Impedance spectroscopy as a nondestructive health interrogation tool for lithium-BCX cells

The objective of this investigation was to study the growth of thick passivating layers on the Li anode in Li/BCX (Li/SOCL[sub 2] + BrCl) cells which were stored for a period of 3 years. Impedance spectroscopy and equivalent circuit models were used to determine characterizing parameters for these cells. The equivalent circuit used for virgin cells includes a faradic contribution and diffusion of the electroactive species. The equivalent circuit for batteries stored 1 or 2 years includes the impedance of a metal/passive film interface, the resistance of the film, and the impedance of the passivating film/electrolyte interface. The equivalent circuit used for batteries stored for 3 years accounts for cathodic contributions in the overall impedance spectrum.