Cation-Deficient Spinel ZnMn2O4 Cathode in Zn(CF3SO3)2 Electrolyte for Rechargeable Aqueous Zn-Ion Battery

Tailoring Three-Dimensional Composite Architecture for Advanced Zinc-Ion Batteries

Rechargeable aqueous Zn-ion batteries (ZIBs) are of considerable interest for future energy storage. Their main limitation, however, is developing suitable cathode materials capable of sustaining the Zn²⁺ repeated intercalation/deintercalation. Herein, a three-dimensional polypyrrole (PPy)-encapsulated Mn₂O₃ composite architecture is developed for advanced ZIBs. The engineering can be easily realized via in situ phase transformation of MnCO₃ microboxes with subsequent self-initiated polymerization of PPy. The abundant open-up pores (∼30 nm) throughout the construction accelerate ion migration and provide a more active interface for Zn²⁺ storage in the Mn₂O₃@PPy bulk electrode. Meanwhile, the PPy skin uniformly wrapped on the Mn₂O₃ microbox not only guarantees a good conductive network for faster electron transport but also inhibits the dissolution of Mn₂O₃ and protects the integrity of the electrode from structural damage. As a result, the Mn₂O₃@PPy electrode can operate at reversible capacity exceeding those of most other cathode materials, but can still provide longer lifetime (no capacity decay over 2000 cycles at 0.4 A g^-1) and higher rate performance than others. Furthermore, theoretical studies show the H⁺ and Zn²⁺ coinsertion storage mechanism and reaction dynamics. The results show that this three-dimensional Mn₂O₃@PPy architecture is a promising cathode material for high-performance ZIBs.

An Electrolytic Zn-MnO2 Battery for High-Voltage and Scalable Energy Storage

Zinc-based electrochemistry is attracting significant attention for practical energy storage owing to its uniqueness in terms of low cost and high safety. However, the grid-scale application is plagued by limited output voltage and inadequate energy density when compared with more conventional Li-ion batteries. Herein, we propose a latent high-voltage MnO₂ electrolysis process in a conventional Zn-ion battery, and report a new electrolytic Zn-MnO₂ system, via enabled proton and electron dynamics, that maximizes the electrolysis process. Compared with other Zn-based electrochemical devices, this new electrolytic Zn-MnO₂ battery has a record-high output voltage of 1.95 V and an imposing gravimetric capacity of about 570 mAh g^-1 , together with a record energy density of approximately 409 Wh kg^-1 when both anode and cathode active materials are taken into consideration. The cost was conservatively estimated at <US$ 10 per kWh. This result opens a new opportunity for the development of Zn-based batteries, and should be of immediate benefit for low-cost practical energy storage and grid-scale applications.

A novel non-enzymatic H2O2 sensor using ZnMn2O4 microspheres modified glassy carbon electrode

With a facile solvothermal technique, ZnMn₂O₄ microspheres were synthesized in this work, which were used as enzyme mimics for the electrocatalytic reduction of H₂O₂. The morphology, crystal phase and structure of the ZnMn₂O₄ microspheres underwent characterization under X-ray diffraction spectroscopy, Raman spectroscopy, energy-dispersive spectroscopy, and scanning electron microscopy. The synthesized ZnMn₂O₄ microspheres showed an average diameter of 2 μm with great crystallinity, and exhibited excellent catalytical activity towards H₂O₂ electroreduction in alkaline media. The glassy carbon electrode modified by ZnMn₂O₄ microspheres showed a linear amperometric response for H₂O₂ in a wide concentration range of 0.02 ˜ 15 mM with detection limit of 0.13 μM under the optimized conditions. Besides, the sensor proposed here was successfully used to determine H₂O₂ in milk, suggesting that ZnMn₂O₄ microspheres can be used for non-enzymatic electrochemical sensor applications.

