A Distributed Analytical Electro-Thermal Model for Pouch-Type Lithium-Ion Batteries

An analytic multi-physics model for pouch-type lithium-ion (Li-ion) batteries is presented. Both electrical and thermal processes are considered in the model to resolve their interplay on heat generation and battery thermal behavior. Voltage response of a sample Li-ion battery during galvanostatic discharge processes is measured to obtain a concentration-independent polarization expression. By numerically solving the charge balance equation on positive and negative electrodes in conjugation with the polarization expression, it is shown that the transfer current between the electrodes remains approximately constant, in particular when depth-of-discharge is less than 90%. Based on this observation, the electrochemical performance of the battery is simplified, and by using the method of separation of variables a closed-form electrical model is proposed. Joule heating on each electrode, calculated from the electrical model, is used as a local heat source in a two-dimensional battery thermal model. The distributed thermal model is solved analytically with the method of integral transform. The analytical results are successfully validated through comparisons with experimental and numerical data. It is confirmed that ohmic heating in the electrodes contributes to a relatively small portion (8-18%) of the total heat generation; nonetheless, since this heat is highly localized it results in spatial non-uniformity in temperature. (C) 2014 The Electrochemical Society. All rights reserved.