Atomic Damage Characterization for Amorphous Silicon Particles of Lithium-Ion Batteries under Potentiostatic/Galvanostatic Cycling: Reactive Force-Field Simulations and Experimental Validation

This study investigates the structural degradation mechanisms of amorphous silicon anodes in lithium-ion batteries under potentiostatic (constant-voltage, CV) and galvanostatic (constant-current, CC) cycling. We introduce the concept of a free volume element (FVE), defined through multiatom geometric enclosures to quantify local void sizes, as a descriptor to systematically characterize the loss of structural integrity induced by void expansion during electrochemical cycling. Molecular dynamics simulations employing a novel approach─combining gradual lithium insertion with a radial electric field─successfully reproduce an equivalent low-rate CC lithiation process. Structural analysis reveals that, under constant-current cycling, the evolution of FVE size during lithiation and delithiation follows similar trends; however, the average free volume during the midstage of delithiation increases by 8.8% compared to the corresponding stage of lithiation in the first cycle. Under constant-voltage cycling, the FVE evolution across multiple cycles demonstrates a more pronounced accumulation of irreversible structural damage. Furthermore, clear differences are observed in the growth gradients of FVE expansion between CC and CV lithiation. Crucially, experimental validation shows that the irreversible capacity loss measured at the end of each CV lithiation/delithiation phase correlates closely with the corresponding simulated FVE values. The consistent trend between irreversible capacity loss and simulated free volume strongly supports the reliability of the FVE concept as a key descriptor of atomic-scale damage evolution in cycled amorphous silicon particles.