Chemical reactions in lithium batteries

[J.P.M.]

Anyway, this is interesting, seeing how subtle differences in understanding brought this discussion this far.

Perhaps somewhat related is what one of my mentors suggested about how miscommunication and bad feeling developed in the organization we both belonged to at the time : "Most of the problems around here have their origins in a lack of communication".

[nebster]

I think the "textbook" is pushing the notion of "reaction".

Redox reactions are one of most important types we have in our known world. They are at the heart of so many processes that we care about, including things like batteries, fire, and cellular respiration. Indeed, they are a critical part of how we living things stay alive.

I'm not sure why you put textbook in quotation marks, but I suppose you may be suggesting it is not a legitimate source. The linked material is very similar to what a first- or second-year chemistry major would study in a degree program. It looks pretty solid to me, but anyone who wants to find other sources can pick up any inorganic chem introductory text and find descriptions of this reaction. Or, less technical descriptions of it can be found on various web sites with a quick search.

Most lay persons will think of a reaction where 2 things are mixed and a 3rd novel item develops or something disappears.

I think you're probably right about what laypersons think, but I don't know what that has to do with a technical forum where we are discussing the intricacies of lithium batteries. If we are not going to be precise and accurate, I submit that we will not advance our collective understanding. Redox reactions are taught in high school chemistry class, and when I wrote my original (accurate) answer, I assumed there was implicit agreement on the basics of how batteries work.

There's no problem if there's a misunderstanding, or if I assumed too much by mistake, but the name-calling and taunting that came along with it was inappropriate.

There's even some contradiction in the text :
"The lithium ion battery is a "rocking chair" battery, so named because charging and discharging involve moving Li⁺ ions from one side to the other"
The ions move back and forth, packing themselves in between layers. The chemicals in the layers don't change into something else, they are simply ion rich. Eventually physical changes occur as the battery ages, but that change is a side effect of imperfections, not the mechanism of the battery function.

That's not a contradiction, it's an elucidation. The nature of the lithium-ion reaction is neat and quite different from some other battery chemistries: the electrolyte does not participate directly in the charge-discharge reaction, and instead the ions themselves travel back and forth across the medium. But when they reach the electrodes, each most certainly undergoes a reaction, because without that there is no way to have a battery!

When those electrodes become saturated/desaturated with ions, the reaction potential changes.

Anyway, this is interesting, seeing how subtle differences in understanding brought this discussion this far.

Agreed; it is really interesting!

[Ampster]

..........
..... The nature of the lithium-ion reaction is neat and quite different from some other battery chemistries: the electrolyte does not participate directly in the charge-discharge reaction, and instead the ions themselves travel back and forth across the medium. But when they reach the electrodes, each most certainly undergoes a reaction, because without that there is no way to have a battery!

When those electrodes become saturated/desaturated with ions, the reaction potential changes.

I have heard the term intercalation used. Does that describe the above?
Does it look like this:
330px-Potassium-graphite-xtal-3D-SF-A.png

[nebster]

I have heard the term intercalation used. Does that describe the above?

I think the "rocking chair" term, is just a cute metaphorical description of the ion behavior, the way the ions move across from anode to cathode without the help of any reaction intermediates in the electrolyte.

The fact that they move over and intercalate on the cathode (or anode) is also interesting, but a separate phenomenon.

Intercalation is just a description of the physical embodiment of the reaction: any chemical where one molecule or ion inserts itself into another in a grid-like manner gets that name, and this same behavior occurs in other compounds that are not used as batteries today. Now, whether that physical manifestation is thought to be a part of why the lithium-ion reaction works so well for storing and releasing energy, I don't know. We'd have to ask an electrochemical engineer, maybe.

[PNjunction]

Ah yes, John Goodenough. Ok, so we're getting to *that* level. (Interestingly enough some of his work was to get early ferromagnetic memory to actually work, ie the "magnetic-core memory" for US Defense computers but I digress)...

