Mg ions intercalated with V3O7·H2O to construct ultrastable cathode materials for aqueous zinc-ion batteries.

V3O7·H2O (VO) stands out as a highly promising cathode material for aqueous zinc-ion batteries (AZIB). However, due to the instability of the VO structure and the limited ion transport rate, achieving the required specific capacity and extended cycling lifespan has been challenging. To tackle this issue, we synthesized Mg-ion intercalated VO (MgVO) using a straightforward hydrothermal method. Introducing Mg2+ as an interlayer support enhanced the flexibility of MgVO within the confined layer space, stabilized its lamellar structure, and expanded the VO layer spacing. The AZIB employing the MgVO cathode demonstrated a high specific capacity of 382.7 mA h g-1 at a current density of 0.1 A g-1 and showed excellent cycling stability. The robust structural stability of MgVO suggests promising applications for large-scale energy storage, while the Mg2+ intercalation strategy presents a novel approach for exploring other potential cathode materials.

Macromolecules Promoting Robust Zinc Anode by Synergistic Coordination Effect and Charge Redistribution.

Zn dendrite formation is the main obstacle to commercializing aqueous zinc-ion batteries (ZIBs). α-cyclodextrin (α-CD) is proposed as an environmentally friendly macromolecule additive in the ZnSO4 -based electrolyte to obtain stable and reversible Zn anodes. The results show that α-CD molecules' unique 3D structure can effectively regulate the mass transfer of the electrolyte components and isolate the Zn anode from H2 O molecules. The α-CD provides abundant electrons to the Zn (002) crystallographic plane, which induces charge density redistribution. Such an effect relieves the reduction and aggregation of Zn2+ cations while protecting the Zn metal anode from water molecules. Finally, a small amount of α-CD additive (0.01 M) can enhance the performance of Zn significantly in Zn||Cu cells (1980 cycles with 99.45% average CE) and Zn||Zn cells (8000 h ultra-long cycle life). The excellent practical applicability was further verified in Zn||MnO2 cells.

Accelerated redox conversion of an advanced Zn//Fe-Co3O4 battery by heteroatom doping.

Herein, Fe-doped Co3O4 (Fe-Co3O4) was prepared to solve the issues of poor electrical conductivity and the lack of active sites in Co3O4 materials. Due to having similar radius and physical/chemical properties to Co, Fe is an ideal choice for doping Co3O4, as it can improve intrinsic conductivity without causing severe lattice distortion. Oxygen vacancies are gradually formed as doping reactions occur to maintain electric neutrality. Owing to the merits of oxygen vacancies in Co3O4, the distribution of the electrons is changed, thus optimizing the material's intrinsic charge/ion states and modifying the band gap by introducing impurity levels. Moreover, the surface area of Fe-Co3O4 is 1.5 times larger than that of the original material. The synergistic effect promotes the electrochemical oxidation reduction reaction and improves the capacitance and cycling stability. Finally, such an advanced Zn//Fe-Co3O4 battery exhibits a discharge-specific capacity of 171.97 mA h g-1, nearly eight times higher than that of the previous Zn//Co3O4 battery (22.38 mA h g-1). In addition, the attenuation of the capacity was almost negligible after 9000 cycles.

Zinc Anode for Mild Aqueous Zinc-Ion Batteries: Challenges, Strategies, and Perspectives.

The rapid advance of mild aqueous zinc-ion batteries (ZIBs) is driving the development of the energy storage system market. But the thorny issues of Zn anodes, mainly including dendrite growth, hydrogen evolution, and corrosion, severely reduce the performance of ZIBs. To commercialize ZIBs, researchers must overcome formidable challenges. Research about mild aqueous ZIBs is still developing. Various technical and scientific obstacles to designing Zn anodes with high stripping efficiency and long cycling life have not been resolved. Moreover, the performance of Zn anodes is a complex scientific issue determined by various parameters, most of which are often ignored, failing to achieve the maximum performance of the cell. This review proposes a comprehensive overview of existing Zn anode issues and the corresponding strategies, frontiers, and development trends to deeply comprehend the essence and inner connection of degradation mechanism and performance. First, the formation mechanism of dendrite growth, hydrogen evolution, corrosion, and their influence on the anode are analyzed. Furthermore, various strategies for constructing stable Zn anodes are summarized and discussed in detail from multiple perspectives. These strategies are mainly divided into interface modification, structural anode, alloying anode, intercalation anode, liquid electrolyte, non-liquid electrolyte, separator design, and other strategies. Finally, research directions and prospects are put forward for Zn anodes. This contribution highlights the latest developments and provides new insights into the advanced Zn anode for future research.

Unravelling V6O13 Diffusion Pathways via CO2 Modification for High-Performance Zinc Ion Battery Cathode.

