Abstract: Three electrolytic manganese dioxide (EMD) samples were characterized by XRD and chemical analyses.
Their electrochemical performances were studied by cyclic voltametry, constant-current discharge, and choronopotentiometry. The results show that the
three samples have the same structure, γ-MnO_2, but their combined water contents are different. The chemical compositions of the three samples
can be formulated as A: Mn⁴⁺_0.881Mn³⁺_0.044O²-_1.655(OH)^-_0.345, B: Mn⁴⁺_0.880Mn³⁺_0.048O^2-_1.666(OH)__0.334 and C:
Mn⁴⁺_0.879Mn³⁺_0.054O^2-_1.677(OH)^-_0.322. The electrochemical performances are influenced by the combined water contents,
which are related to the number of cation-vacancy in the samples. The open circuit potential, the discharge capacity and the peak potential of one
electron reduction increase with the increase of the combined water contents in the samples.

Key words: EMD, combined water, cation-vacancy, electrochemical performance