In Situ XRD Investigation and Thermal Properties of Mg Doped LiCoO2 for Lithium Ion Batteries

Mg-doped LiCoO2 is synthesized by a solid-state reaction as a positive electrode material for lithium-ion batteries. The uniphase solid solution is confirmed by X-ray diffraction (XRD) and Rietveld refinements. The structural changes during charging are calculated theoretically by the general gradient approximation (GGA) ab initio method. A blue-pouched single half-cell was used to collect in-situ XRD patterns while the cell charged and discharged in the range of 3.0∼4.5 V. Good structural reversibility and symmetric cell parameter changes were observed during charging and discharging. The 'W' and inverse 'W' shapes of the a- and c-cell parameter changes, respectively, were also observed. The cell volume changes show an inverse 'W' shape. No large hysteresis occurs during the changes in the cell parameters during the charging-discharging process. The thermally stable Mg-doped LiCoO2 is confirmed by differential scanning calorimetry (DSC) and evolved gas analysis-mass spectrometry (EGA-MS).