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Practical aqueous Zn-ion batteries are appealing for grid-scale energy storage with intrinsic safety and cost-effectiveness, yet their cycling stability and reversibility are limited by unwanted dendrite growth and water-induced erosions on Zn. Herein, a hydrophilic and Zn 2+ -conductive Ni-Al layered double hydroxide (NiAl-LDH) interphase layer is constructed on the surface of Zn, in which NiAl-LDH enables a more uniformly distributed Zn 2+ concentration and interfacial electric field owing to its large internal Zn 2+ channels and favorable charge redistribution effect. Consequently, the NiAl-LDH-integrated Zn anode achieves low voltage hysteresis and high reversibility of Zn plating/stripping with uniform underneath deposition behaviors. Remarkably, the resultant NiAl-2 LDH@Zn delivers superior cycling durability over 2800 h (∼4 months, 0.5 mA cm -2 ), realizes high reversibility with 99.4% average Coulombic efficiency over 1400 cycles, and confers stable operation of full Zn cells with high V 2 O 5 mass loadings. This work offers a facile and instructive interface design approach for achieving highly stable Zn metal anodes.

Metallic zinc (Zn) is a highly promising anode material for aqueous energy storage systems due to its low redox potential, high theoretical capacity, and low cost. However, rampant dendrites/by-products and torpid Zn 2+ transfer kinetics at electrode/electrolyte interface severely threaten the cycling stability, which deteriorate the electrochemical performance of Zn-ion batteries. Herein, an interfacial engineering strategy to construct alkaline earth fluoride modified metal Zn electrodes with long lifespan and high capacity retention is reported. The compact fluoride layer is revealed to guide uniform Zn stripping/plating and accelerate the transfer/diffusion of Zn 2+ via Maxwell-Wagner polarization. A series of in situ and ex situ spectroscopic studies verified that the fluoride layer can guide uniform Zn stripping/plating. Electrochemical kinetics analyses reveal that positive effect on the removal of Zn 2+ solvation sheath provided by fluoride layer. Meanwhile, this fluoride coating layer can act as a barrier between the Zn electrode and electrolyte, providing a high electrode overpotential toward hydrogen evolution reaction to hold back H 2 evolution. Consequently, the fluoride-modified Zn anode exhibited a capacity retention of 88.2% after 4000 cycles under10 A g -1 . This work opens up a new path to interface engineering for propelling the exploration of advanced rechargeable aqueous Zn-ion batteries., (© 2023 Wiley-VCH GmbH.)

Mn-based materials are among the most promising Zn-ion batteries (ZIBs) cathode materials. However, their inherently poor conductivity and structure collapse hinder their practical application. Herein, Mn 2 O 3 @polypyrrole (PPy) porous spheres are prepared using a hydrothermal method. Coating Mn 2 O 3 with PPy, a conductive polymer, improves its conductivity and inhibits Mn dissolution during electrochemical reactions. The Mn 2 O 3 @PPy cathode exhibits remarkable electrochemical performance and an excellent specific capacity of 287.7 mAh·g−1 after 300 cycles at 0.1 A g−1. The cathode maintains a specific capacity of 73.5 mAh·g−1 after 3000 cycles at 3.0 A g−1 and exhibits an excellent cycle life. In addition, the co-insertion/extraction of H+ and Zn2+ and formation/dissolution mechanism of zinc sulfide hydrate of the Mn 2 O 3 @PPy electrode are evaluated theoretically using several methods. The energy density of the cathode at the power density of 98.7 W kg−1 is 602.8 Wh·kg−1, which is higher than those of numerous previously reported advanced ZIBs cathodes. [Display omitted] • Mn 2 O 3 @PPy porous spheres were prepared by hydrothermal method. • PPy skin can inhibit manganese dissolution and improve conductivity. • Excellent electrochemical stability and energy density in ZIBs have been achieved. • Storage mechanism of zinc ion in Mn 2 O 3 @PPy is investigated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Food-grade sorbitol is used as the electrolyte additive of aqueous Zn-ion batteries. • Sorbitol owns good affinity with both H 2 O molecule and Zn metal electrode. • Sorbitol can effectively suppress dendrites, side reactions, and corrosion issue. • The performances of Zn/MnO 2 battery are significantly improved by sorbitol additive. • Sorbitol additive enables good anti-freezing ability and slow self-discharging rate. The benefits from Zn metal anodes and aqueous electrolytes have endowed aqueous zinc-ion batteries with widespread concerns, whereas they are compromised by Zn dendrites, severe side reactions, and poor tolerance to low-temperature environments. Herein, food-grade sorbitol with abundant hydroxyl groups is used as the electrolyte additive, which can interact strongly with both water molecules and Zn electrode, thus tailoring the solvation sheath of hydrated Zn2+ ions, tuning the surface of Zn electrode, improving the wettability with Zn electrode, broadening the working potential of electrolyte, lowering the desolvation activation energy, enhancing the Zn2+ ion transfer number, preventing the corrosion issue, and enhancing the freezing-tolerance ability. According to a series of electrochemical tests as well as in-situ and ex-situ measurements, the addition of 10 % sorbitol into aqueous electrolyte can effectively inhibit dendritic growth and harmful side reactions at the surface of Zn electrode. Hence, the modified electrolyte enables Zn/MnO 2 battery to own superior cyclability (89.5 % capacity retention after 1000 cycles) and slow self-discharge rate. Even at a low temperature of − 10 ℃, the battery can still offer good electrochemical performances, while that without sorbitol additive can not work normally. This work offers a facile strategy to realize durable anti-freezing aqueous batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • LiODFB is firstly adopted as the electrolyte additive for aqueous zinc-ion batteries. • Trace amount of LiODFB can effectively inhibit Zn dendrites and parasitic reactions. • ODFB− anions can be preferentially adsorbed on Zn surface to inhibit "tip-effect". • The solvation sheath of hydrated Zn2+ ions can be regulated by ODFB− anions. • Electrochemical performances of both full and half cells are significantly improved. Aqueous zinc ion batteries have become one of the most promising energy storage technologies due to intrinsic safety, low price, and high capacity. However, zinc metal anode suffers from severe dendrites and harmful side reactions in aqueous electrolytes, resulting in low coulombic efficiency and short life span. Although organic electrolyte additives have proven to be very effective in improving zinc plating/stripping reversibility, they would not only reduce the ionic conductivity of electrolytes but also bring about toxic and flammable issues. Herein, an inorganic lithium salt, i.e. , lithium difluoro(oxalate)borate (LiODFB), is utilized and the following benefits can be realized. Firstly, ODFB− ions can be preferentially adsorbed at the surface of Zn metal to restraint "tip-effect", resist corrosion, and mitigate side reactions. Secondly, the water activity can be significantly weakened through intense interaction between ODFB− and H 2 O. Thirdly, the desolvation process can be promoted. Hence, the LiODFB additive with a very low concentration of 30 mM endows Zn//Zn cell with long lifespan (1000 h at 4 mAh cm−2) and enables Zn//Cu cell to deliver very high coulombic efficiency (average value of 99.74 % during 1500 cycles). Moreover, the rate and cycling performances of Zn//MnO 2 and Zn//V 2 O 5 full batteries can be dramatically improved by the LiODFB additive. This work extends our knowledge of interfacial engineering for aqueous batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • MWCNTs@a-C@MoS 2 with large interlayer and fast kinetics was synthesized. • Amorphous carbon provides necessary conditions for uniform growth of MoS 2. • The optimized material has excellent cycle stability and rate performance. • The flexible quasi-solid-state AZIB has stable properties at extreme bending states. The sluggish diffusion kinetics of divalent Zn2+ in cathode and the limited availability of active material have seriously hindered the practical application of aqueous zinc ion batteries (AZIBs). Herein, multi-walled carbon nanotubes modified by amorphous carbon layer successfully compounded with MoS 2 (MWCNTs@a-C@MoS 2) are designed as the cathode for AZIBs. Benefiting from the large number of oxygenous groups on the loose surface of amorphous carbon, MoS 2 can uniformly nucleate and grow on the MWCNTs, thus avoiding the agglomeration of MoS 2 and improving the utilization of active materials. Therefore, this nanocomposite exhibits long-term cycling stability (78% capacity retention after 1000 cycles at 5 A g-1) and glorious high-rate capability (110 mAh g-1 at 12 A g-1). The electrochemical reaction kinetics of MWCNTs@a-C@MoS 2 electrode were investigated by galvanostatic intermittent titration (GITT), cyclic voltammetry (CV) measurements and molecular dynamics (MD) simulations, indicating its desirable pseudocapacitive behaviors and low Zn2+ diffusion energy barrier. By ex-situ characterizations, the Zn-intercalation mechanism of MWCNTs@a-C@MoS 2 was revealed. This electrode also exhibits stable performance in flexible quasi-solid-state AZIBs even under extreme bending conditions, demonstrating its practicality. [ABSTRACT FROM AUTHOR]

