A microcrystalline soft carbon modified hard carbon coating enhances cycling stability and initial efficiency in natural graphite anodes

Abstract

The natural graphite anode has limited lithium-ion battery applications due to electrolyte co-embedding and irreversible decomposition, triggering layer swelling, pulverization and unstable SEI film formation. To address these issues, this study proposes a dual-coating strategy: natural graphite is first coated with phenolic resin, followed by a secondary coating of bitumen. Experimental results demonstrate that the composite achieves a stable capacity of 376.41 (upgraded by 140%) mA h g⁻¹ and an initial coulombic efficiency of 85.79% after 80 cycles at 0.1C current density, along with a capacity retention of 92% after 200 cycles at 1C current density, highlighting its superior initial charge–discharge efficiency and cycling stability. Mechanistic analysis reveals that the pores formed by phenolic resin pyrolysis are filled with carbon derived from bitumen pyrolysis, enhancing the bonding between the graphite core and the surface carbon layer to form a uniform and dense coating. This structure improves lithium-ion transport rates and serves as a pre-stored lithium reservoir, facilitating rapid lithium-ion intercalation and deintercalation. Furthermore, the hard carbon generated from the bitumen-coated phenolic resin increases the C–C/CC bond ratio, stabilizing the solid electrolyte interface (SEI) film and enhancing its lithium-ion selectivity and chemical bonding strength with the graphite electrode surface. This dual soft@hard carbon coating strategy not only significantly enhances the initial coulombic efficiency and structural stability of natural graphite anodes but also offers a novel approach for designing high-performance lithium-ion battery anode materials.