Sodium Ion Pre-Intercalation of δ-MnO2 Nanosheets for High Energy Density Aqueous Zinc-Ion Batteries

With the merits of low cost, environmental friendliness and rich resources, manganese dioxide is considered to be a promising cathode material for aqueous zinc-ion batteries (AZIBs). However, its low ion diffusion and structural instability greatly limit its practical application. Hence, we developed an ion pre-intercalation strategy based on a simple water bath method to grow in situ δ-MnO₂ nanosheets on flexible carbon cloth substrate (MnO₂), while pre-intercalated Na⁺ in the interlayer of δ-MnO₂ nanosheets (Na-MnO₂), which effectively enlarges the layer spacing and enhances the conductivity of Na-MnO₂. The prepared Na-MnO₂//Zn battery obtained a fairly high capacity of 251 mAh g^-1 at a current density of 2 A g^-1, a satisfactory cycle life (62.5% of its initial capacity after 500 cycles) and favorable rate capability (96 mAh g^-1 at 8 A g^-1). Furthermore, this study revealed that the pre-intercalation engineering of alkaline cations is an effective method to boost the properties of δ-MnO₂ zinc storage and provides new insights into the construction of high energy density flexible electrodes.

Quantitative Regulation of Interlayer Space of NH4 V4 O10 for Fast and Durable Zn2+ and NH4 + Storage

Layered vanadium-based oxides are the promising cathode materials for aqueous zinc-ion batteries (AZIBs). Herein, an in situ electrochemical strategy that can effectively regulate the interlayer distance of layered NH₄ V₄ O₁₀ quantitatively is proposed and a close relationship between the optimal performances with interlayer space is revealed. Specifically, via increasing the cutoff voltage from 1.4, 1.6 to 1.8 V, the interlayer space of NH₄ V₄ O₁₀ can be well-controlled and enlarged to 10.21, 11.86, and 12.08 Å, respectively, much larger than the pristine one (9.5 Å). Among them, the cathode being charging to 1.6 V (NH₄ V₄ O₁₀ -C1.6), demonstrates the best Zn²⁺ storage performances including high capacity of 223 mA h g^-1 at 10 A g^-1 and long-term stability with capacity retention of 97.5% over 1000 cycles. Such superior performances can be attributed to a good balance among active redox sites, charge transfer kinetics, and crystal structure stability, enabled by careful control of the interlayer space. Moreover, NH₄ V₄ O₁₀ -C1.6 delivers NH₄ ⁺ storage performances whose capacity reaches 296 mA h g^-1 at 0.1 A g^-1 and lifespan lasts over 3000 cycles at 5 A g^-1 . This study provides new insights into understand the limitation of interlayer space for ion storage in aqueous media and guides exploration of high-performance cathode materials.

Electrolyte Regulation of Bio-Inspired Zincophilic Additive toward High-Performance Dendrite-Free Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries hold attractive potential for large-scale energy storage devices owing to their prominent electrochemical performance and high security. Nevertheless, the applications of aqueous electrolytes have generated various challenges, including uncontrolled dendrite growth and parasitic reactions, thereby deteriorating the Zn anode's stability. Herein, inspired by the superior affinity between Zn²⁺ and amino acid chains in the zinc finger protein, a cost-effective and green glycine additive is incorporated into aqueous electrolytes to stabilize the Zn anode. As confirmed by experimental characterizations and theoretical calculations, the glycine additives can not only reorganize the solvation sheaths of hydrated Zn²⁺ via partial substitution of coordinated H₂ O but also preferentially adsorb onto the Zn anode, thereby significantly restraining dendrite growth and interfacial side reactions. Accordingly, the Zn anode could realize a long lifespan of over 2000 h and enhanced reversibility (98.8%) in the glycine-containing electrolyte. Furthermore, the assembled Zn||α-MnO₂ full cells with glycine-modified electrolyte also delivers substantial capacity retention (82.3% after 1000 cycles at 2 A g^-1 ), showing promising application prospects. This innovative bio-inspired design concept would inject new vitality into the development of aqueous electrolytes.

