In the United States, drivers rely on passenger cars to cover more than 3.2 trillion miles each year. The safety of vehicles during those journeys is assumed and crucial to building trust between car manufacturers and consumers.
As electric vehicle (EV) adoption continues to gain momentum, the National Renewable Energy Laboratory (NREL) is working with Hyundai Motor Company to ensure EV batteries can travel the distance safely and reliably.
Protecting passengers and the planet
Every vehicle on the market must meet strict safety standards and battery regulations to protect passengers. Both the Insurance Institute for Highway Safety and the National Highway Traffic Safety Administration have concluded that EVs are just as safe — if not safer — than conventional vehicles. In the event of a collision, EV batteries are automatically disconnected from the vehicle to reduce battery damage. In addition, current EV vehicle designs have a lower center of gravity, improved stability and reduced the risk of a rollover accident. Continuing research at NREL aims to further enhance the resilience of EV batteries by improving the thermal response — or the amount of heat the battery can withstand — when damage occurs.
“Our goal is to understand how mechanical damage leads to battery failure and internal short circuits,” said NREL researcher Anudeep Mallarapu. “Cell-level damage tends to set off a chain reaction in the battery. However, if we control the heat generated, we can reduce the chance of thermal runaway and improve the overall safety of the battery.”
Battery Abuse Simulations Informing Safer Designs
To demonstrate the safety of their vehicles, automakers conduct crash assessments to develop advanced models that illustrate crash response scenarios for different vehicle models. Battery research applies this approach on a smaller scale with abuse testing.
The key to designing long-lasting, reliable and safe EV batteries lies in understanding how damage affects the battery module. With battery data in hand, NREL researchers can also develop predictive battery misuse models that integrate easily with existing vehicle crash simulations.
“Developing models for battery-powered vehicles is complicated: in addition to mechanical and thermal response, we also consider complex chemical reactions, implications for high voltage, as well as different length scales and response times for the different physical phenomena,” said Mallarapu.
Where previous industrial research focused on the gradual deformation of battery cells, NREL has introduced new possibilities to evaluate dynamic, fast effects. This approach starts with in-lab stress and compression experiments at the component level to characterize mechanical properties. Next, researchers use state-of-the-art equipment combined with advanced imaging techniques to capture 10,000-40,000 images per second if the cell is damaged. NREL researchers provide a detailed analysis of the thermal and electrochemical reactions simultaneously, measuring how the gas and temperature distribution evolves during battery failure to help inform design improvements.
“Most accidents don’t happen slowly, and battery research needs to reflect realistic scenarios,” Mallarapu said. “High-speed abuse testing is critical to our understanding of the safety and reliability of EV batteries.”
Researchers at NREL and Hyundai are using abuse results to develop mathematical models and advanced computer simulations to streamline crash evaluations for EV batteries. By validating these impact models against the in-lab experiments, researchers can more quickly analyze the battery response to different types of mechanical damage.
Opportunities Demonstration Enhanced Partnership
NREL recently hosted Hyundai leadership to assess the progress of the three-year partnership and new methods to understand the failure
modes, physical processes and complex interactions affecting lithium-ion batteries.
The project team assessed NREL’s internal experimentation capabilities alongside a new toolkit developed for multiphysical modeling of lithium ion batteries. In addition, visitors experimented with NREL’s advanced visualization tools to interpret mechanical, electrical and thermal failures through simulations of battery modules subject to abuse conditions.
“As concerns about the fire safety of high-voltage batteries increase as more electric vehicles come, it is essential that we develop multiphysical simulation techniques that can predict this danger in advance,” said director YongHa Han, who leads Virtual Technology Innovation Research Laboratory. . at the Hyundai Motor Group. “Under these circumstances, collaboration with specialized research institutions such as NREL, which has extensive development experience and capabilities in the field of batteries for electric vehicles, is essential. We hope that the core technologies needed for Hyundai Motor Group will be developed effectively by establishing a continuous joint research and collaboration system.”
In the final phase of this collaboration, NREL and Hyundai will scale this research from battery modules to full vehicle packages to evaluate how EV batteries respond when multiple modules are damaged. Further research will help optimize the modeling toolkit to improve conventional crash simulation technologies and accelerate the evaluation of EV vehicle designs.
Learn more about NRELs sustainable transport and energy storage Research. And sign up for NREL’s quarterly transportation and mobility newsletter, Sustainable mobility is importantto keep up to date with the latest news.
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