单层石墨烯表面钠原子吸附行为的第一性原理  

The formation of Na_xC_(72)(1≤x≤7) on a single layer graphene surface:a first-principles study

作　　者：孙闻[1] 杨绍斌[1] 沈丁[1] 董伟[1] SUN Wen;YANG Shao-bin;SHEN Ding;DONG Wei(College of Material Science and Engineering, Liaoning Technical University, Fuxin 123000, China)

机构地区：[1]辽宁工程技术大学材料科学与工程学院,辽宁阜新123000

出　　处：《新型炭材料》2019年第2期146-152,共7页New Carbon Materials

基　　金：国家自然科学基金(51274119)~~

摘　　要：构建了3种典型的石墨烯吸附钠原子模型(Na_xC_(72)(1≤x≤7)),采用密度泛函理论对其进行了系统计算,研究了最低能量构型的吸附能、平均电压、重叠布居以及原子布居、电荷密度差分、电子局域密度和态密度等性质。通过吸附能确定石墨烯表面最可能的钠原子吸附形式,当钠原子吸附数量x<5时,钠原子优先以双面吸附的形式吸附于石墨烯表面;当x≥5时,钠原子以团簇的形式吸附于石墨烯表面。平均电压计算结果表明,随着x的增加,平均电压先降低后出现升高趋势,对应x=4时石墨烯吸附钠的最大容量达124 mAh/g。电荷密度差分、电子局域密度及Mulliken布居分析表明,临近石墨烯表面的钠原子3s电子转移至石墨烯的反键π轨道,钠原子和碳原子之间形成弱离子键,距离石墨烯表面较远的钠原子3s电子与周围钠原子共享,钠原子之间形成金属键。态密度计算结果表明,随着x的增加,Na_xC_(72)(1≤x≤7)的费米能级向石墨烯反键π轨道移动,导电性增强。The formation of NaxC72 (1≤ x ≤7) on a single layer graphene surface was investigated using a first-principles study based on density functional theory. Adsorption sites, the lowest energy structures, the adsorption energy, Mulliken population, density difference, electron localization function (ELF) and the partial density of states (PDOS) of NaxC72 (1≤ x ≤7) were calculated. It was found, based on the calculation of absorption energy, that the optimum formation mode of NaxC72 (1≤ x ≤7) is that Na atoms are adsorbed on graphene bilaterally when x <5 and a Na cluster is formed when x ≥5. The average voltages of NaxC72 decrease with x when x <5 and increase with x when x ≥5. The maximum sodium storage capacity is 124 mAh/g, corresponding to a structure of Na 4C 72 . The weak ionic bonds between Na atoms and graphene are formed by charge transfer from Na 3s to graphene π^*, and metallic bonds are found between Na atoms in Na cluster as revealed by density difference, ELF and Mulliken population. Moreover, PDOS results show that the Fermi level of NaxC72 (1≤ x ≤7) shifts to the graphene π^* with increasing x , resulting in an increase of electronic conductivity.

关 键 词：钠离子电池 石墨烯 钠团簇 负极材料 

分 类 号：TM912[电气工程—电力电子与电力传动]