Flexible Zinc-air Batteries Research Articles

Highly adhesive hydrogel electrolytes driven by adenosine monophosphate and Fe3+ for high-voltage asymmetric flexible zinc-air batteries

Flexible zinc-air batteries (ZABs) are a promising power source for wearable electronics, owing to their high energy density and low cost. However, the limited operating voltage of about 1.4 V and the complex external packaging of conventional ZABs hinder their practical application. Herein, a hydrogel electrolyte (PAMA-ANa/Fe3+) is rapidly prepared for flexible ZABs using copolymers of acrylamide and acrylic acidic (PAMA), along with sodium adenosine-5′-monophosphate (AMPNa) and Fe3+. By leveraging the synergistic effects of exceptional mechanical properties, strong adhesion and the acidic-alkaline decoupling of the PAMA-ANa/Fe3+ hydrogel electrolyte, an asymmetric flexible ZAB (AF-ZAB) based on an acidic-alkaline double-layer PAMA-ANa/Fe3+ hydrogel electrolyte is assembled in a simple and rapid manner. This AF-ZAB achieves an excellent operating voltage of 2.15 V and a high power density of 75.86 mW cm−2. This study provides a new method and strategy for the development and assembly of novel high-voltage flexible quasi-solid-state batteries and other energy storage devices.

Iron-Cobalt Phosphide Encapsulated in a N-Doped Carbon Framework as a Promising Low-Cost Oxygen Reduction Electrocatalyst for Zinc-Air Batteries.

The oxygen reduction reaction (ORR) plays a vital role in many next-generation electrochemical energy conversion and storage devices, motivating the search for low-cost ORR electrocatalysts possessing high activity and excellent durability. In this work, we demonstrate that iron-cobalt phosphide (FeCoP) nanoparticles encapsulated in a N-doped carbon framework (FeCoP@NC) represent a very promising catalyst for the ORR in alkaline media. The core-shell structured FeCoP@NC catalyst offered outstanding ORR activity with a half-wave potential (E1/2) of 0.86 V vs reversible hydrogen electrode (RHE) and excellent stability in a 0.1 M KOH electrolyte, outperforming commercial Pt/C and many recently reported noble-metal-free ORR electrocatalysts. The superiority of FeCoP@NC as an ORR electrocatalyst relative to Pt/C was further verified in prototype zinc-air batteries (ZABs), with the aqueous and flexible ZABs prepared using FeCoP@NC offering excellent stability, impressive open circuit voltages (1.56 and 1.44 V, respectively), and high maximum power densities (183.5 and 69.7 mW cm-2, respectively). Density functional theory calculations revealed that encapsulating FeCoP nanoparticles in N-doped carbon shells resulted in favorable electron penetration effects, which synergistically regulated the adsorption/desorption of ORR intermediates for optimal ORR performance while also boosting the electronic conductivity. Our findings offer valuable new insights for rational design of transition metal phosphide-based catalysts for the ORR and other electrochemical applications.

Internally connected porous PVA/PAA membrane with cross-aligned nanofiber network for facile and long-lasting ion transport in zinc–air batteries

In response to the growing interest in next-generation wearable devices, the demand for high-performance, safe, and flexible power sources has increased. Flexible zinc–air batteries (ZABs) based on gel polymer electrolytes (GPEs) have emerged as promising candidates for wearable power sources owing to their high energy density, safety, and cost efficiency. However, persistent electrolyte evaporation through the air cathode poses a significant challenge, resulting in poor lifespan characteristics that impede practical applications. In this study, we developed a polymer composite-type GPE composed of cross-aligned nanofibers (NFs) of a polyacrylic acid (PAA)-based framework embedded in a polyvinyl alcohol (PVA) matrix. Upon immersion in a liquid electrolyte (6 M KOH), the superabsorbent PAA spontaneously generated an internally connected porous (IP) structure adjacent to the aligned PAA NFs. These pores served as directional water channels, facilitating rapid hydroxide ion conduction and yielding a remarkable ionic conductivity of 235.7 mS cm−1. The PVA matrix acts as both a packaging material and the main body of the GPE, providing good dimensional stability and mitigating the swelling of PAA, even under conditions of high electrolyte uptake, while also ensuring high flexibility. The IP-PVA/PAA composite GPE demonstrated a high power output, rate performance, and excellent lifespan in flexible ZABs. Furthermore, successful operation at various bending angles provides empirical evidence supporting the viable application of flexible ZABs.

