Potassium type birnessite (K-bir) was synthesized by O-2 oxidizing Mn2+ in aqueous solution of KOH. Co3O4-coated K-bir (Co-K-bir) was prepared by employing a novel coating method, in which the remaining OH- ions on the particle surface of the as-precipitated K-bir reacted with Co2+ ions in aqueous solution, forming CoOOH coverage; the coating layer of CoOOH was subsequently annealed at 300 A degrees C to transform into Co3O4. All the K-bir and Co-K-birs were investigated by scanning electron microscopy, transmission electron microscopy, inductive coupled plasma-atomic emission spectroscopy, Brunauer-Emmett-Teller specific area, and laser particle size analyzing techniques. Their electrochemical properties were also studied by discharging-charging at constant current. The results show that the covering layers of Co3O4 are incompact, and their average thickness are about 0.65-0.78 mu m. Compared to the as-prepared and the annealed K-bir, the Co3O4-coated samples have higher initial discharge capacities and show distinctly improved cycleability performance.
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