One problem encountered in the development of rechargeable lithium batteries is the protection of individual cells from overcharging. In this work the addition of metallocene derivatives to cell electrolytes to provide overcharge protection was investigated. Eleven ferrocene derivatives were studied in terms of their redox potentials and mass transport properties in electrochemical cells and "AA"-size Li/Li=MnO2 rechargeable cells employing 1M LiAsF6 in 50/50 volume percent propylene carbonate/ethylene carbonate (PC/EC) as the electrolyte. The chemical and electrochemical properties of these metallocene derivatives were also studied in terms of the chemical stability of the derivatives toward cell components and electrochemical reversibility in long-term cycling studies. It was found that adsorption of one derivative, di-* Electrochemical Society Active Member.

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The electronic spectroscopic data for zinc, cobalt, and iron perchlorinated phthalocyanines in several oxidation states are discussed.The magnetic properties of the iron(II) and cobalt(II) derivatives from ambient temperature to 5 K are reported. The electrochemical behavior of these three species is reported in solution and as surfaces on highly oriented pyrolytic graphite. The pH dependence of the surface data is analyzed in detail. The first clearly defined reduction process corresponds with M'[Cll6Pc(-2)]"/M'[C1|6Pc(-3)]12" for M = Co and Fe. The iron and cobalt species' MnPc(-2)/[M'Pc(-2)]~r edox process are broad or ill-defined on the surface and absent from solution. The FeIII[Cl16Pc(-2)]+/Fe"[Cl16Pc(-2)] redox process has atypical pH dependence. The data are explained in terms of the acceptor nature of the chlorine substitution. Oxygen reduction data, catalyzed by these species, are also reported.to Union Carbide, Parma, for a gift of highly oriented pyrolytic graphite.

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