Recent Progresses on Vanadium Sulfide Cathodes for Aqueous Zinc-Ion Batteries

Abstract

Aqueous zinc-ion batteries are considered one of the promising large-scale energy storage devices of the future because of their high energy density, simple preparation process, efficient and safe discharge process, abundant zinc reserves, and low cost. However, the development of cathode materials with high capacity and stable structure has become one of the key elements to further development of aqueous zinc-ion batteries. Vanadium-based compounds, as one of the cathode materials for aqueous zinc-ion batteries, have various structures and high reversible capacities. Among them, vanadium-based sulfides have higher academic ability, better electrochemical activity, lower ion diffusion potential barrier, and a faster ion diffusion rate. As a result, vanadium-based sulfides have received extensive attention and research. In this review, we summarize the recent progress of vanadium-based sulfides applied in aqueous zinc-ion batteries, highlighting their effective strategies for designing optimized electrochemical performance and the underlying electrochemical mechanisms. Finally, an overview is provided of current vanadium-based sulfides and their prospects, and other perspectives on vanadium-based sulfide cathode materials for aqueous zinc-ion batteries are also discussed.

1. Introduction

As traditional fossil fuels continue to deplete and due to the gradual increase in the greenhouse effect, there are growing concerns about energy scarcity and environmental issues [1,2,3]. It has become an essential strategy for sustainable development to vigorously develop and replace traditional fossil fuels with reliable, clean, renewable energy. However, wind, solar, and tidal energy, which are constrained by natural conditions, have insufficient effective utilization to support their application in energy storage systems on a large scale. Therefore, it is indispensable to develop new energy conversion and storage systems with high efficiency, low cost, stability, and safety [4,5,6]. Lithium-ion batteries are one of the most widely used electrochemical energy storage systems in commercial applications due to their high energy density, long cycle life, and proven preparation processes. They are attempting to be incorporated into a wide range of power grids in the near future. However, lithium-ion batteries are expensive to manufacture due to the limited global resources of lithium metal. In addition, environmental pollution caused by using organic electrolytes seriously hinders their further development and large-scale application [7,8,9].

Therefore, research workers have turned their attention to secondary aqueous metal-ion batteries, which are abundant in reserves and environmentally friendly [10,11]. Among many aqueous metal-ion batteries, aqueous zinc-ion batteries (AZIBs) have received extensive research for their low cost, high safety, simple fabrication process, high theoretical capacity of 820 mAh·g⁻¹ (~5855 mAh·cm⁻³) of the zinc metal anode, low redox potential of −0.76 V (vs. ~SHE), high stability, etc., all unique advantages that make these batteries widely studied [12,13,14,15,16,17,18,19]. With the development of AZIBs, it has been widely studied that manganese-based compounds, vanadium-based compounds, and Prussian blue analogs can be used as zinc-ion battery cathodes [20]. Manganese-based compounds (MnO₂) [21,22,23] and vanadium-based oxides (V₂O₅) cannot meet the ideal practical requirements due to their unstable crystal structures and poor cycling performance [24], while Prussian blue analogs [Zn₃(Fe(CN)₆)₂] have small capacities (~±50 mAh·g⁻¹) that hinder their practical applications, although their crystal structures are stable [20,25,26,27]. Therefore, developing cathode materials with stable crystal structures and excellent cycling stability is essential to promoting the development of aqueous Zn-ion batteries [28,29,30,31,32].

Based on the variable valence (standard valence states of +2, +3, +4, and +5) and the active nature of the vanadium element, it can carry out multiple electronic transfer redox reactions and thus exhibits a high capacity [25,28,33,34]. Vanadium-based sulfide nanomaterials, due to their unique structure, abundant redox activity, fast ion diffusion kinetics, and low ion diffusion potential, determine them to be a good choice as materials for zinc-ion batteries with aqueous cathodes [35,36,37,38,39]. Figure 1 shows typical types of vanadium-based sulfides and describes the advantages and disadvantages of vanadium-based sulfides for use in aqueous zinc-ion batteries. As the chemical composition and valence of vanadium changes, it allows vanadium atoms to combine with sulfur atoms to exhibit a diverse range of material species, as well as exhibit diverse structures such as layered structure (VS₂), chain-like structure (VS₄), and tunnel structure (V₅S₈), which also determine the various properties of vanadium-based sulfides. Currently, the investigation of V-based sulfides is still at a relatively early stage. There are no articles that review and analyze the recent progress of vanadium-based sulfides as AZIB cathodes. In this review, we summarize recent developments in vanadium-based sulfides as cathode materials for AZIBs, highlighting the mechanisms of zinc-ion storage in the materials and effective ways to optimize electrochemical performance. Finally, some reasonable insights into the current challenges and future applications of vanadium-based sulfides are presented, which may shed light on the research and development of new high-performance vanadium-based sulfide cathode materials for AZIBs.