A lignocellulose-based hydrogel polymer electrolytes with high conductivity and stability for rechargeable flexible zinc-air batteries

Flexible Zinc-Air batteries (FZABs) have been extensively investigated by researchers due to their exceptional safety and high energy density. The sandwich structure employed in FZABs imposes stringent demands on the electrolyte, necessitating good electrical conductivity and alkali resistance. In this paper, a carboxylation@Lignocellulose-based hydrogel polymer electrolyte with high ionic conductivity and excellent alkali resistance has designed and applied in FZABs. The carboxylation@lignocellulose is dissolved in a sodium hydroxide/urea/water system, followed by the incorporation of acrylamide monomers into the lignocellulose solution to prepare the hydrogel polymer electrolyte. The results combined suggest that the solid electrolyte exhibits improved ion conductivity, liquid absorption capability, and alkali resistance. Therefore, it has been confirmed that carboxyl functional groups have a positive effect on the performance of solid electrolytes. These characteristics enable the lignocellulose-based hydrogel polymer electrolyte FZAB to have an open-circuit voltage (1.34 V), a peak power density (141.55 mW cm−2), and a cycle lifetime to 65 h (555 cycles). Compared to FZABs based polyacrylamide-KOH hydrogel polymer electrolyte-based, FZABs utilizing lignocellulose-based hydrogel polymer electrolyte prepared in this paper demonstrate excellent performance.

Electron Spin Broken-Symmetry of Fe-Co Diatomic Pairs to Promote Kinetics of Bifunctional Oxygen Electrocatalysis for Zinc-Air Batteries.

Designing bifunctional catalysts to reduce the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) reaction barriers while accelerating the reaction kinetics is perceived to be a promising strategy to improve the performance of Zinc-air batteries. Unsymmetric configuration in single-atom catalysts has attracted attention due to its unique advantages in regulating electron orbitals. In this work, a seesaw effect in unsymmetric Fe-Co bimetallic monoatomic configurations is proposed, which can effectively improve the OER/ORR bifunctional activity of the catalyst. Compared with the symmetrical model of Fe-Co, a strong charge polarization between Co and Fe atoms in the unsymmetric model is detected, in whom the spin-down electrons around Co atoms are much higher than those spin-up electrons. The seesaw effect occurred between Co atoms and Fe atoms, resulting in a negative shift of the d-band center, which means that the adsorption of oxygen intermediates is weakened and more conducive to their dissociation. The optimized reaction kinetics of the catalyst leads to excellent performance in ZABs, with a peak power density of 215mW cm-2 and stable cycling for >1300 h and >4000 cycles. Flexible Zinc-air batteries have also gained excellent performance to demonstrate their potential in the field of flexible wearables.

Double-skeleton interpenetrating network-structured alkaline solid-state electrolyte enables flexible zinc-air batteries with enhanced power density and long-term cycle life

