锂离子电池碳负极中边缘碳及表面碳原子含量的理论计算

通过理论分析与计算得到边缘碳及表面碳原子含量的表达式。分析了石墨微晶结构与成键特征,研究了石墨微晶中边缘碳原子与基平面碳原子的电化学特性。结果表明:边缘碳原子比基平面碳原子更易于与其他原子或基团形成较为稳固的联接,电化学反应活性较高;在首次充电过程中,边缘碳原子附近电解质的分解与SEI膜成膜反应速度较快,有利于形成联接较为紧密的SEI膜;建立了紧密堆砌的正六棱柱颗粒模型,推导出理想石墨中边缘碳原子及表面碳原子含量与微晶参数、颗粒尺寸之间的关系式。通过引入适当因子,修正了实际石墨颗粒与理想石墨在结构、形貌、孔隙率等方面的差别,得到的表达式可适用于石墨、无定形碳及改性碳等多种碳材料碳原子含量的计算。

Theoretical calculation of fraction of carbon atoms on surface and edge for carbon anode of lithium ion battery

The fractions of carbon atoms on the surface and edge were obtained by theoretical analysis and calculation.The electrochemical characteristics of carbon atoms on the edge and basal plane were determined by analyzing structure of graphite crystal and bond of different carbon atoms.The results show that the atoms on the edge are more active for electrochemical reactions and tend to form stable bond with other atoms and groups.In the initial charge,the electrolyte decomposition and formation of solid electrolyte interface(SEI) on the edge are faster,and tighter SEI is formed there.A hexagonal close-packed model for graphite particle was developed.The fraction of carbon atoms on the surface and edge was derived in expression of crystallographic parameters and particle size.The practical graphite particle and the ideal graphite have some difference in structure,appearance and micro-cavity,which may cause the fractions of surface carbon and edge carbon change,and some correctional factors have been introduced to revise the difference.The revised expression is suitable for calculation on fraction of carbon atoms of carbon materials such as graphite,disordered carbon and modified carbon.