Peak Attribution of the Differential Capacity Profile of a LiCoO<sub>2</sub>-based Three-electrode Li-ion Laminate Cell

Analysis of the differential capacity profile (dQ/dV vs. V), which can capture the changes in the electrode structure inside a battery, is an effective electrochemical method for investigating the degradation behavior and mechanism of Li-ion cells. However, the electrode reactions corresponding to the peaks in a dQ/dV vs. V curve are undefined. Hence, it is difficult to qualitatively analyze the mechanism of cell degradation using this curve. In this work, we propose an original method for attributing the peaks in a dQ/dV vs. V curve. Peak attribution is implemented using a three-electrode Li-ion laminate cell with a LiCoO2 cathode, graphite anode, and lithium reference electrode. During charge and discharge, the potential differences (dE) of the LiCoO2-Li and graphite-Li sides and voltage difference (dV) of the LiCoO2-graphite full cell are measured simultaneously. Meanwhile, the Coulomb amounts (dQ) of the LiCoO2-Li and graphite-Li sides are equivalent to that of the LiCoO2-graphite full cell at a certain time. By comparing the dQ/dV vs. V curve of the full cell to the dQ/dE vs. E curves of the LiCoO2-Li and graphite-Li sides, the peaks in the differential capacity curve can be attributed to specific structural changes in the electrodes. Importantly, this information is acquired without disassembling the cell, making our proposed analytical method a convenient means of studying cell degradation under various conditions, such as low temperature, high temperature, or high-rate charging.