ELECTROCHEMISTRY OF MANGANESE-DIOXIDE IN LITHIUM NONAQUEOUS CELL .3. X-RAY DIFFRACTIONAL STUDY ON THE REDUCTION OF SPINEL-RELATED MANGANESE-DIOXIDE

X-ray diffractional and electrochemical studies of the reduction of a spinel-related manganese dioxide, Li0.27(2)Mn2O4:MnO1.93, were carried out in lithium nonaqueous cells. The reduction of this oxide proceeded topotactically in three steps; a reduction in two phases [cubic: ac = 8.045(6)Å and ac = 8.142(2)Å] was characterized by a constant open-circuit voltage (OCV) of 4.110(5)V for 0.27(2) < x < 0.60(3) in LixMn2O4, a reduction in one phase [cubic: ac = 8.142(2) − 8.239(3)Å] characterized by an S-shaped OCV curve [mid-point, 3.94(1)V] for 0.60(3) < x < 1.0, and a reduction in two phases of cubic [ac = 8.239(3)Å] and tetragonal [aT = 5.649(2)Å and cT = 9.253(5)Å] characterized by an L-shaped OCV curve at 2.957(5)V for 1.0 < x < 2.0. An observed voltage separation of ca. 1V, which begins at a critical composition of Li1.0Mn2O4, was considered from the structural data of LixMn204 to be a difference in a solid-state redox reaction of a MnO6-octahedron, i.e., the MnO6 8−(Oh)/MnO6 9−(Oh) vs. MnO6 8−(Oh)/MnO6 9−(D4h) redox reactions, and an effect of deformation of a MnO6 9−-octahedron from Oh-symmetry to D4h-symmetry (Jahn-Teller distortion) upon an electrode potential of LixMn2O4 was discussed. © 1990, The Electrochemical Society, Inc. All rights reserved.