The alkaline solid-state electrolytes have received widespread attention for their good safety and electrochemical stability. However, they still suffer from low conductivity and poor mechanical properties. Herein, we report the synthesis of double-network featured hydroxide-conductive membranes fabricated by polyvinyl alcohol (PVA) and chitosan (CS) as the double-skeletons. Then, we implanted quaternary ammonium salt guar hydroxypropyltrimonium chloride (GG) as the OH− conductor for high-performance electrochemical devices. By virtue of the unique stripe-like structure shared from the double skeleton with a high degree of compatibility and stronger hydrogen bond interactions, the polyvinyl alcohol/chitosan-guar hydroxypropyltrimonium chloride (PCG) solid-state electrolytes achieved optimal thermal stability (> 300 °C), mechanical property (∼ 34.15 MPa), dimensional stability (at any bending angle), and high ionic conductivity (13 mS cm−1) and ion mobility number (tion ∼ 0.90) compared with chitosan-guar hydroxypropyltrimonium chloride (CG) and polyvinyl alcohol-guar hydroxypropyltrimonium chloride (PG) electrolyte membrane. As a proof-of-concept application, the “sandwich”-type zinc-air battery (ZAB) assembled using PCG membrane as the electrolyte realized a high open-circuit voltage (1.39 V) and an excellent power density (128 mW cm−2). Notably, in addition to its long-term cycle life (30 h, 2 mA cm−2) and stable discharge plateau (12 h, 5 mA cm−2), it could even enable a flexible ZAB (F-ZAB) to readily power light-emitting diodes (LED) at any bending angle. These merits afford the PCG membrane a promising electrolyte for improving the performance of solid-state batteries.

Fe Single Atoms Encased in Nanoscale Zif-8 Dodecahedra for Oxygen Reduction and Flexible Zinc–Air Batteries

Fe Single Atoms Encased in Nanoscale Zif-8 Dodecahedra for Oxygen Reduction and Flexible Zinc–Air Batteries

Kirkendall effect induced the formation of hollow Co2P in Co-N-C for ORR, OER, HER and flexible Zn–Air battery

Enhancing the exposure of active sites and optimizing the electronic structure of the catalysts are indispensable for efficient catalyst design, yet remains challenging in the renewable energy field. Herein, a sequential pyrolyzing and phosphating approach for a well-designed GO/CoTPP gel precursor has been explored to prepare a Co-based carbon catalyst containing single-atom Co-Nx and hollow Co2P active species (Co2P/Co-N-C) for multifunctional electrocatalytic reactions. Kirkendall effect occurring during the template-free one-pot phosphating approach induced the formation of the hollow Co2P structure in the catalyst, simultaneously optimizing the electron structure and allowing the active sites to be exposed to a greater extent. DFT calculations demonstrated that the Co2P and Co-Nx structures enable Co2P/Co-N-C to have a suitable d-band center depending on the electron transfer from Co2P to Co-Nx, which enhances the adsorption of O* and the dissociation of OH* in oxygen electrode reactions, thereby facilitates catalytic reactions. As a result, the Co2P/Co-N-C exhibits excellent trifunctional activity with a half-wave potential of 0.89 V in alkaline for oxygen reduction reaction (ORR), overpotentials of 330 mV for oxygen evolution reaction (OER) and 190 mV for hydrogen evolution reaction (HER), respectively, which are among the best results reported to date for Co-containing carbon-based catalysts. Furthermore, the flexible Zinc-air battery with Co2P/Co-N-C electrodes also demonstrates a high open circuit voltage of 1.35 V, which is applied to build the self-powered device for water splitting continuously. Our work provides a facile strategy to prepare high-performance trifunctional catalysts by morphology/structure control of metal-based NPs on carbon-based materials.

Biomass Solid-State Electrolyte with Abundant Ion and Water Channels for Flexible Zinc-Air Batteries.

Flexible zinc-air batteries are the leading candidates as the next-generation power source for flexible/wearable electronics. However, constructing safe and high-performance solid-state electrolytes (SSEs) with intrinsic hydroxide ion (OH-) conduction remains a fundamental challenge. Herein, by adopting the natural and robust cellulose nanofibers (CNFs) as building blocks, the biomass SSEs with penetrating ion and water channels are constructed by knitting the OH--conductive CNFs and water-retentive CNFs together via an energy-efficient tape casting. Benefiting from the abundant ion and water channels with interconnected hydrated OH- wires for fast OH- conduction under a nanoconfined environment, the biomass SSEs reveal the high water-uptake, impressive OH- conductivity of 175mScm-1 and mechanical robustness simultaneously, which overcomes the commonly existed dilemma between ion conductivity and mechanical property. Remarkably, the flexible zinc-air batteries assemble with biomass SSEs deliver an exceptional cycle lifespan of 310h and power density of 126mWcm-2. The design methodology for water and ion channels opens a new avenue to design high-performance SSEs for batteries.

