How do changes in manufacturing processes and materials affect battery lifespan? New solutions can predict in advance.

As the demand for electric vehicle batteries continues to grow, researchers at the University of Michigan have developed a method to predict how changes in manufacturing processes and materials will affect the lifespan of the batteries.

Engineers at the University of Michigan have determined that the internal resistance measured immediately after the battery is made is a key indicator for measuring the battery's lifespan. The measurement can be completed within a few seconds at the end of the manufacturing process, with almost no additional cost.

Previous studies have shown that life prediction is possible, but it requires repeated cycles - charging, discharging and recharging - to collect the data needed for training the algorithm. The aging tests required to determine the lifespan may take from several weeks to several months to complete. For this reason, the tests are only conducted on a small number of batteries, rather than all the batteries produced.

However, a new study published recently in the journal "Joule" indicates that the exact battery lifespan can be predicted with the help of a resistance measurement, or it can be regarded as a measurement of how much the battery resists the flow of its internal current. This resistance might come from the materials of the internal components, or from electrochemical factors that affect the movement of ions between the battery electrodes. Measuring the resistance at low charge levels is crucial.

The lead author of the study, Andrew Weng, a doctoral student in mechanical engineering, said: "In principle, resistance measurements in the low charge state can be obtained without any cycles, which makes the model training process faster."

The prototype lithium-ion battery constructed by the Battery Laboratory of the University of Michigan was subjected to diagnostic measurements in an environmental control room. Source: University of Michigan

Why is resistance a good indicator for estimating the lifespan of a battery?

It can indicate how much lithium is integrated with the liquid electrolyte. The liquid electrolyte transports ions from one electrode to another within the battery. This bonding layer is called the inter-electrode solid electrolyte interface and it can protect the surface of the electrodes, prolonging their lifespan.

The amount of lithium entering the interphase of the solid electrolyte is usually difficult to measure. However, at low charging states, the internal resistance of the battery is closely related to the amount of lithium entering the interphase of the solid electrolyte. This provides a way to quickly measure the protective layer and to measure the operating capacity of the battery using ordinary equipment.

The research conducted by the Massachusetts Institute of Technology provides a useful tool for automobile manufacturers, as most of them are rapidly shifting their product lines from internal combustion technology to hybrid and electric transportation. This transformation has led the industry to compete in lithium-ion battery materials, seeking to enhance productivity and reduce costs - all of which are happening simultaneously.

As Reuters reported earlier this month, these factors have contributed to the "bottleneck in electric vehicle batteries".

Professor William-Claire Ford's technical professor Anna Stefanopoulou and doctoral student Andrew Weng from the Department of Mechanical Engineering identified an early-life diagnostic signal that can predict the impact of the protocol on battery lifespan without the need for cycle-life testing. Credit: University of Michigan

Automobile manufacturers have been striving to reduce the production costs of cars. Now, they are seeking to make the batteries of electric vehicles as cost-effective as possible. Therefore, the question we are trying to answer is: During the manufacturing process itself, how quickly can you determine the lifespan of the battery?

It has been proven that the answer is: immediately, if you know the key signals that can be obtained in high-throughput testing. Identifying such key measurable features can be simply used for continuous improvement and expansion of domestic battery manufacturing scale.