In situ fabrication of functionalized graphene quantum dots (F-GQDs) with multiple functional groups on a Zn anode suppresses dendrite formation and mitigates side reactions. The F-GQDs-decorated Zn adopts a non-dendritic morphology during repeated Zn plating/stripping and exhibits a long cycle life of 450 h at ultrahigh current density (10 mA cm−2) and areal capacity (5 mAh cm−2). [Display omitted] • Graphene quantum dots are functionalized with multiple functional groups (F-GQDs). • F-GQDs are preferentially decorated on Zn anodes due to the high electronegativity. • F-GQDs can serve as nucleation sites, achieving nanoscale-regulated Zn deposition. • F-GQDs-decorated Zn anode can survive for greater than 450 h at 10 mA cm−2 and 5 mAh cm−2. Rechargeable aqueous Zn-ion batteries have a promising application potential and represent competitive candidates in the field of large-scale energy storage. However, Zn metal is prone to uncontrolled dendrite formation, hydrogen evolution, and corrosion, all of which limit the reversibility of the corresponding batteries. Herein, a novel kind of nanosized and functionalized graphene quantum dots (F-GQDs) is decorated on a Zn anode via in situ electrochemical induction. These quantum dots (∼5 nm) can regulate Zn plating/stripping at the nanoscale. Furthermore, the high electronegativity of polar functional groups (–OH, –COOH, –NH 2 , and -SCN) on the GQDs results in strong Zn2+ affinity and the F-GQDs endow the Zn anode with high hydrophilicity, low nucleation energy barrier, and an evenly distributed electrical field. As a result, the F-GQDs-decorated Zn anode achieves superior Zn plating/stripping for greater than 450 h at 10 mA cm−2 and 5 mAh cm−2, with a low voltage hysteresis of 81 mV. Moreover, when coupled with MnO 2 cathodes, the F-GQDs-decorated Zn enables the fabrication of Zn||MnO 2 full batteries with significantly enhanced rate capability and long-term cycling performance (capacity retention of 78.6 % at 1 A/g after 500 cycles). [ABSTRACT FROM AUTHOR]

• Ti, SS, Ni, Al, and Cu foils are systematically compared as the current collector. • Ti and SS foils own good solvent wettability and excellent anti-corrosion ability. • Severe corrosion happens at the surface of Ni, Al, and Cu foils in the electrolytes. • Only Ti and SS current collectors can enable Zn//MnO 2 batteries to work normally. • SS foil behaves better than Ti foil in both Zn//MnO 2 battery and hybrid capacitor. Benefiting from the advantages in safety, reliability, affordability, and energy/power densities, aqueous zinc-ion batteries (AZIBs) with mildly acidic electrolytes have triggered tremendous research interest. However, Ti foil, as the most widely used current collector for cathodes of AZIBs, is rather expensive. In this work, stainless steel (SS) foil, with a much lower price, is proposed to be a more appropriate current collector than Ti, Ni, Al, and Cu foils. Among them, Ti and SS foils are found to own superior wettability with related solvents, excellent anti-corrosion ability, and strong binding with cathode material. In contrast, Al and Cu foils suffer from severe corrosion in aqueous electrolytes even without external potential, and Ni foil is electrochemically unstable in aqueous electrolytes. Further studies show that only Ti and SS current collectors can enable Zn//MnO 2 battery to work normally. And SS foil behaves slightly better than Ti foil in both Zn//MnO 2 battery and hybrid supercapacitor in terms of specific capacity, rate capability, and cyclability. This work provides guidance for the selection of current collectors for AZIBs and related energy storage devices. [Display omitted] [ABSTRACT FROM AUTHOR]

• A strategy of interlayer and defect engineering is developed for aqueous ZIBs. • The Ca ions and V vacancies synergistically enhance the Zn-ion storage capability. • The structural stability is enhanced over long-term cycling because of Ca ions. • An outstanding electrochemical performance is achieved over 3000 cycles. Layered hydrated vanadium oxides are considered as promising cathode materials for aqueous Zn-ion batteries because of their open layered frameworks and multiple valence states of vanadium. However, they usually exhibit poor electrochemical performance due to the instability of layered frameworks. Herein, Ca-intercalated hydrated vanadium oxide (CaVO) nanobelts have been synthesized by a simple hydrothermal method, accompanied with the formation of cationic V vacancies. The intercalated Ca ions and induced V vacancies can not only synergistically enhance the Zn-ion storage capability by offering numerous active sites, but also effectively stabilize the crystal structure over long-term cycling because of the pinning effect of Ca ions, leading to the enhanced electrochemical performance of hydrated vanadium oxide. Consequently, the CaVO nanobelts deliver a high reversible capacity of 310 mAh g−1 at a current rate of 0.5 A g−1, a superior rate performance of 88 mAh g−1 at 15 A g−1, and an impressive cycling stability with a capacity retention of 91.7% at 10 A g−1 over 3000 cycles. Our present study demonstrates that the synergistic interlayer and defect engineering is a promising strategy to construct advanced layered cathode materials for practical Zn-ion batteries. [ABSTRACT FROM AUTHOR]

Rechargeable aqueous Zn-ion batteries (AZIB) are a promising type of energy storage device but suffer from the growth of uncontrollable Zn dendrites, which result in the shortcut of the battery. Herein, inspired by the regulated nucleation and growth of inorganic minerals from porous organic matrix within the biomineralization process, dopamine derived N-doped carbon spheres with abundant gaps and voids are assembled onto the Zn metal anode (Zn@C) as an artificial solid electrolyte interphase (SEI) layer to modulate the nucleation and growth of a smooth Zn layer without dendrites and suppress the corrosion and hydrogen evolution side reactions. When assembled into Zn-ion batteries, the bioinspired electrode presents comprehensive enhancements in terms of capacity, rate performance, and stability. This unique design of electrode allows long-term stable cycling up to 2100 h at 5 mA cm−2 for a symmetric battery and gives rise to the performance of 315 mAh g−1 at 0.5 A g−2 and 95% retention of its original capacity after 1000 cycles for the Zn@C//V 2 O 5 pouch cell, which outperform most of reported Zn electrodes. The flexible pouch cells displace significant durability towards folding, bending, and piercing, demonstrating its capability for practical applications in wearable devices. [Display omitted] • An artificial SEI layer by learning from the natural biomineralization process is constructed. • The bioinspired SEI layer homogenizes the nucleation for uniform and dendrite-free Zn plating and suppresses the side reactions. • The bioinspired electrode exhibits comprehensive enhancements in capacity, rate performance, and stability. • The pouch cell delivers a capacity of 315 mAh g−1 at 0.5 A g−2 and 95% retaining after 1000 cycles. [ABSTRACT FROM AUTHOR]

