Thin Zn Research Articles

Boosting the Anode and Cathode Stability Simultaneously by Interfacial Engineering via Electrolyte Solvation Structure Regulation Toward Practical Aqueous Zn‐ion Battery

AbstractThe application of zinc‐ion batteries (ZIBs) is seriously challenged by the poor stability of Zn anode and cathode in aqueous solution, which is closely associated with electrolyte structure and water reactivity. Herein, the stability issues both for the cathode and anode can be simultaneously addressed via tuning the electrolyte solvation structure in hybrid electrolyte with tripropyl phosphate (TPP) as co‐solvent. On the Zn anode, a robust poly‐inorganic solid electrolyte interphase (SEI) layer comprised of Zn3(PO4)2‐ZnS‐ZnF2 species is in situ formed, effectively suppressing parasitic reaction and dendrite evolution. For V2O5 cathode, the notorious vanadium dissolution is effectively restricted with improved structure stability achieved. The optimized electrolyte facilitates the reversible redox kinetics both at the cathode and Zn anode. Consequently, Zn||Zn cells display extended cycling lifespans over 3000 h at 1 mA cm−2, 1 mAh cm−2. Zn||V2O5 full cells deliver a high reversible capacity of 261.8 mAh g−1 and hold retention of 73.6% upon 500 cycles even operated in harsh conditions with thin Zn anode (10 µm) and low negative/positive (N/P) ratio of ≈4.3, which also showcase impressive performance with regard to rate and storage performance, further emphasizing the potential of electrolyte regulation tactics in advancing the commercialization of ZIBs.

A Five Micron Thick Aramid Nanofiber Separator Enables Highly Reversible Zn Anode for Energy‐Dense Aqueous Zinc‐Ion Batteries

AbstractThe rampant dendrites growth caused by uncontrolled deposition of Zn2+ ions at Zn metal anode poses a significant obstacle to the practical applications of aqueous zinc‐ion batteries (ZIBs). Herein, an ultrathin (5 µm) aramid nanofiber (ANF) separator is reported to enhance the Zn anode stability and the ZIB energy density. Through systematic experimental studies and DFT simulations, it is demonstrated that the ANF separator with unique surface polarity can modify the solvation configuration, facilitate desolvation, and regulate the deposition orientation of Zn2+ ions. Consequently, the Zn anode with the ANF separator demonstrates an 85‐fold increase in running time beyond 850 h compared with the conventional glass fiber separator at 5 mA cm−2/2.5 mAh cm−2. Even under the harsh depth of discharge conditions of 50% and 80%, the Zn anodes still sustain extended cycling periods of over 475 and 200 h, respectively. As pairing this ANF separator with thin Zn anode and high‐areal‐capacity Mn2.5V10O24∙5.9H2O cathode in a low negative capacity/positive capacity ratio (2.64) full cell, superior gravimetric/volumetric energy density (129.2 Wh kg−1/142.5 Wh L−1) is achieved, far surpassing majority of the ZIB counterparts reported in the literature. This work offers a promising ultrathin separator for promoting the utilization of energy‐dense aqueous ZIBs.

Carbon nanotubes as efficient anode current collectors for stationary aqueous Zn–Br2 batteries

Static Zn–Br2 batteries are considered an attractive option for cost-effective and high-capacity systems for large energy storage. Yet, the corrosive nature of the Zn–Br2 electrolytes entails a careful selection of all cells' ingredients to avoid rapid degradation of the batteries upon cycling. Thanks to their high chemical resistance and excellent conductivity, carbonaceous electrodes are typically utilized as current collectors for the cathode side, while thin Zn or Ti foils are most widely used as the anodes' current collectors. However, these metals tend to corrode fast, thus undermining the desirable performance of the cells as durable and stable rechargeable batteries. We demonstrate the effective utilization of carbon nanotubes (CNT) films as highly stable anode current collector for Zn–Br2 batteries. Dispersion of the CNT beforehand in slurries containing anionic, cationic, or neutral surfactants yielded distinct chemical and physical characteristics of these carbonaceous electrodes. This, in turn, led to significant differences in the morphology of the deposited Zn, consequently affecting the electrochemical performance of the Zn anodes. These findings provide insight into the interactions between Zn cations and the surface of CNTs, offering opportunities for further surface modifications of CNTs as effective anodes’ substrates for Zn–Br2 batteries.

