In the present work, the electrochemical intercalation behaviour and the effect of variation in interlayer spacing on intercalation reaction of $Li_xNiO_2$ and $Li_xCoO_2$ in 1M $LiClO_4$ propylene carbonate solution was studied as a function of intercalated lithium content by using X-ray diffractometry(XRD) and electrochemical impedance spectroscopy. $LiNiO_2$ and $LiCoO_2$ powder was prepared from hydroxide and carbonate salts, respectively and characterized having a layered structure with space group R3m by XRD patterns. Electrochemical impedance measurement was galvanostatically carried out over the frequency range from $10^{-2}$ to $10^5$ Hz. Based upon the impedance spectra of $Li_xNiO_2$ and $Li_xCoO_2$ electrodes in 1M $LiClO_4$ propylene carbonate solution at various potentials, it was suggested that the electrochemical intercalation reaction of lithium ion into these electrodes proceeds via the following three consecutive steps: (ⅰ) charge transfer reaction at the electrode/electrolyte interface, (ⅱ) lattice incorporation of lithium ion into the electrode, (ⅲ) diffusion through the electrode. Impedance spectra for charge transfer reaction at electrode/electrolyte interface and diffusion through the electrode showed a similar feature with lithium content in both the electrodes. On the other hand, as the lithium content of oxide electrodes increased, the impedance for lattice incorporation reaction of lithium into $Li_xNiO_2$ decreased, the reverse tendency was observed in $Li_xCoO_2$. These results were due to variation in interlayer spacing of the two oxide electrodes with lithium content. It was suggested that this difference between the lattice incorporation reaction of $Li^+$ ion into $Li_xNiO_2$ and $Li_xCoO_2$ results from that in $Li_xNiO_2$ the elastic strain energy effect is more dominant than coulombic interaction energy effect and in $Li_xCoO_2$ vice versa.
