Monoclinic VO2(D) hollow nanospheres with super-long cycle life for aqueous zinc ion batteries

Preparation of Thermochromic Vanadium Dioxide Films Assisted by Machine Learning

In recent years, smart windows have attracted widespread attention due to their ability to respond to external stimuli such as light, heat, and electricity, thereby intelligently adjusting the ultraviolet, visible, and near-infrared light in solar radiation. VO2(M) undergoes a reversible phase transition from an insulating phase (monoclinic, M) to a metallic phase (rutile, R) at a critical temperature of 68 °C, resulting in a significant difference in near-infrared transmittance, which is particularly suitable for use in energy-saving smart windows. However, due to the multiple valence states of vanadium ions and the multiphase characteristics of VO2, there are still challenges in preparing pure-phase VO2(M). Machine learning (ML) can learn and generate models capable of predicting unknown data from vast datasets, thereby avoiding the wastage of experimental resources and reducing time costs associated with material preparation optimization. Hence, in this paper, four ML algorithms, namely multi-layer perceptron (MLP), random forest (RF), support vector machine (SVM), and extreme gradient boosting (XGB), were employed to explore the parameters for the successful preparation of VO2(M) films via magnetron sputtering. A comprehensive performance evaluation was conducted on these four models. The results indicated that XGB was the top-performing model, achieving a prediction accuracy of up to 88.52%. A feature importance analysis using the SHAP method revealed that substrate temperature had an essential impact on the preparation of VO2(M). Furthermore, characteristic parameters such as sputtering power, substrate temperature, and substrate type were optimized to obtain pure-phase VO2(M) films. Finally, it was experimentally verified that VO2(M) films can be successfully prepared using optimized parameters. These findings suggest that ML-assisted material preparation is highly feasible, substantially reducing resource wastage resulting from experimental trial and error, thereby promoting research on material preparation optimization.

Reversible Deposition/Dissolution of Double Hydroxides to Modulate Electrolyte pH Enabling High-Performance Aqueous Zinc-Ion Batteries

Vanadium oxide has been extensively studied as a host of zinc ion intercalation but still suffers from low conductivity, dissolution, and byproduct accumulation during cycling. Here, we hydrothermally synthesize the VO2@MXene Ti3C2 (MV) composite and find that in the MV//3 M Zn(CF3SO3)2//Zn system, the double hydroxide Zn12(CF3SO3)9(OH)15·nH2O (ZCOH) uniformly covers VO2 during the charging process and dissolves reversibly during the discharge process. In situ X-ray diffraction of the MV combined with in situ pH measurements reveals that ZCOH acts as a pH buffer during cycling, which is beneficial to the cycling stability of batteries. And the theoretical calculation indicates that the decomposition energy required by ZCOH on the MV surface is lower than that on pure VO2, which is more conducive to ZCOH dissolution. The coin battery exhibits high-rate performance of 65.1% capacity retention at a current density of 15 A g-1 (compared to 0.6 A g-1) and a long cycling life of 20,000 cycles with a capacity retention of 80.7%. For a 22.4 mA h soft-packaged battery, its capacity remains at 72.1% after 2000 cycles. This work demonstrates the active role of ZCOH in the electrochemical process of VO2 and provides a new perspective for exploiting this mechanism to develop high-performance aqueous zinc-ion battery vanadium oxide cathode materials.

High-Performance Aqueous Zinc-Ion Batteries Based on Multidimensional V2O3 Nanosheets@Single-Walled Carbon Nanohorns@Reduced Graphene Oxide Composite and Optimized Electrolyte

