Lithium dynamics in LiMn2O4 probed directly by two-dimensional Li-7 NMR

LiMn2O4 has been studied using magic-angle-spinning nuclear magnetic resona nce (MAS NMR). 1D MAS NMR shows three Li resonances assigned to different c rystallographic sites. At low temperatures an extra peak appears, indicatin g charge ordering of Mn3+ and Mn4+. Direct observation of the lithium dynam ics was possible using rotor-synchronized 2D exchange NMR. A millisecond ti me scale exchange of lithium starts around 285 K between the 8a and the 16c site. At 380 K lithium even starts to hop between more than two sites. The activation energies and Li jump rates are derived and are in agreement wit h those determined macroscopically.