Microcalorimetry of Li/CFx Cells and Discharge Mechanism

Report No. ARL-TR-5043
Authors: Jeffrey Read, Donald Foster, Jeffrey Wolfenstine, and Sheng Zhang
Date/Pages: December 2009; 16 pages
Abstract: The Li-CFx chemistry has been traditionally used for low rate applications at discharge rates of C/1000 or lower. The Army is supporting efforts to engineer Li/CFx batteries for Soldier applications that operate at higher rates, closer to C/10. This effort is based on the favorable specific energy and storage characteristics offered by this chemistry. Heat generation under high rate discharge is one potential concern in these batteries and, therefore, further study of the mechanism of heat generation and the differences in heat generation between various CFx materials is warranted. We demonstrate that the thermal power generated when a Li-CFx cell is discharged appears nearly instantaneously in the cell and ceases nearly as quickly when discharge is interrupted. Extrapolation of the running potential to zero heat results in a predicted voltage for the Li/CFx cell of 4.25 V, very near the theoretical potential calculated by Wood, et al. (1). The microcalorimetry results support the two phase model for discharge where a large overpotential, presumably due to the highly disfavored process of breaking covalent C-F bonds, dominates the OCV and running potential of the cell.
Distribution: Approved for public release
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Last Update / Reviewed: December 1, 2009