Al Corrosion Research Articles

Research on hydrogen generation from rapid hydrolysis of aluminum in sodium fluoride solution

Hydrogen generation from rapid hydrolysis of aluminum in sodium fluoride solution was investigated through a hydrolysis experiment. Rapid and instant hydrogen yield were observed using sodium fluoride as additive. The experimental results demonstrate that the increase of temperature and the amount of additives in a certain range will boost the hydrogen production. The amount of additives outside the range only has an effect on the rapid hydrolysis of the aluminum during the initial stage, but the total amount of hydrogen produced doesn’t increased significantly. Theoretical analysis of the effects of the mixing ratio and the temperature on the hydrogen production rates were performed using the shrinking core model and the kinetic model. The shrinking core model parameter a and k indicate the film change degree of porosity and thickness and the effect of time on the diffusion coefficient. the kinetic model is verified and the activation energy confirming hydrogen yield control by a molecular diffusion process. Correspondingly, mechanisms of Al corrosion in NaF solutions under low and high alkalinity were proposed, respectively.

Flexible hydrogen fuel cell fabricated on paper with embedded aluminium foil

Direct hydrogen fuel cells are generally heavy and rigid systems based on metal or plastic materials, which are not suitable for various miniwatt and flexible devices. In this study, we have developed a lightweight and flexible fuel cell based on paper substrate embedded with an Al foil inside, which is used as an in-situ hydrogen source by reaction with an electrolyte solution during operation. Benefited from the inhibited hydroxyl transportation by the porous cellulose network, the vigorous Al corrosion reaction is well controlled even though strong alkaline electrolyte is adopted, so that the fuel cell can be discharged for more than 5 hours at 1 mA cm-2 (0.83 V) with only 3.5 mg Al foil. The corresponding faradaic and energy efficiencies are as high as 72% and 18.3%, respectively. The fuel cell flexibility is also quite good when facing different bending angles. Considering its moderate power output, this flexible paper-based hydrogen fuel cell is especially suitable for powering various miniwatt and flexible devices, such as wearable electronics, biosensors, RFID tags, etc. However, higher power can be obtained by suitable stacking of the fuel cell.

Aluminum Corrosion Inhibition by 7-(Ethylthiobenzimidazolyl) Theophylline in 1M Hydrochloric Acid: Experimental and DFT Studies

Inhibitive properties of 7-(ethylthiobenzimidazolyl) theophylline (7-ETBT) molecule for the corrosion of aluminum (Al) in one molar hydrochloric acid medium have been investigated using mass loss and Tafel polarization methods. The results suggest spontaneous and predominant physical adsorption of 7-ETBT on the metal surface which obeys Langmuir isotherm model. The studied inhibitor showed excellent inhibition efficiency up to 94.07 % at 298 K for its optimum concentration (2 mM). Moreover, Tafel polarization method revealed that 7-ETBT is a cathodic-type inhibitor. Further investigation on the morphology using scanning electron microscopy (SEM) has confirmed the existence of a protective film of inhibitor molecules on aluminum surface. Theoretical approach for the performance of 7-ETBT as Al corrosion inhibitor is also done using Density Functional Theory (DFT) level with B3LYP exchange correlation functional for 6-31G (d, p) basis set. The results provided by this theoretical study are consistent with the experimental data. All the results have shown an evidence of the effectiveness of the inhibitive effect of 7-ETBT on Al.

Liquid Structures and Transport Properties of Lithium Bis(fluorosulfonyl)amide/Glyme Solvate Ionic Liquids for Lithium Batteries