Rechargeable Aqueous Electrochromic Batteries Utilizing Ti-Substituted Tungsten Molybdenum Oxide Based Zn2+ Ion Intercalation Cathodes

Batteries are used in every facet of human lives. Desirable battery architectures demand high capacity, rechargeability, rapid charging speed, and cycling stability, all within an environmentally friendly platform. Many applications are limited by opaque batteries; thus, new functionalities can be unlocked by introducing transparent battery architectures. This can be achieved by incorporating electrochromic and energy storage functions. Transparent electrochromic batteries enable new applications, including variable optical attenuators, optical switches, addressable displays, touch screen devices, and most importantly smart windows for energy-efficient buildings. However, this technology is in the incipient state due to limited electrochromic materials having satisfactory optical contrast and capacity. As such, triggering electrochromism via Zn²⁺ intercalation is advantageous: Zn is abundant, safe, easily processed in aqueous electrolytes and provides two electrons during redox reactions. Here, enhanced Zn²⁺ intercalation is demonstrated in Ti-substituted tungsten molybdenum oxide, yielding improved capacity and electrochromic performance. This technique is employed to engineer cathodes exhibiting an areal capacity of 260 mAh m^-2 and high optical contrast (76%), utilized in the fabrication of aqueous Zn-ion electrochromic batteries. Remarkably, these batteries can be charged by external voltages and self-recharged by spontaneously extracting Zn²⁺ , providing a new technology for practical electrochromic devices.

Engineering high reversibility and fast kinetics of Bi nanoflakes by surface modulation for ultrastable nickel-bismuth batteries

The exploration of a stable and high-rate anode is of pivotal importance for achieving advanced aqueous rechargeable batteries. Owing to the beneficial properties of high conductivity, suitable negative working voltage, and three-electron redox, bismuth (Bi) is considered as a promising anode material, but it suffers from poor stability. Here, we successfully endow Bi nanoflakes (NFs) with prominent cycling performance by a one-step surface oxidation approach to remarkably boost its reversibility. As a result, the partially oxidized Bi NFs (BiO x ) show an admirable capacity (0.38 mA h cm-2 at 2 mA cm-2), good rate capability and superior long-term stability (almost no capacity decay after 20 000 cycles). Furthermore, a durable aqueous Ni//Bi battery is constructed based on the optimized BiO x anode, which exhibits excellent durability with 96% capacity retention after 5000 cycles. This study could open a new avenue for the rational design of efficient anodes for eco-friendly and reliable aqueous rechargeable batteries.

V2O5 Nanospheres with Mixed Vanadium Valences as High Electrochemically Active Aqueous Zinc-Ion Battery Cathode

A V4+-V2O5 cathode with mixed vanadium valences was prepared via a novel synthetic method using VOOH as the precursor, and its zinc-ion storage performance was evaluated. The products are hollow spheres consisting of nanoflakes. The V4+-V2O5 cathode exhibits a prominent cycling performance, with a specific capacity of 140 mAh g-1 after 1000 cycles at 10 A g-1, and an excellent rate capability. The good electrochemical performance is attributed to the presence of V4+, which leads to higher electrochemical activity, lower polarization, faster ion diffusion, and higher electrical conductivity than V2O5 without V4+. This engineering strategy of valence state manipulation may pave the way for designing high-performance cathodes for elucidating advanced battery chemistry.

Biomimetic Solid-State Zn2+ Electrolyte for Corrugated Structural Batteries

Batteries based on divalent metals, such as the Zn/Zn²⁺ pair, represent attractive alternatives to lithium-ion chemistry due to their high safety, reliability, earth-abundance, and energy density. However, archetypal Zn batteries are bulky, inflexible, non-rechargeable, and contain a corrosive electrolyte. Suppression of the anodic growth of Zn dendrites is essential for resolution of these problems and requires materials with nanoscale mechanics sufficient to withstand mechanical deformation from stiff Zn dendrites. Such materials must also support rapid transport Zn²⁺ ions necessary for high Coulombic efficiency and energy density, which makes the structural design of such materials a difficult fundamental problem. Here, we show that it is possible to engineer a solid Zn²⁺ electrolyte as a composite of branched aramid nanofibers (BANFs) and poly(ethylene oxide) by using the nanoscale organization of articular cartilage as a blueprint for its design. The high stiffness of the BANF network combined with the high ionic conductivity of soft poly(ethylene oxide) enable effective suppression of dendrites and fast Zn²⁺ transport. The cartilage-inspired composite displays the ionic conductance 10× higher than the original polymer. The batteries constructed using the nanocomposite electrolyte are rechargeable and have Coulombic efficiency of 96-100% after 50-100 charge-discharge cycles. Furthermore, the biomimetic solid-state electrolyte enables the batteries to withstand not only elastic deformation during bending but also plastic deformation. This capability make them resilient to different type of damage and enables shape modification of the assembled battery to improve the ability of the battery stack to carry a structural load. The corrugated batteries can be integrated into body elements of unmanned aerial vehicles as auxiliary charge-storage devices. This functionality was demonstrated by replacing the covers of several small drones with corrugated Zn/BANF/MnO₂ cells, resulting in the extension of the total flight time. These findings open a pathway to the design and utilization of corrugated structural batteries in the future transportation industry and other fields of use.

