  We present a linear stability analysis to demonstrate that a flat coherent
phase boundary formed by the (de)intercalation of solutes into a compound is
unstable against perturbations with wavelengths larger than a critical
wavelength. This critical wavelength is controlled by the competition between
the interface energy and the elastic strain energy caused by the misfit between
the solute-rich and solute-poor phases. It increases with the distance between
the phase boundary and free surface of the compound, and so the instability is
most pronounced when the boundary is close to the surface at the early stage of
the (de)intercalation process. Numerical calculations show that such
instability leads to non-uniform intercalation behavior. We find that uniform
intercalation cannot be achieved unless the phase boundary moves at a speed
greater than a critical velocity. Estimate of the magnitude of this velocity
suggests that the stress-induced intercalation instability is generally
operative in intercalation compounds used for battery applications.