The liquid structures and transport properties of electrolytes composed of lithium bis(fluorosulfonyl)amide (Li[FSA]) and glyme (triglyme (G3) or tetraglyme (G4)) were investigated. Raman spectroscopy indicated that the 1:1 mixtures of Li[FSA] and glyme (G3 or G4) are solvate ionic liquids (SILs) comprising a cationic [Li(glyme)]+ complex and the [FSA]− anion. In Li[FSA]-excess liquids with Li[FSA]/glyme molar ratios greater than 1, anionic Lix[FSA]y(y–x)– complexes were formed in addition to the cationic [Li(glyme)]+ complex. Pulsed field gradient NMR measurements revealed that the self-diffusion coefficients of Li+ (DLi) and glyme (Dglyme) are identical in the Li[FSA]/glyme=1 liquid, suggesting that Li+ and glyme diffuse together and that a long-lived cationic [Li(glyme)]+ complex is formed in the SIL. The ratio of the self-diffusion coefficients of [FSA]− and Li+, DFSA/DLi, was essentially constant at ~1.1–1.3 in the Li[FSA]/glyme<1 liquid. However, DFSA/DLi increased rapidly as the amount of Li[FSA] increased in the Li[FSA]/glyme>1 liquid, indicating that the ion transport mechanism in the electrolyte changed at the composition of Li[FSA]/glyme=1. The oxidative stability of the electrolytes was enhanced as the Li[FSA] concentration increased. Furthermore, Al corrosion was suppressed in the electrolytes for which Li[FSA]/glyme>1. A battery consisting of a Li metal anode, a LiNi1/3Mn1/3Co1/3O2 cathode, and Li[FSA]/G3=2 electrolyte exhibited a discharge capacity of 105mAhg−1 at a current density of 1.3mAcm−2, regardless of its low ionic conductivity of 0.2mScm−1.

1‐Ethyl‐3‐Methyl‐Imidazolium Bis (Trifluoromethane‐ sulfonyl) Imide as an Electrolyte Additive in LiFePO4‐ Based Batteries for Suppressing Aluminum Corrosion

AbstractLithium bis (trifluoromethanesulfonyl) imide (LiTFSI) is a potentially useful electrolyte salt for use in Li‐ion batteries. LiTFSI, however, is associated with severe corrosion of Al current collectors. This study investigates the ionic liquid 1‐ethyl‐3‐methyl‐imidazolium bis (trifluoromethanesulfonyl) imide (EMITFSI) as an Al corrosion inhibitor in LiTFSI electrolytes. Different concentrations of EMITFSI are used as additives in 1 m LiTFSI‐based electrolytes to systematically assess the performance of lithium iron phosphate (LiFePO4) cathodes. The results from electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), Cyclic voltammetry (CV) indicate that adding EMITFSI into LiTFSI‐based electrolytes can effectively prevent severe corrosion of Al caused by LiTFSI‐based electrolytes. The LiFePO4 cells that use 1 m LiTFSI+11 % EMITFSI‐based electrolytes demonstrate a superior rate capability and cycling stability when compared to cells that use the LiTFSI‐based electrolyte.

Highly Sensitive Colorimetric Detection of Early Stage Aluminum Corrosion in Water Using Plasmonic Gold Nanoparticle Films

AbstractCorrosion remains the major reason for the failure of metallic parts. Therefore, spotting and evaluating the severity of corrosion at its early stages is of great importance. Herein, a novel optical corrosion probe based on plasmonic gold nanoparticles immobilized on aluminum surface is demonstrated. The measurements confirm that the corrosion rate and mechanism of bare aluminum is identical to that of the developed probe. During Al corrosion, the gold nanoparticles are located entirely at the interface between the inner dense and outer porous layers of the formed aluminum oxide. The growth of the inner oxide layer during corrosion prompts a change in the reflection spectra and the appearance of strong coloration that is easily observed by the naked eye. Numerical modeling reveals that these optical changes occur mainly due to light interference within the inner oxide layer, which is located between the plasmonic gold nanoparticles and the underlying reflective aluminum. The ability of the plasmonic probe is further demonstrated to monitor the aqueous corrosion of thin films, bulk and alloyed Al, as well as Al protected by a self‐assembled monolayer of hydrophobic surfactant, and, hence, the wide applicability of the method.

