When they did a chemical analysis of the electrolyte, the team discovered that the polyethylene terephthalate (PET) in the tape decomposed and created the molecules that led to the self-discharge. Because the molecules can travel between electrodes, just like Lithium ions do, it is called a redox shuttle. That’s what’s causing the discharge, thanks to this continuous movement of the redox shuttle molecules in the background.
I'm picturing this goo around the tape slowly moving around and around between the positive and negative electrodes, ionizing in one direction and getting the electrons back in the other. Very slow movement but going 24 hours a day so depleting it significantly over time.
The case of many lithium batteries is the same as the possible terminals, so the case must insulated from each other and the enclosure. I built a large prismatic lithium pack and used insulating materials between every cell and the case. It sat 18 months and when I finally got to using it, it had not discharged at all.
(post is archived)