Enhanced intercalation dynamics and stability of engineered micro/nano-structured electrode materials: vanadium oxide mesocrystals.

An additive and template free process is developed for the facile synthesis of VO2 (B) mesocrystals via the solvothermal reaction of oxalic acid and vanadium pentoxide. The six-armed star architectures are composed of stacked nanosheets homoepitaxially oriented along the [100] crystallographic register with respect to one another, as confirmed by means of selected area electron diffraction and electron microscopy. It is proposed that the mesocrystal formation mechanism proceeds through classical as well as non-classical crystallization processes, and is possibly facilitated or promoted by the presence of a reducing/chelating agent. The synthesized VO2 (B) mesocrystals are tested as a cathodic electrode material for lithium-ion batteries, and show good capacity at discharge rates ranging from 150-1500 mA g(-1) and a cyclic stability of 195 mA h g(-1) over fifty cycles. The superb electrochemical performance of the VO2 (B) mesocrystals is attributed to the porous and oriented superstructure that ensures large surface area for redox reaction and short diffusion distances. The mesocrystalline structure ensures that all the surfaces are in intimate contact with the electrolyte, and that lithium-ion intercalation occurs uniformly throughout the entire electrode. The exposed (100) facets also lead to fast lithium intercalation, and the homoepitaxial stacking of nanosheets offers a strong inner-sheet binding force that leads to better accommodation of the strain induced during cycling, thus circumventing the capacity fading issues typically associated with VO2 (B) electrodes.