Boosting the zinc ion storage capacity and cycling stability of interlayer-expanded vanadium disulfide through in-situ electrochemical oxidation strategy

Architecting V2O5 with a Triune Crystal Water-Amorphous-Crystalline Feature for Robust Zinc-Ion Batteries

The notorious collapse of the electrode structure and strong electrostatic interactions in aqueous zinc-ion batteries (AZIBs) limit the achievement of a long cycle life. Herein, by designing an ordered/disordered hybrid structure, we have effectively preserved the integrity of the V2O5·1.6H2O (VOH) electrode. Moreover, our approach facilitates the release of stress concentration contributed to by the amorphous component, alleviating the strong electrostatic interaction merited by crystal water and promoting the diffusion kinetics of Zn2+ assisted by the crystalline component. Noteworthy, the crystal water serves as an interlayer pillar significantly enhancing the structural stability of the electrode. As a result, our VOH electrode exhibits high electrochemical performance. It delivered 227.8 mAh g-1 at a higher current density of 2 A g-1, and a high cycle life of 1000 cycles with 95% capacity retention was achieved at a current density of 1 A g-1.

Regulating V2O5 Layer Spacing by a Polyaniline Molecule Chain to Improve Electrochemical Performance in Salinity Gradient Energy Conversion

Salinity gradient energy is a chemical potential energy between two solutions with different ionic concentrations, which is also an ocean energy at the junction of rivers and seas. In our original work, the device "activated carbon//(0.083 M Na2SO4, 0.5 M Na2SO4)//vanadium pentoxide" for the conversion of salinity gradient energy was designed, and the conversion value of 6.29 J g-1 was obtained. However, the low specific surface area of the original V2O5 inevitably resulted in limited active sites and slow ionic transport rates, and the inherent lower conductivity and narrower layer spacing of the original V2O5 also resulted in poor electrode kinetic performance and cycle stability, hindering its practical application. To solve the above problems, the present work provides a strategy of using polyaniline (PANI) molecule chain intercalation to regulate the layer spacing of the original V2O5, and through the expansion and traction of the layer spacing, the composite PANI/V2O5 (PVO) with high specific surface area is prepared and used as an anode material for electrochemical conversion of salinity gradient energy application. The significantly increased layer spacing of the crystal plane (001) corresponding to the original V2O5 was confirmed with the PANI by the hydrogen bonding and the van der Waals force. The high specific surface area of the composite provides more electrochemical active sites to realize a fast Na+ migration rate and high specific capacitance. Meanwhile, the inserted PANI molecule chain, which acts not only as a pillar enlarging the Na+ diffusion channel but also as an anchor locking the gap between V2O5 bilayers, improves the structural stability of the V2O5 electrode during the electrochemical conversion process. The proposed insertion strategy for the conductive polymer PANI has created a new way to improve the cycle stability performance of the salinity gradient energy conversion device.

NH4 + Pre-Intercalation and Mo Doping VS2 to Regulate Nanostructure and Electronic Properties for High Efficiency Sodium Storage

Sodium-ion hybrid capacitors (SIHCs) have attracted much attention due to integrating the high energy density of battery and high out power of supercapacitors. However, rapid Na+ diffusion kinetics in cathode is counterbalanced with sluggish anode, hindering the further advancement and commercialization of SIHCs. Here, aiming at conversion-type metal sulfide anode, taking typical VS2 as an example, a comprehensive regulation of nanostructure and electronic properties through NH4 + pre-intercalation and Mo-doping VS2 (Mo-NVS2) is reported. It is demonstrated that NH4 + pre-intercalation can enlarge the interplanar spacing and Mo-doping can induce interlayer defects and sulfur vacancies that are favorable to construct new ion transport channels, thus resulting in significantly enhanced Na+ diffusion kinetics and pseudocapacitance. Density functional theory calculations further reveal that the introduction of NH4 + and Mo-doping enhances the electronic conductivity, lowers the diffusion energy barrier of Na+, and produces stronger d-p hybridization to promote conversion kinetics of Na+ intercalation intermediates. Consequently, Mo-NVS2 delivers a record-high reversible capacity of 453 mAh g-1 at 3 A g-1 and an ultra-stable cycle life of over 20 000 cycles. The assembled SIHCs achieve impressive energy density/power density of 98 Wh kg-1/11.84 kW kg-1, ultralong cycling life of over 15000 cycles, and very low self-discharge rate (0.84 mV h-1).

