Fluorination of Graphite Oxide and Application to Lithium Battery

采用Hummers法、Staudenmeier法和Brodie法合成了氧化石墨，并用VF_5+F_2和SbF_5+F_2的混合气体在20 ~ 200 ℃的温度下对氧化石墨进行了氟化。Hummers法、Staudenmeier法和Brodie法制备的氧化石墨的最佳焙烧温度依次从50 ℃升高到100 ℃。X射线衍射分析表明，氟化氧化石墨沿c轴方向的重复间距沿着为8.5 ~ 9，与第二阶段型氟化石墨（c_2F）_n的重复间距基本相同。同时，晶格常数沿着a轴由2.48 A增加到2.50 A，与（C_2F）_n的晶格常数一致。红外光谱表明在1200 cm-1处有强吸收，对应于C-F键。研究了氟化氧化石墨在碳酸丙烯酯-1 M LiClO_4溶液中的阴极行为。随着氧化石墨结晶度的增加，氟化氧化石墨的容量和放电电位的平坦性得到改善，过渡金属氟化物和氧化物氟化物离子插层化合物与氧化石墨的结构比较表明，氧化石墨中C-O键的共价性不如氟化石墨。

Graphite oxide has been synthesized by Hummers, Staudenmeier and Brodie methods and fluorinated by fluorine gas and mixtures of VF_5+F_2 and SbF_5+F_2 at temperatures between 20 ^ﾟC and 200^ﾟC. Optimum fluorination temperature increased from 50^ﾟC to 100^ﾟC for graphite oxide prepared by Hummers, Staudenmeier and Brodie methods in that order. Perfect fluorination was difficult, but X-ray diffraction showed that the repeat distance along c-axis of fluorinated graphite oxide was 8.5-9 A, almost the same as that of stage 2 type graphite fluoride (c_2F)_n. At the same time the lattice parameter along a-axis increased from 2.48 A to 2.50 A consistent with that for (C_2F)_n. IR spectrum indicated a strong absorption at 1200 cm corresponding to C-F bonding. These data coincide with the stage 2 type structure model of graphite oxide.The cathodic behavior of fluorinated graphite oxide has been investigated in propylene carbonate-1 M LiCLO_4 solution with Li negative electrode. With increasing crystallinity of graphite oxide, the capacities and flatness of the discharge potentials of fluorinated graphite oxide were impro ved.Comparison of the structures of ionic intercalation compounds of transition metal fluorides and oxide fluorides with that of graphite oxide suggested that the covalency of C-O bond in graphite oxide is not as high as that of graphite fluoride.