Abstract
Predicting temperature rise accurately during fast charge/discharge of a Li-ion cell is essential to avoid thermal runaway and extend battery life. While modeling the temperature rise, it is necessary to model the heat generation correctly. Heat of mixing, one of the four main sources of heat generation in a Li-ion battery, has often been considered insignificant and therefore excluded from modeling. When included, it is modeled using the expression from a Taylor expansion approximation. In this work, we have shown the conditions when including the heat of mixing becomes important and quantified the error associated with using the Taylor expansion, especially under high charge/discharge conditions. Consequently, we carry out the calculation of the rate of enthalpy change and the heat generation rate from the most fundamental equation for the rate of the total enthalpy change without simplifying assumptions or approximations. The heat generation rate calculated doing so naturally includes irreversible, reversible and mixing heat. We then exclusively separate out the heat of mixing by subtracting the rate of enthalpy change by reaction from the rate of the total enthalpy change. Results show that the contribution of heat of mixing in the total heat generated increases with the charge/discharge rate and is as large as 23% for a 6 C discharge. This result suggests that while modeling heat generation for fast charge/discharge, it is necessary to include the heat of mixing and avoid calculating it using the Taylor expansion approximation.
Highlights
To cite this article: Divya Chalise et al 2020 J
In a mathematical sense, the heat of mixing is equivalent to the error induced in calculating the heat generation by only considering the enthalpy change of the reaction at the surface instead of the total enthalpy change of the particle
From the original papers on battery heat generation,[7,13,16] it is evident that the methods commonly used to calculate the rate of enthalpy change such as IUH,surface, or IUH,¥ or the method of Taylor expansion are approximations to the fundamental equation of the rate of total enthalpy change (Eq 6)
Summary
To cite this article: Divya Chalise et al 2020 J. The heat of mixing term is generally computed using an expression obtained by Taylor expansion, which, as discussed later in the paper, is not applicable at high currents where concentration gradients are significant.
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