Electrochemical assessment of a Li-ion full cell with cathode-anode impedance separation via in-situ EIS-DRT and three-electrode configuration

This study employs a novel three-electrode (3E) configuration in a full cell with Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) as the cathode and a mixture of 30 wt% Si with 70 wt% graphite (Si-Gr) as the anode, denoted as SiGr||NCM811 full cell, by inserting a reference electrode between the anode and cathode. This setup allows for precise measurement of individual cathode and anode impedance, along with their variations during charging and discharging. By separating the cathode and anode impedances, notable phenomena such as peak impedance and reduced Li+ diffusivity were observed when either electrode was fully delithiated and at minimal Li+ concentration. In contrast, the impedance and diffusivity data from Li||NCM811 and Li||Si-Gr half cells deviated from those measured directly in the 3E full cell, with these discrepancies attributed to interference from the use of a Li-metal electrode in the half cells. This raises concerns about the accuracy of half-cell measurements in capturing actual Li+ diffusion properties in a full cell. Similarly, measurements using the galvanostatic intermittent titration technique showed limited accuracy in reflecting Li+ diffusivity changes throughout the chargedischarge cycle. The 3E setup, along with detailed DRT analysis, provides more accurate measurements and a clearer understanding of the electrochemical behaviors of the cathode and anode, which is essential for diagnosing battery deterioration and guiding the design of improved electrode materials.