Valence band of LiNixMn2-xO4 and its effects an the voltage profiles of LiNixMn2-xO4/Li electrochemical cells

A high-voltage plateau at 4.7 in LiNixMn2-xO4/Li electrochemical cells appears with the introduction of Ni into the LiMn2O4 spinel. The capacity of the 4.7-V plateau increases linearly at the expense of the 4.1-V plateau as x increases. Using ultraviolet photoelectron spectroscopy, we have studied the top of the valence band of LiNixMn2-xO4 for a series of samples with 0.0 less than or equal to x less than or equal to 0.5. A component attributed to Ni 3d electrons was found at about 0.5-eV higher binding energy than the Mn 3d e(g) electrons. We propose that the increased voltage of the 4.7-V plateau is due to the increased energy required to remove electrons from Ni 3d levels compared to Mn 3d e(g) levels.