Aqueous Metal-ion Batteries Research Articles

Dual zinco-phobic/-philic ferroelectric nanorods coated mesh for stable Zn anode

Aqueous Zn-ion batteries are emerging as a promising option for energy storage systems due to their safety and environmental benefits. However, their stability and reversibility are often hindered by dendrite growth and interfacial side reactions. In this study, we introduce an innovative strategy to address these issues by engineering an artificial interfacial layer (AIL) on Zn anode surface. This AIL is composed of a dual zinco-phobic/-philic ferroelectric nanorods (FE NRs) mesh, which contrasts with the traditional BaTiO3 nanoparticles. The BTO NRs, particularly those with exposed P4/mmm (100) and (211) facets enriched with oxygen vacancy, facilitate a partial phase transition from the FE tetragonal P4mm phase to the paraelectric tetragonal P4/mmm phase, thereby creating dual zinco-phobic/-philic sites. Additionally, the integration of microchannels within the FE BTO NRs mesh can efficiently modulate the electric field distribution and Zn2+ concentration, leading to a more uniform Zn deposition, as conformed by electrochemical simulations. The Zn anode coated with the FE BTO NRs mesh exhibits impressive performance, achieving an ultralong cycle life of 3050 h at 1 mA cm−2 and 1mAh cm−2. It sustains a Coulombic efficiency exceeding 99.8 % over 2000 cycles, highlighting its exceptional reversibility. These findings underscore the potential of the dual zinco-phobic/-philic FE NRs mesh in overcoming the challenges faced in aqueous metal-ion batteries, showcasing its versatility and the significant performance enhancements it can offer.

A Dual Salt/Dual Solvent Electrolyte Enables Ultrahigh Utilization of Zinc Metal Anode for Aqueous Batteries.

Rechargeable aqueous zincbatteriesare promising in next-generation sustainable energy storage. However, the low zinc (Zn) metal anode reversibility and utilization in aqueous electrolytes due to Zn corrosion and poor Zn2+ deposition kinetics significantly hinder the development of Zn-ion batteries. Here, a dual salt/dual solvent electrolyte composed of Zn(BF4)2/Zn(Ac)2 in water/TEGDME (tetraethylene glycol dimethyl ether) solvents to achieve reversible Zn anode at an ultrahigh depth of discharge (DOD) is developed. An "inner co-salt and outer co-solvent" synergistic effect in this unique dual salt/dual solvent system is revealed. Experimental results and theoretical calculations provide evidence that the ether co-solvent inhibits water activity by forming hydrogen bonding with the water and coordination effects with the proton in the outer Zn2+ solvation structure. Meanwhile, the anion of zinc acetate co-salt enters the inner Zn2+ solvation structure, thereby accelerating the desolvation kinetics. Strikingly, based on the electrolyte design, the zinc anode shows high reversibility at an ultrahigh utilization of 60% DOD with 99.80% Coulombic efficiency and 9.39 mAh cm-2 high capacity. The results far exceed the performance reported in electrolyte design work recently. The work provides fundamental insights into inner co-salt and outer co-solvent synergistic regulation in multifunctional electrolytes for reversible aqueous metal-ion batteries.

Biomimetic Superstructured Interphase for Aqueous Zinc-Ion Batteries.

The practical application of aqueous zinc-ion batteries (AZIBs) is greatly challenged by rampant dendrites and pestilent side reactions resulting from an unstable Zn-electrolyte interphase. Herein, we report the construction of a reliable superstructured solid electrolyte interphase for stable Zn anodes by using mesoporous polydopamine (2D-mPDA) platelets as building blocks. The interphase shows a biomimetic nacre's "brick-and-mortar" structure and artificial transmembrane channels of hexagonally ordered mesopores in the plane, overcoming the mechanical robustness and ionic conductivity trade-off. Experimental results and simulations reveal that the -OH and -NH groups on the surface of artificial ion channels can promote rapid desolvation kinetics and serve as an ion sieve to homogenize the Zn2+ flux, thus inhibiting side reactions and ensuring uniform Zn deposition without dendrites. The 2D-mPDA@Zn electrode achieves an ultralow nucleation potential of 35 mV and maintains a Coulombic efficiency of 99.8% over 1500 cycles at 5 mA cm-2. Moreover, the symmetric battery exhibits a prolonged lifespan of over 580 h at a high current density of 20 mA cm-2. This biomimetic superstructured interphase also demonstrates the high feasibility in Zn//VO2 full cells and paves a new route for rechargeable aqueous metal-ion batteries.

