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

[PNjunction]

In the right hands, Nicads ROCKED. They did for me.

A conditioning / balancing charge was even easier - just short all the cells for a few days, reassemble, and recharge. Quality ones that is. Talk about the ease of bottom-balancing if you will.

The problem I had was that even though I could overcharge them for long periods of time, and while they still seemed to maintain the original capacity doing that, the self-discharge rate got really bad. It was a catch-22. The longer I left them on overcharge, the more they demanded to be constantly charged to be ready to use! Kind of like a battery addiction.

So like any battery, it seems that one way or another, there is a price to pay for leaving batteries at the extreme ends of charge, even if the current is low to non-existent. Exposure to prolonged elevated voltages changes the chemistry eventually. Basically I had a 10ah nicad battery, but the rate was no longer C/20, but more like C/100.

Powerful beasts they were, but of course too toxic today. At the risk of turning this thread into something else, I'd rather live with my house on top of a pile of empty lifepo4 carcasses, than have a handful of nicads rusting away in the flowerbed....

Sidenote: GBS cells don't even use PVDF in the electrolyte, but an even less toxic substitute I believe. Might make a difference for those who worry about even the minute amount of solvents in lifepo4....

[inetdog]

I once read an abstract of a government (DOD) sponsored research report on early cylindrical NiCad cells. They were worried about the possible hazards of prolonged low current overcharging. So they took a 1.2V 4AH D cell and subjected it to a month of controlled overcharge. No venting. And at the end of the test they had a perfectly good 10AH cell.
That is not going to happen with Lithium chemistry.

[PNjunction]

Hi Karrak and Willy!

I think it is great to further our understanding lifepo4 beyond such mundane things like voltage and balance believe it or not. Like studying how a solar panel system actually works at the molecular level - I find fascinating.

Maybe so we can all be on the same page, I offer two background materials - one for most of us enthusiasts, and the second for chemists. I can barely keep up with the second one! However, it shows how fluently this guy thinks and what it really took to get here. I'm also waiting for the other shoe to drop from him!

http://qz.com/338767/the-man-who-brought-us-the-lithium-ion-battery-at-57-has-an-idea-for-a-new-one-at-92/

This first one above contains clues about what happens when you no longer have any lithium to intercalate, and how lifepo4 is the latest material. Also a quote from Thomas Edison himself in 1883!

And this one will blow your mind:

http://authors.library.caltech.edu/5456/1/hrst.mit.edu/hrs/materials/public/Goodenough/Goodenough_interview.htm

Essentially though, it is my own understanding that overcharging (too high a voltage, or too long a time even at conservative elevated voltages) results in lithium-plating, reducing cell capacity. On the other hand, too deep a discharge, and for too long with nothing left to intercolate, means that the anode and cathode structure tries to intercolate - and obviously does a bad job of it and just contaminates the electrolyte, grows dendrites, which of course is pretty bad.

Amazingly, this is all 20-year old technology (well the iron-phosphate part) at least.

[Willy T]

Hi, Karrak, good to see you back. Looking forward to see you and PN both present you cases. My 520 amp hr bank ( 2p4s ) is still in it's infancy @ 6 months since commissioning. I have been cycling it in a small range as it only has a small daily load ( coffee pot 24/7 ). It charges to 13.6v = 3.4 per cell and discharges to 12.8v = 3.2 and rests at 3.3 to 3.27. SOC is hard for me to figure as they just don't seem right. I have adjusted the setting perimeters 4-5 times and they do not seem consistent. The balance is still spot on with all cells on the fluke meter and a monitor meter that both have a resolution of 00.00 that I feel is important.

It's my intention to add another 1,000 amp hrs in the fall if I can justify the $$$.

[karrak]

I hope I am not offending anyone by starting a new thread from a discussion that started in this thread http://www.solarpaneltalk.com/showth...what-for/page3 but feel this discussion should have a thread of its own.

PNjunction has given us an outline of mechanisms that degrade Lithium-ion batteries in this well researched and thoughtful post http://www.solarpaneltalk.com/showth...l=1#post163798 which I broadly agree with. More information on these mechanisms that PNjunction has mentioned can be found in this research paper for those who want more technical information http://www.mdpi.com/1996-1944/6/4/1310/pdf.

I am not sure that the parasitic reactions that he talks about only occur when the cell runs out of lithium ions to shunt between the electrodes when the cell is fully charged or empty.

I think these parasitic reactions are more dependant on the voltages within the cell rather that the amount of lithium ions left in the anode and cathode i.e. SOC of the cell. Of course the cell voltage depends on the SOC of the cell, but is also dependant on other factors like rate of charge/discharge, cell resistance, temperature and I am sure other factors.

For this reason I think we should be looking at the range of voltages, rather than the range of SOC we allow the cell to work in to increase the lifespan of the Li-Ion batteries.

Simon