Effect of Fluorine Segments in Fluoropolymer Matrix on the Properties of Gel Polymer Electrolytes

Polymer quasi-solid electrolytes have been paid widely attention in account of their outstanding advantages in safety, flexibility, viscoelasticity and film formation. Fluoropolymer is used as matrix of gel electrolytes not only has high electrochemical stability, but also facilitates the dissociation of lithium salts owning to the strong electron-absorbing C−F groups, which makes it a very promising choice for the further development of gel electrolytes. Due to the different sites of C−F bonds, their activity is also diverse, which results in the difference of the mobility of lithium ions and the LiF composition of SEI film on the surface of lithium metal anode. As a result, distinct fluorine-containing gel polymer electrolytes are prepared by in-situ polymerization of two different monomers, HFMA and TFMA. Compared with −CF₃ on terminal group in TFMA, the gel electrolyte polymerized with HFMA whose C−F group with stronger electronegativity is at the intermediate carbon site, as polymer matrix has better performance. The ionic conductivity achieves 7.02×10⁻³ S cm⁻¹ at room temperature, and the assembled batteries have a capacity retention rate of 91 % after 200 cycles of 1 C. Our research has laid a solid theoretical foundation for the further development of quasi-solid electrolyte.