2. VS₂ and Its Composites in AZIBs

Two-dimensional layered transition metal disulfides (TMDs) have the structural formula MX₂, where M represents transition metal elements, including titanium, vanadium, molybdenum, tungsten, and tantalum, and X represents sulfur group elements, including sulfur, selenium, etc. Based on their unique two-dimensional layered crystal structure and diverse chemical composition, they are not only beneficial as ion transport carriers to accommodate the volume changes during ion insertion but also make these materials have wonderful optoelectronic properties that can be widely used for energy conversion and harvesting [37,40,41,42,43].

VS₂, one of the most common types of TMDs, has a typical two-dimensional layered crystal structure composed of an open sandwich structure of S-V-S, with adjacent layers bonded together by weak van der Waals forces with a layer spacing of 5.76 Å. The large layer spacing also facilitates the insertion/withdrawal of monovalent metal ions (Li⁺~0.69 Å, Na⁺~1.02 Å) and multivalent metal ions (Zn²⁺~0.74 Å, Mg²⁺~1.32 Å), thus enabling fast ion diffusion [44,45]. In addition, in the VS₂ crystal structure, each V atom is surrounded by six sulfur atoms and connected by covalent bonds to S atoms, which belong to the hexagonal crystal system. The advantages of VS_2, such as good metallic properties, high conductivity (~5.0 × 10² S·m⁻¹), and faster ion diffusion rate than 2D layered graphene, make VS₂ widely studied and applied as a novel cathode material [46].

Mai’s team [47] prepared VS₂ nanosheets with thicknesses of 50–100 nm by a simple one-step hydrothermal method and used them for the first time as a cathode material for AZIBs (Figure 2a,b). Subsequently, metallic zinc was used as the anode, a weakly acidic salt solution (ZnSO₄) as the electrolyte, and glass fibers as the isolator (Figure 2c). In the voltage interval of 0.4–1.0 V, the nanosheets exhibited a high reversible capacity of 190.3 mAh·g⁻¹ at 0.05 A·g⁻¹ at current density. As of 200 cycles with a current density of 0.5 A·g⁻¹, the capacity retention rate was 98.0%, demonstrating that VS₂ has long-term cycling stability as a cathode material for AZIBs. As shown in Figure 1d, they investigated the storage mechanism of the Zn/VS₂ system during charging and discharging by non-in situ XRD tests. As the discharge process proceeded, the intensity of the characteristic peak located at 15.4° (001) gradually decreased slightly, and its position shifted to the left, which was caused by the interlayer spacing of the insertion of Zn²⁺ into the crystal plane of (001) being enlarged during the discharge process. Instead, when fully charged, the intensity and position of the characteristic peaks of the (001) crystal plane return to the initial state due to the extraction of Zn²⁺ during the charging process, as shown by the ex situ XRD results of the structural evolution being fully reversible during the discharge/charging process. In addition, in situ Raman, ex situ SAED, ex situ XPS, and ex situ HRTEM tests also demonstrated the reversibility of the structure evolution, which is consistent with ex situ XRD results. The following is a summary of the electrochemical reaction between Zn/VS₂ electrodes.