Achieving Ultralong-Cycle Zinc-Ion Battery via Synergistically Electronic and Structural Regulation of a MnO2 Nanocrystal-Carbon Hybrid Framework

Aqueous rechargeable zinc-ion batteries (ZIBs) have attracted burgeoning interests owing to the prospect in large-scale and safe energy storage application. Although manganese oxides are one of the typical cathodes of ZIBs, their practical usage is still hindered by poor service life and rate performance. Here, a MnO₂ -carbon hybrid framework is reported, which is obtained in a reaction between the dimethylimidazole ligand from a rational designed MOF array and potassium permanganate, achieving ultralong-cycle-life ZIBs. The unique structural feature of uniform MnO₂ nanocrystals which are well-distributed in the carbon matrix leads to a 90.4% capacity retention after 50 000 cycles. In situ characterization and theoretical calculations verify the co-ions intercalation with boosted reaction kinetics. The hybridization between MnO₂ and carbon endows the hybrid with enhanced electrons/ions transport kinetics and robust structural stability. This work provides a facile strategy to enhance the battery performance of manganese oxide-based ZIBs.

Piezoelectric 1T Phase MoSe2 Nanoflowers and Crystallographically Textured Electrodes for Enhanced Low-Temperature Zinc-Ion Storage

Transition metal dichalcogenides (TMDs) are regarded as promising cathode materials for zinc-ion storage owing to their large interlayer spacings. However, their capabilities are still limited by sluggish kinetics and inferior conductivities. In this study, a facile one-pot solvothermal method is exploited to vertically plant piezoelectric 1T MoSe₂  nanoflowers on carbon cloth (CC) to fabricate crystallographically textured electrodes. The self-built-in electric field owing to the intrinsic piezoelectricity during the intercalation/deintercalation processes can serve as an additional piezo-electrochemical coupling accelerator to enhance the migration of Zn²⁺ . Moreover, the expanded interlayer distance (9-10 Å), overall high hydrophilicity, and conductivity of the 1T phase MoSe₂  also promoted the kinetics. These advantages endow the tailored 1T MoSe₂ /CC nanopiezocomposite with feasible Zn²⁺ diffusion and desirable electrochemical performances at room and low temperatures. Moreover, 1T MoSe₂ /CC-based quasi-solid-state zinc-ion batteries are constructed to evaluate the potential of the proposed material in low-temperature flexible energy storage devices. This work expounds the positive effect of intrinsic piezoelectricity of TMDs on Zn²⁺ migration and further explores the availabilities of TMDs in low-temperature wearable energy-storage devices.

Controllable CF4 Plasma In Situ Modification Strategy Enables Durable Zinc Metal Anode

Zn metal with high specific capacity and low redox potential is deemed to be an ideal anode material for aqueous zinc-ion batteries (ZIBs). However, the serious dendrite problems induced by the uneven deposition of zinc shorten the service life and hinder the development of ZIBs. According to the nucleation and growth mechanism, the charge distribution at the anode interface is the critical factor affecting the deposition morphology. Herein, CF₄ plasma technology is applied for the first time to in situ modification of the Zn anode, and then, the uniform nanoscale ZnF₂ particles are formed. Due to the excellent ionic conductivity and poor electronic conductivity of ZnF₂, the ion and electron distribution at the anode interface is orderly regulated, thus guiding uniform and reversible deposition behavior and restraining the dendrite growth. As a result, the Zn@ZnF₂-5 anode exhibits low nucleation overpotential (16 mV), long cycle life (2500 h at 1 mA cm^-2 and 1 mA h cm^-2), and excellent resistance to high current density (20 mA cm^-2) and high discharge depth (16%). Meanwhile, the Zn@ZnF₂-5|I₂@AC full battery shows remarkable cycle stability (1000 cycles) with ∼10% discharge depth of the anode. The novel and practical CF₄ plasma in situ modification strategy provides a new idea for the interface modification of zinc anode.

