Phase-field investigation of lithium electrodeposition under different applied overpotentials and operating temperatures

Despite the high promise, the commercialization of Li-metal-based batteries has been hampered due to the formation of dendrites that lead to mechanical instability, energy loss and eventual internal short circuits. The mechanism of dendrite formation and the strategies to suppress their growth have been studied intensively. However, the effect of applied overpotential and operating temperature on dendrite growth remains to be fully understood. Here, we elucidate the correlation of overpotential and temperature with the surface modulation during electrodeposition using phase-field simulations. We identify an optimal operating temperature of half-cell consisting of a Li metal anode and 1M LiPF6 in EC:DMC(1:1), which increases gradually as the overpotential increases. The investigation reveals that the temperature dependence identified in the simulations and experiments often disagree because they are primarily conducted in galvanostatic and potentiostatic conditions, respectively. The temperature increase under potentiostatic conditions increases the induced current while it decreases the induced overpotential under galvanostatic conditions. Therefore, the analysis and comparison of temperature-dependent characteristics must be carried out with care.

FEATURES OF THE FORMATION OF THE COATING STRUCTURE ON TITANIUM-BASED ALLOYS

Previously shown that coatings formed on titanium by plasma electrolytic oxidation (PEO) in an electrolyte with zirconium sulfate Zr(SO4)2 consisted of ZrO2 and TiO2 oxides, their surface layer is enriched with zirconium, they have good protective properties in chlorine-containing media. The resulting layers have a fairly regular distribution of relatively small pores, with a diameter of about 1 μm or less, on the surface. The composition and structure of PEO layers depend on both the composition of the electrolyte and the modes of formation. It is of scientific and practical interest to elucidate the effect of the conditions for the formation of coatings with ZrO2 on titanium and its alloys on their anticorrosive properties in chlorine-containing media. Samples for research were formed under anodic (unipolar) conditions at the same current density and different formation times. The samples were formed in modes with current density 0.08 A/cm2 and processing time (minutes) − 8.5; 9.5; 10; 11; 12; 13; 14; 15; 20; 30; 40; 60. The duration of treatment was chosen as to maximally repeat the anticorrosive characteristics obtained in the previous case. The work uses modern research methods, including electron microscopy, presents the results of further study of ZrO2 + TiO2 / Ti systems formed in an electrolyte with zirconium sulfate Zr(SO4)2. It has been established that coatings are formed on titanium and its alloys in an electrolyte with zirconium sulfate under galvanostatic conditions of the PEO process at i = 0.08 A / cm2 during a processing time of 11-15 min. There is a correlation between the stages of galvanostatic formation of coatings and their anticorrosive properties.

Classification of Spatio-temporal Patterns in Charging and Discharging of Li-ion Batteries

We classify the dynamic patterns that emerge in charging or discharging of Li-ion batteries, under galvanostatic conditions, using simulations of the two-phase 1D porous model. This work examines the effect of exchange current function, R0(X), which expresses the nature of kinetics and extends our previous study limited to R0=1 for which the same pattern emerges, whether homogeneous or step-wise process made of multiple symmetry breaking events. With the commonly-used asymmetric R0(X) the emerging pattern may be one of the two above or fronts that follow single SB event and lithiation/delithiation behaviors are different. These effects are clear when parameters are uniform; non-uniformity leads to noise that mask the behavior. The full 4-variable model exhibits SB, even in absence of noise, since the liquid potential gradient ( ) works like a perturbation. Similarity between noise and gradient effects allows us to derive approximations to full model behavior, and study various effects.

