The effect of lithium sources and thermal treatment on the structure and electrochemistry of Li_1.2Ti_0.4Mn_0.4O₂ and Li_1.3Nb_0.3Mn_0.4O₂ cathodes

Li-excess cathode materials with a disordered rock-salt structure (DRX) Li1.2Ti0.4Mn0.4O2 and Li1.3Nb0.3Mn0.4O2 were prepared by mechanochemically assisted solid-state synthesis at various synthesis conditions using different lithium sources (Li2O and LiOH). As-prepared samples were characterized by X-ray powder diffraction (XRD), thermal analysis in combination with mass spectrometry (DSC/TG/MS), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), electron paramagnetic resonance spectroscopy (EPR), in situ time-resolved synchrotron powder X-ray diffraction (SPXRD) and galvanostatic cycling. The effects of different lithium sources and synthesis temperature on the crystal and local structure and the impact of additional thermal treatment (re-heating) on electrochemical performance of the DRX oxides were investigated. The results obtained show that the optimal synthesis temperature is 950 degrees C and the use of LiOH as a lithium source leads to the synthesis of the DRX oxides with a fully disordered structure, which is stable when re-heated at a temperature of 600 degrees C. In addition, re-heating leads to further optimization of the properties of the DRX oxides; this results in a significant improvement of their electrochemical properties.