First-principles study of the electronic structure and elastic property of Li x FePO4

Based on density functional theory of the first-principle, the electronic structures of LiFexPO4 (x=0.0, 0.75, 1.0) are calculated. The calculated results show that Fe3d states restrained by crystalline field cannot contribute to free electrons even though Fe3d states cross the Fermi level. Meanwhile, Fe—O bond is beneficial to stabilize the alloy structure due to the p-d hybrid orbital. With lithium ion extraction, the enhanced covalent bonds appear. In LixFePO4 system, the strength of covalent bond is in the order of P—O>Fe—O>Li—O. LixFePO4 system displays brittleness of material characteristic, and the LixFePO4(x=1.0, 0.75) with lithium intercalation have stronger average bonding strength than that of FePO4.