Cathode For Aqueous Zn-ion Batteries Research Articles

A stable ZnMn2O4 cathode for aqueous Zn-ion batteries via Ni doping to suppress Mn dissolution

ZnMn2O4 (ZMO) emerges as a promising cathode for aqueous Zn-ion batteries due to its high theoretical capacity of 224 mAh g−1 and operating voltage of ∼1.9 V (vs. Zn2+/Zn). However, it suffers from capacity degradation over cycling, attributed to the dissolution of redox-active Mn through Mn3+ disproportionation. In this study, we propose a strategy to stabilize ZMO cathodes by transforming Mn3+ into Mn4+ via Ni doping, aiming for charge balance. The ZnMn2−xNixO4 (x = 0, 0.5, 1.0, and 1.5) with different Ni amounts was prepared by straightforward precipitation and calcination. The mitigation of redox-active Mn dissolution enhanced the specific capacity of all Ni-doped ZMO compared to 201 mAh g−1 of ZMO. ZnMn1.5Ni0.5O4 and ZnMnNiO4 exhibit 277 and 278 mAh g−1, respectively, surpassing ZMO’s theoretical capacity (224 mAh g−1) of ZMO. This additional capacity was attributed to MnOx deposition on the cathode and the charge storage reaction with Zn-ion within the MnOx deposit. Furthermore, Ni doping induces a structural transition of the tetragonal into a cubic spinel, expanding the unit cell volume. This structural modification combined with suppressed Mn dissolution contributes to improved cycling stability. ZnMnNiO4 exhibits 80 % retention of initial capacity after 1000 cycles, outperforming ZMO (57 % retention). The expanded unit cell reduces repulsion between inserted Zn ions, enabling a higher rate performance than pure ZMO. The change in Mn valence states induced by Ni doping enhanced the lifespan and rate capability of ZMO cathodes, underscoring their potential as cathodes for Zn-ion batteries.

Exploring the Enhanced Zinc Storage Performance of α-MnSe Polyhedral Microspheres and H+/Zn2+ Co-Insertion Mechanism.

The newly emerged Mn-based selenides as cathodes for aqueous Zn-ion batteries (ZIBs) have drawn researchers' interest because of their lower electronegativity and better electronic conductivity compared with the corresponding Mn-based oxides. Nevertheless, the energy storage mechanism of Mn-based selenides still needs to be further clarified. Herein, the MnSe/Se and MnSe polyhedral microspheres are reported as cathodes for ZIBs, and the MnSe cathode achieves significantly enhanced specific capacity, rate performance, and cycling stability. In-depth kinetic analysis confirms that the MnSe cathode presents better kinetic behavior and density functional theory (DFT) calculations verify the fast diffusion kinetics of the MnSe cathode. More importantly, systematic ex situ characterizations reveal that the microstructured MnSe can exist stably during the charge-discharge process and store energy with H+/Zn2+ co-insertion mechanism, which is greatly different from the phase transformation of the nanostructured α-MnSe reported in the literature. Additionally, it is verified that the different types of separators exhibit remarkably different zinc storage performance of the MnSe cathode. This study not only offers a good guidance for developing high-performance ZIBs Mn-based cathode materials and explores the effect of separators on the zinc storage performance, but also provides new insights into the energy storage mechanism of the MnSe cathode.

High-Performance Aqueous Zinc-Organic Battery with a Photo-Responsive Covalent Organic Framework Cathode.

