Flexible Solid-state Zinc-air Batteries Research Articles

Single-Anion Conductive Solid-State Electrolytes with Hierarchical Ionic Highways for Flexible Zinc-Air Battery.

Flexible zinc-air batteries are leading power sources for next-generation smart wearable electronics. However, flexible zinc-air batteries suffer from the highly-corrosive safety risk and limited lifespan due to the absence of reliable solid-state electrolytes (SSEs). Herein, a single-anion conductive SSE with high-safety is constructed by incorporating a highly amorphous dual-cation ionomer into a robust hybrid matrix of functional carbon nanotubes and polyacrylamide polymer. The as-fabricated SSE obtains dual-penetrating ionomer-polymer networks and hierarchical ionic highways, which contribute to mechanical robustness with 1200% stretchability, decent water uptake and retention, and superhigh ion conductivity of 245 mS·cm-1 and good Zn anode reversibility. Remarkably, the flexible solid-state zinc-air batteries delivers a high specific capacity of 764 mAh·g-1 and peak power density of 152 mW·cm-2 as well as sustains excellent cycling stability for 1050 cycles (350 hours. This work offers a new paradigm of OH- conductors and broadens the definition and scope of OH- conductors.

Synergistic vacancy engineering of Co/MnO@NC catalyst for superior oxygen reduction reaction in liquid/solid zinc-air batteries

The pursuit of efficient and economically viable catalysts for liquid/solid-state zinc-air batteries (ZABs) is of paramount importance yet presents formidable challenge. Herein, we synthesized a vacancy-rich cobalt/manganese oxide catalyst (Co/MnO@NC) stabilized on a nitrogen-doped mesoporous carbon (NC) nanosphere matrix by leveraging hydrothermal and high-temperature pyrolysis strategy. The optimized Co/MnO@NC demonstrates fast reaction kinetics and large limiting current densities comparable to commercial Pt/C in alkaline electrolyte for oxygen reduction reaction (ORR). Moreover, the Co/MnO@NC serves as an incredible cathode material for both liquid and flexible solid-state ZABs, delivering impressive peak power densities of 217.7 and 63.3 mW cm−2 and robust long-term stability (459 h), outperforming the state-of-the-art Pt/C and majority of the currently reported catalysts. Research indicates that the superior performance of the Co/MnO@NC catalyst primarily stems from the synergy between the heightened electrical conductivity of metallic Co and the regulatory capacity of MnO on adsorbed oxygen intermediates. In addition, the abundance of vacancies regulates the electronic configuration, and superhydrophilicity facilitates efficient electrolyte diffusion, thereby effectively ensuring optimal contact between the active site and reactants. Besides, the coexisting NC layer avoids the shedding of active sites, resulting in high stability. This work provides a viable approach for designing and advancing high-performance liquid/solid-state ZABs, highlighting the great potential of energy storage technology.

Preparation of cellulose acetate based flexible separator and its application in zinc–air batteries

Flexible solid-state zinc–air batteries as a wearable energy storage device with great potential, and their separators, which control ion permeability, inhibit zinc dendrite generation, and regulate catalytic active sites, have been developed as gel electrolyte separators with high retention of electrolyte uptake. However, the gel electrolyte separator still has problems such as poor affinity with the electrolyte and poor ionic conductivity, which limits its further application. In order to further improve the electrolyte absorption, ionic conductivity and mechanical strength of cellulose acetate(CA)/polyvinyl alcohol (PVA) nanofibers, TiO2 was added to CA/PVA to increase the porosity, and glutaraldehyde (GA) was used to modify the CA/PVA/TiO2 separator by acetal reaction with CA and PVA to make the molecules closely linked. The results shows that the optimal mass fractions of TiO2 and GA were 2% and 5%, respectively. At this time, the porosity and absorption rate of the separator increased from 48% to 68.2% and 142.4% to 285.3%, respectively. The discharge capacity reached 179 mA cm−3, and the cycle stability rate was 89% after 7 stable constant current charge/discharge cycles.

Double-Faced Atomic-Level Engineering of Hollow Carbon Nanofibers as Free-Standing Bifunctional Oxygen Electrocatalysts for Flexible Zn-Air Battery.

