Formation Of AlF3 Research Articles

Study of the Corrosion Behavior of Cathode Current Collector in LiFSI Electrolyte.

Cycling aging is the one of the main reasons affecting the lifetime of lithium-ion batteries and the contribution of aluminum current collector corrosion to the ageing is not fully recognized. In general, aluminum is corrosion resistant to electrolyte since a non-permeable surface film of alumina is naturally formed. However, corrosion of aluminum current collector can still occur under certain conditions such as lithium bis(fluorosulfonyl)imide (LiFSI)-based electrolyte or high voltage. Herein, we investigates the corrosion of aluminum current collector in the electrolyte of 1.2 M LiFSI in ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed solvents. The electrochemical results shows that the corrosion current of aluminum is enhanced by cycling time and potential, which is correlated with the surface species and morphology. The formation of AlF3, which is induced by deep penetration of F- anions through surface passivation film, leads to internal volume change and the surface crack in the end. Our work will be inspiring for future development of high-energy-density and high-power-density lithium-ion batteries in which the LiFSI salt will be intensively used.

Electrochemical Passivation of Aluminum As a Current Collector for Solid-State Polymer Batteries : PEO/LiTFSI Polymer Electrolyte

Investigation of the electrochemical properties and passivation mechanism of aluminum as a current collector for solid-state polymer batteries is carried out. Herein, electrochemical stabilities of Polyethylene glycol (PEO) based solid-state electrolyte containing Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt are proved using electrochemical dynamic- and transient-mode polarization with surface scratching. These results indicate that Al metal undergoes passivation with a layer below 4.5 V vs. Li+/Li. And then Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) reveal double layers are formed during the passivation on Al metal surface, with the outer layer composed of metal fluorides (AlF3) and the inner layer composed of metal oxides (Al2O3). The formation of the AlF3 layer on Al metal surface is attributed to the reaction between Al2O3 and HF following as Al2O3 + 6HF → 2AlF3 + 3H2O. Therefore, successful passivation achieved by the formation of AlF3 on the Al2O3 surface of Al metal facilitates to be widely used as a current collector for lithium metal polymer batteries. Therefore, successful passivation by the formation of AlF3 on the Al2O3 surface of Al metal making it a promising choice for the positive electrode in lithium metal polymer batteries.

Thermal analysis of microscale aluminum particles coated with perfluorotetradecanoic (PFTD) acid

Micron-diameter aluminum particles (μAl) are highly reactive when combined with a solid oxidizer. However, μAl powder is less reactive in a gaseous air environment, where oxygen is the only available oxidizer, unless very well dispersed. While enthalpy of oxidation for Al is high, many variables influence the viability of harnessing stored chemical energy within a single Al particle whose reaction is diffusion controlled. One way to enhance Al particle reaction is to coat the particle surface with a condensed phase oxidizing agent that is in immediate contact with the particle surface to promote diffusion reactions. Fluorocarbons such as perfluorocarboxylic acids have been used to enhance Al combustion for nanoscale Al (nAl) particles because fluorinated species are also reactive with the Al2O3 passivation shell surrounding the Al core particle. This study extends previous work on nAl toward μAl particles coated with perfluorotetradecanoic acid (PFTD) (F3C(CF2)11CO2H) and then characterizes the μAl-PFTD thermal reactivity. Samples were prepared with varying PFTD concentrations ranging from 0 to 20 mass percent, and experiments were performed using thermogravimetric analysis and high-speed infrared imaging on powder samples. Results show the PFTD-coated μAl particles provide higher apparent reaction temperatures (by about 500 °C) and longer burn times at elevated temperatures (by about 20%). Higher concentrations of PFTD tend to produce more gas-generating reactions with particles ejecting from the loose powder pile, but 9% PFTD coating on μAl particles provides a good balance of stable reactivity with high-temperature reactions (~ 1800 °C) and high-temperature burn times (~ 18 s). The higher temperatures for PFTD-coated μAl particles are attributed to the increased (nearly double) energy produced in the formation of AlF3 (56.10 kJ g−1) compared to Al2O3 (30.98 kJ g−1); both of these product species are identified in XRD analysis. In addition, the formation of AlF3 may reduce the melting and phase transition temperature of Al2O3 by several hundred degrees and contribute to catalytically activating the Al reaction. Overall, coating μAl particles with a fluorinated polymer facilitates reaction in an air environment, even for small concentrations of PFTD coating.

