Recent Advances in Aqueous Zn||MnO_(2)Batteries

Recently,rechargeable aqueous zinc-based batteries using manganese oxide as the cathode(e.g.,MnO_(2))have gained attention due to their inherent safety,environmental friendliness,and low cost.Despite their potential,achieving high energy density in Zn||MnO_(2)batteries remains challenging,highlighting the need to understand the electrochemical reaction mechanisms underlying these batteries more deeply and optimize battery components,including electrodes and electrolytes.This review comprehensively summarizes the latest advancements for understanding the electrochemistry reaction mechanisms and designing electrodes and electrolytes for Zn||MnO_(2)batteries in mildly and strongly acidic environments.Furthermore,we highlight the key challenges hindering the extensive application of Zn||MnO_(2)batteries,including high-voltage requirements and areal capacity,and propose innovative solutions to overcome these challenges.We suggest that MnO_(2)/Mn^(2+)conversion in neutral electrolytes is a crucial aspect that needs to be addressed to achieve high-performance Zn||MnO_(2)batteries.These approaches could lead to breakthroughs in the future development of Zn||MnO_(2)batteries,off ering a more sustainable,costeff ective,and high-performance alternative to traditional batteries.

Freestanding and Flexible Interfacial Layer Enables Bottom-Up Zn Deposition Toward Dendrite-Free Aqueous Zn-Ion Batteries

Aqueous rechargeable zinc ion batteries are regarded as a competitive alternative to lithium-ion batteries because of their distinct advantages of high security,high energy density,low cost,and environmental friendliness.However,deep-seated problems including Zn dendrite and adverse side reactions severely impede the practical application.In this work,we proposed a freestanding Zn-electrolyte interfacial layer composed of multicapsular carbon fibers(MCFs)to regulate the plating/stripping behavior of Zn anodes.The versatile MCFs protective layer can uniformize the electric field and Zn^(2+)flux,meanwhile,reduce the deposition overpotentials,leading to high-quality and rapid Zn deposition kinetics.Furthermore,the bottom-up and uniform deposition of Zn on the Zn-MCFs interface endows long-term and high-capacity plating.Accordingly,the Zn@MCFs symmetric batteries can keep working up to 1500 h with 5 mAh cm^(−2).The feasibility of the MCFs interfacial layer is also convinced in Zn@MCFs||MnO_(2) batteries.Remarkably,the Zn@MCFs||α-MnO_(2)batteries deliver a high specific capacity of 236.1 mAh g^(−1)at 1 A g^(−1)with excellent stability,and maintain an exhilarating energy density of 154.3 Wh kg^(−1) at 33%depth of discharge in pouch batteries.

Understanding of the charge storage mechanism of MnO_(2)-based aqueous zinc-ion batteries:Reaction processes and regulation strategies

Though secondary aqueous Zn ion batteries(AZIBs)have been received broad concern in recent years,the development of suitable cathode materials of AZIBs is still a big challenge.The MnO_(2) has been deemed as one of most hopeful cathode materials of AZIBs on account of some extraordinary merits,such as richly natural resources,low toxicity,high discharge potential,and large theoretical capacity.However,the crystal structure diversity of MnO_(2) results in an obvious various of charge storage mechanisms,which can cause great differences in electrochemical performance.Furthermore,several challenges,including intrinsic poor conductivity,dissolution of manganese and sluggish ion transport dynamics should be conquered before real practice.This work focuses on the reaction mechanisms and recent progress of MnO_(2)-based materials of AZIBs.In this review,a detailed review of the reaction mechanisms and optimal ways for enhancing electrochemical performance for MnO_(2)-based materials is proposed.At last,a number of viewpoints on challenges,future development direction,and foreground of MnO_(2)-based materials of aqueous zinc ions batteries are put forward.This review clarifies reaction mechanism of MnO_(2)-based materials of AZIBs,and offers a new perspective for the future invention in MnO_(2)-based cathode materials,thus accelerate the extensive development and commercialization practice of aqueous zinc ions batteries.

