Recovery of spent lithium-ion batteries : alternative ways to extract poly(vinylidene) fluoride (PVDF)

Abstract

Among different processes and technologies in the recycling of lithium-ion batteries, Contestabile et al had a process flow that could recover all the components of the batteries and simplifies the overall separation process of cobalt and aluminium. One limitation in this process flow was the usage of NMP to extract out PVDF. NMP was toxic and had a high boiling point, which was harder to scale up. Thus, this study attempted to find a cheap and non-toxic replacement for NMP by testing against pure PVDF and carbon residue after acid leaching with aqua regia. Out of the three organic liquids, Tetrahydrofuran could dissolve PVDF at a small amount. The solubility limit of PVDF in Tetrahydrofuran was found to be in the range of between 2 and 6 g/L, which was much lower than NMP of at least 242 g/L. All the inorganic salt solutions could not dissolve PVDF and PVDF was found to be located above the solution. In HCO3 -, CO3 2-, Cl- and I- solution, different amount of PVDF was deposited below the solution, forming a three-layered mixture. As such, NMP was still considered as the most effective solvent to extract PVDF from shredded materials.