Recent progress of self-supported air electrodes for flexible Zn-air batteries

Smart wearable devices are regarded to be the next prevailing technology product after smartphones and smart homes,and thus there has recently been rapid development in flexible electronic energy storage devices.Among them,flexible solid-state zinc-air batteries have received widespread attention because of their high energy density,good safety,and stability.Efficient bifunctional oxygen electrocatalysts are the primary consideration in the development of flexible solid-state zinc-air batteries,and self-supported air cathodes are strong candidates because of their advantages including simplified fabrication process,reduced interfacial resistance,accelerated electron transfer,and good flexibility.This review outlines the research progress in the design and construction of nanoarray bifunctional oxygen electrocatalysts.Starting from the configuration and basic principles of zinc-air batteries and the strategies for the design of bifunctional oxygen electrocatalysts,a detailed discussion of self-supported air cathodes on carbon and metal substrates and their uses in flexible zinc-air batteries will follow.Finally,the challenges and opportunities in the development of flexible zinc-air batteries will be discussed.

Revisiting aluminum current collector in lithium-ion batteries:Corrosion and countermeasures

With the large-scale service of lithium-ion batteries(LIBs),their failures have attracted significant attentions.While the decay of active materials is the primary cause for LIB failures,the degradation of auxiliary materials,such as current collector corrosion,should not be disregarded.Therefore,it is necessary to conduct a comprehensive review in this field.In this review,from the perspectives of electrochemistry and materials,we systematically summarize the corrosion behavior of aluminum cathode current collector and propose corresponding countermeasures.Firstly,the corrosion type is clarified based on the properties of passivation layers in different organic electrolyte components.Furthermore,a thoroughgoing analysis is presented to examine the impact of various factors on aluminum corrosion,including lithium salts,organic solvents,water impurities,and operating conditions.Subsequently,strategies for electrolyte and protection layer employed to suppress corrosion are discussed in detail.Lastly and most importantly,we provide insights and recommendations to prevent corrosion of current collectors,facilitate the development of advanced current collectors and the implementation of next-generation high-voltage stable LIBs.

Reversible aqueous aluminum metal batteries enabled by a water-in-salt electrolyte

Aluminum(Al),the most abundant metallic element on the earth crust,has been reckoned as a promising battery material for its the highest theoretical volume capacity(8046 mAh cm^(-3)).Being rechargeable in ionic liquid electrolytes,however,the Al anode and battery case suffer from corrosion.On the other hand,Al is irreversible in aqueous electrolyte with severe hydrogen evolution reaction.Here,we demonstrate a water-in-salt aluminum ion electrolyte(WISE)based on Al and lithium salts to tackle the above challenges.In the WISE system,water molecules can be confined within the Li^(+)solvation structures.This diminished Al^(3+)-H_(2)O interaction essentially eliminates the hydrolysis effect,effectively protecting Al anode from corrosion.Therefore,long-term Al plating/stripping can be realized.Furthermore,two types of high-performance full batteries have been demonstrated using copper hexacyanoferrate(CuHCF,a Prussian Blue Analogues)and LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM)as cathodes.The reversibility of Al anode laid the foundation for low cost rechargeable batteries suffering for large-scale energy storage.Broader context:Al batteries are expected to become a safe and sustainable alternative to lithium batteries.For decades,chase for a feasible Al secondary battery has not been successful.The key challenge is to find suitable cathode and electrolyte materials,together with which Al anode battery can function reversibly.Currently,fatal drawbacks have impeded the practical application of Al metal batteries(AMBs),such as sustained corrosion of Al anode and battery case in ionic liquid electrolytes,irreversibility issues as well as severe hydrogen evolution reaction during cycling in aqueous electrolyte.Therefore,electrolyte and their electrochemical kinetics play a vital role in the performance and environmental operating limitations of high-energy Al metal batteries.In this work,we demonstrate a nearly neutral Al ion water-in-salt electrolyte(WISE)to tackle the above challenges.The WISE shows excellent stability in the open atmosphere.The distinct solvation-sheath structure of Al^(3+)in the WISE system would protect Al metal anodes from corrosion and eliminate hydrogen evolution reaction effectively,further promoting the reversibility of Al metal anodes with dendrite-free morphology.Moreover,such a WISE exhibits superior compatibility with LiNi_(0.3)Co_(0.3)Mn_(0.3)O_(2)(NCM)and copper hexacyanoferrate(CuHCF)cathodes and long-term stabilities with high coulombic efficiency(CE)can be attained for full batteries with the WISE.The approach in this study can furnish an opportunity to develop reversible AMBs and lay the foundation for other potential multivalent-metalbased secondary batteries suffering from interface passivation and poor reversibility,which suggest the promise of multivalent metal batteries and their applications in large-scale energy storage.

