Electronic structure of spinel-type LiNi1/2Ge3/2O4 and LiNi1/2Mn3/2O4 as positive electrodes for rechargeable Li-ion batteries studied by first-principles density functional theory

Using first-principles density functional theory (DFT), we investigated the relationship between the electrochemical properties of the Li-containing spinel oxides LiNi1/2Ge3/2O4 and LiNi1/2Mn3/2O4 and their crystal and electronic structures in consideration of the possible application of these materials as positive electrodes in rechargeable Li-ion batteries. LiNi1/2Mn3/2O4 is known to exhibit excellent electrochemical performance, whereas LiNi1/2Ge3/2O4 is electrochemically inactive. Thus, we compared these compounds by DFT calculations. The calculated average intercalation voltage and migration energy of Li in LiNi1/2Ge3/2O4 were found to be higher than those in LiNi1/2Mn3/2O4, confirming the reported electrochemical inactivity of LiNi1/2Ge3/2O4. A detailed study of electronic structure revealed that the strong ionic character of NiO bonds in LiNi1/2Ge3/2O4 may be attributed to the inductive effect from the enhanced covalent character of GeO bonds.