Covalent organic framework (COF) materials, known for their robust porous character, sustainability, and abundance, have great potential as cathodes for aqueous Zn-ion batteries (ZIBs). However, their application is hindered by low reversible capacity and discharge voltage. Herein, a donor-acceptor configuration COF (NT-COF) is utilized as the cathode for ZIBs. The cell exhibits a high discharge voltage plateau of ≈1.4V and a discharge capacity of 214 mAh g-1 at 0.2 A g-1 when utilizing the Mn2+ electrolyte additive in the ZnSO4 electrolyte. A synergistic combination mechanism is proposed, involving the deposition/dissolution reactions of Zn4SO4(OH)6·4H2O and the co-(de)insertion reactions of H+ and SO4 2- in NT-COF. Meanwhile, the NT-COF with a donor-acceptor configuration facilitates efficient generation and separation of electron-hole pairs upon light exposure, thereby enhancing electrochemical reactions within the battery. This leads to a reduction in charging voltage and internal overvoltage, ultimately minimizing electricity consumption. Under ambient weather conditions, the cell exhibits an average discharge capacity of 430 mAh g-1 on sunny days and maintains consistent cycling stability for a duration of 200 cycles (≈19 days) at 0.2 A g-1. This research inspires the advancement of Zn-organic batteries for high-energy-density aqueous electrochemical energy storage systems or photo-electrochemical batteries.

Two-dimensional copper vanadate intercalated vanadium carbide MXene nanoplates as a high-performance cathode for aqueous Zn-ion batteries

Cathode materials play a crucial role in the energy-storage performances of zinc ion battery (ZIB). In this paper, the two-dimensional vanadium carbide MXene (V2C-MXene) nanoplates intercalated by Cu3V2O7(OH)2·2 H2O (CuVO) are synthesized. The intercalation of CuVO in the interlayers of V2C-MXene overcomes self-aggregation of CuVO and improves its structural stability. Meanwhile, the enlarged interlayer spacing of highly conductive V2C-MXene upgrades the electron transfer within the composite. As the cathode electrode of ZIB, the CuVO intercalated V2C-MXene (CuVO@V2C-MXene) battery shows capacity as high as 551.8 mAh g−1 when discharged at 0.5 A g−1. The capacity retention rate reaches 91.8% after 3000 cycles at high current density of 6.0 A g−1. As a comparison, the CuVO//Zn battery has capacity only 193.3 mAh g−1 at 0.5 A g−1, with the capacity retention of just 43.1% after 3000 cycles at 6.0 A g−1. Simultaneously, the CuVO@V2C-MXene//Zn illustrates greatly improved rate capability compared with CuVO//Zn. The CuVO@V2C-MXene composite nanoplates in this work show promise in fabrication of high capacity metal ion batteries.

Advanced polyanionic cathode materials for aqueous zinc-ion batteries: from crystal structures, reaction mechanisms, design strategies to future perspectives

This review summarizes the latest research progress in polyanionic cathodes for aqueous Zn-ion batteries from the perspectives of crystal structure, reaction mechanism, and design strategy, finally highlights potential challenges and future outlook.

Co/Mn ratio-regulated hexacyanoferrates as a long-life and high-rate cathode for aqueous Zn-ion batteries

Among all kinds of cathodes for aqueous Zn-ion batteries, Mn-based hexacyanoferrates exhibit advantages of high-voltage and abundant resources. However, they suffer from inferior cycle-life and rate capability, which may be attributed to the structural instability and metal ion dissolution. In this work, a continuous element substitution (Mn replaced by Co) is employed to modify the electrochemical performance of Mn-based hexacyanoferrates. With the increasing ration of Co/Mn, the Mn, Co-based hexacyanoferrate (MnCoHCF) samples show unchanged crystalline phase with similar morphology and increasing Co dopant. Additionally, the initial specific capacity gradually decreases, but the electrochemical polarization is alleviated. Among the samples, MnCoHCF-4 (ratio of Co/Mn of 3:1) exhibits excellent cycling life (71.4% after 3000 cycles at 5 C) and rate performance (81.4 mA h g−1 at 10 C). In-situ techniques reveal the obvious metal ion dissolution with a low ratio of Co/Mn during the electrochemical process, resulting in poor structure stability and reaction kinetics of MnHCF electrode. However, When the ratio of Co/Mn is increased, the metal ion dissolution is effectively suppressed, and the MnCoHCF electrode shows improved structure stability and reaction kinetics. This work proposes an effective modification for hexacyanoferrates and other high-voltage Prussian blue analogues, which may promote the application of aqueous Zn-ion batteries.

