Si_(n)团簇/石墨烯(n≤6)结构稳定性和储锂性能的第一性原理计算

First-principles study of structural stability and lithium storage property of Si_(n) clusters(n≤6)adsorbed on graphene

目前,硅/碳复合材料是锂离子电池最有潜在应用前景的高容量负极材料之一,硅与碳材料的界面状态是影响其电化学性能的重要因素.本文在作为碳材料结构单元的石墨烯表面构建了Si_(n)(n≤6)团簇,采用基于密度泛函理论(DFT)的第一性原理方法研究了Si_(n)团簇/石墨烯(Si_(n)/Gr)的几何构型、结构稳定性和电子性质.结果表明,当Si原子数n≤4时,Si_(n)团簇优先以平行于石墨烯的二维构型沉积在石墨烯表面,当n≥5时,Si_(n)团簇优先以三维立体构型沉积在石墨烯表面.随着n的增大,Si_(n)团簇在石墨烯表面的热力学稳定性显著降低,两者之间的界面结合减弱,并且伴随着Si_(n)团簇与石墨烯之间的电荷转移也越来越少.同时还研究了Si_(n)/Gr复合构型的储锂能力,Li原子主要存储在Si_(n)团簇临近的石墨烯表面和Si_(n)团簇周围,Si_(n)团簇与石墨烯复合形成的协同作用增强了Li原子吸附的热力学稳定性.当n≤4时,存储2个Li原子有利于提高xLiSi_(n)/Gr体系的热力学稳定性,继续增加Li原子数x会导致稳定性降低;当n≥5时,稳定性随着Li原子数x的增多而逐渐降低.

Silicon/carbon composite is one of the most potential high-capacity anode materials for lithium-ion batteries.The interface state between silicon and carbon of silicon/carbon composite is an important factor affecting its electrochemical performance.In this paper,Si_(n)(n≤6)clusters with different numbers of Si atoms are constructed on graphene as a structural unit of carbon material.The geometric configuration,structure stability and electronic property of Si_(n) clusters adsorbed on graphene(Si_(n)/Gr)are studied by the first-principles method based on density functional theory(DFT).The results show that when the number of Si atoms n≤4,the Si_(n) clusters are preferentially adsorbed on graphene in a two-dimensional configuration parallel to graphene.When n≥5,the Si_(n) clusters are preferentially adsorbed on graphene in a three-dimensional configuration.With the increase of the number of Si atoms n,the thermodynamic stability of Si_(n) clusters on graphene decreases significantly,the interface binding strength between Si_(n) clusters and graphene decreases,and the charge transfer between Si_(n) clusters and graphene becomes less.At the same time,the storage capacity of Li atoms in Si_(n)/Gr complex is also studied.Li atoms are mainly stored on the graphene surface near Si_(n) clusters and around Si_(n) clusters.The complex synergistic effect of Si_(n) clusters and graphene enhances the thermodynamic stability of Li adsorption.When n≤4,storing two Li atoms is beneficial to improving the thermodynamic stability of xLi-Si_(n)/Gr system,and the thermodynamic stability decreases with the increase of Li atom number.When n≥5,the thermodynamic stability of xLi-Si_(n)/Gr system decreases with the increase of Li atom number.In the xLi-Si5/Gr system,the C-C bond and Si-Si bond are mainly covalent bonds,while the Li-C bond and Li-Si bond are mainly ionic bonds with certain covalent properties.