets see what you got to show. You keep threatening to show it, play your hand. A123 battery may certainly have something inside. But there is nothing in the docs to indicate so. But even if it does, does not change the fact you can find dozens just like it that do not have anything other than cells inside the box. At 4S is silly to think you could get any one cell so far off without the pack voltage being way below what any equipment can operate with just 7 to 9 volts on a 12 volts.

Many commercial EV's DO NOT MONITOR or CONTROL at cell level voltages. They range from 2S to 4S level. Example Nissan Leaf is 2S or what Nissan calls a Module which is 2s2p. That clearly indicates you do not need to monitor and control at cell levels.



And I was being so nice until you showed up to make trouble.