Exploring the Kinetic Limitations Causing Unusual Low-Voltage Li Reinsertion in Either Layered or Tridimensional Li2IrO3 Cathode Materials

The alpha- and beta-Li2IrO3 polymorphs were recently studied in view of their anionic redox capabilities that were triggered by full Li removal. Herein, we solely focused on the reacting mechanism involved during the first reversible Li removal (Li2IrO3 -> LiIrO3). We found that the charge and discharge processes show significant deviations from the equilibrium potential especially with the appearance of a peculiar low-voltage feature during discharge with increasing the discharge current. Through detailed electrochemical experiments, such as rate dependence and relaxation, we show that this feature is associated with a kinetically limited phase transition behavior. Moreover, we demonstrated that the large voltage hysteresis pertaining to the removal and uptake of one Li from Li2IrO3 is nested in a different way that the biphasic transition proceeds between charge and discharge, as deduced by operando X-ray diffraction. Additionally, electroanalytical measurements coupled with scanning electron microscopy unveils that the sluggish biphasic transition is rooted in the slow diffusion of Li+ ion together with the existence of high nucleation barrier of the biphasic reaction. Finally, the similarities and differences between the kinetics limitations in both Li2IrO3 polymorphs are then discussed with respect to the similar type of limitations occasionally encountered in conventional layered oxides and other cathodes.