Are we trying to introduce Michael Thackery of Zebra-battery fame (sodium-sulfer and variants), who worked with Goodenough and had his own hand in li-ion experiments? Kind of a back-door way to get redox into the picture?

I'm just kind of at a loss for what this thread is about now. Some sort of way for a charger to detect olivine spinel damage with microscopic probes?

I just don't know where or why we are getting to this level of physics about li-ion batteries from a practical standpoint, or what the point is now beyond the level of a materials research lab.

[PNjunction]

Ah, I think I missed much of the very first posts ...

..in the original post from the original question from the newcomer, who was wondering why his charger in CV would deliver fewer and fewer amps over time.

Ah, the battery is simply losing capacity due to normal use and yes, destructive and sometimes unavoidable chemical side reactions occur which reduce capacity. As the battery becomes smaller in capacity internally, the charger dutifully charges it, but being smaller due to usage, age, and abuse, of course less total amperage is needed to charge as the cycles go onwards.

This pdf from NREL shows quite a few of the side-reaction problems:

https://www.nrel.gov/docs/fy14osti/62813.pdf

Did the thread really get out of hand for something as simple as this? Or did I miss the original intent?

[Ampster]

...... ...
Ah, the battery is simply losing capacity due to normal use and yes, destructive and sometimes unavoidable chemical side reactions occur which reduce capacity. ............

Did the thread really get out of hand for something as simple as this? Or did I miss the original intent?

Actually, the original question was more about the taper off of Amps that occurs during the end of the charge cycle. But now that you mention degradation and loss of capacity, that is a subject that I would like to explore further. I have started a new thread but could not find a way to create a link.
I appreciate all the above comments about the chemical reactions/ion exchanges that take place when a lithium battery is charged and discharged. I hope anyone reading this thread in the future understands that it is a complex process. With most of the Lithium chemistries that process has to be done carefully or it can create the risk of fire.

[PNjunction]

Actually, the original question was more about the taper off of Amps that occurs during the end of the charge cycle.

That is just part of the typical CV part of the simple CC/CV charge process. It isn't even lithium-specific, just a general battery charge algo used with lead as well.

Many don't realize that the charger itself is NOT tapering the amperage, but it is merely the battery terminal voltage rising to meet the charger's own *voltage* limit. Current is determined by the difference in voltage potential. A large voltage difference means a lot of current can flow. Very little difference means very little current flows.

Most batteries, once they start to reach about 80% charged, have a terminal voltage that is quite close to the CV protective limitation of the charger. As it charges further, the difference between the battery voltage and charger's CV limit get closer and closer together in voltage. Hence, the ability to pass current gets lower and lower.

So really, the "taper" in current near the end of charge is simply because the battery, as it charges, is nearing the CV limit and there is very little voltage difference between the two. Some chargers will also measure amperage, and at some rate, say 100ma (or whatever it is set to), along with the battery meeting the CV protective limit, will then assume the battery is fully charged, and shut off or change to a different mode.

This basic electronic knowledge is something I'd tackle first, before delving into battery chemistry side reactions.

[PNjunction]

I hope anyone reading this thread in the future understands that it is a complex process. With most of the Lithium chemistries that process has to be done carefully or it can create the risk of fire.

It isn't complex. Operate within the manufacturer's specified guidelines.

BUT, it can be complex if one starts out with used / abused / counterfeit cells or batteries, which need a complex safety belt around them - a virtual trash-can if you will to protect the end user from their ideals of building something great out of unsafe trash.

[Ampster]

It isn't complex. Operate within the manufacturer's specified guidelines.

BUT, it can be complex if one starts out with used / abused / counterfeit cells or batteries, which need a complex safety belt around them - a virtual trash-can if you will to protect the end user from their ideals of building something great out of unsafe trash.

Yes, that is exactly what I meant by complex. Manufacturers's suggested voltages ranges vary by chemistry. Some are more susceptible to thermal runaway than others. Some deliver high rates of discharge while others offer longer life. One cannot just grab a Lithium battery and use it like you can a FLA. You have to make sure the charger is matched to the chemistry. No doubt there are a lot of counterfeit cells as well.

