Various carbon blacks as cathode materials for rechargeable lithium cells were investigated. The charge capacity of lithium cells were approximately proportional to the surface area of carbon blacks. Ketjen black EC has the highest surface area (950 m2/g) and exhibited the highest discharge capacity (398 Ah/kg) in our experiments where cutoff potentials were 1.0V vs. Li/Li+ on discharge and 4.5V on charge. The Ketjen black EC cathode also showed good cycling characteristics at a constant capacity (50 Ah/kg). In contrast to this, acetylene black, which has higher crystalline structure and smaller surface area, exhibited a lower discharge capacity (6 Ah/kg). Such differences of features for various carbon black cathodes were clearly observed in cyclic voltammetry measurements. The cyclic voltammograms and the charge-discharge curves of carbon black cathodes suggested that some electrochemical reaction, such as doping and undoping of ions into the polyaromatic structure of carbon blacks, occurs in the charge-discharge cycling.
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