The drawbacks of poor electronic conductivity and structural instability during the cycling process limit the electrochemical property of vanadium-based cathode materials for aqueous zinc-ion batteries. In addition, continuous growth and accumulation of zinc dendrites can puncture the separator and cause an internal short circuit in the battery. In this work, a unique multidimensional nanocomposite is designed by a facile freeze-drying method with subsequent calcination, consisting of V2O3 nanosheets and single-walled carbon nanohorns (SWCNHs) crosslinked together and wrapped by reduced graphene oxide (rGO). The multidimensional structure can largely enhance the structural stability and electronic conductivity of the electrode material. Besides, additive Na2SO4 in the ZnSO4 aqueous electrolyte not only prevents the dissolution of cathode materials but also suppresses the Zn dendrite growth. After considering the influence of additive concentration on ionic conductivity and electrostatic force for electrolyte, V2O3@SWCNHs@rGO electrode delivers a high initial discharge capacity of 422 mAh g-1 at 0.2 A g-1 and a high discharge capacity of 283 mAh g-1 after 1000 cycles at 5 A g-1 in 2 m ZnSO4 + 2 m Na2SO4 electrolyte. Experimental techniques reveal that the electrochemical reaction mechanism can be expressed as the reversible phase transformation between V2O5 and V2O3 with Zn3(VO4)2.

Critical triple roles of sodium iodide in tailoring the solventized structure, anode-electrolyte interface and crystal plane growth to achieve highly reversible zinc anodes for aqueous zinc-ion batteries

Aqueous rechargeable Zn-ion batteries (ARZIBs) are promising for energy storage. However, the Zn dendrite and corrosive reactions on the surface of Zn anode limit the practical uses of ARZIBs. Herein, we present a valid electrolyte additive of NaI, in which I- can modulate the morphology of Zn crystal growth by adsorbing on specific crystal surfaces (002), and guide Zn deposition by inducing a negative charge on the Zn anode. Simultaneously, it enhances the reduction stability of water molecules by participating in the solvation structure of Zn(H2O)62+ by forming ZnI(H2O)5+. At 10 mA cm-2, the assembled Zn symmetrical batteries can run stably over 1,100 h, and the depth of discharge (DOD) can reach 51.3 %. At 1 A g-1, the VO2||Zn full-cell in 2 M ZnCl2 electrolyte with 0.4 M NaI (2 M ZnCl2-0.4 M NaI) maintains of the capacity retention of 75.7 % over 300 cycles. This work offers an insight into inorganic anions as electrolyte additives for achieving stable zinc anodes of ARZIBs.

Regulating Zinc Storage Behaviors of Tunnel Structure Cathodes Via Tungsten Induction

Aqueous zinc-ion batteries have received continuous interests because of applying low-cost and eco-friendly aqueous electrolytes and having high safety. Beyond energetically to explore new-type cathode materials, it is of great significance to regulate the zinc storage behavior of the existing cathodes in order to understand the underlying working mechanism. Therefore, as a proof of concept, this work achieves the regulation of zinc storage behaviors of the tunnel structure tunnel structure B-phase vanadium dioxide (VO2 (B)) and vanadium oxide (V6 O13 ) cathodes via a simple chemical tungsten-doping induction approach. Under low-concentration tungsten-doping induction of 1, 2 and 3 at.%, the tunnel sizes of VO2 (B) can be controlled readily. Moreover, the V6 O13 with large size tunnels can be achieved by medium-concentration tungsten induction of 6 and 9 at.%. It is demonstrated that tungsten induced VO2 (B) can achieve zinc storage without lattice structure change via operando X-ray diffraction analyses. Remarkably, via operando and non-operando analyses, tungsten induced V6 O13 with lager size tunnels can realize the oriented 1D zinc ion intercalation/deintercalation. The further kinetics analysis shows that the zinc storage is mainly diffusion control, which is different from most of vanadium-based cathodes with capacitance control. This viable tungsten-doping induction strategy provides a new insight into achieving the controllable regulation of zinc storage behaviors.

