Peltier effects in lithium-ion battery modeling

Abstract

A high battery temperature has been shown to be critical for lithium-ion batteries in terms of performance, degradation, and safety. Therefore, a precise knowledge of heat sources and sinks in the battery is essential. We have developed a thermal model for lithium-ion batteries, a model that includes terms not included before, namely, Peltier and Dufour heat effects. The model is derived using non-equilibrium thermodynamics for heterogeneous systems, the only theory which is able to describe in a systematic manner the coupling of heat, mass, and charge transport. The idea of this theory is to deal with surfaces as two-dimensional layers. All electrochemical processes in these layers are defined using excess variables, implying, for instance, that the surface has its own temperature. We show how the Peltier and Dufour heats affect a single cell and may produce an internal temperature rise of 8.5 K in a battery stack with 80 modules. The heat fluxes leaving the cell are also functions of these reversible heat effects. Most of the energy that is dissipated as heat occurs in the electrode surfaces and the electrolyte-filled separator. The analysis shows that better knowledge of experimental data on surface resistances, transport coefficients, and Dufour and Peltier heats is essential for further progress in thermal modeling of this important class of systems.

Review—Reversible Heat Effects in Cells Relevant for Lithium-Ion Batteries

“…32 In a non-equilibrium thermodynamic description, the local entropy balance at the electrode surfaces enters via the Peltier heat. We showed in the Supplementary material of Spitthoff et al 11 how the local reversible heat effect at the two electrode surfaces in LIBs add to the total reversible heat effect under isothermal conditions.…”

“…This problem was also addressed in. 11 Wittingham 45 was first to report the entropy change of LIB halfcells. Experiments were done with Li x TiS 2 (LTS) electrodes with degree of intercalation, x ≈ 0.6 and 1.…”

“…For the complete derivation we refer to. 11,16 We recapitulate for illustration the outcome of step 2 for the electrolyte. The flux-force equations are:…”

“…8,9 The accuracy of single-cell thermal modelling is rather important for modelling of larger battery packs. [9][10][11] Among the thermal effects in LIB, i.e. Joule heating, heating due to electrode overpotentials and reversible heat effects, the reversible ones are special in their relation to the cell entropy changes.…”

“…The stationary state value is needed to predict of the time variation of the interface temperature in LIBs. 11 We shall argue that it is important to continue to measure the thermoelectric potential beyond the initial state until a stationary state has been reached.…”