Understanding the Dissolution and Phase Transformation Mechanisms in Aqueous Zn/α-V₂O₅ Batteries

Abstract

Anhydrous α-V 2 O 5 was the first class of cathodes studied for rechargeable aqueous zinc-ion batteries (AZIBs), mainly due to its layered structure and high theoretical capacity. However, the poor cycle life of Zn/α-V 2 O 5 prevents it from being used as a practical cathode. A critical need for the advancement of high-capacity aqueous Zn/α-V 2 O 5 batteries is a better understanding of the degradation mechanisms in an α-V 2 O 5 cathode. Through a combined experimental and theoretical approach, we here report that the stability of an α-V 2 O 5 cathode in aqueous Zn/ α-V 2 O 5 batteries is fundamentally controlled by its dissolution mechanisms in water and concurrent phase transition to a hydratedwhile its majority is transformed into H-V 2 O 5 . We provide evidence that H-V 2 O 5 is the active material for the storage of Zn 2+ /H + due to its favorable gallery spacing for intercalation chemistry. Overall, presented experimental evidence and gained fundamental insights by this study contribute to the advancement of high-capacity aqueous Zn/α-V 2 O 5 batteries.

Corrosion as the origin of limited lifetime of vanadium oxide-based aqueous zinc ion batteries

“…In AZIBs, however, α-V 2 O 5 is known to require long activation cycles, making it incompatible with practical use 21 . Recently, Huang’s group reported that α-V 2 O 5 undergoes a transformation from its original phase to hydrated vanadium pentoxide within the aqueous zinc electrolyte, and once transformed, it does not need the activation step anymore 44 . With these results in mind, we used a simple sol-gel method to synthesize the hydrated vanadium pentoxide (vanadium oxide xerogel, VOX) to obviate the need for the activation step and employed it as the cathode in an AZIB.…”

“…2a ) did not exhibit any peaks related to the ZVO phase in any selected state in the first cycle, which implies that the ZVO phase did not form during the electrochemical charge /discharge process. Recently, the formation of the ZVO within the aqueous solution containing Zn ions was reported to be associated with the dissolution of vanadium pentoxide and the subsequent precipitation via the following reactions 44 . To establish whether this also applies to the VOX, a simple dissolution test was performed by immersing the VOX electrode in a 3 m Zn(OTf) 2( aq ) solution.…”

“…With this acidification, the pH of the electrolyte could fall below the region in which VO 2 (OH) 2 − exists, whereupon the formation of ZVO is no longer feasible. Recall that VO 2 (OH) 2 − arises from the dissolution of vanadium from VOX and yields the ZVO phase upon reacting with Zn ions from the electrolyte 44 . Hence, the formation reaction of the ZVO is “self-limiting” in that the production of ZVO limits its further production by lowering the pH.…”

“…22a, c ). This tendency is attributed to the higher Zn 2+ desolvation energy of ZnSO 4( aq ) that results in higher charge-transfer resistance as well as the relatively higher affinity of the SO 4 anion for water molecules, which induces the dissolution of vanadium oxides 44 , 46 . Additionally, it is anticipated that the BZSs produced in different electrolytes, Zn 12 (CF 3 SO 3 ) 9 (OH) 15 ·nH 2 O in Zn(OTf) 2( aq ) and Zn 4 (SO 4 )(OH) 6 ·5H 2 O in ZnSO 4( aq ) , affect the cyclability of the corresponding cells 47 , 53 .…”

In‐Situ Lattice Tunnel Intercalation of Vanadium Pentoxide for Improving Long‐Term Performance of Rechargeable Magnesium Batteries

“…In the energy range of 517 and 525 eV, two peaks corresponding to the spin-orbit of V2p 3/2 and V2p 1/2 are detected, which can be separated into two peaks of V 5 + and V 4 + . [15] The N1s XPS spectra of the V 2 O 5 /PANI is shown in Figure 1d, the four peaks at 402.3 401.0, 399.2, and 398.3 eV correspond to protonated imine species (À N=), protonated amine (À NHÀ ), benzenoid imine (À NH + À ) and quinonoid imine (À N + =), respectively. [16] These groups are expected to produce a semi-oxidized state, significantly enhancing the conductivity of PANI.…”