Comparative study on electronic structures of two phases compounds and origin of the structural phase transition in LiFePO₄

LiFePO 4 has normal olivine-structured ( α -LFP) and high pressure ( β -LFP) phases with the former as one of cathode materials for commercial Li-ion batteries. Despite the extensive focus on respective electrochemical properties of two phases, there is a lack of comparative study on electronic and magnetic properties between them, and the origin of the structural phase transition remains unclear. Using first-principles calculations combined with molecular dynamics simulations, we find that the anisotropy compression of Li-O bond drives the structural phase transition from α -LFP to β -LFP with a critical pressure of 20 GPa, while β -LFP undergoes a transition from semiconductor to metal due to the presence of Fe +3 induced by delithiation. Their antiferromagnetic (AFM) ground states are predicted to originate from the negative magnetic exchange interactions between nearest and next-nearest neighbor sites and the corresponding Néel temperature exhibits significant pressure-driven enhancement. Furthermore, compared with α -LFP, β -LFP exhibits the bulk, shear and Young’s moduli with increase of 8%, 13% and 12%, respectively. These findings enrich the physical property data of LiFePO 4 phase compounds and make knowledge reserves for expanding the application scenarios of α -LFP phase under special operating conditions such as high pressure.