X BP index as a predictive tool for fast-charging performance of artificial graphite anodes in lithium-ion batteries

Artificial graphite has garnered significant interest as a high-rate anode material for lithium-ion batteries (LIBs). While previous studies suggest that expanding the graphite interlayer spacing can enhance rate capability, the direct correlation between precursor molecular structure and fast-charging performance remains insufficiently understood. Herein, the ratio of aromatic bridging carbon to peripheral aromatic carbon in the precursor—defined as X_BP—is proposed as a key structural descriptor. Its impact on interlayer spacing and high-rate lithium storage performance is systematically investigated. By selectively isolating macerals to obtain precursors with varying degrees of condensation, the reliability of X_BP is validated, and its role in constructing an ordered, micro-expanded layered structure with enhanced Li⁺ diffusion kinetics is clarified. Specifically, as X_BP increases from 0.212 to 0.486, the 5C discharge capacity improves significantly from 92 to 201 mAh g⁻¹, revealing a strong parabolic relationship. In situ XRD and GITT measurements demonstrate that BCG135 exhibits more complete phase transitions (LiC₁₈ → LiC₁₂ → LiC₆) and faster Li⁺ diffusion compared to commercial natural graphite (Gr), highlighting its superior fast-charging capability. This study not only deepens the understanding of lithium storage mechanisms in artificial graphite but also offers an effective strategy for designing next-generation carbon anodes for high-power LIBs.