class of materials show great potential for the insertion/extraction of multivalent ions (Zn 2+ , Mg 2+ , Al 3+ ) owing to the characteristic of large layer spacing and high conductivity. Among all the TMDs, VS 2 is a typical family member of TMDs with hexagonal system, which shows similar crystal structure to that of graphite lamellar with an interlayer spacing of 5.76 Å. [25,30] There is a vanadium layer between two sulfur layers to form a kind of sandwich structure. In VS 2 crystal structure, each V atom is arranged around six S atoms and connected with S atoms with covalent bonds. The interlayer spacing of VS 2 is so large that enables the convenient insertion/extraction of lithium ions (0.69 Å), sodium ions (1.02 Å), zinc ions (0.74 Å) or their solvation sheath in electrolyte. However, to the best of our knowledge, there is no report about VS 2 as the electrode materials for ZIBs.Herein, the VS 2 nanosheets are synthesized via a facile hydrothermal reaction (Supporting Information), which deliver a high capacity of 190.3 mA h g −1 at a current density of 0.05 A g −1 and exhibit long-term cyclic stability as the cathode for ZIBs. The electrochemical reaction mechanism of such VS 2 electrodes is further investigated systematically through a series of measurements including ex situ X-ray diffraction (XRD), ex situ X-ray photoelectron spectroscopy (XPS), in situ Raman, ex situ transmission electron microscopy (TEM). A reversible insertion/extraction process can be observed from all aspects. Both the ex situ TEM and ex situ XRD results demonstrate that the interlayer space of VS 2 can self adapt to the intercalation of Zn 2+ with an expansion along the c-axis (only 1.73%) and a slightly shrink along the a-and b-axes, which plays a key role in the realization of long-life ZIBs. All the above evidences reveal that the VS 2 is a promising cathode material with high capacity and good cyclic stability for ZIBs.The crystal structure of the as-prepared VS 2 is tested by XRD. All characteristic peaks are in accordance with the standard card of VS 2 (JCPDS NO. 01-089-1640) (Figure 1a). The Raman spectrum of the VS 2 in the range of 100-1100 cm −1 is shown in Figure 1b. Six peaks located at 140.4, 192.0, 282.0, 406.6, 687.8, and 993.2 cm −1 are observed, which correspond to the rocking and stretching vibrations of V-S bonds or their combination. [25] The morphology and microstructures of as-prepared VS 2 are investigated by field emission scanning electron microscopy (SEM) and high-resolution TEM (HRTEM). As shown in Figure 1c, The VS 2 flowers are assembled by nanosheets with a diameter of 5-8 µm and a thickness of 50-100 nm. The d-spacing calculated from selected area electron diffraction (SAED) patterns are 2.89 and 1.64 Å (Figure 2f), which match the d-spacing values of (002) and (110) crystal planes of VS 2 , respectively. TEM and corresponding HRTEM images in Figure 2e show VS 2 nanosheets with a d-spacing of ≈5.76 Å,The continuous researches of energy-storage devices have gained considerable attention in our world ...
Aqueous zinc-ion batteries attract increasing attention due to their low cost, high safety, and potential application in stationary energy storage. However, the simultaneous realization of high cycling stability and high energy density remains a major challenge. To tackle the above-mentioned challenge, we develop a novel Zn/VO rechargeable aqueous hybrid-ion battery system by using porous VO as the cathode and metallic zinc as the anode. The VO cathode delivers a high discharge capacity of 238 mAh g at 50 mA g. 80% of the initial discharge capacity can be retained after 2000 cycles at a high current density of 2000 mA g. Meanwhile, the application of a "water-in-salt" electrolyte results in the increase of discharge platform from 0.6 to 1.0 V. This work provides an effective strategy to simultaneously enhance the energy density and cycling stability of aqueous zinc ion-based batteries.
The aqueous zinc ion batteries (ZIBs) composed of inexpensive zinc anode and nontoxic aqueous electrolyte are attractive candidates for large-scale energy storage applications. However, their development is limited by cathode materials, which often deliver inferior rate capability and restricted cycle life. Herein, the VO 2 nanorods show significant electrochemical performance when used as an intercalation cathode for aqueous ZIBs. Specifically, the VO 2 nanorods display high initial capacity of 325.6 mAh g −1 at 0.05 A g −1 , good rate capability, and excellent cycling stability of 5000 cycles at 3.0 A g −1 . Furthermore, the VO 2 unit cell expands in a, b, and c directions sequentially during the discharge process and contracts back reversibly during the charge process, and the zinc storage mechanism is revealed to be a highly reversible single-phase reaction by operando techniques and corresponding qualitative analyses. Our work not only opens a new door to the practical application of VO 2 in ZIB systems but also broadens the horizon in understanding the electrochemical behavior of rechargeable ZIBs.