Performance of Several Excellent Oxide-Based Intercalation Cathodes for Aqueous Zn-Ion Batteries

Aqueous Zn-ion batteries (ZIBs) have garnered significant interest in recent years due to their advantages in safety, cost, and energy density, which make them suitable for large-scale stationary energy storage. Cathode materials have been a primary research focus in the early stage of ZIBs development since they are widely deemed a limiting factor to the performance. In general, good ZIB cathode materials are found in oxides with layered and open framework structures, and inorganic/organic hybrids, and follow mechanisms of “intercalation”, “conversion” or a combination of both to store Zn2+ and H+ during discharge. However, dissolution of these cathodes into aqueous electrolytes has been a major cause of the performance degradation of aqueous ZIBs. In this presentation, we first show our fundamental understanding of cathode dissolution mechanisms and development of engineering solutions to address the dissolution and instability issues. We then show through several examples how specially engineered V-oxides based cathodes achieve better dissolution resistance and performance stability using aqueous Zn(OTf)2 and ZnSO4 electrolytes as examples. We expect that the insights in this presentation will advance the understanding of dissolution mechanisms and provide design principles for better cathode materials.

Electron structure and defect co-modulation to boost zinc storage performance of urchin-like VS4-based microspheres as advanced cathodes for aqueous Zn-ion batteries

Recently, aqueous zinc ion batteries (AZIBs) have been widely favored for their intrinsic safety, low cost and environmental friendliness; however, the vast volume expansion, poor electrical conductivity and low-density zinc insertion and extraction channels of the cathodes cannot meet the requirements of practical application for AZIBs. Herein, urchin-like Co-doped VS4 microspheres (Co-VS4-δ-x) with the co-regulation of electron structure and defect have been developed and synthesized by a one-step solvothermal procedure as an advanced cathode material for AZIBs. The introduction of active multivalent Co ions achieves the interfacial charge rearrangement of Co-VS4-δ-x electrode and the widening of the layer spacing to reduce the transfer resistance and interfacial attraction of Zn2+ between the layers. Moreover, the formation of sulfur defects shortens the Zn2+ transport distance and enhances the electrical conductivity and electrochemical kinetics of Co-VS4-δ-x material. In addition, the urchin-like micromorphology of the material dramatically increases the contact area between electrolyte and electrode material and the active sites of electrochemical reaction. Based on the above advantages, the zinc storage performance of Co-VS4-δ-x has been greatly enhanced, delivering the specific capacities of 306.4 mAh g−1 and 270.7 mAh g−1 at 0.5A g−1 and 5A g−1, respectively, and exhibiting excellent cycling stability with the capacity retention of 87.0% after 3000 cycles at 5 A g−1. This investigation proposes an effective strategy to develop high-performance vanadium-based cathodes for AZIBs by charge rearrangement, defect modulation and morphology optimization.

Effect of oxygen defects on electrochemical performance of V2O3 cathode in aqueous Zn-ion battery

The oxygen-defective V2O3 (Od-V2O3) was synthesized via a hydrothermal method followed by calcining treatment. Oxygen defects can provide permanent binding sites for some Zn2+, and accelerate the free diffusion of Zn2+ in V2O3. When used as cathode for aqueous Zn-ion batteries, the obtained Od-V2O3 delivers a reversible discharge capacity of 469.2 mAh/g at 0.1 A/g with a capacity retention of 90.1% and a distinguished rate capability. Even at a higher current density of 10 A/g, the glorious capacity of 248.3 mAh/g can be received after 1000 cycles. This paper opens up an avenue for the construction of advanced electrode materials.

Combining Structural Modification and Electrolyte Regulation to Enable Long-Term Cyclic Stability of MoO3-x @TiO2 as Cathode for Aqueous Zn-Ion Batteries.

