Commercial lithium-ion batteries assembled by stacking or winding the electrode sheets contain polyethylene terephthalate (PET) tape to hold the cell stack or jellyroll together. These inactive components have been demonstrated to play a role in promoting battery self-discharge and degradation.

Researchers from Dalhousie University, Canada, discovered that PET tape is not chemically stable and tends toAfter five hours at 70° C PET tape has fully dissolved whereas PP tape is intact. Source: Nat. Mater. (2023). https://doi.org/10.1038/s41563-023-01673-3 depolymerize into its monomer dimethyl terephthalate, which is an unwanted redox shuttle that induces significant self-discharge in a lithium-ion cell. The result is downgraded in performance in terms of both reduced battery longevity and accelerated self-discharge.

An alternative was identified in the form of polypropylene (PP) tape, which was demonstrated to perform as well as PET tape in lithium-ion batteries without the risk of depolymerization. Replacing PET with PP jellyroll tape resulted in slightly better capacity retention, higher Coulombic efficiency and almost a complete elimination of reversible self-discharge. As reported in Nature Materials, using PP tape instead of PET tape enabled lithium-ion batteries to last approximately 10% longer.