Surface structure change and electrode characteristics of carbon materials by fluorination reaction

（1）氟化对石油焦表面结构的影响对石油焦和1860℃、2100 ℃、2300 ℃、2600 ℃、2800℃热处理后的石油焦分别进行了150℃ ~ 300 ℃氟化2 min和90℃ CF_4等离子体处理。通过元素分析获得的氟含量小于1原子%，并且通过XPS获得的表面氟浓度在5-20原子%的范围内。BET表面积没有改变或略有减少，通过表面改性。然而，表面无序增加。透射电子显微镜观察表明，石油焦在高温石墨化过程中，边缘面因碳-碳键的形成而封闭，随着表面无序度的增加，表面粗糙度使封闭的边缘面打开。（2）表面氟化石油焦在有机溶剂中的电极特性采用循环伏安法和恒电流充放电循环法研究了表面氟化石油焦在1 M碳酸亚乙酯（EC）/碳酸二乙酯（DEC）体系中的电极特性。循环伏安法研究表明，在0.6 V vs Li/Li^+下观察到的EC的电化学分解对于PC、PC 1860和PC 2100没有改变，但是对于PC 2300、PC 2600和PC 2800显著降低。在60和150 mA/g的电流密度下的充放电实验表明，PC 2300，PC 2600和PC 2800的第一库仑效率大大增加。这可能是因为石墨化石油焦的封闭边被氧化物打开，封闭边的打开有利于表面成膜和Li^+离子的插入。

(1)Surface structure change of petroleum cokes by fluorinationPetroleum coke and those heat-treated at 1860℃,2100℃,2300℃,2600℃ and 2800℃ were fluorinated by elemental fluorine at 150℃-300℃ for 2 min and by plasma treatment at 90℃ using CF_4. The fluorine contents obtained by elemental analysis were less than 1 at% and surface fluorine concentrations obtained by XPS were in the range of 5-20 at%. BET surface areas were not changed or slightly reduced by surface fluorination. However, surface disorder was increased. Transmission electron microscopic observation revealed that the edge plane of petroleum coke was closed by carbon-carbon bond formation during the graphitization process at high temperatures and surface fluorination opened the closed edge surface with increase in the surface disorder.(2)Electrode characteristics of surface-fluorinated petroleum cokes in organic solventsElectrode characteristics of surface-fluorinated petroleum coke samples were examined by cyclic voltammetry and galvanostatic charge/discharge cycling in 1 M LiClO_4 ethylene carbonate (EC)/diethyl carbonate (DEC) at 25℃. Cyclic voltammetry study showed that electrochemical decomposition of EC observed at 0.6 V vs Li/Li^+ was not changed for PC,PC1860 and PC2100,but significantly reduced for PC2300,PC2600 and PC2800. Charge/discharge experiments at current densities of 60 and 150 mA/g indicated that first coulombic efficiencies of PC2300,PC2600 and PC2800 were highly increased. This would be because the closed edge of graphitized petroleum cokes was opened by fluorination and the opening of the closed edge facilitated the surface film formation and Li^+ ion insertion.