Wood-derived freestanding integrated electrode with robust interface-coupling effect boosted bifunctionality for rechargeable zinc-air batteries

Fabricating non-noble metal-based carbon air electrodes with highly efficient bifunctionality is big challenge owing to the sluggish kinetics of oxygen reduction/evolution reaction(ORR/OER).The efficient cathode catalyst is urgently needed to further improve the performance of rechargeable zinc-air batteries.Herein,an activation-doping assisted interface modification strategy is demonstrated based on freestanding integrated carbon composite(CoNiLDH@NPC)composed of wood-based N and P doped active carbon(NPC)and CoNi layer double hydroxides(CoNiLDH).In the light of its large specific surface area and unique defective structure,CoNiLDH@NPC with strong interfacecoupling effect in 2D-3D micro-nanostructure exhibits outstanding bifunctionality.Such carbon composites show half-wave potential of 0.85 V for ORR,overpotential of 320 mV with current density of 10 mA cm^(-2) for OER,and ultra-low gap of 0.70 V.Furthermore,highly-ordered open channels of wood provide enormous space to form abundant triple-phase boundary for accelerating the catalytic process.Consequently,zinc-air batteries using CoNiLDH@NPC show high power density(aqueous:263 mW cm^(-2),quasi-solid-state:65.8 mW cm^(-2))and long-term stability(aqueous:500 h,quasi-solid-state:120 h).This integrated protocol opens a new avenue for the rational design of efficient freestanding air electrode from biomass resources.

Constructing“π–π”Reinforced Bridge Carbon Nanofibers with Highly Active Co‑N/C@pyridine N/C@CNTs Sites as Free‑Standing Bifunctional Oxygen Electrodes for Zn–Air Batteries

Rechargeable Zn-air batteries(ZABs)have received extensive attention,while their real applications are highly restricted by the slow kinetics of the oxygen reduction and oxygen evolution reactions(ORR/OER).Herein,we report a“bridge”structured flexible self-supporting bifunctional oxygen electrode(CNT@Co-CNFF50-900)with strong active and stable Co-N/C@pyridine N/C@CNTs reaction centers.Benefiting from the electron distribution optimization and the advantages of hierarchical catalytic design,the CNT@Co-CNF_(F50-900)electrode had superior ORR/OER activity with a small potential gap(ΔE)of 0.74 V.Reinforced by highly graphitized carbon and the“π-π”bond,the free-standing CNT@Co-CNFF50-900 electrode exhibited outstanding catalytic stability with only 36 mV attenuation.Impressively,the CNT@Co-CNFF50-900-based liquid ZAB showed a high power density of 371 mW cm^(−2),a high energy density of 894 Wh kg^(−1),and a long cycling life of over 130 h.The assembled quasi-solid-state ZAB also demonstrated a high power density,attaining 81 mW cm^(−2),with excellent charge-discharge durability beyond 100 h and extremely high flexibility under the multi-angle application.This study provides an effective electrospinning solution for integrating high-efficiency electrocatalysts and electrodes for energy storage and conversion devices.