A Double-Functional Additive Containing Nucleophilic Groups for High-Performance Zn-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) have attracted attention for their low cost and environmental friendliness. Unfortunately, commercialization has been hampered by several problems with dendrite growth and side reactions. Herein, we select sodium tartrate (TA-Na) as a dual-functional electrolyte additive to enhance the reversibility of AZIBs. The tartrate anions are preferentially adsorbed on the Zn surface, and then the highly nucleophilic carboxylate will coordinate with Zn2+ to promote the desolvation of [Zn(H2O)6]2+, leading to uniform Zn deposition on the beneficial (002) plane and inhibiting side reactions and dendrite growth. Consequently, the Zn|Zn cells show a long-term cycling stability of over 1500 cycles at 0.5 mA cm-2. Moreover, the Ta-Na additive improves the performance of Zn||MnO2 full cells, evidenced by a cycling life of 1000 cycles at 1 A g-1 under practical conditions with a limited Zn anode (negative/positive capacity ratio of 10/1) and controlled electrolyte (electrolyte/capacity ratio of 20 μL mAh-1).

Understanding H2 Evolution Electrochemistry to Minimize Solvated Water Impact on Zinc-Anode Performance

H₂ evolution is the reason for poor reversibility and limited cycle stability with Zn-metal anodes, and impedes practical application in aqueous zinc-ion batteries (AZIBs). Here, using a combined gas chromatography experiment and computation, it is demonstrated that H₂ evolution primarily originates from solvated water, rather than free water without interaction with Zn²⁺ . Using linear sweep voltammetry (LSV) in salt electrolytes, H₂ evolution is evidenced to occur at a more negative potential than zinc reduction because of the high overpotential against H₂ evolution on Zn metal. The hypothesis is tested and, using a glycine additive to reduce solvated water, it is confirmed that H₂ evolution and "parasitic" side reactions are suppressed on the Zn anode. This electrolyte additive is evidenced to suppress H₂ evolution, reduce corrosion, and give a uniform Zn deposition in Zn|Zn and Zn|Cu cells. It is demonstrated that Zn|PANI (highly conductive polyaniline) full cells exhibit boosted electrochemical performance in 1 M ZnSO₄ -3 M glycine electrolyte. It is concluded that this new understanding of electrochemistry of H₂ evolution can be used for design of relatively low-cost and safe AZIBs for practical large-scale energy storage.

Long-Life Aqueous Zinc-Ion Batteries of Organic Iminodianthraquinone/rGO Cathode Assisted by Zn2+ Binding with Adjacent Molecules

Organic compounds have been extensively used as zinc-ion battery (ZIB) cathodes due to their high capacities and outstanding properties. Nevertheless, poor electrical conductivity limits their developments. RGO (reduced graphene oxide) can well interact with organic compounds through π-π stacking for furnishing capacious ion diffusion paths and active sites to enhance conductivity and capacity. Herein, a 1,1'-iminodianthraquinone (IDAQ)/rGO composite is utilized as cathode of ZIBs, demonstrating ultrahigh stability with 96% capacity retention after 5000 cycles. Zn2+ and H+ synergetic mechanism in IDAQ/rGO has been deeply discussed by ex situ analysis and theoretical calculation. Consequently, the structure of IDAQ2(H+)6(Zn2+) is the most probable product after discharging progress. Prospectively, the IDAQ/rGO material with excellent stability and good performance would provide new insights into designing advanced ZIBs.

A Synergistic Strategy of Organic Molecules Introduced a High Zn2+ Flux Solid Electrolyte Interphase for Stable Aqueous Zinc-Ion Batteries

