Evaluation of battery performance: compared to what?

Scientists often have to wonder, in relation to what? How do laboratory results compare to those obtained by others? How do our theoretical calculations compare to the experimental data?

Answering such questions is particularly crucial for researchers and developers of lithium-ion batteries. Invented four decades ago, lithium-ion batteries now power most portable electronics such as laptops and power tools. They are also under development to meet the high energy storage needs of electric vehicles and power grids. New designs with different electrode and electrolyte compositions – the two key components of the battery – are coming up all the time.

To determine whether an innovation in electrodes or electrolytic materials is actually an improvement, it should be compared to other test results. However, there is no "one size fits all" standard for battery testing. Battery test methods can vary considerably.

Ira Bloom, a battery researcher at Argonne, said, "Industrial engineers and researchers at government and university laboratories often develop their own procedures for characterizing lithium-ion batteries according to the application envisioned by the industry. This makes the comparison of technological innovations extremely complex. "

A team from the Argonne National Laboratory of the United States Department of Energy (DOE), the University of Warwick, OVO Energy, the Hawaii National Energy Institute and Jaguar Land Rover reviewed the literature on the different methods used in the world to characterize the performance of lithium. ion batteries to better understand best practices.

In general, battery researchers use three parameters to define electrochemical performance: capacitance, open-circuit voltage, and resistance. Capacity is a measure of the total charge stored in a battery. The no-load voltage is the voltage available from a battery without power. It represents the maximum voltage of the battery. Resistance is the degree to which the constituent materials interfere with the flow of electrical current, causing a voltage drop.

The problem is that, depending on the application of the battery, researchers can measure these parameters under different test conditions (temperature, discharge rate, state of charge, etc.) and thus obtain a different battery life. The resistance of the battery, for example, can be measured with direct current or alternating current.

"It's complicated," observes Anup Barai, senior researcher and senior researcher at the University of Warwick. "The relevance of a test depends on what the investigator is studying.Our review provides guidance on the most appropriate test method for a given situation." To this end, the team produced a user-friendly table comparing eight test methods, including the main hardware needed, the information generated, and the advantages and disadvantages of each.

"Our hope," adds Bloom, "is that our results will one day allow for more reliable and comparable methods to test lithium-ion batteries for different applications."

The study, titled "A Comparison of Methodologies for the Noninvasive Characterization of Commercial Li-ion Cells", was recently published in the online version of the journal Progress in science of energy and combustion.