Defect Formation Energy in Spinel LiNi0.5Mn1.5O4-δ Using Ab Initio DFT Calculations

Defect formation energies based on an oxygen vacancy model and a metal-excess model in Ni/Mn ordered P4(3)32 and disordered Fd (3) over barm LiNi0.5Mn1.5O4 (LNMO) were evaluated by using ab initio density functional theory (DFT) calculations. The defect formation energy for the metal excess model was lower than that for the oxygen vacancy model in both P4(3)32 and Fd (3) over barm. This indicates that oxygen vacancy formation reactions are unlikely, although interstitial cation occupation at the octahedral vacancies occurred in both P4(3)32 and Fd (3) over barm LNMO spinel compounds. In addition, the corresponding defect formation energy in Fd (3) over barm was lower than that in P4(3)32, indicating that the amount of defects is sensitive to the cation ordering/disordering in the spinel framework. This agrees with the experimental results that show that only Fd (3) over barm tends to possess oxygen defects.