Aqueous rechargeable zinc-ion batteries (ARZIBs) are considered as attractive candidates for the next generation of high-safety and low-cost energy storage in large-scale power grids. However, challenges such as the dendrites and the corrosion on the zinc (Zn) surface result in short battery life and low reversibility of Zn plating/stripping. In this work, a method of preconditioning of a zinc anode in hybrid electrolytes (based on poly(ethylene glycol)-200 and H₂O) to form a solid electrolyte interphase (SEI) that prevents anode corrosion and dendrites is proposed. Though surface composition analysis and density functional theory calculation, this SEI has dense organic and inorganic components due to the induction of organic molecules and anions and has rapid kinetic and high-throughput properties for the transport of zinc ions. As a result, the SEI-modified Zn anode can maintain a low-voltage hysteresis stable cycle for more than 1600 h in aqueous electrolyte. The anode also exhibits impressive reversibility with a high Coulomobic efficiency of 99.23% over 1300 cycles. Furthermore, the ARZIB encapsulated by this anode and Mn-doped V₆O₁₃ cathode enables an outstanding electrochemical stability (181.8 mAh g^-1 after 800 cycles at room temperature, 102.2 mAh g^-1 after 1000 cycles at -15 °C). This work provides an intriguing idea for the stability maintenance of the anode for ARZIBs or other metal-ion batteries.

Recent Progress on Phosphate Cathode Materials for Aqueous Zinc-Ion Batteries

Rechargeable zinc-ion batteries (ZIBs) are attractive for large-scale energy storage due to their superiority in resources, safety, and environmental friendliness. However, the lack of suitable ZIBs cathode materials limits their practical applications. In consideration of the excellent electrochemical performance of phosphate materials in monovalent ion (Li⁺ , Na⁺ ) batteries, they were also employed as ZIBs cathode materials recently and performed well with high potential. But they also suffer from low capacity and poor conductivity, and the energy storage mechanism is not clear yet. This Review provides a state-of-the art overview on the developments of phosphate cathode materials in ZIBs, including NASICON-type phosphates, fluorophosphates, olivine-structured, layered-structured, and novel-structured phosphate materials mainly. This study presents the reaction mechanism and electrochemical performance of phosphate cathode materials in aqueous ZIBs, and future research directions are discussed, which are intended to provide guidance for exploring high-potential cathode materials for ZIBs.

Revealing the Two-Dimensional Surface Diffusion Mechanism for Zinc Dendrite Formation on Zinc Anode

Aqueous zinc-ion battery is regarded as one of the promising devices for large-scale energy storage systems owing to its high safety, cost-effectiveness, and competitive electrochemical properties. However, the dendrite growth on zinc metal anodes dramatically hinders its further practical applications, and the internal mechanism of dendrite evolution is still unclear. The introduction of a protective layer on the anode interface is an effective method to avoid zinc dendrite growth. Herein, a two-dimensional (2D) atomic surface diffusion mechanism is proposed to reveal the evolution of zinc deposition from tiny protrusion to dendrite under uneven electric and ionic fields. Further, the conductive copper nitride (CN) protective layer is constructed on the zinc metal anode by a facile and scalable magnetron sputtering approach. Their protective layer possesses a high zinc affinity and high diffusion barrier for zinc atom migration, leading to spacious nucleation, and uniform zinc deposition, thus significantly boosting the electrochemical stability. For the first time, the role of the restricted 2D atomic surface diffusion mechanism in inhibiting the formation of zinc tiny protrusion that induces uneven electric and ionic fields is revealed. This work can provide a novel insight for future research on dendrite-free zinc metal anodes by interfacial modification.

Regulation and Stabilization of the Zinc Metal Anode Interface by Electroless Plating of a Multifunctionalized Polydopamine Layer

A novel electroless plating technique is utilized by coating a polydopamine layer on zinc foil (Zn@PDA) to regulate the deposition and growth of zinc dendrites, as well as suppress the occurrence of hydrogen evolution and passivation products for aqueous zinc-ion batteries. Polydopamine (PDA) has a strong adsorption ability on Zn foil due to the formation of a bidentate bonding during the electroless plating. Further, it indicates that the abundant hydroxyl groups of PDA react as zinc-philic sites to adsorb Zn²⁺ and further undergo redox by forming carbonyl groups to effectively induce the uniform deposition and growth of zinc dendrites. Meanwhile, the strong coordination of PDA and Zn²⁺ will weaken the solvated structure between Zn²⁺ and H₂O molecules, resulting in an enhanced ionization energy of H₂O and inhibited hydrogen evolution reaction. Thus, Zn@PDA can maintain stable cycling over 900 h at 0.2 mA cm^-2, and a high coulombic efficiency of average 98.5% at 2 mA cm^-2. Moreover, the validity of Zn@PDA has been verified using the Zn@PDA||self-standing VS₂@stainless steel (VS₂@SS) full battery, which displays an impressive capacity retention of 81.3% after 1000 cycles without sacrificing the rate performance. This work provides a simple, reliable, and harmless method to achieve high-performance aqueous zinc-ion batteries.

