LixMnO2 made by ion exchange of glycine-nitrate combustion synthesis-processed (GNP) orthorhombic Na0.44MnO2 (GNP-LixMnO2) has been cycled in lithium/liquid electrolyte cell configurations at room temperature and lithium/polymer cell configurations at 85 degreesC over one hundred times without showing capacity fading or phase conversion to spinel. At 2.5 mA/cm(2) in liquid cells (5C rate) or 1 mA/cm(2) (1.5C rate) in polymer cells, 80-95% of the expected capacity is delivered. The remarkable stability is attributable to the unusual double tunnel structure, which cannot easily undergo rearrangement to spinel. The enhanced rats capability of GNP-LixMnO2 compared to conventionally prepared materials is attributable to the shorter particle length, which allows faster diffusion of lithium ions along the tunnels. (C) 2001 The Electrochemical Society. All rights reserved.