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The rapid depletion of lithium resources and the increasing demand for electrical energy storage have stimulated the pursuit of emerging electrochemical energy storage. Aqueous zinc ion batteries (ZIBs) are highly sought after for their low cost, high safety, and increased environmental compatibility. However, the search for suitable cathode materials is still tricky for a wide range of researchers. Vanadium oxides (VxOy), with their abundant vanadium valence, easily deformable V−O polyhedrons, and tunable chemical compositions, are of significant advantage in developing emerging materials. This work provides a detailed review of different VxOy for the application in aqueous ZIBs. The current problems and optimization strategies of VxOy cathode materials are systematically discussed. Finally, the current challenges and possible directions for future research of VxOy cathode materials in aqueous ZIBs are presented. [ABSTRACT FROM AUTHOR]

• 1. For the first time, the Li 7 [V 15 O 36 (CO 3)] and γ -LiV 2 O 5 as host materials to store Zn2+. • 2. A larger voltage window (0.2–1.9 V) than most other aqueous zinc ion batteries. • 3. The energy density and power density of the Li 7 [V 15 O 36 (CO 3)] and the γ -LiV 2 O 5 is high. • 4. The Zn2+ storage mechanisms of the Li 7 [V 15 O 36 (CO 3)] and the γ -LiV 2 O 5 are proved. Recently, many reports have been published about polyoxovanadates (POVs) with multiple electrons redox activity for energy storage. However, they are easily transformed into solid-state oxides after calcination. We noted that although dehydrated Li 7 [V 15 O 36 (CO 3)] (Li 7 V 15) exhibited a high capacity for lithium-ion batteries (LIBs), it was reported that the electrochemical behavior of the dehydrated sample same as γ -LiV 2 O 5 (γ -LVO) which prepared by annealing the cluster and undehydrated Li 7 V 15 was not redox-active. Interestingly, we were surprised to find that undehydrated Li 7 V 15 and its derivative γ -LVO showed better electrochemical performance than LIBs when first proposed as the cathode to store Zn2+. Both Li 7 V 15 and γ -LVO electrodes provided excellent rate performance and satisfied cyclability (135.0 and 214.1 mAh g−1 at 3 A g−1 after 1000 cycles, respectively). The fast kinetics of Li 7 V 15 and γ -LVO were verified by pseudocapacitive analysis, GITT and EIS tests. Moreover, the Zn2+ storage mechanism and redox behavior of Li 7 V 15 and γ -LVO were examined by ex-situ measurements. First-principles calculations revealed that the Zn2+ was chemisorbed on the clusters and physisorbed between the clusters. This work enriches the POVs cathode chemistry in aqueous energy storage. [ABSTRACT FROM AUTHOR]

[Display omitted] • This work summarizes the application of vanadium oxides as aqueous ZIBs cathodes. • Electrochemical properties and energy storage behavior of different types of vanadium oxide cathodes. • Current challenges and expected development foregrounds of vanadium oxides cathodes in aqueous ZIBs are proposed. The rapid development of science and technology, as well as the trend toward intelligence, has resulted in a surge in the demand for excellent energy storage devices for smart devices. At present, the most widely used lithium ion batteries have limited further development because of their high cost and various disadvantages of electrolytes (flammable and toxic). In spite of the low costs and safety of aqueous zinc-ion batteries, the high radius of the zinc ions and strong electrostatic interactions make cathode materials without excellent performance difficult to find. Various oxidation states, structural diversity, excellent multiplicity performance and high capacity have attracted researchers to vanadium-based oxides in recent years. However, vanadium-based oxides have disadvantages such as poor structural stability and low electrical conductivity, so this paper summarizes the progress of research on vanadium oxide cathode materials such as V 2 O 5 , VO 2 , V 2 O 3 , etc., and provides an outlook on future development directions. [ABSTRACT FROM AUTHOR]

