Influence of calcination temperature on the structural properties of hydrothermally synthesized LiMn_1.5Ni_0.5O₄ cathode material: a comparative study for calculating crystallite size and lattice strain

This paper has successfully employed a hydrothermal method to synthesize spinel LiMn_1.5Ni_0.5O₄ (LMNO) cathode materials. Calcination at 600, 700, and 800 °C is performed to evaluate microstructure properties compared to as-prepared LMNO. The samples are investigated by XRD, SEM, TGA, FTIR. The crystallite sizes are smaller than the particle size of LMNO, revealing their polycrystalline nature. The TGA analysis supports the structural changes after calcined as revealed by XRD spectra. The FTIR spectrum indicates that the LMNO disorder-order transition occurs within the investigated temperature range. The peak broadening is attributable to the contribution of crystallite size and lattice strain, further analyzed according to Scherrer, Williamson-Hall, Size-Strain plot, and Halder-Wagner methods. Additionally, the results gained from different analysis methods are contrasted and discussed, which is the primary focus of this study. Generally, all analysis models indicate that the crystallite grows monotonously larger as temperature increases. The lowest lattice strain is observed in the as-prepared LMNO. However, calcining at 600 °C exhibits the highest developed lattice strain and gradually decreases as temperature increases further. This study also highlights the importance of convolution of size and strain contributions in determining the suitable method for calculating crystallite size and lattice strain.