Recent Progress on Zinc-Ion Rechargeable Batteries

Electrolyte Concentration Regulation Boosting Zinc Storage Stability of High-Capacity K0.486V2O5 Cathode for Bendable Quasi-Solid-State Zinc Ion Batteries

Vanadium-based cathodes have attracted great interest in aqueous zinc ion batteries (AZIBs) due to their large capacities, good rate performance and facile synthesis in large scale. However, their practical application is greatly hampered by vanadium dissolution issue in conventional dilute electrolytes. Herein, taking a new potassium vanadate K_0.486V₂O₅ (KVO) cathode with large interlayer spacing (~ 0.95 nm) and high capacity as an example, we propose that the cycle life of vanadates can be greatly upgraded in AZIBs by regulating the concentration of ZnCl₂ electrolyte, but with no need to approach "water-in-salt" threshold. With the optimized moderate concentration of 15 m ZnCl₂ electrolyte, the KVO exhibits the best cycling stability with ~ 95.02% capacity retention after 1400 cycles. We further design a novel sodium carboxymethyl cellulose (CMC)-moderate concentration ZnCl₂ gel electrolyte with high ionic conductivity of 10.08 mS cm^-1 for the first time and assemble a quasi-solid-state AZIB. This device is bendable with remarkable energy density (268.2 Wh kg^-1), excellent stability (97.35% after 2800 cycles), low self-discharge rate, and good environmental (temperature, pressure) suitability, and is capable of powering small electronics. The device also exhibits good electrochemical performance with high KVO mass loading (5 and 10 mg cm^-2). Our work sheds light on the feasibility of using moderately concentrated electrolyte to address the stability issue of aqueous soluble electrode materials.

Simulation of dendritic growth of a zinc anode in a zinc–nickel single flow battery using the phase field-lattice Boltzmann method

The mechanism of zinc dendrite formation was explored to obtain high-safety zinc nickel single liquid batteries.

Anode Materials for Aqueous Zinc Ion Batteries: Mechanisms, Properties, and Perspectives

Aqueous Zn-ion batteries (ZIBs) are promising safe energy storage systems that have received considerable attention in recent years. Based on the electrochemical behavior of Zn²⁺ in the charging and discharging process, herein we review the research progress on anode materials for use in aqueous ZIBs based on two aspects: Zn deposition and Zn²⁺ intercalation. To date, Zn dendrite, corrosion, and passivation issues have restricted the development of aqueous ZIBs. However, many strategies have been developed, including structural design, interface protection of the Zn anode, Zn alloying, and using polymer electrolytes. The main aim is to stabilize the Zn stripping/plating layer and limit side reactions. Zn²⁺-intercalated anodes, with a high Zn²⁺ storage capacity to replace the current metal Zn anode, are also a potential option. Finally, some suggestions have been put forward for the subsequent optimization strategy, which are expected to promote further development of aqueous ZIBs.

A Review of the Use of GPEs in Zinc-Based Batteries. A Step Closer to Wearable Electronic Gadgets and Smart Textiles

With the flourish of flexible and wearable electronics gadgets, the need for flexible power sources has become essential. The growth of this increasingly diverse range of devices boosted the necessity to develop materials for such flexible power sources such as secondary batteries, fuel cells, supercapacitors, sensors, dye-sensitized solar cells, etc. In that context, comprehensives studies on flexible conversion and energy storage devices have been released for other technologies such Li-ion standing out the importance of the research done lately in GPEs (gel polymer electrolytes) for energy conversion and storage. However, flexible zinc batteries have not received the attention they deserve within the flexible batteries field, which are destined to be one of the high rank players in the wearable devices future market. This review presents an extensive overview of the most notable or prominent gel polymeric materials, including biobased polymers, and zinc chemistries as well as its practical or functional implementation in flexible wearable devices. The ultimate aim is to highlight zinc-based batteries as power sources to fill a segment of the world flexible batteries future market.

