Self-discharge in battery cells remains an important issue in the storage of electrical energy. Recently, Jeff Dahns / Michael Metzgers group discovered that the impurity dimethyl terephthalate (DMT), which leaches from the PET-based fixing tape, used to hold the cell stack in place, causes self-discharge in lithium-ion batteries.

Here, we report the leaching of 2,4-di-tert-butylphenol (2,4-DTBP) from battery packaging material, namely pouch foil, after storage of a state-of-the-art electrolyte (1M LiPF6 in ethylene carbonate/ dimethyl carbonate mixture) in a pouch bag. The contaminant 2,4-DTBP was identified by GC-MS measurements using the NIST database and confirmed by comparison with the pure reference substance. We found that the addition of 2,4-DTBP has a significant effect on the electrochemistry of the battery cells using graphite as the anode, and LiNi1/3Mn1/3Co1/3O2 as the cathode material. The electrochemical effects of the constitutional isomer 2,6-DTBP and DMT on battery cell performance were also investigated for direct comparison. Our results show that all three contaminants not only act as self-discharge promoting agents, but also increase the transition metal dissolution-migration-deposition, a cross-talk phenomenon known to age lithium-ion batteries, thus causing irreversible capacity loss. Moreover, the negative side effects increase in the following order: DMT < 2,4-DTBP < 2,6-DTBP. However, self-discharge, transition metal dissolution, and irreversible capacity loss are somewhat suppressed for all contaminants when the SEI-forming additive VC is present in the electrolyte. Our study clearly shows that more care needs to be taken when selecting inactive battery cell components, as additives can significantly affect the cell chemistry.