Amorphous vanadium oxides for electrochemical energy storage

Vanadium oxides have attracted extensive interest as electrode materials for many electrochemical energy storage devices owing to the features of abundant reserves, low cost, and variable valence. Based on the in-depth understanding of the energy storage mechanisms and reasonable design strategies, the performances of vanadium oxides as electrodes for batteries have been significantly optimized. Compared to crystalline vanadium oxides, amorphous vanadium oxides (AVOs) show many unique properties, including large specific surface area, excellent electrochemical stability, lots of defects and active sites, fast ion kinetics, and high elasticity. This review gives a comprehensive overview of the recent progress on AVOs for different energy storage systems, such as alkali metal ion batteries, multivalent ion batteries, and supercapacitors with a special focus on the preparation strategies. The basic mechanisms for energy storage performance improvements of AVOs as compared to their crystalline counterparts are also introduced. Finally, challenges faced by AVOs are discussed and future development prospects are also proposed. This review aims to provide a comprehensive knowledge of AVOs and is expected to promote the development of high-performance electrodes for batteries.