Outer Sphere Electron Transfer Enabling High-Voltage Aqueous Electrolytes.

Aqueous electrolytes with a low voltage window (1.23 V) and prone side reactions, such as hydrogen evolution reaction and cathode dissolution, compromise the advantages of high safety and low cost of aqueous metal-ion batteries. Herein, introducing catechol (CAT) into the aqueous electrolyte, an outer sphere electron transfer mechanism is initiated to inhibit the water reactivity, achieving an electrochemical window of 3.24 V. In a typical Zn-ion battery, the outer sphere electrons jump from CAT to Zn2+-H2O at a geometrically favorable situation and between the solvation molecules without breaking or forming chemical bonds as that of the inner sphere electron transfers. The excited state π-π stacking further leads to the outer sphere electron transfer occurring at the electrolyte/electrode interface. This high-voltage electrolyte allows achieving an operating voltage two times higher than that of the usual aqueous electrolytes and provides almost the highest energy density and power density for the V2O5-based aqueous Zn-ion full batteries. The Zn//Zn symmetric battery delivers a 4000 h lifespan, and the Zn//V2O5 full battery achieves a ∼380 W h kg-1 energy density and a 92% capacity retention after 3000 cycles at 1 A g-1 and a 2.4 V output voltage. This outer sphere electron transfer strategy paves the way for designing high-voltage aqueous electrolytes.

Tandem Chemistry with Janus Mesopores Accelerator for Efficient Aqueous Batteries.

A reliable solid electrolyte interphase (SEI) on the metallic Zn anode is imperative for stable Zn-based aqueous batteries. However, the incompatible Zn-ion reduction processes, scilicet simultaneous adsorption (capture) and desolvation (repulsion) of Zn2+(H2O)6, raise kinetics and stability challenges for the design of SEI. Here, we demonstrate a tandem chemistry strategy to decouple and accelerate the concurrent adsorption and desolvation processes of the Zn2+ cluster at the inner Helmholtz layer. An electrochemically assembled perforative mesopore SiO2 interphase with tandem hydrophilic -OH and hydrophobic -F groups serves as a Janus mesopores accelerator to boost a fast and stable Zn2+ reduction reaction. Combining in situ electrochemical digital holography, molecular dynamics simulations, and spectroscopic characterizations reveals that -OH groups capture Zn2+ clusters from the bulk electrolyte and then -F groups repulse coordinated H2O molecules in the solvation shell to achieve the tandem ion reduction process. The resultant symmetric batteries exhibit reversible cycles over 8000 and 2000 h under high current densities of 4 and 10 mA cm-2, respectively. The feasibility of the tandem chemistry is further evidenced in both Zn//VO2 and Zn//I2 batteries, and it might be universal to other aqueous metal-ion batteries.

Theoretical insights into surface-phase transition and ion competition during alkali ion intercalation on the Cu4Se4 nanosheet.

The development of stable and efficient electrode materials is imperative and also indispensable for further commercialization of sodium/potassium-ion batteries (SIBs/PIBs) and new detrimental issues such as proton intercalation arise when utilizing aqueous electrolytes. Herein the electrochemical performance of the Cu4Se4 nanosheet was determined for both organic and aqueous SIBs and PIBs. By means of density functional theory calculation, Na+, K+ and H+ intercalations onto both sides of the Cu4Se4 nanosheet were revealed. The Cu4Se4 nanosheet well maintains its metallic electronic conductivity and the changes in lateral lattice parameters are within 4.66% during the whole Na+/K+ intercalation process for both SIBS and PIBs. The theoretical maximum Na/K storage capacity of 188.07 mA h g-1 can be achieved by stabilized second-layer adsorption of Na+/K+. The migration barriers of Na and K atoms on the Cu4Se4 nanosheet are 0.270 and 0.173 eV, respectively. It was discovered that Na/K- intercalation in the first layer is accompanied by a first-order surface phase transition, resulting in an intercalation voltage plateau of 0.659/0.756 V, respectively. The region of the two-surface phase coexistence for PIBs, is shifted toward a lower coverage when compared with that for SIBs. The partially protonated Cu4Se4 nanosheet (HxCu4Se4, x ≤ 10/9) was revealed to be structurally and thermodynamically stable. While the partially protonated Cu4Se4 nanosheet is favorable in acidic electrolytes (pH = 0) when protons and Na/K ions compete, we showed that Na+/K+ intercalated products may be preferred over H+ at low coverages in alkali electrolyte (pH = 14). However, the proton intercalation substantially decreases the battery capacity in aqueous SIBs and PIBs. Our work not only identifies the promising performance of Cu4Se4 nanosheets as an electrode material of SIBs and PIBs, but also provides a computational method for aqueous metal-ion batteries.

