Interfacial resistance of the LiFePO 4-C/PEO-LiTFSI composite electrode for dry-polymer lithium-ion batteries

Abstract

The interfacial resistance between the composite electrode and PEO-based solid polymer electrolyte was examined using two different symmetrical cells and AC impedance measurements in the temperature range of 30–60 °C. Of the four major resistance components identified in our previous study, three components due to the resistances of the polymer electrolyte and the charge transfer resistance between LiFePO 4-C and the electrolyte were assigned; however, one resistance component, in the medium frequency range has not yet been assigned. In this report, the medium frequency range resistance component was investigated using a symmetrical cell with composite electrodes composed of active and inactive materials (LiCoO 2, LiMn 2O 4 and SiO 2), solid polymer electrolyte, and carbon fiber as an electron conductor. The resistance was not affected by the carbon coating in LiFePO 4-C and the conductive carbon additive (VGCF). An electron blocking cell was also prepared and the resistance was measured in the temperature range of 30–60 °C to confirm the effect of the electrode thickness and the electrode composition. The resistance was not affected by the thickness, and decreased with decreasing PEO-LiTFSI electrolyte content in the composite electrode. However, no significant change in the activation energy was evident with the change in the electrode composition.