The nonequilibrium phase transformation and particle shape effects in LiFePO4 materials of Li-ion batteries are explored in this work. A continuum model employing the "mushy-zone" (MZ) approach, accounting for sluggish Li diffusion across the two-phase boundary, has been developed to study the kinetically-induced nonequilibrium phenomenon in Li-ion batteries. A theoretical analysis is presented to show that the nonequilibrium miscibility gap expands and shifts to higher Li composition at high discharge rates, due to insufficient compositional readjustments at the two-phase boundary. Furthermore, critical effects of particle shape on nonequilibrium phase transformation and discharge capacity have been discovered by the model. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3610424] All rights reserved.