Review - Reversible heat effects in cells relevant for lithium-ion batteries

Abstract

We review measurements of reversible heat effects in lithium-ion batteries, i.e. entropy changes and Seebeck coefficients of cells with relevant electrodes. We show how to compute the Peltier heat of battery electrodes from Seebeck coefficients. The Seebeck coefficient depends on the heat of transfer (Soret effect), which is found from the difference of initial and stationary state values of the Seebeck coefficient. We apply non-equilibrium thermodynamics theory and obtain initial Peltier heats not reported before. For the oxidation of lithium metal we propose the value 34 ± 2 kJ mol−1 when the electrolyte contains 1 M LiPF6, while the value is 29 ± 1 kJ mol−1 when the electrolyte contains 1 M LiClO4. The positive values imply that the electrode cools when it serves as an anode. For oxidation of lithium under stationary state conditions, the stationary state Peltier heat is ≈120 kJ mol−1. A large reversible heating effect can then be expected for the single electrode; much larger than expected from the full-cell entropy change. These values have a bearing on thermal modelling of batteries. Peltier heats for anodic reactions are presented in tables available for such modelling. We discuss the need for measurements and point at opportunities.