Polyethylene terephthalate (PET) tape is widely used by well-known lithium-ion battery manufacturers to prevent electrode stacks from unwinding during assembly. PET tape is selected since it has suitable mechanical and electrical properties, but its chemical stability has been largely overlooked. In the absence of effective electrolyte additives, PET can depolymerize into its monomer dimethyl terephthalate, which is an unwanted redox shuttle that induces substantial self-discharge in a lithium-ion cell. This study presents a chemical screening experiment to probe the PET decomposition mechanism involving in situ generated methanol and lithium methoxide from dimethyl carbonate, one of the most common electrolyte solvents in lithium-ion cells. By screening other polymers, it is found that polypropylene and polyimide (Kapton) are stable in the electrolyte. Finally, it is demonstrated that reversible self-discharge of LiFePO4–graphite cells can be virtually eliminated by replacing PET jellyroll tape with chemically stable polypropylene tape.
Maybe not completely relevant, but I spent a fair it of my career working with Kapton tape and then having to pull it out of SO MUCH STUFF due to the realized fire hazard (military aviation).
Interesting stuff. It seems like some battery vendors don't use PET tape in their construction? In that case, I'm surprised that competitive analysis on the part of PET tape using vendors didn't result in this being a known issue ages ago.
Also, judging from the pictures, it looks like the tape degradation is really obvious. Again, surprising that battery manufacturers didn't open up their own batteries after aging / cycling tests and notice that.
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[ 2.1 ms ] story [ 32.4 ms ] threadPolyethylene terephthalate (PET) tape is widely used by well-known lithium-ion battery manufacturers to prevent electrode stacks from unwinding during assembly. PET tape is selected since it has suitable mechanical and electrical properties, but its chemical stability has been largely overlooked. In the absence of effective electrolyte additives, PET can depolymerize into its monomer dimethyl terephthalate, which is an unwanted redox shuttle that induces substantial self-discharge in a lithium-ion cell. This study presents a chemical screening experiment to probe the PET decomposition mechanism involving in situ generated methanol and lithium methoxide from dimethyl carbonate, one of the most common electrolyte solvents in lithium-ion cells. By screening other polymers, it is found that polypropylene and polyimide (Kapton) are stable in the electrolyte. Finally, it is demonstrated that reversible self-discharge of LiFePO4–graphite cells can be virtually eliminated by replacing PET jellyroll tape with chemically stable polypropylene tape.
Interesting stuff. It seems like some battery vendors don't use PET tape in their construction? In that case, I'm surprised that competitive analysis on the part of PET tape using vendors didn't result in this being a known issue ages ago.
Also, judging from the pictures, it looks like the tape degradation is really obvious. Again, surprising that battery manufacturers didn't open up their own batteries after aging / cycling tests and notice that.
https://tpcpack.com/services/converting-services/ev-battery-...