Understanding of Lithium Insertion INto #gamma#-MnO_2 COmpounds

摘要

A large variety of EMD and HTMD samples with various oxygen and water content and various structural paratmeters Pr and Mt has been prepared. We show that the physico-chemicla and sturctural parameters of the #gamma#-MnO_2 compounds are related ot the synthesis conditions. New compounds were obtained with unusual amounts ofintergrowth and twinning defects. The Li insertion study focuses on a comprehensive invesigation of the relationships between the material characteristics ofthe samples and their Li insertion behavior, and on the structural characterization of selected compunds after cycling. The oxygne content draically affects the shape ofhte discharge curve after the first cycle and the total reversible capacity. The amount of structural water has an influence on the transformation kinetics ofthe starting phase. For optimized oxygen cotent, the intrinsic reversible Li insertion capacity is maximum when the amount of microtwinning defects is miniumu mnad when the structrue is either mostly Ramsdellite or faulted Pyrolusite. Results show that, upon cycling, the #gamma#-MnO_2 structure seems to evoluate towards less Pyrolusite defects together with the apparition of new kinds of defects. This work shows that #gamma#-MnO_2 compounds could be good candidates for the cathode applciation of Li-metal rechargeable batteries, provided that the physico-chemical nad structural parameters of the starting compound are well chosen.