Understanding of Lithium Insertion into λ-MnO2 Compounds

Abstract

ABSTRACTA large variety of EMD and HTMD samples with various oxygen and water contents and various structural parameters Pr and Mt has been prepared. We show that the physico-chemical and structural parameters of the λ-MnO2 compounds are related to the synthesis conditions. New compounds were obtained with unusual amounts of intergrowth and twinning defects.The Li insertion study focuses on a comprehensive investigation of the relationships between the material characteristics of the samples and their Li insertion behavior, and on the structural characterization of selected compounds after cycling. The oxygen content drastically affects the shape of the discharge curve after the first cycle and the total reversible capacity. The amount of structural water has an influence on the transformation kinetics of the starting phase. For optimized oxygen content (y= 2 in MnOY), the intrinsic reversible Li insertion capacity is maximum when the amount of microtwinning defects is minimum and when the structure is either mostly Ramsdellite or faulted Pyrolusite. Results show that, upon cycling, the λ-MnO2 structure seems to evoluate towards less Pyrolusite defects together with the apparition of new kinds of defects.This work shows that λ-MnO2, compounds could be good candidates for the cathode application of Li-metal rechargeable batteries, provided that the physico-chemical and structural parameters of the starting compound are well chosen.