Zinc metal is emerging as the promising anode for aqueous Zn-ion batteries. However, corrosion and undesirable Zn dendrite growth limit their practical application in the large-scale energy storage area. Herein, a mountain-valley micro/nanostructure is successfully fabricated on the surface of the Zn anode via a femtosecond-laser filament texturing (FsLFT) technique. Beneficial from the large surface area and spontaneously generated ZnO coating layer, the FsLFT-Zn electrode demonstrates a slow corrosion rate with a current density of 0.62 mA cm -2 and a stable cycle life over 3000 h under 1 mA cm -2 , superior to the original Zn anode. Simulation of the electric fields reveals that the enlarged surface area is responsible for the outstanding performance of the FsLFT-Zn electrode. This study not only proposes a novel strategy to suppress dendrite growth toward highly stable AZIBs but also opens a new avenue to solve similar issues in other metal batteries.

Aqueous Zn-ion batteries (ZIBs) are considered as a potential large-scale renewable energy storage system. Herein, Cu ion implantation is used to improve the electrochemical performance of δ -MnO 2 , resulting in a mixed layer-tunnel material δ -MnO 2 (Cu@ δ -MnO 2) with high capacity, excellent cycle performance, and rate performance as cathode for aqueous ZIBs. The as-obtained Cu@ δ -MnO 2 cathode shows a high specific capacity of 470 mAh g−1 at 0.1 A g−1 and maintains a higher specific capacity during long-term cycles of up to 300 times. Meanwhile, the first-principles theoretical simulations suggest the easier migration of Zn2+ and more Zn2+ adsorption on Cu@ δ -MnO 2 cathode. The theoretical and experimental results show that Cu ion implantation may be an effective strategy to improve the device performance of the Mn-based layer-tunnel hybrid cathode. • Cu ion implanted δ -MnO 2 shows a high capacity and excellent cycle performance as the cathode of aqueous ZIBs. • Cu ion implantation reduces the Zn2+ migration barrier in δ -MnO 2. • Cu ion implantation enhances the Zn2+ adsorption to δ -MnO 2 cathode. [ABSTRACT FROM AUTHOR]

Aqueous Zn-ion batteries hold practical promise for large-scale energy storage because of the safety and affordability of aqueous-based electrolytes; in addition, the manufacturing process is significantly simplified by direct employment of Zn metal as an anode. However, hydrogen evolution due to near-surface water dissociation has hindered large-scale applications of them. Here, we report the suppression of the hydrogen evolution reaction via a CuN 3 -coordinated graphitic carbonitride (CuN 3 -C 3 N 4 ) anticatalytic interface to achieve highly efficient aqueous Zn-ion batteries. Based on in situ gas chromatography and in situ synchrotron-based X-ray diffraction spectroscopy, we demonstrated that the hydrogen evolution reaction triggers the Zn 4 SO 4 (OH) 6 · x H 2 O formation. A combination of in situ infrared spectroscopy and density functional theory simulations has proved to stabilize near-surface H 3 O + species and regulate adsorption of H* intermediates by an anticatalytic interface for hydrogen evolution reaction suppression. Consequently, the anticatalytic interface greatly improves the Coulombic efficiency of Zn plating/stripping to ∼99.7% for 5500 cycles and the cycling reversibility to over 1300 h at 1 mA cm -2 and 1 mAh cm -2 . With an anticatalytic interface, the full cell shows an excellent Coulombic efficiency of 98.3% over 400 cycles at 1C. These findings provide strategic insight for targeted designing of highly efficient aqueous Zn-ion batteries.

Understanding zinc (Zn) deposition behavior and improving Zn stripping and plating reversibility are significant in developing practical aqueous Zn ion batteries (AZIBs). Zn metal is abundant, cost-effective, and intrinsically safe compared with Li. However, their similar inhomogeneous growth regime harms their practicality. This work reports a facile, easily scalable, but effective method to develop a textured Zn with unidirectional scratches on the surface that electrochemically achieves a high accumulated areal capacity of 5530 mAh cm -2 with homogenized Zn deposition. In symmetric cells, textured Zn presents a stable cycling performance of 1100 hours (vs 250 h of bare Zn) at 0.5 mA cm -2 for 0.5 mAh cm -2 and lower nucleation and plating overpotentials of 120.5 and 41.8 mV. In situ optical microscopy and COMSOL simulation disclose that the textured surface topography can 1) homogenize the electron field distribution on the Zn surface and regulate Zn nucleation and growth, and 2) provides physical space to accommodate Zn deposits, prevent the detachment of "dead" Zn, and improve the structural sufficiency of Zn anode. Moreover, differential electrochemical mass spectrometry analysis find that the textured Zn with regulated interfacial electron activity also presents a higher resistance toward hydrogen evolution and other parasitic reactions., (© 2022 Wiley-VCH GmbH.)

Secondary aqueous zinc-ion batteries (ZIBs) are considered as one of the promising energy storage devices, but their widespread application is limited by the Zn dendrite issues. In this work, we propose a rational design of surface protective coatings to solve this problem. Specifically, a silver (Ag) nanoparticle embedded amorphous AlN matrix (AlN/Ag) protective layer is developed. The former would alloy in situ with Zn to form AgZn 3 alloy sites, which subsequently induce the Zn deposition with preferred (002) facets. The latter can effectively alleviate the structural expansion during repeated Zn plating/stripping. Consequently, the delicately designed AlN/Ag@Zn anode delivers an enhanced stability with a long lifespan of more than 2600 h at 1 mA cm -2 and 1 mAh cm -2 . Moreover, the AlN/Ag@Zn||Mn 1.4 V 10 O 24 · n H 2 O full batteries can be operated for over 8000 cycles under 5 A g -1 . Our work not only suggests a promising Zn anode protective coating but also provides a general strategy for the rational design of surface protective layers for metal anodes.

Aqueous Zn-ion batteries are well regarded among a next-generation energy-storage technology due to their low cost and high safety. However, the unstable stripping/plating process leading to severe dendrite growth under high current density and low temperature impede their practical application. Herein, it is demonstrated that the addition of 2-propanol can regulate the outer solvation shell structure of Zn 2+ by replacing water molecules to establish a "eutectic solvation shell", which provides strong affinity with the Zn (101) crystalline plane and fast desolvation kinetics during the plating process, rendering homogeneous Zn deposition without dendrite formation. As a result, the Zn anode exhibits promising cycle stability over 500 h under an elevated current density of 15 mA cm -2 and high depth of discharge of 51.2%. Furthermore, remarkable electrochemical performance is achieved in a 150 mAh Zn|V 2 O 5 pouch cell over 1000 cycles at low temperature of -20 °C. This work not only offers a new strategy to achieve excellent performance of aqueous Zn-ion batteries under harsh conditions, but also reveals electrolyte structure designs that can be applied in related energy storage and conversion fields., (© 2022 Wiley-VCH GmbH.)

