THERMAL, ELECTRICAL AND DIELECTRIC PROPERTIES STUDIES OF LiMn1.977M0.023O4 (M = Ce, Cu) MATERIALS

Abstract

Lithium manganese oxide LiMn2O4 is recently one of the most intensively studied cathode materials for lithium ion batteries, due to its low cost and non-toxic nature when compared with other layered oxides such as LiCoO2 and LiNiO2. However, LiMn2O4shows severe capacity fading with cycling as compared to LiCoO2. Different methods are employed to minimize the aforementioned problems. Spinel LiMn1.977M0.023O4 (M = Cerium, Cu) cathode materials were synthesized by sol-gel method using citric acid as a chelating agent. The materials were characterized by using TGA/DTA, XRD, FT-IR spectroscopy, Raman spectroscopy and inductance, capacitance & resistance (LCR) meter. The TGA/DTA result indicates that exothermic peaks, large weight loss regions, which are attributed to the decomposition of nitrate precursors, are identified. The XRD results of both materials revile the formation of pure spinel phases with Fd-3m space group without any secondary phases or impurities. It is also found that the lattice constant of spinel LiMn1.977Ce0.023O4 (8.26 Å) is larger than that of LiMn1.977Cu0.023O4 (8.249 Å). The FT-IR spectroscopy study shows that Ce 3+ and Cu2+ sabstituted spinels exhibit two strong absorbation spectral bands, which are responsible for the formation of the synthesized materials. Similar results are also found from Raman spectroscopy study. The room temperature conductivity of both samples is found to be 3.0 x 10-5 S/cm for LiMn1.977Ce0.023O4 electrode and 2.58 x 10-5 S/cm for LiMn1.977Cu0.023O4 electrode. From the dielectric constant ε′ as a function of frequency study, it is observed that value of ε′ maximum at lower frequencies and it begins to drop and becomes constant at higher frequencies.