The Role of Ion-Polaron Electrostatic Attraction on Zn Migration in α-VO for Zinc Ion Battery: Insights from First-Principles Calculations.

The migration of Zn ions is significantly more challenging compared to that of Li ions within the same crystalline framework, leading to poor rate performance of zinc-ion batteries (ZIBs). Compared to Li, the slower migration rate of Zn is vaguely attributed to the stronger electrostatic interaction induced by Zn. Herein, the rule of how the size of the migration channel and electrostatic interaction affect Zn and Li migration in α-VO has been systematically investigated by first-principle calculations. It is found that expanding the layer spacing can facilitate Zn migration. Once the layer spacing surpasses a certain threshold, further expansion does not lead to a continued reduction in the migration barrier. The local structure distortions caused by electron small polarons would lead to a decrease in migration channel size, which should have increased the energy barrier for Li and Zn migration. However, interestingly, the electron small polarons decrease the energy barriers, which would be attributed to the ion-polaron electrostatic attraction. The higher activation barriers for the migration of Zn ions compared to those of Li ions can be rationalized by the specific ion-polaron electrostatic attraction for Zn. Moreover, the comparative strength of the polaron-ion electrostatic attraction for alkali and alkaline earth metal ions is unveiled. Overall, this study provides theoretical insights into the role of ion-polaron electrostatic attraction on ion migration.