Molecular Crystal Structure Simulations and Structure-Magnetic Properties of LiFePO4 Composite Particles Optimized by La

In this study LiFePO₄/C composite particles were synthesized using five different carbon sources via a one-step sol-gel method. La-doped LiFePO₄ was also synthesized using the sol-gel method. The XRD pattern of Li<i>_x</i>La<i>_y</i>FePO₄ (<i>x</i> = 0.9~1.0, <i>y</i> = 0~0.1) after being calcined at 700 °C for 10 h indicates that as the doping ratio increased, the sample's cell volume first increased then decreased, reaching a maximum value of 293.36 ų (<i>x</i> = 0.94, <i>y</i> = 0.06). The XRD patterns of Li_0.92La_0.08FePO₄ after being calcined at different temperatures for 10 h indicate that with increasing calcination temperature, the (311) diffraction peak drifted toward a smaller diffraction angle. Similarly, the XRD patterns of Li_0.92La_0.08FePO₄ after being calcined at 700 °C for different durations indicate that with increasing calcination times, the (311) diffraction peak drifted toward a larger diffraction angle. The infrared spectrum pattern of Li<i>_x</i>La<i>_y</i>FePO₄ (<i>x</i> = 0.9~1.0, <i>y</i> = 0~0.1) after being calcined at 700 °C for 10 h shows absorption peaks corresponding to the vibrations of the Li-O bond and PO₄^3- group. An SEM analysis of Li<i>_x</i>La<i>_y</i>FePO₄ (<i>x</i> = 1, <i>y</i> = 0; <i>x</i> = 0.96, <i>y</i> = 0.04; <i>x</i> = 0.92, <i>y</i> = 0.08) after being calcined at 700 °C for 10 h indicates that the particles were irregular in shape and of uniform size. The hysteresis loops of Li_0.92La_0.08FePO₄ after being calcined at 600 °C, 700 °C, or 800 °C for 10 h indicate that with increasing calcination temperature, the Ms gradually increased, while the Mr and Hc decreased, with minimum values of 0.08 emu/g and 58.21 Oe, respectively. The Mössbauer spectra of Li<i>_x</i>La<i>_y</i>FePO₄ (<i>x</i> = 1, <i>y</i> = 0; <i>x</i> = 0.96, <i>y</i> = 0.04; <i>x</i> = 0.92, <i>y</i> = 0.08) after being calcined at 700 °C for 10 h indicate that all samples contained Doublet(1) and Doublet(2) peaks, dominated by Fe²⁺ compounds. The proportions of Fe²⁺ were 85.5% (<i>x</i> = 1, <i>y</i> = 0), 89.9% (<i>x</i> = 0.96, <i>y</i> = 0.04), and 96.0% (<i>x</i> = 0.92, <i>y</i> = 0.08). The maximum IS and QS of Doublet(1) for the three samples were 1.224 mm/s and 2.956 mm/s, respectively.