Recent developments in three-dimensional Zn metal anodes for battery applications

Aqueous zinc(Zn)ion batteries(AZIBs)are regarded as one of the promising candidates for next-generation electrochemical energy storage systems due to their low cost,high safety,and environmental friendliness.However,the commercialization of AZIBs has been severely restricted by the growth of dendrite at the Zn metal anode.Tailoring the planar-structured Zn anodes into threedimensional(3D)structures has proven to be an effective way to modulate the plating/stripping behavior of Zn anodes,resulting in the suppression of dendrite formation.This review provides an up-to-date review of 3D structured Zn metal anodes,including working principles,design,current status,and future prospects.We aim to give the readers a comprehensive understanding of 3D-structured Zn anodes and their effective usage to enhance AZIB performance.

Ultrathin surface coating of Cu enabling long-life Zn metal anodes

Aqueous zinc-ion batteries(AZIBs)are regarded as promising energy storage devices due to their low cost,high capacity,and ecological safety.Nevertheless,the severe dendritic growth and side reactions hinder their practical applicability significantly.Herein,an ultrathin Cu coating layer(~200 nm)is decorated on zinc foils via filtered cathodic vacuum arc deposition technology,aiming to achieve high-performance AZIBs.The Cu layer effectively suppresses chemical corrosion and hydrogen evolution reactions and enables preferential(002)Zn deposition during the stripping/plating cycles.Consequently,the Cu@Zn anode represents an elongated cycle life over 4,000 h at 2 mA·cm^(-2)/2 mAh·cm^(-2).Even in conditions of high current density of 5 and 10 mA·cm^(-2),the Cu@Zn anode shows prolonged cycling stability exceeding 4000 and 2000 h,respectively.Such advantages also bring high Coulombic efficiency of 99.87%under 5 mAh·cm^(-2)in Cu@Ti||Zn half-cell over 1500 cycles.Moreover,the Cu@Zn||MnO_(2)full cell demonstrates a superior cyclability with a specific capacity of 203 mAh·g^(-1)after 500 cycles a1 A·g^(-1).

Electrolytes additives for Zn metal anodes:regulation mechanism and current perspectives

With distinct advantages such as high gravimetric and volumetric capacity(5855 mAh·cm^(-3)and 820mAh·g^(-1)),low redox potential(-0.762 V vs.standard hydrogen electrode(SHE)),high abundance,low toxicity and intrinsic safety of Zn metal anode,Zn-ion batteries have become a potential alternative to Li-ion batteries.However,several challenges still need to be addressed prior to the practical applications of Zn-ion batteries,such as dendrite growth during Zn plating/stripping and interfacial side reactions on the Zn surface.Such issues can be addressed by introducing additives to regulate the components and structures of the electrolyte.In this review,we systematically discussed the core issues of metallic Zn anodes and comprehensively summarized a novel perspective of the regulation mechanism of inhibiting dendrite growth or interfacial side reactions in Zn anodes by introducing additives into aqueous electrolytes.Furthermore,some discussions and prospects for aqueous Zn ion batteries(AZIBs)are presented for future research.

Crystallinity engineering of carbon nitride protective coating for ultra-stable Zn metal anodes

Ineffective control of dendrite growth and side reactions on Zn anodes significantly retards commercialization of aqueous Zn-ion batteries.Unlike conventional interfacial modification strategies that are primarily focused on component optimization or microstructural tuning,herein,we propose a crystallinity engineering strategy by developing highly crystalline carbon nitride protective layers for Zn anodes through molten salt treatment.Interestingly,the highly ordered structure along with sufficient functional polar groups and pre-intercalated Kþendows the coating with high ionic conductivity,strong hydrophilicity,and accelerated ion diffusion kinetics.Theoretical calculations also confirm its enhanced Zn adsorption capability compared to commonly reported carbon nitride with amorphous or semi-crystalline structure and bare Zn.Benefiting from the aforementioned features,the as-synthesized protective layer enables a calendar lifespan of symmetric cells for 1100 h and outstanding stability of full cells with capacity retention of 91.5%after 1500 cycles.This work proposes a new conceptual strategy for Zn anode protection.

