In situ dynamic Ohmic resistivity measurement of LiNi1−yCoyO2 cathodes as a function of the state of discharge

A method for the in situ dynamic measurement of the Ohmic resistivity, Rc, of LiNi1−y CoyO2 cathodes as a function of the state of discharge, x, is developed. It follows the evolution of Rc with only a negligible interference of the discharge process by applying 6–10 short current interruptions and by recording the voltage transients between the cathode and a Li/Li+ reference electrode. It was established with several tens of different LiNi1−yCoyO2 cathodes that the area-specific Ohmic resistivity remains constant in a wide range of x, from 0 up to ca. 0.75, above which a steep linear rise of Rc is observed. This behaviour is in agreement with the expression of the redox potential of the Li insertion electrodes as a function of x proposed by Armand [1] and developed later by Ohzuku et al. [2]. In addition to the logarithmic Volmer–Tafel term this expression contains a linear one kx, which accounts for the close range in layer Li–Li interaction. The parameters of the Rc/x plots can yield valuable information for the effect of the cathode design as well of the cathode active material on the cyclig performance of the cathodes.