Lithium Battery Passivation Layer

[Aaron222]

Hi all,

When I started as a tech in the aerospace field, a coworker told me that the lithium batteries for the Fanuc controllers (and all lithium primary batteries) develop something called a passivation layer when on the shelf. I was told that we needed to de-passify the batteries before changing batts in the Fanuc controls, or else we risk losing the parameters. The issue being that the passivation layer creates a resistance and if the power to the machine is turned off, the sudden current draw on the battery may cause its voltage to dip below minimum and dump the programming. We've always cycled a load on the new batteries before replacing them once per year, 100ohms for 3V and 200ohms for 6V.

I had never heard of it and never done this before changing batts on other PLCs which also use lithium primary cells. Has anyone heard of a depassivation process? Do you do one before changing batts?

Thanks in advance

 

[Bit_Bucket_07]

The passivation layer is what allows lithium cells to have such a long shelf life, and it's true that the passivation layer can cause a voltage drop when a load is initially applied to a lithium battery.

I just question whether the current draw for memory backup is adequate to create a significant voltage drop. I've never personally witnessed a newly installed memory backup battery failing in this manner.

 

[geniusintraining]

Here is a good video from Saft explaining passivation https://www.saftbatteries.com/energizing-iot/what-passivation-primary-battery-video

I have been selling PLC batteries since 2006 and never heard of issues with them but I have a high turn over rate and they dont sit long

 

[parky]

Growth of the passivation layer may occur over long periods, so for batteries that have been stored for sometime putting a load across it may help but high loads initially will probably reduce battery life, personally, I have fitted batteries that have been stored for a couple of years with no problems & little difference in life, in saying that if I am in control of battery replacement then I always fit ones that have been purchased within a year of the replacement I also check the new batteries are only less than one year old where possible, I would replace PLC backup batteries every 12 months regardless.