Kinetic Analysis of LiFePO4 using GITT, EIS and CV /

Abstract

LiFePO4 half-cells were fabricated into CR2032 coin-type cells, inside an Argonfilled glove box using a polypropylene separator and Li metal foil as an anode. The apparent DLi of LFP cells, were established using three techniques namely Galvanostatic Intermittent Titration Technique (GITT), Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) technique. These electrochemical techniques are most extensively used to investigate the diffusion of Li in the electrode materials of LIBs. GITT profiling of the fabricated cell were conducted at room temperature via a high precision four quadrant source measurement unit (SMU) PXIe-4139 by National Instruments. GITT profiling was carried out at two C-rates for the sake of comparison: 0.1 and 0.5 C. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were conducted using an electrochemical workstation model 660E by CH Instruments. CV profile of the cell was obtained using a potential window of 2.8 to 4.3 V at sweep rates of 0.05, 0.1, 0.2, 0.5, and 1 mVs-1 . Whereas EIS measurements were conducted to obtain Nyquist plot having amplitude of 5 mV at frequency scale of 0.1 Hz – 1 MHz. The results demonstrate that the accuracy of the estimation of DLi can be enhanced considerably by an in depth understanding of the electrodes microstructure in conjunction with a balanced use of these three techniques. The DLi rate acquired using the GITT technique fell within the order of 10-1. The average DLi values derived by the results of the EIS and CV techniques fell in the order of 10-1. The average DLi values derived by the results of the EIS and CV techniques fell in the order of 10 –18–192–1–10 cm2s-1.