Nanoporous manganese dioxide (a-MnO_2) is capable of reversibly intercalating close to 2 electron equivalents of various monovalent and polyvalent cations, including lithium, magnesium, zinc, and aluminum. Intercalation capacity in terms of the number of electron equivalents that can be intercalated is the same for the different cations. The chemical identity of the intercalant cation appears unimportant in the reaction thermodynamics. The kinetics of the intercalation of the different cations are also similar. These features are in sharp contrast with those of crystalline intercalation hosts and help provide insight into the fundamental nature of intercalation and the structure-property relationship of intercalation materials. The extremely high capacity exhibited by the material for the reversible intercalation of polyvalent cations also gives rise to the possibility of using the material as the cathode for rechargeable magnesium, zinc, and aluminum batteries, in addition to lithium batteries.
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