Research On The Preparation Of Ionic Liquids Polymer Electrolyte Membranes

Electrolyte membrane is an important part in lithium-ion battery,and the safety performance of the lithium-ion battery largely depends on the property of the electrolyte.The use of Polymer electrolyte could effectively overcome the problems caused by the leakage of traditional liquid electrolyte and gain higher energy density,the battery can become more lightweight and thinner.Ionic liquid arouses much attention of investigators and is considered to become the part of the polymer electrolyte membrane,which has many advantages including non-volatility,non-flammability,low vapor pressure,green and extended electrochemical steady window.In this dissertation,ionic liquid was N-methyl-N-propyl pyrrolidinium bis?trifluoromethanesulfonyl?imide(Py₁₃TFSI)which were prepared by mixing N-methyl-N-propyl pyrrolidinium bromide(Py₁₃Br)with lithium bis?trifluoromethanesulfonyl?imide?LiTFSI?and Diethylethyletherylmethanamine bis?trifluoromethanesulfonyl?imide?DEEYTFSI?.Ionic liquids polymer electrolyte?IL-PE?membrane was prepared by UV crosslinking technology with polyurethane acrylate?PUA?,methyl methacrylate?MMA?,ionic liquid(Py₁₃TFSI,DEEYTFSI),lithium salt?LiTFSI?,ethylene glycol dimethacrylate?EDMA?and benzoyl peroxide?BPO,DMF?.Meanwhile,the single factor experiment was used to optimize and obtain the ideal of ionic liquids polymer electrolyte membranes.The Py₁₃TFSI/PUA/PMMA,DEEYTFSI/PUA/PMMA electrolyte membranes performance was characterized by Scanning Electron Microscope?SEM?,Atomic Force Microscope?AFM?,Thermogravimetric Analysis?TG?,Electrochemical Impedance Spectroscopy?EIS?,Cyclic Voltammetry?CV?,Linear Sweep Voltammetry?LSV?,and stability and the cycle performance of"Li/IL-PE/LiFePO₄"half cell was analyzed.The results indicate that the addition of DEEYTFSI to polymer electrolyte membranes lectrochemical stability window is about 6 V,a very high electrochemical stability.The resultant electrolyte membranes displays the room temperature ionic conductivity of 2.67×10^-4 S·cm^-1 and the lithium ions transference number of 0.34.The addition of Py₁₃TFSI to polymer electrolyte membranes leads to network structures by chain-cross-linking.The IL-PE is stable below 250?and will not decompose until 380?without considering the volatilizing of the residual solvent.The electrochemical stability window of IL-PE is about 4.8 V.The electrolyte membrane has sufficient electrochemical stability.The resultant electrolyte membranes displays the room temperature ionic conductivity of1.37×10^-3 S·cm^-1 and the lithium ions transference number of 0.22.The interfacial resistances between IL-PE and electrodes have the less change after 10 cycles.This indicates that IL-PE has better compatibility with LiFePO₄ electrode and Li electrode.First discharge performance of Li/IL-PE/LiFePO₄ half cell shows a capacity of about 151.9 mAh·g^-1,and coulomb efficiency was 87.9%.The discharge capacity was 131.9 mAh·g^-1 after 80 cycles with 95.5%coulomb efficiency.Therefore,the battery using the IL-PE will exhibit good cycle and rate performance.