Kinetic and galvanostatic studies of a polymer electrolyte for lithium-ion batteries

Quaternary polymer electrolyte (PE) based on poly(acrylonitrile) (PAN), 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid (EMImBF(4)), sulfolane (TMS) and lithium hexafluorophosphate salt (LiPF6) (PAN-EMImBF(4)-sulfolane-LIPF6) was prepared by the casting technique. Obtained PE films of ca. 0.2-0.3 mm in thickness showed good mechanical properties. They were examined using scanning electron microscopy (SEM), thermogravimetry (TGA, DSC), the flammability test, electrochemical impedance spectroscopy (EIS) and galvanostatic charging/discharging. SEM images revealed a structure consisting of a polymer network (PAN) and space probably occupied by the liquid phase (LiPF6 + EMImBF(4) + sulfolane). The polymer electrolyte in contact with an outer flame source did not ignite; it rather underwent decomposition without the formation of flammable products. Room temperature specific conductivity was ca. 2.5 mS cm(-1). The activation energy of the conding process was ca. 9.0 kJ mol(-1). Compatibility of the polymer electrolyte with metallic lithium and graphite anodes was tested applying the galvanostatic method. Charge transfer resistance for the C6Li -> Li+ + e(-) anode processes, estimated from EIS curve, was ca. 48 Omega. The graphite anode capacity stabilizes at ca. 350 mAh g(-1) after the 30th cycle (20 mA g(-1)).