Defect Vacancies in Pitch-Based Hard Carbon Coating for a Long-Life Nature Graphite Anode

Natural spherical graphite, a promising lithium-ion battery anode material, faces challenges like structural collapse and solid electrolyte interphase (SEI) formation during extended cycling, which impair cycle life and storage capacity. This study introduces a method using mixed acid preoxidation followed by carbonization at lower temperatures to produce pitch-based hard carbon materials. These materials maintain excellent cycle stability over 15,000 cycles at a current density of 1 A g–1. By preoxidizing coal-based pitch-coated spherical graphite and carbonizing at 800 °C, we obtain a pitch-based hard carbon with an increased number of sp2-hybridized carbon defect vacancies. The preoxidation disrupts the pitch’s stacking structure and introduces C═O groups that inhibit graphitization, increasing defect sites. These defects enhance Li+ adsorption and facilitate its diffusion while reducing the desolvation energy barrier to 14.96 kJ mol–1. Consequently, Li+ diffusion is improved, and graphite’s swelling and peeling are mitigated. The material’s porous structure and the robust nature of sp2-hybridized carbon provide ample buffer space for lithium ions, limiting swelling and ensuring capacity retention even at high currents. This method offers a simple and effective approach to designing hard carbon–graphite composite anodes, contributing to the development of lithium-ion batteries with a superior cycling performance.