Reduced surfactant uptake in three dimensional assemblies of VO_x Nanotubes Improves Reversible Li⁺ intercalation and charge capacity

The relationship between the nanoscale structure of vanadium pentoxide nanotubes and their ability to accommodate Li⁺ during intercalation/ deintercalation is explored. The nanotubes are synthesized using two different precursors through a surfactant-assisted templating method, resulting in standalone VOx (vanadium oxide) nanotubes and also "nanourchin". Under highly reducing conditions, where the interlaminar uptake of primary alkylamines is maximized, standalone nanotubes exhibit near-perfect scrolled layers and long-range structural order even at the molecular level. Under less reducing conditions, the degree of amine uptake is reduced due to a lower density of V4⁺ sites and less V₂O₅ is functionalized with adsorbed alkylammonium cations. This is typical of the nano-urchin structure. Highresolution TEM studies revealed the unique observation of nanometer-scale nanocrystals of pristine unreacted V ₂O₅ throughout the length of the nanotubes in the nano-urchin. Electrochemical intercalation studies revealed that the very well ordered xerogel-based nanotubes exhibit similar specific capacities (235mA h g^-1) to Na⁺-exchange nanorolls of VOx (200mA h g ^-1). By comparison, the theoretical maximum value is reported to be 240mA h g^-1. The VOTPP-based nanotubes of the nano-urchin 3D assemblies, however, exhibit useful charge capacities exceeding 437mA h g ^-1, which is a considerable advance for VO_x based nanomaterials and one of the highest known capacities for Li⁺ intercalated laminar vanadates.