Any thoughts on extending the life of used Nissan Leaf batteries ?

[Ampster]

........ There is a DIY Electric Car Forum that is all about Lithium and especially Nissan batteries.......

Been there since 2012. Basically the same information that has been repeated here. Probably the best overall information in one spot is the sticky by PNjunction

My cells are at 70% of original capacity and that is what they were at when I bought them two and a half years ago. I used them with a Radian inverter for two years and was charging them to 4.15v per cell and rarely ran them down to 3.75v. I am keeping a eye out for that "sudden death" syndrome.

[PNjunction]

I've experienced sudden death of cells. Mostly from over-discharge down to zero volts. Although I have been able to revive them with very low current recharging techniques done very soon after noticing the event, and even obtained what seemed like near perfect capacity recovery, there is a surprise waiting:

When li-ion (be it lfp or otherwise) is taken below say 2.5v per cell, what starts to happen is the SEI layer starts to dissolve and contaminate the electrolyte.

Think of the SEI layer as an automotive oil filter. You need it to prevent an engine from failing rapidly. However, if it gets clogged with junk, what was once protecting the engine, is now starving it, and the engine fails.

In this case of over-discharge, you have basically melted the filter and all the contaminants into the oil.

Putting a new filter in, (saving the over-discharged cell with very low current revival techniques if done in time), *SEEMS* to revive the cell, as a new SEI layer is created. But the electrolyte in the case of the battery is still contaminated with a special surprise waiting.

Those contaminants are fertile ground for dendrite growth and higher-impedance as time goes on, and the normal growth of the *new* sei layer laid down with recovery grows faster than usual, since the contaminants are in the electrolyte.

The sudden death is that even though there is plenty of active material available, you can't get to it - the lithium can't intercalate through that clogged sei layer that grew faster than usual. It will do it's best, but like a light switch, all of the last remaining pores to intercalate through are closed.

THAT is why I harp so much on using batteries with a known state beforehand. One just doesn't know if sudden death is awaiting from abuse (which can also involve mechanical shock) etc etc.

Doing a "one-off" goof can be pulled off - but there is nothing to learn if hidden internal problems, which can be just 10 cycles away, are laying in wait.

[Ampster]

................

THAT is why I harp so much on using batteries with a known state beforehand. One just doesn't know if sudden death is awaiting from abuse (which can also involve mechanical shock) etc etc.

Doing a "one-off" goof can be pulled off - but there is nothing to learn if hidden internal problems, which can be just 10 cycles away, are laying in wait.

Good advice. As I mentioned I purchased these two years ago. I view them as sunk costs but buying more is another issue. This thread has helped me evaluate a capacity increase. I think I am going to put that off for as long as I can and save up for new CALBs or equivalent. I may look at adding 9 panels to the Skybox first. Currently the Skybox has no panels and I have the roof space. I will have to do some number crunching over the next six months once I finally get on my NEM agreement.