Orthorhombic MoO3 (α-MoO3 ) with multivalent redox couple of Mo6+ /Mo4+ and layered structure is a promising cathode for rechargeable aqueous Zn-ion batteries (AZIBs). However, pure α-MoO3 suffers rapid capacity decay due to the serious dissolution and structural collapse. Meanwhile, the growth of byproduct and dendrite on the anode also lead to the deterioration of cyclic stability. This article establishes the mechanism of proton intercalation into MoO3 and proposes a joint strategy combining structural modification with electrolyte regulation to enhance the cyclic stability of MoO3 without sacrificing the capacity. In ZnSO4 electrolyte with Al2 (SO4 )3 additive, TiO2 coated oxygen-deficient α-MoO3 (MoO3-x @TiO2 ) delivers a reversible capacity of 93.2mA h g-1 at 30 A g-1 after 5000 cycles. The TiO2 coating together with the oxygen deficiency avoids structural damage while facilitating proton diffusion. Besides, the additive of Al2 (SO4 )3 , acting as a pump, continuously supplements protons through dynamic hydrolysis, avoiding the formation of Zn4 SO4 (OH)6 ·xH2 O byproducts at both MoO3-x @TiO2 and Zn anode. In addition, Al2 (SO4 )3 additive facilitates uniform deposition of Zn owing to the tip-blocking effect of Al3+ ion. The study demonstrates that the joint strategy is beneficial for both cathode and anode, which may shed some light on the development of AZIBs.

Vanadium Oxide-Poly(3,4-ethylenedioxythiophene) Nanocomposite as High-Performance Cathode for Aqueous Zn-Ion Batteries: The Structural and Electrochemical Characterization

In this work the nanocomposite of vanadium oxide with conducting polymer poly(3,4-ethylenedioxythiophene) (VO@PEDOT) was obtained by microwave-assisted hydrothermal synthesis. The detailed study of its structural and electrochemical properties as cathode of aqueous zinc-ion battery was performed by scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction analysis, X-ray photoelectron spectroscopy, thermogravimetric analysis, cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The initial VO@PEDOT composite has layered nanosheets structure with thickness of about 30-80 nm, which are assembled into wavy agglomerated thicker layers of up to 0.3-0.6 μm. The phase composition of the samples was determined by XRD analysis which confirmed lamellar structure of vanadium oxide V10O24∙12H2O with interlayer distance of about 13.6 Å. The VO@PEDOT composite demonstrates excellent electrochemical performance, reaching specific capacities of up to 390 mA∙h∙g-1 at 0.3 A∙g-1. Moreover, the electrodes retain specific capacity of 100 mA∙h∙g-1 at a high current density of 20 A∙g-1. The phase transformations of VO@PEDOT electrodes during the cycling were studied at different degrees of charge/discharge by using ex situ XRD measurements. The results of ex situ XRD allow us to conclude that the reversible zinc ion intercalation occurs in stable zinc pyrovanadate structures formed during discharge.

Improved performance of Cu ion implanted δ-MnO2 cathode material for aqueous Zn-ion batteries

Aqueous Zn-ion batteries (ZIBs) are considered as a potential large-scale renewable energy storage system. Herein, Cu ion implantation is used to improve the electrochemical performance of δ-MnO2, resulting in a mixed layer-tunnel material δ-MnO2 (Cu@δ-MnO2) with high capacity, excellent cycle performance, and rate performance as cathode for aqueous ZIBs. The as-obtained Cu@δ-MnO2 cathode shows a high specific capacity of 470 mAhg−1 at 0.1 Ag−1 and maintains a higher specific capacity during long-term cycles of up to 300 times. Meanwhile, the first-principles theoretical simulations suggest the easier migration of Zn2+ and more Zn2+ adsorption on Cu@δ-MnO2 cathode. The theoretical and experimental results show that Cu ion implantation may be an effective strategy to improve the device performance of the Mn-based layer-tunnel hybrid cathode.

