A recent uptick in battery-related fires has drawn attention to the challenge of identifying defects that can cause these catastrophic malfunctions, but are rarely obvious to the naked eye. In hopes of preventing the dangerous glitches that can cause batteries to overheat and catch fire, researchers from Drexel University have developed a standard testing process to give manufacturers a better look at the internal workings of batteries.
In a paper recently published in the journal Electrochimica Acta , the group presented methods for using ultrasound to monitor the electrochemical and mechanical functions of a battery — which would immediately reveal any damage or flaws that could lead to overheating and even cause "thermal runaway."
"While lithium-ion batteries have been studied for nearly half a century and commercialized for over 30 years, we have only recently developed tools that can see inside with high resolution" said Wes Chang, PhD , an assistant professor and primary investigator of the Battery Dynamics Lab in Drexel's College of Engineering , who supervised the project. "In particular, ultrasound has been adapted from other fields, such as geophysics and biomedical sciences, 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's recent work strives to do this, by demonstrating a low-cost, accessible benchtop ultrasonic tool that it hopes can be easily implemented and used by battery engineers, including those who work at automotive companies producing electric vehicles.
According to a Consumer Affairs report individuals use three to four electronic devices powered by batteries each day — from laptops, phones and tablets, to power tools and electric transit, like bikes and scooters — a number that has doubled in the last five years. The rush to supply batteries for all of these devices has created a market for products that can be produced cheaper and faster. This is a concern, according to Chang , because it may allow low-quality cells to enter the market.
"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.
The current safety and quality control processes for manufactured batteries rely heavily on visual inspection and performance testing of select battery cells after they come off the line. Manufactured batteries may also be X-rayed to generate a high-resolution interior image, but this is slow and expensive.
Manufacturers are required to follow these inspection and testing protocols, but with the scale at which batteries are being used, even a small design or manufacturing flaw that is missed can lead to a massive batch of defective batteries making their way into market.
By contrast, the method proposed by the Drexel team uses acoustic imaging — ultrasound — which is faster and less expensive than X-rays and can provide complementary information about the mechanical properties of the battery. Chang's group reported using 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.
"By observing how the sound wave has changed upon interacting with the sample, we can deduce a number of structural and mechanical features," they wrote in the report.
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 important because the presence of gas inside a battery 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, Chang's group worked with research partners at SES AI , a lithium metal battery startup company. Deploying the testing platform at SES AI's research and development site gave the engineers instantaneous access to data during the design and testing process which allowed them to make adjustments and corrections more quickly.
In addition to reporting their process for the ultrasound testing method, the team 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. "Battery scientists want to build better batteries, not develop new tools. We provide a user interface that is easy-to-use with regular software updates. This adds to the existing collection of tools that battery scientists have on hand for measuring and diagnosing next-generation battery performance."
The group plans to continue improving the technology so that it can more easily scan battery electrodes, as well as cells, and produce more detailed three-dimensional images rather than the currently limited two-dimensional scans to better detect defects.
