Delamination behavior of lithium-ion battery anodes: Influence of drying temperature during electrode processing

One essential process step during electrode processing for lithium-ion batteries is the drying of the wet particulate electrode coating. The electrode film solidifies during evaporation of the solvent and a porous film is formed. In this study, we focus on the influence of drying temperature on the internal electrode structure of the dry film. Anode slurries that consist of graphite and an aqueous binder system were coated and subsequently dried. To assure defined and controllable drying conditions, a laboratory set-up with a temperature-controlled substrate carrier and an impingement dryer was used. To facilitate a scale-up to continuously passed dryers, the choice of experimental temperatures was based on a calculation of steady-state temperatures that result from gas temperatures that are commonly applied in industrial drying processes. The delamination behavior of the differently dried electrodes was investigated by means of a 90° peel test. The results show a strong dependency of electrode adhesion on drying temperature. A lower adhesion force at higher temperatures hints at a variation in binder content at the interface between the copper substrate and the coating layer. The formation of a consolidation layer at the air-film interface during drying is identified as a possible explanation and a criterion for consolidation layer formation is suggested.     

In situ photoelectrochemistry and Raman spectroscopic characterization on the surface oxide film of nickel electrode in 30 wt.% KOH solution

The oxide films of nickel electrode formed in 30 wt.% KOH solution under potentiodynamic conditions were characterized by means of electrochemical, in situ PhotoElectrochemistry Measurement (PEM) and Confocal Microprobe Raman spectroscopic techniques. The results showed that a composite oxide film was produced on nickel electrode, in which aroused cathodic or anodic photocurrent depending upon polarization potentials. The cathodic photocurrent at −0.8 V was raised from the amorphous film containing nickel hydroxide and nickel monoxide, and mainly attributed to the formation of NiO through the separation of the cavity and electron when laser light irradiates nickel electrode. With the potential increasing to more positive values, Ni₃O₄ and high-valence nickel oxides with the structure of NiO₂ were formed successively. The composite film formed in positive potential aroused anodic photocurrent from 0.33 V. The anodic photocurrent was attributed the formation of oxygen through the cavity reaction with hydroxyl on solution interface. In addition, it is demonstrated that the reduction resultants of high-valence nickel oxides were amorphous, and the oxide film could not be reduced completely. A stable oxide film could be gradually formed on the surface of nickel electrode with the cycling and aging in 30 wt.% KOH solution.     

钢铁常温发黑

分析了钢铁常温发黑过程的成膜机理。提出了直接成膜的可能性。测定了氧化剂还原的动电位曲线和发黑过程的电位-时间曲线。得到了良好的实践结果。     

Synthesis of electrochemically-reduced graphene oxide film with controllable size and thickness and its use in supercapacitor

An electrochemical synthesis method of reducing graphene oxide (GO) under constant potential is reported. Electrochemical technique offers control over reaction parameters such as the applied voltage, electrical current and reduction time; whereas the desired size and thickness of the film can be pre-determined by controlling the amount of precursor GO deposited on the electrode with defined shape and surface area. This synthesis technique produces high quality electrochemically reduced GO (ERGO) film with controllable size and thickness. Electrochemical symmetrical supercapacitors based on ERGO films achieved a specific capacitance of 128 F/g with an energy density of 17.8 Wh/kg operating within a potential window of 1.0 V in 1.0 M NaNO₃. The supercapacitor was shown to be stable, retaining ca. 86% of the original specific capacitance after 3500 charge–discharge cycles. The results indicate that this simple synthesis technique for providing graphene-like materials has great potential in various applications such as energy storage.     