Quantum Chemical Insight into the LiF Interlayer Effects in Organic Electronics: Reactions between Al Atom and LiF Clusters.

It is well known that the aluminum cathode performs dramatically better when a thin lithium fluoride (LiF) layer inserted in organic electronic devices. The doping effect induced by the librated Li atom via the chemical reactions producing AlF3 as byproduct was previously proposed as one of possible mechanisms. However, the underlying mechanism discussion is quite complicated and not fully understood so far, although the LiF interlayer is widely used. In this paper, we perform theoretical calculations to consider the reactions between an aluminum atom and distinct LiF clusters. The reaction pathways of the Al-(LiF)n (n = 2, 4, 16) systems were discovered and the energetics were theoretically evaluated. The release of Li atom and the formation of AlF3 were found in two different chemical reaction routes. The undissociated Al-(LiF)n systems have chances to change to some structures with loosely bound electrons. Our findings about the interacted Al-(LiF)n systems reveal new insights into the LiF interlayer effects in organic electronics applications.

High temperature versus low temperature Zebra (Na/NiCl2) cell performance

The effect of operating temperature on performance and aging of Zebra cells was investigated. The cells were cycled at 260°C and 350°C using a modified charging regime to accelerate damage. The cathode and solid electrolyte of degraded cells at the end of cycling were analyzed by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. It is hypothesized that the formation of AlF3 on the surface of the β″ alumina electrolyte contributes to the failure of cells at low temperatures. A mechanism based on the overcharge reaction is proposed for the formation of this phase. At 350°C, a significant capacity loss was observed with cycle life, which correlates to nickel particle growth as the cause of this phenomenon. The factors responsible for Ni grain growth are discussed.

Formation and suppression of AlF<sub>3</sub> during HF digestion of rock samples in Teflon bomb for precise trace element analyses by ICP-MS and ID-TIMS

An aluminum fluoride, AlF3, forms during HF digestion of felsic rock samples, for trace element and isotope geochemistry, which use a Teflon bomb at high temperature and pressure. The AlF3 incorporates trace elements (Rb, Sr, Y, Cs, Ba, REE, Pb, Th, and U), and can not be decomposed by conventional methods such as evaporation with HClO4. The production of this AlF3 results in lower yields and poor accuracy in analyses of these trace elements by ICP-MS. The formation of AlF3 is controlled by the chemical composition of the rock samples, in particular, AlF3 does not form during decomposition of mafic samples with relatively high (Mg+Ca)/Al ratios. We have developed a new method to suppress the AlF3 formation, in which excess Mg is added to the sample prior to acid digestion in the bomb. This new method makes it possible to accurately determine the trace element compositions of higher-Al rock samples with lower concentrations of Mg and Ca (e.g. rhyolite and granite). In the trace element analyses by TIMS with isotope dilution techniques (ID-TIMS), AlF3 formation hinders the achievement of isotope equilibrium, resulting in erroneous results. However, the Mg-addition method removed this problem by suppression of AlF3 formation.

Fabrication of ultrafine anisotropic SiO2 mask by the combination of electron beam lithography and SF6 reactive ion beam etching using aluminum lift-off technique

We propose a new process for fabrication of an ultrafine anisotropic SiO2 mask, successfully combining electron beam (EB) lithography and SF6 reactive ion beam etching using an Al lift-off. SiO2 etching had a high selectivity of 50 over Al with an SF6 pressure of 0.9 mTorr and an ion energy of 300 V, because formation of AlF3 near the surface prevented the etching of Al. EB patterns were precisely transferred to the SiO2 mask with a vertical wall. Using this process, lines with widths of 70 nm and dot arrays composed of columns with diameters of 70 nm were realized.