Polymer grafted on carbon nanotubes as a flexible cathode for aqueous zinc ion batteries

We have developed a free-standing, flexible cathode for an aqueous zinc ion battery by grafting cross-linked polydopamine on carbon nanotubes. The cathode is highly stable, with little capacity degradation for 500 cycles. The flexible cathode is environmentally benign and biocompatible which can enable applications from biomedical devices to grid storage.

Flexible Zn-Ion Batteries: Recent Progresses and Challenges

To keep pace with the increasing pursuit of portable and wearable electronics, it is urgent to develop advanced flexible power supplies. In this context, Zn-ion batteries (ZIBs) have garnered increasing attention as favorable energy storage devices for flexible electronics, owing to the high capacity, low cost, abundant resources, high safety, and eco-friendliness. Extensive efforts have been devoted to developing flexible ZIBs in the last few years. This work summarizes the recent achievements in the design, fabrication, and characterization of flexible ZIBs. Representative structures, such as sandwich and cable type, are particularly highlighted. Special emphasis is put on the novel design of electrolyte and electrode, which aims to endow reliable flexibility to the fabricated ZIBs. Moreover, current challenges and future opportunities for the development of high-performance flexible ZIBs are also outlined.

Water in Rechargeable Multivalent-Ion Batteries: An Electrochemical Pandora's Box

Multivalent-ion batteries built on water-based electrolytes represent energy storage at suitable price points, competitive performance, and enhanced safety. However, to comply with modern energy-density requirements, the battery must be reversible within an operating voltage window greater than 1.23 V or the electrochemical stability limits of free water. Taking advantage of its powerful solvation and catalytic activities, adding water to electrolyte preparations can unlock a wider gamut of liquid mixtures compared with strictly nonaqueous systems. However, a point-by-point sweep of all potential formulations is arduous and ineffective without some form of systematic rationalization. The present Review consolidates recent progress, pitfalls, limits, and insights critical to expediting aqueous electrolyte designs to boost multivalent-ion battery outputs.

Ultrafast Na intercalation chemistry of Na2Ti3/2Mn1/2(PO4)3 nanodots planted in a carbon matrix as a low cost anode for aqueous sodium-ion batteries

Na2Ti3/2Mn1/2(PO4)3 nanodots uniformly planted in a carbon matrix are reported for the first time as a promising low-cost anode for aqueous sodium-ion batteries, showing ultrafast Na-intercalation chemistry with stable capacities of 78.8 mA h g-1 at 0.5C and 65.1 mA h g-1 at 10C, and a capacity retention of 93% after 200 cycles.

Prototype System of Rocking-Chair Zn-Ion Battery Adopting Zinc Chevrel Phase Anode and Rhombohedral Zinc Hexacyanoferrate Cathode

Zinc-ion batteries (ZIBs) have received attention as one type of multivalent-ion batteries due to their potential applications in large-scale energy storage systems. Here we report a prototype of rocking-chair ZIB system employing Zn2Mo6S8 (zinc Chevrel phase) as an anode operating at 0.35 V, and K0.02(H2O)0.22Zn2.94[Fe(CN)6]2 (rhombohedral zinc Prussian-blue analogue) as a cathode operating at 1.75 V (vs. Zn/Zn2+) in ZnSO4 aqueous electrolyte. This type of cell has a benefit due to its intrinsic zinc-dendrite-free nature. The cell is designed to be positive-limited with a capacity of 62.3 mAh g−1. The full-cell shows a reversible cycle with an average discharge cell voltage of ~1.40 V, demonstrating a successful rocking-chair zinc-ion battery system.

Synthesis and electrochemical performance of NaV3O8 nanobelts for Li/Na-ion batteries and aqueous zinc-ion batteries

NaV₃O₈ nanobelts were successfully synthesized for Li/Na-ion batteries and rechargeable aqueous zinc-ion batteries (ZIBs) by a facile hydrothermal reaction and subsequent thermal transformation. Compared to the electrochemical performance of LIBs and NIBs, NaV₃O₈ nanobelt cathode materials in ZIBs have shown excellent electrochemical performance, including high specific capacity of 421 mA h g⁻¹ at 100 mA g⁻¹ and good cycle stability with a capacity retention of 94% over 500 cycles at 5 A g⁻¹. The good diffusion coefficients and high surface capacity of NaV₃O₈ nanobelts in ZIBs were in favor of fast Zn²⁺ intercalation and long-term cycle stability.