Regulating zinc ion transport behavior and solvated structure towards stable aqueous Zn metal batteries

Aqueous Zn metal batteries(AZMBs)with intrinsic safety,high energy density and low cost have been regarded as promising electrochemical energy storage devices.However,the parasitic reaction on metallic Zn anode and the incompatibility between electrode and electrolytes lead to the deterioration of electrochemical performance of AZMBs during the cycling.The critical point to achieve the stable cycling of AZMBs is to properly regulate the zinc ion solvated structure and transfer behavior between metallic Zn anode and electrolyte.In recent years,numerous achievements have been made to resolve the formation of Zn dendrite and interface incompatible issues faced by AZMBs via optimizing the sheath structure and transport capability of zinc ions at electrode-electrolyte interface.In this review,the challenges for metallic Zn anode and electrode-electrolyte interface in AZMBs including dendrite formation and interface characteristics are presented.Following the influences of different strategies involving designing advanced electrode structu re,artificial solid electrolyte interphase(SEI)on Zn anode and electrolyte engineering to regulate zinc ion solvated sheath structure and transport behavior are summarized and discussed.Finally,the perspectives for the future development of design strategies for dendrite-free Zn metal anode and long lifespan AZMBs are also given.

3D Artificial Array Interface Engineering Enabling Dendrite-Free Stable Zn Metal Anode

The ripple effect induced by uncontrollable Zn deposition is considered as the Achilles heel for developing high-performance aqueous Zn-ion batteries.For this problem,this work reports a design concept of 3D artificial array interface engineering to achieve volume stress elimination,preferred orientation growth and dendrite-free stable Zn metal anode.The mechanism of MXene array interface on modulating the growth kinetics and deposition behavior of Zn atoms were firstly disclosed on the multi-scale level,including the in-situ optical microscopy and transient simulation at the mesoscopic scale,in-situ Raman spectroscopy and in-situ X-ray diffraction at the microscopic scale,as well as density functional theory calculation at the atomic scale.As indicated by the electrochemical performance tests,such engineered electrode exhibits the comprehensive enhancements not only in the resistance of corrosion and hydrogen evolution,but also the rate capability and cyclic stability.High-rate performance(20 mA cm^(-2))and durable cycle lifespan(1350 h at 0.5 mA cm^(-2),1500 h at 1 mA cm^(-2)and 800 h at 5 mA cm^(-2))can be realized.Moreover,the improvement of rate capability(214.1 mAh g^(-1)obtained at 10 A g^(-1))and cyclic stability also can be demonstrated in the case of 3D MXene array@Zn/VO2battery.Beyond the previous 2D closed interface engineering,this research offers a unique 3D open array interface engineering to stabilize Zn metal anode,the controllable Zn deposition mechanism revealed is also expected to deepen the fundamental of rechargeable batteries including but not limited to aqueous Zn metal batteries.

Dilute Aqueous-Aprotic Electrolyte Towards Robust Zn-Ion Hybrid Supercapacitor with High Operation Voltage and Long Lifespan

With the merits of the high energy density of batteries and power density of supercapacitors,the aqueous Zn-ion hybrid supercapacitors emerge as a promising candidate for applications where both rapid energy delivery and moderate energy storage are required.However,the narrow electrochemical window of aqueous electrolytes induces severe side reactions on the Zn metal anode and shortens its lifespan.It also limits the operation voltage and energy density of the Zn-ion hybrid supercapacitors.Using'water in salt'electrolytes can effectively broaden their electrochemical windows,but this is at the expense of high cost,low ionic conductivity,and narrow temperature compatibility,compromising the electrochemical performance of the Zn-ion hybrid supercapacitors.Thus,designing a new electrolyte to balance these factors towards high-performance Zn-ion hybrid supercapacitors is urgent and necessary.We developed a dilute water/acetonitrile electrolyte(0.5 m Zn(CF_(3)SO_(3))_(2)+1 m LiTFSI-H_(2)O/AN)for Zn-ion hybrid supercapacitors,which simultaneously exhibited expanded electrochemical window,decent ionic conductivity,and broad temperature compatibility.In this electrolyte,the hydration shells and hydrogen bonds are significantly modulated by the acetonitrile and TFSI-anions.As a result,a Zn-ion hybrid supercapacitor with such an electrolyte demonstrates a high operating voltage up to 2.2 V and long lifespan beyond 120,000 cycles.