Polymer electrolytes for flexible zinc-air batteries: Recent progress and future directions

Polymer electrolytes for flexible zinc-air batteries: Recent progress and future directions

In-situ probing polarization-induced stability of single-atom alloy electrocatalysts in metal-air battery via synchrotron-based X-ray diffraction

In this work, a novel single-atom alloy electrocatalyst (SAAE) was developed for enhanced electrocatalysis in next-generation energy technologies. The catalyst, composed of single-atom Rh and bulk Ni on FeV3O8 support, overcomes challenges related to stability and efficiency in electrochemical reactions. The work function difference between Rh and Ni, as confirmed by computational and synchrotron-based analysis, facilitates superior electric polarization and ohmic contact with FeV3O8. The FeV3O8@RhNi demonstrates outstanding performance in oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs), with high half-wave potential (0.90 V) and low overpotential (120 mV at 10 mA cm−2). In zinc-air batteries, it maintains a stable discharge–charge voltage gap, specific capacity of 810 mAh g−1, peak power density of 186 mW cm−2 at 320 mA cm−2, and cycle stabilities exceeding 859 h at 10 mA cm−2. The catalyst also proves its durability in flexible zinc–air batteries, indicating its potential for efficient electrocatalytic reactions in emerging energy technologies.

Mn-modulated Co–N–C oxygen electrocatalysts for robust and temperature-adaptative zinc-air batteries

Flexible zinc-air batteries (FZABs) are featured with safety and high theoretical capacity and become one of the ideal energy supply devices for flexible electronics. However, the lack of cost-effective electrocatalysts remains a major obstacle to their commercialization. Herein, we synthesized a porous dodecahedral nitrogen-doped carbon (NC) material with Co and Mn bimetallic co-embedding (CoxMn1−x@NC) as a highly efficient oxygen reduction reaction (ORR) catalyst for ZABs. The incorporation of Mn effectively modulates the electronic structure of Co sites, which may lead to optimized energetics with oxygen-containing intermediates thereby significantly enhancing catalytic performance. Notably, the optimized Co4Mn1@NC catalyst exhibits superior E1/2 (0.86 V) and jL (limiting current density, 5.96 mA cm−2) compared to Pt/C and other recent reports. Moreover, aqueous ZAB using Co4Mn1@NC as a cathodic catalyst demonstrates a high peak power density of 163.9 mW cm−2 and maintains stable charging and discharging for over 650 h. Furthermore, FZAB based on Co4Mn1@NC can steadily operate within the temperature range of −10 to 40 °C, demonstrating the potential for practical applications in complex climatic conditions.

Self-Healing Ionogel-Enabled Self-Healing and Wide-Temperature Flexible Zinc-Air Batteries with Ultra-Long Cycling Lives.

Hydrogel-based zinc-air batteries (ZABs) are promising flexible rechargeable batteries. However, the practical application of hydrogel-based ZABs is limited by their short service life, narrow operating temperature range, and repair difficulty. Herein, a self-healing ionogel is synthesized by the photopolymerization of acrylamide and poly(ethylene glycol) monomethyl ether acrylate in 1-ethyl-3-methylimidazolium dicyanamide with zinc acetate dihydrate and first used as an electrolyte to fabricate self-healing ZABs. The obtained self-healing ionogel has a wide operating temperature range, good environmental and electrochemical stability, high ionic conductivity, satisfactory mechanical strength, repeatable and efficient self-healing properties enabled by the reversibility of hydrogen bonding, and the ability to inhibit the production of dendrites and by-products. Notably, the self-healing ionogel has the highest ionic conductivity and toughness compared to other reported self-healing ionogels. The prepared self-healing ionogel is used to assemble self-healing flexible ZABs with a wide operating temperature range. These ZABs have ultra-long cycling lives and excellent stability under harsh conditions. After being damaged, the ZABs can repeatedly self-heal to recover their battery performance, providing a long-lasting and reliable power supply for wearable devices. This work opens new opportunities for the development of electrolytes for ZABs.