Estimation of kinetic and transport parameters by quantitative evaluation of EIS and XPS data

The relatively large number of adjustable parameters often precludes the unambiguous interpretation of electrochemical impedance spectra in terms of a unique kinetic model. In the present paper, the possibilities offered by a combination between in situ electrochemical impedance spectroscopic data and ex situ surface analytical information to improve the credibility of the estimates of the kinetic and transport parameters are discussed. Two electrode systems in which passive oxide films are formed—stainless steel in simulated pressurised water reactor coolant and tungsten in sulphate-fluoride solutions—are used as representative examples to demonstrate the different approaches taken to analyse the experimental data in terms of the Mixed-Conduction Model. Ways to extract information on the rate-limiting steps of the process of passive film formation, growth and restructuring by quantitative comparison of the model equations to electrochemical impedance and X-ray photoelectron spectroscopic data are described and the significance of the obtained parameters for the kinetics of the overall process of metal and alloy dissolution in the passive state is discussed.     

Electrochemical synthesis of polyaniline films on zinc-cobalt alloy deposited carbon steel surface in sodium oxalate

Polyaniline (PANI) coatings were electropolymerized on zinc-cobalt alloy deposited carbon steel (CS/ZnCo) electrode from an aqueous sodium oxalate solution using three different scan rates in cyclic voltammetric technique. Scanning electron microscopy (SEM) was used to analyze the surface morphology of the polymer film. The SEM images showed that the increase in scan rate induced an increase in grain size of the PANI film. The corrosion behavior of CS/ZnCo electrodes with and without PANI film in 3.5% NaCl solution were investigated through electrochemical impedance spectroscopy (EIS) and anodic polarization studies. The results of the study showed that the PANI coatings provided significant and effective protection for the CS/ZnCo electrode, in preventing corrosion. In addition, the PANI film that was synthesized at a high scan rate, exhibited the best anti-corrosive performance due to the formation of protective oxide layers through its catalytic efficiency.     

Electrooxidation of alcohols at a nickel oxide/multi-walled carbon nanotube-modified glassy carbon electrode

Electrocatalytic oxidation of methanol and some other primary alcohols on a glassy carbon electrode modified with multi-walled carbon nanotubes and nano-sized nickel oxide (GCE/MWNT/NiO) was investigated by cyclic voltammetry and chronoamperometry in alkaline medium. The results were compared with those obtained on a nickel oxide-modified glassy carbon electrode (GCE/NiO). Both the electrodes were conditioned by potential cycling in the range of 0.1–0.6 V versus Ag/AgCl in a 0.10 M NaOH solution. The effects of various parameters such as scan rate, alcohol concentration, thickness of NiO film, and real surface area of the modified electrodes were also investigated and compared. It was found that the GCE/MWNT/NiO-modified electrode possesses an improved electrochemical behavior over the GC/NiO-modified electrode for methanol oxidation.     

Nitric oxide reduction at noble metal electrodes: a voltammetric study in acid solution

Features of the electrochemical reduction of nitric oxide on platinum, palladium, rhodium and ruthenium in aqueous perchloric acid solutions (0.33–1.0 M) are compared. The results from voltammetric studies (ie linear potential sweep and rotating disc electrode) using the bulk metal electrodes are described and compared with residual current voltage plots in acid electrolyte alone. In general, three nitric oxide reduction peaks are observed on the metals. The most anodic peak, at ca E = 0.15 V vs sce is attributed to the one-electron reduction of nitric oxide to an adsorbed NOH intermediate on a bare metal surface (ie one free of oxides or adsorbed hydrogen). The other two peaks occur in potential regions where adsorbed hydrogen is present on the metal surface (ca E = 0.0 and −0.20 V, respectively). The co-adsorbed hydrogen complicates the analysis and precludes an unambiguous interpretation of these two peaks. However, they apparently reflect nitric oxide reduction to nitrogen, hydroxylamine and/or ammonia. In a cathodic scan on the rhodium electrode, a current plateau is seen instead of the first (most anodic) peak, a probable consequence of oxide film formation with subsequent chemical complications. On the ruthenium electrode the first two (most anodic) peaks are not observed probably due to a relatively stable oxide layer. Reaction selectivities at metal black gas diffusion cathodes operating in an electrogenerative (ie galvanic) mode with perchloric acid electrolyte are compared with the voltammetric results at the corresponding bulk electrodes. Dinitrogen formation is observed on the platinum and rhodium black electrodes as suggested from voltammetric results. A series-parallel reaction sequence is proposed to explain the results. Limitations of using simple voltammetric techniques for predicting behavior of large scale preparative electrochemical reactors are discussed.     

