Electrochemical Generation of Hydrated Zinc Vanadium Oxide with Boosted Intercalation Pseudocapacitive Storage for a High-Rate Flexible Zinc-Ion Battery

Expansion counteraction effect assisted vanadate with rich oxygen vacancies as a high cycling stability cathode for aqueous zinc-ion batteries

In this study, a novel tunnel structure vanadate NaVO (Na0.465V2O5) cathode for aqueous zinc ion batteries (AZIBs) is facilely fabricated by thermal decomposition of polyoxovanadate containing NH4+ ions. The NaVO cathode is characterized by abundant oxygen vacancies and nanometer dimensions. These attributes can offer extra reaction sites and suppress structural collapse during circulation. In the charge-discharge process, a unique phenomenon occurs where NaVO undergoes opposite expansion (positive vs. negative expansion) along its different crystal planes. This opposite expansion produces an "expansion counteraction effect", which effectively buffers the volume change of NaVO. Additionally, the irreversibly inserted Zn2+ ions as "pillars" are maintained in the framework after the first discharge, further improving the structural stability of NaVO. Consequently, the NaVO cathode exhibits superior cycling stability. The capacity retention rate can reach 87.3% after 350 cycles at 0.1 A g-1. With a high current density of 2 A g-1, the specific capacity can be maintained at 206.3 mA h g-1 with a capacity retention of 95.5% after 2100 cycles. This study not only provides a novel approach for synthesizing nanoscale vanadate cathodes with rich oxygen vacancies, but also proposes the "expansion counteraction effect" theory, offering innovative insights into the design of high cycling stability cathodes for AZIBs.

Opportunities and Challenges of Multi-Ion, Dual-Ion and Single-Ion Intercalation in Phosphate-Based Polyanionic Cathodes for Zinc-Ion Batteries

With the continuous development of science and technology, battery storage systems for clean energy have become crucial for global economic transformation. Among various rechargeable batteries, lithium-ion batteries are widely used, but face issues like limited resources, high costs, and safety concerns. In contrast, zinc-ion batteries, as a complement to lithium-ion batteries, are drawing increasing attention. In the exploration of zinc-ion batteries, especially of phosphate-based cathodes, the battery action mechanism has a profound impact on the battery performance. In this paper, we first review the interaction mechanism of multi-ion, dual-ion, and single-ion water zinc batteries. Then, the impact of the above mechanisms on battery performance was discussed. Finally, the application prospects of the effective use of multi-ion, dual-ion, and single-ion intercalation technology in zinc-ion batteries is reviewed, which has significance for guiding the development of rechargeable water zinc-ion batteries in the future.

Highly Stable Photo-Assisted Zinc-Ion Batteries via Regulated Photo-Induced Proton Transfer

Photo-assisted ion batteries utilize light to boost capacity but face cycling instability due to complex charge/ion transfer under illumination. This study identified photo-induced proton transfer (photo-induced PT) as a significant process in photo-(dis)charging of widely-used V2O5-based zinc-ion batteries, contributing to enhanced capacity under illumination but jeopardizing photo-stability. Photo-induced PT occurs at 100 ps after photo-excitation, inducing rapid proton extraction into V2O5 photoelectrode. This process creates a proton-deficient microenvironment on surface, leading to repetitive cathode dissolution and anode corrosion in each cycle. Enabling the intercalated protons from photo-induced PT to be reversibly employed in charge-discharge processes via the anode-alloying strategy achieves high photo-stability for the battery. Consequently, a ~54 % capacity enhancement was achieved in a V2O5-based zinc-ion battery under illumination, with ~90 % capacity retention after 4000 cycles. This extends the photo-stability record by 10 times. This study offers promising advancements in energy storage by addressing instability issues in photo-assisted ion batteries.