A comprehensive review on recent progress in aluminum-air batteries

The aluminum-air battery is considered to be an attractive candidate as a power source for electric vehicles(EVs) because of its high theoretical energy density(8100 Wh kg^(-1)), which is significantly greater than that of the state-of-the-art lithium-ion batteries(LIBs). However,some technical and scientific problems preventing the large-scale development of Al-air batteries have not yet to be resolved. In this review, we present the fundamentals, challenges and the recent advances in Al-air battery technology from aluminum anode, air cathode and electrocatalysts to electrolytes and inhibitors. Firstly, the alloying of aluminum with transition metal elements is reviewed and shown to reduce the selfcorrosion of Al and improve battery performance. Additionally for the cathode, extensive studies of electrocatalytic materials for oxygen reduction/evolution including Pt and Pt alloys, nonprecious metal catalysts, and carbonaceous materials at the air cathode are highlighted.Moreover, for the electrolyte, the application of aqueous and nonaqueous electrolytes in Al-air batteries are discussed. Meanwhile, the addition of inhibitors to the electrolyte to enhance electrochemical performance is also explored. Finally, the challenges and future research directions are proposed for the further development of Al-air batteries.

3D porous reduced graphene cathode and non-corrosive electrolyte for long-life rechargeable aluminum batteries

Owing to their high volumetric capacity,low cost and high safety,rechargeable aluminum batteries have become promising candidates for energy applications.However,the high charge density of Al^(3+)leads to strong coulombic interactions between anions and the cathode,resulting in sluggish diffusion kinetics and irreversible collapse of the cathode structure.Furthermore,AlCl_(3)-based ionic liquids,which are commonly used as electrolytes in such batteries,corrode battery components and are prone to side reactions.The above problems lead to low capacity and poor cycling stability.Herein,we propose a reduced graphene oxide(rGO)cathode with a three-dimensional porous structure prepared using a simple and scalable method.The lamellar edges and oxygen-containing group defects of rGO synergistically provide abundant ion storage sites and enhance ion transfer kinetics.We matched the prepared rGO cathode with noncorrosive electrolyte 0.5 mol·L^(-1) Al(OTF)_(3)/[BMIM]OTF and Al metal to construct a high-performance battery,Al||rGO-150,with good cycling stability for 2700 cycles.Quasi-in-situ physicochemical characterization results show that the ion storage mechanism is codominated by diffusion and capacitance.The capacity consists of the insertion of Al-based species cations as well as synergistic adsorption of Al(OTF)_(x)^((3-x)+)(x<3)and[BMIM]+.The present study promotes the fundamental and applied research on rechargeable aluminum batteries.

Catalytic effect in lithium metal batteries: From heterogeneous catalyst to homogenous catalyst

Lithium metal batteries are regarded as prominent contenders to address the pressing needs owing to the high theoretical capacity.Toward the broader implementation,the primary obstacle lies in the intricate multi-electron,multi-step redox reaction associated with sluggish conversion kinetics,subsequently giving rise to a cascade of parasitic issues.In order to smooth reaction kinetics,catalysts are widely introduced to accelerate reaction rate via modulating the energy barrier.Over past decades,a large amount of research has been devoted to the catalyst design and catalytic mechanism exploration,and thus the great progress in electrochemical performance has been realized.Therefore,it is necessary to make a comprehensive review toward key progress in catalyst design and future development pathway.In this review,the basic mechanism of lithium metal batteries is provided along with corresponding advantages and existing challenges detailly described.The main catalysts employed to accelerate cathode reaction with emphasis on their catalytic mechanism are summarized as well.Finally,the rational design and innovative direction toward efficient catalysts are suggested for future application in metal-sulfur/gas battery and beyond.This review is expected to drive and benefit future research on rational catalyst design with multi-parameter synergistic impacts on the activity and stability of next-generation metal battery,thus opening new avenue for sustainable solution to climate change,energy and environmental issues,and the potential industrial economy.