In the cathode:

VS₂ + 0.09Zn²⁺ + 0.18e⁻ ↔ Zn_0.09VS₂

(1)

Zn_0.09 VS₂ + 0.14Zn²⁺ + 0.28e⁻ ↔ Zn_0.23VS₂

(2)

In the cathode:

Zn²⁺ + 2e⁻ ↔ Zn

(3)

However, as a result of structural instability during charging and discharging, VS₂ cathode materials have been seriously hindered in their development [37]. The Du team [48] constructed fluffy and porous VS₂/VO_x cathode materials by in situ electrochemical pretreatment (first charging to 1.8 V) (Figure 2e–i), taking advantage of the chemical instability of VS₂ in aqueous electrolytes. Because of the internal electric field of the heterogeneous interface, the high conductivity of VS₂, and the high chemical stability of VO_x (V₆O₁₃/VO₂/V₂O₅), the average working potential of VS₂/VO_x with a heterogeneous structure is increased by 0.25 V. A high current density of 10.0 A g⁻¹ produces a high capacity of 156 mAh g⁻¹ at voltages between 0.2 and 1.8 V, with a capacity retention rate of 75% at a high current density of 1 A g⁻¹ after 3000 cycles. In addition, Figure 2j illustrates the VS₂/VO_x shift of the diffraction peak of VS₂/V₆O₁₃/V₂O₅ in ex situ XRD, proving the process of Zn²⁺ de-intercalation.

In addition to in situ electrochemical oxidation, with the in-depth study of VS₂, Jiao’s team [49] used glucose as a template to prepare 1T-VS₂ nanospheres by a one-step hydrothermal method (Figure 3a,b). It strengthened the layered structure of VS₂ by simply modulating the charge cut-off voltage, which allowed a part of Zn²⁺ to reside in the interlayer as zinc pillars during repeated insertion/extraction. The 1T-VS₂ nanospheres with abundant active sites and stable layered structure facilitate the penetration of the aqueous electrolyte and ensure rapid electron/ion transfer, resulting in excellent rate performance and an ultra-long cycle life of the material in AZIBs. These nanospheres demonstrated excellent reversible capacities of 212.9 and 102.1 mAh·g⁻¹ at current densities of 0.1 and 0.5 A·g⁻¹, respectively, in the voltage range of 0.4–0.85 V. At a current density of 2A·g⁻¹ and 2000 cycles, the capacity retention was 86.7%. As shown in Figure 3c,d, the results by ex situ XRD indicate that the shift in the diffraction peak of (001) indicates the existence of an electron/ion reversible insertion/desertion process. When charged to 1.0 V, the (001) diffraction peak completely returns to its original position, compared to 0.85 V, where the (001) diffraction peak is still on the left side of the original position, indicating that some Zn²⁺ is still present in the interlayer of VS₂. The results of ex situ XPS, ex situ HRTEM, and ex situ EDX are consistent with ex situ XRD results (Figure 3e–i). In contrast, in the voltage range of 0.4–1.0 V, the “dead Zn²⁺” residing in the VS₂ nanospheres can completely separate from the layers due to the large charging cutoff voltage. With the charge and discharge cycle, the 1T-VS₂ nanospheres are prone to structural collapse. As a result, the electrochemical performance of the material at 1.0 V is decreased compared with that at 0.85 V (Figure 3j).

Binders are generally electrochemically inert substances, and their presence reduces the specific gravity of the active material of cathode materials; developing binder-free cathode materials is a new idea to enhance the specific capacity of batteries [50,51,52,53]. To solve this problem, the composite method of cathode material and carbon-based material can not only enhance the material’s overall conductivity, promote the electrochemical reaction kinetics, and improve the rate performance, but also effectively alleviate the instability of the layered structure of VS₂. Wang’s team [54] prepared rose-like nanoflowers composed of VS₂ nanosheets by a simple one-step hydrothermal method, and by vacuum filtration after ultrasonication in a DMF solution C-VS₂ thin films were prepared (Figure 4a,b). The electrode films prepared by chemical bond integration under binder-free conditions enhance the interaction forces and provide fast electron transfer kinetics. In the voltage interval of 0.3–1.5 V, the composite films exhibited high specific capacities of 205.3 and 135.4 mAh·g⁻¹ and excellent rate performance at the current densities of 0.1 and 10.0 A·g⁻¹, respectively, and at current densities of 0.5 and 5 A·g⁻¹ capacity retention rates of 90% and 72% after 200 and 1500 cycles, respectively. In addition, the high percentage of the active material of the cathode material and the high electrical and mechanical conductivity of the SWCNTs also make the C-VS₂ film highly conductive and flexible, so that the soft-pack battery composed of C-VS₂ film exhibits stable electrochemical performance under different bending states. When the bending radii of the soft-pack battery are 2.0 cm and 1.0 cm, the discharge capacities of the device are 129.6 mAh·g⁻¹ in the 40th cycle and 127.5 mAh·g⁻¹ in the 61st cycle (Figure 4c,d illustrate that only 2.1 mAh·g⁻¹ of battery discharge capacity was lost following the bending test).