Influence of Salt Concentration on Electrochemical Stability Window in Aqueous Electrolytes

The thermodynamic limit of water electrolysis restricts the output voltage of aqueous metal ion batteries (MIBs) due to the low electrochemical stability window of water (1.23 V) in dilute electrolytes. It occurs due to the electrolysis of free water molecules into O2 or H2. Such value is unfortunately too low for many applications. For effective utilization of this technology, the ESW needs to be expanded to at least 2 V to achieve high energy density in metal batteries. Interestingly, water electrolysis can be suppressed by binding free water content with high concentrations of salts in highly concentrated water-in-salt electrolytes.In this work, low-cost non-flammable aqueous Zn(ClO4)2 electrolytes have been studied for their electrochemical behaviour at different concentrations. The electrolytes have been evaluated via Raman spectroscopic analysis to examine the modification in local water structures associated with increasing salt concentration. We also used linear sweep voltammetry on a glassy carbon electrode to determine the electrochemical stability window of the electrolytes. Electrochemical results indicate the existence of two distinct regions in the concentration behavior of the onset potential for oxygen evolution reaction (OER) at a cut-off current density of 0.1 mA cm-2. In dilute electrolytes, the overpotential in OER increases with a low slope with increasing concentration, while there is a sharper overpotential increase at higher salt concentrations in the water-in-salt electrolytes. Raman spectroscopic analysis provides evidence of this electrochemical stability expansion as being a result of the disruption of the hydrogen bonding network present in pure water. A more compact and strongly coordinated ion hydration structure occurs in the water-in-salt electrolytes. In this way, a significant increase in oxidative stability and a decline in the Zn oxidation overpotential has been achieved in the highly concentrated water-in-salt electrolytes. Our results indicate that the Zn(ClO4)2 water-in-salt electrolytes offer more efficient Zn redox reactions and a higher electrochemical stability window than the diluted aqueous electrolytes, which is particularly beneficial for the development of high-voltage aqueous Zn ion batteries [1].

Investigation on corrosion inhibitors for zinc batteries: Sodium sulphate

To store energy rechargeable batteries had developed widely. Over the concern of safety and cost-efficient, rechargeable aqueous metal-ion batteries are mostly favored. Various studies have been performed on different aqueous metal-ion batteries. Out of them, zinc-ion batteries have some unique and outstanding benefits. The aqueous electrolytes give assurance against exploding by their non-flammable nature. The zinc anodes are being used as it benefits the stability and redox reversibility. Zinc anodes have a higher theoretical capacity (820 mAh g−1) and low redox potential [−0.76 V vs. SHE (standard hydrogen electrode)]. As a measure to increase corrosion resistance, sodium sulphate is being used as an inhibitor. The zinc anode is being analyzed at different concentrations of the inhibitor and the best concentration is being identified for the battery applications. Potentiostatic EIS (Electrochemical Impedance Spectroscopy) and Tafel analysis are done to determine the corrosion behavior of the zinc with the addition of the inhibitor.

Nanoscale Ultrafine Zinc Metal Anodes for High Stability Aqueous Zinc Ion Batteries

Aqueous Zn batteries (AZBs) are a promising energy storage technology, due to their high theoretical capacity, low redox potential, and safety. However, dendrite growth and parasitic reactions occurring at the surface of metallic Zn result in severe instability. Here we report a new method to achieve ultrafine Zn nanograin anodes by using ethylene glycol monomethyl ether (EGME) molecules to manipulate zinc nucleation and growth processes. It is demonstrated that EGME complexes with Zn2+ to moderately increase the driving force for nucleation, as well as adsorbs on the Zn surface to prevent H-corrosion and dendritic protuberances by refining the grains. As a result, the nanoscale anode delivers high Coulombic efficiency (ca. 99.5%), long-term cycle life (over 366 days and 8800 cycles), and outstanding compatibility with state-of-the-art cathodes (ZnVO and AC) in full cells. This work offers a new route for interfacial engineering in aqueous metal-ion batteries, with significant implications for the commercial future of AZBs.