High-Energy, Single-Ion-Mediated Nonaqueous Zinc-TEMPO Redox Flow Battery

Two distinct advantages of nonaqueous redox flow batteries (RFBs) are the feasibility of building a high cell voltage (without a constraint of the water-splitting potential) and the operability at low temperatures (without a concern of freezing below 0 °C). However, electrochemically active organic redox couples are usually selectively soluble in specific nonaqueous solvents, and their solubility is relatively low (in contrast to that in aqueous solutions). The selective and low solubility of redox couples seriously constrict the practical energy density of nonaqueous RFBs. Herein, we present a hybrid nonaqueous RFB with a solid zinc anode and a liquid (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) cathode. Toward accessing a high solubility of the TEMPO cathode and to sufficiently accommodate the discharge products of a Zn anode, asymmetric electrolyte solvents, viz., propylene carbonate (PC) and acetonitrile (ACN), have, respectively, been employed at the cathode and anode. To prevent a mixing of the two asymmetric electrolyte solvents, a NASICON-type Na⁺-ion conductive solid-state electrolyte (SSE, Na₃Zr₂Si₂PO₁₂) is employed to serve as a mediator-ion separator. The shuttling of Na⁺ ions through the Na₃Zr₂Si₂PO₁₂ SSE sustains the ionic charge balance between the two electrodes. The Zn-TEMPO nonaqueous cell with a stable energy density of ca. 12-18 Wh L^-1 over 50 cycles was demonstrated.

Defected vanadium bronzes as superb cathodes in aqueous zinc-ion batteries

There is a growing need for fast, efficient, safe, and low-cost energy storage. Aqueous zinc-ion batteries (AZIBs) may be able to address this need, but suffer from fast capacity fade and poor ion diffusion kinetics due to unstable structures and non-optimised interspacing of layered cathode materials. Herein, we propose a structural engineering strategy by synergistically inducing anionic defects and cationic groups within vanadium bronze structures to improve kinetics and boost capacity. The materials discovered and used as the cathodes in AZIBs showed a high capacity of 435 mA h g-1 at a current density of 0.2 A g-1 and excellent stability with 95% capacity retention after 1500 cycles at 10 A g-1. This combined experimental and computational study systemically indicated that rapid Zn2+ storage was achieved from both a highly porous structure and enlarged d-spacing combined with improved electron conductivity as determined by density of states calculations. The modification of vanadium bronze-type cathodes achieved by controlled pre-intercalated species and tailored oxygen deficiency opens up an avenue for the realization of superior material design, whose feasibility is proved in this work.

An In Situ Cross-Linked Nonaqueous Polymer Electrolyte for Zinc-Metal Polymer Batteries and Hybrid Supercapacitors

This work reports the facile synthesis of nonaqueous zinc-ion conducting polymer electrolyte (ZIP) membranes using an ultraviolet (UV)-light-induced photopolymerization technique, with room temperature (RT) ionic conductivity values in the order of 10^-3 S cm^-1 . The ZIP membranes demonstrate excellent physicochemical and electrochemical properties, including an electrochemical stability window of >2.4 V versus Zn|Zn²⁺ and dendrite-free plating/stripping processes in symmetric Zn||Zn cells. Besides, a UV-polymerization-assisted in situ process is developed to produce ZIP (abbreviated i-ZIP), which is adopted for the first time to fabricate a nonaqueous zinc-metal polymer battery (ZMPB; VOPO₄ |i-ZIP|Zn) and zinc-metal hybrid polymer supercapacitor (ZMPS; activated carbon|i-ZIP|Zn) cells. The VOPO₄ cathode employed in ZMPB possesses a layered morphology, exhibiting a high average operating voltage of ≈1.2 V. As compared to the conventional polymer cell assembling approach using the ex situ process, the in situ process is simple and it enhances the overall electrochemical performance, which enables the widespread intrusion of ZMPBs and ZMPSs into the application domain. Indeed, considering the promising aspects of the proposed ZIP and its easy processability, this work opens up a new direction for the emergence of the zinc-based energy storage technologies.