A novel boron-based ionic liquid electrolyte for high voltage lithium-ion batteries with outstanding cycling stability

Advanced ionic liquid-based electrolyte is herein characterized for the application in high voltage lithium-ion batteries. The electrolyte based on N-propyl-N-methylpiperidiniumdifluoro(oxalate)borate (PP13DFOB), lithium bis(trifluoromethanesulfonyl)-imide (LiTFSI) and dimethyl carbonate (DMC) is fully characterized in terms of anodic corrosion behavior, electrochemical properties and cathode-electrolyte interphase stability. Experimental and computational results show that the preferential oxidation of PP13DFOB results in a stable and low impedance solid electrolyte interface (SEI) film on the surface of LiNi0.5Mn1.5O4 (LNMO) cathode and a passivation layer on Al foil, which suppress transition metal dissolution and Al corrosion at high voltage. As a result, the Li/LNMO and Li/graphite coin cells with ionic liquid-based electrolyte achieve excellent electrochemical performance, displaying a discharge capacity of 121.2 mAh g−1 and 369.2 mAh g−1 after 100 cycles at 0.5 C respectively and demonstrating no distinct capacitance attenuation during charge-discharge cycles.

Localized High-Concentration Sulfone Electrolytes for High-Efficiency Lithium-Metal Batteries

Summary To enable next-generation high-energy-density lithium (Li)-metal batteries (LMBs), an electrolyte that has simultaneous high Li-metal Coulombic efficiency (CE) and high anodic stability on cathodes is of significant importance. Sulfones are known for strong resistance against oxidation, yet their application in LMBs is restricted because of their poor compatibility with Li-metal anodes, high viscosity, and poor wettability. Here, we demonstrate that a high Li CE over 98% can be achieved in concentrated sulfone-based electrolytes. Furthermore, the viscosity and wettability issues of sulfones are resolved by the addition of a fluorinated ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, to form a localized high-concentration electrolyte (LHCE), which not only provides further improvement in Li CE (98.8%) but also remains anodically stable with high-voltage cathodes, suppresses Al corrosion, and enables LMBs to operate in a wide temperature range. As a result, significantly improved cycling performance of LMBs has been realized with sulfone-based LHCE.

An Environmentally Friendly Approach Towards Mitigation of Al Corrosion in Hydrochloric Acid by Yellow Colour Ripe Arecanut Husk Extract: Introducing Potential and Sustainable Inhibitor for Material Protection

The effect of extracts of yellow colour ripe arecanut husk on the inhibition of Al corrosion in 0.5 M HCl solution was examined through weight loss and electrochemical techniques. Weight loss results show that yellow colour ripe arecanut husk extract acts as a good adsorption green corrosion inhibitor for Al metal in 0.5 M HCl solution. The protection efficiency of the inhibitor varied with the inhibitor concentration. The protective action of the yellow colour ripe arecanut husk extract increased with the increase in its amounts in 0.5 M HCl solution. The Langmuir isotherm model shows that yellow colour ripe arecanut husk extract inhibits the Al corrosion in 0.5 M HCl solution by adsorption mechanism. Tafel curves proved that yellow colour ripe arecanut husk extract is mixed-type inhibitor. Results of Nyquist curves confirmed that adsorption of yellow colour ripe arecanut husk extract species led to a enhance in charge transfer resistance values and decrease in the values of double-layer capacitance. Both scanning electron microscopy and atomic force microscopy techniques are used to examine the Al surface morphology without and with the yellow colour ripe arecanut husk extract. Protection efficiency obtained by chemical and electrochemical techniques at different inhibitor concentrations.

Investigation of the N-butyl-N-methyl pyrrolidinium trifluoromethanesulfonyl-N-cyanoamide (PYR14TFSAM) ionic liquid as electrolyte for Li-ion battery

