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New Drop Tower Helps Develop Safer, Reliable, and More Efficient Batteries

Researchers pierce lithium-ion cells and crush them, soak them in saltwater, roast them, and short circuit them. They also overcharge and over-discharge them. Moreover, they can even use lasers to shoot them.

Sandia National Laboratories engineers June Stanley and Chris Grosso demonstrate how the drop tower they built abuses batteries to understand how the lithium-ion cells respond to different types of stress. (Image credit: Randy Montoya)

At Sandia National Laboratories, the researchers’ job is to test lithium-ion cells beyond their limits. Hence, those humble batteries never stood a chance against that team.

Now, with an innovative indoor tower that enables battery-abuse researchers to place 200 pounds or more on the unmatched lithium-ion cells, the team has developed yet another technique to learn much more about the way batteries react to stress.

This becomes our ninth way of killing a battery. It hits with so much force that so far we are just chopping the batteries in half.

Chris Grosso, Battery-Abuse Testing Engineer, Sandia National Laboratories

Lithium-ion batteries can be mostly found in aircraft, electric cars, medical equipment, and computers. These batteries are becoming more robust all the time. Moreover, the constant demand for more power and storage spurs the need for numerous tests like those provided by the novel drop tower, stated Sandia mechanical engineer June Stanley.

As far as we know nobody in the U.S. has done any drop tests for impact testing like this,” Stanley added. The data obtained will help the industry in designing batteries that are safer, more reliable, and also deliver more efficient performance. In addition, the data will help in responding to electric-vehicle crashes and other emergencies, she stated.

An impact test like this is more real world, more realistic to what would happen. The test can give us a better understanding for first responders and how they handle an emergency. It can also be beneficial for industry researching and developing new technology.

June Stanley, Mechanical Engineer, Sandia National Laboratories

Gravity Takes Over

Within a hangar-type building, the drop tower looms which can be easily vented and cleared if smoke emerges from a battery fire. The tower is remotely controlled by researchers, who observe all the action on monitors within a trailer parked approximately 30 yards away.

What the team observed is that the drop tower reaches upward to just under the 14-foot ceiling. A battery is mounted in a steel tray that, in turn, is connected to a load cell to determine the impact force at the tower base as a weight of no less than 200 pounds is placed above at heights of up to 8’, 8”.

The weight is unleashed by simply pushing a button. Gravity then takes over and this is followed by an intense impact of weight on the battery. Wires that are joined to the tower and the battery determine voltage, temperature, force, and speed. Cameras record the collision and ensuing carnage, while computers inside the trailer receive data.

To date, the researchers have tested single-cell lithium-ion batteries as well as a 12-pack of such batteries joined together. Although the tests failed to create the heat and sparks that would take place in a slower-moving hydraulic crush test, they have nevertheless obtained valuable data, stated Stanley.

In the repercussion of the drop, the batteries are not stable and, moreover, the safety status of approximately half the cells is not known, she stated. “It certainly helps with a better understanding for first responders to handle a situation like that.”

Testing Leads to Improvement

The highest weight that can be used for crushing, smashing, or chopping a battery is 500 pounds and this is due to the components selected, Grosso stated. “That can easily be upgraded, if needed, and we can keep adding weight to get more force.”

Off-the-shelf rails and bearings as well as welded tube steel make it cost-effective to maintain the drop tower, even if it is less than sophisticated to look at, added Grosso, who engineered the electronics and operating software of the tower.

When the inevitable fire comes, parts can be replaced cheaply. It doesn’t have to be pretty, but it does have to be effective, and we have to be able to justify the cost to our customers.

Chris Grosso, Battery-Abuse Testing Engineer, Sandia National Laboratories

About two and a half years ago, Stanley teamed up with Grosso and eventually enhanced the safety, mechanical design, and engineering controls to move the drop tower from concept to reality.

According to Stanley, who led the development and installation of the drop tower, the team is planning to enhance the contraption as more tests are carried out and customers demand for different kinds of tests.

This is just the base design,” she stated. “We have hopes and plans to improve on it.”

Upcoming enhancements will be to integrate gas-pressurized pistons or springs to increase the weight’s downward acceleration, thus boosting the impact force.

To get more impact force we can increase the mass or the acceleration of the object impacting the battery, or both,” Stanley stated. “Right now, we are accelerating at the rate of gravity. Our goal is to have a much higher rate of acceleration, thus more force!”

Other plans will emerge as industry continues to extend the limits of the power that can be generated and stored by batteries. Since these batteries can work their way into more day-to-day devices, the Sandia team will continue to get better at abusing these products.

It's that desire to push batteries beyond their limits that will eventually spur advancements. The availability of more data will allow developers to design advanced storage devices that have better safety, reliability, and performance.

As an added capability to what we are already doing, the drop tower is very cool,” Grosso stated. “Our customers have been asking for something like this, and it just shows that we have got some serious brain power in our lab.”


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