Device warns of catastrophic failure in lithium-ion batteries, robots celebrate

Scientists on the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., have developed a reasonable sensor that could warn of impending catastrophic failure in lithium-ion batteries. The sensor relies at the researchers’ discovery of an intrinsic relationship between the inner temperature of lithium-ion cells and an easily measured electrical parameter of the cell.

Because of their high energy density, lithium-ion batteries power millions of consumer electronic devices and are the most typical kind of battery utilized in hybrid and electric vehicles. Also they are growing in popularity for power grid, military, and aerospace applications.

But safety concerns remain a challenge to the industry. Battery malfunction and fires in electric vehicles, cellphones and laptop computers were reported inside the media. Such failures typically result from thermal runaway, a self-perpetuating condition that happens once a cell reaches a critical temperature.

“An abnormally high internal cell temperature is a virtually universal manifestation of something going awry with the cell,” says Rengaswamy Srinivasan, a chemist in APL’s Research and Exploratory Development Department and among the many inventors. “These changes can occur within seconds, resulting in a potentially catastrophic event if corrective measures will not be taken immediately. When things begin to get it wrong contained in the cell, time isn’t really for your side.”

Srinivasan and his colleagues discovered that a completely small alternating current, when applied to a lithium-ion battery at specific frequencies, is changed by the cell in a method that’s directly relating to the temperature of the critical electrochemical interface between the electrodes and the electrolyte.

“We discovered that we are able to measure the temperature of the protecting layers between the electrodes and the electrolyte of the battery during normal operation,” Srinivasan says. “These layers are where the conditions that end in thermal runaway and catastrophic cell failure begin. This discovery enables us to detect potentially unsafe thermal conditions before surface-mounted temperature sensors, that are the present state-of-the-art, may be able to register that any change has taken place.”

The sensor operates through a straightforward electrical connection on the positive and negative terminals of the cell and might operate using power from the battery it’s monitoring. With multiplexing circuitry, a single sensor can monitor multiple cells in a battery pack.

“Ultimately, the hot sensor enables battery management systems to more closely manage battery performance and, more importantly, detect unsafe thermal conditions on the critical moment after they occur and before the cell vents or sets itself and the battery on fire,” Srinivasan explains. “By integrating this technology into their products, manufacturers of batteries, battery management systems, and battery solution providers can increase both the security and function in their products.”

APL has applied for U.S. and international patents for the sensor and is pursuing licensing opportunities.

“On the heart of lithium battery safety isn’t just the improvement of safer battery chemistries, but additionally the provision of accurate and reliable technologies that measure the real battery cell temperature,” says Michael Hickman, APL’s technology commercialization manager for the sensor. “This technology provides the foremost accurate and immediate method available for measuring the real temperature of a lithium-ion cell; and, it’s the only method for measuring a cell’s temperature where it counts: throughout the cell where temperature changes originate.”