Effect of interlayer K ordering on water intercalation behavior in -type layered manganese dioxide

Okamoto, Norihiko*; Yoshisako, Hiroki*; Ichitsubo, Tetsu

Layered manganese dioxide (birnessite) that contains K cations and water molecules at interlayers exhibits reversible heat storage properties via a water-intercalation mechanism (0.5 mol HO per KMnO). However, a certain amount of an irreversible capacity of water intercalation is observed after the initial thermal cycle, which limits the reversibly available energy density of the material for the subsequent cycles. In this study, crystal structures of the K-containing birnessite, KMnO, was analyzed before and after heat treatment, by electron diffraction and atomic-resolution scanning transmission electron microscopy, to elucidate the origin of the initial irreversible capacity (0.83 mol per KMnO).