Li-ion kinetics in LiFePO4/carbon nanocomposite prepared by a two-step process: The role of phase composition

LiFePO4/Carbon nanocomposite was synthesised by two-step procedure ̶ hydrothermal synthesis in the presence of ascorbic acid followed by mixing of the product with citric acid and heating at 600 °C under a reducing atmosphere. During the first-step, slab or cuboid-shaped LiFePO4 particles were formed with sizes of ∼100-150 nm in width and ∼300-600 nm in length. The second-step produced deformed slab or cuboid-like LiFePO4/Carbon nanocomposite with shapes somewhat resembling that of the precursor. The electrochemical properties were examined by electrochemical impedance spectroscopy (EIS) and potentiostatic intermittent titration technique (PITT) at a series of equilibrium potentials within the voltage range 2.7-4.2 V. From the PITT measurements of cathodes with two thicknesses, the LiFePO4/Carbon nanocomposite exhibits a specific discharge capacity of 150.3 mAh/g and 164.3 mAh/g, for 9.4 μm and 6.9 μm thickness, respectively. The current relaxation measurements also showed that the kinetics of Li-ion transfer depends strongly on the phase composition; in the solid-solution regions the Li-ion kinetics is dominated by diffusion whereas in the two-phase region it is by phase transformation.