Silicon-doped LiNi0.5Mn1.5O4 as a high-voltage cathode for Li-ion batteries

To improve the electrochemical performance of the LiNi0.5Mn1.5O4 high voltage cathode for Lithium Ion Batteries, silicon-doped LiNi0.5Mn1.5−xSixO4 samples (0.00 ≤ x ≤ 0.35) were prepared by different synthesis routes (solid-state reaction and ball milling) and characterized. The X-ray diffraction investigation and structural and profile Rietveld refinement put into evidence that effective spinel doping is obtained by the ball milling route: a solubility limit is achieved for x = 0.10 and silicon preferentially occupies the 8a tetrahedral site of the spinel structure, thus causing lithium to occupy both the tetrahedral and octahedral sites. In contrast, segregation of lithium silicates in the solid-state synthesis is observed. SEM images show that, independent on the synthesis method, silicon controls the particles morphology and grain size. The doped samples show improved electrochemical performances, which can be ascribed to the role of silicon in increasing cations disorder and controlling particles size.