Direct evidence of the non-uniform electrodeposition of zinc at the early stage

Aqueous zinc-ion batteries (ZIBs) are regarded as one of the most promising electrical energy-storage systems for their eco-friendliness, low cost and high-safety. Although there have been a lot of studies recently on the Zn metal anode, little attention has been paid to its initial nucleation and growth behavior, which is critical to the understanding of fundamental mechanisms of the Zn plating. Herein, the digital holographic surface imaging (DHSI) method, combined synchronously with electrochemical tests, is employed to in-situ observe the non-uniform concentration changes on the surface of the copper substrate caused by the Zn nucleation and growth at the early stage. It is the first time to observe the early uneven depositions from a perspective of solution concentration changes in a symmetrical battery system. Results show that the later dendritic growth of Zn is closely related to the nucleation and earlier deposition process. Based on the phase maps obtained with in-situ DHSI technique, the nucleation and growth during the Zn electrodeposition can be closely investigated and vividly demonstrated, offering a promising avenue towards the understanding of the interfacial electrochemistry in all aqueous metal-ion batteries.

Microstructure Modulation of Zn Doped VO2(B) Nanorods with Improved Electrochemical Properties towards High Performance Aqueous Batteries

Vanadium dioxide with monoclinic structure is theoretically a promising layered cathode material for aqueous metal-ion batteries due to its excellent specific capacity. However, its poor cycling stability limits its application as an electrode material. In this study, a series of Zn-doped VO2 (V1−xZnxO2) nanorods were successfully fabricated by the technology of one-step hydrothermal synthesis. The XRD result indicated that there was a slight lattice distortion caused by doped Zn2+ with a larger ion radius. The positron lifetime spectrum showed that there were vacancy cluster defects in all the samples. The electrochemical measurement demonstrated the enhancement of the specific capacitance of V1−xZnxO2 electrodes compared with the undoped sample. In addition, the discharge capacitance of the sample remained around 86% after 1000 charge/discharge cycles. This work proves that Zn2+ doping is a valid tactic for the application of nano-VO2(B) in energy storage electrode materials.

Proton Chemistry Induced Long-Cycle Air Self-Charging Aqueous Batteries.

Air self-charging aqueous metal-ion batteries usually suffer from capacity loss after self-charging cycles due to the formation of basic salts on cathodes in the near-neutral electrolytes. Here, air self-charging Pb/pyrene-4,5,9,10-tetraone (PTO) batteries based on proton chemistry are developed in acidic electrolyte. The fast kinetics of H+ uptake/removal endows the battery with enhanced electrochemical performance. Owing to the high standard electrode potential of oxygen in acid electrolyte, the discharged cathodes are spontaneously oxidized by oxygen in air along with H+ extraction and thus achieve self-charging without external power supply. Notably, the air self-charging mechanism involved H+ -based redox can effectively avoid the generation of basic salts on self-charging electrodes and thus guarantee long-term self-charging/galvanostatic discharging cycles of Pb/PTO batteries. This work provides a promising strategy for designing long-cycle air self-charging systems.

Surface Selenization Strategy for V2CTx MXene toward Superior Zn-Ion Storage.

