To the best of our knowledge, these are the first room temperature Li PFG NMR diffusion measurements on battery electrodes. The room-temperature lithium self-diffusion coefficients in LixNb18W8O69 are orders-of-magnitude faster than that of common battery electrode materials 1 and are more comparable to the fastest superionic lithium sulfide electrolytes (LiTi2(PS4)3 at 1.2´10 - 11 m 2 •s -1 ; Li11Si2PS12 at 3.5´10 -12 m 2 •s -1 ). For comparison, room-temperature Li + diffusion in 1.0 M PF6 in organic carbonate electrolytes is 8.3-25´10 -11 m 2 •s -1 and Ag + diffusion in the fastest known superionic conducting solid¾AgRb4I5¾is 2´10 -10 m 2 •s -1 . At higher lithium concentrations, T1 and T2 relaxation were too fast to allow sufficient diffusion distances or the application of a sufficient gradient pulse, respectively. We note that elevated temperatures were also required to overcome rapid T2 relaxation in our previous study demonstrating Li PFG NMR diffusion measurements on LixNb16W5O55 at x = 6.3 and 8.4. It is expected that Nb16W5O55 and Nb18W8O69 become metallic at higher lithium contents and the nuclear relaxation is enhanced by conduction electrons. The transition from wide band gap insulator to conductor is supported by optical measurements.