Development of Novel Vanadium Oxide Compound for Lithium Ion Secondary Battery

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Vanadium oxides have been attracting attentions as a candidate for a cathode material of secondary lithium ion batteries because of non-toxicity, availability, low cost and safety. CoV_3O_8 was synthesized by solid-state reaction and the crystal structure was analyzed by X-ray powder diffraction and the Rietveld method. CoV_3O_8 has tunnel-like space along c-axis in the crystal structure. During the 1st discharge or lithium insertion, three potential plateaus were observed at around 2.3, 2.05 and 1.9 V. This indicates that lithium was inserted into CoV_3O_8 by three-step reaction. By the 1st discharge, lithium was inserted to x=2.6 in Li_xCoV_3O_8. In contrast, during the 1st charge or lithium deinsertion, only one plateau was observed. This means that the lithium deinsertion proceeded in one-step reaction. By the 1st charge, lithium was deinserted to x=0.6. In the 2nd discharge-charge cycle or later, both lithium insert ion and deinsertion proceeded in one-step reaction as in the 1st lithium deinsertion, and quantity of inserted lithium was almost equal to that of deinserted lithium. It was indicated that lithium was inserted into and deinserted from the sample reversibly. This sample exhibited excellent discharge-charge cycle performance. This cobalt vanadium oxide is promising for novel electrode material of lithium ion rechargeable battery.