Compared to the electrochemical performance for LIBs and NIBs, NaV₃O₈ nanobelts electrode for ZIBs shows excellent electrochemical performance, including high specific capacity of 421 mA h g⁻¹ at 100 mA g⁻¹, good rate performance and cycle performance.

Two-Dimensional Unilamellar Cation-Deficient Metal Oxide Nanosheet Superlattices for High-Rate Sodium Ion Energy Storage

Cation-deficient two-dimensional (2D) materials, especially atomically thin nanosheets, are highly promising electrode materials for electrochemical energy storage that undergo metal ion insertion reactions, yet they have rarely been achieved thus far. Here, we report a Ti-deficient 2D unilamellar lepidocrocite-type titanium oxide (Ti_0.87O₂) nanosheet superlattice for sodium storage. The superlattice composed of alternately restacked defective Ti_0.87O₂ and nitrogen-doped graphene monolayers exhibits an outstanding capacity of ∼490 mA h g^-1 at 0.1 A g^-1, an ultralong cycle life of more than 10000 cycles with ∼0.00058% capacity decay per cycle, and especially superior low-temperature performance (100 mA h g^-1 at 12.8 A g^-1 and -5 °C), presenting the best reported performance to date. A reversible Na⁺ ion intercalation mechanism without phase and structural change is verified by first-principles calculations and kinetics analysis. These results herald a promising strategy to utilize defective 2D materials for advanced energy storage applications.

A ZnCl2 water-in-salt electrolyte for a reversible Zn metal anode

We report a low-cost water-in-salt electrolyte, of 30 m ZnCl2, which enables a dendrite-free Zn metal anode to possess a high coulombic efficiency (CE). In asymmetric Zn‖Zn cells with a limited mass of plated Zn as the working electrode, the ZnCl2 WiSE improves the average CE of the Zn anode to 95.4% from 73.2% in 5 m ZnCl2.

Dendrite Suppression Membranes for Rechargeable Zinc Batteries

Aqueous batteries with zinc metal anodes are promising alternatives to Li-ion batteries for grid storage because of their abundance and benefits in cost, safety, and nontoxicity. However, short cyclability due to zinc dendrite growth remains a major obstacle. Here, we report a cross-linked polyacrylonitrile (PAN)-based cation exchange membrane that is low cost and mechanically robust. Li₂S₃ reacts with PAN, simultaneously leading to cross-linking and formation of sulfur-containing functional groups. Hydrolysis of the membrane results in the formation of a membrane that achieves preferred cation transport and homogeneous ionic flux distribution. The separator is thin (30 μm-thick), almost 9 times stronger than hydrated Nafion, and made of low-cost materials. The membrane separator enables exceptionally long cyclability (>350 cycles) of Zn/Zn symmetric cells with low polarization and effective dendrite suppression. Our work demonstrates that the design of new separators is a fruitful pathway to enhancing the cyclability of aqueous batteries.

A Long-Cycle-Life Self-Doped Polyaniline Cathode for Rechargeable Aqueous Zinc Batteries

Rechargeable aqueous zinc batteries are promising energy-storage systems for grid applications. Highly conductive polyaniline (PANI) is a potential cathode, but it tends to deactivate in electrolytes with low acidity (i.e. pH >1) owing to deprotonation of the polymer. In this study, we synthesized a sulfo-self-doped PANI electrode by a facile electrochemical copolymerization process. The -SO₃ ^- self-dopant functions as an internal proton reservoir to ensure a highly acidic local environment and facilitate the redox process in the weakly acidic ZnSO₄ electrolyte. In a full zinc cell, the self-doped PANI cathode provided a high capacity of 180 mAh g^-1 , excellent rate performance of 70 % capacity retention with a 50-fold current-density increase, and a long cycle life of over 2000 cycles with coulombic efficiency close to 100 %. Our study opens a door for the use of conducting polymers as cathode materials for high-performance rechargeable zinc batteries.

Manganese-Oxide-Based Electrode Materials for Energy Storage Applications: How Close Are We to the Theoretical Capacitance?