A new asymmetrical anion, trifluoromethanesulfonyl-N-cyanoamide (TFSAM−), was paired with N-butyl-N-methyl pyrrolidinium (PYR14+) to prepare PYR14TFSAM. It has been investigated for Li-ion battery application and compared to its PYR14+ analogs paired with either the dicyanamide anion (DCA−) or other anions (i.e. bis(trifluoromethanesulfonyl) imide (TFSI−), bis(fluorosulfonly)imide (FSI−), trifluoromethanesulfonyl-fluorosulfonyl imide (FTFSI−)). The conductivity of PYR14TFSAM is not only higher than that of PYR14TFSI, but also higher than that of PYR14FTFSI with 3.8mScm−1 at 20°C and 12.6mScm−1 at 60°C. In addition, the ionic liquid does not crystallize and exhibits a viscosity similar to that of PYR14FSI (and even lower above 30°C, which also results in a higher conductivity at high temperature). Compared to PYR14DCA, PYR14TFSAM has a higher anodic stability, more compatible with state-of-the-art cathodes such as NCM, even though the PYR14DCA electrolyte also allowed surprisingly good cycling results of NCM cathode considering its low anodic stability. PYR14TFSAM also allows Li+ (de-)/insertion into graphite, using vinylene carbonate as additive. When used in conventional Li-ion electrolyte solvents, it leads to moderate conductivity (as compared with LiFSI or LiTFSI), although much higher than LiDCA. Additionally, it is shown that, even in EC/DMC-based electrolyte, LiTFSAM does not induce Al corrosion at 4.2V.

Effect of propylene carbonate-Li+ solvation structures on graphite exfoliation and its application in Li-ion batteries

The effect of propylene carbonate (PC)-Li+ solvation structures on graphite exfoliation was investigated over a range of concentrations of PC-based electrolytes. At low concentrations of lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) in PC (1.3M and 2.1M), the graphite anode was exfoliated. However, the graphite exfoliation could be effectively suppressed when the concentrations of dissolved LiTFSI were increased to 2.5M and 3.3M. The results of spectroscopic analyses and density functional theory (DFT) calculations revealed that electrochemical exfoliation of the graphite anode is closely associated with a special spatial configuration of Li+-(PC)n (1≤n≤4) solvation structures at various Li-salt concentrations and corresponding solid electrolyte interface (SEI) film formation mechanisms. When the concentration of LiTFSI increased from 1.3 to 3.3M, the spatial configuration of Li+-(PC)n (1≤n≤4) solvation gradually changed from a tetrahedron (occupied space of 10.19Å) to planar (occupied space of 3.05Å), which reduced the structure change for co-intercalation into the graphite interlayers of Li+-(PC)n (1≤n≤4) solvates. Meanwhile, the affinity between Li+-(PC)n (1≤n≤4) solvation cations and TFSI− anions was increased, leading to the significant contribution of TFSI− anions to SEI formation on the surface of graphite. Additionally, Al corrosion was not of concern in concentrated LiTFSI electrolyte. The 3.3M LiTFSI/PC concentrated electrolyte exhibits promising electrochemical performance in graphite||LiNi1/3Co1/3Mn1/3O2 full cells.

Inhibition of Al corrosion in 0.5 M HCl solution by Areca flower extract

The corrosion inhibition property of Areca flower extract species on the Al surface in acid (0.5MHCl) medium was tested by weight loss, Tafel plot, impedance, scanning electron microscopy and atomic force microscopy techniques. The influence of different concentrations of Areca flower extract, 0.5MHCl solution temperature and aluminum immersion (contact) time was also evaluated. Parameters such as Ea, ΔH∗, ΔS∗, Kads and ΔG°ads were calculated by the gravimetric (weight loss) technique. Results of mass loss technique indicated that, the Areca flower extract molecules are strongly adsorbed at Al- 0.5MHCl solution interface and follows the law of the Langmuir adsorption model. Tafel curves show that, the Areca flower extract molecules effectively adsorbed on the active Al sites by replacing the H2O molecules and strongly interact with cathodic and anodic sites impeding the dissolution reaction by mixed mode. Hence, Al metal is protected. Electrochemical impedance results indicate that, area of a semicircle (Nyquist plots) in the presence of the Areca flower extract is high compared to the bare system. The variation in the surface topography of aluminum was analyzed through scanning electron microscopy and atomic force microscopy techniques. Further, AFM results show that, surface roughness values in the protected Al system are low compared to the unprotected Al system.