MXenes are promising cathode materials for aqueous zinc-ion batteries (AZIBs) owing to their layered structure, metallic conductivity, and hydrophilicity. However, they suffer from low capacities unless they are subjected to electrochemically induced second phase formation, which is tedious, time-consuming, and uncontrollable. Here we propose a facile one-step surface selenization strategy for realizing advanced MXene-based nanohybrids. Through the selenization process, the surface metal atoms of MXenes are converted to transition metal selenides (TMSes) exhibiting high capacity and excellent structural stability, whereas the inner layers of MXenes are purposely retained. This strategy is applicable to various MXenes, as demonstrated by the successful construction of VSe2@V2CTx, TiSe2@Ti3C2Tx, and NbSe2@Nb2CTx. Typically, VSe2@V2CTx delivers high-rate capability (132.7 mA h g-1 at 2.0 A g-1), long-term cyclability (93.1% capacity retention after 600 cycles at 2.0 A g-1), and high capacitive contribution (85.7% at 2.0 mV s-1). Detailed experimental and simulation results reveal that the superior Zn-ion storage is attributed to the engaging integration of V2CTx and VSe2, which not only significantly improves the Zn-ion diffusion coefficient from 4.3 × 10-15 to 3.7 × 10-13 cm2 s-1 but also provides sufficient structural stability for long-term cycling. This study offers a facile approach for the development of high-performance MXene-based materials for advanced aqueous metal-ion batteries.

First-row transition metal compounds for aqueous metal ion batteries

In recent years, a series of aqueous metal ion batteries (AMIBs) has been developed to improve the safety and cost-efficiency of portable electronics and electric vehicles. However, the significant gaps in energy density, power density, and cycle stability of AMIBs directly hinder them from replacing the currently widely used non-aqueous metal ion batteries, which stems from the lack of reasonable configuration and performance optimization of electrode materials. First-row transition metal compounds (FRTMCs), with the advantages of optional voltage ranges (from low to high), adjustable crystal structures (layered and tunnel types with large spacing), and designable morphology (multi-dimensional nanostructures), are widely used to construct high-performance AMIBs. However, no comprehensive review papers were generated to highlight their specific and significant roles in AMIBs. In this review, we first summarize the superiority and characteristics of FRTMCs in AMIBs. Then, we put forward control strategies of FRTMCs from subsurface engineering to inner construction to promote capacitance control and diffusion control energy storage. After that, the electrochemical performance of the FRTMCs regulation strategies in AMIBs is reviewed. Finally, we present potential directions and challenges for further enhancements of FRTMCs in AMIBs. The review aims to provide an in-depth understanding of regulation strategies for enhancing energy storage to build high-performance AMIBs that meet practical applications.

Al-doped α-MnO2 coated by lignin for high-performance rechargeable aqueous zinc-ion batteries.

Zn/MnO2 batteries, one of the most widely studied rechargeable aqueous zinc-ion batteries, suffer from poor cyclability because the structure of MnO2 is labile with cycling. Herein, the structural stability of α-MnO2 is enhanced by simultaneous Al3+ doping and lignin coating during the formation of α-MnO2 crystals in a hydrothermal process. Al3+ enters the [MnO6] octahedron accompanied by producing oxygen vacancies, and lignin further stabilizes the doped Al3+via strong interaction in the prepared material, Al-doped α-MnO2 coated by lignin (L + Al@α-MnO2). Meanwhile, the conductivity of L + Al@α-MnO2 improves due to Al3+ doping, and the surface area of L + Al@α-MnO2 increases because of the production of nanorod structures after Al3+ doping and lignin coating. Compared with the reference α-MnO2 cathode, the L + Al@α-MnO2 cathode achieves superior performance with durably high reversible capacity (∼180 mA h g−1 at 1.5 A g−1) and good cycle stability. In addition, ex situ X-ray diffraction characterization of the cathode at different voltages in the first cycle is employed to study the related mechanism on improving battery performance. This study may provide ideas of designing advanced cathode materials for other aqueous metal-ion batteries.

Near-Atomic-Thick Bismuthene Oxide Microsheets for Flexible Aqueous Anodes: Boosted Performance upon 3D → 2D Transition

Aqueous batteries provide safety, but they usually suffer from low energy and short lifetimes, limiting their use for large-scale energy storage. Two-dimensional materials with infinite lateral dimensions have inherent properties such as high surface area and remarkable power density and cycling stability that are shown to be critical for the next generation of energy storage systems. Here, ultrathin bismuthene oxide with a large aspect ratio is studied as an anode material for rechargeable aqueous metal-ion batteries. The metal oxides are prepared via a novel electrochemical system allowing for a smooth, high-quality transition of bismuthene to bismuthene oxide in a short time. This anodic system is shown to overcome major limiting factors of such batteries, including low capacity and irreversible and unstable redox reactions in aqueous electrolytes. The essential energy storage properties of two-dimensional (2D) microsheets, without the addition of conductive additives and binders, are compared with those of the corresponding three-dimensional (3D) structures. Notably, the battery performance of 2D microsheets is significantly better than that of nanoparticles from all examined aspects, including power density and potential and cycling stability, while exhibiting a capacity density close to their theoretical value. Moreover, 2D microsheets have shown impressive mechanical flexibility related to the ultrathin thickness of individual microsheets and strong interaction between them after film deposition. Combining the excellent energy storage properties of bismuthene oxide, the simple electrode preparation procedure, the inherent flexing characteristic, and the nontoxicity of both the battery material and the electrolyte makes this 2D material an exceptional candidate for large-scale wearable green electronics.

