Impedance studies of Li+ diffusion in nickel manganese cobalt oxide (NMC) during charge/discharge cycles

One of the diagnostic tools of lithium-ion batteries aging process is the determination of the solid-state lithium ion diffusion coefficient. This parameter was calculated for LiNi1/3Mn1/3Co1/3O2 secondary particles. Electrochemical impedance spectroscopy of three-electrode Swagelok cells was used to monitor the evolution of parameters such as the contact resistance, the charge transfer resistance, the double layer capacitance and the lithium ion diffusion coefficient as functions of the open circuit voltage while charging and discharging. The effect of higher cut-off voltages on these parameters was also studied. Phenomena such as transition metal dissolution and oxygen release are suggested to be more predominant at these higher cut-off potentials. They have a significant effect on the lithium ion diffusion path inside the cathode particles and thus diminish the lithium ion diffusion coefficient. (C) 2020 Elsevier B.V. All rights reserved.