Optimizing the electrochemical performance of Li2MnO3 cathode materials for Li-ion battery using solution combustion synthesis: Higher temperature and longer syntheses improves performance

Abstract

Li2MnO3 is the parent compound and a component of the well-studied Li-rich Mn-based layered materials (xLi2MnO3·(1−x)LiMO2) for high capacity Li-ion batteries. Different combinations of citric acid fuel and metal nitrates (C/N) were used to optimize the electrochemical performance of Li2MnO3 nanoparticles by the solution combustion synthesis. Thermodynamic modelling and thermogravimmetric analysis show that the variations of C/N molar ratio affected the combustion process and the Li2MnO3 powder characteristics such as morphology and crystallinity. The fuel-rich composition (C/N = 0.555) with the highest adiabatic flame temperature produced Li2MnO3 cathode materials with the best electrochemical performance. The influence of sintering temperature on the crystallinity of the Li2MnO3 sample was investigated with high-temperature synchrotron XRD. The Li2MnO3 synthesized at a lower temperature (400 °C) had a better initial discharge capacity than the one synthesized at a much higher temperature (800 °C) however, it showed far poorer cycling stability. These differences in their electrochemical performance were explained on the basis of their microstructure and morphology. Furthermore, increasing annealing time at 800 °C (from 2 to 20 h) achieved phase pure materials and improved the electrochemical performance of Li2MnO3 powders. This improvement was due to the well defined, developed and larger particles of the samples annealed at longer times. The results show that apart from increasing synthesis temperature, varying annealing times at optimum temperature could be used to improve the functional performance of ceramic oxides.