Unraveling the Factors of Host Materials Affecting the Kinetics of Electrochemical Anion Intercalation Reaction

Electrochemical intercalation reactions of various ions into host materials are used as electrode reactions for various secondary batteries, and it is important to understand the factors that affect the reaction kinetics. In this study, the activation energies of internal anion diffusion and interfacial anion transfer were evaluated using carbon materials with different properties by electrochemical impedance spectroscopy, and the factors of the materials affecting activation energies of these processes were investigated. It was found that the activation energies of internal anion diffusion were dominated by the oxygen content in the carbon materials, and they linearly increased with increasing oxygen content. On the other hand, the activation energy of interfacial anion transfer increased with increasing oxygen content near the edge surface of the material and decreased with increasing the initial interlayer distance. Therefore, it was revealed that the difference in the properties of the host material affects the activation energy of interfacial ion transfer in the case of anion transfer, which has low desolvation energy, unlike the case of lithium-ion transfer, which requires large desolvation energy. It suggests that the design of active materials become more important than ever for next-generation secondary batteries which employ reactions with small desolvation energies for superior rate capabilities.