Stable structure and fast ion diffusion: N-doped VO2 3D porous nanoflowers for applications in ultrafast rechargeable aqueous zinc-ion batteries

Aqueous rechargeable zinc-ion batteries (ARZIBs) are promising candidates for fast-charging energy-storage systems. The issues of stronger interactions between Zn²⁺ and the cathode for ultrafast ARZIBs can be partially addressed by enhancing mass transfer and ion diffusion of the cathode. Herein, via thermal oxidation for the first time, N-doped VO₂ porous nanoflowers with short ion diffusion paths and improved electrical conductivity were synthesized as ARZIBs cathode materials. The introduction of nitrogen derived from the vanadium-based-zeolite imidazolyl framework (V-ZIF) contributes to enhanced electrical conductivity and faster ion diffusion, while the thermal oxidation of the VS₂ precursor assists the final product in exhibiting a more stable three-dimensional nanoflower structure. In particular, the N-doped VO₂ cathode shows excellent cycle stability and superior rate capability with the delivered capacities of 165.02 mAh g^-1 and 85 mAh g^-1, at 10 A g^-1 and 30 A g^-1, and the capacity retention of 91.4% after 2200 cycles and 99% after 9000 cycles, respectively. Remarkably, the battery takes less than 10 s to be fully charged at 30 A g^-1. Hence, this work provides a new avenue for designing unique nanostructured vanadium oxides and developing electrode materials suitable for ultrafast charging.

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.

Vanadium Oxide-Based Cathode Materials for Aqueous Zinc-Ion Batteries: Energy Storage Mechanism and Design Strategy

Aqueous zinc ion batteries (AZIBs) are an ideal choice for a new generation of large energy storage devices because of their high safety and low cost. Vanadium oxide-based materials have attracted great attention in the field of AZIB cathode materials due to their high theoretical capacity resulting from their rich oxidation states. However, the serious structural collapse and low intrinsic conductivity of vanadium oxide-based materials cause rapid capacity fading, which hinders their further applications in AZIB cathode materials. Here, the structural characteristics and energy storage mechanisms of vanadium oxide-based materials are reviewed, and the optimization strategies of vanadium oxide-based cathode materials are summarized, including substitutional doping, vacancy engineering, interlayer engineering, and structural composite. Finally, the future research and development direction of vanadium oxide-based AZIBs are prospected in terms of cathode, anode, electrolyte, non-electrode components, and recovery technology.

Flexible Ammonium-Ion Pouch Cells Based on a Tunneled Manganese Dioxide Cathode

Aqueous ammonium-ion (NH₄⁺) batteries are becoming the competitive energy storage candidate on account of their safety, affordability, sustainability, and intrinsically peculiar properties. Herein, an aqueous NH₄⁺-ion pouch cell is investigated based on a tunneled manganese dioxide (α-MnO₂) cathode and a 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) anode. The MnO₂ electrode possesses a high specific capacity of ∼190 mA h g^-1 at 0.1 A g^-1 and displays excellent long cycling performance after 50,000 cycles in 1 M (NH₄)₂SO₄, which outperforms the most reported ammonium-ion host materials. Besides, a solid-solution behavior is revealed about the migration of NH₄⁺ in the tunnel-like α-MnO₂. The battery displays a splendid rate capacity of 83.2 mA h g^-1 even at 10 A g^-1. It also exhibits a high energy density of ∼78 W h kg^-1 as well as a high power density of ∼8212 W kg^-1 (based on the mass of MnO₂). What is more, the flexible MnO₂//PTCDA pouch cell based on the hydrogel electrolyte shows excellent flexibility and good electrochemical properties. The topochemistry results of MnO₂//PTCDA point to the potential practicability of ammonium-ion energy storage.

A design of MnO-CNT@C3N4 cathodes for high-performance aqueous zinc-ion batteries

