Single-phase specimens of alpha-MnO2 (hollandite-type) and beta-MnO2 (rutile-type) were synthesized by the acid digestion of Mn2O3 under reflux conditions. The type of polymorph of MnO2 products was strongly dependent on the reaction temperature. type of acid used, and its concentration. The pH titration curve of alpha-MnO2 displayed a monobasic acid behavior toward Li+, but beta-MnO2 showed a poor ion-exchange property. In contrast, both alpha-MnO2 and beta-MnO2 acted as a rechargeable active material in a liquid organic electrolyte lithium cell. The initial discharge capacities of both electrodes exceeded 200 mAh/g (cut-off voltage: 2 V). After discharge-charge repetition, the alpha-MnO2 structure was still retained without structure collapse, although the beta-MnO2 structure was destroyed. These findings show that Li+ ions can be inserted only into the hollandite-type tunnels in alpha-MnO2 and cannot diffuse the rutile-type linkages in alpha-MnO2 as well as those in beta-MnO2 without structure collapse. (C) 2008 Elsevier B.V. All rights reserved.