Multiscale simulation approaches have become essential for understanding fast-charging phenomena in lithium-ion batteries, particularly for graphite and silicon anode systems. These simulations bridge the gap between atomistic mechanisms and macroscopic cell behavior, enabling researchers to optimize fast-charging protocols while mitigating degradation risks such as lithium plating and thermal runaway. The integration of electrochemical, thermal, and mechanical models provides a comprehensive framework for analyzing fast-charging performance across multiple length and time scales.

At the atomistic scale, molecular dynamics simulations reveal lithium-ion diffusion pathways and plating nucleation mechanisms on graphite and silicon surfaces. Lithium plating, a critical failure mode during fast charging, initiates when the local overpotential drives lithium deposition rather than intercalation. In graphite anodes, simulations show that plating preferentially occurs at edge sites with higher surface energy, while in silicon anodes, the large volume expansion exacerbates local stress concentrations, further promoting plating. Density functional theory calculations quantify the energy barriers for lithium-ion desolvation and intercalation, which are critical rate-limiting steps during fast charging. These atomistic insights inform continuum-scale models by providing kinetic parameters such as exchange current densities and diffusion coefficients.

Moving to the particle scale, phase-field models simulate lithium concentration gradients and stress evolution within active materials. For graphite, anisotropic diffusion leads to nonuniform intercalation, particularly at high C-rates, while silicon particles experience severe stress-induced fracture due to its 300% volume expansion. These models couple lithium transport with elastic-plastic deformation, predicting particle cracking and solid-electrolyte interphase (SEI) damage. The resulting loss of active material and increased impedance are key contributors to capacity fade during fast cycling. Particle-scale simulations also quantify the competition between intercalation and plating, with results showing that plating onset occurs at C-rates above 1.5C for graphite and lower for silicon due to its slower diffusion kinetics.

At the electrode scale, porous electrode theory integrates the particle behavior into a homogenized framework, solving coupled lithium conservation and charge balance equations. The Doyle-Fuller-Newman model, extended with thermal and mechanical effects, predicts local current distributions that drive heterogeneous degradation. Simulations reveal that fast charging exacerbates current hot spots near the separator, where plating risk is highest. For silicon composite electrodes, the binder network's viscoelastic response must be modeled to accurately capture the electrode's structural integrity during cycling. Electrode-scale models also incorporate SEI growth dynamics, which accelerate under the elevated temperatures typical of fast charging.

Cell-level simulations combine the electrochemical models with thermal and mechanical analyses. The heat generation terms include reversible entropy changes and irreversible losses from ohmic heating, polarization, and side reactions. Thermal models solve the energy balance equation with appropriate boundary conditions, predicting temperature distributions that strongly influence plating behavior. A 10°C temperature rise can decrease plating overpotential by 30 mV, significantly increasing risk. Mechanical models simulate the stack pressure evolution, which affects porosity and tortuosity changes that feed back into transport properties. For pouch cells, the swelling forces during fast charging can exceed 1 MPa, particularly with silicon anodes.

The coupling between these phenomena creates complex interactions. For example, localized plating increases ohmic resistance, generating more heat that further accelerates plating in a positive feedback loop. Conversely, proper thermal management can suppress this effect, demonstrating the need for integrated simulations. Multiphysics models solve these coupled equations simultaneously, often using finite element methods with adaptive meshing to capture the different scales efficiently.

Validation against experimental fast-charge cycling data is critical. Half-cell studies with reference electrodes provide plating onset measurements, while in-situ diffraction techniques track lithium concentration gradients. Infrared thermography maps surface temperatures, and post-mortem analysis quantifies plating morphology and SEI composition. For graphite anodes, simulations accurately predict the transition from intercalation to plating at specific C-rates, matching experimental voltage plateau observations. Silicon anode models reproduce the characteristic capacity fade trends caused by particle isolation and contact loss.

Practical applications of these simulations include fast-charging protocol optimization. Pulse charging strategies derived from multiscale models can reduce plating by allowing concentration gradients to relax. Thermal management system designs benefit from the temperature distribution predictions, guiding cooling channel placement and phase change material integration. Material improvements also emerge, such as graphite particle size optimization and silicon nanostructure designs that mitigate stress.

Challenges remain in fully capturing all relevant phenomena. The SEI's evolving nature during fast cycling requires more sophisticated degradation models. Silicon's complex fracture patterns demand advanced fracture mechanics approaches. Machine learning techniques are increasingly employed to accelerate the multiscale simulations while maintaining accuracy.

The continued development of multiscale simulation frameworks will enable safer, faster-charging batteries by providing fundamental insights into the interconnected physical processes. As these tools mature, they will play a central role in designing next-generation anode materials and battery systems optimized for rapid energy delivery without compromising lifetime or safety.