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MM: Fachverband Metall- und Materialphysik

MM 36: Functional materials II: Batteries II

MM 36.1: Vortrag

Mittwoch, 9. März 2016, 11:45–12:00, H53

Phase field modeling of Li-insertion kinetics in single LiFePO₄− nano-particles for rechargeable Li-ion battery application — •Michael Fleck, Philipp Amendt, Holger Federmann, and Heike Emmerich — Materials and Process Simulation, University of Bayreuth, Germany

LiFePO₄ is widely considered to be a promising cathode material for Li-ion rechargeable batteries. The lithiation process in LiFePO₄− nano-particles proceeds via a coherent solid-solid phase transformation between the LiFePO₄ (LFP-phase) and FePO₄ (FP-phase). We develop a continuum phase field model for solid-solid phase transformations in single- LiFePO₄−nano-particles, embedded in an elastically soft electrolyte-phase. The model-description explicitly includes anisotropic (orthorhombic) and inhomogeneous elastic effects, resulting from coherency strain, as well as anisotropic (1D) Li-diffusion insight the nano-particles. The moving LFP/FP-phase boundary is modeled as a diffuse interface of finite width. Here, with the inclusion of the elastically soft electrolyte-phase, we consider also non-rectangular shaped LiFePO₄− particles in a fully anisotropic 3D-framework. The resulting model is employed to investigate effects of the nano-particle’s size and shape on the kinetics of FP to LFP phase transformations, relating to single particle charge rates. In respective model studies, we find that in flat particles the transformation velocity increases over more than two orders of magnitudes with decreasing particle-hight. We show that in contrast to Cahn-Hilliard-type models this behavior can be regularized in Allen-Cahn-type phase-field formulations.