Identification of Material Parameters in Lithium-ion Batteries

Abstract

Abstract As the world is shifting towards electric vehicles, there is a need for high performing batteries which can be achieved by studying the material parameters in a battery cell in order to understand its behavior. In this thesis work, half cells and 3-electrode cells are assembled with cell chemistries NMC111, NMC622 and NMC811 each as cathodes. Electrochemical techniques are used to estimate material parameters. Galvanostatic Intermittent Titration Technique(GITT) is performed on half cells and three electrode cells. Three methods are used to analyse the GITT results and obtain a range of diffusion coefficients. Electrochemical Impedance Spectroscopy (EIS) is performed on a 3-electrode cell, and the measurement is done between cathode and Li-reference ring. The results of the EIS are analysed using an equivalent circuit model resembling a physical cell. Diffusion coefficients are calculated from both GITT and EIS and a comparative study is presented for each cell chemistry. Some other parameters like the double layer capacitance, exchange current density and cathode electrolyte interface capacitance are also estimated from EIS and a comparative study between different cell chemistries is presented. The diffusion coefficients from GITT are in the order of 10−15 [m2/s] whereas from the EIS test, it is in the order of 10−12[m2/s].