Characteristics of the 4 V plateau in LiMn_2(O_4-xF_x) studied by in situ synchrotron X-ray diffraction

摘要

Fluorine--substituted Li_xMn_2O_4 was studied by synchrotron X-ray diffraction using Bellcore-type plastic batteries placed directly in the synchrotron beam. The results show that the '4 V plateau' actually contains three regions f (l) a single-phase range for 0.59 ≤ x ≤ l, (2) a two-phase range for 0.23 ≤ x ≤ 0.59, (3) a narrow single-phase range for x ≤ 0.23. These three domains are fully reversible, but the plastic battery undergoes extraneous oxidation reactions for voltages ≥ 4.4 V. The structural features of this compound are qualitatively similar to those of stoichiometric Li_xMn_2O_4. In particular, no suppression of the two-phase range such as that observed on non-stoichiometric or Ni-substituted LiMn_2O_4 was found.