Manganese oxides have been regarded as one of the most promising candidates in rechargeable aqueous zinc ion batteries due to their high specific capacity, high operating voltage, low cost and no-toxicity. Nevertheless, the grievous dissolution of manganese and the sluggish Zn²⁺ ions diffusion kinetics deteriorate the long cycling stability and the rate performance. Herein, we propose a combination of hydrothermal and thermal treatment strategy to design a MnO-CNT@C₃N₄ composite cathode material where MnO cubes are coated by carbon nanotubes (CNTs) and C₃N₄. Owing to the enhanced conductivity by CNTs and the alleviation of the dissolution of Mn²⁺ from the active material by C₃N₄, the optimized MnO-CNT@C₃N₄ exhibits an excellent rate performance (101 mAh g^-1 at a large current density of 3 A g^-1) and a high capacity (209 mAh g^-1 at a current density of 0.8 A g^-1), which is much better than its MnO counterpart. The energy storge mechanism of MnO-CNT@C₃N₄ is confirmed to be the co-insertion of H⁺/Zn²⁺. The present work provides a viable strategy for the design of advanced cathodes for high-performance zinc ion batteries.

Unlocking the High Capacity Ammonium-Ion Storage in Defective Vanadium Dioxide

Aqueous ammonium-ion storage has been considered a promising energy storage competitor to meet the requirements of safety, affordability, and sustainability. However, ammonium-ion storage is still in its infancy in the absence of reliable electrode materials. Here, defective VO₂ (d-VO) is employed as an anode material for ammonium-ion batteries with a moderate transport pathway and high reversible capacity of ≈200 mAh g^-1 . Notably, an anisotropic or anisotropic behavior of structural change of d-VO between c-axis and ab planes depends on the state of charge (SOC). Compared with potassium-ion storage, ammonium-ion storage delivers a higher diffusion coefficient and better electrochemical performance. A full cell is further fabricated by d-VO anode and MnO₂ cathode, which delivers a high energy density of 96 Wh kg^-1 (based on the mass of VO₂ ), and a peak energy density of 3254 W kg^-1 . In addition, capacity retention of 70% can be obtained after 10 000 cycles at a current density of 1 A g^-1 . What's more, the resultant quasi-solid-state MnO₂ //d-VO full cell based on hydrogel electrolyte also delivers high safety and decent electrochemical performance. This work will broaden the potential applications of the ammonium-ion battery for sustainable energy storage.

Zinc ion thermal charging cell for low-grade heat conversion and energy storage

Converting low-grade heat from environment into electricity shows great sustainability for mitigating the energy crisis and adjusting energy configurations. However, thermally rechargeable devices typically suffer from poor conversion efficiency when a semiconductor is employed. Breaking the convention of thermoelectric systems, we propose and demonstrate a new zinc ion thermal charging cell to generate electricity from low-grade heat via the thermo-extraction/insertion and thermodiffusion processes of insertion-type cathode (VO2-PC) and stripping/plating behaviour of Zn anode. Based on this strategy, an impressively high thermopower of ~12.5 mV K-1 and an excellent output power of 1.2 mW can be obtained. In addition, a high heat-to-current conversion efficiency of 0.95% (7.25% of Carnot efficiency) is achieved with a temperature difference of 45 K. This work, which demonstrates extraordinary energy conversion efficiency and adequate energy storage, will pave the way towards the construction of thermoelectric setups with attractive properties for high value-added utilization of low-grade heat.

A facile method for pre-insertion of cations and structural water in preparing durable zinc storage vanadate cathodes

For improving the overall energy storage performance of aqueous zinc-ion battery (ZIB) systems, it is important to identify new cathode materials with superior characteristics. Along these lines, in this work,...

Recent Developments and Challenges of Vanadium Oxides (Vx Oy ) Cathodes for Aqueous Zinc-Ion Batteries

The rapid depletion of lithium resources and the increasing demand for electrical energy storage have stimulated the pursuit of emerging electrochemical energy storage. Aqueous zinc ion batteries (ZIBs) are highly sought after for their low cost, high safety, and increased environmental compatibility. However, the search for suitable cathode materials is still tricky for a wide range of researchers. Vanadium oxides (V_x O_y ), with their abundant vanadium valence, easily deformable V-O polyhedrons, and tunable chemical compositions, are of significant advantage in developing emerging materials. This work provides a detailed review of different V_x O_y for the application in aqueous ZIBs. The current problems and optimization strategies of V_x O_y cathode materials are systematically discussed. Finally, the current challenges and possible directions for future research of V_x O_y cathode materials in aqueous ZIBs are presented.

