The present invention relates to nano structures of metal oxides having a nanostructured shell (or wall), and an internal space or void. Nanostructures may be nanoparticles, nanorod/belts/arrays, nanotubes, nanodisks, nanoboxes, hollow nanospheres, and mesoporous structures, among other nanostructures. The nanostructures are composed of polycrystalline metal, oxides such as SnO2. The nanostructures may have concentric walls which surround the internal space of cavity. There may be two or more concentric shells or walls. The internal space may contain a core such ferric oxides or other materials which have functional properties. The invention also provides for a novel, inexpensive, high-yield method for mass production of hollow metal oxide nanostructures. The method may be template free or contain a template such as silica. The nanostructures prepared by the methods of the invention provide for improved cycling performance when tested using rechargeable lithium-ion batteries.