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As the demand for electric vehicle batteries continues to grow, researchers at the University of Michigan have developed a method to predict the impact of changes in manufacturing processes and materials on battery life. .
UM engineers have identified internal resistance, measured immediately after cell manufacture, as a key indicator of battery life. Measurements can be performed within seconds of the end of the manufacturing process at little or no additional cost.
Previous research has shown that life prediction is possible, but it requires repeated cycles (loading, unloading, and reloading) in order to collect the data needed to train the algorithm. Aging tests necessary to determine lifespan can take weeks or even months. For this reason, tests are performed on only a few cells and not on all cells produced.
But the new study, recently published in Joule, shows that precise battery lifetimes can be predicted using a resistance measurement or a measurement of the battery’s ability to fight current flow. inside. This resistance can come from the materials used for the internal components or from electrochemical factors that affect the way the ions move between the electrodes of the battery. It is essential to measure resistance at low load levels.
“The resistance measurement, at low state of charge, can, in principle, be obtained without any cycles, which makes the training process of the model much faster,” said Andrew Weng, mechanical engineering doctoral student and lead author of the study.
Why is resistance such a good barometer for estimating battery life?
It can give an indication of the amount of lithium fused with the liquid electrolyte which carries the ions from one electrode to another inside the battery. This combination layer, known as solid electrolyte interphase, can protect the electrode surface and allow longer lifetimes.
The amount of lithium entering the interphase of the solid electrolyte is generally difficult to measure. But at a low state of charge, the internal resistance of the battery is closely related to the amount of lithium entering the interphase of the solid electrolyte. This provides a quick measurement of this protective layer, as well as the operating capacity of the battery, with ordinary equipment.
UM’s research provides a useful tool for automakers at a time when most are rapidly moving their product lines away from internal combustion technology to embrace hybrid and electric transport. This change is pushing the industry to fight for lithium-ion battery materials, seeking to increase productivity and reduce costs, all at the same time.
As Reuters reported earlier this month, these factors have contributed to a “bottleneck for electric vehicle batteries.”
“Automakers are always trying to reduce the cost of producing cars, and right now they are looking to make electric vehicle batteries as cost effective as possible,†said Anna Stefanopoulou, William Clay Ford professor of technology and research team leader. “So the question we tried to answer is, ‘How fast can you learn more about battery life during the manufacturing process itself? ”
“Turns out the answer is, ‘Immediately, if you know the critical signal that can be acquired during a high throughput test. The discovery of these key measurable characteristics can simply be used for continued improvements and scaling up of domestic battery manufacturing. “
The research was funded by the National Science Foundation. The team carried out experiments in the UM battery laboratory. A collaborator from Stanford University contributed to the analysis.
Summary of the study: Predict the impact of training protocols on battery life immediately after manufacture
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