Quantitative optical absorption spectra of the cation radicals and the dications of canthaxanthin (I), -carotene (II), 7′-cyano-7′-ethoxycarbonyl-7′-apo--carotene (III), and 7′,7′-dimethyl-7′-apo--carotene (IV) in dichloromethane solution are reported. Exclusive formation of dications occurs when the carotenoids are oxidized with ferric chloride. Addition of neutral carotenoid to the dications results in equilibrium formation of cation radicals. Oxidation with iodine in dichloromethane affords only cation radicals; electrochemical oxidation under suitable conditions yields both dications and cation radicals. Values of the optical parameters depend on the nature of the oxidative medium. The oscillator strengths calculated for gas phase cation radicals and dications of I-IV using the INDO/S method show the same trend as the experimental values.

While the energy and power density of lithium-ion batteries (LIBs) are steadily improving, thermal safety continues to remain a critical challenge. Under abuse conditions, exothermic reactions may lead to the release of heat that can trigger subsequent unsafe reactions. The situation worsens in a module configuration, as the released heat from an abused cell can activate a chain of reactions in the neighboring cells, causing catastrophic thermal runaway. This work focuses on experimental elucidation and analysis of different LIB module configurations to characterize the thermal behavior and determine safe practices. The abuse test consists of a heat-to-vent setting where a single cell in a module is triggered into thermal runaway via a heating element. The cell-to-cell thermal runaway propagation behavior has been characterized. Results have shown that increasing the inter-cell spacing in a module containing cylindrical cells significantly decreases the probability of thermal runaway propagation. Additionally, it was determined that appropriate tab configuration combined with cell form factors exhibit a major influence on thermal runaway propagation. Different thermal insulation materials have been analyzed to determine their ability to ameliorate and/or potentially mitigate propagation effects.

While the popularity of lithium-ion batteries (LIBs) has increased significantly in recent years, safety concerns due to the high thermal instability of LIBs limit their use in applications with zero tolerance for a catastrophic failure. Industries such as aerospace and automotive must be very stringent in their selection and design of lithium-ion cells and modules to meet safety requirements. A safety issue of particular interest is a scenario called thermal runaway in which one or more exothermic side-reactions occur, leading to elevated temperature ranges that in turn lead to an uncontrollable and excessive release of heat. This work aims to characterize the effect of these reactions by utilizing a thermal abuse model that predicts single-cell behavior when subjected to an elevatedtemperature. The experimental test of the thermal safety behavior includes a constant-power heating element to trigger a thermal runaway event. This study takes an existing thermal abuse model and modifies it to emulate the conditions during a constant-power heating test. The result is found to be in agreement with the experimental data for different cell configurations. The influence of convection condition, cell physical configuration, and electrolyte combustion on the cell thermal behavior is also investigated.

This report is the first effort to use atomic layer deposition method for deposition of nanosized-thin and highly conformal Al(2)O(3) coatings onto LiMn(2)O(4) cathodes with precise thickness-control at atomic scale. The coated cathodes exhibit significantly enhanced cycleability than bare cathodes, as the dense ALD coating protects the cathode material from severe dissolution.

The mechanisms driving the thermo-electrochemical response of commercial lithium-ion cells under extreme overdischarge conditions (< 0.0 V) are investigated in the context of copper dissolution from the anodic current collector. A constant current discharge with no lower cutoff voltage was used to emulate the effects of forced overdischarge, as commonly experienced by serially connected cells in an unbalanced module. Cells were overdischarged to 200% DOD (depth of discharge) at C/10 and 1C rates to develop an understanding of the overdischarge extremes. Copper dissolution began when a cell reached its minimum voltage level (between −1.3 V and −1.5 V), where the anode potential reached a maximum value of ∼4.8 V vs. Li/Li + . Deposition of copper on the cathode, anode, and separator surfaces was observed in all overdischarged cells, verified with EDS/SEM results, which further suggests the formation of internal shorts, although the cell failures proved to be relatively benign. The maximum cell surface temperature during overdischarge was found to be highly rate-dependent, with the 1C-rate cell experiencing temperatures as high as 79 • C. Concentration polarization and solid electrolyte interphase (SEI) layer breakdown prior to the initiation of copper dissolution are proposed to be the main sources of heat generation during overdischarge.

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Overdischarge is a potential problem in large battery packs since cells in a series string are discharged under the same load, despite having different capacities. Although a single overdischarge does not necessarily cause a safety hazard, it forces electrodes outside their safe potential range and adversely affects the integrity of cell components. This work aims to fill the knowledge gap about the combined effect of aging-induced and overdischarge–induced degradation mechanisms. Graphite/LCO pouch cells are cycled at a moderate rate using four lower cutoff voltages: 2.7 V, 1.5 V, 0.0 V, and −0.5 V. The cells aged above the onset of reverse potential have an extended cycle life with aging-induced solid electrolyte interphase (SEI) growth and electrolyte decomposition as the main degradation mechanisms. In contrast, the cells aged under reversal condition (Elower ≤ 0.0 V) exhibit fast degradation, dictated by the interplay among lithium plating, cathode particle cracking, and dissolution of Cu current collector. The analysis is complemented with a comparative study of various state of health (SoH) indicators, including an internal resistance based dimensionless SoH descriptor. The results prove that overdischarge-induced abuse although benign, may turn into a malignant condition when alternated with continuous charging.