ORNL team proposes new electrode design to mitigate risk of battery failure in accidents; inspired by safety glass
Researchers at Oak Ridge National Laboratory (ORNL) are proposing a new design concept for lithium-ion batteries that introduces slits in the electrodes—a feature which may mitigate the risk of battery failure during automobile accidents. The concept, presented in a paper in the journal Joule, could allow manufacturers to scale down the housing materials that commonly protect batteries in electric cars from mechanical damage, improving the overall energy density and cost.
The concept is based on introducing breakable electrodes that, upon impact, isolate the damaged part from the rest of the electrode to limit the current going through any short circuit. The new design in essence allows the large automotive cells used in most vehicles to fragment into many small batteries if damaged in a collision, explained Nancy Dudney, an author on the study and an energy storage researcher at the Materials Science and Technology Division of Oak Ridge National Laboratory.
Small batteries pose a much smaller hazard when they are accidentally shorted than do very large batteries. With such an innovation, device manufacturers can reduce the weight and expense of heavy-duty containers that are normally needed to protect their batteries from mechanical abuse.—Nancy Dudney
The researchers used patterns of slits to realize the breakable electrodes, which in principle add little cost and can be produced by the roll-to-roll process.
Safety glass was the inspiration for the team. Sometimes the best way to help protect against a dangerous failure is to allow a component to fail or break gracefully and safely under mechanical abuse, said Dudney.
The team tested the model against a standard lithium-ion battery by pressing a large metal ball into each. The modified battery was distorted like a potato chip but continued to function at 93% of its original capacity. Similar damage to a standard battery causes a full discharge and failure.
This technology involves electrically isolating the internally shorted part of the battery from the rest of the cell before the separator is punctured. By limiting the current passing through the shorted area, heat generation can be minimized to prevent thermal runaway. Using an IR camera, we showed that this approach leads to a significantly lower increase in the temperature compared with a standard battery experiencing mechanical abuse.
We performed computer simulations on electrochemical systems to identify the level of separation needed for mitigating thermal runaway. FEM analysis was conducted to validate the proposed slit pattern for fragmenting the electrodes and current collectors under cell indentation. The breakable electrodes were realized by introducing a certain slit pattern using a modified clicker die without affecting the conventional roll-to-roll production for battery electrodes. Batteries with slitted electrodes exhibited capacities and voltage profiles similar to those of standard batteries. When mechanically abused by heavy deformation, the modified battery did not short-circuit, while the standard one shorted and became nonfunctional. The modified battery retained 93% of its capacity after the mechanical abuse test and was electrochemically viable.—Naguib et al.
Since the electrode slits only added a minimal cost to the production of their redesigned lithium-ion battery and didn’t call for significant changes in how the battery was made, the team believes this technology could be scaled up in the future. However, there are more tests to run.
The research was supported by the Department of Energy’s Advanced Research Projects Agency-Energy program.
Michael Naguib, Srikanth Allu, Srdjan Simunovic, Jianlin Li, Hsin Wang, Nancy J. Dudney (2017) “Limiting Internal Short-Circuit Damage by Electrode Partition for Impact-Tolerant Li-Ion Batteries” Joule doi: 10.1016/j.joule.2017.11.003