EFFECT OF CYCLING ON THE LITHIUM ELECTROLYTE INTERFACE IN ORGANIC ELECTROLYTES

The successful operation of ambient temperature secondary lithium cell s is primarily dependent on the lithium/electrolyte interface properti es. In this study, an attempt has been made to study the effect of cel l cycling on the lithium/electrolyte interface by nondestructive metho ds such as a.c. impedance spectroscopy and microcalorimetry. Experimen tal Li-TiS2 cells were constructed and activated with different electr olytes. The cells delivered 30 to 300 cycles at 100% depth-of-discharg e depending on the electrolyte. The reactivity of both uncycled and cy cled lithium towards various electrolytes was studied by measuring the heat evolved from the cells under open-circuit condition at 25-degree s-C by microcalorimetry. Cycled cells at the end of charge/discharge s howed considerably higher heat output compared with the uncycled cells . After thirty days of storage, the heat output of the cycled cells is similar to that of the uncycled cells. A.c. impedance analysis result s indicate that the cell internal resistance increases with cycling, a nd this is attributed to the degradation of the electrolyte with cycli ng. The value R(f) was found to decrease with cycling. The observed de crease in R(f) is probably due to the increase in the surface area of the lithium anode due to cycling. The peak frequency was found to be i n the range, 400 to 1000 Hz for both uncycled and cycled cells suggest ing that the passivating film composition does not change significantl y with cycling.