Electrical and hydrogen reduction enhances kinetics in doped zirconia and ceria: II. Mapping electrode polarization and vacancy condensation in YSZ

Knowing the correlation between grain boundary mobility and oxygen potential in yttria‐stabilized zirconia (YSZ), we have utilized the grain size as a microstructural marker to map local oxygen potential. Abrupt oxygen potential transition is established under a large current density and in thicker samples. Cathodically depressed oxygen potential can be easily triggered by poor electrode kinetics or in an oxygen‐lean environment. Widespread cavitation in the presence of highly reducing oxygen potential suggests oxygen vacancy condensation instead of oxygen bubble formation as commonly assumed for solid oxide fuel/electrolysis cells. These results also suggest electrode kinetics has a direct influence on the microstructure and properties of ceramics sintered under a large electric current.     

Passive and transpassive behaviour of CoCrMo in simulated biological solutions

In this work, the behaviour of a CoCrMo alloy under simulated body conditions was investigated. More specifically, the electrochemical properties of the alloy and the relevant mechanisms in the passive and transpassive states were studied in detail. Electrochemical techniques such as potentiodynamic and potentiostatic polarisation, cyclic voltammetry, rotating disc electrode and electrochemical impedance spectroscopy were employed. Further, ex situ X-ray photoelectron spectroscopy analysis of the passive films was carried out. A good correlation between the results obtained from all the experimental techniques was achieved. Overall, it was found that the passive film on CoCrMo changed in composition and thickness with both potential and time. The passive behaviour of the CrCrMo alloy is due to a formation an oxide film highly enriched with Cr (≈90% Cr oxides) on the alloy surface. The passive and transpassive behaviour of the alloy is hence dominated by the alloying element Cr. In the transpassive region, strong thickening of the oxide film takes place, combined with a change in the composition of the film, and strongly increased dissolution rate. In the transpassive region, all alloying elements dissolve according to the composition of the alloy. The metal ion release is also very strongly enhanced by cyclic variation of the potential between reducing and oxidizing conditions. In this case, during activation/repassivation cycles, cobalt dissolution is greater than expected from the composition of the alloy. Therefore, active dissolution behaviour is mainly dominated by the alloying element Co.     

Measurement of the adhesion of diamond films on tungsten and correlations with processing parameters

Adhesion between diamond films and tungsten substrates is reported as a function of the deposition processing parameters. Diamond films were grown by a hot filament method as a function of seven different processing parameters: substrate scratching prior to diamond deposition, substrate temperature, methane content of the input gas mixture, filament temperature, filament-substrate distance, system pressure, and total gas flow rate. Adhesion was measured by using a Sebastian Five A tensile pull tester. Testing was complicated by the non-uniformity of the film thickness, diamond quality, film cohesion, and surface preparation across the full substrate surface area. Various types of film failure mode were observed, which did not correlate with the film processing parameters. The measured adhesion values showed larger variations from point to point across the sample surface and from identically prepared samples than variations as a function of the film processing parameters. Weak correlations of adhesion with the processing parameters were found using statistical analysis of the results from multiple pulls on a large number of samples. The statistical results suggest that substrate preparation, gas flow rate, and gas pressure are the most important processing parameters affecting the film adhesion, while the temperature of the hot filament has little or no effect on the adhesion of the film. However, improvements in film processing and adhesion testing need to be made before true quantitative adhesion testing of high-quality diamond films can be accomplished.     

