Development of VO Nanostructures for Alkali Metal Ion Batteries: A Novel Approach through Mild Metal Vapor Reduction and Interface Engineering.

VO has been extensively researched as a battery electrode material due to its ample reserves and high theoretical capacity. However, the synthesis of valence-sensitive VO presents technical challenges as it requires a strict combination of high-temperature treatment and a narrow range of oxygen partial pressures. This study proposes a gentle Li vapor-assisted thermal reduction method to synthesize pure-phase VO at a relatively low temperature of 480 °C without any hazardous gases. It has been discovered that reducing the temperature also improves the specific surface area of the nanoto-mesoscale hierarchical structures and enhances the reactive sites between their secondary grains. These advantages enable the VO micronano particles to store higher levels of Li, Na, and K, increase ionic transport, and tolerate volume expansion. It demonstrates a significant capacity of 767 mA h g in lithium-ion batteries, 393 mA h g in sodium-ion batteries, and 209 mA h g in potassium-ion batteries. It has also been discovered that the crystal structure of VO is easily adjustable by varying the synthesis temperature, which significantly affects the electrochemical storage mechanism. The VO synthesized at 480 °C with low crystallinity exhibits a notable intercalation reaction, facilitating the electrochemical kinetics of reversible insertion/extraction of Li, Na, and K. In contrast, the highly crystalline sample synthesized at 580 °C displays pseudocapacitance behavior instead of an intercalation reaction. The highly crystalline sample synthesized at 680 °C exhibits a thorough pseudocapacitance reaction possessing the capacitive functionality for the electrochemical storage of Na or K with larger ion radii. This study describes a new synthesis strategy and rational modification of vanadium-based electrodes for alkali metal ion batteries, leading to the development of reasonably priced rechargeable battery systems with applications extending beyond lithium-ion batteries.