Enhanced bifunctional oxygen electrochemical catalytic performance using La-doped CoFe2O4 spinel supported by 3D-G for Zn-air batteries

The preparation of bifunctional catalysts for oxygen reduction (ORR) and oxygen evolution (OER) is crucial for Zn-air batteries. Here, we report a La doped CoFe2O4 spinel catalyst supported on three-dimensional graphene (3D-G), where La can facilitate electron transfer from Co to Fe, leading to increased electron cloud density in Fe and improved catalytic performance. The redshift of the G peak in the Raman spectra indicates the interaction between the π bond of 3D-G and d orbitals in La0.2CoFe1.8O4. La0.2CoFe1.8/3D-G exhibits superior ORR performance (E1/2 = 0.86 V vs. RHE) and OER performance (Ej=10 = 1.55 V vs. RHE) to CoFe2O4/3D-G (E1/2 = 0.831 V vs. RHE, Ej=10 = 1.603 V vs. RHE). Furthermore, it demonstrates excellent bifunctional oxygen catalytic performance while maintaining high power density and stability in liquid zinc-air batteries (ZABs) and flexible ZABs (F-ZABs). This work presents a viable strategy for utilizing rare earth element doped spinels to enhance oxygen catalyst and ZABs performance.

Research progress in flexible zinc-air battery cathode based on carbon nanotube materials

Research progress in flexible zinc-air battery cathode based on carbon nanotube materials

Graphene Oxide Nanoribbon-Based Composite Gel Polymer Electrolytes: Enhancing Mechanical Strength and Ionic Conductivity for Long Cycling Lifetime of Flexible Zinc–Air Batteries

Graphene Oxide Nanoribbon-Based Composite Gel Polymer Electrolytes: Enhancing Mechanical Strength and Ionic Conductivity for Long Cycling Lifetime of Flexible Zinc–Air Batteries

Carbon Fiber Film with Multi-Hollow Channels to Expedite Oxygen Electrocatalytic Reaction Kinetics for Flexible Zn-Air Battery.

The high oxygen electrocatalytic overpotential of flexible cathodes due to sluggish reaction kinetics result in low energy conversion efficiency of wearable zinc-air batteries (ZABs). Herein, lignin, as a 3D flexible carbon-rich macromolecule, is employed for partial replacement of polyacrylonitrile and constructing flexible freestanding air electrodes (FFAEs) with large amount of mesopores and multi-hollow channels via electrospinning combined with annealing strategy. The presence of lignin with disordered structure decreases the graphitization of carbon fibers, increases the structural defects, and optimizes the pore structure, facilitating the enhancement of electron-transfer kinetics. This unique structure effectively improves the accessibility of graphitic-N/pyridinic-N with oxygen reduction reaction (ORR) activity and pyridinic-N with oxygen evolution reaction (OER) activity for FFAEs, accelerating the mass transfer process of oxygen-active species. The resulting N-doped hollow carbon fiber films (NHCFs) exhibit superior bifunctional ORR/OER performance with a low potential difference of only 0.60V. The rechargeable ZABs with NHCFs as metal-free cathodes possess a long-term cycling stability. Furthermore, the NHCFs can be used as FFAEs for flexible ZABs which have a high specific capacity and good cycling stability under different bending states. This work paves the way to design and produce highly active metal-free bifunctional FFAEs for electrochemical energy devices.

NiFe layered double hydroxide (LDH) anchored, Fe single atom and nanoparticle embedded on nitrogen-doped carbon-CNT (carbon nanotube) framework as a bifunctional catalyst for rechargeable zinc-air batteries