Manganese dioxide (MnO 2) is a promising cathode candidate for advanced rechargeable Zn-ion batteries (ZIBs) owing to its low cost, high theoretical capacity and high output voltage. However, the poor stability and low practical capacity has greatly hampered its commercialization. Herein, we demonstrate a crystal form modulation strategy to enhance the capacity and cycling durability of commercial γ-MnO 2 as robust ZIBs cathode material. By introducing new β-MnO 2 crystal form with compact (1 × 1) tunnel structure after simple calcination, the γ- and β- co-existed MnO 2 (denoted as m -MO) shows enhanced electrical conductivity and structural stability. Consequently, the m -MO cathode exhibits an excellent capacity of 273.6 mAh g–1 at 0.25 A g–1 with good cycle stability, much higher than the pristine γ-MnO 2 cathode (156.7 mAh g–1). Furthermore, an aqueous ZIBs based on m -MO cathode delivers a large peak energy density of 349.1 W h kg–1 at 0.322 kW kg–1 and power density of 4.77 kW kg–1 at 123.01 W h kg–1. This work presents an effective crystal form modulation strategy to construct high-performance ZIBs cathodes based on commercial MnO 2 , which is highly potential for further commercial applications. [Display omitted] • A new kind of γ- and β- co-existed MnO 2 (m -MO) is developed from commercial γ-MnO 2 via crystal form modulation strategy. • The introduction of β-MnO 2 enables m -MO electrode with enhanced capacity and reaction kinetics. • An aqueous rechargeable Zn// m -MO battery with high capacity (273.6 mAh g–1 at 0.25 A g–1) is constructed. [ABSTRACT FROM AUTHOR]

Due to the low redox potential and high volumetric capacity, Zn metal anode is regarded as an ideal anode material for aqueous Zn-ion batteries (AZBs). However, the critical issues of uncontrolled dendrite propagation and side reactions with Zn anodes have hindered their practical applications. Herein, a thin and mesoporous polypyrrole (PPy) paper is proposed as an advanced zincophilic interlayer to tackle these problems. We show that the high surface area of the PPy interlayer promises enhanced reaction kinetics, and the excellent affinity to Zn2+ and uniform pore size distribution render homogeneous Zn2+ flux. Moreover, a compact PPy paper interlayer with high surface flatness can be readily made by mechanical compression, which enables much more intimate contact with the Zn anode at the nanoscale level, facilitating enhanced anti-corrosion property and dendrite-free deposition with nearly full surface coverage during repeated depositing/stripping. Consequently, the modulation of surface flatness engineered PPy paper interlayer enables dendrite-free Zn anode with an outstanding cycling performance at simultaneous high current densities and areal capacities (930 h at 5 mA cm−2 for 5 mAh cm−2). The feasibility of the PPy paper interlayer is verified in PANI/V 2 O 5 -based AZBs and activated carbon-based Zn-ion capacitors. Our work provides a facile and sustainable strategy and new insight into constructing efficient interface layers for practical AZBs by surface geometry engineering. [Display omitted] • A thin, flexible, and lightweight PPy paper acts as an advanced zincophilic interface layer. • The mesoporous PPy interlayer with high surface area renders enhanced reaction kinetics and uniform Zn2+ flux. • Surface flatness engineered PPy paper enables more intimate contact with the Zn anode at the nanoscale level. • Achieved cycling performance at simultaneous high current density and areal capacity (930 h at 5 mA cm−2/5 mAh cm−2). [ABSTRACT FROM AUTHOR]

The burgeoning Li-ion battery is regarded as a powerful energy storage system by virtue of its high energy density. However, inescapable issues concerning safety and cost aspects retard its prospect in certain application scenarios. Accordingly, strenuous efforts have been devoted to the development of the emerging aqueous Zn-ion battery (AZIB) as an alternative to inflammable organic batteries. In particular, the instability from the anode side severely impedes the commercialization of AZIB. Constructing an artificial interphase layer (AIL) has been widely employed as an effective strategy to stabilize the Zn anode. This review specializes in the state-of-the-art of AIL design for Zn anode protection, encompassing the preparation methods, mechanism investigations, and device performances based on the classification of functional materials. To begin with, the origins of Zn instability are interpreted from the perspective of electrical field, mass transfer, and nucleation process, followed by a comprehensive summary with respect to functions of AIL and its designing criteria. In the end, current challenges and future outlooks based upon theoretical and experimental considerations are included., (© 2022 Wiley-VCH GmbH.)

Aqueous Zn-ion batteries (AZIBs), being safe, inexpensive, and pollution-free, are a promising candidate for future large-scale sustainable energy storage. However, in a conventional AZIBs setup, the Zn metal anode suffers oxidative corrosion, side reactions with electrolytes, disordered dendrite growth during operation, and consequently low efficiency and short lifespan. In this work, we discover that purging CO 2 gas into the electrolyte could address these issues by eliminating dissolved O 2 , inhibiting side reactions by buffering the local pH change, and preventing dendrite growth by inducing the in situ formation of a ZnCO 3 solid electrolyte interphase layer. Moreover, the CO 2 -purged electrolyte could enable a highly reversible plating/stripping behavior with a high Coulombic efficiency of 99.97% and an ultralong lifespan of 32,000 cycles (1600 h) even under an ultrahigh current density of 40 mA cm -2 . Consequently, the CO 2 -purged symmetrical cells deliver long cycling stability at a high depth of discharge of 57%, while the CO 2 -purged Zn/V 2 O 5 full cells exhibit outstanding capacity retention of 66% after 1000 cycles at a high current density of 5 A g -1 . Our strategy, the simple introduction of CO 2 gas into the electrolyte, could effectively mediate the zinc anode's critical issues and provide a scalable and cost-effective pathway for the commercialization of AZIBs.

[Display omitted] • Li 2 Mn 3 O 7 is firstly reported as the new cathode for aqueous Zn-ion battery. • Complex storage mechanism is discussed by In-situ XRD and ex-situ XPS. • Excellent performance is related to reversible Li+/H+ co-extraction/insertion. • Dynamic mechanism of electrode and reason of capacity variation were pointed. Aqueous Zn-ion batteries (ZIBs) are expected to be used for practical energy storage and grid-scale applications because of their low-cost, high-safety and environmental friendliness. However, it is still a major challenge to achieve a suitable cathode for ZIBs with a high energy density and long cycle life. Herein, we reported a new cathode Li 2 Mn 3 O 7 for aqueous ZIBs and have studied in detail the role of Li+ as electrolyte additives in further improving electrochemical performance. The Li+ in the additive-contained electrolyte itself not only facilitates the reversible extraction/insertion of Li+ in Li 2 Mn 3 O 7 but also effectively reduce the decomposition effect of Li 2 Mn 3 O 7 caused by the charge process through the re-insertion of Li+ in subsequent discharge process and thus realizes the reversible deintercalation/intercalation of H+. Owing to the realization of the reversible Li+ and H+ co-extraction/insertion caused by the use of Li+ additive, the Li 2 Mn 3 O 7 electrode exhibits a high reversible specific capacity of 242 mAh g−1 with nearly 100% coulombic efficiency at 200 mA g−1 current density. In particular, due to the enhanced capacitive contribution, Li 2 Mn 3 O 7 electrode presented an impressive life span at high current density 2 A g−1, and after 1000 cycles, a stable specific capacity greater than 100 mAh g−1 can be maintained, which is significantly better than that of manganese oxide-based cathode materials in ZIBs. Furthermore, by In-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS), we discuss in detail the complex energy storage mechanism of Li 2 Mn 3 O 7 as cathode material for ZIBs with electrolyte containing Li+ additive for the first time. Based on the high specific capacity and big current life span, aqueous ZIBs with Li 2 Mn 3 O 7 exbibit a great potential for large scale electrical energy storage. [ABSTRACT FROM AUTHOR]