Van der Waals Interaction-Driven Self-Assembly of V2O5 Nanoplates and MXene for High-Performing Zinc-Ion Batteries by Suppressing Vanadium Dissolution

Aqueous zinc-ion batteries (AZIBs) are attractive energy storage devices that benefit from improved safety and negligible environmental impact. The V₂O₅-based cathodes are highly promising, but the dissolution of vanadium is one of the major challenges in realizing their stable performance in AZIBs. Herein, we design a Ti₃C₂T_x MXene layer on the surface of V₂O₅ nanoplates (VPMX) through a van der Waals self-assembly approach for suppressing vanadium dissolution during an electrochemical process for greatly boosting the zinc-ion storage performance. Unlike conventional V₂O₅/C composites, we demonstrate that the VPMX hybrids offer three distinguishable features for achieving high-performance AZIBs: (i) the MXene layer on cathode surface maintains structural integrity and suppresses V dissolution; (ii) the heterointerface between V₂O₅ and MXene enables improved host electrochemical kinetics; (iii) reduced electrostatic repulsion exists among host layers owing to the lubricating water molecules in the VPMX cathode, facilitating interfacial Zn²⁺ diffusion. As a result, the as-made VPMX cathode shows a long-term cycling stability over 5000 cycles, surpassing other reported V₂O₅-based materials. Especially, we find that the heterointerface between V₂O₅ and MXene and lubricated water molecules in the host can achieve an enhanced rate capability (243.6 mAh g^-1 at 5.0 A g^-1) for AZIBs.

Structural Regulation of Oxygen Vacancy-Rich K0.5 Mn2 O4 Cathode by Carbon Hybridization for Enhanced Zinc-Ion Energy Storage

High-voltage manganese-based materials are considered as promising cathode materials for aqueous zinc-ion batteries (AZIBs). Herein, oxygen vacancy-rich K_0.5 Mn₂ O₄ sheets were anchored uniformly onto honeycomb-like interconnected carbon nanoflakes (CNF@K_0.5 Mn₂ O₄ ) for AZIB cathode applications. In the composite, the CNFs provided excellent intergranular electron transport capability, while the oxygen vacancies enhanced the electron transport efficiency inside crystals, and the embedded K ions expanded the interlayer spacing and stabilized the layered crystal structure. A reversible specific capacity of 241 mAh g^-1 could be maintained by the composite at 0.5 A g^-1 for 400 cycles. A combination of ex-situ analytical methods and density functional theory calculations was carried out to elucidate the electrochemical mechanism of reversible zinc storage. In addition, flexible quasi-solid-state batteries of Zn//CNF@K_0.5 Mn₂ O₄ were constructed by substituting the traditional aqueous electrolyte for a quasi-solid-state gel electrolyte, which worked efficiently and exhibited high bending durability.

Unlocking Layered Double Hydroxide as a High-Performance Cathode Material for Aqueous Zinc-Ion Batteries

Advanced cathode materials play an important role in promoting aqueous battery technology for safe energy storage. Transition metal double hydroxides are usually elusive as a stable cathode for aqueous zinc-ion batteries (AZIBs) due to their unstable crystal structure, sluggish ion transportation, and insufficient active sites for zinc-ion storage. Here, a trinary layered double hydroxide (LDH) with hydrogen vacancies (Ni₃ Mn_0.7 Fe_0.3 -LDH) is reported as a new cathode material for AZIBs. A reversible high capacity up to 328 mAh g^-1 can be obtained and cycle stably over 500 cycles with a capacity retention of 85%. Experimental and theoretical studies reveal that the hydrogen vacancies in LDH can expose lattice oxygen atoms as active sites for zinc-ion storage and accelerate ion diffusion by reducing the electrostatic interactions between zinc ions and the host structure. In addition, the synergy of the trinary transitional metal cations can suppress the Jahn-Teller distortion of manganese (III) oxide octahedron and enable long cycle stability. This work provides not only a series of high-performance cathode materials for AZIBs but also a novel materials design strategy that can be extended to other multi-valence metal-ion batteries.

