Catalyzing Zinc-ion Intercalation in Hydrated Vanadates for Aqueous Zinc-ion Batteries
Hydrated vanadium pentoxide (VOH) can deliver a gravimetric capacity as high as 400 mAh/g owing to the variable valence states of V cation from 5+ to 3+ in an aqueous zinc ion battery. Incorporation of divalent transition metal cations has demonstrated to overcome the structural instability, sluggish kinetics, fast capacity degradation, and serious polarization. The current study reveals that the catalytic effects of transition metal cations are likely the key for the significantly improved electrochemical properties and battery performance because the higher covalent character of 55% in Cu-O bond in comparison with 32% of Mg-O bond in the respective samples. Cu (II) pre-inserted VOH (CuVOH) possesses much enhanced intercalation storage capacity, increased discharge voltage, great transport properties, and reduced polarization, while both VOH and Mg (II) pre-inserted VOH (MgVOH) demonstrate similar electrochemical properties and performance, indicating that the incorporation of Mg cations has little or no impacts. For example, CuVOH has a redox voltage gap of 0.02 V, much smaller than 0.25 V of VOH and 0.27 V of MgVOH. CuVOH shows an enhanced exchange current density of 0.23 A/g, compared to 0.20 A/g of VOH and 0.19 A/g of MgVOH. CuVOH delivers a zinc ion storage capacity of 379 mAh/g, higher than 349 mAh/g of MgVOH and 337 mAh/g of VOH at 0.5 A/g. CuVOH performs an energy efficiency of 72%, superior to 53% of VOH and 55% of MgVOH. All the results suggest that pre-inserted Cu (II) cations played a critical role in catalyzing the zinc ion intercalation reaction while Mg (II) cations did not exert detectable catalytic effect.
- This article is part of the themed collection: Journal of Materials Chemistry A HOT Papers