Similar to our analysis of the self-diffusion coefficient, D * , we separate our Li-defect concentration data into normal and superionic subsets, which results in two regimes that exhibit distinct Arrhenius relationships. From our Li(2) vacancy concentration data, we assign defect formation energies of E f,n = 0.72(6) eV, and E f,s = 0.38 eV to the normal and superionic regimes within a 95% confidence interval, respectively. This change may be attributed to defect-defect interactions that lower the average formation energy at a critical defect concentration reached at T s . The fraction of Li sites that are vacant reaches the value of 1% at ≈ T s . Across the superionic transition, the defect formation energies decrease by a similar factor as the diffusion activation energies, compared to their low-temperature values. This result suggests that the superionic transition is facilitated by a decrease in defect formation energy at T s . Low migration energy barriers, E m , calculated from nudged elastic band , already suggested that the bottleneck for diffusion came from E f and not E m .