Impedance Analysis and Cyclability Evaluation of Graphite Composite Electrodes with All-Solid-State Three-Electrode Cells

Alternating current (AC) impedance measurements have contributed to understanding the electrochemical behavior of electrodes, such as rate-limiting processes of electrodes for lithium-ion batteries. In this study, we report the AC impedance analysis of graphite composite electrodes to clarify their rate-limiting processes in all-solid-state systems using all-solid-state three-electrode cells. The graphite impedance consists of ionic transfer resistance in the solid electrolyte layer (i), resistance related to the decomposition products of the solid electrolyte at the active material|electrolyte interface (ii), charge-transfer resistance between the graphite electrolyte and solid electrolyte (iii), and lithium-ion diffusion resistance in graphite particles as Warburg impedance (iv). Resistance ii forms in the first lithiation process, which leads to the irreversible capacity loss of the graphite electrode. We also report the change in the impedance components during the charge–discharge cycle (durability) tests. At room temperature, there are few changes not only in the charge–discharge profile but also in the impedance characteristics for 500 cycles. On the other hand, the graphite electrode shows a significant decrease in charge/discharge capacity through the charge–discharge cycle test at 333 K. The increase in resistance ii during the durability test at 333 K indicates that the deterioration mainly originates from the decomposition process of the solid electrolyte at high temperatures.