PASSIVITY OF FE IN ANHYDROUS PROPYLENE CARBONATE

The passivation behavior of Fe in anhydrous propylene carbonate (PC) containing 0.5M LiClO4 was studied. The effect of small water additions on the passivation observed was also studied. The air-formed film was found to be stable and protective over a wide range of applied potential. Scratched electrode tests showed that bare Fe can also passivate in anhydrous solution. This passivation occurs via oxidative chemisorption of PC molecules at potentials below the oxidation potential of PC and via an Fe(ClO4)2 salt film at higher potentials. Water was found to be deleterious to the passivity, with as little as 100 ppm leading to an activation of the surface and higher levels preventing the passivation altogether. In addition, the oxidation of ClO4- was found to cause pitting. Since long-term integrity depends directly upon the protective ability of the passive film that forms, a much better understanding of passivity in non-aqueous solutions is of great importance to the production of reliable lithium batteries.