Molecular dynamic study on mechanisms of polyvinylidene fluoride decomposition by using supercritical water

Abstract

As a thermoplastic fluoropolymer, polyvinylidene fluoride (PVDF) has been widely used as a binder in lithium batteries. However, PVDF is hard to be degraded naturally. Due to the unique properties of supercritical water (SCW), SCW conversion of polymers is considered as a clean and efficient conversion technology. The effects of different reaction parameters on the decomposition of PVDF in SCW were analyzed by the molecular dynamics (MD) method. The results show that higher reaction temperature, longer reaction time, lower raw material concentration, and the addition of oxidant are more conducive to the decomposition of PVDF in SCW. In addition, the molecular structure of products, product yield, and reaction rate of PVDF in SCW under different conditions were analyzed. The decomposition path, HO2 radical formation mechanism, and F element migration path of PVDF in SCW were also studied by using the MD visualization tool. Compared with SCWO, SCWG has a lower reaction rate and the products from SCWG has a longer molecular chain. The main path for HF generation is the direct interaction between the free F atom and H atom in the water molecules.