3. VS₄ and Its Composites in AZIBs

VS₄ was first discovered in the Whinstone mineral, and its crystal structure was elucidated in 1964 and has been widely studied in recent years as an AZIB cathode material with high performance [55,56,57].

The crystal structure of VS₄ is a one-dimensional “linear atomic chain” compound consisting of V⁴⁺ with two sulfur dimers (S₂²⁻)₂ coordinated along the c-axis; Figure 5a shows the results [58]. Each VS₄ atomic chain is held together by weak van der Waals forces between the bond, and the spacing between the atomic chains is 5.83 Å [59], which is significantly larger than the effective ionic diameter of Zn²⁺ (0.74 Å) [16]. There are plenty of active sites for Zn²⁺ storage and diffusion between the open channels between the atomic chains.

However, an electrochemical reaction’s kinetics are affected by the poor electron/ion conductivity of VS₄, and this makes electrode materials challenging to meet high-performance requirements [60,61,62]. Wang’s team [63] prepared VS₄@rGO nanomaterials with a simple hydrothermal method and used them as high-performance positive electrode materials for AZIBs (Figure 5b). The use of rGO with superior electrical conductivity as the conductive substrate [60,64,65] improves the electrical conductivity of the VS₄@rGO composite, enabling the electrode material to maintain a capacity retention rate of 93.3% while providing a high capacity of 180 mAh·g⁻¹ after 200 cycles at a current density of 1 A·g⁻¹. Additionally, the reaction process is accompanied by the formation of Zn₃(OH)₂V₂O₇·2H₂O and sulfur, per the ex situ XRD data (Figure 5c), and with the reversible shift of the (011) crystal plane also suggests a reversible insertion/extraction reaction mechanism of Zn²⁺:

2VS₄ + 11H₂O + 3Zn²⁺ → Zn₃(OH)₂V₂O₇·2H₂O + 8S + 16H⁺ + 10e⁻

(4)

VS₄ + xZn²⁺ + 2xe⁻ ↔ Zn_xVS₄

(5)

Similarly, Sun’s team [66] used a one-step hydrothermal method to prepare nano-flower-like VS₄/CNT cathode materials with a rich mesoporous structure (Figure 5d), which increased the contact area with the electrolyte, shortened the diffusion distance of Zn²⁺, and improved the electron transport capacity of the cathode. High reversible capacities of 265 and 182 mAh·g⁻¹ were provided at current densities of 0.25 and 7 A·g⁻¹, respectively, and it has a 93% capacity retention rate after 1200 cycles at a current density of 5 A·g⁻¹. As shown in Figure 5e,f, the charge/discharge cycle in the first turn is significantly different from the subsequent charge/discharge cycles, indicating the occurrence of a phase transition in the first turn. Based on ex situ XRD and XPS, the mechanism of the phase change reaction of VS₄ during the first cycle and the reversible intercalation of Zn²⁺ during the subsequent cycles are described (Figure 5g–i). In the first discharge process (1D 1.0~0.2 V), the characteristic peak of VS₄ gradually weakened, and the crystalline phase of ZVO (Zn₃(OH)₂V₂O₇.2H₂O) and monomeric S appeared. During the following charging process, the characteristic peak of ZVO still exists, and the characteristic peak of the resulting monomeric sulfur disappears as it is dissolved in the electrolyte. As shown in Figure 4j, the relevant reaction mechanisms following the phase change are given:

VS₄ + 11H₂O + 3Zn²⁺ + 6e⁻ → Zn₃(OH)₂V₂O₇·2H₂O + 4S₂²⁻ + 8H⁺ + 4H₂

(6)

The acidic conditions are as follows:

H₂S₂ → S + S²⁻ + 2H⁺

(7)