Flexible solid-state zinc-air batteries (ZABs) with low cost, excellent safety, and high energy density has been considered as one of ideal power sources for portable and wearable electronic devices, while their practical applications are still hindered by the kinetically sluggish cathodic oxygen reduction and oxygen evolution reactions (ORR/OER). Herein, a Janus-structured flexible free-standing bifunctional oxygen electrocatalyst, with OER-active O, N co-coordinated Ni single atoms and ORR-active Co3O4@Co1-xS nanosheet arrays being separately integrated at the inner and outer walls of flexible hollow carbon nanofibers (Ni-SAs/HCNFs/Co-NAs), is reported. Benefiting from the sophisticated topological structure and atomic-level-designed chemical compositions, Ni-SAs/HCNFs/Co-NAs exhibits outstanding bifunctional catalytic activity with the ΔE index of 0.65 V, representing the current state-of-the-art flexible free-standing bifunctional ORR/OER electrocatalyst. Impressively, the Ni-SAs/HCNFs/Co-NAs-based liquid ZAB show a high open-circuit potential (1.45 V), high capacity (808 mAh g-1 Zn), and extremely long life (over 200 h at 10 mA cm-2), and the assembled flexible all-solid-state ZABs have excellent cycle stability (over 80 h). This work provides an efficient strategy for developing high-performance bifunctional ORR/OER electrocatalysts for commercial applications.

Hierarchically Nanostructured Solid-State Electrolyte for Flexible Rechargeable Zinc-Air Batteries.

The construction of safe and environmentally-benign solid-state electrolytes (SSEs) with intrinsic hydroxide ion-conduction for flexible zinc-air batteries is highly desirable yet extremely challenging. Herein, hierarchically nanostructured CCNF-PDIL SSEs with reinforced concrete architecture are constructed by nanoconfined polymerization of dual-cation ionic liquid (PDIL, concrete) within a robust three-dimensional porous cationic cellulose nanofiber matrix (CCNF, reinforcing steel), where plenty of penetrating ion-conductive channels are formed and undergo dynamic self-rearrangement under different hydrated levels. The CCNF-PDIL SSEs synchronously exhibit good flexibility, mechanical robustness, superhigh ion conductivity of 286.5 mS cm-1 , and decent water uptake. The resultant flexible solid-state zinc-air batteries deliver a high-power density of 135 mW cm-2 , a specific capacity of 775 mAh g-1 and an ultralong cycling stability with continuous operation of 240 hours for 720 cycles, far outperforming those of the state-of-the-art solid-state batteries. The marriage of biomaterials with the diversity of ionic liquids creates enormous opportunities to construct advanced SSEs for solid-state batteries.

Bioinspired Tough Solid-State Electrolyte for Flexible Ultralong-Life Zinc-Air Battery.

Manufacturing advanced solid-state electrolytes (SSEs) for flexible rechargeable batteries becomes increasingly important but remains grand challenge. The sophisticated structure of robust animal dermis and good water-retention of plant cell in nature grant germane inspirations for designing high-performance SSEs. Herein, tough bioinspired SSEs with intrinsic hydroxide ion (OH- ) conduction are constructed by in situ formation of OH- conductive ionomer network within a hollow-polymeric-microcapsule-decorated hydrogel polymer network. By virtue of the bioinspired design and dynamic dual-penetrating network structure, the bioinspired SSEs simultaneously obtain mechanical robustness with 1800% stretchability, good water uptake of 107g g-1 and water retention, and superhigh ion conductivity of 215 mS cm-1 . The nanostructure of bioinspired SSE and related ion-conduction mechanism are revealed and visualized by molecular dynamics simulation, where plenty of compact and superfast ion-transport channels are constructed, contributing to superhigh ion conductivity. As a result, the flexible solid-state zinc-air batteries assembled with bioinspired SSEs witness high power density of 148 mW cm-2 , specific capacity of 758 mAh g-1 and ultralong cycling stability of 320 h as well as outstanding flexibility. The bioinspired methodology and deep insight of ion-conduction mechanism will shed light on the design of advanced SSEs for flexible energy conversion and storage systems.

