Kinetics of Heterosite Iron Phosphate Lithiation by Chemical Reduction

Understanding the kinetics of the charging and discharging processes in battery materials is important to improving high power performance. As such, we here investigate the kinetics of LiFePO4 relithiation by reduction with lithium iodide. Unlike standard electrochemical kinetic analysis, which yields a convoluted response of all the components of the composite electrode, this approach probes only the kinetics of the electroactive material particles. The kinetic data was compared to the Avrami solid state reaction model and a statistical model by Bai and Tian, Electrochim. Acta, 2013, 89, 644. Different from chemical delithiation, the lithiation reaction does not fit a solid solution one-dimensional diffusion model, rather it follows the Avrami equation (Avrami exponent 0.6) with an activation energy of 50 kJ mol(-1). The obtained reaction rate information is central to the development of physically accurate quantitative battery models.