A thermodynamic approach for characterizing the degradation of Li-ion batteries

Lithium-ion (Li-ion) batteries have emerged as the essential energy storage alternatives, offering high energy density and long-term reliability for various applications. Nevertheless, a major concern is that the performance of Li-ion batteries deteriorates with the number of discharge cycles, and the extent of degradation is influenced by the battery's type and manufacture. To gain rapid insight into characterizing the battery's performance, we employ the general principles of irreversible thermodynamics for a degrading system that establishes a linear correlation between the measure of degradation rate (ẇ) and the entropy generation rate (Ṡg), through the proportionality constant called the degradation coefficient B. We propose to quantify ẇ by measuring the slope of the discharge voltage (V˙), and the S˙g using the discharge voltage, current, and surface temperature. By performing a series of single discharge experiments on different types of Li-ion batteries (18650 batteries with different capacities, a polymer battery, and a 21700 battery), we have established the existence of a linear relationship between ẇ and Ṡg, i.e., a constant value of B under different experimental conditions are validated. This finding is additionally authenticated for different-capacity batteries experiencing multiple discharge cycles. Additional validations are presented that use independent results from published papers. We show that the proposed approach can rapidly distinguish a lower capacity from a higher capacity battery. It can also rapidly assess the performance of batteries with the same capacity rating but their discharge characteristics are different. •Principles of irreversible thermodynamics are applied to assess battery degradation.•Extensive experimental results with single and multiple discharge cycles are presented.•Battery degradation can be quantified using entropy generation.•Li-ion battery performance can be determined rapidly with a few minutes of testing.