In Situ Monitored (N, O)-Doping of Flexible Vertical Graphene Films with High-Flux Plasma Enhanced Chemical Vapor Deposition for Remarkable Metal-Free Redox Catalysis Essential to Alkaline Zinc-Air Batteries.

Rechargeable zinc–air batteries (ZABs) have attracted great interests for emerging energy applications. Nevertheless, one of the major bottlenecks lies in the fabrication of bifunctional catalysts with high electrochemical activity, high stability, low cost, and free of precious and rare metals. Herein, a high‐performance metal‐free bifunctional catalyst is synthesized in a single step by regulating radicals within the recently invented high‐flux plasma enhanced chemical vapor deposition (HPECVD) system equipped with in situ plasma diagnostics. Thus‐derived (N, O)‐doped vertical few‐layer graphene film (VGNO) is of high areal population with perfect vertical orientation, tunable catalytic states, and configurations, thus enabling significantly enhanced electrochemical kinetic processes of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with reference to milestone achievements to date. Application of such VGNO to aqueous ZABs (A‐ZABs) and flexible solid‐state ZABs (S‐ZABs) exhibited high discharge power density and excellent cycling stability, which remarkably outperformed ZABs using benchmarked precious‐metal based catalysts. The current work provides a solid basis toward developing low‐cost, resource‐sustainable, and eco‐friendly ZABs without using any metals for outstanding OER and ORR catalysis.

Self-Healing and Anti-CO2 Hydrogels for Flexible Solid-State Zinc-Air Batteries.

Flexible solid-state zinc-air batteries (ZABs) generally suffer from poor electrolyte/electrode contact and mechanical degradation in practical applications. In addition, CO2 corrosion is also a common issue for ZABs with alkaline electrolyte. Herein, we report a thermoreversible alkaline hydrogel electrolyte that can simultaneously solve the aforementioned problems. Through a simple cooling process, the hydrogel electrolyte transforms from solid state to liquid state that can not only restore the deformed electrolyte layer to its original state but also rebuild intimate contact between electrode and electrolyte. Moreover, the ZAB based on this hydrogel electrolyte exhibits an unprecedented anti-CO2 property. As a result, such a battery shows almost 2.5 times discharge duration than that of ZAB based on liquid electrolyte.

Ultrafine Ni nanoparticles anchored on carbon nanofibers as highly efficient bifunctional air electrodes for flexible solid-state zinc-air batteries

Development of well-designed bifunctional electrocatalysts with high activity for OER (oxygen evolution reaction) and ORR (oxygen reduction reaction) are a crucial topic owing to their promising applications in rechargeable Zinc (Zn)-air battery. Herein, a facile adsorption-pyrolyzation strategy is proposed for preparing ultrafine Ni nanoparticles anchored on carbon nanofiber (Ni/CNF), which derives from pyrolyzation of bacterial cellulose (BC) (with pre-adsorbed of Ni2+) via a two-step heat-treatment procedure (firstly 360 ℃, and then 750 ℃) (Ni/CNF-750) and used as an excellent oxygen electrocatalyst for flexible all solid-state Zn-air cell. The resultant ultrafine Ni/CNF-750 with plentiful pore structure and relatively high specific surface area of 449.0 m2 g−1, delivering overpotential of 293 mV at current density of 10 mA cm−2 for OER, obtaining an onset potential of 0.93 V vs. RHE and half-wave potential of 0.76 V vs. RHE for ORR. Moreover, a home-made flexible all solid-state battery is constructed by using Ni/CNF-750 as air electrodes, which provides a power density of 56.8 mW cm−2 and wonderful cycling durability with maintaining 50 cycles, and can drive a light-emitting-diode (LED) device. Our work may provides a reliable approach for fabricating ultrafine metal nanoparticles anchored on carbon based substrate with high activity for next-generation energy conversion and storage devices.

