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Predicting High-Temperature Decomposition of Lithiated Graphite: Part I. Review of Phenomena and a Comprehensive Model

Journal of the Electrochemical Society

Shurtz, Randy S.; Engerer, Jeffrey D.; Hewson, John C.

Heat release that leads to thermal runaway of lithium-ion batteries begins with decomposition reactions associated with lithiated graphite. We broadly review the observed phenomena related to lithiated graphite electrodes and develop a comprehensive model that predicts with a single parameter set and with reasonable accuracy measurements over the available temperature range with a range of graphite particle sizes. The model developed in this work uses a standardized total heat release and takes advantage of a revised dependence of reaction rates and the tunneling barrier on specific surface area. The reaction extent is limited by inadequate electrolyte or lithium. Calorimetry measurements show that heat release from the reaction between lithiated graphite and electrolyte accelerates above ~200°C, and the model addresses this without introducing additional chemical reactions. This method assumes that the electron-tunneling barrier through the solid electrolyte interphase (SEI) grows initially and then becomes constant at some critical magnitude, which allows the reaction to accelerate as the temperature rises by means of its activation energy. Phenomena that could result in the upper limit on the tunneling barrier are discussed. The model predictions with two candidate activation energies are evaluated through comparisons to calorimetry data, and recommendations are made for optimal parameters.

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TYPE Journal Article YEAR 2018
DOIOSTI

Total Hemispherical Emissivity of Metals Applicable to Radiant Heat Testing

Shurtz, Randy S.

Total hemispherical emissivities are a commonly used property in radiative heat transfer analysis. Measurements made in the course of testing become far more useful to thermal analysts if they are compiled with a sufficient level of detail, and summarized in a manner that allows the most appropriate value or trend to be located quickly. This report collects emissivity measurements from recent years, made in the course of testing metallic surfaces at Sandia's Radiant Heat Test Facility, and compares them to a selection of previous summary documents. These measurements are organized by material type, surface finish, and degree of oxidation. The comparisons also consider the temperature dependence of total hemispherical emissivity. Materials considered include Inconel 600, SS304, 17-4PH SS, silicon carbide, and aluminum alloys. A limited selection of high-temperature paints and other surface coatings are also considered. Recommendations are made for frequency of measurements and level of detail in reporting emissivities in future test series. A more limited scope is recommended for the use of high-temperature paints at Sandia's Radiant Heat Test Facility; pre-oxidation of Inconel and stainless steel surfaces is preferred in many circumstances.

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TYPE SAND Report YEAR 2018
DOIOSTI

Predicting high-temperature decomposition of lithiated graphite: Part II. Passivation layer evolution and the role of surface area

Journal of the Electrochemical Society

Shurtz, Randy S.; Engerer, Jeffrey D.; Hewson, John C.

The surface area dependence of the decomposition reaction between lithiated graphites and electrolytes for temperatures above 100◦C up to ~200◦C is explored through comparison of model predictions to published calorimetry data. The initial rate of the reaction is found to scale super-linearly with the particle surface area. Initial reaction rates are suggested to scale with edge area, which has also been measured to scale super-linearly with particle area. As in previous modeling studies, this work assumes that electron tunneling through the solid electrolyte interphase (SEI) limits the rate of the reaction between lithium and electrolyte. Comparison of model predictions to calorimetry data indicates that the development of the tunneling barrier is not linear with BET surface area; rather, the tunneling barrier correlates best with the square root of specific surface area. This result suggests that tunneling though the SEI may be controlled by defects with linear characteristics. The effect of activation energy on the tunneling-limited reaction is also investigated. The modified area dependence results in a model that predicts with reasonable accuracy the range of observed heat-release rates in the important temperature range from 100◦C to 200◦C where transition to thermal runaway typically occurs at the cell level.

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TYPE Journal Article YEAR 2018
DOIOSTIScopus
Results 51–75 of 77
Results 51–75 of 77