Anti-aggregation growth and hierarchical porous carbon encapsulation enables the C@VO_(2) cathode with superior storage capability for aqueous zinc-ion batteries

Self-aggregation and sluggish transport kinetics of cathode materials would usually lead to the poor electrochemical performance for aqueous zinc-ion batteries(AZIBs).In this work,we report the construction of C@VO_(2) composite via anti-aggregation growth and hierarchical porous carbon encapsulation.Both of the morphology of composite and pore structure of carbon layer can be regulated by tuning the adding amount of glucose.When acting as cathode applied for AZIBs,the C@VO_(2)-3:3 composite can deliver a high capacity of 281 m Ah g^(-1) at 0.2 A g^(-1).Moreover,such cathode also exhibits a remarkably rate capability and cyclic stability,which can release a specific capacity of 195 m Ah g^(-1) at 5 A g^(-1) with the capacity retention of 95.4%after 1000 cycles.Besides that,the evolution including the crystal structure,valence state and transport kinetics upon cycling were also deeply investigated.In conclusion,benefited from the synergistic effect of anti-aggregation morphology and hierarchical porous carbon encapsulation,the building of such C@VO_(2) composite can be highly expected to enhance the ion accessible site,boost the transport kinetics and thus performing a superior storage performance.Such design concept can be applied for other kinds of electrode materials and accelerating the development of highperformance AZIBs.

Rational construction of Ag@MIL-88B(V)-derived hierarchical porous Ag-V_(2)O_(5) heterostructures with enhanced diffusion kinetics and cycling stability for aqueous zinc-ion batteries

With the advantages of the multiple oxidation states and highly open crystal structures,vanadium-based composites have been considered as the promising cathode materials for aqueous zinc-ion batteries(ZIBs).However,the inherent inferior electrical conductivity,low specific surface area,and sluggish Zn^(2+)diffusion kinetics of the traditional vanadium-based oxides have greatly impeded their development.Herein,a novel hierarchical porous spindle-shaped Ag-V_(2)O_(5) with unique heterostructures was rationally designed via a simple MOF-assisted synthetic method and applied as stable cathode for aqueous ZIBs.The high specific surface area and hierarchically porous superstructures endowed Ag-V_(2)O_(5) with sufficient electrochemical active sites and shortened the diffusion pathways of Zn^(2+),which was beneficial to accelerate the reversible transport of Zn^(2+)and deliver a high specific capacity(426 mA h g^(-1) at 0.1 A g^(-1) and 96.5%capacity retention after 100 cycles).Meanwhile,the self-built-in electric fields at the heterointerface of Ag-V_(2)O_(5) electrode could strengthen the synergistic coupling interaction between Ag and V_(2)O_(5),which can effectively enhance the electric conductivity and maintain the structural integrity,resulting in superb rate capability(326.1 mA h g^(-1) at 5.0 A g^(-1))and remarkable cycling stability(89.7%capacity retention after 2000 cycles at 5.0 A g^(-1)).Moreover,the reversible Zn^(2+)storage mechanism was further investigated and elucidated by kinetics analysis and DFT calculations.

Quench-tailored Al-doped V_(2)O_(5) nanomaterials for efficient aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries(ZIBs)are regarded as a promising competition to lithium-ion batteries as energy storage devices,owing to their high safety and low cost.However,the development of high-performance ZIBs is largely hindered by the shortage of ideal cathode materials with high-rate capability and long-cycle stability.Herein,we address this bottleneck issue by the quenching-tailored surface chemistry of V_(2)O_(5) cathode nanomaterial.By rapid quenching from high temperatures,Al ions are doped into V_(2)O_(5) lattice(Al-V_(2)O_(5))and abundant oxygen vacancies are formed on the surface/nearsurface,which facilitate the desired rapid electron transfers.Our density functional theory(DFT)simulations elucidate that the doping of Al ions into V_(2)O_(5) remarkably reduces the Zn^(2+)-diffusion barriers and improves the electrical conductivity of V_(2)O_(5).As a proof-of-concept application,the thus-optimized AlV_(2)O_(5) cathode delivers a superior specific capacity of 532 m Ah g^(-1) at 0.1 A g^(-1) and a long-cycling life with76%capacity retention after 5000 cycles,as well as a good rate performance.This work provides not only a novel strategy for tuning the surface chemistry of V_(2)O_(5) to boost the Zn^(2+)storage but also a general pathway of modifying metal oxides with improved electrochemical performance.

