Solid Polymer Electrolytes Based On(Fluorosulfonyl)(Pentafluoroethylsulfonyl)Imide Anion:synthesis,Characterization,And Properties

Solid polymer electrolytes（SPEs） are comprised of polymers and conductive lithium salts by co-blend process. Compared to traditional liquid electrolytes, SPEs not only could solve the problems about liquid leakage, workability and safety, but also could inhibit the growth of lithium dendrites in lithium metal polymer batteries. On the superior advantages of above, lithium batteries with SPEs express good cycle performance and safety. As a kind of excellent performance electrolyte, SPEs have received significant attention and extensive research.Firstly, lithium（fluorosulfonyl）（pentafluoroethylsulfonyl）imide（Li[N（SO₂F）（SO₂C₂F₅）], LiFPFSI） was synthesized by using pentafluoroethyl iodide（C₂F₅I） as raw material and via the sulfinatodehalogenation reaction. The SPEs, PEO/LiFPFSI electrolyte, was prepared with high molecular weight poly（ethylene oxide）（PEO） by the solution cast method. The fundamental physicochemical properties and electrochemical properties of SPEs have been studied in terms of phase behavior, phase diagram, ionic conductivity, lithium- ion transference number, electrochemical stability and interfacial behavior of SPEs and lithium metal electrode. Compared to the most representative, PEO/LiTFSI electrolyte（Li[N（SO₂CF₃）₂], LiTFSI）, the effect to SPEs properties with two kinds of isomers of lithium salts were explored. The results indicate that SPEs with LiFPFSI show lower crystallinity（χc） and glass transition temperature（Tg）, when [EO]/[Li⁺]（molar ratio） is 16, χc and Tg are 25% and-39 oC respectively. Meanwhile when [EO]/[Li⁺] is 8, the ionic conductivity of PEO/LiFPFSI electrolyte can up to 1.10 × 10^-5 S·cm^-1 at 25 oC and 3.09 × 10^-4S·cm^-1 at 80 oC. And PEO/LiFPFSI electrolyte has a similar electrochemical stability with PEO/LiTFSI electroylte. However, the most important is that PEO/LiFPFSI electrolyte show a better interfac ial stability with lithium metal electrode. The interface resistances（Ri） of PEO/LiFPFSI electrolyte remain relativity stable and is only 104 Ω·cm² after storage 120 days at 80 oC. Moreover, the concentration of lithium salts is one of the important factors to affect the stability of the interfac ial stability behavior and the higher lithium salt concentration can significantly reduce compatibility between SPEs and lithium metal electrode.