Novel Organic Cathode with Conjugated N-Heteroaromatic Structures for High-Performance Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are being considered new choices of batteries not only because of their inherent safety but also because of their low price advantage. Nevertheless, it is still an important task to develop organic cathode materials with green sustainability and high performance. Hexaazatriphenylene (HAT)-based organic materials have shown great potential for use in AZIBs. Herein, 5,6,11,12,17,18-hexaazatrinaphthylene-2,8,14-tricarboxylic acid (HATTA) is designed and prepared as the AZIB cathode. Benefiting from the conjugative effect of -COOH, extended π-conjugated structure, and abundant active sites, the HATTA electrode exhibits a high capacity (225.8 mA h g^-1 at 0.05 A g^-1), an outstanding rate performance (136.1 mA h g^-1 at 25 A g^-1), and a long-term cycling lifespan (84.07% of the initial capacity after 10,000 cycles at 25 A g^-1). Meanwhile, the characterization results of ex situ spectroscopic tests prove that the unsaturated bond (C═N) is the redox-active moiety of HATTA. In addition, the flexible Zn//HATTA battery also exhibits impressive long-term cycling stability and good flexibility, showing its promising application in wearable electronics. This work provides a strategy with rational designing for constructing high-performance AZIBs with organics.

Zn3V4(PO4)6: A New Rocking-Chair-Type Cathode Material with High Specific Capacity Derived from Zn2+/H+ Cointercalation for Aqueous Zn-Ion Batteries

Phosphate cathode materials with a stable and open framework structure are expected to be one of the favorable cathode materials for aqueous zinc-ion batteries (AZIBs). However, the slow migration rate of Zn²⁺ and complex mechanism in aqueous electrolyte are serious problems that limit their application at the present. Here, a new rocking-chair-type cathode material Zn₃V₄(PO₄)₆@C (ZVP@C) for AZIBs is synthesized for the first time and evaluated using a composite carbon coating to improve the electronic conductivity. Benefiting from the two-electron reaction of vanadium and the cointercalation of Zn²⁺/H⁺, ZVP@C/30%BP delivers a specific capacity as high as 120 mAh·g^-1 at 0.04 A·g^-1. A good capacity retention of 80% after 400 cycles at 1 A·g^-1 is also obtained, which is attributed to the stable crystal structure and the cointercalation reaction of Zn²⁺/H⁺. The reaction mechanism is investigated by in situ X-ray diffraction (XRD), ex situ XRD, ex situ X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDS). This work not only provides a new phosphate cathode material for AZIBs but also gives a new strategy for improving the specific capacity of phosphate cathode material.

Insight on Cathodes Chemistry for Aqueous Zinc-Ion Batteries: From Reaction Mechanisms, Structural Engineering, and Modification Strategies

By virtue of low cost, eco-friendliness, competitive gravimetric energy density, and intrinsic safety, more and more attention has increasingly focused on aqueous zinc ion batteries (AZIBs) as a promising alternative for scalable energy storage. However, plagued by a complex interfacial process, sluggish dynamics, lability of electrodes and electrolytes, insufficient energy density, and poor cycle life heavily restrict practical applications of AZIBs, indicating that profound understandings on cathode storage chemistry are necessarily needed. Hence, this paper comprehensively summarizes recent advance in cathodes with critical insight on the energy storage mechanism. Furthermore, the issues and challenges for high-performance cathodes are meticulously explored, presenting inspiring structural engineering and modification strategies. Finally, rational evaluations on representative cathodes are rendered, suggesting the potential development direction of AZIBs.

