Local electronic structure of LiMn2O4 probed by solid state Li-7-NMR

Crystalline LiMn2O4 materials were synthesized through a low temperature re flux (LTR) process. The LTR material exhibits an essential electrochemical behavior to present only one transition during the charge/discharge process and gives promises for the future application. The X-ray data hardly disti nguishes either conventional high temperature (HT) or LTR material since bo th materials possess similar molecular structure. However, solid-state NMR results suggest substantial difference for their electronic structure. The Li-7-NMR of HT material exhibits the isotropic peak at 529 ppm and spreads for 160 kHz wide indicating the interaction between the lithium nucleus and the conducting electrons around the nucleus. The LTR material presents the main isotropic peak at 217 ppm but spreads for almost 400 kHz wide asymmet rically implying the existence of multiple electronic environments. (C) 200 1 Elsevier Science Ltd. All rights reserved.