Figure shows the resistance (R = d A e ) calculated as a function of the SEI thickness d and normalized to an area of A = 1 cm 2 . For the individual SEI components, the resistance of Li 3 N and Li 3 P are relatively low (10 1 ⇠ 10 6 ⌦ at 300 K) due to their high electronic conductivity (see Table ). For Li 2 O and Li 3 PO 4 , we used the upper limit of their electronic conductivity (under Li-rich condition in Table ) to obtain the lower limit of the resistance, which still significantly high, at least 10 21 ⌦. The SEI layer resistance (black square in Figure ) reflects a stoichiometrically-weighted average of the resistance of the individual SEI components, according to the mass ratio in Eq. 1. Unsurprisingly, it is close to the highest component resistance (i.e., the Li 3 PO 4 resistance), indicating that the SEI layer is insulating. A comparison between the SEI resistance for T formation of 300K and 500 K can be found in Figure of the SI.