Template synthesis of polypyrrole-coated spinel LiMn2O4 nanotubules and their properties as cathode active materials for lithium batteries

Tubules of 200 nm outer diameter spinel LiMn2O4 were prepared by thermal decomposition of an aqueous solution containing lithium nitrate and manganese nitrate at 1:2 molar ratio using a nanoporous alumina membrane as a template. After dissolving the template membrane, the resulting nanotubule array of LiMn2O4 was coated with polypyrrole to investigate the galvanostatic charge-discharge characteristics. The polypyrrole-coated LiMn2O4 tubule electrodes exhibited higher capacities than the polypyrrole-coated LiMn2O4 thin-film electrode prepared under the same conditions, except for the use of the alumina membrane; it was ca. 2.5 times greater at 0.1 mA cm(-2) and became ca. 12 times greater with an increase in current density to 1.0 mA cm(-2). The observed high capacity of the tubule electrode seems to have resulted from two kinds of effects: a decrease in real current density of high specific surface area at the tubule electrode and a decrease in thickness of LiMn2O4 solid phase for Li+ ions to diffuse through during the charging and discharging reactions.