Rationalization of Diversity in Spinel MgFe2O4 Surfaces

Abstract Spinel magnesium ferrite (MgFe 2 O 4 ) is a prospective anode material for lithium ion batteries (LIBs). Here, using density functional theory the first systematic study of diverse MgFe 2 O 4 surfaces is reported in three types of spinel structures: normal, mixed, inverse, which can have significant impact on the initial lithiation. The results show that the faceting and therefore the shape of MgFe 2 O 4 crystals strongly depend on the bulk structures. Upon going from normal, mixed to inverse spinel, the energetically preferred facets of MgFe 2 O 4 vary from the combination of (1 0 0) and (3 1 1), soly {1 0 0} to a combination of (1 0 0), (0 0 1), (1 1 1), and (3 1 1), respectively, depending on the distribution of Mg 2+ in the spinel structure. However, there is one common descriptor to the stable surfaces among all three MgFe 2 O 4 systems: high density of Mg 2+ exposed to the surface. This study rationalizes the essential effect of the substitution of Zn 2+ for Mg 2+ in ferrites and provides new insights on how to control the shape of ferrite materials and thus tune the performances of LIBs.