Molybdenum-optimized electronic structure and micromorphology to boost zinc ions storage properties of vanadium dioxide nanoflowers as an advanced cathode for aqueous zinc-ion batteries

Recently, vanadium dioxide (VO2) has been recognized as one of the most prospective cathodes for aqueous zinc ion batteries (AZIBs) for its high reversible specific capacity; nevertheless, its Zn2+ diffusion kinetics and cycling stability have not yet met expectations. Herein, Mo ions are introduced into VO2 to optimize the intrinsic electronic structure and micromorphology of VO2, achieving significantly enhanced zinc-ion storage. It is found that the substitution of Mo for V narrows the band gap of VO2 and thus enhances the conductivity of the material, while VO2 nanorods are transformed into VO2 nanoflowers which are self-assembled from ultra-thin nanosheets after the introduction of Mo, exposing much more active sites to enhance the migration kinetics of Zn2+. Consequently, the Mo-substituted VO2 (0.5-Mo-VO2) exhibits excellent electrochemical properties, presenting a high initial capacity of 494.5 mAh/g at 0.5 A/g, excellent rate capability of 336 mA h g-1 at 10 A/g and brilliant cycling stability with the capacity retention of 82% over 2000 cycles at 10 A/g. This work provides significant guidance for the design of advanced cathodes for AZIBs by optimizing the electronic structure and tailoring morphology of V-based materials.

A Functional Janus Ag Nanowires/Bacterial Cellulose Separator for High-Performance Dendrite-Free Zinc Anode Under Harsh Conditions

Aqueous zinc-ion batteries (AZIBs) offer promising prospects for large-scale energy storage due to their inherent abundance and safety features. However, the growth of zinc dendrites remains a primary obstacle to the practical industrialization of AZIBs, especially under harsh conditions of high current densities and elevated temperatures. To address this issue, a Janus separator with an exceptionally ultrathin thickness of 29 µm is developed. This Janus separator features the bacterial cellulose (BC) layer on one side and Ag nanowires/bacterial cellulose (AgNWs/BC) layer on the other side. High zincophilic property and excellent electric/thermal conductivity of AgNWs make them ideal for serving as an ion pump to accelerate Zn2+ transport in the electrolyte, resulting in greatly improved Zn2+ conductivity, deposition of homogeneous Zn nuclei, and dendrite-free Zn. Consequently, the Zn||Zn symmetrical cells with the Janus separator exhibit a stable cycle life of over 1000 h under 80 mA cm-2 and are sustained for over 600 h at 10 mA cm-2 under 50 °C. Further, the Janus separator enables excellent cycling stability in AZIBs, aqueous zinc-ion capacitors (AZICs), and scaled-up flexible soft-packaged batteries. This study demonstrates the potential of functional separators in promoting the application of aqueous zinc batteries, particularly under harsh conditions.

Challenges and Strategies in the Development of Zinc-Ion Batteries

Although promising, the practical use of zinc-ion batteries (ZIBs) remains plagued with uncontrollable dendrite growth, parasitic side reactions, and the high intercalation energy of divalent Zn²⁺ ions. Hence, much work has been conducted to alleviate these issues to maximize the energy density and cyclic life of the cell. In this holistic review, the mechanisms and rationale for the stated challenges shall be summarized, followed by the corresponding strategies employed to mitigate them. Thereafter, a perspective on present research and the outlook of ZIBs would be put forth in hopes to enhance their electrochemical properties in a multipronged approach.

Vanadium Oxides with Amorphous-Crystalline Heterointerface Network for Aqueous Zinc-Ion Batteries

Rechargeable aqueous Zn-VO_x batteries are attracting attention in large scale energy storage applications. Yet, the sluggish Zn²⁺ diffusion kinetics and ambiguous structure-property relationship are always challenging to fulfil the great potential of the batteries. Here we electrodeposit vanadium oxide nanobelts (VO-E) with highly disordered structure. The electrode achieves high capacities (e.g., ≈5 mAh cm^-2 , 516 mAh g^-1 ), good rate and cycling performances. Detailed structure analysis indicates VO-E is composed of integrated amorphous-crystalline nanoscale domains, forming an efficient heterointerface network in the bulk electrode, which accounts for the good electrochemical properties. Theoretical calculations indicate that the amorphous-crystalline heterostructure exhibits the favorable cation adsorption and lower ion diffusion energy barriers compared to the amorphous and crystalline counterparts, thus accelerating charge carrier mobility and electrochemical activity of the electrode.