In situ separator modification via CVD-derived N-doped carbon for highly reversible Zn metal anodes

Attention toward aqueous zinc-ion battery has soared recently due to its operation safety and environmental benignity.Nonetheless,dendrite formation and side reactions occurred at the anode side greatly hinder its practical application.Herein,we adopt direct plasma-enhanced chemical vapor deposition strategy to in situ grow N-doped carbon(NC)over commercial glass fiber separator targeting a highly stabilized Zn anode.The strong zincophilicity of such a new separator would reduce the nucleation overpotential of Zn and enhance the Zn-ion transference number,thereby alleviating side reactions.Symmetric cells equipped with NC-modified separator harvest a stable cycling for more than 1,100 h under 1 mA·cm^(−2)/1 mAh·cm^(−2).With the assistance of NC,the depth of discharge of Zn anode reaches as high as 42.7%.When assembled into full cells,the zinc-ion battery based on NC-modified separator could maintain 79%of its initial capacity(251 mAh·g^(−1))at 5 A·g^(−1) after 1,000 cycles.

Recent progress,mechanisms,and perspectives for crystal and interface chemistry applying to the Zn metal anodes in aqueous zinc-ion batteries

The need for large-scale electrochemical energy storage devices in the future has spawned several new breeds of batteries in which aqueous zinc ion batteries(AZIBs)have attracted great attention due to their high safety,low cost,and excellent electrochemical performance.In the current research,the dendrite and corrosion caused by aqueous electrolytes are the main problems being studied.However,the research on the zinc metal anode is still in its infancy.We think it really needs to provide clear guidelines about how to reasonably configure the system of AZIBs to realize high-energy density and long cycle life.Therefore,it is worth analyzing the works on the zinc anode,and several strategies are proposed to improve the stability and cycle life of the battery in recent years.Based on the crystal chemistry and interface chemistry,this review reveals the key factors and essential causes that inhibit dendrite growth and side reactions and puts forward the potential prospects for future work in this direction.It is foreseeable that guiding the construction of AZIBs with high-energy density and long cycle life in various systems would be quite possible by following this overview as a roadmap.

Metal-organic frameworks and their derivatives in stable Zn metal anodes for aqueous Zn-ion batteries

Zn metal anode is believed to be a promising anode material for aqueous Zn-ion batteries(ZIBs)due to the mer-its such as low electrochemical potential,low cost,high theoretical specific capacity,high hydrogen evolution overpotential,less-reactive property,environmental friendliness and easy processing.However,issues including uncontrollable growth of Zn dendrites,corrosion by aqueous electrolyte,large volume change and unstable in-terface hinder its further development.Recently,multifunctional metal-organic frameworks(MOFs)and their derivatives have shown huge advantages in solving the issues facing Zn metal anode,and large advances have been achieved.MOFs and their derivatives can stabilize Zn metal anode by interface engineering,designing host,decorating separator,constructing solid-state electrolyte and so on.Here we carefully summarize and analyse these advances.Meanwhile,some perspectives and outlooks are put forward.This review can promote the de-velopment of MOFs,Zn metal anode as well as aqueous ZIBs.