Effect of lithium or aluminum substitution on the characteristics of graphite for anode of lithium ion batteries

Modification of graphite for anode of lithium ion batteries is investigated.Results of X-ray diffraction shows lithium and aluminum exists as Li compound (CH_3COOLi.2 H_2O) andAl compound (AlD_3) in the graphite, respectiovely. The Brunauer-Emmer-Teller (BET) surface area ofthe modified graphite increases. According to the electrochemical measurements of Li/C cell andprototype Li-ion batteries, the Li-doped graphite has large reversible capacity of 312.2 mA.h/g, lowirreversible capacity of 52.9 mA.h/g, and high initial coulombic efficiency of 85.51 percent. The063448 size prototype battery with Li-doped graphite anode has large discharge capacity of 845 mA.hand good cycling performance. The initial charge/discharge characteristic of Al-doped graphite isclose to those of undoped graphite, but the prototype battery with Al-doped anode shows the bestcycling performance with capacity retention ratio of 94.06 percent at the 200 th cycle.

Recent progress in rechargeable alkali metal-air batteries

Rechargeable alkali metal-air batteries are considered as the most promising candidate for the power source of electric vehicles(EVs) due to their high energy density. However, the practical application of metal-air batteries is still challenging. In the past decade, many strategies have been purposed and explored, which promoted the development of metal-air batteries. The reaction mechanisms have been gradually clarified and catalysts have been rationally designed for air cathodes. In this review, we summarize the recent development of alkali metal-air batteries from four parts: metal anodes, electrolytes, air cathodes and reactant gases, wherein we highlight the important achievement in this filed. Finally problems and prospective are discussed towards the future development of alkali metal-air batteries.

Effect of Ga on microstructure and electrochemical performance of Al−0.4Mg−0.05Sn−0.03Hg alloy as anode for Al−air batteries

The effects of 0.01 wt.%Ga on microstructure and electrochemical performance of Al−0.4Mg−0.05Sn−0.03Hg anodes in NaOH solutions were investigated.Potentiodynamic polarization,electrochemical impedance spectroscopy,and galvanostatic discharge tests were used to assess the electrochemical performance of the Al−Mg−Sn−Hg−Ga anodes.The results show that the addition of 0.01 wt.%Ga in Al−0.4Mg−0.05Sn−0.03Hg anode enhances its corrosion resistance and discharge activity.It is benefited from the refined second phases and homogenous microstructure of Al−Mg−Sn−Hg−Ga anode,which restrains the local crystallographic corrosion and chunk effect.Compared with Al−Mg−Sn−Hg anode,the corrosion current density and the mass loss rate of Al−Mg−Sn−Hg−Ga anode decrease by 57%and 93%,respectively.When discharging at the current density of 20 mA/cm^(2),the discharge voltage,current efficiency and specific capacity of the single Al−air battery with Al−0.4Mg−0.05Sn−0.03Hg−0.01Ga anode are 1.46 V,33.1%,and 1019.2 A·h·kg^(−1),respectively.The activation mechanism of Ga on Al−Mg−Sn−Hg−Ga anode materials was also discussed.

In-situ emb e dding zeolitic imidazolate framework derived Co–N–C bifunctional catalysts in carbon nanotube networks for flexible Zn–air batteries

Recently, the development of high-performance bifunctional oxygen catalysts integrated with flexible conductive scaffolds f or rechargeable metal-air batteries has attracted considerable interest, driving by fastgrowing wearable electronics. Herein, we report a flexible bifunctional oxygen catalyst thin film consisting of Co–N–C bifunctional catalysts embedding in carbon nanotube(CNT) networks. The catalyst is readily prepared by pyrolysis of cobalt-based zeolitic imidazolate frameworks(ZIF-67) that are in-situ synthesized in CNT networks. Such catalyst film demonstrates very high catalytic activities for oxygen reduction(onset potential: 0.91 V, and half-wave potential: 0.87 V vs. RHE) and oxygen evolution(10 m Acm^-2 at 1.58 V) reactions, high methanol tolerance property, and long-term stability(97% current retention). Moreover, our integrated catalyst film shows very good structure flexibility and robustness. Based on the obtained film air electrodes, flexible Zn–air batteries demonstrate low charging and discharging overpotentials(0.82 V at 1 m A cm^-1) and excellent structure stability in the bending tests. These results indicate that presently reported catalyst films are potential air electrodes for flexible metal–air batteries.