Gold Nanoparticles As a Tool for Probing Corrosion Processes

Optical corrosion probes provide several advantages, enabling remote sensing, probing in variable media (gas, liquid) and temperatures, and imaging with high spatial resolution. The optical properties (reflection, transmission) of plasmonic nanoparticles (NPs) in the proximity of a metal mirror strongly depend on the dielectric properties of the immediate environment, characteristic of localized surface plasmon resonance (LSPR) systems, and the separation between the NPs and the metal surface, forming a Fabry-Pérot interferometer with the plasmonic array.1-3 A plasmonic corrosion probe combines a film of corroding metal of interest and a chemically and morphologically stable plasmonic nanostructure (Au NP array).4 Au NPs can be immobilized on the surface of the chemically active metal by adsorption from a colloid solution, or deposited by vacuum evaporation as a film of Au nano-islands. We studied the corrosion of aluminum in hot water using the optical response of Au NPs immobilized on the chemically active metal surface. Oxidation of Al in water in the temperature range 40–100 oC produces a non-uniform hydroxide layer, with a dense layer adjacent to the metal and an outer porous part consisting of rough platelets of pseudoboehmite. High-resolution scanning electron microscopy (HRSEM) images (Figure 1) of a fully oxidized plasmonic probes show that the oxide layer is more dense below the Au NPs and has a rough, open structure on the solution side (above the Au NPs), closely resembling the structure with no plasmonic layer. The Au NP layer embedded in the oxide preserves its integrity, while the separation between the Au NPs and the glass after complete corrosion of the Al film remains nearly constant for Au NPs evaporated or immobilized from solution. Cross-sectional HRSEM and transmission electron microscopy (TEM) images show that the separation between the plasmonic layer and the corroding metal increases with time while preserving the morphology of the oxide layer. Corrosion of plasmonic probes exhibits large changes in the reflection spectra. The changes were measured quantitatively in-situ using a conventional fiber-optics system. In the course of the Al corrosion the visual appearance (color) of the probe continuously varies. Changes in the reflection spectra and the probe color can be quantified, allowing evaluation of the propagation of the corrosion front. The high color contrast also allows visualization of lateral inhomogeneities in the corroding layer. The combination of plasmonic probes and image processing opens the possibility of simultaneous measurement of local corrosion rates over a macroscopic area. Plasmonic corrosion probes are simple to implement, while the results may be useful in the design of effective optical sensors for practical applications. With certain modifications, the plasmonic corrosion probe approach may be applicable to other active metals of practical importance. References. 1. Aussenegg, F. R.; Brunner, H.; Leitner, A.; Lobmaier, C.; Schalkhammer, T.; Pittner, F. Sensors and Actuators B-Chemical 1995, 29, 204. 2. Sannomiya, T.; Balmer, T. E.; Heuberger, M.; Voros, J. Journal of Physics D-Applied Physics 2010, 43. 3. Kedem, O.; Sannomiya, T.; Vaskevich, A.; Rubinstein, I. The Journal of Physical Chemistry C 2012, 116, 26865. 4. Tesler, A. B.; Sabatani, E.; Vaskevich, A.; Rubinstein, I. Annual Meeting of the Israel Chemical Society 2016, Tel Aviv, Israel. Figure 1

Ionic liquid-based electrolyte with dual-functional LiDFOB additive toward high-performance LiMn2O4 batteries

Manganese oxide-based cathodes are one of the most promising lithium-ion battery (LIB) cathode materials due to their cost-effectiveness, high discharge voltage plateau (above 4.0 V vs. Li/Li+), superior rate capability, and environmental benignity. However, these batteries using conventional LiPF6-based electrolytes suffer from Mn dissolution and poor cyclic capability at elevated temperature. In this paper, the ionic liquid (IL)-based electrolytes, consisting of 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfon)imidate (PYR1,4-TFSI), propylene carbonate (PC), lithium bis(trifluoromethanesulfon)imide (LiTFSI), and lithium oxalyldifluoroborate (LiDFOB) additive, were explored for improving the high temperature performance of the LiMn2O4 batteries. It was demonstrated that LiTFSI-ILs/PC electrolyte associated with LiDFOB addition possessed less Mn dissolution and Al corrosion at the elevated temperature in LiMn2O4/Li batteries. Cyclic voltammetry and electrochemical impedance spectroscopy implied that this kind of electrolyte also contributed to the formation of a highly stable solid electrolyte interface (SEI), which was in accordance with the polarization measurement and the Li deposition morphology of the symmetric lithium metal cell, thus beneficial for improving the cycling performance of the LiMn2O4 batteries at the elevated temperature. Cyclic voltammetry and electrochemical impedance spectroscopy implied that the cells using this kind of electrolyte exhibited better interfacial stability, which was further verified by the polarization measurement and the Li deposition morphology of the symmetric lithium metal cell, thus beneficial for improving the cycling performance of the LiMn2O4 batteries at the elevated temperature. These unique characteristics would endow this kind of electrolyte a very promising candidate for the manganese oxide-based batteries.

