Troubleshooting the Limited Zn²⁺ Storage Performance of the Ag₂V₄O₁₁ Cathode in Zinc Sulfate Electrolytes via Favorable Synergism with Reduced Graphene Oxides

Abstract

A zinc-ion battery (ZIB) employing an aqueous electrolyte, that is, an aqueous zinc-ion battery (AZIB), represents a unique combination of high energy and high power with much-desired safety. In this respect, vanadium oxide-based cathodes, with open frameworks and rich valence states, have shown promising characteristics toward hosting the Zn 2+ ions. Nevertheless, the degradation of the host during continuous (de-)intercalation and structural dissolution in the aqueous electrolyte affects the capacity and cycle life. Herein, we represent a high capacity and long cycle life AZIB based on an Ag 2 V 4 O 11 @reduced graphene oxide composite as a cathode in 1 M ZnSO 4 electrolyte. We demonstrate the combined effect of the intercalation−displacement mechanism and partially irreversible formation of zinc hydroxyl sulfate as the charge storage mechanism in 1 M ZnSO 4 electrolyte. We observed a comparatively quick capacity fading for the pristine Ag 2 V 4 O 11 ; however, the capacity, rate capability, and cycle stability could be dramatically improved when the Ag 2 V 4 O 11 was hydrothermally grown in situ in the presence of reduced graphene oxide (rGO). The charge storage mechanism, kinetics of charge storage, Zn 2+ diffusion coefficient, effect of cycling on the phase/crystallinity, and morphology of the electrode materials were investigated. A morphological transformation from nanorod to ultrathin sheet/micro-belt-type Ag 2 V 4 O 11 was observed with increasing rGO content. The rGO wrapped the Ag 2 V 4 O 11 sheets/microbelts and thus reduced the charge transfer resistance and provided structural integrity during continuous cycling. The favorable synergism between the Ag 2 V 4 O 11 and optimized rGO content could offer a high initial specific capacity of 328 mA h/g at 0.1 A/g, excellent rate capability with ∼150 mA h/g, specific capacity at 5 A/g, and long cycle stability with only 7% capacity loss over 3000 cycles.

Aging-Responsive Phase Transition of VOOH to V10O24·nH2O vs Zn2+ Storage Performance as a Rechargeable Aqueous Zn-Ion Battery Cathode

“…EIS was carried out within the frequency range of 100 kHz–0.1 Hz and has been represented in terms of Nyquist plots in Figure b. The impedance profiles had a starting depressed semicircle in the mid-frequency range, reflecting the diffusion of the Zn 2+ ions in the surface layer and charge transfer process followed by an approximate linear part in the low-frequency region, reflecting the solid-state diffusion of the ions. , The Nyquist plots were fitted with an equivalent electrical circuit (shown in the inset of Figure b), which consists of a resistor ( R s ) at high frequency, reflecting the total resistance of the electrolyte, separator, and electrical contacts, charge transfer resistance ( R ct ), a pair of constant phase elements corresponding to the surface film and double layer capacitance, and a Warburg impedance ( W ) arising from the Zn 2+ diffusion within the bulk electrode. Notably, all the cells had comparable R s values but had noticeable differences in the semicircle size, reflecting the difference in their interfacial charge transfer resistances.…”

“…Recently, the vanadium-based oxides and their derivatives have been the center of interest due to the variable oxidation states of V (V 2+ to V 5+ ), suitable layer structure, and abundance of active sites for Zn-ion hosting. , Also, an extensive investigation has been performed to modify the crystal structure of the vanadium oxides by introducing different guest cations (Li + , Na + , Ag + , Ca 2+ , Zn 2+ , etc.) to facilitate the Zn 2+ ion insertion/extraction and thereby increase the ZIB performances. ,− In addition, the structural water molecule has been reported to work as a lubricant to facilitate ion (de)­intercalation. − Till date, different vanadium oxides, such as orthorhombic V 2 O 5 , layered V 2 O 5 · n H 2 O, V 10 O 24 , V 3 O 7 ·H 2 O, V 6 O 13 , VO 2 , V 2 O 3 , etc., and metal vanadates with varying vanadium oxidation states (mostly V 5+ or V 4+ or both) and crystal structures have been investigated as aqueous zinc-ion battery (AZIB) cathodes. , However, till now, very few studies focus on low-valent vanadium­(III) materials as the AZIB cathode. Previously, VOOH as the AZIB cathode has been reported to produce zinc vanadium oxide via in situ electrochemical transitions with excellent electrochemical performance.…”

Fabrication of an Energy-Dense, Binder-Free Zn//V5O12·6H2O Solid-State In-Plane Flexible Battery via a Rapid and Scalable Approach

“…VOs have mixed valence (V 2+ to V 5+ ), an open structure, layered frameworks, and an easily controllable interlayer spacing, making them an excellent contender for a wide range of redox-dependent applications. , Much efforts have been made to fabricate zinc-vanadium oxide rechargeable batteries in conventional coin cell configurations. Different phases of VOs, e.g., V 2 O 5 , V 3 O 7 , V 2 O 3 , V 6 O 13 , VO 2 , V 10 O 24 , metal-doped vanadium oxides, , etc., have been explored as cathode materials. − Most approaches have been made through either conventional solvothermal or hydrothermal reactions, and calcination at high temperatures, which requires various hazardous chemicals with a high-temperature synthesis technique and consequently increases the overall cost …”

Poly(3,4-ethylenedioxythiophene) encapsulating hydrated vanadium oxide nanobelts boosts their conductivity and zinc-ion storage properties

“…Among the various cathode materials for AZIBs, such as manganese-based oxides, 22 Prussian blue analogues 4 and vanadium-based materials, 23 vanadium oxides (VOs) have received significant attention due to their diverse open structures and changeable valence states (+5–+2). 24–26 For example, Zhou et al 27 demonstrated that V 2 O 5 exhibits superior electrochemical performance in various electrolytes.…”

“…[16][17][18] To address these issues and improve the electrochemical properties for practical applications, significant progress has been made in promoting the cathode, anode and electrolyte. [19][20][21] Among the various cathode materials for AZIBs, such as manganese-based oxides, 22 Prussian blue analogues 4 and vanadium-based materials, 23 vanadium oxides (VOs) have received significant attention due to their diverse open structures and changeable valence states (+5-+2). [24][25][26] For example, Zhou et al 27 demonstrated that V 2 O 5 exhibits superior electrochemical performance in various electrolytes.…”