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Stress effects on the initial lithiation of crystalline silicon nanowires: reactive molecular dynamics simulations using ReaxFF

Summary

ReaxFF (Fan et al. Si–Li parameterization) MD in LAMMPS studies lithiation of an h112-oriented crystalline silicon nanowire (~5976 Si) with a Li reservoir, emphasizing (111) layerwise insertion, amorphization, a sharp amorphous–crystalline interface (ACI), and compressive stress that can stall the reaction front at ~300 K. The article also reports high-temperature behavior including amorphous-to-crystalline Li–Si transitions near 1200 K at Li:Si ≈ 4.2:1, connecting kinetic lithiation pathways to phase behavior accessible at elevated T in simulation. This PCCP article is the version-of-record-style entry paired in the corpus with a proof-PDF sibling slug documented in docs/corpus/NON_PRIMARY_ARTICLE_PAPER_SLUGS.md.

Methods

Force-field training (validation against QM)

ReaxFF Si–Li (Fan parameters within the van Duin formulation) with EEM charges; QM reference: DFT NEB and related benchmarks for Li diffusion in c-Si/a-Si used to validate migration barriers as discussed in the article.

MD application (atomistic dynamics)

Reactive molecular dynamics in LAMMPS lithiates an h112 crystalline Si nanowire containing ~5976 Si atoms in a cell ~8.43×9.22 nm² in cross-section with periodic boundary conditions (PBC) along x,y ([110]/[111]), a Li reservoir, a reflective top boundary, and a fixed bottom layer. Equilibration: NVT with Nosé–Hoover thermostat from ~1 K (10 ps) then temperature ramp to 600 K at 0.048 K/fs, then hold for ~2.2 ns in the equilibration segment described in the paper. Production: velocity Verlet with Δt = 0.25 fs; NVE segments are used where noted alongside NVT; virial stress tracks chemo-mechanical fields at the ACI. Barostat / NPT pressure: N/A for the summarized constant-volume nanowire workflow. Electric field / umbrella or metadynamics: N/A.

Findings

  • ReaxFF Li diffusion barriers in bulk c-Si/a-Si match DFT benchmarks (e.g., ~0.58 eV path discussed vs DFT ~0.55 eV).
  • Lithiation proceeds by Li insertion between (111) bilayers, peeling layers and amorphizing; high local Li needed to break Si–Si bonds explains sharp ACI; compressive stress at ACI can retard the reaction front (~300 K conditions).
  • At ~1200 K, Li:Si ≈ 4.2:1 shows amorphous→crystalline Li–Si behavior as reported, illustrating temperature-driven ordering distinct from room-temperature frontal lithiation.

Limitations

ReaxFF training limits; NW model vs experimental TEM cells; reflection/thermostat choices affect front kinetics; 2D periodic NW idealization omits full electrode microstructure. Electrolyte and SEI chemistry are absent, so voltage-dependent driving forces for Li insertion are not modeled explicitly in the reactive MD shown.

Relevance to group

Core van Duin / Penn State Si anode ReaxFF application paper on chemomechanical lithiation. The PCCP article is frequently cited alongside other Si nanostructure lithiation simulations in the corpus when discussing stress-retarded reaction fronts and amorphization at sharp interfaces.

Citations and evidence anchors

DOI 10.1039/C4CP05198J.