High-Performance Aqueous Zinc-Ion Batteries Realized by MOF Materials

Rechargeable aqueous zinc-ion batteries (ZIBs) have been gaining increasing interest for large-scale energy storage applications due to their high safety, good rate capability, and low cost. However, the further development of ZIBs is impeded by two main challenges: Currently reported cathode materials usually suffer from rapid capacity fading or high toxicity, and meanwhile, unstable zinc stripping/plating on Zn anode seriously shortens the cycling life of ZIBs. In this paper, metal-organic framework (MOF) materials are proposed to simultaneously address these issues and realize high-performance ZIBs with Mn(BTC) MOF cathodes and ZIF-8-coated Zn (ZIF-8@Zn) anodes. Various MOF materials were synthesized, and Mn(BTC) MOF was found to exhibit the best Zn2+-storage ability with a capacity of 112 mAh g-1. Zn2+ storage mechanism of the Mn(BTC) was carefully studied. Besides, ZIF-8@Zn anodes were prepared by coating ZIF-8 MOF material on Zn foils. Unique porous structure of the ZIF-8 coating guided uniform Zn stripping/plating on the surface of Zn anodes. As a result, the ZIF-8@Zn anodes exhibited stable Zn stripping/plating behaviors, with 8 times longer cycle life than bare Zn foils. Based on the above, high-performance aqueous ZIBs were constructed using the Mn(BTC) cathodes and the ZIF-8@Zn anodes, which displayed an excellent long-cycling stability without obvious capacity fading after 900 charge/discharge cycles. This work provides a new opportunity for high-performance energy storage system.

MnO2 Heterostructure on Carbon Nanotubes as Cathode Material for Aqueous Zinc-Ion Batteries

Due to their cost effectiveness, high safety, and eco-friendliness, zinc-ion batteries (ZIBs) are receiving much attention nowadays. In the production of rechargeable ZIBs, the cathode plays an important role. Manganese oxide (MnO2) is considered the most promising and widely investigated intercalation cathode material. Nonetheless, MnO2 cathodes are subjected to challenging issues viz. limited capacity, low rate capability and poor cycling stability. It is seen that the MnO2 heterostructure can enable long-term cycling stability in different types of energy devices. Herein, a versatile chemical method for the preparation of MnO2 heterostructure on multi-walled carbon nanotubes (MNH-CNT) is reported. Besides, the synthesized MNH-CNT is composed of δ-MnO2 and γ-MnO2. A ZIB using the MNH-CNT cathode delivers a high initial discharge capacity of 236 mAh g-1 at 400 mA g-1, 108 mAh g-1 at 1600 mA g-1 and excellent cycling stability. A pseudocapacitive behavior investigation demonstrates fast zinc ion diffusion via a diffusion-controlled process with low capacitive contribution. Overall, the MNH-CNT cathode is seen to exhibit superior electrochemical performance. This work presents new opportunities for improving the discharge capacity and cycling stability of aqueous ZIBs.

Binder-Free α-MnO2 Nanowires on Carbon Cloth as Cathode Material for Zinc-ion Batteries

Recently, rechargeable zinc-ion batteries (ZIBs) have gained a considerable amount of attention due to their high safety, low toxicity, abundance, and low cost. Traditionally, a composite manganese oxide (MnO2) and a conductive carbon having a polymeric binder are used as a positive electrode. In general, a binder is employed to bond all materials together and to prevent detachment and dissolution of the active materials. Herein, the synthesis of α-MnO2 nanowires on carbon cloth via a simple one-step hydrothermal process and its electrochemical performance, as a binder-free cathode in aqueous and nonaqueous-based ZIBs, is duly reported. Morphological and elemental analyses reveal a single crystal α-MnO2 having homogeneous nanowire morphology with preferential growth along {001}. It is significant that analysis of the electrochemical performance of the α-MnO2 nanowires demonstrates more stable capacity and superior cyclability in a dimethyl sulfoxide (DMSO) electrolyte ZIB than in an aqueous electrolyte system. This is because DMSO can prevent irreversible proton insertion as well as unfavorable dendritic zinc deposition. The application of the binder-free α-MnO2 nanowires cathode in DMSO can promote follow-up research on the high cyclability of ZIBs.

Bifunctional Oxygen Electrocatalyst of Mesoporous Ni/NiO Nanosheets for Flexible Rechargeable Zn-Air Batteries

One approach to accelerate the stagnant kinetics of both the oxygen reduction and evolution reactions (ORR/OER) is to develop a rationally designed multiphase nanocomposite, where the functions arising from each of the constituent phases, their interfaces, and the overall structure are properly controlled. Herein, we successfully synthesized an oxygen electrocatalyst consisting of Ni nanoparticles purposely interpenetrated into mesoporous NiO nanosheets (porous Ni/NiO). Benefiting from the contributions of the Ni and NiO phases, the well-established pore channels for charge transport at the interface between the phases, and the enhanced conductivity due to oxygen-deficiency at the pore edges, the porous Ni/NiO nanosheets show a potential of 1.49 V (10 mA cm-2) for the OER and a half-wave potential of 0.76 V for the ORR, outperforming their noble metal counterparts. More significantly, a Zn-air battery employing the porous Ni/NiO nanosheets exhibits an initial charging-discharging voltage gap of 0.83 V (2 mA cm-2), specific capacity of 853 mAh g Zn -1 at 20 mA cm-2, and long-time cycling stability (120 h). In addition, the porous Ni/NiO-based solid-like Zn-air battery shows excellent electrochemical performance and flexibility, illustrating its great potential as a next-generation rechargeable power source for flexible electronics.

