Sodium‐Ion Substituted Water Molecule in Layered Vanadyl Phosphate Enhancing Electrochemical Kinetics and Stability of Zinc Ion Storage

Abstract

Vanadyl phosphate (VOPO4·2H2O) has been regarded as one of the most promising cathode materials for aqueous Zn‐ion batteries due to its distinct layered structure. However, VOPO4·2H2O has not yet demonstrated the exceptional Zn ion storage performance owing to the structural deterioration during repeated charging/discharging process and poor intrinsic conductivity. In this work, 2D sodium vanadyl phosphate (NaVOPO4·0.83H2O, denoted as NaVOP) is designed as a cathode material for Zn‐ion batteries, in which sodium ions are preinserted into the interlayer, replacing part of water. Benefiting from the in situ surface oxidization, improved electronic conductivity, and increased hydrophobicity, the NaVOP electrode exhibits a high discharge capacity of 187 mAh g−1 at 0.1 A g−1 after activation, excellent rate capability and enhanced cycling performance with 85% capacity retention after 1500 cycles at 1 A g−1. The energy storage mechanism of the NaVOP nanoflakes based on the rapid Zn2+ and H+ intercalation pseudocapacitance are investigated via multiple ex situ characterizations.

Enhancing reversible Na-ion intercalation by introducing K-ions into layered vanadyl phosphate for sodium-ion battery cathodes

“…Therefore, the collective results of TGA, XRD, Raman and XPS confirm that layered KVOP and NaVOP were successfully synthesized through chemically potassiating and sodiating VOP, respectively, and their compositions were estimated to be K 0. 020) and (220) diffractions can be clearly seen, and the angle between the (200) and (020) planes is 90 • which agrees with the layered structure of VOP [44,46], once again suggesting that the layered structure of VOP remained in KVOP and NaVOP. Using the same precursor to synthesize KVOP and NaVOP can retain the same morphological and structural features between the two, which is crucial to investigate our approach of using K-containing KVOPO 4 to improve the SIB performance in terms of excluding competing factors such as size, orientation, etc.…”

“…Figure 1(c) shows the Raman spectra of KVOP, NaVOP and VOP. VOP has four peaks VOP shows a predominant peak of V 5+ at 517.8 eV [43], with a weak shoulder peak at 517.8 eV, indicating a very small amount of V 4+ , which is possibly due to the partial reduction of V 5+ caused by H 3 O + intercalation during the reflux process and/or vacuum drying process [44]. After being potassiated, KVOP shows only V 4+ signal at 515.9 eV, due to the full reduction of V 5+ to V 4+ accompanied by K intercalation.…”

Bulk-to-surface co-modification of layered hydrated vanadate cathode for aqueous zinc ion batteries

“…This suggests a stronger interaction between Ca and the V–O layer, which may cause water molecules in the layer to be squeezed out, resulting in a smaller CaVO-4 layer spacing compared to that of VO. 39,40 Additionally, the pH level of the precursor solution used in hydrothermal synthesis affects the bound water content of the samples. An acidic environment promotes the formation of bound water, which widens the interlayer spacing.…”

Recent advance and design strategies of chalcogenides for high-performance aqueous zinc-ion batteries

“…Significant advancements have been made in enhancing the electrochemical performance of cathode materials, such as manganese-based oxides [18][19][20], vanadium-based oxides [21][22][23], Prussian blue analogues [24][25][26], and organic compounds [27][28][29]. These materials possess either a tunneltype structure with ion channels or a layered-type structure with large interlayer spacing (figure 1).…”