Freestanding CuV 2 O 6 /reductive acidified carbon nanotube (CVO/RCNTs) composite films with excellent flexibility and conductivity were prepared via a vacuum filtration strategy and made into the aqueous Zn//CVO/RCNTs gel battery, which exhibited stable electrochemical properties under different bending conditions. [Display omitted] • Free-standing CuV 2 O 6 /RCNTs composite films with high flexibility were achieved. • RCNTs provided a 2 µm conductive substrate for the film as a current colletor. • The aqueous Zn//CVO/RCNTs gel battery exhibited stable electrochemical properties. • Great potential as flexible wearable energy storage devices. Rechargeable aqueous zinc-ion batteries (ZIBs) have become a key research object in the field of new generation energy storage devices due to their high safety, low cost and eco-friendliness, and show a promising potential application. In this work, CuV 2 O 6 nanobelts were synthesized by the hydrothermal method and freestanding CuV 2 O 6 /reductive acidified carbon nanotube (CVO/RCNTs) composite film without any binder was synthesized by vacuum filtration. The aqueous Zn//CVO/RCNTs batteries presented a admirable reversible capacity of 353 mAh g−1 at 0.1 A g−1 and the cycling performance with a high reversible capacity of 174.7 mAh g−1 and 61.5% capacity retention after 1400 cycles at 5 A g−1,making rings round the vast majority reported zinc ion batteries.More importantly, the CVO/RCNTs composite films had stable electrochemical properties under different bending degrees after preparation into flexible gel batteries, demonstrating great potential in the field of flexible wearable zinc ion batteries. [ABSTRACT FROM AUTHOR]

The practical application of the Zn-metal anode for aqueous batteries is greatly restricted by catastrophic dendrite growth, intricate hydrogen evolution, and parasitic surface passivation. Herein, a polyanionic hydrogel film is introduced as a protective layer on the Zn anode with the assistance of a silane coupling agent (denoted as Zn-SHn). The hydrogel framework with zincophilic -SO 3 - functional groups uniformizes the zinc ions flux and transport. Furthermore, such a hydrogel layer chemically bonded on the Zn surface possesses an anti-catalysis effect, which effectively suppresses both the hydrogen evolution reaction and formation of Zn dendrites. As a result, stable and reversible Zn stripping/plating at various currents and capacities is achieved. A full cell by pairing the Zn-SHn anode with a NaV 3 O 8 ·1.5 H 2 O cathode shows a capacity of around 176 mAh g -1 with a retention around 67% over 4000 cycles at 10 A g -1 . This polyanionic hydrogel film protection strategy paves a new way for future Zn-anode design and safe aqueous batteries construction., (© 2022 Wiley-VCH GmbH.)

The instability of Zn anode caused by severe dendrite growth and side reactions has restricted the practical applications of aqueous zinc-ion batteries (AZIBs). Herein, an enamel-like layer of nanohydroxyapatite (Ca 5 (PO 4 ) 3 (OH), nano-HAP) is constructed on Zn anode to enhance its stability. Benefiting from the ion exchange between Zn 2+ and Ca 2+ , the adsorption for Zn 2+ in enamel-like nano-HAP (E-nHAP) layer can effectively guide Zn deposition, ensuring homogeneous Zn 2+ flux and even nucleation sites to suppress Zn dendrites. Meanwhile, the low pH of acidic electrolyte can be regulated by slightly soluble nano-HAP, restraining electrolyte corrosion and hydrogen evolution. Moreover, the E-nHAP layer features high mechanical flexibility due to its enamel-like organic-inorganic composite nanostructure. Hence, symmetric cells assembled by E-nHAP@Zn show superior stability of long-term cycling at different current densities (0.1, 0.5, 1, 5, and 10 mA cm -2 ). The E-nHAP@Zn∥E-nHAP@Cu cell exhibits an outstanding cycling life with high Coulombic efficiency of 99.8% over 1000 cycles. Notably, the reversibility of full cell based on CNT/MnO 2 cathode can be effectively enhanced. This work shows the potential of drawing inspiration from biological nanostructure in nature to develop stable metal electrodes.

• Vertically aligned 1 T phase MoS 2 nanosheet array was prepared by a simple method. • Synergistic effect of 1 T phase and unique structure endows outstanding properties. • The cathode shows excellent specific capacity and outstanding cycling stability. • The mechanism was clarified by combining characterizations and DFT calculations. Recently, low-cost and environment-friendly rechargeable aqueous Zn-ion batteries have attracted extensive attention. However, the development of excellent performance cathode is still one of major challenge. Herein, for the first time, we successfully fabricated a free-standing cathode with vertically aligned 1 T phase MoS 2 nanosheet array on carbon cloth and comprehensively investigated its rechargeable aqueous Zn-ion batteries performance. Benefiting from the synergistic effect of vertically aligned 1 T phase MoS 2 nanosheet array and free-standing structure, the free-standing cathode displays a outstanding specific capacity of 198 mA h g−1 at the current density of 100 mA g−1. Impressively, it exhibits distinguished cycling stability, even when cycled at current density of 2000 mA g−1, that the specific capacity retention of 97.2% and 87.8% can be obtained after 1000 and 2000 cycles, respectively. Furthermore, the mechanisms involved were clarfied by combining systematical characterizations and density functional theory calculations. This work will bring new insights for preparing high-performance rechargeable aqueous Zn-ion batteries cathode materials for large-scale energy storage. [ABSTRACT FROM AUTHOR]

• Metal coordinated phthalocyanine improves Zn2+ intercalation reversibility. • The types of metal ligand have affected on Zn2+ adsorption efficiency. • Iron-phthalocyanine maximizes energy capacity, and electrochemical reliability. • Phthalocyanine-ITO-PET electrode is highly efficient Zn ion flexible battery. Aqueous Zn-ion battery has developed as an alternative to overcome the limitations of conventional Li-ion batteries, but its application is insufficient due to low reversibility and electrochemical reliability. In this study, we developed a cathode for aqueous Zn-ion battery with improvement of reversibility and electrochemical reliability utilizing phthalocyanine (PTC) that efficiently transports metal ions and electrons. The intercalation/de-intercalation reaction of Zn2+ ions changes according to the central metal ligand ion of PTC, and iron (II) coordinated PTC exhibited the outstanding energy storage capacity (161.34 mAh/g) and electrochemical reliability (99%, 100 cycles). Based on maximized electrochemical performance and reliability, Zn-ion flexible battery was successfully demonstrated by utilizing air-spray coating. [ABSTRACT FROM AUTHOR]

The lack of suitable cathode materials with a high capacity and good stability is a crucial problem affecting the development of aqueous Zn-ion batteries. Herein, a novel strategy for the modification of V 2 CT x through molten salt thermal treatment is proposed. In the novel route, S heteroatoms were introduced into V 2 CT x through a substitution reaction during the dissolution of Li 2 S in LiCl-KCl molten salts. Then, surface V 2 O 5 was obtained through the in situ electrochemical charging/discharging of the S-doped V 2 CT x (MS-S-V 2 CT x ) cathode. The assembled Zn/MS-S-V 2 CT x battery showed a high reversible discharge capacity of 411.3 mAh g -1 at a current density of 0.5 A g -1 , an 80% capacitance retention after long cycle stability tests at 10 A g -1 for 3000 cycles, and a high energy density of 375.5 Wh kg -1 in 2M ZnSO 4 . Density functional theory calculations demonstrate that the improved electrochemical performance of the cathode can be attributed to the introduced S heteroatoms, which considerably reduced the ion diffusion energy barrier for Zn 2+ ions and improved the stability of V 2 O 5 . This work provides a novel method to produce highly active and stable vanadium-based cathodes for aqueous Zn-ion batteries.

