Based on a four-probe electrical measurement, we have developed a Battery Internal Temperature Sensor. BITS,
unlike a surface-mounted thermocouple, provides a direct measure of the internal temperature. We have
demonstrate in several different rechargeable lithium-ion cells ranging in capacity from 2- to 50-Ah, the existence of
an intrinsic relationship between a cell's internal temperature and a readily measurable electrical parameter. Today,
container rupture and fire are the most detrimental consequences of thermal runaway in rechargeable Li-ion cells.
Although storing or operating Li-ion cells in high-temperature environments is not advisable, high internal
temperature has a greater potential to initiate catastrophic events. Measuring the environmental temperature at any
proximity to the surface of the cell is insufficient to know or intervene with fast-rising internal heat. For example,
monitoring internal temperature in real time has direct relevance to the thermal runaway caused by external and
internal short circuits that may have no relevance to the external temperature. Yet, until now, there has been no
simple technique to monitor the internal temperature of a single cell or multiple cells in Li-ion batteries. BITS,
developed by the Johns Hopkins University Applied Physics Laboratory, is a miniature instrument, with
demonstrated capability to measure and report internal temperature of individual cells in a multi-cell battery pack at
the rate of 200-ms/cell.