CoS2 is a promising anode material for lithium-ion batteries (LIBs) because of its high theoretical capacity. However, its practical application is hampered by severe volume expansion during cycling. In this study, fluorine-doped carbon-coated CoS2 (F-CoS2@C) was synthesized via NaCl template-assisted carbon coating using petroleum-derived pyrolyzed fuel oil, followed by CF4 plasma treatment. The proposed method of synthesis enables control of the carbon layer thickness, formation of a void structure, and introduction of fluorine functional groups. F–CoS2@C delivered 295 mAh/g at 5 A/g and retained 375 mAh/g after 500 cycles at 1 A/g. The enhanced electrochemical performance is attributed to the void carbon structure and fluorine-induced interfacial stabilization. The carbon structure increased electrolyte penetration and electrical conductivity, and mitigated volume changes. Fluorine doping promoted the formation of a LiF-rich solid electrolyte interphase layer and enhanced the electronic transport by semi-ionic C-F bonds. This study offers a promising strategy for the development of transition metal sulfide/carbon composites as high-performance LIB anodes.

Coke aggregates and carbon artifacts were produced to investigate the interactions of coke and pitch during the kneading process. In addition, the kneading ratio of the coke and binder pitch for the coke aggregates was controlled to identify the formation of voids and pores during carbonization at 900°C. Experiments and thermogravimetric analysis revealed that carbon yields were improved over the theoretical yield calculated by the weight loss of the coke and binder pitch; the improvement was due to the binding interactions between the coke particles and binder pitch by the kneading process. The true, apparent, and bulk densities fluctuated according to the kneading ratio. This study confirmed that an excessive or insufficient kneading ratio decreases the density with degradation of the packing characteristics. The porosity analysis indicated that formation of voids and pores by the binder pitch increased the porosity after carbonization. Image analysis confirmed that the kneading ratio affected the formation of the coke domains and the voids and pores, which revealed the relations among the carbon yields, density, and porosity.