FIG. . Formation energy ( ED,q) of native point defects in Li 2 O as a function of Fermi energy (EFermi) under (a) the most Li-rich or reducing ( µLi = 0 eV, voltage vs. Li/Li + is 0 V) and (b) the most Li-poor or oxidizing ( µLi = 3.02 eV, voltage vs. Li/Li + is 3.02 V) conditions within the phase stability region constrained by Li and Li