Built-in sensors make Li-ion batteries safer

January 7, 2016

By eeNews Europe

RF transmission Test and Measurement Batteries / Power Supplies

Although in general Li-ion batteries – which are commonly used as power sources in mobile electronics and electric vehicles – are safe, they have been linked with battery fires on airliners and more recently in hoverboards. Li-ion batteries contain a flammable electrolyte solution that under normal usage is not dangerous.

However, if the battery is punctured, as may happen in a car accident, or overcharged due to a malfunction, a problem called thermal runaway can occur. When this happens, the battery may overheat and the battery pack catch on fire. As devices get smaller and the demand for energy increases, safety becomes a greater concern.

“Your cell phone charge can now last for a week instead of a day, but it is still the same size. The battery has a lot more energy density, you are compressing more and more energy into a smaller space, and you have to be careful when you do that,” says Chao-Yang Wang, William E. Diefenderfer Chair of Mechanical Engineering and professor of mechanical engineering, chemical engineering, and materials engineering. “Our job is to come up with solutions to provide safety while at the same time increasing performance.”

Penn State researchers are looking at delivering greater safety by placing temperature sensors inside Li-ion batteries to monitor internal temperatures, detect problems, and provide early warning for intervention. The technology is called internal reaction temperature sensing (RTS).

“We have a unique capability to put sensors inside of cells," says Chris Rahn, professor of mechanical engineering.

Battery cells generate heat from the inside and it can take a long time for the external temperature to rise because of the battery case. By the time an external sensor measuring voltage, current, or temperature registers a problem it might be too late to prevent a fire.

RTS directly monitors the temperature inside the cell where the reaction is taking place and can detect temperature spikes more quickly and accurately than surface sensors. If the sensor detects that the inside is too hot, it will shut down the current flow in the battery.

Penn State was the first university to make large-format Li-ion cells in the lab and it is that technology that allows researchers to insert and test these sensors.

“We make the batteries in our lab and then test them in our lab,” says Guangsheng Zhang, research associate in mechanical engineering. “Very few universities have the capabilities to make their own batteries.”

RTS is a step toward a larger vision at Penn State to create smart batteries. Smart batteries would have numerous built-in sensors and actuators to enhance battery performance, life, and safety. Battery operators could not only detect what is happening inside the battery, but they could also change the internal state of the battery – for example heating a battery so that it would work in extreme cold.

Emerging technologies such as robots and drones are limited by the capabilities of the batteries needed to power them. Enhanced batteries would provide an opportunity to improve those technologies.

For more, see the paper in the journal Scientific Reports: Reaction temperature sensing (RTS)-based control for Li-ion battery safety