Doping effects on structure and electrode performance of K-birnessite-type manganese dioxides for rechargeable lithium battery

The potassium birnessites doped with Al, Ni, and Co were prepared by calcination and aqueous treatment, which showed that single phase products were obtained with Ni and Al up to 5 at.% and Co up to 25 at.% addition to strating KMnO4. The discharge–recharge capacities and capacity retentions in an aprotic Li cell were not improved by the Ni and Al dopings, but those of the cobalt doped birnessite were improved. The initial discharge capacities of the undoped and cobalt doped birnessites were 170 and 200 mAh g−1 with capacity retentions of 56 and 80% during the initial 20 cycles, respectively. The reasons for the improvement of the battery performance by Co doping were considered as follows: (i) a change in the stacking structure, (ii) a decrease in the charge transfer resistance, and (iii) improved structural stability of the oxide. Their micro structures were evaluated by X-ray diffraction, photoelectron and Raman spectroscopies, and electron microscopy. Also, potassium birnessite synthesized by adding about 3 times excess potassium indicated that the stacking structure was similar to the 30 at.% cobalt doping sample, furthermore, the better capacity retention was achieved as cathode in a Li cell.