Instantaneous Measurement of the Internal Temperature in Lithium-Ion Rechargeable Cells

Reference#: P02884

The Battery Internal Temperature Sensor (BITS), developed by the Johns Hopkins Applied Physics Laboratory, is a miniature instrument with demonstrated capability to measure and report the internal temperature of individual cells in a multi-cell Li-ion battery pack at the rate of 200-ms/cell. Unlike surface-mounted thermocouples, BITS provides a direct measure of the internal temperature of Li-ion cells through a simple electrical connection at the positive and negative terminals of the cell. It is designed to operate using power from the battery it is testing and can be used in a multiplex mode across multiple cells.

The patent-pending technique that APL has developed is non-intrusive; nothing is inserted into the cell. BITS works by perturbing the cell's terminals with a low-amplitude AC current and measuring the phase shift of the resulting voltage output. This phase shift is independent of the battery state-of-charge and relates directly to the temperature of the anode and the cathode. It measures the internal temperature online, i.e. when the cell is under charge, discharge, or rest conditions.

BITS is the most accurate and immediate method available for measuring the true temperature of a Li-ion cell. And it is the only method for measuring a cell's temperature where it counts: inside the cell where temperature changes originate.

BITS enables battery management systems to more closely manage battery performance and, more importantly, to detect unsafe thermal conditions at the critical moment when they occur before they have propagated to the surface of the cell. By integrating BITS into their products, manufacturers of batteries, battery management systems, and battery solution providers can increase both the safety and performance of their products.

BITS works with standard off-the shelf Li-ion batteries. A prototype device has been built and tested on the following rechargeable lithium-ion cells: 53-Ah GS Yuasa LSE50-002, 4.4-Ah Boston Power Swing 4400, and 2.3-Ah A123 ANR26650. Detailed test results are available.

Mr. E. Chalfin
Phone: (443) 778-7473