Of the transition metals, Mn has the greatest number of different oxides, most of which have a special tunnel structure that enables bulk redox reactions. The high theoretical capacitance and capacity results from a greater number of accessible oxidation states than other transition metals, wide potential window, and the high natural abundance make MnO_x species promising electrode materials for energy storage applications. Although MnO_x electrode materials have been intensely studied over the past decade, their electrochemical performance is still insufficient for practical applications. Currently, there is a trade-off between specific capacitance and loading mass. MnO_x species have intrinsically poor electrical conductivity, and current structural designs are not sophisticated enough to accommodate enough redox-active sites. Recent studies have certainly made progress in increasing capacitance through making use of electrically conductive components and controlling the morphology of the MnO_x species to expose more surface area. To increase the capacitance of MnO_x electrodes to the largest extent without limiting loading mass, further structural design at the nanoscale and manipulation of the electrically conductive component are required. An ideal nanostructure is proposed to guide future research toward closing the gap between achieved and theoretical capacitance, without limiting the loading mass.

Self-Healing Lamellar Structure Boosts Highly Stable Zinc-Storage Property of Bilayered Vanadium Oxides

Rechargeable aqueous zinc-ion batteries have been considered one of the promising alternative energy-storage systems to lithium ion-batteries owing to their low cost and high safety. However, there is lack of long-life positive materials, which severely restricts the development of zinc-ion batteries. The strong interactions present between the intercalated multivalent cations and host materials inevitably cause structural distortions and create large migration barriers for the diffusion of cations, resulting in poor cycling stability and limited rate performance. Here, we report the application of bilayered ammonium vanadium oxide (NH₄V₄O₁₀) as the cathode material for zinc-ion batteries. A self-healing lamellar structure, which combines a macroscopically reversible morphological transformation and a microscopically adjustable interlayer spacing to accommodate the strong interactions, is observed upon insertion and release of cations. This stable architecture enables a specific capacity of 147 mA h g^-1 at a current density of 200 mA g^-1 (voltage window: 1.7-0.8 V vs Zn²⁺/Zn) and a capacity retention of more than 70.3% over 5000 cycles (5000 mA g^-1). Our finding provides a new alternative for zinc-ion batteries and inspiration for how to further develop advanced positive electrodes by employing materials with flexible microarchitectures.

Novel Alkaline Zn/Na0.44MnO2 Dual-Ion Battery with a High Capacity and Long Cycle Lifespan

A rechargeable aqueous Zn/Mn battery is a promising device for large-scale energy storage because of its abundant resources, low cost, and high safety. However, its application is plagued by a poor life cycle because of the electrochemical instability of MnO₂ in aqueous electrolytes. Here, an alkaline Zn-Na_0.44MnO₂ dual-ion battery (denoted AZMDIB) is developed for the first time using Na_0.44MnO₂ as the cathode, a zinc metal sheet as the anode, and a 6 M NaOH aqueous solution as the electrolyte. When the discharge cutoff voltage is lowered to 0.3 V (vs Zn/Zn²⁺), the Na_0.44MnO₂ cathode delivers a high capacity of 345.5 mA h g^-1 but with a poor cycling performance. The charge-discharge mechanism and structural evolution of the Na_0.44MnO₂ cathode in an extended potential window (1.95-0.3 V) are also explored. The Na_0.44MnO₂ electrode experiences two different electrochemical processes: Na⁺ ions insert/extract reversibly in the potential range of 1.95-1.1 V, and a phase transition occurs from Na_0.559MnO₂ to Mn(OH)₂ below 1.1 V. The latter irreversible reaction is probably due to proton insertion, leading to a severe capacity fade. Nevertheless, in a narrower voltage range (2.0-1.1 V), the AZMDIB full cell exhibits a high reversible capacity (80.2 mA h g^-1 at 0.5 C), high rate capability (32 mA h g^-1 at 50 C), and excellent cycling stability (73% capacity retention over 1000 cycles at 10 C). Benefiting from the merits of environmental friendliness, cost-effectiveness, and high electrochemical performance, the rechargeable AZMDIB is a promising contender for grid-scale energy storage applications.