Vanadium-based oxide is widely investigated as a zinc ion battery (ZIB) cathode due to its ability to react reversibly with Zn2+. Despite its successful demonstration, modification with simple molecules has shown some promise in enhancing the performance of ZIBs. Thus, this presents an immense opportunity to explore simple molecules that can dramatically improve the electrochemical performance of electrodes. Thus, the effect of CO2 modification is studied in this work by decomposing oxalic acid within a hydrated V6O13 framework. Based on the collective results, the presence of CO2 drastically lowers the relative energy of Zn2+ diffusion through the pathways by forming weak electrostatic interactions between OCO2 and Zn2+. This leads to an enlarged diffusion contribution, which consequently results in enhanced stability and better rate performance. The as-synthesized CO2-V6O13 electrode delivers one of the highest specific capacities reported for vanadium-based oxides of ca. 471 mAh g-1. Furthermore, an excellent cyclic stability of 80% capacity retention after 4000 cycles at 2 A g-1 is recorded for CO2-V6O13, which suggests the importance of simple molecules in the material framework toward the enhancement of ZIB cathode performance.

Binder-free V2O5/CNT paper electrode for high rate performance zinc ion battery.

Organic compounds, such as polyvinylidene fluoride (PVDF), have been widely used as a binder in battery electrode preparations. While such an approach does not have a significant impact on the performance of the batteries that utilize low valence ions, such as the Li ion battery (LIB), the diffusion of high valence ions (such as Zn2+) will be severely impaired. This will be especially pronounced if the polymeric binder contains highly electronegative atoms, such as fluorine. The high charge density ions, such as Zn2+, tend to adsorb onto these electronegative atoms, thus the mobility of these ions across the material is inevitably affected. As such, it becomes highly necessary to consider the binder-free electrode architecture when designing a high rate performing and cycling-stable zinc ion battery (ZIB) cathode. Herein, this work demonstrates an improved Zn ion battery by adopting a freestanding electrode. The obtained V2O5/CNT paper electrode delivers a specific capacity of 312 mA h g-1, while achieving a respectable 75% retention in capacity after increasing the current density by 10-fold. Furthermore, excellent cycling stability is recorded with 81% capacity retention after 2000 cycles at 1.0 A g-1. Thus, this work clearly demonstrated that the freestanding electrode is a promising approach for high valence ion batteries.

Bi2S3 for Aqueous Zn Ion Battery with Enhanced Cycle Stability.

Aqueous Zn ion batteries (ZIBs) are promising in energy storage due to the low cost, high safety, and material abundance. The development of metal oxides as the cathode for ZIBs is limited by the strong electrostatic forces between O2- and Zn2+ which leads to poor cyclic stability. Herein, Bi2S3 is proposed as a promising cathode material for rechargeable aqueous ZIBs. Improved cyclic stability and fast diffusion of Zn2+ is observed. Also, the layered structure of Bi2S3 with the weak van der Waals interaction between layers offers paths for diffusion and occupancy of Zn2+. As a result, the Zn/Bi2S3 battery delivers high capacity of 161 mAh g-1 at 0.2 A g-1 and good cycling stability up to 100 cycles with ca. 100% retention. The battery also demonstrates good cyclic performance of ca. 80.3% over 2000 cycles at 1 A g-1. The storage mechanism in the Bi2S3 cathode is related to the reversible Zn ion intercalation/extraction reactions and the capacitive contribution. This work indicates that Bi2S3 shows great potential as the cathode of ZIBs with good performance and stability.

3D MnCo2O4.5 Nanorod Arrays on Ni Foam as Binder-Free Anodes for Li-Ion Batteries.

It is a key to develop novel electrode materials with high energy and power density for advanced batteries to meet the demand of electric vehicles (EVs). Manganese cobalt oxides which can react with a large number of ions from the electrolyte for electrochemical energy storage are developing into the promising electrode materials. In this work, well-ordered MnCo2O4.5 nanorod arrays (MCO NRAs) are prepared on Ni foam by a general route of hydrothermal growth and low-temperature annealing treatment. The samples deliver a high initial capacity of 1402.6 mAh g-1 at the current density of 100 mA g-1 and rate capacity of 528 mAh g-1 when the current density is improved 10 times as binder-free anodes for Li-ion batteries (LIBs). After 60 cycles at the current density of 200 mA g-1, the MnCo2O4.5 nanorods still achieve 603 mAh g-1 with capacity retention of 66% (compared with the second discharge capacity). The superior electrochemical properties are due to the fascinating architecture which increases the reaction area and structural stability, reduces ion and electron transport distance and provides good strain release. Hence, MnCo2O4.5 nanorod arrays are promised as advanced anodes for future LIBs with completely meeting the demand of EVs.

In Situ Growth of Free-Standing All Metal Oxide Asymmetric Supercapacitor.

