A primary electrochemical cell including a cell housing, an anode including metallic lithium, a liquid SOCl2 cathode and a separator separating the anode from the cathode. The liquid SOCl2 cathode material includes a salt of a Lewis base with a Lewis acid dissolved in the SOCl2 to form an electrolyte solution and an amount of SnCl2 dissolved in the electrolyte solution. The cell has a higher TMV and lower cell impedance after extended periods of cell storage at room or higher temperatures as compared to similar prior art primary Li/SOCl2 cells that do not include the SnCl2 additive.