Vanadium-based materials have been extensively studied as promising cathode materials for zinc-ion batteries because of their multiple valences and adjustable ion-diffusion channels. However, the sluggish kinetics of Zn-ion intercalation and less stable layered structure remain bottlenecks that limit their further development. The present work introduces potassium ions to partially substitute ammonium ions in ammonium vanadate, leading to a subtle shrinkage of lattice distance and the increased oxygen vacancies. The resulting potassium ammonium vanadate exhibits a high discharge capacity (464 mAh g -1 at 0.1 A g -1 ) and excellent cycling stability (90% retention over 3000 cycles at 5 A g -1 ). The excellent electrochemical properties and battery performances are attributed to the rich oxygen vacancies. The introduction of K + to partially replace NH 4 + appears to alleviate the irreversible deammoniation to prevent structural collapse during ion insertion/extraction. Density functional theory calculations show that potassium ammonium vanadate has a modulated electron structure and a better zinc-ion diffusion path with a lower migration barrier.

Manganese oxide is a promising cathode material for rechargeable aqueous zinc-ion batteries (ZIBs). However, the low electronic conductivity and unstable structure evolution of manganese materials often result in poor rate performance and rapid capacity decay. Herein, we design N-doped Na 2 Mn 3 O 7 (N-NMO) by combining sodium preintercalation and nitridation treatment strategies to stabilize the crystalline structure and reaction interface. Sodium preintercalation not only enlarges the interlayer distance for fast Zn 2+ ion diffusion but also serves as a robust pillar to stabilize the crystalline structure during cycling. Meanwhile, the nitridation layer on the surface of Na 2 Mn 3 O 7 particles is favorable for enhancing the electronic conductivity and inhibiting the cathode dissolution issue during repeated cycling. Consequently, the as-prepared N-NMO exhibits high reversible capacity (300 mAh g -1 at 0.2 A g -1 ), good rate capability (100 mAh g -1 at 10 A g -1 ), and outstanding long-term cycling stability (high capacity retention of 78.9% after 550 cycles at 2 A g -1 ). Considering the facile and simple synthesizing methods, the synergistic engineering of the interlayer structure and interface is expected to provide new opportunities for the development of high-performance Mn-based cathode materials for aqueous ZIBs.

• Storage mechanisms of aqueous Zn2+ batteries for Mn-based cathode are summarized. • Optimal strategies for Mn-based aqueous Zn2+ batteries are analyzed. • The bottlenecks and relevant ways of Mn-based aqueous Zn2+ batteries are reviewed. Aqueous Zn-ion rechargeable batteries have been regarded as a promising large-scale energy storage system due to their abundant resources, high security, environmental friendliness and acceptable energy density. Various manganese-based compounds with low cost and high theoretical capacity are widely used in aqueous Zn-ion batteries (AZIBs). In addition, AZIBs using manganese-based cathode materials have different energy storage mechanism. In this review, four different zinc ion storage mechanisms of AZIBs with manganese-based cathode materials are analyzed in detail on the basis of previous studies, and various strategies for improving the electrochemical performance of manganese-based positive electrode materials are analyzed, including structural design, synthesis of manganese-based composites, intercalation, defect engineering, interfacial modification and electrolyte optimization. Finally, we discuss the limitations that need to be overcome and perspectives on AZIBs are summarized to provide potential future research directions. [ABSTRACT FROM AUTHOR]

• A facile and scalable strategy is developed to synthesize a new cathode material. • A thin layer of polypyrrole is coated on the surface of MnO 2 /Mn 2 O 3 nanocomposite. • The polypyrrole coating can effectively alleviate the dissolution of Mn2+ ions. • The product shows significantly improved electrochemical performances. • The electrochemical kinetics and stability are considerably enhanced. Rechargeable aqueous zinc-ion batteries based on Mn-based cathode materials are of considerable interest for large-scale energy storage. However, the intrinsic low electronic conductivity and the dissolution issue of Mn-based cathode materials result in slow reaction kinetics and fast capacity fading. Herein, a facile and scalable strategy combining molten salt synthesis and self-initiated polymerization is developed to in-situ generate a thin layer of polypyrrole onto the surface of MnO 2 /Mn 2 O 3 nanocomposite, aiming to resolve the problems mentioned above. The obtained product provides large specific capacity (289.8 mAh g−1 at 0.2 A g−1), remarkable rate capability (199.8 mAh g−1 at 3 A g−1), and excellent cycling stability (96.7% after 1000 cycles at 1 A g−1, compared to the 2nd cycle). The cyclability remains good when Mn2+ ions are not pre-added into the electrolyte. Also, the obtained product exhibits slight electrochemical polarization, low charge transfer impedance after cycling, high capacitive contribution, and large electrolyte ion diffusion coefficient. All these performances and properties are significantly superior to that of MnO 2 /Mn 2 O 3 nanocomposite without polypyrrole coating. This work opens a new path towards long-life and fast-discharging electrode materials. [ABSTRACT FROM AUTHOR]

Ammonium vanadium bronze (NH 4 V 4 O 10) has garnered increasing attention due to its extensive electrochemical applications. The development of NH 4 V 4 O 10 with high conductivity and fast ion diffusion ability remains to be a significant challenge. In this work, we report a facile synthesis of Mo-doped NH 4 V 4 O 10 via a one-step hydrothermal reaction. The morphology evolution process and phase transformation of Mo-doped NH 4 V 4 O 10 are investigated by controlling the Mo concentration. When investigated as an aqueous Zn-ion battery cathode material, the as-optimized Mo-doped NH 4 V 4 O 10 exhibits a high capacity of 335.0 mAh g−1 at a current density of 0.1 A g−1, and it is also able to demonstrate superior capacity retention and better cycle performance than the undoped NH 4 V 4 O 10. The enhanced electrochemical performance is mainly due to the expansion of the (001) interlayer spacing of NH 4 V 4 O 10 caused by the intercalation of Mo into the framework, which provides more space for Zn ion intercalation. Moreover, the doping of Mo decreases the band gap of NH 4 V 4 O 10 , which is verified by the UV–Vis (Ultraviolet-visible spectroscopy) spectrum and DFT (density-functional theory) calculations. The reduced band gap leads to a higher intrinsic carrier concentration, which in turn improves the electrical conductivity and the Zn ion diffusion coefficient of the material. Thus, based on these results, this work may present a new strategy in designing potential cathode for Zn-ion battery. • Mo-doped NH 4 V 4 O 10 was firstly obtained by a facile hydrothermal reaction. • Band gap of NH 4 V 4 O 10 was narrowed after Mo doping, convinced by UV-Vis spectrum and DFT calculations. • Mo entering into the structure of NH 4 V 4 O 10 through insertion of interlayers and substitution of V. • The capacity and cycle performance was enhanced in an optimized Mo doping condition. [ABSTRACT FROM AUTHOR]