A High-Rate and Stable Quasi-Solid-State Zinc-Ion Battery with Novel 2D Layered Zinc Orthovanadate Array

Zinc-ion batteries are under current research focus because of their uniqueness in low cost and high safety. However, it is still desirable to improve the rate performance by improving the Zn²⁺ (de)intercalation kinetics and long-cycle stability by eliminating the dendrite formation problem. Herein, the first paradigm of a high-rate and ultrastable flexible quasi-solid-state zinc-ion battery is constructed from a novel 2D ultrathin layered zinc orthovanadate array cathode, a Zn array anode supported by a conductive porous graphene foam, and a gel electrolyte. The nanoarray structure for both electrodes assures the high rate capability and alleviates the dendrite growth. The flexible Zn-ion battery has a depth of discharge of ≈100% for the cathode and 66% for the anode, and delivers an impressive high-rate of 50 C (discharge in 60 s), long-term durability of 2000 cycles at 20 C, and unprecedented energy density ≈115 Wh kg^-1 , together with a peak power density ≈5.1 kW kg^-1 (calculation includes masses of cathode, anode, and current collectors). First principles calculations and quantitative kinetics analysis show that the high-rate and stable properties are correlated with the 2D fast ion-migration pathways and the introduced intercalation pseudocapacitance.

Graphene-Boosted, High-Performance Aqueous Zn-Ion Battery

Given their low cost and eco-friendliness, rechargeable Zn-ion batteries (ZIBs) have received increasing attention as a device with great potential for large-scale energy storage. However, the development of ZIBs with high capacities and long lifespans is challenging because of the dendritic growth of Zn and the absence of suitable cathode materials. Herein, we report a novel rechargeable aqueous Zn-ion battery (AZIB) that consist of Zn coated with reduced graphene oxide as the anode and V₃O₇·H₂O/rGO composite as the cathode. The new AZIB exhibits excellent cycle stability with a high capacity retention of 79% after 1000 cycles. Moreover, it can deliver a high power density of 8400 W kg^-1 at 77 W h kg^-1 and a high energy density of 186 W h kg^-1 at 216 W kg^-1, and the former is higher than those of previously reported AZIBs. Our work provides a new perspective in developing rechargeable ZIBs and would greatly accelerate the practical applications of rechargeable ZIBs.

High-Performance Cable-Type Flexible Rechargeable Zn Battery Based on MnO2@CNT Fiber Microelectrode

Nowadays, linear-shaped batteries have received increasing attentions because the unique one-dimensional architecture offers an omni-directional flexibility. We developed a cable-type flexible rechargeable Zn microbattery based on a microscale MnO₂@carbon nanotube fiberlike composite cathode and Zn wire anode. The Zn-MnO₂ cable microbattery exhibits a large specific capacity, good rate performance, and cyclic stability. The capacity of Zn-MnO₂ cable batteries are 322 and 290 mAh/g based on MnO₂ with aqueous and gel polymer electrolyte, corresponding to the specific energy of 437 and 360 Wh/kg, respectively. Besides, the Zn-MnO₂ cable battery shows excellent flexibility, which can be folded into arbitrary shapes without sacrificing electrochemical performance. Furthermore, we studied electrochemical properties of Zn-MnO₂ cable microbatteries with different Zn salt electrolytes, such as Zn salt with small anions (ZnSO₄ or ZnCl₂, etc.) and Zn salt with bulky anions (Zn(CF₃SO₃)₂, etc.). With the merits of impressive electrochemical performance and flexibility, this first flexible rechargeable Zn-MnO₂ cable-like battery presents a new approach to develop high-performance power sources for portable and wearable electronics.

Polyaniline-intercalated manganese dioxide nanolayers as a high-performance cathode material for an aqueous zinc-ion battery

Rechargeable zinc-manganese dioxide batteries that use mild aqueous electrolytes are attracting extensive attention due to high energy density and environmental friendliness. Unfortunately, manganese dioxide suffers from substantial phase changes (e.g., from initial α-, β-, or γ-phase to a layered structure and subsequent structural collapse) during cycling, leading to very poor stability at high charge/discharge depth. Herein, cyclability is improved by the design of a polyaniline-intercalated layered manganese dioxide, in which the polymer-strengthened layered structure and nanoscale size of manganese dioxide serves to eliminate phase changes and facilitate charge storage. Accordingly, an unprecedented stability of 200 cycles with at a high capacity of 280 mA h g-1 (i.e., 90% utilization of the theoretical capacity of manganese dioxide) is achieved, as well as a long-term stability of 5000 cycles at a  utilization of 40%. The encouraging performance sheds light on the design of advanced cathodes for aqueous zinc-ion batteries.

