Evaluation of Olivine LiFePO<sub>4</sub> Polyanionic Cathode Material Using Density Functional Theory

The first principles study on the LiFePO4 and FePO4 crystal has been evaluated using the density functional theory encrypted in the Cambridge Serial Total Energy Package (CASTEP) computer code. The structural properties, electronic properties, and intercalation voltage of the cathode material are presented. Without the Hubbard U parameter, the conventional functional of GGA-PBE and GGA-PBEsol unable to produce the experimental open-circuit voltage (OCV) and band gap (BG) of cathode material correctly. Generally, the value of the lattice parameter, OCV, and BG will increase as the U value is increased. For OCV, the suitable U value for the GGA-PBE and GGA-PBEsol is 3 eV, whereas, for BG, the appropriate U value for both functional is around 4.3 eV to 4.5 eV. Different Hubbard U value is needed for different functional. It is found that GGA-PBEsol + U is the best parameter to calculate the electrical properties of LiFePO4 ­­­­material.