Jair Scarminio

Electrochromism and photochromism in amorphous molybdenum oxide films

Abstract In this paper, we present a study of the influence of the oxygen flow rate (φ) during r.f. sputtering of molybdenum metal targets on the resulting MoOx thin films. The optical behavior upon Li+ electrochemical intercalation (electrochromic effect) or UV irradiation (photochromic effect) is analyzed. At low φ, blue substoichiometric molybdenum oxide films are formed. At high φ, the composition of the oxide films approaches that of transparent, stoichiometric MoO3. The optical gap for the as-grown films increases with the increase of φ, in the range 2.8 eV for low φ to 3.2 eV at high φ. Lithium intercalation or UV irradiation promoted transmittance changes. The highest electrochemical and photochemical transmittance change was obtained for the sample deposited at low φ.

Electrochromism in nickel oxide films obtained by thermal decomposition

Presentation of a new method of growing electrochromic nickel oxide films by thermal decomposition of nickel nitrate. The films were very adherent and homogeneous, and had electrochromic efficiencies comparable with films produced by other methods

Li diffusion and electrochromism in amorphous and crystalline vanadium oxide thin film electrodes

Amorphous vanadium oxide films were synthesized onto ITO-coated glass substrates by the hot filament metal oxide deposition technique. The as-deposited samples were heat-treated in an argon atmosphere. X-ray diffraction analysis revealed that the films treated at 200 and 300 oC were still amorphous, while those treated at 400 and 500 oC were crystalline, with a V2O5 structure. All electrodes were electrochemically reversible for Li+ intercalation, exhibiting the electrochromic effect, observed from optical transmittance measurements at 632.8 nm. The Li-diffusion coefficient, DC, was measured by the galvanostatic intermittent titration technique (GITT) as function of the inserted charge. For the crystalline films it was observed that the optical absorbance and the DC increase with increasing Li insertion in the single-phase regions of crystalline LixV2O5 and decrease in the two-phase regions. For the latter, an effective DC was considered. The presence of other vanadium oxides mixed to the V2O5 matrix was inferred for the crystalline films from the chronopotentiometric and DC measurements.

Tungsten Oxide Films of High Electrochromic Efficiencies Obtained by Deposition

Amorphous tungsten oxide films of high electrochromic efficiency were produced by a chemical vapor deposition technique in which the precursors of film formation are generated at the surface of a heated tungsten filament by reactions of tungsten with oxygen. The film deposition rate was determined as a function of the filament temperature and oxygen pressure. Molecular structure investigations using X-ray photoelectron spectroscopy revealed that the tungsten oxide was in the WO 3 stoichiometry. The electrochromic properties of the films were studied for Li + intercalation. Optical efficiencies as high as 78 and 125 cm 2 /C at 632.8 and 950 nm, respectively, and absorbance changes from 0.07 to 1.1 were measured between the bleached and the colored states at 632.8 nm.

FOTOCROMISMO EM FILMES FINOS DE ÓXIDOS DE TUNGSTÊNIO DE DIFERENTES COMPOSIÇÕES

Tungsten oxide thin films with three different compositions were deposited by reactive sputtering in an oxygen-argon plasma. In a system composed of a home made photochemical reactor coupled with an optic fiber spectrophotometer, the photochromic effect was studied in these oxide films as function of UV irradiation time, in ethanol, methanol and formaldehyde atmospheres. It was observed that the photochromic efficiency depends on the vapor chemical nature where the film is irradiated as well as the film composition. Kinetic analysis suggest that two kinds of optical absorption centers should respond by the photochromic effect in these films, one generated at film surface and other inside it, which one presenting a different time constant.

A closed-loop process to recover Li and Co compounds and to resynthesize LiCoO2 from spent mobile phone batteries

In the last decades, the demand for lithium-ion batteries (LIBs) has been growing fast to attend the markets of electric and hybrid vehicles and of electric portable devices. As scarce metals like cobalt and lithium are employed in their manufacturing the recycling of spent LIBs is a strategic solution for the sustainability of these minerals and also the maintenance of the LIBs production. Therefore, efforts should be driven to produce low cost, environment-friendly and industrially scalable recycling processes. In this study, a closed-loop process with these characteristics was developed to recover cobalt and lithium compounds from LiCoO2 cathodes of spent cell phone lithium-ion batteries. The process employs citric acid as green leaching agent to recover cobalt as CoC2O4.2H2O and Co3O4 and lithium as Li2CO3. Lithium compound was recovered from a proposed new and original method based on simple chemical procedures as evaporation-calcination and water dissolution. The developed process also allows the resynthesis of LiCoO2 as a stoichiometric, well crystallized and structurally ordered compound from the recovered Co and Li compounds, in a closed-loop recycling process. The obtained results indicate that the developed process has great potential to be scaled up to a recycling industrial plant of spent lithium-ion batteries.

ANALYSIS OF A COMMERCIAL PORTABLE LITHIUM-ION BATTERY UNDER LOW CURRENT CHARGE-DISCHARGE CYCLES

The dependence between the transferred charge and the corresponding transference time to charge and discharge a portable cell phone Li-ion battery (LiCoO2/C) under cycles of low intensity currents was studied in detail. The voltage curve profile between 3.0 and 4.2 V and the charging and discharging time are strongly influenced by the applied current intensity. A linear dependence between the stored and extracted charges, into and from the battery, with the intensity of applied current was also observed. Allometric equations were found to describe the correlation between the charge transference time and the applied current intensity to charge and discharge the battery.

Time evolution of the residual stress of plasma-polymerized acetylene films in various ambients

The behavior of the residual stress with time of plasma‐polymerized acetylene films in various ambients has been investigated. The plasma polymers were deposited on thin glass substrates in dc and rf discharges of acetylene. After deposition, the specimens were mounted in a chamber that could be evacuated or filled with air, oxygen, or nitrogen. Stress measurements were carried out by the bending beam method, using a He‐Ne laser. A steady rise in the stress during time periods of several hours following film deposition was observed in most of the samples studied. Stress increments of more than one order of magnitude were detected in some of the films upon exposure to air. Pronounced stress increments were also observed during exposure to oxygen. Rises in the stress were detected even in a vacuum ambience. Nitrogen exposure was found to have little effect on the stress. The effect of the moisture content of air on the stress was also examined. The evolution of the stress was found to depend also on the fil...