Dual-function protective layer for highly reversible Zn anode

The thermodynamic instability of zinc anodes in aqueous electrolytes leads to issues such as corrosion,hydrogen evolution reactions(HER), and dendrite growth, severely hindering the practical application of zinc-based aqueous energy storage devices. To address these challenges, this work proposes a dualfunction zinc anode protective layer, composed of Zn-Al-In layered double oxides(ILDO) by rationally designing Zn-Al layered double hydroxides(Zn-Al LDHs) for the first time. Differing from previous works on the LDHs coatings, firstly, the ILDO layer accelerates zinc-ion desolvation and also captures and anchors SO_(4)^(2-). Secondly, the in-situ formation of the Zn-In alloy phase effectively lowers the nucleation energy barrier, thereby regulating zinc nucleation. Consequently, the zinc anode with the ILDO protective layer demonstrates long-term stability exceeding 1900 h and low voltage hysteresis of 7.5 m V at 0.5 m A cm^(-2) and 0.5 m A h cm^(-2). Additionally, it significantly enhances the rate capability and cycling performance of Zn@ILDO//MnO_(2) full batteries and Zn@ILDO//activated carbon zinc-ion hybrid capacitors.This simple and effective dual-function protective layer strategy offers a promising approach for achieving high-performance zinc-ion batteries.

Surface Patterning of Metal Zinc Electrode with an In‑Region Zincophilic Interface for High‑Rate and Long‑Cycle‑Life Zinc Metal Anode

The undesirable dendrite growth induced by non-planar zinc(Zn)deposition and low Coulombic efficiency resulting from severe side reactions have been long-standing challenges for metallic Zn anodes and substantially impede the practical application of rechargeable aqueous Zn metal batteries(ZMBs).Herein,we present a strategy for achieving a high-rate and long-cycle-life Zn metal anode by patterning Zn foil surfaces and endowing a Zn-Indium(Zn-In)interface in the microchannels.The accumulation of electrons in the microchannel and the zincophilicity of the Zn-In interface promote preferential heteroepitaxial Zn deposition in the microchannel region and enhance the tolerance of the electrode at high current densities.Meanwhile,electron aggregation accelerates the dissolution of non-(002)plane Zn atoms on the array surface,thereby directing the subsequent homoepitaxial Zn deposition on the array surface.Consequently,the planar dendrite-free Zn deposition and long-term cycling stability are achieved(5,050 h at 10.0 mA cm^(−2) and 27,000 cycles at 20.0 mA cm^(−2)).Furthermore,a Zn/I_(2) full cell assembled by pairing with such an anode can maintain good stability for 3,500 cycles at 5.0 C,demonstrating the application potential of the as-prepared ZnIn anode for high-performance aqueous ZMBs.

Robust ZnS interphase for stable Zn metal anode of high-performance aqueous secondary batteries

Although Zn metal is an ideal anode candidate for aqueous batteries owing to its high theoretical capacity,lower cost,and safety,its service life and efficiency are damaged by severe hydrogen evolution reaction,self-corrosion,and dendrite growth.Herein,a thickness-controlled ZnS passivation layer was fabricated on the Zn metal surface to obtain Zn@ZnS electrode through oxidation–orientation sulfuration by the liquid-and vapor-phase hydrothermal processes.Benefiting from the chemical inertness of the ZnS interphase,the as-prepared Zn@ZnS electrode presents an excellent anti-corrosion and undesirable hydrogen evolution reaction.Meanwhile,the thickness-optimized ZnS layer with an unbalanced charge distribution represses dendrite growth by guiding Zn plating/stripping,leading to long service life.Consequently,the Zn@Zn S presented 300 cycles in the symmetric cells with a 42 mV overpotential,200 cycles in half cells with a 78 mV overpotential,and superb rate performance in Zn||NH;V;O;full cells.

In situ construction of a stable composite solid electrolyte interphase for dendrite-free Zn batteries

Building a stable solid electrolyte interphase(SEI)has been regarded to be highly effective for mitigating the dendrite growth and parasitic side reactions of Zn anodes.Herein,a robust inorganic composite SEI layer is in situ constructed by introducing an organic cysteine additive to achieve long lifetime Zn metal batteries.The chemisorbed cysteine derivatives are electrochemically reduced to trigger a local alkaline environment for generating a gradient layered zinc hydroxide based multicomponent interphase.Such a unique interphase is of significant advantage as a corrosion inhibitor and Zn^(2+)modulator to enable reversible plating/stripping chemistry with a reduced desolvation energy barrier.Accordingly,the cells with a thin glass fiber separator(260μm)deliver a prolonged lifespan beyond 2000 h and enhanced Coulombic efficiency of 99.5%over 450 cycles.This work will rationally elaborate in situ construction of a desirable SEI by implanting reductive additives for dendrite-free Zn anodes.

