A Graphical Approach for Identifying the Limiting Processes in Lithium-Ion Battery Cathode Using Electrochemical Impedance Spectroscopy

Electrochemical impedance spectroscopy (EIS) has been proposed as an in situ strategy for the analysis of materials properties applied in the study of lithium-ion batteries (LIBs). However, the number and physical nature of the processes occurring simultaneously, combined with the typical interpretation of EIS spectra make the study challenging. To make the EIS interpretation more inclusive, in this work a graphical Bode diagram deconvolution is proposed, utilizing time constants τ (R-CPE), associated with relaxation of the phenomena occurring in battery composite electrodes. Since the effect of the additives on the electrode composite is still controversial and difficult to analyze for other in situ techniques, the graphical strategy is first applied to a LiFePO4 cathode with PVDF as the binder, to discriminate the contribution of each τ during different state of charge (SOC). This is done by removing the influence of counter electrode using a commercial three-electrode set-up cell. Then, the same cathode was evaluated, but with a Single Lithium-Ion Conducting Binder (SLICB). The electrode modification was easily observed with the graphical analysis. The results show that SLICB improved the speed of the processes, moving them to high frequencies, given that the polymer provides a continuous supply of ions diminishing concentration polarization.