In order to further improve zinc-ion storage capacity, the construction of heterogeneous structures with sufficient interfaces and grain boundaries is a highly promising and effective strategy. Cheng’s team [67] used as a proof of concept the oxidation of VS₄ prepared by a one-step hydrothermal method to a VS₄/V₂O₃ heterostructure in a tube furnace after depilatory oxidation in contact with an external source of oxygen. Concomitantly, by comparing with the precursor VS₄ and the fully converted product V₂O₃, the VS₄/V₂O₃ heterostructure has a higher zinc-ion storage capacity, providing a capacity of 163 mAh·g⁻¹ at a current density of 0.1 A g⁻¹ in the voltage range of 0.3–1.2 V, which is much higher than that of VS₄ (47 mAh·g⁻¹) and V₂O₃ (74 mAh·g⁻¹) in the same voltage range.

Similarly, Du’s team [68] again used an in situ electrochemically induced phase transition method (the same method used to prepare VS₂/VO_x heterostructures) to prepare S/VO_x composites by simple in situ electrochemical oxidation using VS₄ as a precursor. The initial discharge capacity of 376 mAh·g⁻¹ was provided at a current density of 0.05 A·g⁻¹ in the voltage range of 0.1–1.8 V, and 260 mAh g⁻¹ at a current density of 2 A·g⁻¹, with 100% capacity retention after 2000 cycles, demonstrating the excellent rate performance and ultra-long cycle life of the composites. Combined with ex situ XRD, a reversible insertion and removal of Zn²⁺ after phase transition has been demonstrated as an energy storage mechanism.

4. Other Vanadium Sulfides and Their Composites in AZIBs

Due to their chemical stability, variety of crystal structures, and high electrical conductivity, intermediate transition metal–sulfur compounds (TMDCs) are frequently utilized as cathode materials in metal-ion battery systems [41]. However, when repeated cycling is performed on layered TMDC materials, the high polarization of zinc ions can result in structural collapse and severe anisotropic diffusion, leading to a weakened zinc-ion intercalation efficiency and reduced electrical resistance [15,38,49,69,70]. These intrinsic shortcomings are a serious impediment to further developing stable, high-rate, layered TMDCs as cathode materials. The solution to these issues lies in designing TMDCs with tunnel-like structures or unique NiAs structures, which is a potentially effective strategy.

4.1. V₅S₈

Zhu’s team [71] developed a V₅S₈ cathode material with a tunnel-like structure and applied it to AZIBs for the first time. By a simple calcination method, depletion in an Ar atmosphere caused the dimeric S₂²⁻ to monomeric S²⁻ transformation in VS₄, thus facilitating the phase transition from one-dimensional chained VS₄ to tunneled V₅S₈ (Figure 6a,b). Due to ordered vacancies in a NiAs-type structure, vanadium atoms in V₅S₈ partially occupy one-fourth of the available S-S octahedral sites between two adjacent VS₂ monolayers. This creates multiple ion paths that enable quick and reversible de-embedding of zinc ions while ensuring structural and electrochemical property stability. As a result, the V₅S₈ cathode material provides a high specific capacity of 240 mAh·g⁻¹ at a current density of 0.1 A·g⁻¹, exhibits an excellent rate performance of 193.8 mAh·g⁻¹ at a current density of 10 A·g⁻¹, and has a capacity retention rate of 94% after 1000 cycles. In addition, as shown in Figure 6c,d, V₅S₈ exhibits stronger metallic properties, lower hopping energy barriers, and better Zn ion diffusion paths based on density flooding theory calculations (DFT). As shown in Figure 6e–h, sequential and reversible H⁺, Zn²⁺ de/intercalation reaction mechanisms are also proposed based on in situ XRD and ex situ XPS characterization:

Cathode:

xZn²⁺ + 6yH⁺ + V₅S₈ + 2(x + 3y) e⁻ ↔ H_6yZn_xV₅S₈

(8)

4y[Zn(H₂O)₆]²⁺ + ySO₄²⁻ ↔ yZn₄(OH)₄SO₄·5H₂O + 13yH₂O + 6yH⁺

(9)

Anode:

(x + 3y)Zn ↔ (x + 3y)Zn²⁺ + 2(x + 3y) e⁻

(10)

4yZn²⁺ + 24yH₂O ↔ 4y[Zn(H₂O)₆]²⁺

(11)

