  We consider the effects of anisotropic coherency strain (due to lattice
mismatch) on phase separation in intercalation materials, motivated by the
high-rate Li-ion battery material \fepo. Using a phase-field model coupled to
elastic stresses, we analyze spinodal decomposition (linear instability of the
homogeneous state) as well as nonlinear evolution of the phase pattern at
constant mean filling. We consider fully anisotropic coherency strain and focus
on the novel case of simultaneous expansion and contraction along different
crystal axis, as in the case of \fepo, which leads to tilted, striped phase
boundaries in equilibrium.