[PNjunction]

One makes it complex when they operate outside the boundaries of what the manufacturer specifies. "Doctor, it hurts when I pee". Response: "Stop doing that".

I just have to stop as it seems more a subject for the debate club, than any real-world practical benefit for the end user.

[Ampster]

.......
I just have to stop as it seems more a subject for the debate club, than any real-world practical benefit for the end user.

Yes. debate over whether it was a chemical reaction is how the original thread got hijacked.. Having the moderator put those comments into a new thread got us into the weeds of intercalation. At least the name calling stopped.

[Sunking]

Actually, the original question was more about the taper off of Amps that occurs during the end of the charge cycle. .

It is not complex, it is stupid simple Ohm's Law. That may sound complex to some folks, but it is simple 5th Grade math, a fact lost on Nebster's response and you missed.

Charge Current Amps = Battery Charger Voltage - Battery OCV / Battery Internal Resistance.

It is no more/less complicated than that of Ohm's Law. Not my opinion, it is the Law of Physics which no one can debate. Ohm's Law states Current = Voltage / Resistance. AS PN stated correctly, you need to tackle and understand the electrical theory first before destroying brain cells on the chemistry. It does not matter what the battery chemistry is NiFe, NiMh, NiCd, Li, Pb. Au, alphabet soup or a ham sandwich, they all charge the same. What changes is electrical, not chemical. What make Lithium different is how the Internal Resistance changes with respect to SOC. Since it is not a Chemical Reaction where Resistance changes significantly depending on SOC is what makes it unique. Just about all chemistries Internal Resistance remains relatively constant over the full range of SOC. Lithium is different and the charge/discharge curves will tell you this if you know how to read than and understand stupid simple Ohm's Law. Voltage = Current x Resistance. This is what causes those sharp knees in a Li Charge/Discharge curve. When a Li reaches full charge, it resistance spikes, and thus the voltage spikes. When they reach fully discharge, the resistance falls off the cliff. That is when excess heat is generated and thermal runaway occurs because then, YOU HAVE STARTED CHEMICAL REACTIONS from organic solvents becoming too hot, generating oxygen, which makes more heat, which makes more oxygen, which makes more heat, which makes more oxygen, which makes more heat, which makes more oxygen, which makes more heat, which makes more oxygen, which makes more heat, which makes more oxygen, which makes more heat, which makes more oxygen, which makes more heat, which makes more oxygen, and BOOM you have thermal runaway. That simple.

Mike made a very good analogy on what are Intercalations are with his rocking chair example. Perhaps just as simple is a Hour Glass, or water sloshing around in a sealed tank on truck. PN, experts, and myself are correct. Li batteries do not use chemical reactions to charge and discharge. It is Ion exchange, and that is a fact. That i snot to say there are not chemical reactions because if there were not Li batteries would last forever. But those chemical reactions as side reactions of using organic solvents which are controlled by age and heat, not the charge/discharge process. So please stop spinning your wheels listening to Pretenders. They are dangerous and a waste of time like lawyers and politicians. They are after what is in your pockets. I certainly understand why you want to think Lithium batteries are the super battery, but they are not. They have niche applications, extremely expensive and not the longest lasting by a long shot.

[Ampster]

Well, that should conclude this thread. It got started by Sunking ranting about chemical reactions and he wrapped it up with a grand finally including a dissertation about Ohm's law.

I don't think there has ever been a disagreement in this thread about the taper of Amps during a charge cycle. Sunking and I will just have to agree to disagree about whether ion exchange is a type of chemical reaction or not. I understand his need to to be right and he is entitled to his opinion. Sources for the other opinion have previously been cited. Others are free to form their own conclusion.

FWIW, I have been using Ohm's since i built my first Heathkit in 1956. We do not disagree about how Ohm's law works. That was a thorough explanation of Ohm"s law with regard to overcharging and the creation of oxygen that feeds the thermal runaway.