Across the United States, drivers rely on passenger vehicles to travel over 3.2 trillion miles each year. Vehicle safety during these trips is a prerequisite and essential to building trust between car manufacturers and consumers.
As electric vehicle (EV) adoption continues to accelerate, the National Renewable Energy Laboratory (NREL) is working with Hyundai Motor Company to ensure that EV batteries can safely and reliably go the distance.
Protecting passengers and the planet
Every vehicle on the market must meet strict 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 electric cars 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, offer improved stability and reduce the likelihood of a rollover accident. Ongoing 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 shorting,” said NREL researcher Anudeep Mallarapu. “Damage at the cell level tends to cause a chain reaction in the battery. But if we manage the heat generated, we can reduce the likelihood of thermal runaway and improve overall battery safety.”
Battery abuse simulations inform safer designs
To demonstrate the safety of their vehicles, automakers conduct crash evaluations to develop advanced models that illustrate crash response scenarios for various vehicle models. Battery research uses this approach on a smaller scale with abuse testing.
The key to designing durable, 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 abuse models that can be easily integrated with existing car accident simulations.
“Developing models for battery-powered vehicles is complicated: in addition to mechanical and thermal response, we also consider complex chemical reactions, high-voltage implications, as well as varied length scales and response times for the various physical phenomena,” said Mallarapu.
Where previous industry research focused on the gradual deformation of battery cells, NREL has introduced new capabilities to evaluate dynamic, high-velocity impacts. This approach starts with tension and compression experiments in the laboratory at the component level to characterize mechanical properties. Next, researchers use advanced equipment combined with advanced imaging techniques to take 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 the gas and temperature distributions evolve during 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 critical to our understanding of the safety and reliability of EV batteries.”
NREL and Hyundai researchers 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 laboratory experiments, researchers can more quickly analyze the battery’s response to different types of mechanical damage.
Demonstration of capabilities strengthens partnership
NREL recently hosted Hyundai management to review progress on the three-year collaboration and new methods for understanding the failure
states, physical processes and complex interactions affecting lithium-ion batteries.
The project team reviewed NREL’s internal experimentation capabilities along with a new toolkit developed for multiphysics modeling of lithium-ion batteries. Additionally, 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 with greater use of electric vehicles, it is important that we develop multi-physics simulation techniques capable of predicting this hazard in advance,” said director YongHa Han, who heads the Virtual Technology Innovation Research Laboratory in Hyundai Motor Group. “Under these circumstances, cooperation 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 necessary 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 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 NREL’s sustainable transportation and energy storage research. And sign up for NREL’s quarterly transportation and mobility research newsletter, Sustainable Mobility Matters, to stay updated on the latest news.
Originally published at NREL. By Rebecca Martineau
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