Investigation of graphite intercalation compounds of some transition metal chlorides as the cathodematerials for lithium rechargeable battery

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Graphite intercalation compounds (GIC) of some transition metal chlorides have rigid layered structures and high electronic conductivity. In this study, electrochemical insertion of lithium into the GICs of some transition metal chlorides was investigated in order to apply the GICs to the cathode materials for lithium secondary batteries.The electrochemical lithiation behavior of a 1 st stage GIC of tantalum pentachloride, C_<20>TaCl_5, was investigated in 1 M LiClO_4/propylene carbonate electrolyte. The degradation of the stage number from 1 st to higher stages was confirmed at the beginning of the discharge, indicating that the deintercalation of tantalum species from the host material occurred. The pentavalent tantalum species, which is in the host material or in the electrolyte, were considered to be reduced to the lower oxidation states. On the other hand, the charge was impossible.These results showed that the GICs of tantalum chloride are not suit able for cathode materials for lithium secondary batteries. However, it was suggested that lithium can be inserted into the higher stage GICs containing the transition metals which can take various valence states without destruction of the layered structures.