Nitrite Molten Salt for use in Intermediate Temperature Lithium Cells

The LiNO 2 -KNO 2 (40–60 m/o) molten salt, which melts at 120°C, has been employed as an electrolyte in intermediate temperature lithium cells. The behavior of solid lithium in this electrolyte is analogous to the behavior of lithium in the similar intermediate temperature alkali nitrate electrolyte. Lithium reacts with the melt to form a thin, lithium ion conducting, protective layer which is believed to be Li 2 O. The electrolyte is electrochemically reduced below 1.9 volts versus Li + /Li, and is oxidized to lithium metal and NO 2 gas above 3.5 volts versus Li + /Li. This electrolyte can be used in secondary cells with lithium or high lithium activity negative electrodes, and lower lithium activity positive electrodes which react reversibly with lithium. The resistance of the protective layer on lithium increases with time as the thickness increases. Its resistance is of the order of 1–10 ohms after 10 hours at 150° C.