Essential Role of Spinel ZnFe2O4 Surfaces during Lithiation

Spinel zinc ferrite (ZnFe 2 O 4 ) is a well-known anode material in lithium ion batteries (LIBs) because of its large theoretical capacity. However, the high potentials observed at the initial stage of lithiation cannot be captured using a model of Li + intercalation into the stoichiometric ZnFe 2 O 4 bulk. Here, using density functional theory, we report for the first time that the ZnFe 2 O 4 surfaces are responsible for the measured initial potentials. Among the three identified stable surfaces, ZnFeO 2 -terminated ZnFe 2 O 4 (1 1 0), O-terminated ZnFe 2 O 4 (1 1 1), and Zn-terminated ZnFe 2 O 4 (1 1 1), both (1 1 1) surfaces display higher lithiation potentials than the (1 1 0) surface, and the estimated potentials based on Zn-terminated (1 1 1) fit well with the experimental observations, whereas using the models based on ZnFe 2 O 4 (1 1 0) and previously ZnFe 2 O 4 bulk, the estimated potentials are much lower. In terms of Li + diffusion, the Zn-terminated ZnFe 2 O 4 (1 1 1) surface is the most active, where the energetically favorable saturation of Li + on the surface is able to facilitate the process. Our results provide a new strategy for the design of LIB materials, via controlling the particle shape and the associated surface characteristics, thus enhancing the discharging performance.