Interfacial properties of Ca3(PO4)2 - incorporated poly(ethylene oxide)-based nanocomposite electrolytes investigated by XPS and FTIR studies

In last three decades intensive research has been made to replace the existing non-aqueous electrolytes with solid polymer electrolytes in rechargeable secondary lithium batteries. Polymer electrolyte-based lithium batteries provide attractive features such as high energy density, no-leakage of electrolyte, orientation freedom, flexible geometry and improved safety. Recently, nanocomposite polymer electrolytes (NCPE) have come to be identified as potential candidates by virtue of their enhanced mechanical strength and favorable interfacial properties. Polymer electrolyte-lithium metal interface plays a vital role in the electrochemical behavior of the lithium polymer cells. The surface layer and elemental composition of a lithium-metal electrode before and after contact with NCPEs comprising PEO/Ca3(PO4)2/LiX (X = N(CF3SO2)2, ClO4) were analyzed by x-ray photoelectron spectroscopy. The analysis showed the presence of Li2CO3/LiOH in the outer layer and Li2O in the inner layer of the passive surface film. The origin of LiF in the film was traced to reaction between lithium metal and LiN(CF3SO2)2 in the NCPE. Li/NCPE/Li symmetric cells were assembled, and the thickness of the solid electrolyte interface as a function of time was analyzed at 60°C. This paper also describes FTIR spectroscopic studies of the interface between lithium metal and NCPE. The results suggest that the surface chemistry of lithium electrodes in contact with the NCPE is dominated by compounds with Li–P and C–O–Li bonding.