Lithium-Carbon Monofluoride Li- CF X

Limited pulse current capability of coin and low-capacity types makes them robust against temperature rise due to short circuit. However, temperature rise and internal pressure are still a concern, and system-level safety devices such as PTC devices may be required in most applications to make sure batteries stay below dangerous Hmits. High discharge rate, accidental charging, and cell reversal can all lead to cell venting, temperature rise, and possible expulsion of electrolyte. Puncture tests have resulted in hydraulic vent and case temperatures in excess of 100 °C [3]. Crushing showed similar results. 

Lithium-sulfur dioxide (Li-S02), a liquid cathode system, is one of the more advanced lithium-based chemistries and is used mainly in military, industrial, and space applications. A lithium metal anode is paired with an electrolyte that contains an inorganic salt dissolved in SO2, with a porous carbon current collector. Its high specific energy (greater than 260 Wh kg ) and excellent low-temperature performance make it a good candidate for these harsh environments where volume and weight are prime considerations. 

This cell contains a hthium metal foil anode, and therefore uses a nonaqueous electrolyte composed of sulfur dioxide and an organic solvent. The electrolyte remains conductive at low temperatures, giving the cell its characteristic high-rate low-temperature performance. The undischarged cell is pressurized to nominally 3-4 X 10 Pa (approximately 3 atm), and this pressure increase as cell temperature increases. For this reason, cells are always built with a vent feature to release excessive pressure build up. During discharge, the SO2 is consumed and the cell pressure decreases somewhat. 

Balancing of active materials within the ceU is critical to safe operation near end-of-life, similarly to Li-SOCl2, but, in contrast to the case of Li-SOCl2, there is a consensus among researchers that lithium limiting (anode-limited method) is the safest approach to end-of-Ufe protection. As the cell is driven into reversal, lithium dendrites plate on the carbon cathode, and reaction with the SO2 forms a passivated protective layer. 

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