Microstructure reconstruction and impedance spectroscopy study of LiCoO2, LiMn2O4 and LiFePO4 Li-ion battery cathodes

Cathode materials have been the focal point of research in the quest for high-performance secondary battery technology in consumer electronics and electric vehicles. The present work investigates the effect of the microstructural morphology of major cathode materials (LiCoO2, LiMn2O4, and LiFePO4) on the performance of the Li-ion battery related to the charge and species transport. Simulated annealing method (SAM) was implemented to generate a virtual 3D domain of the electrode microstructure using a spherical particles, average radius of 3 and 6 mu m. An equivalent circuit composed of resistance, capacitance and Warburg impedance was used to model the impedance response of the overall electrochemical reaction occur inside a typical battery system. Electrochemical impedance spectroscopy (EIS) results show that the ionic and electronic mobility in the solid electrode and bulk electrolyte were significantly determined by the morphology of the electrode microstructure. Higher porosity microstructures usually tend to have larger solid-electrolyte interface (SEI) area and lower pore tortuosity which improves the ionic diffusivity in solid and electrolyte phase. Furthermore, the Bruggeman's exponent for effective conductivity and diffusivity was derived from geometrical parameters of the reconstructed microstructure. The real and imaginary parts of the impedance were then presented in Nyquist plot on a frequency range of 20 kHz to 10 mHz.