Achieving Highly Reversible Zinc Anodes via N, N-Dimethylacetamide Enabled Zn-Ion Solvation Regulation

Although aqueous zinc-ion batteries (ZIBs) are promising for scalable energy storage application, the actual performance of ZIBs is hampered by the irreversibility. Optimization of electrolyte composition is a relatively practical and facile way to improve coulombic efficiency (CE) and Zn plating/stripping reversibility of ZIBs. N,N-Dimethylacetamide (DMA) has a higher Gutmann donor number (DN) than that of H₂ O, abundant polar groups, and economic price. Herein, a mixture electrolyte containing 10 vol% DMA and ZnSO₄ , which has an enhanced Zn reversibility almost fourfold higher than that of pure ZnSO₄ electrolyte, is demonstrated. The density functional theory (DFT) calculation and spectroscopic analysis reveal DMA has the ability to reconstruct the solvation structure of Zn²⁺ and capture free water molecules via forming Hbonds. The inhibited dendrite growth on Zn anode is further clarified by an in situ characterization. This work provides a feasible way for the development of long-lifespan ZIBs.

Interface Engineering to Improve the Rate Performance and Stability of the Mn-Cathode Electrode for Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs), especially the aqueous zinc-manganese batteries, have received considerable attention due to their low cost, safety, and environmental benignity. However, manganese oxide cathode materials usually suffer from unsatisfactory cycling stability. In this study, we report an interface engineering strategy to improve the performance of the Mn-based cathode electrode for ZIBs. Both the results of experiments and density functional theory confirmed that SnO₂ can act as a "glue" to strengthen the interfacial interaction between the conductive graphene substrate and MnOOH, which plays a vital role during the charging/discharging process of manganese oxide. By this interface engineering strategy, the cycling stability of the in situ deposited Mn-based electrode was significantly improved, and a specific capacity of 271 mA h g^-1 can be retained even after 1500 cycles. This study may provide a thought or establish a framework for the rational design of high-performance cathode materials for ZIBs via interface engineering.

Construction of Bio-inspired Film with Engineered Hydrophobicity to Boost Interfacial Reaction Kinetics of Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries typically suffer from sluggish interfacial reaction kinetics and drastic cathode dissolution owing to the desolvation process of hydrated Zn²⁺ and continual adsorption/desorption behavior of water molecules, respectively. To address these obstacles, a bio-inspired approach, which exploits the moderate metabolic energy of cell systems and the amphiphilic nature of plasma membranes, is employed to construct a bio-inspired hydrophobic conductive poly(3,4-ethylenedioxythiophene) film decorating α-MnO₂ cathode. Like plasma membranes, the bio-inspired film can "selectively" boost Zn²⁺ migration with a lower energy barrier and maintain the integrity of the entire cathode. Electrochemical reaction kinetics analysis and theoretical calculations reveal that the bio-inspired film can significantly improve the electrical conductivity of the electrode, endow the cathode-electrolyte interface with engineered hydrophobicity, and enhance the desolvation behavior of hydrated Zn²⁺ . This results in an enhanced ion diffusion rate and minimized cathode dissolution, thereby boosting the overall interfacial reaction kinetics and cathode stability. Owing to these intriguing merits, the composite cathode can demonstrate remarkable cycling stability and rate performance in comparison with the pristine MnO₂ cathode. Based on the bio-inspired design philosophy, this work can provide a novel insight for future research on promoting the interfacial reaction kinetics and electrode stability for various battery systems.

AmV2O5 with Binary Phases as High-Performance Cathode Materials for Zinc-Ion Batteries: Effect of the Pre-Intercalated Cations A and Reversible Transformation of Coordination Polyhedra

