Abstract
(R3m; 
in hexagonal setting) was prepared and examined in nonaqueous lithium cells using 1M 
propylene carbonate solution at 30°C. The oxidation of 
and the reduction of 
proceeded reversibly in the voltage region above 3.9 V. X‐ray diffraction (XRD) examinations indicated the reaction proceeded in a topotactic manner, i.e., two‐phase reactions 
and a single‐phase reaction 
. A monoclinic phase 
was observed in 
in addition to that at about 
. Detailed open‐circuit voltage measurements were carried out. The open‐circuit voltage are invariable at 3.92 V for 
and at 4.50 V for 
. The two straight lines are connected smoothly by a composition‐dependent curve for 
, which was consistent with the XRD observations. The differences and similarities between the solid‐state redox reactions of 
and 
were discussed by comparing the structural and electrochemical data. Possible lithium ordering at 
for this type of material is described in terms of a 
superlattice in a triangular lattice of sites.