Recent advances in energy storage mechanism of aqueous zinc-ion batteries

Aqueous rechargeable zinc-ion batteries(ZIBs)have recently attracted increasing research interest due to their unparalleled safety,fantastic cost competitiveness and promising capacity advantages compared with the commercial lithium ion batteries.However,the disputed energy storage mechanism has been a confusing issue restraining the development of ZIBs.Although a lot of efforts have been dedicated to the exploration in battery chemistry,a comprehensive review that focuses on summarizing the energy storage mechanisms of ZIBs is needed.Herein,the energy storage mechanisms of aqueous rechargeable ZIBs are systematically reviewed in detail and summarized as four types,which are traditional Zn^(2+)insertion chemistry,dual ions co-insertion,chemical conversion reaction and coordination reaction of Zn^(2+)with organic cathodes.Furthermore,the promising exploration directions and rational prospects are also proposed in this review.

CNT@MnO_(2) composite ink toward a flexible 3D printed micro-zinc-ion battery

Flexible energy storage devices have played a significant role in multiscenario applications,while flexible zinc-ion batteries(ZIBs),as an essential branch,have developed rapidly in recent years.Three-dimensional(3D)printing is an extremely advanced technology to design and modify the structure of batteries and provides unlimited possibilities for the diversified development of energy storage equipment.Herein,by utilizing 3D printing technology,carbon nanotube(CNT)is coated by MnO_(2) to form a flexible CNT@MnO_(2) ink as a cathode for flexible aqueous micro-ZIBs for the first time and zinc powder ink is used as an anode due to its high flexibility and bendability.The Zn//CNT@MnO_(2) flexible battery shows a stable capacity of 63μAh cm^(−2) at 0.4mA cm^(−2).When the battery is bent in different states,the maximum capacity loss compared with the initial value is only 2.72%,indicating its stability.This study shows the potential of 3D printing technology in the development of flexible manganese-based ZIBs.

Weaker Interactions in Zn^(2+)and Organic Ion-pre-intercalated Vanadium Oxide toward Highly Reversible Zinc-ion Batteries

Driven by safety issues,environmental concerns,and high costs,rechargeable aqueous zinc-ion batteries(ZIBs)have received increasing attention in recent years owing to their unique advantages.However,the sluggish kinetics of divalent charge Zn^(2+)in the cathode materials caused by the strong electrostatic interaction and their unsatisfactory cycle life hinder the development of ZIBs.Herein,organic cations and Zn^(2+)ions co-pre-inserted vanadium oxide([N(CH_(3))_(4)]_(0.77),Zn_(0.23))V_(8)O_(20)·3.8H_(2)O are reported as the cathode for ultra-stable aqueous ZIBs,in which the weaker electrostatic interactions between Zn^(2+)and organic ion-pinned vanadium oxide can induce the high reversibility of Zn^(2+)insertion and extraction,thereby improving the cycle life.It is demonstrated that([N(CH_(3))_(4)]_(0.77),Zn_(0.23))V_(8)O_(20)·3.8H_(2)O cathodes deliver a discharge capacity of 181 mA h g^(-1)at8 A g^(-1)and ultra-long life span(99.5%capacity retention after 2000 cycles).A reversible Zn^(2+)/H^(+)ions(de)intercalation storage process and pseudocapacitive charge storage are characterized.The weaker interactions between organic ion and Zn^(2+)open a novel avenue for the design of highly reversible cathode materials with long-term cycling stability.

