The physical origin of the activation barrier in Li-ion intercalation processes: the overestimated role of desolvation

Abstract

The energetically hindered step of lithium-ion desolvation in the course of ion intercalation into cathode or anode materials for Li-ion batteries is frequently considered to be responsible for the pronounced rate-limitations in the low-temperature and high-power limits of battery operation. In this work, we provide strong evidence for an alternative structure of the intercalation activation barrier, with the rate-limiting step being dependent on both the solvent and the electrode material nature. We combine the experimental measurements of the activation energies for LiCoO2 and LiMn2O4 electrodes in aqueous, carbonate-, acetonitrile-, and diglyme-based electrolytes with classical molecular dynamics simulations and conclude that ionic desolvation can become a rate-limiting step only in cases when resistive layers (commonly referred to as a Cathode/Electrolyte Interface) do not form at the surface of the electrode materials. In conventional carbonate-based electrolytes, the rate-limiting step is associated with the electrochemical step of ion transfer across the electrode/electrolyte interface. The results of this study reveal the overestimated role of desolvation in ion intercalation processes.