A-site deficient perovskite nanofibers boost oxygen evolution reaction for zinc-air batteries

Among the various perovskites, Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) has been theoretically proved to have the prominent intrinsic oxygen evolution reaction (OER) catalytic activity in the alkaline solutions. Whereas, most of the measured bulk BSCF samples suffer the unsatisfactory OER activities which are much more inferior than that of the state-of-the-art catalyst of IrO2. In this work, we synthesize the A-site deficient BSCF nanofibers with the diameter of 300 nm by electrospinning for the first time. Thanks to the one dimensional (1D) nanofiber structure and A-site deficiency, the optimized BSCF nanofibers (BSCF-80-ES) demonstrate the remarkably enhanced OER activity with a low potential of 1.54 V at 10 mA cm−2 in 1 M KOH and an improved oxygen reduction reaction (ORR) activity. It is noteworthy that the OER potential of BSCF-80-ES keeps almost unchanged during the long-term test, indicating an excellent OER stability. Moreover, BSCF-80-ES with the high bifunctional catalytic activity and superb stability can be used as a promising oxygen catalyst for aqueous and flexible solid-state zinc-air batteries.

Efficiently optimizing the oxygen catalytic properties of the birnessite type manganese dioxide for zinc-air batteries

It is of great significance to design and develop the high-efficiency and low-cost bifunctional oxygen catalysts. Manganese dioxide (MnO2) is one of the most widely studied catalysts for oxygen reduction reaction (ORR) on account of the high reserves and environmental friendliness. Whereas, the catalytic activity of MnO2 for oxygen evolution reaction (OER) is so inferior that it cannot be used as the bifunctional oxygen catalysts. In this work, the assembled nanospheres of cobalt ion intercalated birnessite type MnO2 with a unique lamellar structure are synthesized by a very facile one-step liquid-phase method under mild conditions. Importantly, compared with the pristine MnO2, the optimized cobalt ion intercalated δ-MnO2 (24Co–MnO2) shows the greatly enhanced OER catalytic activity and stability. Specially, 24Co–MnO2 displays a low OER overpotential of 430 mV at 10 mA cm−2 in 0.1 M KOH. In addition, 24Co–MnO2 shows much higher bifunctional oxygen catalytic activity than most of the manganese oxide based catalysts. Moreover, 24Co–MnO2 as the bifunctional oxygen catalyst is assembled in the aqueous and flexible solid-state zinc-air batteries (ZABs), showing the high peak power density and outstanding cycling stability.

An amorphous trimetallic (Ni–Co–Fe) hydroxide-sheathed 3D bifunctional electrode for superior oxygen evolution and high-performance cable-type flexible zinc–air batteries

A 3D integrated bifunctional electrode of NiCo2O4@NiCoFe–OH nanoarrays is demonstrated for highly efficient oxygen evolution and flexible solid-state zinc–air batteries.

Self-supported N-doped CNT arrays for flexible Zn–air batteries

N-Doped carbon nanotube arrays with encapsulated CoFe nanoparticles were directly grown on carbon fiber cloth as a self-supported air-cathode for flexible solid-state zinc–air batteries which can work even under extreme bending conditions.

Flexible Hydrogel Electrolyte with Superior Mechanical Properties Based on Poly(vinyl alcohol) and Bacterial Cellulose for the Solid-State Zinc-Air Batteries.

Flexible solid-state zinc-air batteries are promising energy technologies with low cost, superior performance and safety. However, flexible electrolytes are severely limited by their poor mechanical properties. Here, we introduce flexible bacterial cellulose (BC)/poly(vinyl alcohol) (PVA) composite hydrogel electrolytes (BPCE) based on bacterial cellulose (BC) microfibers and poly(vinyl alcohol) (PVA) by an in situ synthesis. Originating from the hydrogen bonds among BC microfibers and PVA matrix, these composites form load-bearing percolating dual network and their mechanical strength is increased 9 times (from 0.102 MPa of pristine PVA to 0.951 MPa of 6-BPCE). 6-BPCE shows extremely high ionic conductivities (80.8 mS cm-1). In addition, the solid-state zinc-air batteries can stably cycle over 440 h without large discharge and charge polarizations equipped with zinc anode and Co3O4@Ni cathode. Moreover, flexible solid-state zinc-air batteries can cycle well at any bending angle. As flexible electrolytes, they open up a new opportunity for the development of superior-performance, flexible, rechargeable, zinc-air batteries.

Electronic reconfiguration of Co2P induced by Cu doping enhancing oxygen reduction reaction activity in zinc–air batteries

Cu-Doped Co2P nanoparticles anchored on 2D heteroatom-doped ultrathin carbon exhibit excellent oxygen reduction reaction performance in flexible solid state zinc–air batteries.

