Most of the battery-powered electronics you use, as well as battery packs in electric-powered and hybrid vehicles, rely on lithium-ion batteries. They are popular for their high energy density, resulting in growing interest from other industries. However, cases of battery fires have been responsible for recalls of many devices in recent years, raising safety concerns among consumers and manufacturers.
To help prevent batteries from reaching dangerously high temperatures, scientists at the Hopkins Applied Physics Lab have developed an inexpensive sensor to monitor the internal temperature of the battery.
Publishing their findings in Electronica Acta, the group found that by passing a small alternating current of electricity at a specific frequency though the battery, which could be powered by the battery's normal operations, they can assess the internal temperature of the battery.
Their work was also presented at the SPIE conference on Defense, Security and Sensing. In addition, the details of their work in developing the sensor have been published in the Journal of Power Sources.
According to Rengaswamy Srinivasan, a chemist at the Applied Physics Lab and lead author of the papers, the battery can be shutoff via an on-off switch at the first sign of trouble by monitoring the internal temperature of the battery.
"The anode and cathode temperature rises as the cell is discharged. The anode and the cathode temperature should not exceed certain limit (for example: 70 ºC in some cells), and if they tend toward such a high value, the cell should be disabled from discharge," he wrote in an email to The News-Letter.
Currently, electronics rely on external temperature sensors to physically assess the temperature of the battery, which may not be accurate. "At present, there are surface-mounted temperature sensors that monitor the temperature the cell's outside surface, and some algorithm in a microchip infers the internal temperature. The present approach could be wrong and potentially misleading," Srinivasan wrote.
"Our technique shows that the rate of change and the direction of change of the anode and cathode temperatures do not correlate with the direction or rate of change of the surface temperature."
Their sensor functions by detecting phase changes in the alternating-current that passes through the battery, which has a correlation to the temperature of the battery's interior. Like waves, electricity peaks at specific points in time and location, and a phase change arises from a shift in where and when these peaks are, as measured through the resulting voltage from the applied current.
Phase changes can vary depending on the conditions of the medium that the electricity passes through, such as the temperature of the inner components of the battery. Specifically, the researchers found that a current alternating with a frequency of 40Hz gives the best signal that the researchers can use for their sensor.
The researchers have applications on file for international and US patents for their work, and have been exploring licensing opportunities for their work. According to Srinivasan, several manufactures have also been in contact with the Applied Physics Laboratory's Office of Technology Transfer.
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