In-situ electrochemical etching of V4AlC3 MAX to V2O5/C composite as Zn-ion storage host

Although V2O5 is considered as promising cathode for aqueous Zn-ion batteries (AZIBs), the poor intrinsic conductivity and unstable structure can significantly hamper its electrochemical energy storage capability. In this work, an in-situ formation strategy of V2O5/C composite nanosheets-derived from V4AlC3 MAX is reported, as an efficient Zn2+ storage host via electrochemically etching-induced phase transition strategy. And the mechanism behind the V4AlC3 MAX electrode conversion were systematically studied. The results revealed that the V-Al bond and Al 1s peak of V4AlC3 were gradually disappearing at prolonged cycling, meanwhile the high valence state vanadium was formed simultaneously as the V2O5/C composite. Benefiting from the efficient reaction kinetics endowed by the V2O5/C nanosheets, such V4AlC3 MAX derived electrode can deliver a high specific capacity of 102 mA h g−1 (20 A/g) at the cut-off voltage of 2.0 V, Furthermore, discharge capacity of 158 mA h g−1 after 3000 cycles at 10 A/g can be retained, confirming it a superior rate capability and cycling stability. The work demonstrates an effective strategy for green and advanced cathode material design and high-performance AZIBs.

In situ growth of petal-like MoS2–MoO2 heterostructure on carbon cloth for superior Zn-ion storage

Suffered from inherent low ionic/electronic conductivity of semiconductor 2H phase, the performance of pristine MoS2 cathode for aqueous Zn-ion batteries has always been disappointing. Here, we fabricated a MoS2–MoO2 heterostructure with petal-like three-dimensional nanoarrays in situ grown on carbon cloth (MoS2–MoO2@CC) by seed-assisted hydrothermal method. The metallic phase MoO2 cooperates with the carbon cloth substrate to boost the ionic/electronic conductivity of the composite material, while the presence of the heterogeneous structure accelerates the electron conductivity at the interface and promotes fast reaction kinetics. The synthesized MoS2–MoO2@CC electrode exhibits a high discharge capacity of 259.6 mAh g−1 at 0.1 A g−1 and maintains a stable discharge capacity of 122.6 mAh g−1 at 2.0 A g−1 after 1000 cycles, reflecting outstanding cycling stability.

Molten Salt Thermal Treatment Synthesis of S-Doped V2CTx and Its Performance as a Cathode in Aqueous Zn-Ion Batteries.

The lack of suitable cathode materials with a high capacity and good stability is a crucial problem affecting the development of aqueous Zn-ion batteries. Herein, a novel strategy for the modification of V2CTx through molten salt thermal treatment is proposed. In the novel route, S heteroatoms were introduced into V2CTx through a substitution reaction during the dissolution of Li2S in LiCl-KCl molten salts. Then, surface V2O5 was obtained through the in situ electrochemical charging/discharging of the S-doped V2CTx (MS-S-V2CTx) cathode. The assembled Zn/MS-S-V2CTx battery showed a high reversible discharge capacity of 411.3 mAh g-1 at a current density of 0.5 A g-1, an 80% capacitance retention after long cycle stability tests at 10 A g-1 for 3000 cycles, and a high energy density of 375.5 Wh kg-1 in 2M ZnSO4. Density functional theory calculations demonstrate that the improved electrochemical performance of the cathode can be attributed to the introduced S heteroatoms, which considerably reduced the ion diffusion energy barrier for Zn2+ ions and improved the stability of V2O5. This work provides a novel method to produce highly active and stable vanadium-based cathodes for aqueous Zn-ion batteries.

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-friendliness, and acceptable electrochemical performance. However, developing a cathode material with fast kinetics and durable structural stability for Zn2+ 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.