[Display omitted] Vanadate, as an advanced inorganic material, has been a major object of scientific research due to its flexible valence states and the multi-electron transfer mechanism of vanadium. This review concentrates on the application of vanadates in aqueous ZIBs, which facilitates researchers to understand the latest research progress on vanadate-based cathodes for ZIBs. Furthermore, the limitations of current vanadate-type cathodes are pointed out and the perspectives for their application in emerging energy storage areas are presented. • This work comprehensively summarizes the application of vanadates as aqueous ZIBs cathodes. • Electrochemical performance and energy storage behavior of vanadates cathodes are further discussed. • Current challenges and expected development foregrounds of vanadates cathodes in aqueous ZIBs are proposed. With the increasing pursuit of electronic products with high specific energy and outstanding environmental compatibility, developing advanced new power sources is urgent. As the representative of new energy, rechargeable aqueous zinc ion batteries (ZIBs) have gained much focus recently in the field of energy storage owing to their advantages of safety, cost-effectiveness, and environmental sustainability. Nevertheless, the progression of suitable Zn-storage cathode materials remains a huge challenge, limited by commercial requirements. Vanadate, as an advanced inorganic material, has been a major object of scientific research due to its flexible valence states and the multi-electron transfer mechanism of vanadium. Undeniably, understanding the electrochemical Zn-storage properties and mechanisms of this class of materials plays a crucial role in facilitating their development. However, there is a paucity of reviews on vanadates as cathodes for aqueous ZIBs. This review concentrates on the application of vanadates in aqueous ZIBs, which facilitates researchers to understand the latest research progress on vanadate-based cathodes for ZIBs. Finally, the limitations of current vanadate-type cathodes are pointed out and the perspectives for their application in emerging energy storage areas are presented. [ABSTRACT FROM AUTHOR]

For cost and safety reasons, aqueous batteries are suitable for large-scale energy storage. Among all aqueous batteries, the rechargeable aqueous zinc ion batteries (ZIBs) are promising choices owing to the low equilibrium potential and high volumetric capacity of zinc. However, its development is also severely hindered by the limited available cathode materials, which generally display poor cycling capabilities. As one of the most investigated POVs (polyvanadates) today, (V 10 O 28)6− has been demonstrated to be feasible in the energy storage rely on the well-defined structure and fascinating material activity. Herein, we propose a polyvanadate-Na 6 V 10 O 28 with (V 10 O 28)6− anion as a support structure and serve it for the first time as aqueous ZIBs cathode. The high stability of the (V 10 O 28)6− cluster permits the material to tolerate the reversible (de)insertion of Zn2+. As a result, the Na 6 V 10 O 28 cathode delivers a high capacity of 279.5 mAh g−1 and extraordinary lifespan over 2000 cycles. Furthermore, the pseudocapacitance analysis and GITT test reveal the pseudocapacitance behavior and high Zn2+ diffusion coefficient (10−10 cm2 s−1) of the Na 6 V 10 O 28 /Zn cell, respectively. Not only that, ex-situ XRD, XPS, and TEM are also employed to analyze the storage mechanism of Zn2+, indicating the synergistic Zn-storage capacity of Na 6 V 10 O 28 and irreversible products. Overall, this work presents new insights into the application of Na 6 V 10 O 28 in aqueous ZIBs and also demonstrates the competitive potential of POVs for energy storage. [Display omitted] • For the first time, the Na 6 V 10 O 28 cathode is applied for aqueous zinc ion batteries. • Na 6 V 10 O 28 delivers excellent cycling stability and the high specific discharge capacity. • The Zn2+ ion diffusion rate of Na 6 V 10 O 28 is as high as 10−10 cm2 s−1. • The high reversibility of Zn2+ insertion/extraction in Na 6 V 10 O 28 is demonstrated by ex-situ XRD. For cost and safety reasons, aqueous batteries are suitable for large-scale energy storage. Among all aqueous batteries, rechargeable aqueous zinc-ion batteries (ZIBs) are promising choices owing to the low equilibrium potential and high volumetric capacity of zinc. However, its development is also severely hindered by the limited available cathode materials, which generally display poor cycling capabilities. As one of the most investigated POVs (polyvanadates) today, (V 10 O 28)6− has been demonstrated to be feasible in energy storage rely on the well-defined structure and fascinating material activity. Herein, we propose a polyvanadate-Na 6 V 10 O 28 with (V 10 O 28)6− anion as a support structure and serve it for the first time as an aqueous ZIBs cathode. The high stability of the (V 10 O 28)6− cluster permits the material to tolerate the reversible (de)insertion of Zn2+. As a result, the Na 6 V 10 O 28 cathode delivers a high capacity of 279.5 mAh g−1 after activation and an extraordinary lifespan over 2000 cycles. Furthermore, the pseudocapacitance analysis and GITT test reveal the pseudocapacitance behavior and high Zn2+ diffusion coefficient (10−10 cm2 s−1) of the Na 6 V 10 O 28 /Zn cell, respectively. Not only that, ex-situ XRD, XPS, and TEM are also employed to analyze the storage mechanism of Zn2+, indicating the synergistic zinc-storage capacity of Na 6 V 10 O 28 and irreversible products. Overall, this work presents new insights into the application of Na 6 V 10 O 28 in aqueous ZIBs and also demonstrates the competitive potential of POVs for energy storage. [ABSTRACT FROM AUTHOR]