Reactive force-field simulation and experimental validation of cyclic defects in silicon anodes for lithium-ion batteries

Silicon anodes for lithium-ion batteries offer high theoretical capacity but face practical challenges of capacity fading due to significant volumetric changes during charge-discharge cycles. To reveal the underlying mechanisms, we employ reactive force fields (ReaxFFs) in molecular dynamics simulations to conduct atomic analyses of lithiation and delithiation cycles of silicon particles with three diameters. Our simulations demonstrate a volumetric expansion exceeding 280%, primarily along the ⟨110⟩ direction, with an inward movement of the interface between lithiated and unlithiated regions. We introduce a metric, “geometric defect,” derived from the centroid deviation of neighboring atoms, to evaluate the structural integrity of the silicon anode. Geometric defect state of charge curves show a 5% capacity fade due to silicon loss after the initial cycle. Experimental validation confirms a capacity loss exceeding 40% after the first cycle, attributed to internal defects within silicon particles, aligning well with our simulation results.