08: The Use of Debondable Adhesives

Hi everyone! In this post, I will be talking about debondable adhesives and how they might facilitate the battery recycling process.

Debondable Adhesives

Another way to tackle some of the issues is through the use of debondable adhesives. Debondable adhesives are designed to create a strong bond between two surfaces but can also be easily removed or debonded without damaging the materials or leaving residue behind. The primary stimuli for debonding are magnetic, ultrasound, UV light, chemical, thermal, and electrical.

In Battery Recycling

At the cell level, debondable adhesives used for binding the electrode current collectors to the active materials can be debonded, in milliseconds, using focussed, high-powered ultrasound as the stimulus. This process has several significant benefits: ultrasound is not generally experienced during material lifetime, reducing the risk of accidental debonding; recycling metrics are substantially better than for other techniques; and while already efficient, there is potential for future improvement with modification of the adhesive (binder) used. Therefore, on a cellular level, debonding of adhesives could be highly beneficial for recycling.

Unfortunately, there are numerous issues with debondable adhesives at battery pack and module level due mostly to the service conditions and the materials used. UV is an inappropriate stimulus, as the bonded substrates are not transparent at the appropriate wavelengths and the possibility of exposure to UV radiation during product lifetime is high. Within modules, thermally conductive adhesives are generally required to facilitate cooling, rendering thermal debonding highly problematic. In addition, a battery pack that falls apart on exposure to high or low temperatures would be catastrophic during vehicle lifetime, particularly in extreme weather events or during vehicle fires. Use of electrically debonding adhesives would also be highly unsuitable, as the conductive additives would cause short circuits and fires. Magnetic debonding also poses issues, due to the presence of magnetic components within the battery pack. Chemical debonding is also limited as many reagents are incompatible with the battery pack. All chemical redox reagents must be avoided for debonding due to risk of metal corrosion and water is too prevalent in the environment to be a safe debonding stimulus. Thus, while it is possible debondable adhesives could have some use in battery packs, however a more sensible strategy would focus on design that minimize adhesive use.

Sources

Mulcahy, K. R.; Kilpatrick, A. F. R.; Harper, G. D. J.; Walton, A.; Abbott, A. P. Debondable adhesives and their use in recycling. Green Chemistry 2022, 24 (1), 36–61. https://doi.org/10.1039/d1gc03306a.