NREL: Electric Vehicle Battery Models Inform Crash Simulation Evaluations To Improve Real-World Safety, Reliability
Across the United States, drivers rely on passenger vehicles to travel over 3.2 trillion miles each year. Vehicle safety during those trips is presumed and crucial to building trust between automobile manufacturers and consumers.
As electric vehicle (EV) adoption increasingly gains momentum, the National Renewable Energy Laboratory (NREL) is collaborating with Hyundai Motor Company to ensure EV batteries can safely and reliably go the distance.
Protecting Passengers and the Planet
Every vehicle on the market must meet stringent battery safety standards and regulations to protect passengers. Both the Insurance Institute for Highway Safety and the National Highway Traffic Safety Administration have concluded that EVs are as safe—if not safer—than conventional vehicles. In a collision, EV batteries automatically disconnect from the vehicle to reduce battery damage. In addition, current EV vehicle designs boast a lower center of gravity, offer improved stability, and decrease the likelihood of a rollover accident. Continued research at NREL aims to further strengthen the resilience of EV batteries by improving the thermal response—or the amount of heat the battery is able to withstand—when damage occurs.
“Our goal is to understand how mechanical damage leads to battery failure and internal short-circuiting,” NREL researcher Anudeep Mallarapu said. “Cell-level damage tends to cause a chain reaction within the battery. However, if we manage the heat generated, we can reduce the likelihood of thermal runaway and improve overall battery safety.”
To demonstrate the safety of their vehicles, automotive manufacturers perform collision evaluations 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 durable, reliable, and safe EV batteries lies in understanding how damage impacts the battery module. With battery data in hand, NREL researchers can also develop predictive battery abuse models that easily integrate with existing vehicle crash simulations.
“Developing models for battery-powered vehicles is complicated: Besides mechanical and thermal response, we also consider complex chemical reactions, high voltage implications, as well as varied length scales and response times for the different physical phenomena,” Mallarapu said.
Where prior industry research focused on the gradual deformation of battery cells, NREL has introduced new capabilities to evaluate dynamic, high-speed impacts. This approach starts with in-lab tension and compression experiments at the component level to characterize mechanical properties. Next, researchers use state-of-the-art equipment coupled with advanced imaging techniques to capture 10,000–40,000 images per second as the cell is damaged. NREL researchers provide a detailed analysis of the thermal and electrochemical reactions simultaneously, measuring how gas and temperature distribution evolves throughout battery failure to help inform design improvements.
“Most accidents don’t happen slowly, and battery research should reflect real-world scenarios,” Mallarapu said. “High-speed abuse testing is crucial to our understanding of the safety and reliability of EV batteries.”
NREL and Hyundai researchers use 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.
Capabilities Demonstration Bolsters Partnership
A man operates a laptop computer in a lab while three other people watch
Mechanical engineer researcher Anudeep Mallarapu demonstrates NREL’s battery safety modeling and experimentation. Photo by Werner Slocum, NREL
NREL recently hosted Hyundai leadership to review progress on the three-year collaboration and new methods of understanding the failure modes, physical processes, and complex interactions that affect lithium-ion batteries.
The project team reviewed NREL’s in-house experimentation capabilities alongside a new toolkit developed for multiphysics modeling of lithium-ion batteries. In addition, visitors experimented with NREL’s advanced visualization tools to interpret mechanical, electrical, and thermal failure through simulations of battery modules subject to abuse conditions.
“As concerns about the fire safety of high-voltage batteries increase with greater adoption of electric vehicles, it is essential that we develop multiphysics simulation techniques capable of predicting this danger in advance,” said Director YongHa Han, who leads Virtual Technology Innovation Research Laboratory in Hyundai Motor Group. “Under these circumstances, collaboration with specialized research institutions such as NREL, which has abundant development experience and capabilities related to electric vehicle batteries, is essential. We hope that the core element technologies needed for Hyundai Motor Group will be effectively developed by establishing a continuous joint research and cooperation system.”
In the final phase of this collaboration, NREL and Hyundai will scale this research from battery modules to entire vehicle packs to evaluate how EV batteries react 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.