Aqueous Zn-storage behaviors of MoS 2 -based cathodes mainly rely on the ion-(de)intercalation at edge sites but are limited by the inactive basal plane. Herein, an in-situ molecular engineering strategy in terms of structure defects manufacturing and O-doping is proposed for MoS 2 (designated as D-MoS 2 -O) to unlock the inert basal plane, expand the interlayer spacing (from 6.2 to 9.6 Å), and produce abundant 1T-phase. The tailored D-MoS 2 -O with excellent hydrophilicity and high conductivity allows the 3D Zn 2+ transport along both the ab plane and c-axis, thus achieving the exceptional high rate capability. Zn 2+ diffusion through the basal plane is verified by DFT computations. As a proof of concept, the wearable quasi-solid-state rechargeable Zn battery employing the D-MoS 2 -O cathode operates stably even under severe bending conditions, showing great application prospects. This work opens a new window for designing high-performance layered cathode materials for aqueous Zn-ion batteries., (© 2021 Wiley-VCH GmbH.)

Aqueous Zn-ion batteries (ZIBs), a new green energy storage system, have enormous development potential among various aqueous batteries due to the superiorities of good environmental friendliness, low production costs, high operational safety, high theoretical capacity, and excellent rate performance. Compared with traditional cathode materials like manganese oxides and vanadium oxides, Prussian blue analogues (PBAs) with a firm 3D framework and large ion channels are more suitable for zinc ions insertion/extraction. Here, environmentally friendly sodium manganese hexacyanoferrate (NaMnHCF) is applied to aqueous ZIBs, and its excellent electrochemical performance is characterized by varieties of analytical techniques. The charge/discharge profiles display a rather flat operating platform with extremely small redox polarization (less than 0.05 V). Under the current density of 50 mA g−1, NaMnHCF can attain an initial charged specific capacity of 55.3 mAh g−1. Meanwhile, it also exhibits a superior electrochemical rate performance. Furthermore, the mechanism of zinc ions insertion/extraction in the NaMnHCF frameworks is revealed through a deep exploration of the relationship between element states, storage kinetics, crystal structure, and electrochemical properties. From a practical standpoint, the environmentally friendly NaMnHCF exhibits favorable rate capability and cycling stability, which makes it be a perfect choice for aqueous ZIBs of the application in the green new energy industry. Unlabelled Image • Zinc ions are successfully inserted into NaMnHCF framework for the first time. • NaMnHCF exhibits favorable cycling and rate capability in aqueous ZIBs. • NaMnHCF display extremely small polarization (< 0.05 V) for zinc ions storage. • Ex-situ techniques unveil the zinc ions storage mechanism in NaMnHCF. [ABSTRACT FROM AUTHOR]

• Organic pillar intercalation and dual-valence regulation were adopted in this work. • Organic PAN/THF can expand the interlayers and support the structure of V 2 O 5 ·3H 2 O. • Mixed V4+/V5+ is good for achieving higher electrochemical reactivity of V 2 O 5 ·3H 2 O. • PAN/THF pre-intercalated V4+-V 2 O 5 ·3H 2 O displays 1000 cycles at 10 A g−1. As cathodes for aqueous Zn-ion batteries, the repetitive insertion/extraction and strong polarization of Zn2+ during cycles will severely wreck the structure of layered vanadium oxides, resulting in rapid capacity recession. Hence, the ingenious strategy of PAN/THF-pillars intercalation and V4+/V5+ dual-valence regulation was designed to fabricate PAN or THF pre-intercalated V4+-V 2 O 5 ·3H 2 O, denoted as P-VO or T-VO. Owing to the interlayer expansion of organic molecules and the electrochemical reactivity enhancement of mixed V4+/V5+ valence, severe structural collapse of cathodes and strong polarization of Zn2+ can be alleviated. Hence, P-VO and T-VO cathodes can exhibit larger interlayer distances of 13.67 and 14.41 Å, more robust construction, faster Zn2+ transmission, and better electrical conductivity. P-VO and T-VO electrodes furnish high zinc storage performance of 251 and 336 mAh g−1 at 500 mA g−1, and persistently maintain considerable reversible capacities of 133 and 100 mAh g−1 after 1000 cycles at a high current density of 10 A g−1. And the capacitive contribution ratios of P-VO and T-VO can reach up to 75% and 86.4%, respectively. Meanwhile, both two cathodes can endure extreme ambient conditions from −15 °C to 45 °C. In addition, the insertion mechanism of Zn2+ was also investigated via in-situ XRD and ex-situ XPS. [ABSTRACT FROM AUTHOR]

Aqueous rechargeable Zn batteries are attractive for emerging generations of large-scale energy storage due to their high safety, low cost, and high energy density. It is regrettable that the poor cycling performance limits its further commercialization due to the troublesome dendrite growth and short-circuiting issue of the traditional planar Zn anode. Herein, in this work, a three-dimensional porous Zn anode (3D ZnP/CF) composed of highly conductive carbon fiber-based network and active zinc powder fillers is designed for long lifespan aqueous Zn batteries. The new 3D ZnP/CF exhibits controlled deposition behavior and scarce short-circuiting benefiting from the fast ionic/electronic transfer and sufficient deposition space, which are enabled by the porous structure and conducting network of the anode. The symmetric cell based on 3D ZnP/CF exhibits small voltage hysteresis of 25.1 mV and extraordinarily long cycling stability of 3000 h, particularly excellent high-rate performance (8 mA cm−2, 8 mA h cm−2, 700 h), which is superior to those of the reported static Zn metal batteries. Furthermore, the assembled full cell with manganese oxide as cathode exhibits superb capacity retention of 93.2% over 7000 cycles. The structural and compositional design provides another effective approach for the commercialization of aqueous rechargeable Zn batteries. Image 1 • 3D ZnP/CF electrodes were prepared through the vacuum filtration process. • It can distribute the current density and induce homogeneous deposition of Zn. • The symmetric cells exhibit a high stability with a small voltage hysteresis. • The full cells show capacity retention of 93.2% over 7000 cycles. [ABSTRACT FROM AUTHOR]

• The few-layered MoS 2 nanosheets with different phase contents were prepared by an efficient controllable phase engineering. • The optimized material shows outstanding specific capacity and excellent long cycling performances. • The mechanisms involved were elucidated by systematical characterizations. • The DFT simulations reveal that the 1T phase MoS 2 has much lower Zn diffusion energy barriers. Recently, aqueous rechargeable Zn-ion batteries have attracted extensive attention, owing to their low-cost, high operational safety and environmental friendliness. However, the aqueous zinc-ion battery is still in a very infant stage, and the main challenge is to develop the ideal cathode due to the sluggish kinetics and low reversibility of divalent zinc ions. Herein, for the first time, we report controllable phase engineered few-layered MoS 2 nanosheet as cathode materials for rechargeable aqueous Zn-ion batteries and systematically study their performance. We found that the obtained MoS 2 with different phase contents showed distinct performance in the rechargeable aqueous zinc-ion battery. In particular, the MoS 2 nanosheets with ~70% 1T phase content displays excellent specific capacity and shows outstanding long-term cyclic stability. The mechanisms involved were clarified by not only comprehensive characterizations, but also the density functional theory (DFT) simulations that reveal the 1T phase MoS 2 has much lower Zn diffusion energy barriers. This study provides new insight into the effect of different phases on the performance of MoS 2 -based electrodes and will improve our understanding of developing better cathodes for the aqueous rechargeable Zn-ion batteries. [ABSTRACT FROM AUTHOR]

