Electrochemical Li insertion in lamellar (birnessite) and tunnel manganese oxides (todorokite)

摘要

A comparison of Li insertion in manganese oxide phases with a tunnel (todorockite) framework, its two-dimensional layered precursor (birnessite/buserite), and Li-exchanged materials are presented. The results outline the effect of the MnO_6 octahedral arrangement and framework comosition on the electrochemical response. The interlayer cations in the lamellar materials are exchangeable for Li, giving rise to a lithiated birnessite that displays a sustainable capacity of 125 mAh/g. For todorokite, molten salt exchange using LiNO_3 results in displacement of water from the tunnels, and incorporation of additional Li into the structure. Some of this Li is extractable during charge, resulting in a reversible capacity of 172 mAh/g in the voltage window 4.2-2.0V.