Fast-Charging Reliability of Hard-Carbon Anodes in Sodium-Ion Batteries: Interfacial Stability, Transport Heterogeneity, and Mechanical Integrity
Abstract
Reliable fast charging of sodium-ion batteries is constrained by heterogeneous transport, interfacial degradation, thermal accumulation, and mechanically driven failure in hard-carbon anodes. Here, a two-dimensional microstructure-informed multiphysics framework is developed to quantify the coupled degradation pathways governing porous hard-carbon electrodes under C/20–5 C charging. The model integrates sodium-ion transport, electronic conduction, Butler–Volmer interfacial kinetics, adsorption–insertion–pore-filling storage, SEI growth, heat generation, and sodiation-induced stress within spatially heterogeneous electrodes representing different degrees of carbon structural ordering. The results reveal a critical transition above 1 C, where capacity retention decreases from 80.8% at 1 C to 63.4% at 2 C and 36.0% at 5 C, accompanied by a nonlinear rise in polarization. Spatially resolved analysis shows that fast charging amplifies local current density, accelerates SEI thickening, and promotes thermal and mechanical localization; the current localization factor increases from 1.37 at 1 C to 2.91 at 5 C, while the maximum temperature rise reaches 18.4 K. The maximum Von Mises stress and hard-carbon degradation index identify 2C–5 C operation as degradation-prone despite partial capacity accessibility. Experimental validation against capacity, interfacial resistance, SEI thickness, and temperature rise confirms predictive accuracy. This study establishes localized degradation descriptors for designing fast-charge-compatible hard-carbon anodes with improved transport uniformity and interfacial robustness.