Nanocrystalline alpha-MnO_2 Nanowires by Electrochemical Step-Edge Decoration

摘要

alpha-and gamma-MnO_2 are promising candidate materials for cathodes in lithium ion batteries.Both of these materials can be converted by electrochemical Li~+ intercalation into the cubic spinel,Li_(1-x)Mn_2O_4 which has channels through which Li~+ can move.Once the lithiated spinel is formed,the spinel framework of the Li_(1-x)Mn_2O_4 cathode is conserved as Li~+ is extracted during discharge and inserted during charging.The kinetics of the Li~+ intercalation reaction coupled with the transport rate for Li~+ in the cathode determines the achievable discharge rates.6 This fact has motivated an interest in nanometer-scale MnO2 materials and significant progress has been reported including the synthesis of nanocrystalline MnO2 films,7 dispersions of discrete MnO2 nanoparticles,8-9 and MnO2 nanowires,nanorods,and nanofibers.10"17 1-D materials are of particular interest because this morphology simultaneously minimizes the distance over which Li~+ must diffuse during the discharge while providing for electrical continuity.