Overcoming Challenges: Extending Cycle Life of Aqueous Zinc-Ion Batteries at High Zinc Utilization through a Synergistic Strategy.

Aqueous zinc-ion batteries (AZIBs) face challenges in achieving high energy density compared to conventional lithium-ion batteries (LIBs). The lower operating voltage and excessive Zn metal as anode pose constraints on the overall energy storage capacity of these batteries. An effective approach is to reduce the thickness of the Zn metal anode and control its mass appropriately. However, under the condition of using a thin Zn anode, the performance of AZIBs is often unsatisfactory. Through experiments and computational simulations, the electrode structural change and the formation of dead Zn as the primary reasons for the failure of batteries under a high Zn utilization rate are identified. Based on this understanding, a universal synergistic strategy that combines Cu foil current collectors and electrolyte additives to maintain the structural and thermodynamic stability of the Zn anode under a high Zn utilization rate (ZUR) is proposed. Specifically, the Cu current collectors can ensure that the Zn anode structure remains intact based on the spontaneous filling effect, while the additives can suppress parasitic side reactions at the interface. Ultimately, the symmetric cell demonstrates a cycling duration of 900 h at a 70% ZU, confirming the effectiveness of this strategy.

Hybrid electrolyte engineering enables reversible Zn metal anodes at ultralow current densities

Parasitic reactions in aqueous Zn metal batteries tend to be intensified along with the decrease of current density, deteriorating the cycling stability of Zn anodes, which unfortunately have been overlooked in previous studies. Herein, an organic solvent N-Methylacetamide (NMA) is introduced into ZnSO4 electrolyte for improving the reversibility of Zn anodes. Combined with theoretical and experimental investigations, it is uncovered that NMA additives are capable of entering not only the pristine Zn2+ solvation structure ([Zn(H2O)x]2+) but also the electrical double layer structure, reducing active H2O molecule proportions and thus suppressing the corrosion reactions. Meanwhile, nucleation and growth processes are also constrained with NMA additive for its strong coordination with Zn2+, inducing dendrite-free Zn depositions. Consequently, an average Coulombic efficiency (CE) of 98.5% for 600 cycles in Zn|Cu half-cells with NMA/ZnSO4 electrolyte is obtained at an ultralow current density of 0.3 mA cm−2. Moreover, Zn|Zn symmetric cells utilizing 20 vol% NMA additive exhibit stable cycle lifespan of 1000 h. Benefitting from the enhanced reversibility of Zn anodes in NMA/ZnSO4 electrolytes, full-cells assembled with carbon cloth as cathodes deliver high performance of 5200 cycles at the current density of 64 mA g−1 with 10 μm thin Zn anodes, favoring the practical applications.

Simulation of new thin film Zn(O,S)/CIGS solar cell with bandgap grading

Copper-Indium-Gallium-diSelenide (CIGS) thin film solar cell is a promising candidate for energy harvesting because of its high absorption coefficient and low cost compared to silicon-based solar cells. Absorber layer bandgap grading is a suitable method to improve CIGS thin film solar cell performance. Bandgap grading leads to a decrease in the recombination rate at the rear surface, which increases the open circuit voltage. Furthermore, bandgap grading improves the short circuit current due to the enhancement of collection probability. This paper introduces various routes for improving the performance of thin film CIGS solar cells by using bandgap grading. As a first step, both the bandgap energy and the thickness of the CIGS absorber layer of a uniform bandgap profile are optimized to get the best performance. Simulation is performed using SCAPS software and optimization results show that CIGS absorber layer with a bandgap of 1.2 eV and a thickness of 0.7 μm achieves a 22.48% efficiency. Then, bandgap grading with a parabolic distribution of various profiles is investigated and compared. It is found that with a parabolic double bandgap grading profile, which is a combination of front and back grading, an efficiency of up to 24.16% is achieved. This improvement is obtained using a gallium composition ratio of 0.1 for the minimal bandgap at 0.1 μm and 0.13 μm from the back contact and front contact, respectively. This result represents a 7.47% improvement compared to the baseline structure of a CIGS solar cell.

