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

LiMn2O4 has been studied using magic-angle-spinning nuclear magnetic resonance (MAS NMR). 1D MAS NMR shows three Li resonances assigned to different crystallographic sites. At low temperatures an extra peak appears, indicating charge ordering of Mn3+ and Mn4+. Direct observation of the lithium dynamics was possible using rotor-synchronized 2D exchange NMR. A millisecond time 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 with those determined macroscopically.