A novel improvement strategy and a comprehensive mechanism insight for α-MnO_(2) energy storage in rechargeable aqueous zinc-ion batteries

Aqueous zinc-ion batteries have been regarded as the most potential candidate to substitute lithium-ion batteries.However,many serious challenges such as suppressing zinc dendrite growth and undesirable reactions,and achieving fully accepted mechanism also have not been solved.Herein,the commensal composite microspheres withα-MnO_(2) nano-wires and carbon nanotubes were achieved and could effectively suppress ZnSO_(4)·3Zn(OH)_(2)·nH_(2)O rampant crystallization.The electrode assembled with the microspheres delivered a high initial capacity at a current density of 0.05 A g^(-1) and maintained a significantly prominent capacity retention of 88%over 2500 cycles.Furthermore,a novel energy-storage mechanism,in which multivalent manganese oxides play a synergistic effect,was comprehen-sively investigated by the quantitative and qualitative analysis for ZnSO_(4)·3Zn(OH)_(2)·nH_(2)O.The capacity contribution of multivalent manganese oxides and the crystal structure dissection in the transformed processes were completely identified.Therefore,our research could provide a novel strategy for designing improved electrode structure and a comprehensive understanding of the energy storage mechanism of α-MnO_(2) cathodes.

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

AV4+-V2O5 cathode with mixed vanadium valences was prepared via a novel synthetic method using VOOH as the precursor,and its zinc-ion storage performance was evaluated.The products are hollow spheres consisting of nanoflakes.The V4+-V2O5 cathode exhibits a prominent cycling performance,with a specific capacity of 140 mAhg-1 after 1000 cycles at 10 A g.1,and an excellent rate capability.The good electrochemical performance is attributed to the presence of V4+,which leads to higher electrochemical activity,lower polarization,faster ion diffusion,and higher electrical conductivity than V2O5 without V4+.This engineering strategy of valence state manipulation may pave the way for designing high-performance cathodes for elucidating advanced battery chemistry.

From aqueous Zn-ion battery to Zn-MnO_(2) flow battery:A brief story

Aqueous Zn-ion battery(AZIB)has become an attractive technology because of its unique features of low cost,high safety and the eco-friendliness.MnO_(2) is the model cathode material for AZIB since the first report on reversible Zn-MnO_(2) battery,but recent studies have unveiled different charge storage mechanisms.Due to revamping of the electrochemistry and redesigning of the electrolyte and interface,there is tremendous performance enhancement in AZIB.This mini Review will first give a brief introduction of ZIB,including fundamentals of materials and components,and the progress in recent years.Then,a general classification of working mechanisms related to MnO_(2) in neutral and mildly acidic electrolyte is elaborated.Our focus is put on the recent blossoming Zn-MnO_(2) electrolytic mechanism,which has given birth to the Zn-MnO_(2) redox flow batteries that are highly promising for large-scale static energy storage.

Constructing high-capacity and flexible aqueous zinc-ion batteries with air-recharging capability using organic cathodes

Flexible aqueous zinc-ion batteries(AZIBs)with air-recharging capability are a promising self-powered system applied in future wearable electronics.It is desired to develop high-capacity air-rechargeable AZIBs.Herein,we developed a flexible AZIB with air-recharging capability based on trinitrohexaazatrinaphthylene(TNHATN)cathode and a ZnSO_(4)electrolyte.The flexible Zn//TNHATN battery exhibits high volumetric energy density(21.36 mWh/cm^3)and excellent mechanical flexibility.Impressing,the discharged flexible Zn//TNHATN battery can be chemical self-charged via the redox reaction between TNHATN cathode and O_(2)from the air.After oxidation in air for 15 h,such flexible Zn//TNHATN battery can deliver a high specific capacity of 320 mAh/g at 0.5 A/g,displaying excellent air-recharging capability.Notably,this flexible Zn//TNHATN battery also works well in chemical or/and galvanostatic charging mixed modes,showing reusability.This work provides a new insight for designing flexible aqueous self-powered systems.

High?Voltage Flexible Aqueous Zn?Ion Battery with Extremely Low Dropout Voltage and Super?Flat Platform

Flexible rechargeable aqueous zinc-ion batteries(ZIBs)have attracted extensive attentions in the energy storage field due to their high safety,environmental friendliness,and outstanding electrochemical performance while the exploration of high-voltage aqueous ZIBs with excellent rate capability is still a great challenge for the further application them in flexible and wearable electronics.Herein,we fabricated a 2.4 V high-voltage flexible aqueous ZIB,being among the highest voltage reported in aqueous ZIBs.Moreover,it exhibits extremely flat charging/discharging voltage platforms and the dropout voltage is only 0.1 V,which is the smallest gap in all aqueous batteries to our best knowledge.Furthermore,the prepared ZIB performs high rate capability of 25 C and energy density of 120 Wh kg?1 and exhibits excellent safety under various destructive conditions including hammering,sewing,punching,and soaking.These extraordinary results indicate the great application potential of our high-voltage flexible aqueous ZIB in wearable electronics.