3D printing of layered vanadium disulfide for water-in-salt electrolyte zinc-ion batteries

Miniaturized aqueous zinc ion batteries are attractive energy storage devices for wearable electronics, owing to their safety and low cost. Layered vanadium disulfide (VS2) has demonstrated competitive charge storage capability for aqueous zinc ion batteries, as a result of its multivalent states and large interlayer spacing. However, VS2 electrodes are affected by quick oxide conversion, and they present predefined geometries and aspect ratios, which hinders their integration in wearables devices. Here, we demonstrate the formulation of a suitable ink for extrusion-based 3D printing (direct ink writing) based on micro flowers of layered VS2 obtained using a scalable hydrothermal process. 3D printed architectures of arbitrary design present electrochemically active, porous and micron-sized struts with tuneable mass loading. These were used as cathodes for aqueous zinc-ion battery electrodes. The 3D printed VS2 cathodes were assembled with carbon/zinc foil anodes to form full cells of zinc-ion, demonstrating a capacity of ∼1.98 mA h cm-2 with an operating voltage of 1.5 V. Upon cycling a capacity retention of around 65% was achieved after ∼100 cycles. The choice of the electrolyte (a water-in-salt electrolyte) and the design of the pre-processing of the 3D printed cathode ensured improved stability against dissolution and swift oxidation, notorious challenges for VS2 in an aqueous environment. This works paves the way towards programmable manufacturing of miniaturized aqueous batteries and the materials processing approach can be applied to different materials and battery systems to improve stability.

One-Stone-for-Two-Birds Strategy for VSe2 to Enable High Capacity and Long-Life Zinc Storage

Based on a specific zinc storage mechanism and excellent electronic conductivity, transition metal dichalcogenides, represented by vanadium diselenide, are widely used in aqueous zinc-ion battery (AZIB) energy storage systems. However, most vanadium diselenide cathode materials are presently limited by low specific capacity and poor cycling life. Herein, a simple hydrothermal process has been proposed for obtaining a vanadium diselenide cathode for an AZIB. The interaction of defects and crystal planes enhances zinc storage capacity and reduces the migration energy barrier. Moreover, abundant lamellar structure greatly increases reaction sites and alleviates volume expansion during the electrochemical process. Thus, the as-obtained vanadium diselenide AZIB exhibits an excellent reversible specific capacity of 377 mAh g-1 at 1 A g-1, and ultralong cycle stability of 291 mAh g-1 after 3200 cycles, with a nearly negligible capacity loss. This one-stone-for-two-birds strategy would be expected to be applied to large-scale synthesis of a high-performance zinc-ion battery cathode in the future.

Methods for Characterizing Intercalation in Aqueous Zinc Ion Battery Cathodes: A Review

Aqueous zinc ion batteries have gained research attention as a safer, economical and more environmentally friendly alternative to lithium-ion batteries. Similar to lithium batteries, intercalation processes play an important role in the charge storage behaviour of aqueous zinc ion batteries, with the pre-intercalation of guest species in the cathode being also employed as a strategy to improve battery performance. In view of this, proving hypothesized mechanisms of intercalation, as well as rigorously characterizing intercalation processes in aqueous zinc ion batteries is crucial to achieve advances in battery performance. This review aims to evaluate the range of techniques commonly used to characterize intercalation in aqueous zinc ion battery cathodes, providing a perspective on the approaches that can be utilized to rigorously understand such intercalation processes.

