DFT + U Study of structural, electronic, optical and magnetic properties of LiFePO4 Cathode materials for Lithium-Ion batteries

Abstract

In this study, we have employed a DFT+U calculation using quantum-espresso (QE) code to investigate the structural, electronic, optical, and magnetic properties of LiFePO$\rm_{4}$ cathode material for Li-ion batteries. Crystals of LiFePO$\rm_{4}$ and related materials have recently received a lot of attention due to their very promising use as cathodes in rechargeable lithium-ion batteries. The structural optimization was performed and the equilibrium parameters such as the lattice constants, and the bulk modulus are calculated using QE code and found to be a=4.76 {\AA}, b=6.00 {\AA}, c=10.28 {\AA}, B=90.2 GPa, respectively. The projected density of states (PDOS) for the LiFePO$\rm_{4}$ material is remarkably similar to experimental results in literature showing the transition metal $3d$ states forming narrow bands above the O $2p$ band. The results of the various spin configurations suggested that the ferromagnetic configuration can serve as a useful approximation for studying the general features of these systems. In the absence of Li, the majority spin transition metal $3d$ states are well-hybridized with the O 2p band in FePO$\rm_{4}$. The result obtained with a DFT + U showed that LiFePO4 is direct band gap materials with a band gap of 3.82 eV, which is within the range of the experimental values. The PDOS analyses show qualitative information about the crystal field splitting and bond hybridization and help rationalize the understanding of the structural, electronic, optical, and magnetic properties of the LiFePO$\rm_{4}$ as a novel cathode material. On the basis of the predicted optical absorbance, reflection, refractive index, and energy loss function, LiFePO$\rm_{4}$ is demonstrated to be viable and cost-effective, which is very suitable as a cathode material for Li-ion battery.