Electrode Alignment: Ignored but Important Design Parameter in Assembling Coin-Type Full Lithium-Ion Cells

Abstract

Electrode alignment is one of design parameters that must be carefully controlled for reliable full cells with limited lithium ion inventory. Especially, since punched disk-type cathodes and anodes are movable during assembling coin-type cells, the misalignment of electrodes cannot be completely prevented. Furthermore, this misalignment is not only mixed with other defects but also sometimes leads to better electrochemical characteristics. To systematically unveil this ignored but important parameter, herein, we fabricate coin-type LiNi0.6Mn0.2Co0.2O2/graphite full cells with different electrode alignments and evaluate them to figure out any noticeable changes in their electrochemical properties. As frequently reported, the misaligned cell shows lower specific discharge capacity and initial coulombic efficiency than the well-aligned one due to an irreversible Li plating on the coin cell bottom during the first charging process. However, we have not recognized the misaligned cell can exhibit a smaller low-frequency semicircle in the AC impedance spectra and lower DC-IRs at lowly charged states than those of the well-aligned cell because of the less lithiated state of the misaligned cathode. Thus, to exclude data from misaligned full cells, it is necessary to verify the electrode alignment even after the cell evaluation process.