Improved cycling stability of coke-based graphite anodes via micro-expansion assisted by thermal healing

Coke-derived highly graphitized graphite (CG) was prepared via graphitization at 2800°C and further engineered through a two-step “micro-expansion–thermal healing” protocol to improve its performance as a lithium-ion battery anode. Micro-expansion was first induced by a mild de-intercalation treatment at 300°C for 6 h under N2, producing micro-expanded graphite (ECG) with slightly opened interlayers and more accessible ion-transport pathways. Subsequently, thermal healing was carried out by annealing ECG at 800°C for 1 h under N2 to partially restore layered stacking and electronic connectivity while preserving the introduced defects/porosity, yielding the healed sample (DECG). Multiscale characterizations indicate that DECG exhibits a narrowed (002) peak relative to ECG, suggesting partial recovery of long-range graphitic order; meanwhile, Raman spectroscopy shows the highest ID/IG for DECG, implying an increased density of local defects/edge sites. Nitrogen adsorption–desorption isotherm measurements further confirm enhanced micro–mesopore connectivity with increased specific surface area and pore volume. Electrochemically, DECG delivers a reversible capacity of 305.6 mAh/g at 100 mA/g with an initial Coulombic efficiency of 81.5% and retains 270.9 mAh/g after 300 cycles at 500 mA/g. Impedance fitting further reveals a markedly reduced charge-transfer resistance (Rct). The results demonstrate that controlled defect/porosity introduction coupled with subsequent stacking repair enables a balanced synergy between ion transport and electronic conduction without a pronounced penalty in initial coulomb efficiency (ICE). Owing to the abundant coke feedstock and scalable processing, this route provides a practical strategy for structural control and manufacturing of novel graphite anodes from abundant sources.