In this work, five vanadium oxide materials with a series of pre-intercalated cations A (A_mV₂O₅), including Zn²⁺, Mg²⁺, NH₄⁺, Li⁺, and Ag⁺, have been successfully prepared by a two-step method. All of them possess binary monoclinic and orthorhombic V₂O₅ phases with an open layered structure that allows the ionic storage and diffusion of hydrated cations. The interlayer space for the monoclinic V₂O₅ phase is strongly dependent on the radii of hydrated cations A, while the one for the orthorhombic V₂O₅ phase remains the same regardless of the radii of cations A. Among them, A_mV₂O₅ with pre-intercalated Zn²⁺ (ZVO) has the best storage ability of Zn²⁺ with a reversible capacity close to 400 mAh g^-1, and A_mV₂O₅ with pre-intercalated Ag⁺ shows the highest rate capacity with a nearly 40% capacity retention at a current of 20 A g^-1 (≈25 C). Kinetic studies have clearly shown that pseudocapacitive behavior dominates the electrochemical reaction on ZVO. During the Zn²⁺ (de)intercalation reaction, a highly reversible transformation of binary monoclinic or orthorhombic V₂O₅ phases into a single triclinic Zn_xV₂O₅·nH₂O phase is demonstrated on ZVO. Vanadium atoms are identified as the redox centers that undergo the mutual transition among the chemical states of V³⁺, V⁴⁺, and V⁵⁺. They together with oxygen atoms constitute reasonable V-O coordination polyhedra to generate a layered structure with a suitable interlayer space for the insertion or removal of zinc ions. Actually, the intrinsic coordination chemistry changes between VO₅ square pyramids and VO₆ octahedra account for the phase transformation during the Zn²⁺-(de)intercalation reaction.

Enriching Oxygen Vacancy Defects via Ag-O-Mn Bonds for Enhanced Diffusion Kinetics of δ-MnO2 in Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) have received great attention due to their environmental friendliness and high safety. However, cathode materials with slow diffusion dynamics and dissolution in aqueous electrolytes hindered their further application. To address these issues, in this work, a MnO₂-2 cathode doped with 1.12 wt % Ag was prepared, and after 1000 cycles of charge/discharge at 1 A·g^-1, the capacity remained at 114 mA·h·g^-1 (only 57.7 mA·h·g^-1 for pristine MnO₂). Cyclic voltammetry (CV), the galvanostatic intermittent titration technique (GITT), the electrochemical quartz crystal microbalance (EQCM) method, and density functional theory (DFT) calculation on pristine δ-MnO₂ and MnO₂-2 also proved the superior performance of MnO₂-2. More investigation disclosed that its superior performance is attributed to the improved diffusion kinetics of the cathode brought by the enriched oxygen vacancy defects due to the formation of Ag-O-Mn bonds. Meanwhile, the kinetic mechanism of the Zn/MnO₂-2 cell can be described as a reversible process of the dissolution/precipitation of the ZHS phase and consequent insertion/extraction of Zn²⁺ and H₃O⁺. Herein, the primary issues of ZIB cathode materials have been addressed and solved to a certain extent. More importantly, such a modification in the design of the advanced manganese-based aqueous ZIB cathode materials can provide further insight and facilitate the development and application of this large-scale energy storage system in the near future.

Boosting the Cycling Stability of Aqueous Zinc-Ion Batteries through Nanofibrous Coating of a Bead-like MnOx Cathode

Rechargeable aqueous zinc-ion batteries (AZIBs) are close complements to lithium-ion batteries for next-generation grid-scale applications owing to their high specific capacity, low cost, and intrinsic safety. Nevertheless, the viable cathode materials (especially manganese oxides) of AZIBs suffer from poor conductivity and inferior structural stability upon cycling, thereby impeding their practical applications. Herein, a facile synthetic strategy of bead-like manganese oxide coated with carbon nanofibers (MnO_x-CNFs) based on electrospinning is reported, which can effectively improve the electron/ion diffusion kinetics and provide robust structural stability. These benefits of MnO_x-CNFs are evident in the electrochemical performance metrics, with a long cycling durability (i.e., a capacity retention of 90.6% after 2000 cycles and 71% after 5000 cycles) and an excellent rate capability. Furthermore, the simultaneous insertion of H⁺/Zn²⁺ and the Mn redox process at the surface and in the bulk of MnO_x-CNFs are clarified in detail. Our present study not only provides a simple avenue for synthesizing high-performance Mn-based cathode materials but also offers unique knowledge on understanding the corresponding electrochemical reaction mechanism for AZIBs.