Stable and dendrite-free Zn anode with artificial desolvation interface layer toward high-performance Zn-ion capacitor

Aqueous Zn-based energy storage devices possess tremendous advantages, such as low cost, high safety,and competitive energy density, due to employing a Zn metal anode and aqueous electrolyte. However,the cycling stability and rate ability of a Zn anode are hindered by Zn dendrite growth and sluggish ion transfer in the electrode/electrolyte interface. Herein, the interfacial properties of Zn anodes are improved through the introduction of a silver(Ag) protective layer, which facilitates uniform Zn deposition and regulates Zn ion transport. As a result, Ag-coated Zn anodes display stable cycling performance(600 h at 1 m A cm^(-2)) and low overpotential(150 mV at 50 mA cm^(-2)after 2000 cycles). The Ag layer in situ electrochemically converts into an AgZn_(3) layer and promotes Zn ion desolvation and threedimensional diffusion processes. Moreover, a Zn-ion capacitor assembled with an Ag-coated Zn anode and active carbon cathode shows a capable cycling lifespan and rate performance. This study provides a feasible strategy for constructing a stabilized and dendrite-free Zn anode for the development of high-performance Zn-based energy storage devices.

Bilayer separator enabling dendrite-free zinc anode with ultralong lifespan >5000 h

Aqueous zinc(Zn)batteries with Zn metal anodes are promising clean energy storage devices with intrinsic safety and low cost.However,Zn dendrite growth severely restricts the use of Zn anodes.To effectively suppress Zn dendrite growth,we propose a bilayer separator consisting of commercial butter paper and glassfiber membrane.The dense cellulose-based butter paper(BP)with low zincophilicity and high mechanical properties prevents the pore-filling behavior of deposited Zn and related separator piercing,effectively suppressing the Zn dendrite growth.As a result,the bilayer separators endow the ZnjjZn symmetrical batteries with a superlong cycling life of Zn anodes(over 5000 h)at 0.5 mA cm^(-2) and the full batteries enhanced capacity retention,demonstrating the advancement of the bilayer separator to afford excellent cyclability of aqueous metal batteries.

Selection of Negative Charged Acidic Polar Additives to Regulate Electric Double Layer for Stable Zinc Ion Battery

Zinc-ion batteries are promising for large-scale electrochemical energy storage systems,which still suffer from interfacial issues,e.g.,hydrogen evolution side reaction(HER),self-corrosion,and uncontrollable dendritic Zn electrodeposition.Although the regulation of electric double layer(EDL)has been verified for interfacial issues,the principle to select the additive as the regulator is still misted.Here,several typical amino acids with different characteristics were examined to reveal the interfacial behaviors in regulated EDL on the Zn anode.Negative charged acidic polarity(NCAP)has been unveiled as the guideline for selecting additive to reconstruct EDL with an inner zincophilic H_(2)O-poor layer and to replace H_(2)O molecules of hydrated Zn^(2+)with NCAP glutamate.Taking the synergistic effects of EDL regulation,the uncontrollable interface is significantly stabilized from the suppressed HER and anti-self-corrosion with uniform electrodeposition.Consequently,by adding NCAP glutamate,a high average Coulombic efficiency of 99.83%of Zn metal is achieved in Zn|Cu asymmetrical cell for over 2000 cycles,and NH4V4O10|Zn full cell exhibits a high-capacity retention of 82.1%after 3000 cycles at 2 A g^(-1).Recapitulating,the NCAP principle posted here can quicken the design of trailblazing electrolyte additives for aqueous Zn-based electrochemical energy storage systems.

