Dual Effect of Structure and Hydration on Magnesium-Ion Insertion into Electrodeposited V <sub>2</sub> O <sub>5</sub> Thin Films
Hakeem K. Henry, Brandon Johnston, Darrin Liau, Emily Sahadeo, Sang Bok Lee
Abstract
In recent years there has been some discrepancy about whether crystalline or amorphous V 2 O 5 is the superior cathode material for magnesium-ion batteries, with many publications suggesting that amorphous V 2 O 5 more readily stores magnesium ions. In this work, we report the systematic investigation of magnesium ion storage in crystalline and amorphous V 2 O 5 electrodeposited thin films. Our results indicate that the electrochemical performance of V 2 O 5 thin films is primarily impacted by the presence of adsorbed water. This study finds that the adsorbed water left over from aqueous electrodeposition is mostly responsible for the observed improved performance of amorphous V 2 O 5 thin films, thereby indicating that the drying conditions, rather than the crystal structure, play a direct role in enhancing the electrochemical performance. We propose an explanation for this observation in that the amorphous thin film has much larger water content, leading to increased interlayer spacing within the disordered structure and possible charge shielding for magnesium-ion storage. Ultimately, this study demonstrates the importance of considering the effect of adsorbed water, especially when comparing the electrochemical performance of amorphous and crystalline V 2 O 5 synthesized from wet electrodeposition techniques.