EDTA as a corrosion inhibitor for Al in 0.5 M HCl: adsorption, thermodynamic and theoretical study

<p class="Default"><span lang="EN-US">In this study; EDTA is used in very small amount (10<sup>-10</sup> M) as an inhibitor for the Al corrosion in 0.5 M HCl. Thermodynamic and adsorption parameters are calculated. The result shows that, in this range of concentrations, EDTA is chemisorbed at the Al surface, forming a stable complex with Al and give inhibition efficiency up to 89 %. For more con­centration, unstable complex is formed and acceleration of corrosion occurs. The adsorp­tion fit well to Langmuir, Temkin isotherms and El-awady model. Density functional theory (DFT) is used to study the geometrical optimizations of EDTA. From the obtained optimized structure, The highest occupied molecular orbital (EHOMO), the lowest unoc­cupied molecular orbital (ELUMO and their energy difference (ΔE), the total energy (TE), electronegativity (χ), dipole moment (µ), global hardness (η), global softness (σ), elec­tron affinity (A), ionization potential (I), the fraction of electrons transferred (∆N) and were determined using B3LYP/6-31G(d,p) basis set.</span></p>

Ion Transport Mechanism of a Gel Electrolyte Comprising a Salt in Binary Plastic Crystalline Mixtures Confined inside a Polymer Network

We discuss here the ion transport mechanism of a gel electrolyte comprising lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) solvated by two plastic crystalline solvents, one a solid (succinonitrile, abbreviated as SN) and another (a room temperature ionic liquid) (1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, (abbreviated as IL) confined inside a linear network of poly(methyl methacrylate) (PMMA). The concentration of the IL component (x) determines the physical properties of the unconfined electrolyte (i.e., SN1-xILx-LiTFSI) and when confined inside the polymer network (GPE-x). The extent of disorder in the SN1-xILx-LiTFSI and the GPE-x electrolytes is enhanced compared to both the bare SN-LiTFSI and IL-LiTFSI electrolytes. The enhanced disordering in the plastic phase alters both the local ion environment and viscosity. These changes strongly influence the ion mobility and nature of predominant charge carriers and thus the ion conduction mechanism in SN1-xILx-LiTFSI and GPE-x. The proposed SN1-xILx-LiTFSI and the GPE-x electrolytes show predominantly anion conduction (tTFSI ≈ 0.5); however, lithium transference number (tLi ≈ 0.2) is nearly an order higher than the IL-LiTFSI (tLi ≈ 0.02-0.06). The ionic conductivity of SN1-xILx-LiTFSI is much higher (especially for x ≈ 0.1) compared to both SN-LiTFSI and IL-LiTFSI. The ionic conductivity of the GPE-x, though lower than the unconfined SN1-xILx-LiTFSI electrolytes, is still very promising, displaying values of ∼10-3 Ω-1 cm-1. The GPE-x displayed compliable mechanical properties, stable Li-electrode/electrolyte interface, low rate of Al corrosion, and stable cyclability over several tens of charge-discharge cycles when assembled in a separator-free Li-graphite cell. The promising electrochemical performance further justifies the simple strategy of employing mixed physical state plasticizers to tune the physical properties of polymer electrolytes requisite for application in rechargeable batteries.

