Measuring Irreversible Heat Generation in Lithium-Ion Batteries: An Experimental Methodology

Abstract

Lithium-ion battery research has historically been driven by power and energy density targets. However, the performance of a lithium-ion cell is strongly influenced by its heat generation and rejection capabilities which have received less attention. The development of adequate thermal metrics able to capture the anisotropic thermal conductivity and uneven internal heat generation rates characteristic of lithium-ion cells is therefore paramount. The Cell Cooling Coefficient (CCC), in W.K−1, has been introduced as a suitable metric to quantify the rate of heat rejection of a given cell and thermal management method. However, there is no standardised methodology defining how to measure the heat generation capabilities of a cell. In this study, we applied the CCC empirical methodology to evaluate the rates of irreversible heat generation at various operation conditions, providing maps which give a complete insight into cell thermal performance. The maps derived show how the most important operational variables (frequency, C-rate, SOC and temperature) influence the cell thermal performance. These maps can be used along with the CCC by pack engineers to optimise the design of thermal management systems and to down select cells according to their thermal performance.