Study On Lithium-ion Conducting Membranes Based On Single-ion Polymer Electrolytes

Rechargeable polymer Lithium-ion batteries are expected to be usedmore widely for hybrid and completely electric vehicles as well as forportable electronics. Polymer electrolytes have received considerableattention because they have the flexible, compact structures which arefree from leak. To date, most conventional polymer electrolytes aredual-ion conductors, which causes a concentration polarization and thuslead to some poor performances of the cell. To solve this problem is toprepare single lithium-ion conductors. This paper obtains the single-ionpolymer electrolytes based on the perfluoroionomeric polymer matrix.The main content of this paper contain:(1) Novel solid-state lithium-ion conducting polymer electrolytes areprepared by blending lithiated perfluorinated sulfonic with polyethyleneglycol dimetyl ether (PEGDE, CH3O(CH2CH2O)nCH3，n=3-8) in variousmolar ratios of ethylene oxide unite to Li+(EO/Li+). The fundamentalproperties of the solid polymer electrolytes are comparatively studied, interms of thermal stability, ionic conductivities and lithium-iontransference number (tLi). The results show that the polymer electrolytes are thermally stable up to250℃and the maximum tensile strength is upto4.25Mpa. At a EO/Li+ratio of20, high ionic conductivities of4.26×10-4S cm-1and2.16×10-5S cm-1are obtained at100℃and40℃，respectively. The solid polymer exhibits single Lithium-ion conductingbehavior withtli>0.9.(2) Nafion-Li/PC/SiO2gel polymers with different SiO2content areprepared by the solution-cast method. The fundamental properties of thegel polymer electrolytes are comparatively studied, in terms of thermalstability, ionic conductivities and lithium-ion transference number(tLi).TGAresult shows that the polymer electrolytes just have5%weightloss at400℃，and high ionic conductivities obtained at the SiO24wt.%is2.29×10-4S cm-1at room temperature. The electrochemical stability of thepolymer electrolyte is up to4.5V, which is sufficient for use as a separatorin lithium-ion batteries. A lithium battery was assembled using LiFeO4asthe cathode, Nafion-Li/PC/4%SiO2GPE as the electrolyte and Lithium foilas the anode. Finally, the big current discharge and cycle performance aretested. The results show that the first charge-discharge capacity is130mAhg-1at0.1C rate, and the cycle performance and rate discharge performanceis excellence. The discharge capacity retention is about92.3%after50cycles. Conductivities exceeding10-4S cm-1with transference numbersof unity are achieved making the polymer electrolytes potentially usefulin rechargeable Lithium polymer batteries.