Influence of heat transfer on anodic oxidation of aluminium

The influence of convective heat transfer on constant current density anodizing of aluminium in sulfuric acid has been examined in a wall-jet electrode reactor. The uniformity of the anodic film thickness is related to the local electrode temperature distribution, which is dependent on the convection. The higher the local temperature, the greater the local oxide thickness. An increased local temperature enhances local field assisted oxide dissolution at the pore bases, and consequently acts to increase the local current density. At relatively high current densities, local features develop on the electrode surface, accompanied by high initial, local temperature rises. The relevance of such local features, limiting useful oxide growth, is considered further.     

The effect of potential bias on the formation of ionic liquid generated surface films on Mg alloys

An electrochemical approach to the formation of a protective surface film on Mg alloys immersed in the ionic liquid (IL), trihexyl(tetradecyl)phosphonium-bis 2,4,4-trimethylpentylphosphinate, was investigated in this work. Initially, cyclic voltammetry was used with the Mg alloy being cycled from OCP to more anodic potentials. EIS data indicate that, under these circumstances, an optimum level of protection was achieved at intermediate potentials (e.g., 0 or 0.25 V versus Ag/AgCl). In the second part of this paper, a small constant bias was applied to the Mg alloy immersed in the IL for extended periods using a novel cell design. This electrochemical cell allowed us to monitor in situ surface film formation on the metal surface as well as the subsequent corrosion behaviour of the metal in a corrosive medium. This apparatus was used to investigate the evolution of the surface film on an AZ31 magnesium alloy under a potential bias (between ±100 mV versus open circuit) applied for over 24 h, and the film evolution was monitored using electrochemical impedance spectroscopy (EIS). A film resistance was determined from the EIS data and it was shown that this increased substantially during the first few hours (independent of the bias potential used) with a subsequent decrease upon longer exposure of the surface to the IL. Preliminary characterization of the film formed on the Mg alloy surface using ToF-SIMS indicates that a multilayer surface exists with a phosphorous rich outer layer and a native oxide/hydroxide film underlying this. The corrosion performance of a treated AZ31 specimen when exposed to 0.1 M NaCl aqueous solution showed considerable improvement, consistent with electrochemical data.     

Simplified point defect model for growth of anodic passive films on iron

We present a simplified point defect model to describe the growth of the primary passive oxide film on the surface of iron. The model postulates a reduced set of elementary interfacial reactions to describe the formation and dissolution of the oxide film. By casting the model in dimensionless form, we obtain a relatively small set of parameters that must be assigned values. Parameter values are set by matching the film thickness predicted by the model with one experimental data point. The model is then used to predict variations in film thickness with time, temperature, and applied potential, yielding reasonable agreement with experimental data. The model also gives the correct qualitative trend in the dependence of film thickness on electrolyte pH. Although the model parameters used in our comparisons are probably not unique, they suggest that physical picture embodied in the model provides a suitable starting point for modeling the growth of passive films on Fe.     

Gas film formation time and gas film life time during electrochemical discharge phenomenon

The formation of a gas film around an electrode is at the origin of the electrochemical discharges in aqueous solutions and in molten salts. The study of the electrochemical discharge phenomenon from the current signal point of view is conducted to identify the gas film formations and the following discharges. This is performed using the wavelet analysis as a denoising tool with the discrete Meyer wavelet as base function. The proposed algorithm allows to measure experimentally the gas film life time and its necessary building time prior to each series of discharges. The accuracy of the algorithm is evaluated using generated signals and its application to real data is demonstrated. From the experimental data, it is concluded that the gas film is more stable at high terminal voltages whereas its formation time decreases with it. Electrochemical and thermal interpretations for the measured statistics are proposed.     

