By using ultrasound to monitor the electrochemical and mechanical functions of a battery, thy have been able to immediately reveal any damage or flaws that could lead to overheating and even cause “thermal runaway.”
According to Wes Chang, PhD, an assistant professor and primary investigator of the Battery Dynamics Lab in Drexel’s College of Engineering, “Ultrasound has been adapted from other fields for battery diagnostics only in the past decade. Because it is such a new technique in the battery and electric vehicle industries, there is a need to teach battery engineers how it works and why it is useful.”
The team has been able to demonstrate a low-cost, accessible benchtop ultrasonic tool that it hopes can be easily implemented and used by battery engineers.
“While the vast majority of lithium-ion batteries today are high performing and safe, defects are bound to exist when thousands of cells are used within electric vehicles and there are millions of electric vehicles being produced every year,” Chang said.
Current safety processes rely on visual inspection and performance testing of select battery cells after they come off the line, and batteries may also be X-rayed to generate a high-resolution interior image, but this is slow and expensive. However, small design or manufacturing flaws can be missed leading to a massive batch of defective batteries making their way into market.
The team at Drexel has used acoustic imaging - ultrasound - which is faster and less expensive than X-rays and can provide complementary information about the mechanical properties of the battery. The team used scanning acoustic microscopy technology to send low-energy sound waves through a commercial pouch cell battery.
Without affecting its internal operations or affecting its performance, the speed of the waves is altered as it passes through the various materials inside a battery. This allows researchers to get a complete, detailed and quick look at the chemical changes within battery materials as it is being used.
The process can help to detect structural defects or damage that could cause an electrical short, material deficiencies or imbalances that could hamper performance, as well as indicators that problems are likely to occur. One substance the scan is particularly good at detecting is gas, which is an indication of dry areas that could cause the cell to fail while it is being used.
The sensitivity of ultrasound makes it useful not just for detecting defects in manufacturing, but also for gauging how new battery chemistries fail in research and development labs.
As part of the research, the research group worked with partners at SES AI, a lithium metal battery startup company and provided engineers with instantaneous access to data during the design and testing process which allowed them to make adjustments and corrections.
The team has also developed open-source software to run the instrument and produce a rapid analysis of the resulting data.
“We hope that by lowering the barrier to entry, ultrasonic testing can become a routine part of battery research and development,” Chang said.
