O ] = 2.7⇥10 9 9.16⇥10 3 cm 3 . Overall, the defects that can mediate Li di↵usion show a total concentration of ⇠10 5 cm 3 (300 K) and ⇠10 12 cm 3 (500 K). The net free electron concentration [e net ] is ⇠0 cm 3 ; precisely, it is in the order of 10 32 cm 3 at 300 K and 10 11 cm 3 at 500 K. Therefore, [e net ] for Li 2 O is negligible at 300-500 K under the most Li-rich condition (equilibrium with Li metal). It is notable that the di↵erence in the defect thermodynamics is negligible between the T formation of 300 K and 500 K. Such negligible di↵erences do not alter our conclusions, qualitatively or quantitatively, and therefore, in the rest of Section II we will focus only on the results calculated for T formation of 300 K. Results for the defect thermodynamics for T formation of both 300 K and 500 K can be found in Tables S1-S4 of the Supporting Information (SI).