Electric-vehicle Batteries are Like Olives…
Sometimes while I'm reading a standard press release about something that I thought I understood kind of, I come across a bit of a gap in my knowledge. This week, Nissan says it has opened its lithium ion battery manufacturing plant in Tennessee. The release states, "The first batteries produced at the plant have completed the required aging process and are now ready to receive their first charge."
Um... what the what? Do these things need to be put on a shelf and cured like olives?
Nissan helpfully includes a really nice graphic describing the manufacturing process, most of which does sound familar to me. In the fourth flow-chart box, after the electrolyte is injected with what looks like a hypodermic needle, the text explains "Cells are aged to allow the cell chemistry to be properly formed." Then they go on to be tested, trimmed to size and charged.
If you are a battery geek, I'd love to hear your idea of what the chemistry formation is and what it does for the battery.
My only guess is that the pause is needed for the formation of the solid electrolyte interface (SEI) on the anode - or negative electrode. This layer is formed with the help of the electrolyte (and there are SEI additives for electrolytes to make the process better). It protects the surface of the anode from the degrading environment of the battery when it is recharged. The SEI layer may be composed of various stuff, depending on the particular materials used in the battery but are commonly Li2CO3, LiOH, LiF, or Li2O.
Nissan explains its battery manufacturing process: