Lithium carbon monofluoride primary batteries have a high energy density (2180 Wh/kg of active materials based on the typical discharge potential) and low self-discharge. They have traditionally been used in medical devices like pacemakers with low rates of several years [1]. The high energy density of Li/CFx batteries also make them attractive for higher rate uses like aerospace or military applications; however, rate capability and heat generation can pose a significant challenge at higher rates. The theoretical potential of a CFx battery is around 4.5 V, but practical cells operate at 3 V or lower. The ~1.5 V overpotential is attributed to the strength of the C-F bonds, which results in slow kinetics and significant heat generation, especially when considering high rate (e.g., >C/10) and energy dense cell designs. Other challenges include the deposition of insulating lithium fluoride and large volume changes in each electrode [2].

Our work focuses on a high-energy density primary battery with a CFx cathode and lithium anode, designed for high rates with intermittent pulse power requirements. Physics-based modeling is an important tool that can clarify underlying mechanisms and help guide design to satisfy multiple constraints. To understand the challenges posed by this chemistry at higher rates, we have developed a zero-dimensional (0D) physics-based model that captures some of the complex phenomena within the CFx cathode. Included in the model are kinetics described by a concentration-dependent expression, changing porosity and electrochemical active area, and Nernstian thermodynamics. The model may also include a treatment of methods that increase the capabilities beyond the typical limits for the CFx chemistry. The implications of various conditions will be explored, such as the effect of the porosity and loading. The model results will be compared to experimental data from coin cells.

Acknowledgments

The authors would like to thank the Intelligence Advanced Research Projects Agency for funding this work.

References

1. Zhang, K. J. Takeuchi, E. S. Takeuchi, and A. C. Marschilok, Phys. Chem. Chem. Phys., 17, 22504 (2015).
2. S. Zhang, D. Foster, J. Wolfenstine, and J. Read, J. Power Sources, 187, 233 (2009).