Magneto-electrochemistry driven ultralong-life Zn-VS2 aqueous zinc-ion batteries

The development of high energy density and long cycle lifespan aqueous zinc ion batteries is hindered by the limited cathode materials and serious zinc dendrite growth. In this work, a defect-rich VS2 cathode material is manufactured by in situ electrochemical defect engineering under high charge cut-off voltage. Owing to the rich abundant vacancies and lattice distortion in the ab plane, the tailored VS2 can unlock the transport path of Zn2+ along the c-axis, enabling 3D Zn2+ transport along both the ab plane and c-axis, and reduce the electrostatic interaction between VS2 and zinc ions, thus achieving excellent rate capability (332 mA h g-1 and 227.8 mA h g-1 at 1 A g-1 and 20 A g-1, respectively). The thermally favorable intercalation and 3D rapid transport of Zn2+ in the defect-rich VS2 are verified by multiple ex situ characterizations and density functional theory (DFT) calculations. However, the long cycling stability of the Zn-VS2 battery is still unsatisfactory due to the Zn dendrite issue. It can be found that the introduction of an external magnetic field enables changing the movement of Zn2+, suppressing the growth of zinc dendrites, and resulting in enhanced cycling stability from about 90 to 600 h in the Zn||Zn symmetric cell. As a result, a high-performance Zn-VS2 full cell is realized by operating under a weak magnetic field, which shows an ultralong cycle lifespan with a capacity of 126 mA h g-1 after 7400 cycles at 5 A g-1, and delivers the highest energy density of 304.7 W h kg-1 and maximum power density of 17.8 kW kg-1.

How About Vanadium-Based Compounds as Cathode Materials for Aqueous Zinc Ion Batteries?

Aqueous zinc-ion batteries (AZIBs) stand out among many monovalent/multivalent metal-ion batteries as promising new energy storage devices because of their good safety, low cost, and environmental friendliness. Nevertheless, there are still many great challenges to exploring new-type cathode materials that are suitable for Zn2+ intercalation. Vanadium-based compounds with various structures, large layer spacing, and different oxidation states are considered suitable cathode candidates for AZIBs. Herein, the research advances in vanadium-based compounds in recent years are systematically reviewed. The preparation methods, crystal structures, electrochemical performances, and energy storage mechanisms of vanadium-based compounds (e.g., vanadium phosphates, vanadium oxides, vanadates, vanadium sulfides, and vanadium nitrides) are mainly introduced. Finally, the limitations and development prospects of vanadium-based compounds are pointed out. Vanadium-based compounds as cathode materials for AZIBs are hoped to flourish in the coming years and attract more and more researchers' attention.

Carbon Foam-Supported VS2 Cathode for High-Performance Flexible Self-Healing Quasi-Solid-State Zinc-Ion Batteries

As the new generation of energy storage systems, the flexible battery can effectively broaden the application area and scope of energy storage devices. Flexibility and energy density are the two core evaluation parameters for the flexible battery. In this work, a flexible VS₂ material (VS₂ @CF) is fabricated by growing the VS₂ nanosheet arrays on carbon foam (CF) using a simple hydrothermal method. Benefiting from the high electric conductivity and 3D foam structure, VS₂ @CF shows an excellent rate capability (172.8 mAh g^-1 at 5 A g^-1 ) and cycling performance (130.2 mAh g^-1 at 1 A g^-1 after 1000 cycles) when it served as cathode material for aqueous zinc-ion batteries. More importantly, the quasi-solid-state battery VS₂ @CF//Zn@CF assembled by the VS₂ @CF cathode, CF-supported Zn anode, and a self-healing gel electrolyte also exhibits excellent rate capability (261.5 and 149.8 mAh g^-1 at 0.2 and 5 A g^-1 , respectively) and cycle performance with a capacity of 126.6 mAh g^-1 after 100 cycles at 1 A g^-1 . Moreover, the VS₂ @CF//Zn@CF full cell also shows good flexible and self-healing properties, which can be charged and discharged normally under different bending angles and after being destroyed and then self-healing.