Metal oxides have attracted renewed interest in applications as energy storage and conversion devices. Here, a new design is reported to acquire an asymmetric supercapacitor assembled by all free-standing metal oxides. The positive electrode is made of 3D NiO open porous nanoribbons network on nickel foam and the negative electrode is composed of SnO2/MnO2 nanoflakes grown on carbon cloth (CC) substrate. The combination of two metal oxide electrodes which replaced the traditional group of carbon materials together with metal oxide has achieved a higher energy density. The self-supported 3D NiO nanoribbons network demonstrates a high specific capacitance and better cycle performance without obvious mechanical deformation despite of undergoing harsh bulk redox reactions. The SnO2/MnO2 nanoflakes as the pseudocapacitive electrode exhibit a wide range of voltage window (-1 to 1 V), which is conducive to electrochemical energy storage. The (CC/SnO2/MnO2)(-)//(NiO/Ni foam)(+) asymmetric supercapacitor device delivers an energy density of 64.4 Wh kg-1 (at a power density of 250 W kg-1) and two devices in series are applied to light up 24 red LEDs for about 60 s. The outstanding electrochemical properties of the device hold great promise for long-life, high-energy, and high-power energy storage/conversion applications.

Hybrid ZnO/ZnS nanoforests as the electrode materials for high performance supercapacitor application.

Heterostructured ZnO/ZnS nanoforests are prepared through a simple two-step thermal evaporation method at 650 °C and 1300 °C in a tube furnace under the flow of argon gas, respectively. A metal catalyst (Au) to form a binary alloy has been used in the process. The as-obtained ZnO/ZnS products are characterized by using a series of techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersion X-ray spectroscopy (EDS), Raman spectroscopy and photoluminescence. A possible growth mechanism is temporarily proposed. The hybrid structures are also directly functionalized as supercapacitor (SC) electrodes without using any ancillary materials such as carbon black or binder. Results show that the as-synthesized ZnO/ZnS heterostructures exhibit a greatly reduced ultraviolet emission and dramatically enhanced green emission compared to pure ZnO nanorods. The SCs data demonstrate high specific capacitance of 217 mF cm(-2) at 1 mA cm(-2) and excellent cyclic performance with 82% capacity retention after 2000 cycles at a current density of 2.0 mA cm(-2).

Removal of Congo red dye molecules by MnO2 nanorods.

Uniform MnO2 nanorods were synthesized successfully via a facile and effective hydrothermal approach. Scanning electron microscope images showed that the average diameter of the as-synthesized nanorod is about 30 nm and the length of that is about 5 µm, respectively. Photocatalytic experimental results indicate that Congo red can be degraded nearly completely (over 97%) after visible light irradiation of 120 min, demonstrating potential applications of such nanorod structures for wastewater purification.

Hydrothermal synthesis and photocatalytic performance of uniform α-Fe2O3 nanocubes.

In this paper, large scale uniform α-Fe2O3 nanocubes are synthesized through a facile and effective hydrothermal route. The structure and morphology of the resultant products are characterized by X-ray diffraction (XRD), and scanning electron microscope (SEM). A possible growth mechanism for α-Fe2O3 nanocubes is proposed based on the experimental results. Photocatalytic test reveals that Congo red can be degraded nearly completely (over 95%) after visible light irradiation of 40 min. In addition, methyl orange and methylene blue aqueous solution degradation experiments also are conducted in the same condition, revealing the versatile potential applications of the product in wastewater purifications.

Visible light driven α-Fe2O3 nanorod photocatalyst.

α-Fe2O3 nanorods are controlled prepared by a facile hydrothermal process followed by a calcination treatment. The experiment results indicate that the morphology of the as-obtained product depends greatly on the quantity of NaOH. The photocatalytic performances of the as-prepared samples were evaluated by photocatalytic decolorization of Congo red solution at ambient temperature. The results indicate that the photocatalytic activity of the α-Fe2O3 nanorods is superior to α-Fe2O3 nanoparticles and microplates, revealing the versatile potential applications of the product in wastewater purifications.

Cuprous Chloride Nanocubes Grown on Copper Foil for Pseudocapacitor Electrodes.

In this paper, for the first time, we report the synthesis of nanoscale cuprous chloride (CuCl) cubic structure by a facile hydrothermal route. A possible mechanism for the growth of those nanostructures is proposed based on the experimental results. It is discovered that the existence of HCl could affect the surface of CuCl nanocubes. This unique cube-like nanostructure with rough surface significantly enhances the electroactive surface areas of CuCl, leading to a high special capacitance of 376 mF cm-2 at the current density of 1.0 mA cm-2. There is still a good reversibility with cycling efficiency of 88.8 % after 2,000 cycles, demonstrating its excellent long-term cycling stability and might be the promising candidates as the excellent electrode material.