A blade-like CoZn metal organic framework-based flexible quasi-solid Zn-ion battery

Wearable flexible electronics has become more and more significant and popular in daily life. Here, a flexible quasi-solid Zn-ion battery consisting of CoZn-metal organic frameworks (MOFs) grown on carbon cloth as an all-in-one cathode working with a hydrogel electrolyte is developed. CoZn MOFs display a blade-like morphology, which is significant for rapid transfer of ions and electrons. The battery bending at angles from 0° to 180° displays high capacities and good capacity retention, and the capacity remains stable as the flexible battery twists to 90°. In addition, the capacity exceeds 101.4 mA h g^-1 as the battery is folded to 180° for 30 times, which indicates that the developed Zn-ion batteries would be applicable for a large variety of wearable devices such as foldable cellphones and pads.

Intercalation Pseudocapacitance of Cation-Exchanged Molybdenum-Based Polyoxometalate for the Fast and Stable Zinc-Ion Storage

Recently, intercalation pseudocapacitance has received significant interest as an abnormal charge storage mechanism owing to the battery-like intercalation energy storage into the bulk electrodes and the fast charge storage kinetics of electrochemical capacitors. However, intercalation pseudocapacitance of molybdenum-based polyoxometalates (POMs) for high-performance Zn ion battery (ZIB) cathodes is yet to be exploited. Herein, we demonstrate the fast and reversible intercalation pseudocapacitance of vanadium-substituted Keggin-type molybdenum-based POMs (XPMoV), where H of HPMoV is replaced by X cations (X = Li, Na, K, or Rb). This cation exchange allows cation-exchanged XPMoV to exhibit the morphological evolution into an anisotropic rodlike structure and to achieve a pillar effect on the improved chemical and structural integrity. Despite the micron-size rod morphology and the contracted lattice of (100) plane, the intercalation pseudocapacitance kinetics of XPMoV was dominated by the fast surface-confined electrochemistry and became highly reversible after the 1st cycle activation process by co-intercalation of Li+ and Zn2+ ions. Therefore, the ZIB with the KPMoV cathode delivered a high rate capability of 74.0 mAh g-1 at 20,000 mA g-1 and 87% capacity retention over 2000 cycles at 1000 mA g-1, far exceeding HPMoV and other Mo-based cathodes. This study paves the way to design the fast and reversible intercalation pseudocapacitance of POMs and the cation exchange chemistry into the improved (electro)chemical and structural integrity.

Stabilization of VOPO4·2H2O voltage and capacity retention in aqueous zinc batteries with a hydrogen bond regulator

The transformation of polyanion cathodes into oxides in aqueous Zn batteries results in voltage decay. Herein, we uncover a polyanion dissolution and oxide re-electrodeposition process for this transformation. Accordingly, the dissolution is inhibited by reducing the water activity in the electrolyte with the hydrogen bond regulator of glucose (Glu). In the 4 m Zn(OTf)₂/5.5 m Glu electrolyte, the VOPO₄·2H₂O cathode maintains the redox reactions at a high voltage of 1.6 V/1.5 V with stable capacity retention during cycling at different rates. It also shows promising electrochemical activity and stability at temperatures down to -20 °C.

A Comprehensive Understanding of Interlayer Engineering in Layered Manganese and Vanadium Cathodes for Aqueous Zn-ion Batteries

Rechargeable aqueous zinc-ion batteries (AZIBs) hold a budding technology for large-scale stationary energy storage devices due to their inherent safety, cost-effectiveness, eco-friendly, and acceptable electrochemical performance. However, developing a cathode material with fast kinetics and durable structural stability for Zn 2+ intercalation is still an arduous challenge. Compared with other cathode materials, layered manganese/vanadium (Mn/V) oxides that feature merits of adjustable interlayer spacing and considerable specific capacity have attracted much interest in AZIBs. However, the intrinsic sluggish reaction kinetics, inferior electrical conductivity, and notorious dissolution of active materials still obstruct the realization of their full potentials. Interlayer engineering of pre-intercalation is regarded as an effective solution to overcome these problems. In this review, we start from the crystal structure and reaction mechanism of layered Mn/V oxide cathodes to critical issues and recent progress in interlayer engineering. Finally, some future perspectives are outlined for the development of high-performance AZIBs.

Binder-free three-dimensional interconnected CuV2O5•nH2O nest as cathodes for high-loading aqueous zinc-ion batteries

In large-scale energy storage applications, aqueous zinc ion batteries (ZIBs) with low cost, safety, high theoretical capacity, and environmentally friendly have wide application prospects. In the reported cathode materials, the...

