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 Li4/3+xTi5/3O4 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 Liþ 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).