Origin of two-dimensional electron gas in Zn1−xMgxO/ZnO heterostructures

Although the two-dimensional electron gas (2DEG) in (001) Zn$_{1-x}$Mg$_x$O/ZnO heterostructures has been discovered for about twenty years, the origin of the 2DEG is still inconclusive. In the present letter, the formation mechanisms of 2DEG near the interfaces of (001) Zn$_{1-x}$Mg$_x$O/ZnO heterostructures were investigated via the first-principles calculations method. It is found that the polarity discontinuity near the interface can neither lead to the formation of 2DEG in devices with thick Zn$_{1-x}$Mg$_{x}$O layers nor in devices with thin Zn$_{1-x}$Mg$_{x}$O layers. For the heterostructure with thick Zn$_{1-x}$Mg$_{x}$O layers, the oxygen vacancies near the interface introduce a defect band in the band gap, and the top of the defect band overlaps with the bottom of the conduction band, leading to the formation of the 2DEG near the interface of the device. For the heterostructure with thin Zn$_{1-x}$Mg$_{x}$O layers, the absorption of hydrogen atoms, oxygen atoms, or OH groups on the surface of Zn$_{1-x}$Mg$_{x}$O film plays a key role for the formation of 2DEG in the device. Our results manifest the sources of 2DEGs in Zn$_{1-x}$Mg$_x$O/ZnO heterostructures on the electronic structure level.

Durable modulation of Zn(002) plane deposition via reproducible zincophilic carbon quantum dots towards low N/P ratio zinc-ion batteries.

Aqueous zinc-ion batteries (ZIBs) are promising candidates for next-generation energy storage systems due to their intrinsic safety, environmental friendliness, and low cost. However, the uncontrollable Zn dendrite growth during cycling is still a critical challenge for the long-term operation of ZIBs, especially under harsh lean-Zn conditions. Herein, we report nitrogen and sulfur-codoped carbon quantum dots (N,S-CDs) as zincophilic electrolyte additives to regulate the Zn deposition behaviors. The N,S-CDs with abundant electronegative groups can attract Zn2+ ions and co-deposit with Zn2+ ions on the anode surface, inducing a parallel orientation of the (002) crystal plane. The deposition of Zn preferentially along the (002) crystal direction fundamentally avoids the formation of Zn dendrites. Moreover, the co-depositing/stripping feature of N,S-CDs under an electric field force ensures the reproducible and long-lasting modulation of the Zn anode stability. Benefiting from these two unique modulation mechanisms, stable cyclability of the thin Zn anodes (10 and 20 μm) at a high depth of discharge (DOD) of 67% and high Zn||Na2V6O16·3H2O (NVO, 11.52 mg cm-2) full-cell energy density (144.98 W h Kg-1) at a record-low negative/positive (N/P) capacity ratio of 1.05 are achieved using the N,S-CDs as an additive in ZnSO4 electrolyte. Our findings not only offer a feasible solution for developing actual high-energy density ZIBs but also provide in-depth insights into the working mechanism of CDs in regulating Zn deposition behaviors.

Atomically Thin Zn2GeO4 Nanoribbons: Facile Synthesis and Selective Photocatalytic CO2 Reduction toward CO

Atomically Thin Zn₂GeO₄ Nanoribbons: Facile Synthesis and Selective Photocatalytic CO₂ Reduction toward CO

Three Birds with One Stone: Tetramethylurea as Electrolyte Additive for Highly Reversible Zn‐Metal Anode

