Nanostructured amorphous manganese oxide cryogel as a high-rate lithium intercalation host

Amorphous manganese oxides have received increasing attention in recent years as high-capacity intercalation cathodes for rechargeable lithium batteries. Nanostructured electrodes have been shown to exhibit enhanced rate capabilities. In this paper, a nanostructured amorphous manganese oxide cryogel is reported that combines the advantages of the amorphous structure and the nano-architecture, leading to high lithium intercalation capacity and high rate capability. The cryogel is prepared by freeze-drying a Mn(IV) oxide hydrogel formed in situ via reduction of sodium permanganate solution with solid fumaric acid. The cryogel exhibits a nanoporous structure and a specific surface area of 350 m(2)/g. X-ray and electron diffraction reveals the amorphous nature of this freeze-dried gel. The material exhibits specific capacities of 289, 217 and 174 mAh/g at C/100, C/5 and 2C rates, respectively, demonstrating high capacity and excellent rate capability. This work shows the feasibility of the freeze-drying method for obtaining manganese oxides with nano-architecture and high specific surface area, and suggests the promise of the synthesis route to nanostructured amorphous manganese oxides via a hydrogel. (C) 2003 Elsevier Science B.V. All rights reserved.