Dendrite-free Zn anodes enabled by functional nitrogen-doped carbon protective layers for aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries possess the merits of good environmental benignity, high operational safety and high energy density. Nevertheless, the practical application of zinc-ion batteries is severely obstructed by the inhomogeneous deposition of metallic Zn on the anode, which results in serious capacity fading, poor coulombic efficiency, and electrolyte consumption. Herein, we propose a simple strategy of constructing a functional nitrogen-doped carbon network coating layer on zinc foil for dendrite-free Zn stripping/plating. On one hand, the good conductivity of the artificial Zn/electrolyte interface can quickly balance the electric field and lower the nucleation overpotential. On the other hand, the porosity feature and functional groups of the protective layer can provide a fast Zn2+ transportation pathway and generate well-dispersed nucleation seeds. Therefore, the protective layer can effectively hamper the growth of metallic Zn dendrites and resist side reactions. The as-prepared N-C/Zn anode displays superior cycling stability (800 h at 2 mA cm-2 with the capacity of 2 mA h cm-2) and a satisfactory coulombic efficiency of 98.76% during the Zn stripping/plating process. A long cycle life and high specific capacity (162.10 mA h g-1 after 500 cycles at 2.0 A g-1) are also obtained for N-C/Zn||ZnSO4||V2O5 full cells. The strategy provides a facile and effective opportunity for constructing high-performance rechargeable aqueous zinc-ion batteries.

Boosting High-Rate Zinc-Storage Performance by the Rational Design of Mn2O3 Nanoporous Architecture Cathode

Manganese oxides are regarded as one of the most promising cathode materials in rechargeable aqueous Zn-ion batteries (ZIBs) because of the low price and high security. However, the practical application of Mn2O3 in ZIBs is still plagued by the low specific capacity and poor rate capability. Herein, highly crystalline Mn2O3 materials with interconnected mesostructures and controllable pore sizes are obtained via a ligand-assisted self-assembly process and used as high-performance electrode materials for reversible aqueous ZIBs. The coordination degree between Mn2+ and citric acid ligand plays a crucial role in the formation of the mesostructure, and the pore sizes can be easily tuned from 3.2 to 7.3 nm. Ascribed to the unique feature of nanoporous architectures, excellent zinc-storage performance can be achieved in ZIBs during charge/discharge processes. The Mn2O3 electrode exhibits high reversible capacity (233 mAh g-1 at 0.3 A g-1), superior rate capability (162 mAh g-1 retains at 3.08 A g-1) and remarkable cycling durability over 3000 cycles at a high current rate of 3.08 A g-1. Moreover, the corresponding electrode reaction mechanism is studied in depth according to a series of analytical methods. These results suggest that rational design of the nanoporous architecture for electrode materials can effectively improve the battery performance.

Bi2S3 for Aqueous Zn Ion Battery with Enhanced Cycle Stability

Aqueous Zn ion batteries (ZIBs) are promising in energy storage due to the low cost, high safety, and material abundance. The development of metal oxides as the cathode for ZIBs is limited by the strong electrostatic forces between O2- and Zn2+ which leads to poor cyclic stability. Herein, Bi2S3 is proposed as a promising cathode material for rechargeable aqueous ZIBs. Improved cyclic stability and fast diffusion of Zn2+ is observed. Also, the layered structure of Bi2S3 with the weak van der Waals interaction between layers offers paths for diffusion and occupancy of Zn2+. As a result, the Zn/Bi2S3 battery delivers high capacity of 161 mAh g-1 at 0.2 A g-1 and good cycling stability up to 100 cycles with ca. 100% retention. The battery also demonstrates good cyclic performance of ca. 80.3% over 2000 cycles at 1 A g-1. The storage mechanism in the Bi2S3 cathode is related to the reversible Zn ion intercalation/extraction reactions and the capacitive contribution. This work indicates that Bi2S3 shows great potential as the cathode of ZIBs with good performance and stability.