Abstract
X‐ray diffractional (XRD) and electrochemical studies of 
prepared from heat‐treated electrolytic manganese dioxide (250°C, 7 days) were carried out in the rechargeable region 
of this material in lithium nonaqueous cells. The shape in the midpoint voltage curve between charge and discharge curves was observed to be quite different between the ranges 
and 
. XRD data indicated that the reaction proceeded in a homogeneous phase throughout the whole region. However, a discontinuous change in the orthorhombic unit cell parameters vs. x in 
plots was observed at 
. In order to explain such discontinuity in electrochemical and structural data, the Jahn‐Teller deformation of a 
octahedron in 
was considered assuming a possible 
octahedral linkage to form an orthorhombic unit cell. Our results indicated that the 
phase in the region
is not the same as that in the region 
. The discontinuity observed in the electrochemical and structural data are ascribed to a phase transition at 
. The effect of the Jahn‐Teller distortion of 
octahedra upon the electrochemical behavior of several 
is discussed.