Supercharging a MnO Nanowire: An Amine-Altered Morphology Retains Capacity at High Rates and Mass Loadings.

The influence of hexamethylenetetraamine (HMTA) on the morphology of δ-MnO and its properties for electrical energy storage are investigated-specifically for ultrathick δ-MnO layers in the micron scale. Planar arrays of gold@δ-MnO, core@shell nanowires, were prepared by electrodeposition with and without the HMTA and their electrochemical properties were evaluated. HMTA alters the MnO in three ways: First, it creates a more open morphology for the MnO coating, characterized by "petals" with a thickness of 6 to 9 nm, rather than much thinner δ-MnO sheets seen in the absence of HMTA. Second, the electronic conductivity of the δ-MnO is increased by an order of magnitude. Third, δ-MnO prepared in HMTA shows a (001) interlayer spacing that is expanded by ≈30% possibly accelerating Li transport. The net effect of "HTMA doping" is to dramatically improve high rate performance, culminating in an increase in the specific capacity for the thickest MnO shells examined here by a factor of 15 at 100 mV/s.