[sup 6]Li Magic Angle Spinning NMR Study of the Cathode Material LiNi[sub x]Mn[sub 2−x]O[sub 4]: The Effect of Ni Doping on the Local Structure during Charging

magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy has been used to study the local structure of synthesized by solid-state reactions. When the extent of doping is small and 0.1), several resonances are observed, which are assigned to lithium local environments containing different numbers of and ions. As the doping level increases and the average manganese oxidation state rises, the intensity of the resonances assigned to lithium environments containing a greater number of higher-oxidation state manganese ions increases; this results in a gradual shift of the center of mass of the spectrum to higher frequency. By only ions are present, and only one major resonance, due to the lithium local environment is observed; this is consistent with Mn/Ni ordering on the octahedral sites of the spinel structure. The variable temperature NMR behavior of these samples is indicative of different magnetic behavior for the undoped and doped materials. A plot of shift) vs. temperature is consistent with the predominance of antiferromagnetic correlations for low doping level samples, while antiferromagnetic correlations clearly dominate the behavior of the sample, resulting in overall ferrimagnetic behavior. spectra were also collected following various levels of charging. In the case of is deintercalated from the different local sites sequentially: lithium ions in the local environment containing manganese ions with an average oxidation state of +3.5 are deintercalated first, followed by lithium ions in sites containing progressively more ions. In contrast, for where the deintercalation process involves oxidation of only, no changes in the lithium local environments were observed during the charging process: the shift position remained constant during the charging cycle and only a loss of the intensity of the lithium signal was observed. © 2001 The Electrochemical Society. All rights reserved.