Overall:

(x + 3y)Zn + yZnSO₄ + 11yH₂O + V₅S₈ ↔ yZn₄(OH)₆SO₄·5H₂O + H_6yZn_xV₅S

(12)

4.2. V₃S₄

An essential member of the vanadium sulfide family, as shown in Figure 7a, V₃S_4, with its unique NiAs type, usually occurs as V_0.5VS₂ (consisting of a VS₂ monomolecular layer and a 0.5V atom linking two adjacent layers. In this structure, due to the intense contact between the V³⁺ and V⁴⁺ cations, the intercalated V atoms (V³⁺) exhibit metallic conduction along the c-axis direction, which should aid in the transmission of electrons along their c-axis path [72,73,74,75,76,77].

Pan’s team [78] developed a composite cathode material with a NiAs-type structure of V₃S₄. As shown in Figure 7b,c, the material was first prepared by electrostatic spinning and calcination of a new composite flexible carbon matrix (a novel composite flexible substrate containing acidified halloysite, carbon fibers, and carbon nanotubes) with high electrical conductivity and strong hydrophilicity, followed by a one-step hydrothermal method to obtain nanospherical V₃S₄ attached to the filamentary new composite flexible carbon matrix, which was applied to flexible AZIBs. The composite cathode material HCC-V₃S₄ has a high specific capacity of 148 mAh·g⁻¹ after 200 cycles at a current density of 0.5 A·g⁻¹ and a specific capacity of 102 mAh·g⁻¹ after 1000 cycles at a current density of 5 A·g⁻¹ in the voltage range of 0.5–1.5 V. This design of loading nanomaterials onto conductive carbon substrates promotes electron transfer and avoids using conductive agents and binders, thus improving electrochemical properties. The energy storage device’s carbon substrate’s increased surface hydrophilicity also enhances the composite’s electrochemical characteristics. In addition, the energy storage mechanism of the HCC-V₃S₄ cathode was investigated by a series of non-in situ characterizations, as shown in Figure 7d–h. In addition, the reaction expression is proposed for Zn₄SO₄(OH)₆·5H₂O generated during the charging process:

4Zn²⁺ + 6OH⁻ + SO₄²⁻ + 5H₂O ↔ Zn₄SO₄(OH)₆·5H₂O

(13)

5. Summary and Outlook

AZIBs, as new green and environmentally friendly secondary batteries, are widely studied for their low production cost, high safety, simple preparation process, and environmental friendliness, and are expected to be widely used in areas such as large-scale energy storage and electronic devices. As an extremely promising cathode material for AZIBs, vanadium-based sulfides show great potential for development in AZIBs due to their low development costs, diverse material combinations, rich crystal structures (layer, chain, and tunnel), and valence changes (V²⁺, V³⁺, V⁴⁺, and V⁵⁺).

Table 1. Summary of the structure and mechanism of vanadium sulfide cathode materials in AZIBs.

Types of Vanadium Sulfides	Crystal Structure Models	Interplanar Crystal Spacing (Å)	Reaction Mechanisms	Ref.
VS2		5.76	Interlayer mechanism	[50]
VS4		5.83	Transformation/ interlayer mechanism	[58]
V5S8		11.32	Interlayer mechanism	[71]
V3S4		5.681	Interlayer mechanism	[78]

summarizes the structure and reaction mechanisms of different types of vanadium sulfides in AZIBs.

In this review, we provide an overview of recent research advances in vanadium-based sulfide and their composites as cathode materials for aqueous zinc-ion batteries and highlight their various design strategies and the structural characteristics and energy storage mechanisms of the materials, providing some insights into the design of new high-performance cathode materials for AZIBs and facilitating the practical application of AZIBs. The main direction of the application of vanadium-based sulfides in AZIBs is their use as cathode materials. Figure 8 and

Table 2. Summary of electrochemical performance of vanadium sulfide cathode materials in AZIBs.

