Preparation And Characterization Of Solid Polymer Electrolyte With Super-Delocalized Sulfonimide Lithium

In recent years,Lithium salts with fluoriated sulfonylimide anion have been extensively studied owing to their good electrochemical properties,in which the super-delocalized sulfonylimide anion shows a series of superior properties due to its more delocalized structure,more flexible molecular structure,weak coordination.The conductive lithium salts based on the anion are expected to obtain excellent basic physicochemical properties and electrochemical properties in the solid electrolyte system,so the research on this kind of lithium salts are of great significance.Lithium bis(trifluoromethylsulfonyl)imide/polyethylene oxide((Li[N(SO2CF3)2],LiTFSI)/PEO)is widely used in SPEs.However,it has been revealed that LiTFSI displays poor compatibility toward negative electrode(e.g.,lithium metal and graphite),corrosive behavior against aluminum foil in a high potential region(3-5 V vs.Li/Li+),which limits its wide application.Herein,a novel sulfonimide lithium salt,(S-(trifluoromethyl))-N-((trifluoromethyl sulfonyl)sulfinyl)Perfluorobutylsulfonyl)imide lithium(Li[CF3SO2N=S(=O)(CF3)N(SO2C4F9];Li[sTNFSI])was designed,in which an "O",atom in the TFSI-anion was substituted by an electron-withdrawing group"C4F9SO2N?" and futher synthesized via different methods.The structure of product was vertified by nuclear magnetic resonance(NMR),fourier transform infrared spectroscopy(FT-IR),and high resolution mass spectrometry(ESI-MS).In addition,the polymer electrolyte comprising of Li[sTNFSI]/PEO([EO]/[Li+]20,ratio by mole)was prepared,of which,several physicochemical properties,including the phase transition behavior,electrical conductivity(?),lithium ion migration number(tLi+),compatibility toward metallic lithium anode etc.,were preliminarily characterized.It is demonstrated that Li[sTNFSI]/PEO polymer electrolyte has a glass transition temperature(Tg)of-39.1?,which is significantly lower than LiTFSI/PEO(Tg =-35.4?),which shows that Li[sTNFSI]behaves stronger plasticizing effect on PEO than LiTFSI,moderate conductivity(e.g.,6.84×10-4 S cm-1,80?),high oxidation resistance(5.58 V vs.Li/Li?).At low current density(0.1 mA cm-2),Li[sTNFSI]/PEO display good compatibility toward metal lithium electrodes(Li | Li symmetric battery is stable for 450 h without short circuit).In addition,the Li/LiFePO4 battery containing Li[sTNFSI]/PEO electrolyte show good cycle stability for more than 130 cycles,and the capacity retention rate is as high as 90%.