APPLICATIONS OF METALLOCENES IN RECHARGEABLE LITHIUM BATTERIES FOR OVERCHARGE PROTECTION

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/LixMnO2 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, dimethylaminomethylferrocene, on the LixMnO2 electrode (DELTA-G(ads) = -3.8 kcal mol-l based on the Langmuir adsorption isotherm), blocked the intercalation of Li+ ions into the LixMnO2 electrode.