Cationic Surfactant-Type Electrolyte Additive Enables Three-Dimensional Dendrite-Free Zinc Anode for Stable Zinc-Ion Batteries

Zn metal has been considered as a promising anode material for rechargeable aqueous metal-ion batteries. However, the propensity of dendrite growth during plating restricts its practical applicatio...

Binder-free coaxially grown V6O13 nanobelts on carbon cloth as cathodes for highly reversible aqueous zinc ion batteries

For stable, high-capacity aqueous zinc ion batteries (AZIBs), layered metal oxides, especially with multivalent metal ions, are promising active materials (cathodes) with high operating voltages. However, when uses in batteries prepared with conventional electrode fabrication methods, these materials suffer from low electrical conductivity and high active material detachment from the current collector, leading to poor electrochemical performance. Here, we present the synthesis of ultrathin V6O13 nanobelts containing multiple valences (V4+ and V5+) grown coaxially on carbon cloth (CC) using a hydrothermal method for the first time. The ultrathin V6O13 integrated into CC shows advantages such as fast electron transfer between the active material and current collector, low active material detachment, and short diffusion length in metal ion insertion-extraction. In AZIBs, V6O13@CC displays promising reversible galvanostatic charge-discharge capacity retention during cycling with excellent rate capability. An initial specific capacity of 227 mAh g−1 is obtained at 9 A g−1 and nearly 99% is retained after 1000 cycles. This stable reversible capacity is attributed to enhanced electrical conductivity and low active material detachment from the current collector (carbon cloth). This report discusses the hydrothermal preparation of a flexible cathode on CC that is promising for high-performance aqueous metal ion batteries.

Prussian blue analogues as aqueous Zn-ion batteries electrodes: Current challenges and future perspectives

Abstract The urgency of integrating renewable energy sources in the power grid has pushed the development of aqueous metal-ion batteries because of their low cost, nontoxicity, high safety, and environmentally friendliness. Among the variety of aqueous metal-ion batteries that are currently under development, aqueous Zn-ion batteries (A-ZIBs) have recently gained a great attention because of their high specific energy and high reversibility in aqueous solutions, together with the low cost and high abundancy of the zinc. In this article, the authors intend to present an overview of the Prussian blue analogue materials, which are among the most promising materials for positive electrodes in A-ZIBs because of their easier synthesis route, reversible ion-insertion, high safety, and low toxicity, highlighting their strength points and open challenges.

Voltage issue of aqueous rechargeable metal-ion batteries.

Over the past two decades, a series of aqueous rechargeable metal-ion batteries (ARMBs) have been developed, aiming at improving safety, environmental friendliness and cost-efficiency in fields of consumer electronics, electric vehicles and grid-scale energy storage. However, the notable gap between ARMBs and their organic counterparts in energy density directly hinders their practical applications, making it difficult to replace current widely-used organic lithium-ion batteries. Basically, this huge gap in energy density originates from cell voltage, as the narrow electrochemical stability window of aqueous electrolytes substantially confines the choice of electrode materials. This review highlights various ARMBs with focuses on their voltage characteristics and strategies that can effectively raise battery voltage. It begins with the discussion on the fundamental factor that limits the voltage of ARMBs, i.e., electrochemical stability window of aqueous electrolytes, which decides the maximum-allowed potential difference between cathode and anode. The following section introduces various ARMB systems and compares their voltage characteristics in midpoint voltage and plateau voltage, in relation to respective electrode materials. Subsequently, various strategies paving the way to high-voltage ARMBs are summarized, with corresponding advancements highlighted. The final section presents potential directions for further improvements and future perspectives of this thriving field.