Chemical interaction between PVDF and Li cations during LiCl crystallization in VMCr

Lithium is a highly reactive and flammable alkali metal. Due to its high reactivity it is not found in nature as such but is found in minerals. It has applications in electronics, medicine, optics, etc. The lithium demand is continuously growing, in particular for lithium-ion battery industry for electric vehicles and energy storage systems. LiCl can be obtained in solid form by vacuum membrane crystallization (VMCr) using polypropylene membranes or suitably hydrophobized ceramic membranes. On the contrary, to the knowledge of these authors, PVDF membranes did not allow the formation of the solid phase. In this work, for the first time, experimental evidence is shown documenting the inability of PVDF based-membranes to obtain LiCl crystals and it is shown how this is to be attributed to the chemical interaction between lithium and the polymeric PVDF-based matrix. This paper illustrates how the calculation of the variation of surface energy ΔσS between the virgin membrane and the used one, together with EDX, SEM, FTIR and Raman analyses allowed to demonstrate the modification of the original PVDF-based membrane in contact with a lithium-containing solution.