Constructing oxygen deficiency-rich V_(2)O_(3)@PEDOT cathode for high-performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries(AZIBs)have attracted widespread attention due to the advantages of high safety and environmental friendliness.Although V_(2)O_(3) is a promising cathode,the strong electrostatic interaction between Zn^(2+) and V_(2)O_(3) crystal,and the sluggish reaction kinetics still limit their application in AZIBs.Herein,the oxygen defects rich V_(2)O_(3) with conducive poly(3,4-ethylenedioxythiophene)(PEDOT)shell(V_(2)O_(3)-Od@PEDOT)was fabricated for AZIBs by combining the sulfur-assisted thermal reduction and in-situ polymerization method.The introduced oxygen vacancies of V_(2)O_(3)–Od@PEDOT weaken the electrostatic interaction between Zn^(2+) and the host material,improving the interfacial electron transport,while the PEDOT coating enhances the structural stability and conductivity of V_(2)O_(3),thus accelerating the reaction kinetics.Based on the advantages,V_(2)O_(3)–Od@PEDOT electrode delivers a reversible capacity of 495 mAh·g^(−1) at 0.1 A·g^(−1),good rate capability(189 mAh·g^(−1)at 8.0 A·g^(−1)),and an impressive cycling stability with 90.1%capacity retention over 1000 cycles at 8.0 A·g^(−1).The strategy may provide a path for exploiting the other materials for high performance AZIBs.

V_(2)O_(3)/VO_(2)@S/N-C nanofibers with excellent cycling stability and superior rate capability in aqueous zinc ion batteries

The development of aqueous zinc-ion batteries (AZIBs) marks a significant advancement in the field of sustainable and environmentally friendly energy storage.To address the challenges faced by singlephase vanadium-based oxides,such as poor conductivity and dissolution in electrolytes,this study introduces vacuum S/N doping to fabricate V_(2)O_(3)/VO_(2)@S/N-C nanofibers,improving the cycling stability and enhancing the capacity.The V_(2)O_(3)/VO_(2)@S/N-C electrode exhibits exceptional cyclic stability,retaining a capacity of 133.3 m A h g^(-1)after 30,000 cycles at a high current density of 100 A g^(-1)and a capacity retention of 81.8%after 150,000 cycles at 200 A g^(-1).Characterizations using ex-situ X-ray diffraction and ex-situ X-ray photoelectron spectroscopy reveal co-intercalation of H^(+)and Zn^(2+)in the V_(2)O_(3)/VO_(2)@S/N-C electrode.Due to the presence of S_(2)^(2-),more phases changed to V_(10)O_(24).12H_(2)O,making the V_(2)O_(3)/VO_(2)@S/N-C electrode better reversible.By elucidating the zinc storage mechanism and demonstrating the stable performance of the doped electrode,this work contributes valuable insights into the optimization of the electrode materials for future energy storage solutions.

Freestanding reduced graphene oxide/sodium vanadate composite films for flexible aqueous zinc-ion batteries

With the booming development of portable and wearable electronic devices, flexible energy storage devices have attracted great attention. Among various energy storage devices, aqueous zinc ion batteries(ZIBs) are one of the promising candidates due to their low cost, good safety, high energy and power densities. However, the conventional cathodes of aqueous ZIBs were often prepared by mixing active materials with binders and conductive additives and then coating them onto current collectors. The resultant cathodes often suffer from unsatisfied flexibility. Herein, we fabricated freestanding reduced graphene oxide/NaV_3O_8·1.5H_2O(RGO/NVO) composite films with interlinked multilayered architecture by a vacuum filtrating process. Such composite films exhibit excellent mechanical property and high electronic conductivity. Owing to unique architecture, they display a high capacity of 410 mA h g^(-1) and excellent cycling performance up to 2000 cycles with a high capacity retention of 94%. Moreover, RGO/NVO composite films can directly serve as the cathodes of flexible aqueous ZIBs. As a proof of concept,flexible ZIBs were assembled based on the composite films. Impressively, they exhibit stable performance at different bending states, demonstrating great potential application in flexible energy storage devices.

