Crosslinking and Structural Integration for Vacuum Residue-Derived Isotropic Coating Pitch Using Cyanuric Chloride

Isotropic pitch derived from low-cost vacuum residue (VR) represents a promising precursor for carbon coating materials in lithium-ion battery anodes; however, its practical deployment is constrained by inherently low crosslinking density, which yields poor carbon retention, excessive volatile evolution, and cracked or porous coatings after carbonization. Here, we present a molecular-engineering strategy using cyanuric chloride (TCT), a triazine-based molecule bearing three reactive chlorine atoms, as a bifunctional modifier to induce crosslinking while covalently integrating VR into a high-performance isotropic coating pitch. Under controlled thermal polymerization at 410 °C, TCT undergoes homolytic C–Cl cleavage to generate chlorine radicals that abstract aromatic hydrogen from VR constituents; these radicals promote intermolecular condensation, while the resulting crosslinked network restricts the mobility and planar rearrangement of polycyclic aromatic hydrocarbons (PAHs), thereby helping to maintain optical isotropy under appropriate processing conditions. Concurrently, the triazine core is incorporated into the growing aromatic network, supplying a rigid, nitrogen-rich motif that enhances structural integrity and increases carbon yield. The optimized TCT-modified pitch (5 wt % TCT, 410 °C, 5 h) exhibits an elevated softening point (218 °C), markedly improved carbon yield at 800 °C (52.1 vs 43.7% for unmodified VR pitch), and preserved optical isotropy. When applied to natural graphite, the resulting pitch-derived carbon layer is dense, uniform, and defect-free, yielding superior electrochemical performance: higher initial Coulombic efficiency (83.27 vs 78.73%), enhanced rate capability, and outstanding cycling stability over 1000 cycles. This work establishes a “crosslinking-induction and structural-integration” paradigm for converting low-cost heavy carbon resources into high-performance isotropic coating pitches via rational molecular design.