Development of Novel Vanadium Oxide Compound for Lithium Ion Secondary Battery

钒氧化物作为二次锂离子电池的正极材料，因其无毒、易得、价廉、安全等优点而备受关注。采用固相反应法合成了CoV_3O_8，并用X射线粉末衍射和Rietveld方法分析了其晶体结构。CoV_3O_8的晶体结构中沿c轴沿着具有隧道状空间。在第一次放电或嵌锂过程中，在2.3、2.05和1.9 V附近观察到三个电位平台。这表明锂通过三步反应嵌入CoV_3O_8中。通过第一次放电，锂嵌入到Li_xCoV_3O_8中x=2.6。相反，在第一次充电或锂脱嵌期间，仅观察到一个平台。这意味着锂脱嵌在一步反应中进行。通过第一次充电，锂脱嵌至x=0.6。在第2次或以后的充放电循环中，与第1次锂脱嵌一样，锂嵌入离子和脱嵌都在一步反应中进行，并且嵌入的锂的量几乎等于脱嵌的锂的量。结果表明，锂离子在样品中的嵌入和脱嵌是可逆的。该样品表现出优异的充放电循环性能。该钴钒氧化物有望成为新型锂离子二次电池电极材料。

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.