Structural engineering of cathodes for improved Zn-ion batteries

Aqueous zinc-ion batteries(ZIBs) are attracting considerable attention because of their low cost,high safety and abundant anode material resources.However,the major challenge faced by aqueous ZIBs is the lack of stable and high capacity cathode materials due to their complicated reaction mechanism and slow Zn-ion transport kinetics.This study reports a unique 3 D ’flower-like’ zinc cobaltite(ZnCo_(2)O_(4-x)) with enriched oxygen vacancies as a new cathode material for aqueous ZIBs.Computational calculations reveal that the presence of oxygen vacancies significantly enhances the electronic conductivity and accelerates Zn^(2+) diffusion by providing enlarged channels.The as-fabricated batteries present an impressive specific capacity of 148.3 mAh g^(-1) at the current density of 0.05 A g^(-1),high energy(2.8 Wh kg^(-1)) and power densities(27.2 W kg^(-1)) based on the whole device,which outperform most of the reported aqueous ZIBs.Moreover,a flexible solid-state pouch cell was demonstrated,which delivers an extremely stable capacity under bending states.This work demonstrates that the performance of Zn-ion storage can be effectively enhanced by tailoring the atomic structure of cathode materials,guiding the development of low-cost and eco-friendly energy storage materials.

Synergistic Effect of Cation and Anion for Low-Temperature Aqueous Zinc-Ion Battery

Although aqueous zinc-ion batteries have gained great development due to their many merits,the frozen aqueous electrolyte hinders their practical application at low temperature conditions.Here,the synergistic e ect of cation and anion to break the hydrogen-bonds network of original water molecules is demonstrated by multi-perspective characterization.Then,an aqueous-salt hydrates deep eutectic solvent of 3.5 M Mg(ClO_(4))_(2)+1 M Zn(ClO_(4))_(2)is proposed and displays an ultralow freezing point of-121℃.A high ionic conductivity of 1.41 mS cm-1 and low viscosity of 22.9 mPa s at-70℃ imply a fast ions transport behavior of this electrolyte.With the benefits of the low-temperature electrolyte,the fabricated Zn||Pyrene-4,5,9,10-tetraone(PTO)and Zn||Phenazine(PNZ)batteries exhibit satisfactory low-temperature performance.For example,Zn||PTO battery shows a high discharge capacity of 101.5 mAh g^(-1)at 0.5 C(200 mA g^(-1))and 71 mAh g^(-1)at 3C(1.2 A g^(-1))when the temperature drops to-70℃.This work provides an unique view to design anti-freezing aqueous electrolyte.

Deciphering H^(+)/Zn^(2+) co-intercalation mechanism of MOF-derived2D MnO/C cathode for long cycle life aqueous zinc-ion batteries

Poor conductivity,sluggish ion diffusion kinetics and short cycle life hinder the further development of manganese oxide in aqueous zinc-ion batteries(AZIBs).Exploring a cathode with high capacity and long cycle life is critical to the commercial development of AZIBs.Herein,a two-dimensional(2D) MnO/C composite derived from metal organic framework(MOF) was prepared.The 2D MnO/C cathode exhibits a remarkably cyclic stability with the capacity retention of 90.6% after 900 cycles at 0.5 A·g^(-1) and maintains a high capacity of 120.2 mAh·g^(-1)after 4500 cycles at 1.0 A·g^(-1).It is demonstrated that MnO is converted into Mn_(3)O_(4) through electrochemical activation strategy and shows a Zn^(2+)and H^(+)co-intercalation mechanism.In general,this work provides a new path for the development of high-performance AZIBs cathode with controllable morphology.