Multiscale modeling of electrochemical-mechanical coupling at battery interfaces is a critical approach for understanding the complex degradation mechanisms in high-energy-density battery systems. The interplay between electrochemical reactions and mechanical stress evolution governs performance limitations in advanced anodes such as silicon and lithium metal, where large volume changes and interfacial instabilities lead to capacity fade and safety concerns. This article examines the integration of density functional theory (DFT), molecular dynamics (MD), and continuum methods to predict stress accumulation, contact loss, and fracture phenomena during cycling, with particular emphasis on anode-electrolyte interfaces.

At the atomic scale, DFT calculations provide fundamental insights into the thermodynamic and kinetic properties of interfacial reactions. For silicon anodes, DFT reveals the formation energies of lithiated phases (Li_xSi) and their mechanical properties. The transition from crystalline silicon to amorphous Li_3.75Si results in a theoretical volume expansion of 280%, inducing significant stress at the particle level. Similarly, DFT studies of lithium-metal anodes quantify the surface energy anisotropy and diffusion barriers of Li atoms, which influence dendrite nucleation and growth. These calculations also predict the elastic moduli of solid electrolyte interphase (SEI) components, such as Li_2O (150-200 GPa) and LiF (65-70 GPa), which govern their fracture resistance during cycling.

Molecular dynamics simulations bridge atomic-scale interactions with mesoscale morphology evolution. Reactive force fields enable MD studies of SEI formation dynamics, capturing the decomposition of electrolytes like LiPF_6 in ethylene carbonate at silicon or lithium surfaces. Simulations show that compressive stresses exceeding 1 GPa develop in silicon nanoparticles during lithiation, leading to plastic flow and particle pulverization. For lithium-metal anodes, MD reveals how inhomogeneous plating generates localized tensile stresses that initiate voids at the Li-SEI interface. The simulations also quantify the role of grain boundaries in lithium, where diffusivity can be 2-3 orders of magnitude higher than in bulk crystals, accelerating stress relaxation.

Continuum models integrate these insights into larger-scale predictions of electrode behavior. Phase-field formulations couple Li diffusion with elasticity and fracture, reproducing the experimentally observed crack patterns in silicon thin films. The models incorporate concentration-dependent material properties, such as the Young's modulus reduction from 90 GPa in pure silicon to 30 GPa in fully lithiated Li_3.75Si. For lithium-metal anodes, coupled electrochemical-thermomechanical models simulate dendrite penetration through ceramic electrolytes, predicting critical current densities for short-circuit prevention. These models solve the stress-modified Butler-Volmer equation, where mechanical pressure alters the overpotential for plating reactions.

The multiscale framework addresses three key interfacial phenomena. First, stress evolution during cycling is tracked from atomic displacements to macroscopic deformation. Silicon anodes exhibit cyclic hardening due to dislocation accumulation, while lithium anodes show stress reversal between plating and stripping. Second, contact loss at current collector interfaces is predicted through cohesive zone models that incorporate adhesion energy measurements from surface science experiments. Third, fracture mechanics approaches quantify SEI cracking, with critical strain energy release rates ranging from 0.5-5 J/m² depending on composition.

Validation relies on in situ characterization techniques. X-ray tomography measures the three-dimensional pore formation in silicon composite electrodes, confirming model predictions of percolation thresholds at 20-30% porosity. Neutron depth profiling provides lithium concentration gradients that constrain the diffusion-stress coupling parameters. Atomic force microscopy measurements of SEI mechanical properties match the modulus values derived from MD simulations. Cryogenic electron microscopy identifies the nanocrystalline domains in lithium deposits that correspond to stress hotspots in the models.

In silicon systems, the models explain capacity fade through two mechanisms. Repeated fracture and healing of the SEI consume active lithium, while contact loss between particles increases electrode impedance. The simulations guide design solutions such as yolk-shell architectures with optimized void space and binder formulations with tailored adhesion strength. For lithium-metal batteries, the multiscale approach identifies electrolyte compositions that promote homogeneous SEI formation and current collector designs that mitigate localized plating.

Challenges remain in fully capturing the dynamic interface evolution. The nucleation and growth of new phases, such as lithium hydride in humid environments, require more accurate reaction pathways from DFT. The viscoelastic response of polymer-containing SEI layers demands advanced constitutive models in continuum simulations. Machine learning potentials are emerging to bridge the time and length scale gaps between quantum calculations and macroscopic predictions.

The integration of multiscale modeling with experimental diagnostics forms a virtuous cycle for battery interface engineering. By quantifying the electrochemical-mechanical coupling mechanisms, these tools enable rational design of durable high-capacity anodes, accelerating the development of next-generation energy storage systems. Future advancements will require closer coupling between modeling and characterization at operando conditions, particularly for probing buried interfaces under realistic cycling rates and temperatures.