Design of pore and matter architectures in manganese oxide charge-storage materials

We describe the preparation of a manganese oxide polymorph in which the sol id-pore architecture of the material is controllably varied. All MnO2 gels derived from a KMnO4-based sol-gel synthesis and annealed to 300 degrees C crystallize in the 2 x 2 tunnel structure of cryptomelane (KdeltaMnO2 or al pha-MnO2), but exhibit markedly different final pore structures based on ho w the pore fluid is removed from the wet gel. The mesoporous structure of t he initial gel is maintained by removing pore fluid under conditions where the capillary forces that result from extraction are either low (to form an ambigel) or nonexistent (to form an aerogel). These nanoscale mesoporous m aterials have higher Li:MnO2 capacities at high cycling rates than can be o btained for bulk cryptomelane. Finite-diffusion processes describe the elec trochemical association of Li+ with the networked, nanoscale MnO2 crystalli tes. Controlling both the pore and solid architecture on the nanoscale offe rs a strategy for the design of new battery and charge-storage materials. ( C) 2000 The Electrochemical Society. S1099-0062(00)03-143-6. All rights res erved.