Reduced Surfactant Uptake in Three Dimensional Assemblies of VO_<i>x</i> Nanotubes Improves Reversible Li⁺ Intercalation and Charge Capacity

Abstract

Abstract 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 VO x (vanadium oxide) nanotubes and also “nano‐urchin”. 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 V 4+ sites and less V 2 O 5 is functionalized with adsorbed alkylammonium cations. This is typical of the nano‐urchin structure. High‐resolution TEM studies revealed the unique observation of nanometer‐scale nanocrystals of pristine unreacted V 2 O 5 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 (235 mA h g −1 ) to Na + ‐exchange nanorolls of VO x (200 mA h g −1 ). By comparison, the theoretical maximum value is reported to be 240 mA h g −1 . The VOTPP‐based nanotubes of the nano‐urchin 3D assemblies, however, exhibit useful charge capacities exceeding 437 mA 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.