Density Functional Theory Study of Li Intercalation Voltage Near Cathode Interfaces

Interfaces are ubiquitous and important in battery electrode as they occur in regions of material intergrowth, in compositional gradients and also at interfaces with protective coatings. In this work, we study the Li intercalation voltage behavior across the interface of olivine FePO₄-MPO₄ (M=Co, Ti, Mn). These olivine-structured interfaces provide a representative model to help us further understand the physics of Li intercalation across material interfaces with different intercalation voltages. We find that as one moves across the interface from high to low Li intercalation voltage material the voltage stays constant in the higher voltage material and decays approximately linearly in the lower voltage region.  This effect is shown to be due to electron transfer from the intercalated Li across the interface. The existence of the higher voltage material and the interface can significantly enhance the Li intercalation voltage in the lower voltage region within a 1-2 nm scale. Implications of this result for cathode structures will be discussed.