An investigation of battery performance in Li-ion batteries doped by Dy

In this thesis, structural, magnetic and electrochemical properties of LiCoO2 cathode materials in layered structure modified with Dy instead of Co ions were investigated. During the study, LiCo1-xDyxO2 where x=0.01, 0.02, 0.03, 0.04, 0.05, 0.1, 0.5, 1 were successfully fabricated by conventional solid state reaction technique. Structural properties of the fabricated samples were analyzed using XRD, FTIR, Raman and XAS measurements. The lattice parameters were calculated using Fullprof open source program and it is found that the lattice volume increases by increasing Dy content in the structure. The bond structure and Raman active modes of samples were investigated in Dy doped samples. Co K-edge spectra of the samples were measured and the XANES and EXAFS data were examined. The local structure of the samples was determined with the Athena open source program. Cr2032 coin cells were used for the investigation of the electrochemical properties and battery performance of the cells using Dy modified LiCoO2 as a cathode material. There are anodic and cathodic peaks in the CV charts of the samples and galvanostatic tests have been examined for up to 100 cycles. The C-rate performance of the cells was also measured at room temperature. It was found that the battery performance of the sample of x=0.04 exhibit better capacity and capacity fade value when compared pure LiCoO2 which is a promising result for commercial battery fabrication. The capacity fade mechanism was also investigated by using ex-situ FTIR, RAMAN, XRD and XAS measurement and it is found that improvement of the cycling performance of the cells with the addition of Dy was related the structural stability.