Cathode materials for aqueous zinc-ion batteries: A mini review

Although lithium-ion batteries (LIBs) have many advantages, they cannot satisfy the demands of numerous large energy storage industries owing to their high cost, low security, and low resource richness. Aqueous zinc-ion batteries (ZIBs) with low cost, high safety, and high synergistic efficiency have attracted an increasing amount of attention and are considered a promising choice to replace LIBs. However, the existing cathode materials for ZIBs have many shortcomings, such as poor electron and zinc ion conductivity and complex energy storage mechanisms. Thus, it is crucial to identify a cathode material with a stable structure, substantial limit, and suitability for ZIBs. In this review, several typical cathode materials for ZIBs employed in recent years and their detailed energy storage mechanisms are summarized, and various methods to enhance the electrochemical properties of ZIBs are briefly introduced. Finally, the existing problems and expected development directions of ZIBs are discussed.

(NH4 )2 V7 O16 Microbricks as a Novel Anode for Aqueous Lithium-Ion Battery with Good Cyclability

Searching for novel anode materials to address the issues of poor cycle stability in the aqueous lithium-ion battery system is highly desirable. In this work, ammonium vanadium bronze (NH₄ )₂ V₇ O₁₆ with brick-like morphology has been investigated as an anode material for aqueous lithium-ion batteries and Li⁺ /Na⁺ hybrid ion batteries. The two novel full cell systems (NH₄ )₂ V₇ O₁₆ ||Li₂ SO₄ ||LiMn₂ O₄ and (NH₄ )₂ V₇ O₁₆ ||Na₂ SO₄ ||LiMn₂ O₄ both demonstrate good rate capability and excellent cycling performance. A capacity retention of 78.61 % after 500 cycles at 300 mA g^-1 was demonstrated in the (NH₄ )₂ V₇ O₁₆ ||Li₂ SO₄ ||LiMn₂ O₄ system, whereas no capacity attenuation is observed in the (NH₄ )₂ V₇ O₁₆ ||Na₂ SO₄ ||LiMn₂ O₄ system. The reaction mechanisms of the (NH₄ )₂ V₇ O₁₆ electrode and impedance variation of the two full cells were also researched. The excellent cycling stability suggests that layered (NH₄ )₂ V₇ O₁₆ can be a promising anode material for aqueous rechargeable lithium-ion batteries.

VO2(B)@carbon fiber sheet as a binder-free flexible cathode for aqueous Zn-ion batteries

A flexible VO2(B)@CFS electrode exhibits a high capacity and a long cycle life for zinc-ion batteries.

Willow-Leaf-Like ZnSe@N-Doped Carbon Nanoarchitecture as a Stable and High-Performance Anode Material for Sodium-Ion and Potassium-Ion Batteries

ZnSe is regarded as a promising anode material for energy storage due to its high theoretical capacity and environment friendliness. Nevertheless, it is still a significant challenge to obtain superior electrode materials with stable performance owing to the serious volume change and aggregation upon cycling. Herein, a willow-leaf-like nitrogen-doped carbon-coated ZnSe (ZnSe@NC) composite synthesized through facile solvothermal and subsequent selenization process is beneficial to expose more active sites and facilitate the fast electron/ion transmission. These merits significantly enhance the electrochemical performances of ZnSe@NC for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). The obtained ZnSe@NC exhibits outstanding rate performance (440.3 mAh g^-1 at 0.1 A g^-1 and 144.4 mAh g^-1 at 10 A g^-1 ) and ultralong cycle stability (242.2 mAh g^-1 at 8.0 A g^-1 even after 3200 cycles) for SIBs. It is noted that 106.5 mAh g^-1 can be retained after 550 cycles and 71.4 mAh g^-1 is still remained after 1500 cycles at 200 mA g^-1 when applied as anode for PIBs, indicating good cycle stability of the electrode. The possible electrochemical mechanism and the ionic diffusion kinetics of the ZnSe@NC are investigated using ex situ X-ray diffraction, high-resolution transmission electron microscopy, and a series of electrochemical analyses.