Highly concentrated polycarbonate‐based solid polymer electrolytes having extraordinary electrochemical stability

ABSTRACTSolid polymer electrolytes (SPEs) are compounds of great interest as safe and flexible alternative ionics materials, particularly suitable for energy storage devices. We study an unusual dependence on the salt concentration of the ionic conductivity in an SPE system based on poly(ethylene carbonate) (PEC). Dielectric relaxation spectroscopy reveals that the ionic conductivity of PEC/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte continues to increase with increasing salt concentration because the segmental motion of the polymer chains is enhanced by the plasticizing effect of the imide anion. Fourier transfer‐infrared (FTIR) spectroscopy suggests that this unusual phenomenon arises because of a relatively loose coordination structure having moderately aggregated ions, in contrast to polyether‐based systems. Comparative FTIR study against PEC/lithium perchlorate (LiClO4) electrolytes suggests that weak ionic interaction between Li and TFSI ions is also important. Highly concentrated electrolytes with both reasonable conductivity and high lithium transference number (t+) can be obtained in the PEC/LiTFSI system as a result of the unusual salt concentration dependence of the conductivity and the ionic solvation structure. The resulting concentrated PEC/LiTFSI electrolytes have extraordinary oxidation stability and prevent any Al corrosion reaction in a cyclic voltammetry. These are inherent effects of the highly concentrated salt. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2442–2447

Allotropic Control: How Certain Fluorinated Carbonate Electrolytes Protect Aluminum Current Collectors by Promoting the Formation of Insoluble Coordination Polymers

Presently, there is a strong incentive for increasing the operation voltage of Li-ion cells above 4.5 V in order to increase the density of stored energy. Aluminum is an inexpensive, lightweight metal that is commonly used as a positive electrode current collector in these cells. Imide LiX salts, such as lithium bis(trifluoromethylsulfonyl)imide (X = TFSI), and lithium bis(fluorosulfonyl)imide (X = FSI), are chemically stable on the energized lithiated transition metal oxide electrodes, but their presence in the electrolyte causes rapid anodic dissolution and pitting of Al current collectors at potentials exceeding 4.0 V versus Li/Li+. For LiBF4 and LiPF6, the release of HF near the energized surfaces passivates the exposed Al metal, inhibiting this pitting corrosion, but it also causes the gradual degradation of the cathode active material, negating this important advantage. Here we report that in certain electrolytes containing fluorinated carbonate solvents and LiX salts, the threshold voltage for safe operation of Al current collectors can be increased to 5.5 V versus Li/Li+. Interestingly, the most efficient solvent also facilitates the formation of an insoluble gel when AlX3 is introduced into this solvent. We suggest that this solvent promotes the aggregation of coordination polymers of AlX3 at the exposed Al surface that isolate this surface from the electrolyte, thereby preventing further Al dissolution and corrosion. Other examples of Al collector protection may also involve this mechanism. Our study suggests that such “allotropic control” could be a way of widening the operation window of Li-ion cells without electrode deterioration, Al current collector corrosion, and electrolyte breakdown.

Film Properties of Al Thin Films Depending on Process Parameters and Film Thickness Grown by Sputter

We developed an Al sputtering process by varying the plasma power, process temperature, and film thickness. We observed an increase of hillock distribution and average diameter with increasing plasma power, process temperature, and film thickness. Since the roughness of a film increases with the increase of the distribution and average size of hillocks, the control of hillock formation is a key factor in the reduction of Al corrosion. We observed the lowest hillock formation at 30 W and 100 oC. This growth characteristic of sputtered Al thin films will be useful for the reduction of Al corrosion in the future of the electronic packaging field.

Improvement of Aluminum–Air Battery Performances by the Application of Flax Straw Extract

The effect of a flax straw extract on Al corrosion inhibition in a strong alkaline solution was studied by using electrochemical measurements, weight-loss analysis, SEM, and FTIR spectroscopy. Flax straw extract added (3 vol %) to the 5 m KOH solution to act as a mixed-type Al corrosion inhibitor. The electrochemistry of Al in the presence of a flax straw extract in the alkaline solution, the effect of the extract on the Al morphology and surface films formed, and the corrosion inhibition mechanism are discussed. Finally, the Al-air battery discharge capacity recorded from a cell that used the flax straw extract in the alkaline electrolyte is substantially higher than that with only a pure alkaline electrolyte. This improved sustainability of the Al anode is attributed to Al corrosion inhibition and, consequently, to hydrogen evolution suppression.