further development. [2] Hence, exploring novel approaches to achieve more efficient energy storage is highly demanded. Recently, aqueous batteries are attracting unprecedented attention particularly owing to their high safety, high ion conductivity, low cost, and environmental friendliness. [3] To date, numerous aqueous batteries based on Li + , Na + , K + , Mg 2+ , Ca 2+ , Zn 2+ , Al 3+ , Fe 3+ , and/or mixed metal ions as charge carriers have been reported, [4] which find potential applications in fields such as grid-scale energy storage, wearable devices, and etc. [5] Among them, as a promising candidate, the rechargeable aqueous Zn-based batteries (AZBs) including Zn-ion batteries (mild electrolyte), [6] Zn-Co/Ag/ Ni alkaline batteries [7] and Zn-air batteries in alkaline electrolyte [8] have been extensively studied due to their unparalleled advantages of Zn anode. In general, metal Zn has the features of high theoretical capacity (820 mAh g −1 ), high electrical conductivity, nontoxicity, easy processing, and suitable redox potential (−0.76 V vs standard hydrogen electrode). [9] However, most of AZBs reported so far have encountered the same challenges, which are the narrow voltage window, unsatisfactory capacity, and poor cycling performance. [10] For example, all Zn-ion batteries operated in mild electrolyte including Zn//V-based, Zn//Mn-based, and Zn//Prussian blue analogs-based hold a narrow voltage window of 0.3-1.6, 0.9-1.8, and 0.2-1.8 V, respectively. [11] Even though AZBs in alkaline electrolyte display a higher voltage than that achieved in mild medium, their voltage windows are still only about 1.2-1.9 V. [12] Meanwhile, the alkaline electrolytes show stronger corrosion than mild neutral electrolytes, which greatly limit their wide applications. Moreover, the unstable cycling performance in AZBs due to the Zn dendrites and side reaction on the surface of Zn anode is also unsatisfactory. [10] To date, the electrolyte optimization or structural design are the common ways to suppress the growth of Zn dendrite and improve the cycling stability. For example, Chen and co-workers reported that aqueous electrolyte Zn(CF 3 SO 3 ) 2 can suppress the formation of detrimental dendrites in AZBs owing to the better reversibility and faster kinetics of Zn deposition/dissolution than that in ZnSO 4 electrolyte. [13] However, Zn(CF 3 SO 3 ) 2 is too expensive (≈$ 8.1 g −1 , prices from Sigma-Aldrich) to be applied With the increasing energy crisis and environmental pollution, rechargeable aqueous Zn-based batteries (AZBs) are receiving unprecedented attention due to their list of merits, such as low cost, high safety, and nontoxicity. However, the limited voltage window, Zn dendrites, and relatively low specific capacity are still great challenges. In this work, a new reaction mechanism of reversible Mn 2+ ion oxidation deposition is introduced to AZBs. The assembled Mn 2+ /Zn 2+ hybrid battery (Mn 2+ /Zn 2+ HB) based on a hybrid storage mechanism including Mn 2+ ion deposition, Zn 2+ ion insertion, and co...
attention. [9][10][11] AZIBs are considered as one of the most ideal candidates for largescale energy storage owing to their following advantages:i) The excellent properties of zinc: According the data in Table 1, the abundance of zinc in the earth's crust is 79 ppm, and ranks fourth in the world metal production, so zinc has a low market price. Zn metal anode has good electrical conductivity (5.91 µΩ cm), high volumetric energy density (5851 mAh cm −3 ), high theoretical capacity (819 mAh g −1 ), and relatively low redox potential (−0.76 V vs standard hydrogen electrode) which is more suitable in aqueous solution. In addition, multivalent zinc ion can transfer two electrons to facilitate more energy storage than the univalent batteries. [12] At the same time, the ionic radius of zinc ions is 0.74 Å, which is smaller than that of sodium ions (1.02 Å) and close to that of lithium ions (0.69 Å). Moreover, zinc is the essential trace element for human body. [9] In brief, Zn has the superiorities of low cost, low-toxicity, abundant resource, easily recycle, and environmental friendliness.ii) The higher ionic conductivity and safety of aqueous electrolytes: The aqueous electrolytes offer two orders of higher magnitude ionic conductivities (≈1 S cm −1 ) than that of organic electrolytes (≈10 −2 -10 −3 S cm −1 ), so aqueous battery usually has higher power density. [3,13] Meanwhile, the organic electrolytes are usually toxic and flammable, while the aqueous electrolytes are nontoxic and safe, which can mitigate the environmental disruption and recycling costs. iii) The facile assembly process: AZIBs can be assembled in the air condition owing to the stability of zinc anode and aqueous electrolyte. Compared with the batteries assembled in the inert-gas glove box, the manufacturing costs of ZIBs are greatly reduced. The facile manufacture and recycling of AZIBs is an important advantage in the large-scale storage applications.Combining the above advantages, low-cost, safe, and green next-generation AZIBs are suitable specifically for large-scale stationary storage applications. So far, AZIBs are still at the infancy stage. The related researches mainly focused on cathode materials. We count the publication numbers of the reported cathodes for AZIBs in the period from 2012 to February 2019 (1, Supporting Information). As illustrated in Figure 1a, the number of annual publications on cathodes for AZIBs continues to increase rapidly in the recent years. However, in the preliminary stage, Electrochemical energy storage devices will definitely play a vital role in the future energy landscape of the world. The innovation of electrode materials is a key task for the breakthrough of present bottleneck faced by electrochemical energy storage devices. Aqueous zinc-ion batteries (AZIBs) are gaining rapid attention, and they offer tremendous opportunities to explore the low-cost, safe, and next-generation green batteries for large-scale stationary storage applications. In this review, the authors aim to give a comprehensive overview ...
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