Phase transitions in electrode materials are typically accompanied by lattice distortions and defect formations. These microscopic configurations affect an electrochemical cycle and influence the physical properties of electrode materials. Here, we explore the coupling between the lattice arrangements and Li-ion composition field in a representative FePO$4_{}$electrode particle. We develop and apply a 2D Cahn-Hilliard – phase-field crystal model that couples the Li-composition field with the underlying lattice symmetry of the FePO4 particle to describe phase transitions. We use this coupled model to explore lattice arrangements in uniformly lithiated/de-lithiated electrode particles, and to describe the lattice distortions across a diffuse phase boundary. Next, we model a Cahn-Hilliard type of diffusion for the Li-composition field and compute the accompanying structural evolution of atomic arrangements. In this theoretical study, we track the shape, size and orientation of grains during an electrochemical cycle. Furthermore, we report the electrode particles ability to reduce crystallographic imperfections through grain rotations and grain boundary migrations during an electrochemical cycle.