A high-performance MnO2 cathode doped with group Ⅷ metal for aqueous Zn-ion batteries: In-situ X-Ray diffraction study on Zn2+ storage mechanism

MnO2-based cathodes for aqueous Zn-ion batteries (AZIBs) suffer from the sluggish kinetics of Zn2+ migration and chemical instability during cycling, severely impeding its practical application. The group Ⅷ metal (Fe, Co and Ni) doping in MnO2 is an intriguing idea to improve the electrochemical performance of MnO2-based electrodes for AZIBs due to its special electronic structure of d shell. According to density functional theory calculation results, the doping-element facilitates the increase in kinetics of Zn2+ migration and increase chemical stability during cycling. When tested in AZIBs, a Fe-doping MnO2 (FMO) electrode exhibits a superior cycling stability (a high specific capacity of 338.2 mAh g−1 at 1 A g−1 with a capacity retention of 86.3% after 200 cycles), as same as that of Co and Ni-doping MnO2 electrode. In combination of in-situ X-ray diffraction and ex-situ transmission electron microscope studies reveal that layered-FMO undergoes a structural transition to ZnxMnO2, Mn3O4 and ZnMn2O4, accompanying with the formation of ZnSO4(OH)6·5H2O during discharging process, while those phases revert back to the parent phase during the subsequent Zn extraction. This study might build a solid foundation for developing powerful cathode in AZIBs.

Ultra-High-Capacity and Dendrite-Free Zinc-Sulfur Conversion Batteries Based on a Low-Cost Deep Eutectic Solvent.

Traditional cathodes for aqueous Zn-ion batteries are afflicted by a limited specific capacity and fearful Zn dendrites. Herein, these troubles are disposed of with a conversion-type Zn-S battery and low-cost deep eutectic solvent (DES). By utilizing the optimized electrolyte, the symmetrical Zn battery can stably cycle over 3920 h, which also confers on the Zn-S battery an ultrahigh specific capacity of ∼846 mA h gS-1 and energy density of 259 W h kg-1 at 0.5 A g-1. Importantly, the conversion chemistry of S and ZnS is responsible for the superior anti-self-discharge behavior (capacity retention: 94.58 and 68.58% after standing for 72 and 288 h versus Zn//VO2 battery: 76.82 and 47.80% after resting for 24 and 72 h versus Zn//MnO2 battery: 95.96 and 91.57% after resting for 24 and 72 h, respectively). This work is the first authentication of Zn-S batteries based on a newly developed low-cost DES-based electrolyte, which meanwhile settles the deep-rooted low specific capacity and infamous Zn dendrite issues in conventional (de)intercalation Zn-ion batteries.

Low-cost, low-strain and lattice-water-rich Mn0.25(VO)0.75PO4·2.25H2O as high-rate and stable cathodes for aqueous Zn-ion batteries

Aqueous zinc‐ion batteries (ZIBs) have become a promising alternative to lithium-ion batteries (LIBs) for grid‐scale energy storage. However, the bivalent nature and large radius of zinc hydrated ions commonly lead to a strong electrostatic interaction with the host lattice and a huge strain feature during zinc-ion insertion, which results in slow diffusion kinetics and poor cycling stability. Herein, a lattice-water-rich V-based polyanionic cathode, named Mn0.25(VO)0.75PO4·2.25H2O (MnVP), is mass-producible and in which the sufficient lattice water weakens the electrostatic interactions and facilitates the rapid Zn2+ migration kinetics. The introduced Mn3+ ions partially replaced the V elements, which made the crystal structure more stable during the cycle. Besides, the doping of inactive Mn3+ can introduce the crystal water, which lower the stress and strain of the host lattice during zinc-ion insertion. Thus, the MnVP cathode delivers a high specific capacity (207.7 mAh g−1 at 0.1 A g−1), excellent rate capability (93.5% retention at 5 A g−1) and long cycle durability (after 700 cycles with a capacity retention of 88.4 %). Furthermore, the simple preparation and low cost make this cathode expect to be used in large‐scale energy storage systems.

Doping-Induced Static Activation of MnO2 Cathodes for Aqueous Zn-Ion Batteries

Doping-Induced Static Activation of MnO₂ Cathodes for Aqueous Zn-Ion Batteries