  A theoretical investigation of the effects of elastic coherency on the
thermodynamics, kinetics, and morphology of intercalation in single LiFePO4
nanoparticles yields new insights into this important battery material.
Anisotropic elastic stiffness and misfit strains lead to the unexpected
prediction that low-energy phase boundaries occur along {101} planes, while
conflicting reports of phase boundary orientations are resolved by a partial
loss of coherency in the {100} direction. Elastic relaxation near surfaces
leads to the formation of a striped morphology, whose characteristic length
scale is predicted by the model and yields an estimate of the interfacial
energy. The effects of coherency strain on solubility and galvanostatic
discharge are studied with a reaction-limited phase-field model, which
quantitatively captures the influence of misfit strain, particle size, and
temperature on solubility seen in experiments. Coherency strain strongly
suppresses phase separation during discharge, which enhances rate capability
and extends cycle life. The effects of elevated temperature and the feasibility
of nucleation are considered in the context of multi-particle cathodes.
