Hello,

I am battling with a mystery high-impedance coating that is appearing on the battery terminals of a lithium ion battery. Frankly, I'm not even sure its corrosion, but - as it's an intermetallic joint - it's my best guess so far! I've uploaded a couple of magnified photos, showing how the coating looks like after scratching the surface a little.

http://files.engineering.com/getfile.aspx?folder=b...
http://files.engineering.com/getfile.aspx?folder=7...

As well as these photos, here is some more information:

• I actually do not know what metal the contact is. I have asked the supplier and hope to know this Friday.
• The material of the other contact is gold. I have read a little about white plague, and purple plague, but I read that this is relevant to aluminium, and those contacts don't look like aluminium.
• The impedance of the coating must be reasonable. The contact force is normal to the surface, so there's no "scraping" action there, and the coating is preventing this 3.7V cell from being detected by the charging unit.
• I cannot discount the possibility of this being some sort of resin/flux that's leftover from an unsuited assembly process. If this doesn't look, or sound like corrosion to anyone here then this becomes the most likely possibility.

As I said above, I'll know more after receiving more feedback from the supplier on Friday. Was just wondering whether anyone had any thoughts in the meantime.

Best,

Eddie

Edward Matos
MEng (Hons.), AMIMechE