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A mechanistic model of atmospheric bimetallic corrosion with a simplified empirical approach to the onset of localized corrosion attacks is presented. The model was built for a typical bimetallic sample containing aluminum alloy 1050 and stainless steel 316L sheets. A strategy was developed that allowed the model to be calibrated against the measured galvanic current, geometrical corrosion attack properties, and corrosion products. The pitting-onset simplification sets all pits to be formed at a position near the nobler metal and treated all pits as being of the same shape and size. The position was based on the location of the highest pitting events and the pit attributes on an average of the deepest pits. For 5 h exposure at controlled RH (85%, 91%, and 97%) and salt load (86 μg NaCl/cm2), the model was shown to be promising: both for analysis of local bimetallic corrosion chemistry, such as pH and corrosion products, and for efficient assessment of pitting damage by computing a single largest pit depth. Parametric studies indicated that the pitting-onset approximation deviated the most at the beginning of exposure and when RH was below 91%. [ABSTRACT FROM AUTHOR]

In this study, the local electrochemical activity of untreated and passivated (natural or chemical passivation) zinc specimens was observed during immersion in a 0.1‐M NaCl solution. The localized anodic activity during the exposure, measured with the scanning vibrating electrode technique, was linked to zinc dissolution by the pitting corrosion mechanism. It was correlated to specific corrosion products characterized by Fourier transmission infrared (FTIR) microscopy. FTIR molecule maps were produced from individual pitting corrosion sites (100–200 µm in width). With argon ion beam milling and latest energy‐dispersive X‐ray spectroscopy (EDS) technology, element maps with a high spatial resolution (≪100 nm) were recorded from abrasion‐ and beam‐sensitive corrosion products, showing a residual layer structure. This study demonstrates the capability of FTIR mapping, cross‐section polishing, and state‐of‐the‐art scanning electron microscopy imaging, and EDS element mapping to produce high‐resolution elemental, molecular, and visual information about pitting corrosion mechanisms on a hot‐dip galvanized steel sample. [ABSTRACT FROM AUTHOR]

A full electrochemical investigation of the lithium intercalation processes in a commercially available PAN-based carbon fiber, Toho Tenax IMS65 (unsized and sized) primarily intended to be used in structural lithium-ion batteries, has been performed. In order to extract the electrochemical properties, a specially designed microelectrode system consisting of a single fiber working electrode, lithium-foil counter electrode and well-characterized battery materials were utilized. The properties, for 5 to 100% state-of-charge (SOC), were mainly determined from electrochemical impedance spectroscopy (EIS) measurements by fitting of a physics-based model, and electronic conductivity examination. The study shows excellent mass transport and kinetic properties, especially at high SOCs for this specific carbon fiber compared to other negative electrode materials. Some electrochemical parameters vary depending on sizing, but are too small to affect the actual electrochemical performance. A strong SOC dependence is shown for most electrochemical properties, including the electronic conductivity. [ABSTRACT FROM AUTHOR]

A short-circuited lithium-ion battery cell is likely to generate sufficient heat to initiate exothermic side reactions causing thermal runaway. A 2D coupled electrochemical-thermal model was developed to investigate a prismatic LiNi0.8Co0.15Al0.05O2∣LiPF6, EC/EMC (3:7)∣MAG-10 battery cell that is short-circuited. Three short-circuit scenarios are investigated during the events from when short circuit occurs until exothermic side reactions initiate. The scenarios are an external short circuit, a nail penetration and an impurity-induced short circuit. The model is used to predict the temperature increase within the cell and to explain how the interrelation between the electrochemical processes and the thermal properties affects the increase. Important safety measures are also examined with the model. The simulation results highlight general short-circuit characteristics and critical distinctions between the scenarios. The mass transport of lithium ions in the electrolyte is found to be the most important general characteristic that determines the rate of the temperature increase. The electric resistance distinguishes the scenarios from each other. The rate of the temperature increase is dictated by the mass transport in the electrolyte even when large variations in available active material are made and it is shown to be difficult to slow down the rate by cooling. [ABSTRACT FROM AUTHOR]

An experimentally validated model was developed to analyze the polarization of a LiNi0.8Co0.15Al0.05O2Ι1.2 M LiPF6 in ethylene carbonate (EC):ethyl methyl carbonate (EMC) (3:7)ΙMAG-l0 battery cell during a hybrid pulse power characterization (HPPC) cycle. The analysis was made with a method where the polarization was split up into parts associated with activation of the electrochemical reactions, mass transport of species in the electrolyte and in the solid phase, and inadequate contact between the materials in the electrodes. Each contribution to the polarization was quantified as a snapshot in time and as an average over the HPPC cycle. The polarization during a cycle according to EUCAR was analyzed in detail for state of charge (SOC) 40 and 80. It arose mainly due to the mass transport in the electrolyte, e.g., at SOC 40 it contributed to 43% of the total polarization. In an ISO (International Organization for Standardization)-energy cycle where the current loads are higher and applied for longer times than the EUCAR cycle, the mass transport by diffusion in the electrolyte and in the solid phase of the negative electrode became more significant. The presented method offers the possibility to find a battery cells optimal operational condition and design. [ABSTRACT FROM AUTHOR]

Abstract: This study presents an extensive characterization of a standard Li-ion battery (LiB) electrolyte containing different concentrations of the flame retardant triphenyl phosphate (TPP) in the context of high power applications. Electrolyte characterization shows only a minor decrease in the electrolyte flammability for low TPP concentrations. The addition of TPP to the electrolyte leads to increased viscosity and decreased conductivity. The solvation of the lithium ion charge carriers seem to be directly affected by the TPP addition – as evidenced by Raman spectroscopy and increased mass-transport resistivity. Graphite/LiFePO4 full cell tests show the energy efficiency to decrease with the addition of TPP. Specifically, diffusion resistivity is observed to be the main source of increased losses. Furthermore, TPP influences the interface chemistry on both the positive and the negative electrode. Higher concentrations of TPP lead to thicker interface layers on LiFePO4. Even though TPP is not electrochemically reduced on graphite, it does participate in SEI formation. TPP cannot be considered a suitable flame retardant for high power applications as there is only a minor impact of TPP on the flammability of the electrolyte for low concentrations of TPP, and a significant increase in polarization is observed for higher concentrations of TPP. [Copyright &y& Elsevier]