Dry surface cleaning of plasma-etched high electron mobility transistors

Fabrication of submicron high electron mobility transistors (HEMTs) involves dry etch removal of GaAs from an underlying AlGaAs or InGaAs stop layer. The etch selectivity is achieved by formation of AlF3 on AlGaAs, or InCl3 and InF3 on InGaAs, which must be removed before processing can proceed. Wet chemical cleaning has difficulty in such a situation because of surface tension effects. We have investigated use of electron cyclotron resonance (ECR) H2 or Ar discharges, or hexafluoroacetylacetone (HFAC) vapor, for in situ dry etch cleaning of HEMTs exposed to low-bias BCl3/SF6 discharges. The HFAC vapor can remove most of the remnant fluorine, but is effective only when the sample is heated above ∼250 °C. This relatively high temperature is not compatible with in situ cleaning of the etched device. Low-bias (−75 V) sputter cleaning with an Ar discharge removes all remnant Cl and ∼40% of the F, but direct-current biases above −125 V are required for complete cleaning, and this ion bombardment can lead to damage in the HEMT. ECR H2 discharge exposure is effective in removing all Cl- and F-related residues in a short period (∼5 min) with low direct-current biases (−25 V) on the sample.

Dry Surface Cleaning of Plasma-Etched Hemts

ABSTRACTFabrication of sub-micron high electron mobility transistors (HEMTs) involves dry etch removal of GaAs from an underlying AlGaAs or InGaAs stop layer. The etch selectivity is achieved by formation of AlF3 on AlGaAs, or InCl3 and InF3 on InGaAs, which must be removed before processing can proceed. Wet chemical cleaning has difficulty in such a situation because of surface tension effects. We have investigated use of Electron Cyclotron Resonance (ECR) H2 or Ar discharges, or hexafluoroacetylacetone (HFAC) vapor, for in-situ dry etch cleaning of HEMTs exposed to low bias BCl3/SF6 discharges. The HFAC vapor can remove most of the remnant fluorine, but is effective only when the sample is heated above ∼250°C. This relatively high temperature is not compatible with in-situ cleaning of the etched device. Low-bias(−75V) sputter cleaning with an Ar discharge removes all remnant Cl and ∼40% of the F, but dc biases above -125V are required for complete cleaning, and this ion bombardment can lead to damage in the HEMT. ECR H2 discharge exposure is effective in removing all Cl- and F-related residues in a short period (∼5 mins) with low dc biases (−25 V) on the sample.

Inorganic fluorides production in fluor treatment of phosphate raw material in the USSR

The manufacture of inorganic fluorine compounds by phosphate raw material treatment ranks in the USSR a significant place as to providing country with fluoride products. At present over 35% of technical fluoride salts in the country is produced by mineral fertilizers plants. P:F ratio in apatite cocentrate is 5.8, while its 4.1 in Karatau phosphate concentrate obtained by flotation. With due account of the commercially possible value of fluorine recovery (40–60%), fluorine reserves in phosphate rocks of the USSR 2–3 times exceed those in fluorspar. The fluorine utilization of phosphate raw materials is realized almost exclusively from Kola apatite concentrate. In the manufacture of fertilizers and phosphoric acid by the wet process, the off-gases containing fluorine are trapped in the scrubbing systems, the thus obtained silicohydrofluoric acid solutions are fed for further treatment with the formation of AlF3, Na3AlF6, Na2SiF6, K2SiF6, (NH4)zSiF6,NH4HF2 and NaF. The various fluoride production routes are used in the USSR, which secure in most of cases product quality meeting the requirements of world market. Moreover, the production processes of granular fluoride salts, calcium fluoride have been developed; in continuous operation are the plant production of anhydrous hydrogen fluoride and hydrofluoric acid from bifluoride-fluoride ammonium. The USSR is exporting aluminium fluoride, Na2SiF6 and is prepared to increase the export of fluorine products if the respective production lines are retrofitted.