Novel cathode material for lithium rechargeable battery : graphite intercaration compounds of some transition metal chlorides

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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 discharge and charge characteristics of a 1st stage GIC of cobalt dichloride, CィイD25.5ィエD2CoCィイD2l2.2ィエD2, was investigated in various organic electrolytes containing 1 M LiClOィイD24ィエD2. The kinds of organic electrolytes did not affect the potentials during insertion of lithium but the amounts of accommodated lithium in the GIC. X-ray diffraction of the GIC showed that the layered structures were broken after insertion of lithium. Furthermore, the extraction of lithium from the lithiated GICs was almost impossible.The electrochemical lithiation behavior of a 4th stage GIC of niobium pentachloride, CィイD224ィエD2NbCiィイD25.2ィエD2, was investigated in 1 M LiClOィイD24ィエD2 / PC electrolyte. The layered structure of the GIC was preserved during reduction from pentavalent to tetravalent. However, the extraction of lithium from the lithiated GIC was impossible. Furthermore, the liberation of chloride ions from the GIC occurred irreversibly during reduction from tetravalent to trivalent.These results showed that the GICs of both cobalt and niobium chlorides are not suitable 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.