A Study of the Effect of Graphite Surface Properties on the Cycle Life of Lithium Ion Battery By the Analysis of SEI Layer

Much work has described the influence of anodic SEI (Solid Electrolyte Interphase) on the cycle stability of a lithium secondary battery. Especially, it was reported that the characteristics of SEI Layer were greatly affected by the crystallographic and chemical properties of graphite. The purpose of this study was the identification of the effect of functional groups of graphite on the chemical composition and distribution of SEI Layer. Also the correlation between the SEI film properties and cycle life of battery was investigated through the analysis of composition and distribution of the components that constitute the SEI film. Two kinds of commercial natural graphite active materials prepared by different surface modification process were used for the comparison of the functional groups. These active materials were manufactured as powders by POSCO-Chemtech (PCT-H, PCT-3). The PCT-H was modified by surface reforming process, and PCT-3 was fabricated from the graphitization of natural graphite with carbon layer of surface. With these anode materials, the cyclic test was performed using 2032 - typed coin cell. After 300th cycle, the anode was isolated from coin cell to inhibit the chemical change of SEI layer. XPS and TEM-EELS analyses on the anode were followed for the comparison of the characteristics under inert atmosphere. In this work, It was found that the modification method of graphite strongly Influenced on the SEI layer. Therefore, this result can be utilized to improve the compatibility of the anode to the electrolytes.