Electrochemical impedance spectroscopic study of the rate-determining step of Li ion intercalation and deintercalation in LixNiO2 cathodes

The rate-determining step of the intercalation and deintercalation process of lithium ions in LixNiO2 cathodes was studied by electrochemical impedance spectroscopic (EIS) analysis. EISs of the electrode process are composed of two semicircles. The higher frequency semicircle is related to the charge transfer resistance (Rct) and the double layer capacitance (Cdl), while the lower frequency semicircle results from ion incorporation impedance (Rlattice) and space charge capacitance (Csc). The assignment of the latter capacitance is discussed. It is found that Rlattice is 1000 times larger than Rct. Accordingly, in most cases the ion incorporation into the lattice dominates the kinetic behavior. But for the ideal hexagonal phase, in the deintercalated state the Warburg impedance becomes important. As a result, the ion diffusion in the lattice is the rate-determining step.