EFFECT OF BI-DOPING ON THE ELECTROCHEMICAL-BEHAVIOR OF LAYERED MNO2 AS LITHIUM INTERCALATION COMPOUND

Electrochemical lithium insertion into layered MnO2 forms containing bismuth is reported. A low temperature technique based on a slow coprecipitation in acidic medium in the presence of KMnO4 and a bismuth (III) salt is applied, leading to amorphous MnO2 forms. A chronopotentiometric study has shown that the lithium insertion process occurs in one step located at 3 V and is found to be reversible in the whole range 0 < x < 0.8. The influence of the bismuth and water content on the galvanostatic cycling curves has been studied. These results are discussed and compared with the electrochemical behaviour of the sol-gel birnessite MnO1.84, nH(2)O. The best results are obtained for the lowest Bi content with a high specific capacity of 120 Ah kg(-1) recovered after the 50th cycle at a discharge-charge rate of C/8, while the lover the water content, the poorer the cycling behaviour. From the better reversible behaviour found for the Bi-doped MnO2 structure in comparison with the sol-gel birnessite compound, one can suggest that a pillaring effect due to interlayer Bi3+ ions minimizes the magnitude of structural changes.