Toward better electrode/electrolyte interfaces in the ionic-liquid-based rechargeable aluminum batteries

The past decade has witnessed the germination of rechargeable aluminum batteries(RABs)with the colossal potential to enact as a device for the large scale energy storage and conversion.The Majority of investigations are dedicated to the exploration of suitable cathode materials,while less is known about the electrode/electrolyte interfaces that determine the electrochemistry of batteries.In this perspective,we will highlight the significance of electrode/electrolyte interface for RABs,in overall kinetics and capacity retention.Emphasis will be laid on the complicated yet basic understandings of the phenomena at the interfaces,including the dendrite growth,surface Al2O3 and solid–electrolyte-interphase(SEI).And we will summarize the reported practice in effort to build better electrode/electrolyte interfaces in RAB.In the end,outlook regarding to the challenges,opportunities and directions is presented.

Recent Advances on MOF Derivatives for Non-Noble Metal Oxygen Electrocatalysts in Zinc-Air Batteries

Oxygen electrocatalysts are of great importance for the air electrode in zinc-air batteries(ZABs).Owing to the high specific surface area,controllable pore size and unsaturated metal active sites,metal-organic frameworks(MOFs)derivatives have been widely studied as oxygen electrocatalysts in ZABs.To date,many strategies have been developed to generate efficient oxygen electrocatalysts from MOFs for improving the performance of ZABs.In this review,the latest progress of the MOF-derived non-noble metal-oxygen electrocatalysts in ZABs is reviewed.The performance of these MOF-derived catalysts toward oxygen reduction,and oxygen evolution reactions is discussed based on the categories of metal-free carbon materials,single-atom catalysts,metal cluster/carbon composites and metal compound/carbon composites.Moreover,we provide a comprehensive overview on the design strategies of various MOF-derived non-noble metal-oxygen electrocatalysts and their structure-performance relationship.Finally,the challenges and perspectives are provided for further advancing the MOF-derived oxygen electrocatalysts in ZABs.

A review on system and materials for aqueous flexible metal-air batteries

The exploration of aqueous flexible metal-air batteries with high energy density and durability has attracted many research efforts with the demand for portable and wearable electronic devices.Aqueous flexible metal-air batteries feature Earth-abundant materials,environmental friendliness,and operational safety.Each part of one metal-air battery can significantly affect the overall performance.This review starts with the fundamental working principles and the basic battery configurations and then highlights on the common issues and the recent advances in designing high-performance metal electrodes,solid-state electrolytes,and air electrodes.Bifunctional oxygen electrocatalysts with high activity and long-term stability for constructing efficient air electrodes in flexible metal-air batteries are summarized including metal-free carbon-based materials and nonprecious Co/Fe-based materials(alloys,metal oxides,metal sulfites,metal phosphates,metal nitrates,single-site metal-nitrogen-carbon materials,and composites).Finally,a perspective is provided on the existing challenges and possible future research directions in optimizing the performance and lifetime of the flexible aqueous solid-state metal-air batteries.

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

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

Carbon-based cathode materials for rechargeable zinc-air batteries: From current collectors to bifunctional integrated air electrodes

Rechargeable zinc-air batteries(ZABs)have attracted much attention as the next-generation energy conversion and storage devices due to the abundance and environmental friendliness of zinc(Zn)for anode materials,as well as the safety and low cost of aqueous electrolytes.However,rational design of nonprecious and low-cost integrated air cathode materials with a desirable bifunctional oxygen electrocatalytic performance remains a great challenge for the commercialization of rechargeable ZABs.In previous research studies,various cost-effective carbon-supported electrocatalysts and light-weight carbon-based current collectors for air cathodes have been developed,showing vast potential in the application of carbon-based materials.To improve the bifunctional performance and integration of air cathodes,efforts with respect to the design of morphology,defects,and synergistic effects of carbon-based materials have been made.In this perspective,the general understanding of the air cathode construction and the battery working mechanism is discussed.The recent progress in the design of carbon-based materials for air cathodes in rechargeable ZABs is summarized.Several possible future research directions and the expected development trends are also discussed,aiming to facilitate the commercialization of advanced rechargeable ZABs in our life.

