From our analysis, it is clear that all dopants, with the exception of Y, result in a drastic increase in the V ′ Li con-centration at RT. Ta-doping results in the largest estimated equilibrium [V ′ Li ] at RT of 7.4×10 19 cm -3 corresponding to ∼ 0.02 defects per formula unit. The [Ta Zr ] frozen in at the sintering temperature is also 7.4 × 10 19 thus it can be assumed that this is solely responsible for the increased [V .