Michael Welland1 Olle Heinonen2 3

1, Canadian Nuclear Laboratory, Chalk River, Ontario, Canada
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 [1].

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.

[1] 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.