Synthesis and lithium ion insertion/extraction properties of hollandite-type MnO2 prepared by acid digestion of Mn2O3

Single-phase specimens of alpha-MnO(2) (hollandite-type) and beta-MnO(2) (rutile-type) were synthesized by the acid digestion of Mn(2)O(3) under reflux conditions. The type of polymorph of MnO(2) products was strongly dependent on the reaction temperature. type of acid used, and its concentration. The pH titration curve of alpha-MnO(2) displayed a monobasic acid behavior toward Li(+), but beta-MnO(2) showed a poor ion-exchange property. In contrast, both alpha-MnO(2) and beta-MnO(2) 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-MnO(2) structure was still retained without structure collapse, although the beta-MnO(2) structure was destroyed. These findings show that Li(+) ions can be inserted only into the hollandite-type tunnels in alpha-MnO(2) and cannot diffuse the rutile-type linkages in alpha-MnO(2) as well as those in beta-MnO(2) without structure collapse. (C) 2008 Elsevier B.V. All rights reserved.