Synthesis of metal-doped todorokite-type MnO2 and its cathode characteristics for rechargeable lithium batteries

Todorokite-type MnO2-doped with Co and Fe has been synthesized by hydrothermal treatment of layered metal-doped manganese oxide, buserite, in water at 120-200 deg C. The prepared todorokite products have been characterized by XRD and energy dispersive X-ray spectroscopic (EDX) measurements, TEM observation and thermogravimetric analysis. These measurements showed that the hydrothermal products are the metal-doped todorokite phase having large (3 x 3) tunnel structure, and the chemical compositions are shown to be MgxMyMn1-yO2zH2O, where x = 0.08-0.10, y = 0.23-0.29, z = 0.35-0.54 in M = Co and x = 0.13-0.14, y = 0.03-0.16, z = 0.19-0.28 in M = Fe. The preliminary electrochemical characteristics including charge-discharge cyclings of the metal-doped-todorokite electrodes were examined as lithium insertion hosts for cathodes in rechargeable lithium batteries. The metal-doped todorokite exhibited S-shaped discharge behavior and the Co-doped one with x=0.10, y=0.29 showed a high discharge capacity of ca. 132 mAh g-1-oxide and cycling capacity of 90-100 mAh g-1.