Operando pH Measurements Decipher H+/Zn2+ Intercalation Chemistry in High-Performance Aqueous Zn/δ-V2O5 Batteries

Vanadium oxides have been recognized to be among the most promising positive electrode materials for aqueous zinc metal batteries (AZMBs). However, their underlying intercalation mechanisms are still vigorously debated. To shed light on the intercalation mechanisms, high-performance δ-V₂O₅ is investigated as a model compound. Its structural and electrochemical behaviors in the designed cells with three different electrolytes, i.e., 3 m Zn(CF₃SO₃)₂/water, 0.01 M H₂SO₄/water, and 1 M Zn(CF₃SO₃)₂/acetonitrile, demonstrate that the conventional structural and elemental characterization methods cannot adequately clarify the separate roles of H⁺ and Zn²⁺ intercalations in the Zn(CF₃SO₃)₂/water electrolyte. Thus, an operando pH determination method is developed and used toward Zn/δ-V₂O₅ AZMBs. This method indicates the intercalation of both H⁺ and Zn²⁺ into δ-V₂O₅ and uncovers an unusual H⁺/Zn²⁺-exchange intercalation-deintercalation mechanism. Density functional theory calculations further reveal that the H⁺/Zn²⁺ intercalation chemistry is a consequence of the variation of the electrochemical potential of Zn²⁺ and H⁺ during the electrochemical intercalation/release.

A Chemically Polished Zinc Metal Electrode with a Ridge-like Structure for Cycle-Stable Aqueous Batteries

Aqueous rechargeable zinc (Zn) metal batteries show great application prospects in grid-scale energy storage devices due to their good safety, low cost, and considerable energy density. However, the electrical and topographical inhomogeneity caused by the native passivation layer of metallic Zn foil leads to inhomogeneous electrochemical plating and stripping of metallic Zn, and the limited accessible area to the electrolyte of the regular foil electrode causes the poor rate capability, which together hinder the practical application of the Zn metal electrode in rechargeable aqueous batteries. In this work, we show that the native passivation layer on the Zn foil electrode can be removed by a simple chemical polishing strategy, associated with the formation of a three-dimensional ridge-like structure of metallic Zn (r-Zn) on the surface of the Zn foil electrode due to the selective etching of weak crystallographic planes and grain boundary of metallic Zn. The clean and uniform surface of the metallic Zn electrode enables homogeneous plating and stripping of metallic Zn, and the ridge-like structure of r-Zn increases the accessible surface area to the electrolyte and reduces the local current density, which elevates the electrochemical performance of the Zn metal anode with regard to the cycling stability and rate capability. It is demonstrated that a r-Zn anode cycles stably for over 200 h at 1 mA cm^-2 and 0.5 mA h cm^-2 with a low overpotential of 20 mV, which far outperforms 39 h of cycling with an overpotential of 72 mV for its pristine metallic Zn counterpart.

Preparation and electrochemical performance of VO2(A) hollow spheres as a cathode for aqueous zinc ion batteries

Rechargeable aqueous zinc ion batteries (ZIBs), owing to their low-cost zinc metal, high safety and nontoxic aqueous electrolyte, have the potential to accelerate the development of large-scale energy storage applications. However, the desired development is significantly restricted by cathode materials, which are hampered by the intense charge repulsion of bivalent Zn2+. Herein, the as-prepared VO2(A) hollow spheres via a feasible hydrothermal reaction exhibit superior zinc ion storage performance, large reversible capacity of 357 mA h g-1 at 0.1 A g-1, high rate capability of 165 mA h g-1 at 10 A g-1 and good cycling stability with a capacity retention of 76% over 500 cycles at 5 A g-1. Our study not only provides the possibility of the practical application of ZIBs, but also brings a new prospect of designing high-performance cathode materials.