Iteraction of polyvinylidene fluoride (pvdf)-based binders with strongly alkaline solutions

Abstract

A careful methodology to monitor binder degrading phenomena in alkaline media is proposed, which should assist experts in ?eld of battery research and development, as it can evaluate the expected stability of ?uorinated binders, prior to being tested in assembled galvanic cells. By this, it saves time, effort, and expedites work. While poly(tetra?uoroethylene),PTFE,has proven chemically inert, it poses a severe technological challenge, being dif?cult to process due to its ?brillation. Alternate binders are poly(1,1-di?uoroethylene), PVDF, and its copolymers, known under the trade name of Kynar R, which are signi?cantly easier to use. Nevertheless, when kept in contact with stronglyalkalinesolutions,thechemicalstabilityofKynarsiscompromised.They may under go elimination reactions with the release of ?uorideions and the formation of double bonds. These ? 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 binderdecompositioninalkalinemediawasinvestigatedintwosteps:(i)purebindersweretestedbyexposingthem 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 determining the concentration of released ?uoride ions, monitoring color change and precipitate formation and recording and interpreting FT-IR spectra.