AbstractAqueous Zn‐metal batteries are the most promising system for large‐scale energy storage due to their high capacity, high safety, and low cost. The Zn‐metal anode, however, suffers from continuous parasitic reactions, random dendrite growth, and sluggish kinetics in aqueous electrolytes. Herein, a high donor number solvent, tetramethylurea (TMU), is introduced as electrolyte additive to enable highly reversible Zn‐metal anode, where the TMU can 1) preferentially adsorb on the Zn surface to inhibit Zn corrosion and suppress parasitic reaction, 2) solvate with Zn2+ and exclude the H2O from Zn2+ solvation sheath to weaken water activity significantly, and 3) contribute to form an inorganic‐organic bilayer solid electrolyte interphase to enable homogeneous and rapid Zn2+ transport kinetic for dendrite‐free Zn deposition. Benefiting from these three merits, the resulting aqueous electrolyte demonstrates a highly reversible Zn plating/stripping cycling in a Zn||Ti asymmetric cell for over 1200 cycles and in a Zn||Zn symmetric cell for over 4000 h. As a proof‐of‐concept, the aqueous Zn‐metal full cells assembled with various state‐of‐the‐art cathodes also deliver excellent cycling performance even with a 10 µm thin Zn anode, favoring the practical application.

Ultrafast ultrasonic-assisted transient liquid bonding Al/Mg in air

We used ultrasonic-assisted transient liquid bonding (UATLP) to join dissimilar Al/Mg alloys with pure Zn interlayer in the air to prevent the formation of AlMg intermetallic compounds (IMCs). The effects of bonding temperature, ultrasonic power, sonotrode pressure, and interlayer thickness on the microstructure and mechanical properties of the bonded joints were studied. Results showed that the addition of Zn interlayer could effectively depress the AlMg IMCs. The oxide layer on the Al substrate is incompletely removed at bonding temperature below 380 °C, the Mg side is bonded by eutectic phase, and the Al side is bonded by diffusion. The joint is characterized by MgZn eutectic (containing ternary IMCs) and IMCs of MgZn and MgZn2 layer. MgZn2 is the weak point of the joint under such a condition, and the joint has shear strength of approximately 20 MPa. The oxide layer on the Al substrate is completely removed when the temperature exceeds 380 °C, the large amount of Al that flows into the joint results in a Mg32(Al,Zn)49 layer adjacent to the Al substrate. The joint gains its maximum strength of 28.4 MPa when thin MgZn2 and discontinuous Mg32(Al,Zn)49 exist adjacent to the Al substrate. High ultrasonic power, large sonotrode pressure, and thin Zn interlayer could reduce the thickness of MgZn2.

How Is Cycle Life of Three-Dimensional Zinc Metal Anodes with Carbon Fiber Backbones Affected by Depth of Discharge and Current Density in Zinc-Ion Batteries?

Zinc (Zn) metal is an attractive anode material for aqueous Zn-ion batteries (ZIBs). Three-dimensional (3D) carbon frameworks may serve as lightweight and robust hosts to enable porous Zn electrodes with a long cycle life. However, Zn electrode tests under a low depth of discharge (DOD) and current density often yield unreliable promises. We used 3D Zn electrodes with carbon nanofiber framework (CNF) backbones (Zn@CNF) as model electrodes to reveal how DOD and current density affect their performance. Plasma-treated CNFs provide sufficient surface hydrophilicity and surface area to allow uniform Zn plating/stripping of a thin and uniform Zn coating (5 mAh cm-2). CNFs only take a small weight fraction (17.5-19.7 wt. %) in the composite electrodes. The 3D structure and graphitic surface efficiently suppress dendrite growth. The cycle life of Zn@CNF can reach 843 h under 10% DOD and 0.5 mA cm-2 in symmetric cells. However, high DOD and current density are detrimental to the stability of 3D Zn electrodes. The cycle life drops to 60.75 h under 60% DOD and 4 mA cm-2. Full cells assembled using Zn@CNF as anodes and V2O5 as cathodes with an N/P capacity ratio of 2.4 delivered a capacity of 133.4 mAh g-1 at 0.1 A g-1. The full cells also showed excellent capacity retention of 92.1% after 260 cycles under 0.5 A g-1 with a high average DODZn of 15.5%. Our results suggest that 3D Zn electrodes with CNF backbones are promising anodes for ZIBs. Studying Zn metal electrodes under practical DOD and current density is essential to access their potential accurately.

