2, Argonne National Laboratory, Argonne, Illinois, United States
3, Northwestern-Argonne Institute for Science and Engineering, Evanston, Illinois, United States
A 3D multiphysics phase-field model is developed to study phase segregation in LiFePO4 nanoparticles, of interest due to their high (dis)charge rates. Spinodal decomposition into Li-rich and –poor phases is modified and can be suppressed by mesoscopic effects, which influences the kinetic and mechanical performance of this material as a battery electrode. Elastic and structural constants, diffusivity, and surface energy are highly anisotropic and concentration dependent, necessitating a 3D treatment. Previous work has shown the ability of surface wetting to stabilize minority phases, modifying the (dis)charge voltage profile .
The model includes spinodal decomposition, anisotropic, concentration-dependent elastic moduli, misfit strain, and facet dependant surface wetting within a Cahn-Hilliard framework. Simulations are carried out on realistic, plate-like particles of varying sizes in 3D in order to examine modification to phase segregation. The stability of a phase at an intermediate composition, sometimes seen experimentally, is also examined.
 Welland, M.J., Karpeyev, D., O’Connor, D.T., Heinonen, O, “Miscibility gap closure, interface morphology and phase microstructure of 3D LixFePO4 nanoparticles from surface wetting and coherency strain”, Submitted to ACS Nano, 2015.