Electronic structure of FePO 4 , LiFePO 4 , and related materials

The electronic structures of FePO4 and LiMPO4, where M5Mn, 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 O 2p orbitals is greater in FePO4 than in LiFePO4. Nevertheless, LiFePO4 is calculated to have a greater binding energy than its FePO4 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.