Effect of pitch crystallinity on electrochemical performance of graphite carbon coatings

Abstract

Natural graphite has been primarily used as an active anode material for lithium-ion batteries, and carbon coatings are commonly used to enhance its performance. Pitch has been proposed as a promising material for carbon coatings, but it comprises various chemical species and cannot be regarded as a single substance. Consequently, different types of pitch variably alter the electrochemical properties of the graphite carbon coating. In this study, we focus on the relationship between the crystallinity and electrochemical performance of the carbon coating layer, which is formed based on the optical properties of pitch and can be categorized as isotropic or mesophase. To apply the pitch onto the natural graphite, a dry coating method was employed and it was then heat-treated with a temperature range of 900–1700 °C. Both carbon coatings enhanced the initial Coulombic efficiency by reducing the edge plane of natural graphite. In particular, the carbon layer coated with an isotropic pitch exhibited a disordered structure, thereby improving the output characteristics. The synergistic effect of the conductivity of the carbon coating layer and the amorphous arrangement of the carbon crystals provided a pathway for ion diffusion, effectively reducing the polarization resistance that arose during the charge and discharge cycles. This report establishes a connection between graphite-coated carbon layers and electrochemical performance and provides a novel evaluation of the properties of coating pitches that are in high demand for commercial applications.