Abstract

PAGLIARO, Leonard  and  LOWY, Daniel A.. INTERACTION OF POLYVINYLIDENE FLUORIDE (PVDF)-BASED BINDERS WITH STRONGLY ALKALINE SOLUTIONS. La Granja [online]. 2019, vol.29, n.1, pp.17-31. ISSN 1390-8596.  https://doi.org/10.17163/lgr.n29.2019.02.

A careful methodology to monitor binder degrading phenomena in alkaline media is proposed, which should as- sist experts in field of battery research and development, as it can evaluate the expected stability of fluorinated binders, prior to being tested in assembled galvanic cells. By this, it saves time, effort, and expedites work. While poly(tetrafluoroethylene), PTFE, has proven chemically inert, it poses a severe technological challenge, being difficult to process due to its fibrillation. Alternate binders are poly(1,1-difluoroethylene), PVDF, and its copolymers, known under the trade name of Kynar R , which are significantly easier to use. Nevertheless, when kept in contact with strongly alkaline solutions, the chemical stability of Kynars is compromised. They may undergo elimination reactions with the release of fluoride ions and the formation of double bonds. These π bonds may further degrade by oxidation, in contact with oxidizers incorporated in the cathode. Such undesired chemical processes may inhibit the binding properties and, ultimately, may reduce shelf life of galvanic cells, depleting battery performance. In this paper PVDF binder decomposition in alkaline media was investigated in two steps: (i) pure binders were tested by exposing them to 32 wt % aqueous KOH solution, at 60◦C, a temperature that accelerates degrading processes, and next (ii) binders incorporated in cathode paste were investigated under similar conditions. Binder degrading was evaluated by deter- mining the concentration of released fluoride ions, monitoring color change and precipitate formation and recording and interpreting FT-IR spectra.

Keywords : Kynar; poly(1,1-difluoroethylene); PVDF; PTFE; dehydrohalogenation; cathode binder; galvanic cells.

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