Cathode Material	Electrolyte	Voltage Range (V)	Capacity (mAh·g−1@A g−1)	Cycle Stability	Ref.
VS2	1 M ZnSO4	0.4–1.0	[email protected]	98% after 200 cycles at 0.5 A g−1	[47]
VS2@VOOH	3 M ZnSO4	0.4–1.0	[email protected]	82% after 400 cycles at 2.5 A g−1	[79]
VS2@SS	1 M ZnSO4	0.4–1.0	[email protected]	80% after 1600 cycles at 1.0 A g−1	[50]
rGO-VS2	3 M Zn (CF3SO3)2	0.2–1.8	[email protected]	93% after 1000 cycles at 5.0 A g−1	[80]
D-VS2	1 M ZnSO4	0.2–1.7	[email protected]	94% after 100 cycles at 0.1 A g−1	[81]
VS2@N-C	3 M Zn (CF3SO3)2	0.2–1.8	[email protected]	97% after 600 cycles at 1.0 A g−1	[82]
VS2·NH3	2 M Zn (CF3SO3)2	0.2–1.7	[email protected]	110% after 2000 cycles at 3.0 A g−1	[83]
VS2/VOx	25 M ZnCl2	0.1–1.8	[email protected]	75% after 3000 cycles at 1.0 A g−1	[48]
V2O5·3H2O@VS2 (SVO)	3 M ZnSO4	0.3–1.6	[email protected]	69.7% after 6700 cycles at 5.0 A g−1	[84]
VS2	1 M ZnSO4	0.2–1.0	[email protected]	72% after 200 cycles at 1.0 A g−1	[85]
1T-VS2	2.5 M Zn (CF3SO3)2	0.4–0.85	[email protected]	86.7% after 2000 cycles at 2.0 A g−1	[49]
VS2@SWCNT(C-VS2)	3 M Zn (CF3SO3)2	0.3–1.5	[email protected]	72% after 1500 cycles at 5.0 A g−1	[54]
VS4@rGO	1 M Zn (CF3SO3)2	0.35–1.8	[email protected]	93.3% after 165 cycles at 1.0 A g−1	[63]
VS4	1 M ZnSO4	0.2–1.6	[email protected]	85% after 500 cycles at 2.5 A g−1	[58]
VS4/CNTs	2 M Zn (CF3SO3)2	0.2–1.7	[email protected]	93% after 1200 cycles at 5.0 A g−1	[66]
S/VOx	30 M ZnCl2	0.1–1.8	[email protected]	100% after 2000 cycles at 2.0 A g−1	[68]
VS4/V2O3	3 M Zn (CF3SO3)2	0.3–1.2	[email protected]	-	[67]
Mn-VS4	1 M Zn (CF3SO3)2 /ACN (1:1)	0.3–2.0 V	[email protected]	97.83% after 1000 cycles at 1.0 A g−1	[86]
V5S8	3 M ZnSO4	0.2–1.6	[email protected]	94% after 1000 cycles at 10.0 A g−1	[71]
HCC-V3S4	2 M ZnSO4	0.5–1.5	[email protected]	95% after 200 cycles at 0.5 A g−1	[78]

summarize the timeline and electrochemical performance of vanadium-based sulfides and their composites as cathode materials for aqueous zinc-ion batteries. In addition, there is a lack of investigation into more directions on ZIBs for vanadium-based sulfides (e.g., electrolytes, separator, anode protection, etc.), which may be a significant direction for future research. Although vanadium-based sulfides have made tremendous progress as positive electrode materials for AZIBs, these materials are currently immature for practical applications, and their further development still faces several challenges, such as typically lower operating voltage, easier dissolution in aqueous electrolytes, easier structural collapse during cycling, and more complex zinc storage mechanisms. Meanwhile, according to the defects of vanadium-based sulfides as AZIBs cathode materials, the following optimization strategies are proposed: (1) acting as pillars by embedding metal ions, etc., which can effectively reinforce the material structure; (2) using carbon materials as the substrate to improve the conductivity of the material; (3) in situ electrochemical activations to build heterogeneous structures, which can promote the rapid intercalation of ions and alleviate the volume expansion during cycling; (4) developing binder-free cathode materials, which can improve the overall conductivity of the material, promote the kinetics of electrochemical reactions, and effectively enhance the multiplier performance. In summary, the development of integrated cathode materials with stable structure, higher ionic/electronic conductivity, abundant active sites, and easy Zn²⁺ de/intercalation between layers is the key to realizing the wide application of AZIBs.