Intrinsic carbon fiber electrodes for load-bearing aluminum-ion structural battery composites: Multifunctional performance and intercalation mechanism

The development of aluminum-ion structural battery composites (Al-SBCs) is currently hindered by the trade-off between electrochemical activity and mechanical integrity. Conventional surface modification strategies often introduce weak boundary layers, leading to premature structural failure. Herein, we propose an intrinsic aluminum storage strategy utilizing pristine mesophase pitch-based carbon fiber (TC600) to achieve a synergistic enhancement of both mechanical and electrochemical performance. Benefiting from the high degree of graphitization and highly ordered microstructure, the pristine fiber delivers a substantial specific capacity of 62.7 mAh/g without extrinsic activation. Crucially, this intrinsic approach significantly bolsters interfacial mechanical properties: the composite interface achieves a maximum lap-shear load of 3413 N and a lap-shear strength of 5.46 MPa, representing a 156.3% improvement over the coated counterpart, and retains 91.6% of the pristine single-fiber tensile strength after cycling. Operando characterizations coupled with theoretical simulations elucidate the underlying storage mechanism: in situ XRD and Raman spectroscopy reveal a bulk intercalation process governed by the Daumas-Hérold model, characterized by the dynamic evolution of Stage4 graphite intercalation compounds and a structural transition from ordered AB stacking to a turbostratic texture. Furthermore, simulations uncover a novel “rotation-assisted translation” diffusion mechanism for bulky AlCl4− anions within the confined gallery. This mechanism exhibits an ultra-low migration barrier (0.15–0.25 eV), enabling rapid diffusion kinetics. This work not only identifies the critical microstructural determinants for intrinsic aluminum storage but also provides a theoretical foundation for designing next-generation high-performance structural batteries.