Poly(vinylidene fluoride-hexafluopropylene)-based gel electrolytes for lithium ion secondary batteries

For a thin film lithium-ion secondary battery, it is important to use a polymer or gel electrolyte with high ionic conductivity and good mechanical strength. In this work, two types of poly(vinylidene fluoride hexafluopropylene) (PVdF-HFP) were compared as preparing gel electrolyte for lithium-ion secondary battery. The PVdF-HFP copolymers polymerized by the emulsion method (PVdF-HFPc) and the suspension method (PVdF-HFPS), were applied in this study. The gel electrolyte was prepared by casting the THF solution of mixture of PVdF-HFP, ethylene carbonate (EC), propylene carbonate (PC) and LiClO4 salt. All of the gel electrolytes exhibited a typical arrhenius behavior in temperature dependence of ionic conductivity, and gave a high ionic conductivity of 1-3 mS cm(-1) at ambient temperature when adding the 1.75 mi plasticizer to Ig PVdF-HFP. Especially, the PVdF-HFP, gel showed a higher- mechanical strength over 4 M Pa. With the cyclic voltammetry, the PVdF-HFP, gel electrolyte showed anodic stability up to above 4.0 V on Ni, Al, and stainless steel (SUS), and cathodic stability down to Li deposition potential on Cu, Ni and SUS. It was also suggested that the anode (MCMB) or cathode (LiCoO2) active material could work in the PVdF-HFP, gel electrolyte.