, where H f (Li 3 PO 4 ) is the formation enthalpy of Li 3 PO 4 (a constant). A voltage axis vs. Li/Li + is also shown in Figure . Note that we only plotted the phases limiting the stability Li 3 PO 4 , and phases such as P that do not share boundaries with Li We calculated the native defect thermodynamics at the limiting points A and C (Figure ). The range of Fermi energy is set by the band gap, which is estimated to be 9.55 eV using the GW approximation. Compared to binary components, the defect plots of Li 3 PO 4 ( phase, calculated from ICSD#10257, space group P mn2 1 ) are more complex, in part, due to the multiple Wycko↵ sites (two Li sites, and three O sites), which are indicated by multiple lines of the same color for each defect on Li or O sites in Figure .