Multiscale Electrochemical–Mechanical Modeling of Hard Carbon Anodes in Na-Ion Batteries

Na-ion batteries are being explored as promising alternatives to Li-ion batteries because of the relative abundance of sodium in the Earth’s crust. Among various battery materials, the anode is an important component that governs the overall energy density of the battery. In addition, a good anode material is needed to suppress various degradation mechanisms like Solid-Electrolyte Interface (SEI) formation, plating, and dendrite formation. Hard carbon (HC) is a promising anode material for Na-ion batteries because of its low volumetric expansion and good energy density. However, it faces challenges related to low cycling performance, low rate capabilities, and complex sodium storage mechanisms. To systematically investigate the influence of the anode structure on the cell-level performance, we developed a multiscale approach to model sodium-ion battery (SIB) electrodes. The physical properties of the HC anode are determined using molecular dynamics (MD), and these properties are used in the system-level physics-based model to gain insights into intercalation-induced stresses occurring within the battery. Results from MD simulations show that the Young’s modulus and the Poisson’s ratio of the HC anode decrease upon Na intercalation, while the Na diffusivity depicts a nonmonotonic behavior. Integrating these properties with cell-level models showed that a lower anode particle radius results in smaller intercalation stresses. Furthermore, the Na diffusivity in HC had minimal effect on the cell voltage for a smaller particle radius. Our multiscale modeling framework is material-agnostic and can be readily used to evaluate other anode/cathode materials.