Characteristics of the 4 V plateau in LiMn2(O4-xFx) studied by in situ synchrotron X-ray diffraction

Fluorine-substituted LixMn(2)O(4) was studied by synchrotron X-ray diffract ion using Bellcore-type plastic batteries placed directly in the synchrotro n beam. The results show that the '4 V plateau' actually contains three reg ions: (1) a single-phase range for 0.59 less than or equal to x less than o r equal to 1, (2) a two-phase range for 0.23 less than or equal to x less t han or equal to 0.59, (3) a narrow single-phase range for x less than or eq ual to 0.23. These three domains are fully reversible, but the plastic batt ery undergoes extraneous oxidation reactions for voltages greater than or e qual to 4.4 V. The structural features of this compound are qualitatively s imilar to those of stoichiometric LixMn2O4. In particular, no suppression o f the two-phase range such as that observed an non-stoichiometric or Ni-sub stituted LiMn2O4 was found. (C) 1999 Elsevier Science S.A. All rights reser ved.