Oxygen Defect Hydrated Vanadium Dioxide/Graphene as a Superior Cathode for Aqueous Zn Batteries

Zinc ion batteries have become a new type of energy storage device because of the low cost and high safety. Among the various cathode materials, vanadium-oxygen compounds stand out due to their high theoretical capacity and variable chemistry valence state. Here, we construct a 3D spongy hydrated vanadium dioxide composite (O_d-HVO/rG) with abundant oxygen vacancy defects and graphene modifications. Thanks to the stable structure and abundant active sites, O_d-HVO/rG exhibits superior electrochemical properties. In aqueous electrolyte, the O_d-HVO/rG cathode provides high initial charging capacity (428.6 mAh/g at 0.1 A/g), impressive rate performance (186 mAh/g even at 20 A/g), and cycling stability, which can still maintain 197.5 mAh/g after 2000 cycles at 10 A/g. Also, the superior specific energy of 245.3 Wh/kg and specific power of 14142.7 W/kg are achieved. In addition, MXene/O_d-HVO/rG cathode materials are prepared and PAM/ZnSO₄ hydrogel electrolytes are applied to assemble flexible soft pack quasi-solid-state zinc ion batteries, which also exhibit excellent flexibility and cycling stability (206.6 mAh/g after 2000 cycles). This work lays the foundation for advances in rechargeable aqueous zinc ion batteries, while revealing the potential for practical applications of flexible energy storage devices.

Tremella-like Hydrated Vanadium Oxide Cathode with an Architectural Design Strategy toward Ultralong Lifespan Aqueous Zinc-Ion Batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) are promising systems for energy storage due to their operational safety, low cost, and environmental friendliness. However, the development of suitable cathode materials is plagued by the sluggish dynamics of Zn²⁺ with strong electrostatic interaction. Herein, an Al³⁺-doped tremella-like layered Al_0.15V₂O₅·1.01H₂O (A-VOH) cathode material with a large pore diameter and high specific surface area is demonstrated to greatly boost electrochemical performance as ZIB cathodes. Resultant ZIBs with a 3 M Zn(CF₃SO₃)₂ electrolyte deliver a high specific discharge capacity of 510.5 mAh g^-1 (0.05 A g^-1), and an excellent energy storage performance is well maintained with a specific capacity of 144 mAh g^-1 (10 A g^-1) even after ultralong 10,000 cycles. The decent electrochemical performance roots in the novel tremella-like structure and the interlayer of Al³⁺ ions and water molecules, which could improve the electrochemical reaction kinetics and structural long cycle stability. Furthermore, the assembled coin-type cells could power a light-emitting diode (LED) lamp for 2 days. We believed that the design philosophy of unique morphology with abundant active sites for Zn²⁺ storage will boost the development of competitive cathodes for high-performance aqueous batteries.

Regulating the Interlayer Spacing of Vanadium Oxide by In Situ Polyaniline Intercalation Enables an Improved Aqueous Zinc-Ion Storage Performance

Vanadium pentoxide (V₂O₅) possesses great potential for application as cathode materials for aqueous zinc-ion batteries due to abundant valences of vanadium. Unfortunately, the inferior electronic conductivity and confined interlayer spacing of pristine V₂O₅ are not able to support fast Zn²⁺ diffusion kinetics, leading to significant capacity degradation, the dissolution of active species, and unsatisfactory cycling life. Herein, Zn²⁺ (de)intercalation kinetics is improved by the design of in situ polyaniline (PANI)-intercalated V₂O₅. The intercalated PANI can not only improve the conductivity and structural stability of V₂O₅ but also efficiently expand its interlayer spacing (1.41 nm), offering more channels for facile Zn²⁺ diffusion. Benefiting from these virtues, a high specific capacity of 356 mA h g^-1 at 0.1 A g^-1 is achieved for the PANI-intercalated V₂O₅ (PVO) cathode as well as a superior cycling performance (96.3% capacity retention after 1000 cycles at 5 A g^-1) in an aqueous electrolyte. Furthermore, the Zn²⁺ storage in PVO is mainly dominated by the capacitive contribution. This work suggests that intercalating PANI in V₂O₅ may aid in the future development of advanced cathodes for other multivalent metal ion batteries.