A STUDY OF COKES USED AS ANODIC MATERIALS IN LITHIUM ION RECHARGEABLEBATTERIES

A variety of cokes pretreated at different temperatures are used as an odic materials and their electrochemical characteristics are examined by cyclic voltammetry. It is found that for some cokes such as petrole um coke (preheated at 1300 degrees C), pitch coke (1300 degrees C), ne edle coke (1900 degrees C), metallurgical coke (1900 degrees C), high capacity and cyclic efficiency are achieved. Needle coke (1900 degrees C) and metallurgical coke (1900 degrees C) in particular give a capac ity of over 200 mAh/g and a cyclic efficiency of nearly 100%, whereas poor performance is exhibited by those pretreated at higher or lower t emperatures, e.g., petroleum cokes (500 degrees C, 2800 degrees C), pi tch coke (500 degrees C) and needle coke (2800 degrees C). The cyclic voltammograms show two electrochemical processes, one at about 0.1 V v s. Li+/Li which is electrochemically reversible, and may be attributed to the intercalation/deintercalation of lithium ions while the other, at about 0.6 V vs. Li+/Li, is electrochemically irreversible and may be assigned to the decomposition of the electrolyte solvent, which lea ds to formation of the passive film on the anode surface. The experime ntal results strongly suggest that the pretreatment temperature of cok es and of the solvent are determining factors for the growth, structur e and properties of the passive film.