Zinc hexacyanoferrate film as an effective protecting layer in two-step and one-step electropolymerization of pyrrole on zinc substrate

The two-step and one-step electrosynthesis processes of polypyrrole (PPy) films on the zinc substrate are described. The two-step process includes (i) the zinc surface pretreatment with hexacyanoferrate ion in the aqueous medium in order to form a zinc hexacyanoferrate (ZnHCF) film non-blocking passive layer on the surface and with the view to prevent its reactivity and (ii) electropolymerization of pyrrole on the ZnHCF|Zn-modified electrode in aqueous pyrrole solution. In this context, both the non-electrolytic and electrolytic procedures were adapted, and the effect of some experimental conditions such as supporting electrolyte, pH and temperature of the solution at the zinc surface pretreatment step as well as pyrrole concentration and electrochemical techniques at the polymerization step was investigated. By optimizing the experimental conditions in both steps, we have obtained a homogeneous and strongly adherent PPy films on the zinc substrate.The one-step process is based on the use of an aqueous medium containing Fe(CN)₆⁴⁻ and pyrrole. The ferrocyanide ion passivates the substrate by formation of ZnHCF film during the electropolymerization process of pyrrole and therefore makes it possible to obtain strongly adherent PPy films, with controlled thickness, either by cyclic voltammetry or by electrolysis at constant current or constant potential without any previously treatment of the zinc electrode surface. The polypyrrole films deposited on the zinc electrode were characterized by cyclic voltammetry and scanning electron microscopic (SEM) measurement.     

Nature and stability of anodic oxide films formed on molybdenum in chloride solutions

The formation and stability of anodic oxide films on molybdenum in chloride solutions was tested using impedance and polarization measurements. The efficiency of oxide formation increases as the acidity of the formation medium increases. The film is highly stable and resistive to attack and dissolution regardless of the chloride concentration, pH or film thickness. The corrosion potential did not vary with variation of immersion time, solution composition or film thickness and recorded 0.000V vs SCE indicating the high insulating properties of the film. Polarization measurements on previously anodized molybdenum electrode showed that the electrode is ideally polarized over a potential region not less than 2V. The magnitude of that potential region increases as the film thickness increases. The anodic film cannot be reduced or removed by galvanostatic cathodic polarization. The impedance behaviour of the anodized molybdenum electrode was found to be purely capacitive and the oxide film may be treated approximately as a perfect dielectric material.     

Ellipsometric response of titanium electrodes in sulphate acid solutions under different potential perturbations

Optical characteristics and thickness of thin oxide films potentiodynamically formed on a titanium electrode in acidic sulphate solutions at pH 4.0 were investigated by dynamic and steady ellipsometric measurements. The dynamic ellipsometric response of an electrode polarized up to 1.0 V vs rhe depends on the charge involved in the massive oxide electroformation. Cycling the electrode at a constant potential sweep rate between −0.65 and 0 V produces a decrease on film thickness and the electrode reactivation. This electrode treatment becomes less effective as oxide electroformation is repeated several times. Experiments performed by holding the potential at the negative limit were not so effective in reducing film thickness and an appreciable change on optical constants was found. Results were interpreted as hydrogenated species formation within the oxide film.     

AZ91D镁合金表面氧化工艺及性能研究

采用硝酸氧化法在AZ 91D镁合金表面形成一层具有较好耐蚀性能的氧化膜.采用扫描电子显微镜对镁合金氧化层的微观形貌进行观察分析,系统讨论了活化时间和氧化时间对氧化层表面微观形貌的影响.结果表明:在活化时间为0.5min,氧化时间为2 min的条件下得到的氧化层表面均匀、完整,具有较好的耐点滴实验性能.     

锂离子电池电极材料SEI膜的研究概况*

综述了锂离子电池电极材料表面的“固体电解质界面膜”（SEI 膜） 的成膜机理及研究概况,并分析了电解液、温度和电流密度对SEI膜形成过程的影响;在此基础上,对SEI膜的改性（主要包括电极材料的改性和添加电解液添加剂）进行了分析,认为SEI膜的研究将对电极材料和电解液添加剂的改进研究产生重要影响。