Modification mechanism of graphite anode in lithium-ion battery coated with ethylene tar pitch

Coating modification is a convenient method to improve the electrochemical properties of graphite anode in lithium-ion batteries. Ethylene tar pitch is a proper precursor as the coating material for its advantages of high C/H ratio, low ash content, and easy accessibility. After liquid coating and carbonization, an amorphous carbon layer could be coated on the natural graphite to improve the insertion approach of the lithium ions. In the charging and discharging processes, graphite was separated from the electrolyte by the carbon layer, creating a stable solid electrolyte interface to prevent the exfoliation of the graphite sheet and decrease the occurrence of side reactions on the surface. The improved compatibility with the electrolyte could reduce the transfer resistance and facilitate the migration of the lithium ions. A uniform and stable coating layer on the graphite apparently improved the electrochemical performance, particularly the long cycle stability and high-rate performance. After coating, the capacity retention after 500 cycles increased from 49 to 74%, while the specific capacity was ~ 145 mAh g⁻¹ at 4 C in the coating sample compared with ~ 20 mAh g⁻¹ in the natural graphite.