Insight into delithiation process on the LiFePO4 (010) surface from a novel viewpoint of the work function

Abstract

To understand Li (de)intercalation and related processes on the LiFePO4 (010) surface is of great importance for formulating effective approaches to further improve the rate performance of LiFePO4 cathode. In this article, we propose a new method that surface work function can be used to insight into the delithiation process on the LiFePO4 (010) surface. Density functional theory (DFT) calculations indicate that the extraction of Li from surface layer has a significant effect on the work function of LiFePO4 (010) surface, which in turn provides evidence for whether Li atoms are present in the outermost layer of LiFePO4 (010) surface or not. Moreover, the redox potentials and formation energies for Li extraction from various Li layers in the LiFePO4 (010) surface are also investigated. The calculated results indicate that Li extraction from surface-layer has the lowest redox potential and formation energy, indicating that it is energetically favorable to extract Li first from the surface layer. However, the large difference between the Li vacancy formation energy in the surface layer and the deeper subsurface layer creates a high surface barrier for Li diffusion along the [010] channel. Additionally, we evaluate two simple delithiation models for the LiFePO4 (010) surface, and finding that the work functions are also sensitive to the different delithiation processes. Our results suggest the surface work function as a promising method of identifying the delithiation process on the LiFePO4 (010) surface.