The lithium-ion battery: Study of alternative current conduction mechanisms on the Li3PO4-based solid electrolyte

Lithium-ion batteries have been dominating as a power source in digital cameras, laptop computers, mobile phones and electric/hybrid electric vehicles. This can be explained by their high life cycle and power density which differentiate them from other battery types. Lithium phosphate is considered among the favored solid electrolyte materials for the lithium-ion battery because of its high ionic conductivity. In this study, Lithium phosphate (Li3PO4) compound was obtained by the classic ceramic method. The X-ray powder diffraction pattern indicates that at room temperature, Li3PO4 crystallized in the orthorhombic system with Pnma space group. The morphology and composition of Li3PO4 were performed by scanning transmission electron microscope coupled with energy dispersive X-ray spectroscopy (STEM-EDS). Infrared spectroscopy was confirmed the presence of (PO4)3- anion and its vibrations. The measurements of the electrical properties were performed in the 100 Hz to 1 MHz frequency range and 528?713 K temperature intervals. The interpretation of Nyquist curves revealed the presence of three electrically active areas equivalent to the electrode processes, distribution of grain boundaries and bulk mechanism. The alternative current electrical conduction in Li3PO4 was interpreted through several processes, which can be associated to two different models: the non-overlapping small polaron tunneling (NSPT) model in the region I and the overlapping large polaron tunneling (OLPT) model in the region II. Elliot?s theory was used to interpret the conduction mechanism, and all Elliot?s parameters were determined.