Advanced Low-Cost, High-Voltage, Long-Life Aqueous Hybrid Sodium/Zinc Batteries Enabled by a Dendrite-Free Zinc Anode and Concentrated Electrolyte

Aqueous batteries are promising energy storage systems but are hindered by the limited selection of anodes and narrow electrochemical window to achieve satisfactory cyclability and decent energy density. Here, we design aqueous hybrid Na-Zn batteries by using a carbon-coated Zn (Zn@C) anode, 8 M NaClO₄ + 0.4 M Zn(CF₃SO₃)₂ concentrated electrolyte coupled with NASICON-structured cathodes. The Zn@C anode achieves stable Zn stripping/plating and improved kinetics without Zn dendrite formation due to the porous carbon film facilitating homogeneous current distribution and Zn deposition. Furthermore, the concentrated electrolyte offers a large electrochemical window (∼2.5 V) and permits stable cycling of cathodes. As a result, the hybrid batteries exhibit extraordinary performance including high voltage, high energy density (100-150 Wh kg^-1 for half battery and 71 Wh kg^-1 for full battery), and excellent cycling stability of 1000 cycles.

Oxygen-Vacancy and Surface Modulation of Ultrathin Nickel Cobaltite Nanosheets as a High-Energy Cathode for Advanced Zn-Ion Batteries

The development of high-capacity, Earth-abundant, and stable cathode materials for robust aqueous Zn-ion batteries is an ongoing challenge. Herein, ultrathin nickel cobaltite (NiCo2 O4 ) nanosheets with enriched oxygen vacancies and surface phosphate ions (P-NiCo2 O4-x ) are reported as a new high-energy-density cathode material for rechargeable Zn-ion batteries. The oxygen-vacancy and surface phosphate-ion modulation are achieved by annealing the pristine NiCo2 O4 nanosheets using a simple phosphating process. Benefiting from the merits of substantially improved electrical conductivity and increased concentration of active sites, the optimized P-NiCo2 O4-x nanosheet electrode delivers remarkable capacity (309.2 mAh g-1 at 6.0 A g-1 ) and extraordinary rate performance (64% capacity retention at 60.4 A g-1 ). Moreover, based on the P-NiCo2 O4-x cathode, our fabricated P-NiCo2 O4-x //Zn battery presents an impressive specific capacity of 361.3 mAh g-1 at the high current density of 3.0 A g-1 in an alkaline electrolyte. Furthermore, extremely high energy density (616.5 Wh kg-1 ) and power density (30.2 kW kg-1 ) are also achieved, which outperforms most of the previously reported aqueous Zn-ion batteries. This ultrafast and high-energy aqueous Zn-ion battery is promising for widespread application to electric vehicles and intelligent devices.

Ultrafast Zn2+ Intercalation and Deintercalation in Vanadium Dioxide

Although rechargeable aqueous zinc-ion batteries have attracted extensive interest due to their environmental friendliness and low cost, they still lack suitable cathodes with high rate capabilities, which are hampered by the intense charge repulsion of bivalent Zn²⁺ . Here, a novel intercalation pseudocapacitance behavior and ultrafast kinetics of Zn²⁺ into the unique tunnels of VO₂ (B) nanofibers in aqueous electrolyte are demonstrated via in situ X-ray diffraction and various electrochemical measurements. Because VO₂ (B) nanofibers possess unique tunnel transport pathways with big sizes (0.82 and 0.5 nm² along the b- and c-axes) and little structural change on Zn²⁺ intercalation, the limitation from solid-state diffusion in the vanadium dioxide electrode is eliminated. Thus, VO₂ (B) nanofibers exhibit a high reversible capacity of 357 mAh g^-1 , excellent rate capability (171 mAh g^-1 at 300 C), and high energy and power densities as applied for zinc-ion storage.

A Hollow-Structured Manganese Oxide Cathode for Stable Zn-MnO₂ Batteries

Aqueous rechargeable zinc-manganese dioxide (Zn-MnO₂) batteries are considered as one of the most promising energy storage devices for large scale-energy storage systems due to their low cost, high safety, and environmental friendliness. However, only a few cathode materials have been demonstrated to achieve stable cycling for aqueous rechargeable Zn-MnO₂ batteries. Here, we report a new material consisting of hollow MnO₂ nanospheres, which can be used for aqueous Zn-MnO₂ batteries. The hollow MnO₂ nanospheres can achieve high specific capacity up to ~405 mAh g⁻¹ at 0.5 C. More importantly, the hollow structure of birnessite-type MnO₂ enables long-term cycling stability for the aqueous Zn-MnO₂ batteries. The excellent performance of the hollow MnO₂ nanospheres should be due to their unique structural properties that enable the easy intercalation of zinc ions.