Physico-Chemical Properties of NaV3O8 Prepared by Solid-State Reaction

Sodium–vanadium oxide NaV3O8 is synthesized via solid-state method and optimum synthesis conditions are chosen based on the data of DSC and TG analysis. The material synthesized is characterized by X-ray phase analysis, Raman spectroscopy and scanning electron microscopy. The ratio V4+/V5+ in the sample obtained is determined by X-ray photoelectron spectroscopy. Conductivity of the material synthesized was measured by impedance spectroscopy, pulse potentiometry and DC method over the range RT–570 °C. It is shown that NaV3O8 has rather high conductivity essentially electron in type (6.3 × 10−2 at room temperature). AC and DC conductivity measurements are performed and cycling of symmetricNaV3O8|Na3.85Zr1.85Nb0.15Si3O12|NaV3O8 cell in galvanostatic conditions. Thermal stability is studied across 25–570 °C temperature range. The results obtained are compared with the properties of NaV3O8 produced via aqueous solution.

Simulation of 3D Electrochemical Phase Formation: Mixed Growth Control

Processes of nucleation and growth largely determine the structure and properties of thin films obtained by electrodeposition on foreign substrates. Theoretical aspects of the initial stages of electrochemical phase formation under constant and variable overpotentials are considered in this work. Simulation of multiple nucleation with mixed (charge transfer, and diffusion) controlled growth was performed for three cases (cyclic voltammetry, potentiostatic electrodeposition, and galvanostatic electrodeposition). The influence of the bulk concentration of depositing ions and the exchange current density at the electrolyte/nucleus interface on cyclic voltammograms (CVs), transients of current and overpotential, as well as the number and size of non-interacting new-phase nuclei was analyzed. It is found that, under galvanostatic conditions, the number of nuclei decreases as the concentration of depositing ions increases due to a more rapid decrease in overpotential. The proposed model was applied to determine the diffusion coefficient, exchange current density, and transfer coefficient considering the experimental CV.

Oscillatory Copper Deposition on Conical Iron Electrodes in a Nonuniform Magnetic Field

We report the effect of a magnetic field on the deposition of copper ions on a conically shaped iron probe. In our setup, the magnetic forces and buoyancy are the key factors influencing the electrolyte flow and the mass transfer. Without external current, a spontaneous reduction of copper on the iron cone occurs, known as electroless deposition. Mach–Zehnder and differential interferometry indicate a variation in the concentration of copper ions near the cone. After an initial transient of about 60 s, temporal oscillations in the copper concentration are found under the effect of a magnetic field. In galvanostatic conditions, a similar oscillatory behavior of the concentration of the electrolyte is observed. Numerical simulations show that the oscillations are caused by the magnetic gradient, Lorentz force, and buoyancy force counteracting one another, and the oscillation frequency is estimated analytically based on this mechanism. Furthermore, we present a study on the oscillation frequency for both electroless and galvanostatic conditions with different current densities. The results of this study may stimulate future research aimed at the local control of the deposition rate and the realization of miniaturized, regularly structured deposits using magnetic fields.

Plug-and-play aqueous electrochemical atom transfer radical polymerization

‘Plug-and-play’ simplified electrochemical atom transfer radical polymerisation of PEGA480 under potentiostatic and galvanostatic conditions proceeds with very good control to conversions up to 83%.

Electrodeposition of aluminum-doped thin silicon films from the KF-KCl-KI-K2SiF6-AlF3 melt

Cyclic voltammetry, chronoamperometry, scanning electron microscopy, atomic force microscopy, and Raman spectroscopy were used to study the regularities of silicon and aluminum co-deposition on glassy carbon from KF-KCl (2:1) - 75 mol% KI - 0.15 mol% K2SiF6 - (up to 0.15 mol%) AlF3 melts at 998 K. Cyclic voltammograms demonstrated the presence of only one cathodic peak (or nucleation loop at a low reverse potential) and the corresponding anodic peak. The cathodic peak shifted in the cathodic direction with a decrease in the concentration of aluminum ions in the melt or an increase in the scan rate. The Scharifker - Hills model was used to analyze potentiostatic current density transients and estimate the values of the apparent diffusion coefficient and the number density of nuclei. The morphology and elemental analysis of the samples obtained during potentiostatic and galvanostatic deposition for 30-60 s were studied. Continuous thin silicon films doped with aluminum were obtained under galvanostatic conditions.