Sensor detects lithium battery fires

January 12, 2012 - via

JOHNS HOPKINS (US) — An inexpensive new sensor can detect overheating and potential fires in common rechargeable lithium-ion batteries. The sensor is based, its inventors at Johns Hopkins University say, on the discovery that an easily measured electrical parameter reveals the internal temperature of a lithium-ion cell.

Lithium-ion batteries, with their high energy density, power millions of consumer electronic devices and are the most common type of battery in hybrid and electric vehicles. They are also growing in popularity for power grid, military, and aerospace applications.

But safety concerns have been a challenge. Battery malfunction, including overheating and fires, has been reported. Millions of computer batteries have been recalled in recent years. Failures can result from thermal runaway, a self-perpetuating condition that occurs once a cell reaches a critical temperature.

“An abnormally high internal cell temperature is a nearly universal manifestation of something going awry with the cell,” says Rengaswamy Srinivasan, a chemist at the Applied Physics Laboratory and one of the inventors of the sensor that is described in the journal Electrochimica Acta.

“These changes can occur within seconds, leading to a potentially catastrophic event if corrective measures are not taken immediately,” he says. “When things start to go wrong inside the cell, time is not on your side.”

Srinivasan and colleagues discovered that a very small alternating current, when applied to a lithium-ion battery at specific frequencies, is changed by the cell in a way directly related to the temperature of a critical electrochemical interface inside.

“We discovered that we can measure the temperature of the protective layers between the electrodes and the electrolyte of the battery during normal operation,” Srinivasan says. “These layers are where the conditions that lead to thermal runaway and catastrophic cell failure begin.”

The AC-based sensor detects potentially unsafe heat sooner than surface-mounted temperature sensors, he says. It operates through a simple electrical connection at the positive and negative terminals of the cell; it can use power from the very battery it is monitoring. With multiplexing circuitry, a single sensor can monitor multiple cells in a battery pack.

“Ultimately, the new sensor enables battery management systems to more closely manage battery performance and, more importantly, detect unsafe thermal conditions at the critical moment when 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 safety and performance of their products.”

The Johns Hopkins Applied Physics Laboratory has applied for U.S. and international patents for the sensor and is pursuing licensing opportunities.

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Author:Dennis O'Shea