Promising vanadium oxide and hydroxide nanostructures: from energy storage to energy saving

The great energy demand for fossil fuels impacts air pollution and water pollution, which significantly influences human life today, and thus efficient utilization of energy has directed a global trend towards a diversified energy portfolio, particularly focusing on energy storage and saving applications. Owing to their special structural characteristics, vanadium oxides have received particular interest for efficient energy utilization, and the search for new kinds of vanadium oxides in the applications of the energy issues has been highlighted in recent years. This review surveys recent advances in tackling energy utilization issues, such as organic electrolyte or aqueous electrolyte lithium-ion batteries (LIB), by the development of vanadium oxide nanostructures, as well as energy-saving applications, via regulating the desired structure and morphology characteristics of vanadium oxides. The nanoarchitectured vanadium oxides with valence state from +3 to +5 all seem ripe for further development for the organic-electrolyte LIB application with improved energy density and cycling performance. In addition, solution-based synthesis gives a facile and inexpensive route to grow and assemble their nanoarchitectures for organic-electrolyte LIB applications. Moreover, although the application of vanadium oxides in aqueous LIB is still in its infant stage, controlling the morphology and structure of vanadium oxides also plays a vital role in the improvement of the aqueous LIB performance. Furthermore, the energy-saving application of vanadium oxides, which arises from the smart switching properties, bring us drastic changes in electrical conductivity and near-IR optical properties for the energy-saving application as the "smart window" coatings. The challenges and ongoing research strategies of the application of vanadium oxides for efficient energy utilization are also discussed in this review article.