The team from the University of Warwick, car maker Jaguar Land Rover and energy company OVO Energy worked with the Argonne National Laboratory and Hawaii National Energy Institute in the US on the review of battery test protocols. They looked at the wide range of methods used around the world to characterize the performance of lithium-ion batteries in order to provide insight on best practices.
Typically, battery researchers use three parameters to define electrochemical performance: capacity, open-circuit voltage, and resistance. Capacity is a measure of the total charge stored in a battery. The open-circuit voltage is the voltage available from a battery with no current flow. It represents the battery's maximum voltage. The resistance is the degree to which the component materials impede the flow of electric current, resulting in a voltage drop.
The problem is that, depending on battery application, researchers may measure these parameters under different test conditions (temperature, rate of discharge, state of charge, etc.), and thereby obtain a different battery operating life. Battery resistance, for example, can be measured with either a direct current or alternating current.
"It's complicated," said Anup Barai, a principal investigator and senior research fellow at the University of Warwick. "The appropriateness 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 that end, the team has produced an easy-to-use table comparing eight test methods, including the main equipment needed, the information generated, and the advantages and drawbacks for each.