In Situ Activation of 3D Porous Bi/Carbon Architectures: Toward High-Energy and Stable Nickel-Bismuth Batteries

To achieve high-energy and stable aqueous rechargeable batteries, state-of-the art of anode materials are needed. Bismuth (Bi) has recently emerged as an attractive anode material due to its highly reversible redox reaction and suitable negative operating working window. However, the capacity and durability of currently reported Bi anodes are still far from satisfactory. Here, an in situ activation strategy is reported to prepare a 3D porous high-density Bi nanoparticles/carbon architecture (P-Bi-C) as an efficient anode for nickel-bismuth batteries. Taking advantages of the fast channels for charge transfer and ion diffusion, enhanced wettability, and accessible surface area, the highly loaded P-Bi-C electrode delivers a remarkable capacity of 2.11 mA h cm^-2 as well as high rate capability (1.19 mA h cm^-2 at 120 mA cm^-2 ). To highlight, a robust aqueous rechargeable Ni//Bi battery based on the P-Bi-C anode is first constructed, achieving decent capacity (141 mA h g^-1 ), impressive durability (94% capacity retention after 5000 cycles), and admirable energy density (16.9 mW h cm^-3 ). This work paves the way for designing superfast nickel-bismuth batteries with high energy and long-life and may inspire new development for aqueous rechargeable batteries.

Investigation of V2O5 as a low-cost rechargeable aqueous zinc ion battery cathode

Rechargeable aqueous zinc ion batteries (ZIBs) are highly desirable for large-scale energy storage due to their advantages of safety and low-cost. Development of advanced cathodes for use in aqueous ZIBs is urgently needed. Herein, we report a low-cost rechargeable aqueous Zn-V2O5 cell with 3 M ZnSO4 electrolyte that demonstrates high zinc storage capability. We also investigated the effect of different types/concentrations of the aqueous electrolytes on the performance of the Zn-V2O5 cells.

Aqueous rechargeable zinc/sodium vanadate batteries with enhanced performance from simultaneous insertion of dual carriers

Rechargeable aqueous zinc-ion batteries are promising energy storage devices due to their high safety and low cost. However, they remain in their infancy because of the limited choice of positive electrodes with high capacity and satisfactory cycling performance. Furthermore, their energy storage mechanisms are not well established yet. Here we report a highly reversible zinc/sodium vanadate system, where sodium vanadate hydrate nanobelts serve as positive electrode and zinc sulfate aqueous solution with sodium sulfate additive is used as electrolyte. Different from conventional energy release/storage in zinc-ion batteries with only zinc-ion insertion/extraction, zinc/sodium vanadate hydrate batteries possess a simultaneous proton, and zinc-ion insertion/extraction process that is mainly responsible for their excellent performance, such as a high reversible capacity of 380 mAh g-1 and capacity retention of 82% over 1000 cycles. Moreover, the quasi-solid-state zinc/sodium vanadate hydrate battery is also a good candidate for flexible energy storage device.

Na2V6O16·3H2O Barnesite Nanorod: An Open Door to Display a Stable and High Energy for Aqueous Rechargeable Zn-Ion Batteries as Cathodes

Owing to their safety and low cost, aqueous rechargeable Zn-ion batteries (ARZIBs) are currently more feasible for grid-scale applications, as compared to their alkali counterparts such as lithium- and sodium-ion batteries (LIBs and SIBs), for both aqueous and nonaqueous systems. However, the materials used in ARZIBs have a poor rate capability and inadequate cycle lifespan, serving as a major handicap for long-term storage applications. Here, we report vanadium-based Na₂V₆O₁₆·3H₂O nanorods employed as a positive electrode for ARZIBs, which display superior electrochemical Zn storage properties. A reversible Zn²⁺-ion (de)intercalation reaction describing the storage mechanism is revealed using the in situ synchrotron X-ray diffraction technique. This cathode material delivers a very high rate capability and high capacity retention of more than 80% over 1000 cycles, at a current rate of 40C (1C = 361 mA g^-1). The battery offers a specific energy of 90 W h kg^-1 at a specific power of 15.8 KW kg^-1, enlightening the material advantages for an eco-friendly atmosphere.