Full-, Half-, and Symmetrical Cell Analysis of Lithium-Ion Battery Using Impedance and Nonlinear Frequency Response

This study presents an in-depth analysis of the cathode and anode of a commercial 18650 lithium-ion battery by comparing their dynamic behaviors systematically with that of two additional experimental cell setups: (i) full-cell in a three-electrode setup and (ii) symmetrical cathode and anode cells. The analysis involves subjecting the cells to electrochemical impedance spectroscopy, distribution of relaxation times, and nonlinear frequency response analysis at different state-of-charges. Our findings highlight the importance of analyzing the electrodes in all three setups. The impedance and nonlinear frequency response features of the full-cell are also observed in the electrode-resolved cells. Symmetrical cells exhibit stronger impedance and nonlinear responses compared to the commercial cell and the cell with reference electrode, yet they allow identifying contributions of the single cells without artifacts from inductive loops caused by the reference electrode. By correlating nonlinear signals and characteristic peaks across different cell setups, cathode and anode processes and their respective characteristic frequencies can be clearly identified.