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 Delta sigma(s) 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.

Automated summary

Lithium, a reactive alkali metal, is widely used in electronics, medicine, and optics due to its high reactivity. The demand for lithium is continuously increasing, especially in the lithium-ion battery industry for electric vehicles and energy storage systems. This study demonstrates that polyvinylidene fluoride (PVDF) membranes cannot form LiCl crystals due to the chemical interaction between lithium and the PVDF matrix. Experimental evidence and various analyses show the modification of the PVDF membrane in contact with a lithium-containing solution.