The detailed structural change in the charge-discharge process for the 10 and 20 mol % manganese-substituted nickel hydroxide was investigated by using high-energy synchrotron X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). On the charge-discharge process, the 10 and 20 mol % manganese-substituted nickel hydroxide showed the beta-Ni(OH)(2)/gamma-NiOOH and the alpha-Ni(OH)(2)/gamma-NiOOH phase transformation, respectively. The manganese ions were inserted on the only nickel sites for the 10 mol % manganese-substituted nickel hydroxide, and on both nickel sites and 18h sites for the 20 mol % manganese-substituted nickel hydroxide. The alpha-Ni(OH)(2) structure could be stabilized by the presence of the manganese ions on the 18h sites. The structural refinement for the manganese-substituted nickel hydroxides has been done successfully on the basis of two phase models of the ideal phases and the fault ones. As compared to ideal phases, the fault phases were characterized by the shift of the nickel atoms, and showed a larger amount of the intercalated potassium ions and H2O (OH-) molecules in the interlayer. The occupancy sites for the potassium ions and H2O molecules were contained for the refinements, bringing about a better agreement between the observed and calculated patterns. (c) 2008 The Electrochemical Society. [DOI: 10.1149/1.2987947] All rights reserved.