Electronic structure ofFePO4,LiFePO4,and related materials

Abstract

The electronic structures of ${\mathrm{FePO}}_4$ and $\mathrm{Li}M{\mathrm{PO}}_4,$ where $M=\mathrm{Mn},$ Fe, Co, and Ni, are studied within the framework of density-functional theory. These materials have interesting magnetic properties and have promising technological interest as cathode materials in rechargeable batteries. A comparison of results for various spin configurations suggests that the ferromagnetic configuration, while not seen experimentally, can serve as a useful approximation for studying general features of the electronic structure. The partial densities of states and contour plots of electron densities show that covalent bonding between Fe $3d$ and $\mathrm{O}2p$ orbitals is greater in ${\mathrm{FePO}}_4$ than in ${\mathrm{LiFePO}}_4.$ Nevertheless, ${\mathrm{LiFePO}}_4$ is calculated to have a greater binding energy than its ${\mathrm{FePO}}_4$ and Li metal components; the corresponding open circuit voltage for the cathode discharge is calculated to be 3.2 V, which is comparable to (although smaller than) the experimentally measured value.