Nanocrystalline RuO₂ was electrochemically lithiated using a ⁶Li-enriched negative electrode, and selected samples at various states of lithiation-delithiation were characterized ex situ by ⁶Li magic-angle spinning nuclear magnetic resonance (⁶Li MAS NMR). In the first plateau (up to one Li per RuO₂), a signal with considerable shift and loss of intensity is observed, showing a strongly paramagnetic character for the LiRuO₂ phase. A signal due to solid electrolyte interphase (SEI) appears at 0 ppm on this first plateau, but significantly grows only on the subsequent conversion plateau (from 1 to 4 Li/RuO₂). Li₂O is detected only at the very end of the latter plateau. On further lithiation (4 to 5.5 Li/RuO₂), the magnitude of the Li₂O signal remains constant, and a new signal at 4 ppm appears, that we can assign to interfacial Li hypothesized earlier in this system. Upon subsequent delithiation, NMR shows that the interfacial Li first disappears, then Li₂O also disappears, and the reconstructed Li-RuO₂ phase is clearly different from the one formed during the initial lithiation of RuO₂. Besides, the SEI signal slightly changes but does not decrease in magnitude upon delithiation. NMR results are in satisfactory agreement with the characteristic features of the proposed “job-sharing” mechanism.< Leer menos