Critical Factors Dictating Reversibility of the Zinc Metal Anode

With high energy density and improved safety,rechargeable battery chemistries with a zinc(Zn)metal anode offer promising and sustainable alternatives to those based on lithium metal or lithium-ion intercalation/alloying anode materials;however,the poor electrochemical reversibility of Zn plating/stripping,induced by parasitic reactions with both aqueous and non-aqueous electrolytes,presently limits the practical appeal of these systems.Although recent efforts in rechargeable Zn metal batteries(RZMBs)have achieved certain advancements in Zn metal reversibility,as quantified by the Coulombic efficiency(CE),a standard protocol for CE has not been established,and results across chemistries and systems are often conflicting.More importantly,there is still an insufficient understanding regarding the critical factors dictating Zn reversibility.In this work,a rigorous,established protocol for determining CE of lithium metal anodes is transplanted to the Zn chemistry and is used for systematically examining how a series of factors including current collector chemistry,current density,temperature,and the upper voltage limit during stripping affect the measured reversibility of different Zn electrolytes.With support from density functional theory calculations,this standardized Zn CE protocol is then leveraged to identify an important correlation between electrolyte solvation strength toward Zn2+and the measured Zn CE in the corresponding electrolyte,providing new guidance for future development and evaluation of Zn electrolytes.

Flat Zn deposition at battery anode via an ultrathin robust interlayer

Rechargeable aqueous zinc(Zn)ion batteries(AZIBs)using low-cost and safe Zn metal anodes are considered promising candidates for future grid-scale energy storage systems,but the Zn dendrite problem severely hinders the further prospects of AZIBs.Regulating Zn depositing behaviors toward horizontal alignment is highly effective and thus has received huge attention.However,such a strategy is usually based on previous substrate engineering,which requires complex preparation or expensive equipment.Therefore,it is essential to develop a novel solution that can realize horizontally aligned Zn flake deposition via easy operation and low cost.Herein,we report an ultrathin and robust Kevlar membrane as the interlayer to mechanically suppress Zn dendrite growth.Compared to the randomly distributed flaky dendrites in the control group,the deposited Zn sheets would grow into parallel alignment with the existence of such interlayer.As the dendrites are effectively suppressed,Zn||Cu asymmetric,Zn||Zn symmetric,and Zn||MnO_(2)full batteries using Kevlar interlayer deliver significantly improved cycling stabilities.Furthermore,the Zn||MnO_(2)pouch cell using a Kevlar interlayer delivers stable cycling performance and shows stable operation during multi-angle folding.We believe this work provides a new possibility for regulating Zn deposition from a crystallographic perspective.

Cell-nucleus structured electrolyte for low-temperature aqueous zinc batteries

Rechargeable aqueous zinc(Zn) batteries hold great promise for large-scale energy storage,but their implementation is plagued by poor Zn reversibility and unsatisfactory low-temperature performance.Herein,we design a cell-nucleus structured electrolyte by introducing low-polarity 1,2-dimethoxyethane(DME) into dilute 1 M zinc trifluoromethanesulfonate(Zn(OTf)_(2)) aqueous solution,which features an OTf--rich Zn2^(+)-primary solvation sheath(PSS,inner nucleus) and the DMEmodulated Zn^(2+)-outer solvation sheath(outer layer).We find that DME additives with a low dosage do not participate in the Zn2+-PSS but reinforce the Zn-OTf-coordination,which guarantees good reaction kinetics under ultralow temperatures.Moreover,DME breaks the original H-bonding network of H2O,depressing the freezing point of electrolyte to-52.4℃.Such a cell-nucleus-solvation structure suppresses the H_(2)O-induced side reactions and forms an anion-derived solid electrolyte interphase on Zn and can be readily extended to 1,2-diethoxyethane.The as-designed electrolyte enables the Zn electrode deep cycling stability over 3500 h with a high depth-of-discharge of 51.3% and endows the Zn‖V_(2)O_(5)full battery with stable cycling over 1000 cycles at 40℃.This work would inspire the solvation structure design for low-temperature aqueous batteries.