Olivine-type orthophosphate LiFePO4 is being used as alternative cathode material for rechargeable lithium ion batteries. We report an atomistic simulation study of the defects, dopant energetics and crystal morphology of this system. The simulations successfully reproduce the complex orthorhombic structure and suggest that the most energetically favorable intrinsic defect involves interchange of pairs of Li/Fe ions. The low exothermic energy for this process indicates that the defect concentration will depend on synthesis conditions and thermal history. Profiles of Li migration reveal highly anisotropic behavior, with motion predominantly along one-dimensional Li channels. Dopant incorporation calculations suggest that supervalent dopant additions (e.g., Al, Ti, Zr, Nb) are energetically unfavourable. As the electrochemical performance of the cathode is strongly influenced by particle size and shape, as well as surface structure, the relaxed energies of a large number of low index surfaces are calculated and used to predict the equilibrium morphology of LiFePO4 crystals.
Materials by design for sustainable solutions in the energy, medical, transport, and engineering sectors
