Effects of lithium content on the electrochemical lithium intercalation reaction into LiNiO2 and LiCoO2 electrodes

The electrochemical lithium intercalation reaction into LiNiO2 and LiCoO2 electrodes in 1 M LiClO4—propylene carbonate solution is investigated as a function of lithium content in the oxide electrodes by using X-ray diffractometry (XRD), electrochemical impedance spectroscopy (EIS), and a galvanostatic intermittent titration technique (GITT). Li1-δNiO2 shows a greater loss in capacity during the first intermittent discharge, as well as a higher resistance for the electrochemical intercalation reaction, in comparison with Li1-δCoO2. This is attributed to a partial cation mixing in Li1-δNiO2 which is substantiated by XRD studies. The electrochemical impedance spectra of the Li1-δNiO2 electrode reveals that the magnitude of the intermediate frequency arc that is associated with the absorption reaction decreases with increasing lithium content, (1 — δ), in the range from 0.5 to 0.7. By contrast, Li1-δCoO2 exhibits the reverse behaviour.—The component diffusivities of lithium ions display a nearly constant value, in the order of 10−11 cm2 s−1, for both electrodes at room temperature, irrespective of the value of (1 — δ) over the range 0.5–0.7. It is suggested that lithium-ion diffusion through both the layered oxides is affected by the number of empty sites within the lithium-ion layer, and not by the lattice parameter.