Lithium-7 nuclear magnetic resonance and Ti K-edge X-ray absorption spectroscopic investigation of electrochemical lithium insertion in Li4/3+xTi5/3O4

The spinel compound Li 4/3+xTi 5/3O 4 is known to undergo reversible lithium intercalation up to x=1 with almost no change in lattice parameters, hence its designation as a "zero strain" intercalation compound. Structural changes that accompany electrochemical Li intercalation into this compound were studied by both 7Li nuclear magnetic resonance (NMR) and Ti K-edge X-ray absorption fine structure (XAFS). The NMR results demonstrate that Li occupancies do not follow a simple distribution between two possible sites, one tetrahedral and one octahedral. The presence of at least one additional octahedral site is suggested. Line width measurements show that the Li + ions do not return to their original distribution after cycling. XAFS results indicate the presence of modest static disorder in Ti-O and Ti-Ti distances above x = 0.5. Both methods thus reveal subtle structural details previously unobserved by X-ray diffraction (XRD).