Theoretically Designed Li3PO4 (100)/LiFePO4 (010) Coherent Electrolyte/Cathode Interface for All Solid-State Li Ion Secondary Batteries

Controlling the electrolyte/electrode interface is of great importance to promote new-generation solid-state Li ion secondary batteries. In this paper, we report a theoretically designed electrolyte/cathode coherent interface at the density functional theory level, where gamma-Li3PO4 and LiFePO4 are used as an electrolyte and a cathode, respectively. At the stoichiometric Li3PO4 (100)/LiFePO4 (010) coherent interface, there are vacant Li-sites that give the chance for Li ions to migrate. From the density functional molecular dynamics at 1500 K, it is found that this interface is stable and no impurity phase is produced, and also that Li ions in the Li3PO4 phase around the interface can diffuse with large diffusion coefficients. The dynamic behavior of these Li ions is also reflected in the layered phonon spectra of Li ions; the diffusible Li ions around the interface have the same spectrum.