Synthesis, Characterization and Electrochemical Evaluation of Layered Vanadium Phosphates as Cathode Material for Aqueous Rechargeable Zn-ion Batteries

Abstract

The potential application of rechargeable multivalent ion batteries in portable devices and renewable energy grid integration have gained substantial research interest in aqueous Zn-ion batteries (ZIBs). Compared to Li-based batteries, ZIBs offer lower costs, higher energy density, and safety that make them more attractive for energy storage in grid integration applications. Currently, more research is required to find a suitable cathode material for ZIBs with high capacity and structural stability during charge/discharge cycling. Vanadium phosphate (VOP) compounds as cathode material for ZIBs have been of particular interest, owing to vanadium’s diverse oxidation states. In this present work, two VOP compounds, [H0.6(VO)3(PO4)3(H2O)3].4H2O and VOPO4.2H2O, were synthesized from phosphoric acid and different sources of vanadium via a simple hydrothermal method. Various characterization techniques were carried out, revealing the layered structure of both products and high purity of [H0.6(VO)3(PO4)3(H2O)3].4H2O. Zn/VOP batteries were prepared using Zn metal as counter and reference electrode and 3 M ZnSO4.7H2O as electrolyte. Electrochemical tests were conducted to evaluate the cycling performance of VOPs as cathode material for aqueous Zn-ion batteries. Based on the results, both compounds have shown highly reversible Zn-ion intercalation and deintercalation. VOPO4.2H2O achieved a higher specific capacity of up to 85 mAh/g during discharging, as opposed to 65 mAh/g for the hydrated VOP complex. However, [H0.6(VO)3(PO4)3(H2O)3].4H2O is more stable with higher reproducibility than VOPO4.2H2O during cycling. Nevertheless, more research is still required to enhance the specific capacity and improve the cycling performance of VOP-based cathodes for their prospective use in aqueous ZIBs.

Multifunctional Carbon Modification Enhancement for Vanadium-Based Phosphates as an Advanced Cathode of Zinc-Ion Batteries

“…In the crystal structure of VOPO 4 •2H 2 O, a two-dimensional VO 6 -PO 4 plate was built on the base plane, and the produced VOPO 4 layer was joined along the C-axis by water molecules. 34 This robust layered structure can accommodate the intercalate/deintercalate of divalent Zn 2+ while preserving the lattice integrity during cycling. However, the low electrical conductivity, sluggish ion diffusion kinetics, and facile solubility in aqueous electrolytes of VOPO 4 •2H 2 O during the charging and discharging process induce its structural collapse and poor cycle stability, which impedes its future utilization.…”

“…The cathode materials of ZIBs consist primarily of manganese oxides, vanadium oxides, polyanionic compounds, analogues of Prussian blue, and organic compounds. , As a cathode material, vanadium oxide phosphate has been extensively investigated due to its layered structure and abundance of electrochemically active sites. In the crystal structure of VOPO 4 ·2H 2 O, a two-dimensional VO 6 -PO 4 plate was built on the base plane, and the produced VOPO 4 layer was joined along the C -axis by water molecules . This robust layered structure can accommodate the intercalate/deintercalate of divalent Zn 2+ while preserving the lattice integrity during cycling.…”

Vanadium Oxide with Elevated Interlayers for Durable Aqueous Hybrid Li+/Zn2+ Batteries

“…22 Mn-doped V 10 O 24 , 23 VO 2 , 24 and V 6 O 13 25 cathodes also have been synthesized and applied to ZIBs for improving the stability and electrochemical performance. 26,27 Based on previous literature, the important and positive effects of preinserted Li + , Na + , K + , and Mn 2+/3+ ions can be speculated: (1) These alien ions serving as "pillars" play a key role to stabilize the crystal structure; (2) increased more active sites contribute to enlarged specific surface area and facilitated electrochemical activity; (3) the improved interlayer distance is conducive to the repeated ion insertion/extraction; (4) restraining dissolution of vanadium oxides in aqueous solutions promotes cycling lifespan. 18−20 Further, the synergetic effect of multiple ions has been determined by cathode materials, boosting the transport of ions and the enhancement of electrochemical performance.…”

Electrodeposited Layered Sodium Vanadyl Phosphate (NaxVOPO4·nH2O) as Cathode Material for Aqueous Rechargeable Zinc Metal Batteries

“…There are few recent reports, which demonstrate the stable cycling of VOPO 4 ·2H 2 O in mild electrolyte-based ARZMBs, eliminating the requirement of concentrated electrolytes, unlike VOPO 4 . , Compared to VOPO 4 , the structure of VOPO 4 .nH 2 O consists of pre-intercalated water molecules in the interlayer galleries of the VOPO 4 layers, resulting in increased interlayer spacing beyond 7.0 Å. , The improved interlayer spacing provides a cushioning effect, minimizing the strain developed during the insertion/extraction of large-sized hydrated Zn 2+ ions, preventing the collapse of the VOPO 4 crystal structure even in mild electrolytes. Besides, the charge shielding effect induced by the intercalated H 2 O and increased interlayer spacing help in decreasing the electrostatic repulsive interactions between the Zn 2+ ions and the host, facilitating the reversible insertion/extraction process. ,, There are also attempts to further increase the VOPO 4 .nH 2 O layer spacing by intercalation of foreign species such as organic molecules. , For instance, Hu et al.…”

“…There are few recent reports, which demonstrate the stable cycling of VOPO 4 •2H 2 O in mild electrolyte-based ARZMBs, eliminating the requirement of concentrated electrolytes, unlike VOPO 4 . 36,37 Compared to VOPO 4 , the structure of VOPO 4 .nH 2 O consists of pre-intercalated water molecules in the interlayer galleries of the VOPO 4 layers, resulting in increased interlayer spacing beyond 7.0 Å. 22,32 The improved interlayer spacing provides a cushioning effect, minimizing the strain developed during the insertion/extraction of large-sized hydrated Zn 2+ ions, preventing the collapse of the VOPO 4 crystal structure even in mild electrolytes.…”