Electrochemical Characteristics of Zn-Ion Hybrid Supercapacitors Based on Aqueous Solution of Different Electrolytes

Electrochemical behaviour of Zn cation based various aqueous electrolytes (ZnSO4, Zn(BF4)2, zinc di[bis(trifluoromethylsulfonyl)imide], Zn(TFSI)2, and zinc trifluoromethanesulfonate, Zn(OTf)2) has been studied in thin Zn foil∣ carbon cloth hybrid supercapacitor cell and compared with Zn(ClO4)2 aqueous electrolyte electrochemical characteristics using cyclic voltammetry, constant current charge/discharge and electrochemical impedance methods. The Ragone plots have been calculated from constant power measurements data. At moderate specific power values (10 kW kg−1) noticeable decrease of specific energies can be seen in the order of electrolytes: Zn(ClO4)2 ≥ Zn(BF4)2 > Zn(OTf)2 > Zn(TFSI)2 > ZnSO4. The stability of Zn-ion hybrid supercapacitor cells under study has been tested using the long lasting (up to 10000 cycles) constant current charge/discharge method and is very good for Zn(OTf)2, Zn(ClO4)2 and ZnSO4.

Oxidation of MBE-Grown ZnTe and ZnTe/Zn Nanowires and Their Structural Properties.

Results of comparative structural characterization of bare and Zn-covered ZnTe nanowires (NWs) before and after thermal oxidation at 300 °C are presented. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, and Raman scattering not only unambiguously confirm the conversion of the outer layer of the NWs into ZnO, but also demonstrate the influence of the oxidation process on the structure of the inner part of the NWs. Our study shows that the morphology of the resulting ZnO can be improved by the deposition of thin Zn shells on the bare ZnTe NWs prior to the oxidation. The oxidation of bare ZnTe NWs results in the formation of separated ZnO nanocrystals which decorate crystalline Te cores of the NWs. In the case of Zn-covered NWs, uniform ZnO shells are formed, however they are of a fine-crystalline structure or partially amorphous. Our study provides an important insight into the details of the oxidation processes of ZnTe nanostructures, which could be of importance for the preparation and performance of ZnTe based nano-devices operating under normal atmospheric conditions and at elevated temperatures.

Use of interface phonon-polaritons for the alloy determination in ZnO/(Zn,Mg)O multiple quantum wells

A method based on infrared reflectance spectroscopy is presented by which the Mg content in ZnO/(Zn,Mg)O multiple quantum wells with very thin barriers can be determined. The method relies on the observation of interface phonon-polaritons which appear as sharp dips in the p-polarized reflectance spectra at oblique incidence near the longitudinal optical (LO)-phonon frequencies of both QW and barrier materials. By fitting the reflectance spectra to a dielectric function model, the LO phonon frequency of the (Zn,Mg)O barrier layers can be determined. The LO phonon frequency depends on the Mg content. Comparing to Mg content calibration via cathodoluminescence, a linear relationship between the reflectance dip frequency and the Mg content is obtained. The presented method serves as a rapid means to determine the Mg content on final structures with very thin (Zn,Mg)O layers -such as device structures- where alternative, destructive methods cannot be used.

Over 15% efficient wide-band-gap Cu(In,Ga)S2 solar cell: Suppressing bulk and interface recombination through composition engineering

Over 15% efficient wide-band-gap Cu(In,Ga)S2 solar cell: Suppressing bulk and interface recombination through composition engineering

Biostimulant action of Lithothamnium sp. promoting growth, yield, and biochemical and chemical changes on onion

The development of new natural biostimulant sources for a sustainable agriculture is a strategic issue aiming to improve the healthy food production. In this sense, the goal was to identify the biostimulant action of the calcareous alga Lithothamnium sp. (Rhodophyta) on onion in two experiments, (i) in pots and (ii) at field under organic system, both in factorial scheme with two onion cultivars and foliar sprays with micronized Lithothamnium sp. at concentration of 1.5 and 3.0 g L−1. The plant growth promotion and commercial yield improvement of two onion cultivars were achieved and related to changes on amino acid metabolism and source-to-sink flow stimuli. Better nutrient acquisition also was achieved related to the stimuli to thin roots growth, with N, Mg, Mn, Zn, and Cu content in bulbs improved at 3.0 g L−1, while 1.5 g L−1 allowed highest Ca, Mg, Mn, and Zn content in bulbs. Thus, the results presents Lithothamnium sp. as novel biostimulant source to grow onion, which effects related to the presence of bioactive humic acid that calcareous algae release by micronization.