Despite their potential as a next-generation alternative to current state-of-the-art lithium (Li)-ion batteries, rechargeable aqueous zinc (Zn)-ion batteries still lag in practical use due to their low energy density, sluggish redox kinetics, and limited cyclability. In sharp contrast to previous studies that have mostly focused on materials development, herein, a new electrode architecture strategy based on a 3D bicontinuous heterofibrous network scaffold (HNS) is presented. The HNS is an intermingled nanofibrous mixture composed of single-walled carbon nanotubes (SWCNTs, for electron-conduction channels) and hydrophilic cellulose nanofibers (CNFs, for electrolyte accessibility). As proof-of-concept for the HNS electrode, manganese dioxide (MnO 2 ) particles, one of the representative Zn-ion cathode active materials, are chosen. The HNS allows uniform dispersion of MnO 2 particles and constructs bicontinuous electron/ion conduction pathways over the entire HNS electrode (containing no metallic foil current collectors), thereby facilitating the redox kinetics (in particular, the intercalation/deintercalation of Zn 2+ ions) of MnO 2 particles. Driven by these advantageous effects, the HNS electrode enables substantial improvements in the rate capability, cyclability (without structural disruption and aggregation of MnO 2 ), and electrode sheet-based energy (91 Wh kg electrode -1 )/power (1848 W kg electrode -1 ) densities, which lie far beyond those achievable with conventional Zn-ion battery technologies., (© 2020 Wiley-VCH GmbH.)

Mn-based cathodes are admittedly the most promising candidate to achieve the practical applications of aqueous zinc-ion batteries because of the high operating voltage and economic benefit. However, the design of Mn-based cathodes still remains challenging because of the vulnerable chemical architecture and strong electrostatic interaction that lead to the inferior reaction kinetics and rapid capacity decay. These intrinsic drawbacks need to be fundamentally addressed by rationally decorating the crystal structure. Herein, an oxygen-defective Mn-based cathode (Oc u -Mn 2 O 3 ) is designed via a doping low-valence Cu-ion strategy. The oxygen defect can modify the internal electric field of the material and enhance the substantial electrostatic stability by compensating for the nonzero dipole moment. With the merits of oxygen deficiency, the Oc u -Mn 2 O 3 electrode exhibits the significant diffusion coefficient in the range from 1 × 10 -6 to 1 × 10 -8 , and good rate performance. In addition, the Oc u -Mn 2 O 3 maintains the highly reversible cyclic stability with the capacity retention of 88% over 600 cycles. The charge storage mechanism is explored as well, illustrating that the oxygen defects can improve the electrochemical active sites of H + insertion, achieving a better charge-storage capacity than Mn 2 O 3 .

Among various energy storage devices, aqueous zinc-ion batteries (ZIBs) have captured great attention due to their high safety and low cost. One of the most promising cathodes of aqueous ZIBs is layered vanadium-based compounds. However, they often suffer from the capacity decaying during cycling. Herein, we prepared KV 3 O 8 ·0.75H 2 O (KVO) and further incorporated it into a single-walled carbon nanotube (SWCNT) network, achieving freestanding KVO/SWCNT composite films. The KVO/SWCNT cathodes exhibit a Zn 2+ /H + insertion/extraction mechanism, resulting in fast kinetics of ion transfer. In addition, the KVO/SWCNT composite films possess a segregated network structure, which offers the fast kinetics of electron transfer and guarantees an intimate contact between KVO and SWCNTs during cycling. As a result, the resultant batteries deliver a high capacity of 379 mAh g -1 , excellent rate capability, and an ultralong cycle life up to 10,000 cycles with a high capacity retention of 91%. In addition, owing to the high conductivity and flexibility of KVO/SWCNT films, flexible soft-packaged ZIBs based on KVO/SWCNT film cathodes were assembled and displayed stable electrochemical performance at different bending states.

Rechargeable aqueous Zn‐based batteries are attractive candidates as energy storage technology, but the uncontrollable Zn dendrites, low stripping/plating coulombic efficiency, and inefficient utilization of Zn metal limit the battery reliability and energy density. Herein, for the first time, a novel presodiated TiS2 (Na0.14TiS2) is proposed and investigated as an intercalated anode for aqueous Zn‐ion batteries, showing a capacity of 140 mAh g−1 with a suitable potential of 0.3 V (vs Zn2+/Zn) at 0.05 A g−1 and superior cyclability of 77% retention over 5000 cycles at 0.5 A g−1. The remarkable performance originates from the buffer phase formation of Na0.14TiS2 after chemically presodiating TiS2, which not only improves the structural reversibility and stability but also enhances the diffusion coefficient and electronic conductivity, and lowers cation migration barrier, as evidenced by a series of experimental and theoretical studies. Moreover, an aqueous "rocking‐chair" Zn‐ion full battery is successfully demonstrated by this Na0.14TiS2 anode and ZnMn2O4 cathode, which delivers a capacity of 105 mAh g−1 (for anode) with an average voltage of 0.95 V at 0.05 A g−1 and preserves 74% retention after 100 cycles at 0.2 A g−1, demonstrating the feasibility of Zn‐ion full batteries for energy storage applications. [ABSTRACT FROM AUTHOR]

Aqueous Zn-ion batteries, which are being proposed as large-scale energy storage solutions because of their unparalleled safety and cost advantage, are composed of a positive host (cathode) material, a metallic zinc anode, and a mildly acidic aqueous electrolyte (pH ≈ 3-7). Typically, the charge storage mechanism is believed to be reversible Zn 2+ (de)intercalation in the cathode host, with the exception of α-MnO 2 , for which multiple vastly different and contradicting mechanisms have been proposed. However, our present study, combining electrochemical, operando X-ray diffraction, electron microscopy in conjunction with energy-dispersive X-ray spectroscopy, and in situ pH evolution analyses on two oxide hosts-tunneled α-MnO 2 and layered V 3 O 7 ·H 2 O vis-à-vis two nonoxide hosts-layered VS 2 and tunneled Zn 3 [Fe(CN) 6 ] 2 , suggests that oxides and nonoxides follow two dissimilar charge storage mechanisms. While the oxides behave as dominant proton intercalation materials, the nonoxides undergo exclusive zinc intercalation. Stabilization of H + on the hydroxyl-terminated oxide surface is revealed to facilitate the proton intercalation by a preliminary molecular dynamics simulation study. Proton intercalation for both oxides leads to the precipitation of layered double hydroxide (LDH)-Zn 4 SO 4 (OH) 6 ·5H 2 O with a ZnSO 4 /H 2 O electrolyte and a triflate anion (CF 3 SO 3 - )-based LDH with a Zn(SO 3 CF 3 ) 2 /H 2 O electrolyte-on the electrode surface. The LDH precipitation buffers the pH of the electrolytes to a mildly acidic value, sustaining the proton intercalation to deliver large specific capacities for the oxides. Moreover, we also show that the stability of the LDH precipitate is crucial for the rechargeability of the oxide cathodes, revealing a critical link between the charge storage mechanism and the performance of the oxide hosts in aqueous zinc batteries.