Zinc-air batteries (ZAB) have significant potential for practical energy storage, but their rechargeability has been limited by the lack of a suitable bifunctional catalyst. Here, we developed NiFe LDH-A-Fe/NC-CNT, a remarkable bifunctional catalyst that is built on a hierarchically porous nitrogen-doped carbon and carbon nanotube (NC-CNT) framework enriched with iron single atoms and nanoparticles, with nickel‑iron layered double hydroxides (NiFe LDH) anchored onto it. The NiFe LDH-A-Fe/NC-CNT exhibited remarkable performance in the ORR, with Eonset of 0.94 V, a half-wave potential of 0.84 V, and a limited current of 6.89 mA cm−2. A remarkable Eonset of 1.47 V and a potential of 1.59 V at 10 mA cm−2 (Ej = 10) in the OER were also observed. Significantly, the difference in potential (ΔE) between the ORR and OER was only 0.74 V. The stability tests, tolerance assessments, and poisoning experiments consistently demonstrated the superior performance of this cutting-edge catalyst in comparison to the commercial Pt/C and RuO2. In ZAB tests, it achieves a discharge capacity of 818 mAhg−1 and an impressive power density of 293 mWcm−2, enduring nearly 1000 cycles (320h). Flexible ZABs with this catalyst maintain a 629 mAhg−1 capacity, a power density of 195 mWcm−2, and a lifespan of 95 h (280 cycles), outperforming benchmark catalysts. In conclusion, a remarkable bifunctional catalyst was synthesized, demonstrating its immense capacity for utilization in zinc-air batteries.

External Field-Responsive Ternary Non-Noble Metal Oxygen Electrocatalyst for Rechargeable Zinc-Air Batteries.

Despite the increasing effort in advancing oxygen electrocatalysts for zinc-air batteries (ZABs), the performance development gradually reaches a plateau via only ameliorating the electrocatalyst materials. Herein, a new class of external field-responsive electrocatalyst comprising Ni0.5Mn0.5Fe2O4 stably dispersed on N-doped Ketjenblack (Ni0.5Mn0.5Fe2O4/N-KB) is developed via polymer-assisted strategy for practical ZABs. Briefly, the activity indicator ΔE is significantly decreased to 0.618V upon photothermal assistance, far exceeding most reported electrocatalysts (generally >0.680V). As a result, the photothermal electrocatalyst possesses comprehensive merits of excellent power density (319mW cm-2), ultralong lifespan (5163 cycles at 25mA cm-2), and outstanding rate performance (100mA cm-2) for liquid ZABs, and superb temperature and deformation adaptability for flexible ZABs. Such improvement is attributed to the photothermal-heating-enabled synergy of promoted electrical conductivity, reactant-molecule motion, active area, and surface reconstruction, as revealed by operando Raman and simulation. The findings open vast possibilities toward more-energy-efficient energy applications.

Construction of Fe Nanoclusters/Nanoparticles to Engineer FeN4 Sites on Multichannel Porous Carbon Fibers for Boosting Oxygen Reduction Reaction

AbstractFe–N–C catalysts are emerging as promising alternatives to Pt‐based catalysts for the oxygen reduction reaction (ORR), while they still suffer from sluggish reaction kinetics due to the discontented binding affinity between the Fe‐N4 sites and oxygen‐containing intermediates, and unsatisfactory stability. Herein, a flexible multichannel carbon fiber membrane immobilized with atomically dispersed Fe‐N4 sites and neighboring Fe nanoclusters/nanoparticles (FeN4‐FeNCP@MCF) is synthesized. The optimized geometric and electronic structures of the Fe atomic sites brought by adjacent Fe nanoclusters/nanoparticles and hierarchically porous structure of the carbon matrix endow FeN4‐FeNCP@MCF with outstanding ORR activity and stability, considerably outperforming its counterpart with FeN4 sites only and the commercial Pt/C catalyst. Liquid and solid‐state flexible zinc–air batteries employing FeN4‐FeNCP@MCF both exhibit outstanding durability. Theoretical calculation reveals that the Fe nanoclusters can trigger remarkable electron redistribution of the FeN4 sites and modulate the hybridization of central Fe 3d and O 2p orbitals, facilitating the activation of O2 molecules and optimizing the adsorption capacity of oxygen‐containing intermediates on FeN4 sites, and thus accelerating the ORR kinetic. This work offers an effective approach to constructing coupling catalysts that have single atoms coexisting with nanoclusters/nanoparticles for efficient ORR catalysis.