(Invited) FTIR Spectroscopical Imaging of the Substrate / Polymer Interface upon Exposure to Corrosive Environments

Organic coating is an efficient method to protect metal surfaces from corrosive atmospheres but is dependent on the presence of a stable interface between the substrate and the polymer coating. However, coatings based on polymers have mostly only limited barrier properties for water and oxygen. Transport of water to the interfacial region is for most coatings inevitable upon prolonged exposure in aqueous environments. Ingress of water molecules can destabilize the substrate / polymer interface and lead to delamination of the polymer coating and initiation of corrosion processes. In this work was spectrochemical imaging of the substrate / polymer interfacial region using a FTIR-microscope with a focal plane array (FPA) detector is performed in order to follow the water up-take at the substrate / polymer interfacial region with micrometer sized lateral resolution. Chemical imaging of the interfacial region between substrates, such as Ge and Ge with thin Zn metallic layers, and organic coatings was performed during exposure to 0.1 M NaCl and humid air (95 %RH). The water uptake and water induced alterations in the substrate / polymer interfacial region on the microscale was followed. Simultaneous electrochemical impedance measurements allowed correlation of electrochemical information from the coated metal with the chemical imaging of the interfacial region.

Microscopic appraisal and mechanical behavior of hybrid Cu/Al joints fabricated via friction stir spot welding-brazing and modified friction stir clinching-brazing

This paper focuses on the improvement of hybrid Cu/Al weld performance via a combination of self-reacting brazing mechanism (for stable metallurgical transformation) and process modification approach (for the elimination of tool profile-induced stress-raiser). The modified friction stir clinching-brazing (MFSC-B) and friction stir spot welding-brazing (FSSW-B) of dissimilar AA5083-H321 aluminum and commercially pure Cu alloys are investigated with the use of a thin Zn intermediate layer. The load-bearing capacity, fracture behavior, and microstructure of the respective joints are investigated and compared. The results show that plausible intermetallic phases of Al–Cu (Al2Cu and Al4Cu9) and Cu–Zn are present at the stir zones of all the joints while the brazed zone of the MFSC-B joint is predominated by uniform lamellar eutectic structure due to higher heat input, localized two-fold Zn melting, and frictional-stirring activated eutectic transformation. The increase in the load-bearing area (brazed + stir zones) of the MFSC-B joint improved the fracture resistance of the joint by 59% as the average tensile-shear loads of about 7.0 and 4.4 kN were obtained in the MFSC-B and FSSW-B joints respectively. The use of MFSC-B is thus recommended as a reasonable alternative for improving the weld performance of dissimilar reactive metals.

Structural, optical, electrical and catalytic properties of precursor solution-aged spray deposited undoped, Zn-doped and Ag-doped CdO thin films

Photocatalytic performance of precursor solution-aged undoped, Zn-doped CdO (CdO:Zn) and Ag-doped CdO (CdO:Ag) thin films has been reported in this paper. Perfume atomizer is adopted to deposit the films. CdO, CdO:Zn and CdO:Ag thin films exhibit cubic crystal structure. The crystallite size values were 34, 31 and 27 nm, respectively, for the CdO, CdO:Zn and CdO:Ag thin films. In the EDX spectra of the CdO:Zn and CdO:Ag thin films, Zn and Ag were observed along with Cd and O. The CdO:Zn and CdO:Ag thin films exhibit increased transparency and widened band gap values. PL spectra showed peaks related to oxygen vacancies for all the films. Reduced resistivity was evinced for the CdO:Zn and CdO:Ag thin films. The degradation efficiencies of the CdO, CdO:Zn and CdO:Ag thin films against methyl orange after 75 min light exposure were 76.4, 84.3 and 90.4%, respectively. The CdO:Zn and CdO:Ag catalysts exhibit satisfactory stability with better reusable nature and are suitable for the effective treatment of organic toxic dyes.