Defect-rich carbon fiber electrocatalysts with porous graphene skin for flexible solid-state zinc–air batteries

Rechargeable flexible Zn–air batteries have attracted great attentions as promising next-generation energy storage devices for portable and wearable electronics. Bifunctional oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) electrocatalysts on the air electrode are critical for improving the energy storage performance of Zn–air batteries. Free-standing electrocatalysts with superb OER/ORR reactivity render promising flexible power sources for the wearable and stretchable devices. In this contribution, a metal-free electrocatalyst based on surface modification of flexible carbon cloth is proposed. A coaxial cable-like structure with carbon fiber skeleton coated by nanostructured porous and defect-rich graphene skin is in situ fabricated through a facile H2 etching approach. With abundant heteroatoms and defects as active sites, the nanocarbon shells coated carbon cloth exhibits excellent OER/ORR bifunctional activity. The OER and ORR current densities on graphene skin modified carbon fiber are 20 and 3 times higher than those of pristine carbon cloth, respectively. This emerging carbon cloth derived electrocatalyst with porous graphene skin also serves as the air electrode in a rechargeable flexible solid-state Zn air battery with polymer gel electrolyte, and demonstrates stable charge/discharge cycling even under bending. This strategy of constructing nanostructures directly on carbon fibers benefits the rational design of flexible and functionalized materials for electrocatalytic energy applications.

Electrochemical approach to prepare integrated air electrodes for highly stretchable zinc-air battery array with tunable output voltage and current for wearable electronics

Efficient stretchable and flexible energy devices are urgently required due to their promising application in wearable devices. Although flexible solid-state zinc-air batteries have been developed in previous studies, no stretchable Zn-air batteries with large stretchability (> 20%) have been reported. We first present a planar rechargeable stretchable and flexible Zn-air battery array fabricated by layer-by-layer assembly of 2 × 2 electrode arrays, a polymer gel electrolyte, serpentine-shaped copper circuits, and a rubber substrate. Vertical Co3O4 nanosheets were fabricated by a binder-free and simple manner and were grown in situ on carbon cloth as an integrated cathode. The Zn-air battery array displayed stable electrochemical behaviors, with a large tensile strain of 100%. Furthermore, the battery array could be discharged stably at 1V at a high current density of 2mAcm–2 under high-frequency dynamic stretching (~ 100% strain per second) and bending conditions. In addition, by redesigning the arrangement of the electrode array, the stretchable Zn-air battery array could be configured to provide a wide range of output voltages, specifically from 1 to 4V. The resulting Zn-air battery array was sewn onto cloth and applied to power a green light band (3.0V) with 60 light-emitting diodes (LEDs), proving the feasibility of its application in wearable energy-storage electronics.

Nitrogen‐Doped Co3O4 Mesoporous Nanowire Arrays as an Additive‐Free Air‐Cathode for Flexible Solid‐State Zinc–Air Batteries

The kinetically sluggish rate of oxygen reduction reaction (ORR) on the cathode side is one of the main bottlenecks of zinc-air batteries (ZABs), and thus the search for an efficient and cost-effective catalyst for ORR is highly pursued. Co3 O4 has received ever-growing interest as a promising ORR catalyst due to the unique advantages of low-cost, earth abundance and decent catalytic activity. However, owing to the poor conductivity as a result of its semiconducting nature, the ORR activity of the Co3 O4 catalyst is still far below the expectation. Herein, we report a controllable N-doping strategy to significantly improve the catalytic activity of Co3 O4 for ORR and demonstrate these N doped Co3 O4 nanowires as an additive-free air-cathode for flexible solid-state zinc-air batteries. The results of experiments and DFT calculations reveal that the catalytic activity is promoted by the N dopant through a combined set of factors, including enhanced electronic conductivity, increased O2 adsorption strength and improved reaction kinetics. Finally, the assembly of all-solid-state ZABs based on the optimized cathode exhibit a high volumetric capacity of 98.1 mAh cm-3 and outstanding flexibility. The demonstration of such flexible ZABs provides valuable insights that point the way to the redesign of emerging portable electronics.