A cerium vanadate/S heterostructure for a long-life zinc-ion battery: efficient electron transfer by the anchored sulfur

Ce_0.25V₂O₅(H₂O)·H₂O (CeVO) or Ce_0.3V₂O₅(H₂O)·H₂O/S (CeVS) was synthesized based on a facile one-step hydrothermal reaction of Ce(SO₄)₂ and V₂O₅ or VS₂. Rietveld refinement of CeVO unveils the intercalation of Ce ions into layered V₂O₅ with a large (001) lattice spacing of 12.1 Å. CeVS is a CeVO/S heterostructure, which originates from the hydrothermal transformation of VS₂ → V₂O₅ + S₈ and the simultaneous intercalation of Ce ions. The pre-intercalation of Ce ions leads to a Zn²⁺ migration barrier of 1.32 eV in CeVO, and CeVO shows a capacity of 376 mA h g^-1 at 0.1 A g^-1. However, CeVS exhibits a higher capacity (438 mA h g^-1) and an ultralong lifespan with a capacity retention of 100% over 10 500 cycles at 5 A g^-1. The conversion between S⁰ and vanadium sulfide (yS⁰ + 2e^- ↔ S_y^2-) in CeVS during the discharge and charge process can not only provide extra capacity, but also maintain the crystallinity and stability of CeVO, in which S transfers electrons like an electron shuttle to avoid the structural collapse and fast capacity fading of CeVO.

Electrolyte Engineering Enables High Performance Zinc-Ion Batteries

Zinc-ion batteries (ZIBs) feature high safety, low cost, environmental-friendliness, and promising electrochemical performance, and are therefore regarded as a potential technology to be applied in large-scale energy storage devices. However, ZIBs still face some critical challenges and bottlenecks. The electrolyte is an essential component of batteries and its properties affect the mass transport, energy storage mechanisms, reaction kinetics, and side reactions of ZIBs. The adjustment of electrolyte formulas usually has direct and obvious impacts on the overall output and performance. In this review, advanced electrolyte strategies are overviewed for optimizing the compatibility between cathode materials and electrolytes, inhibiting anode corrosion and dendrite growth, extending electrochemical stability windows, enabling wearable applications, and enhancing temperature tolerance. The underlying scientific mechanisms, electrolyte design principles, and recent progress are presented to provide a better understanding and inspiration to readers. In addition, a comprehensive perspective about electrolyte design and engineering for ZIBs is included.

Recent Advances of Transition Metal Chalcogenides as Cathode Materials for Aqueous Zinc-Ion Batteries

In recent years, advances in lithium-ion batteries (LIBs) have pushed the research of other metal-ion batteries to the forefront. Aqueous zinc ion batteries (AZIBs) have attracted much attention owing to their low cost, high capacity and non-toxic characteristics. Among various cathodes, transition metal chalcogenides (TMCs) with a layered structure are considered as suitable electrode materials. The large layer spacing facilitates the intercalation/de-intercalation of Zn²⁺ between the layers. In this mini-review, we summarize a variety of design strategies for the modification of TMCs. Then, we specifically emphasize the zinc storage capacity of the optimized electrodes. Finally, we propose the challenges and future prospects of cathode materials for high-energy AZIBs.

Recent Advance and Modification Strategies of Transition Metal Dichalcogenides (TMDs) in Aqueous Zinc Ion Batteries

In recent years, aqueous zinc ion batteries (ZIBs) have attracted much attention due to their high safety, low cost, and environmental friendliness. Owing to the unique layered structure and more desirable layer spacing, transition metal dichalcogenide (TMD) materials are considered as the comparatively ideal cathode material of ZIBs which facilitate the intercalation/ deintercalation of hydrated Zn²⁺ between layers. However, some disadvantages limit their widespread application, such as low conductivity, low reversible capacity, and rapid capacity decline. In order to improve the electrochemical properties of TMDs, the corresponding modification methods for each TMDs material can be designed from the following modification strategies: defect engineering, intercalation engineering, hybrid engineering, phase engineering, and in-situ electrochemical oxidation. This paper summarizes the research progress of TMDs as cathode materials for ZIBs in recent years, discusses and compares the electrochemical properties of TMD materials, and classifies and introduces the modification methods of MoS₂ and VS₂. Meanwhile, the corresponding modification scheme is proposed to solve the problem of rapid capacity fading of WS₂. Finally, the research prospect of other TMDs as cathodes for ZIBs is put forward.