Reversible Al^(3+) storage mechanism in anatase TiO_(2) cathode material for ionic liquid electrolyte-based aluminum-ion batteries

Rechargeable aluminum ion battery(AIB) with high theoretical specific capacity, abundant elements and low cost engages considerable attention as a promising next generation energy storage and conversion system. Nevertheless, to date, one of the major barriers to pursuit better AIB is the limited applicable cathode materials with the ability to store aluminum highly reversibly. Herein, a highly reversible AIB is proposed using mesoporous TiO2 microparticles(M-TiO2) as the cathode material. The improved performance of Ti O2/Al battery is ascribed to the high ionic conductivity and material stability, which is caused by the stable architecture with a mesoporous microstructure and no random aggregation of secondary particles. In addition, we conducted detailed characterization to gain deeper understanding of the Al^(3+) storage mechanism in anatase Ti O2 for AIB. Our findings demonstrate clearly that Al^(3+)can be reversibly stored in anatase TiO2 by intercalation reactions based on ionic liquid electrolyte. Especially, DFT calculations were used to investigate the accurate insertion sites of aluminum ions in M-Ti O2 and the volume changes of M-TiO2 cells during discharging. As for the controversial side reactions in AIBs, in this work, by normalized calculation, we confirm that M-Ti O2 alone participate in the redox reaction. Moreover, cyclic voltammetry(CV) test was performed to investigate the pseudocapacitive behavior.

Efficient spinel iron‐cobalt oxide/nitrogen‐doped ordered mesoporous carbon catalyst for rechargeable zinc‐air batteries

A robust oxygen‐related electrocatalyst,composed of spinel iron‐cobalt oxide and nitrogen‐dopedordered mesoporous carbon(NOMC),was developed for rechargeable metal‐air batteries.Electrochemicaltests revealed that the optimal catalyst Fe_(0.5)Co/NOMC exhibits superior activity with ahalf‐wave potential of 0.89 V(vs.reversible hydrogen electrode)for the oxygen reduction reactionand an overpotential of 0.31 V at 10 mA cm^(−2)for the oxygen evolution reaction.For demonstration,the catalyst was used in the assembly of a rechargeable zinc‐air battery,which exhibited an exceptionallyhigh energy density of 820 Wh kg−1 at 100 mA cm^(−2),a high power density of 153 mW cm^(−2)at1.0 V,and superior cycling stability up to 432 cycles(144 h)under ambient air.

Sulfur-linked carbonyl polymer as a robust organic cathode for rapid and durable aluminum batteries

Rechargeable aluminum batteries are believed as a promising next-generation energy-storage system due to abundant low-cost Al sources and high volumetric specific capacity.The Al-storage cathodes,however,are plagued by strong electrostatic interaction between host materials and carrier ions,leading to large overpotential and undesired cycling stability as well as sluggish ion diffusion kinetics.Herein,sulfur-linked carbonyl polymer based on perylene-3,4,9,10-tetracarboxylic dianhydride(PTCDA) as the cathode materials for ABs is proposed,which demonstrates a small voltage polarization(135 mV),a reversible capacity of 110 mAh g^(-1) at 100 mA g^(-1) even after 1200 cycles,and rapid Al-storage kinetics.Compared with PTCDA,the sulfide polymer possesses higher working voltage because of its lower LUMO energy level according to theoretical calculation.The ordered carbonyl active sites in sulfide polymer contribute to the maximized material utilization and rapid ion coordination and dissociation,resulting in superior rate capability.Besides,the bridged thioether bonds endow the polysulfide with robust and flexible structure,which inhibits the dissolution of active materials and improves cycling stability.This work implies the importance of ordered arrangement of redox active moieties for organic electrode,which provides the theoretical direction for the structural design of organic materials applied in multivalent-ion batteries.