Overall, Li 3 P contains substantially fewer Li-related defects that mediate Li-ion di↵usion and more net free As the only ternary SEI component, Li 3 PO 4 exhibits a more complex phase diagram compared to the binary components. In constructing the phase diagram, we considered all competing phases in the ternary Li-P-O chemical space, including ICSD phases that are calculated and reported in the NREL Materials Database and the Materials Project. The competing phases comprise: Li 3 P, LiP, Li 3 P 7 , LiP 7 , P, Li 4 P 2 O 7 , Li 2 O, Li 2 O 2 , and O 2 . By excluding the chemical conditions that favor the formation of these competing phases, we obtained the accessible range of elemental chemical potentials for the stability of Li 3 PO 4 . In the computed phase diagram (Figure ), we find that Li 3 PO 4 is not in thermodynamic equilibrium with Li metal ( µ Li = 0 eV).